Dolomite Stability Sinkhole Investigation.pdf

MERAFONG CITY LOCAL MUNICIPALITY: OUTFALL SEWER PIPELINE SOUTH OF KHUTSONG EXTENSION 3: DOLOMITE STABILITY SINKHOLE INVESTIGATION VGI3737 S12

Compiled by: VGIconsult Projects P.O. BOX 604 FOURWAYS 2055 TEL : (011) 469 0854 FAX : (011) 469 0961 FAX : 0866892847 e-mail: [email protected]

Client: Merafong City Local Municipality No 3 Halite Street Carletonville 2500

Consulting Engineering Geologists & Engineers

VGIconsult VGIconsult Projects (Pty.) Ltd. Registration number 2003/015042/07

MERAFONG CITY LOCAL MUNICIPALITY No 3 Halite Street CARLETONVILLE 2500

Telephone Direct : (011) 469 0854 Fax : (011) 469 0961 Fax : 0866892847 E-mail [email protected]

ATTENTION: L. MAJA

Your reference

P.O. Box 604 Fourways 2055 Gauteng

Our reference

Date

VGI3737 S12

10 OCTOBER 2016

MERAFONG CITY LOCAL MUNICIPALITY: OUTFALL SEWER PIPELINE SOUTH OF KHUTSONG EXTENSION 3: DOLOMITE STABILITY SINKHOLE INVESTIGATION SUMMARY This report presents the results of dolomite stability investigations and recommendations on improvements to the subsurface and the affected outfall sewer line located south of Mzwanzwa Street, Khutsong Extension 3 where the sewer line collapsed into a sinkhole, within the Merafong City Local Municipality. A 5m diameter size sinkhole extending to a depth of approximately 4m occurred on the outfall sewer line, on 21July 2016. It is presumed that subsurface erosion of highly erodible dolomite residuum (wad) material was initially triggered by a leak on the sewer line over an extended period of time. As a result of the initial leak, the sewerline settled and failure of the wet service occurred, leading to the formation of a sinkhole. The investigation area covers approximately 2800m2 (70m by 40m). The regional topography of the area falls from 1480m AMSL in the north to 1479m AMSL in the south. Locally surface water runoff takes place as sheetwash down the gradient in a southerly direction towards the Mooirivierloop located 600m south of the site. Existing subsurface services located in the affected area including a damaged northwest to southeast aligned sewer line of unknown diameter and material type. The site is underlain by dolomite and chert of the Malmani Subgroup of the Chuniespoort Group of the Transvaal Supergroup. The dolomite bedrock over most of the site is blanketed by weathered soil derivatives. The investigated area can be described in terms of one dolomite Hazard Zone: Hazard Zone: The geotechnical data gathered during this investigation permits the dolomite hazard of the area of the sinkhole and the directly surrounding area as largely reflecting a high susceptibility of large to very large size (with sub-areas reflecting a medium susceptibility of largesize) sinkhole and subsidence formation with respect to ingress of water and a low susceptibility of all-size sinkhole and subsidence formation with respect to groundwater drawdown. Composite Inherent Hazard Class 7/8(4)//1. In the event of groundwater level drawdown the Inherent Hazard Class remains unchanged.

Directors: D.B. Buttrick Ph. D. (Eng. Geol.), MSAIEG, Pr. Sci. Nat. ; A.A. Gerber B. Eng., Pr. Eng. ASB: N.Y.G. Trollip M. Sc. (Eng. &Env.), Pr. Sci. Nat., AMSAIEG ; I. Kleinhans M. Sc. (Eng. &Env.), Pr. Sci. Nat.

2 This report documents recommendations and procedures on the improvement of subsurface conditions and stabilisation, replacement of wet services, improvement of surface water run-off, minimum standards of precautionary measures and monitoring actions. The following option dealing with the affected area is outlined in this report, namely: ‰

The use of the Inverted Filter Method to rehabilitate the sinkhole and a limited Compaction Grouting (i.e. backfilling) programme to backfill voids at depth along the sewer line in the affected area.

MERAFONG CITY LOCAL MUNICIPALITY: OUTFALL SEWER PIPELINE SOUTH OF KHUTSONG EXTENSION 3: DOLOMITE STABILITY SINKHOLE INVESTIGATION SUMMARY TABLE OF CONTENTS 1. 2. 3.

4. 5.

6.

7.

8.

9.

10.

Preface PAGE NUMBER

INTRODUCTION ................................................................................................................... 1 TERMS OF REFERENCE AND SCOPE OF WORK ............................................................. 1 AVAILABLE INFORMATION ................................................................................................ 1 3.1. Topographic Data....................................................................................................... 1 3.2. Geological Information ............................................................................................... 1 3.3. Industry Standards ..................................................................................................... 1 3.4. Geotechnical Reports ................................................................................................. 2 3.5. Geohydrological Information ...................................................................................... 2 DESCRIPTION OF THE STUDY AREA ................................................................................ 2 PROCEDURES USED IN THIS STUDY ................................................................................ 3 5.1. Site Inspection by VGIconsult..................................................................................... 3 5.2. Assimilation of Available Data -Information sources ................................................... 4 5.3. Gravity Surveys .......................................................................................................... 4 5.4. Rotary Percussion Boreholes ..................................................................................... 4 5.5. Thickness and depth concepts ................................................................................... 5 5.6. Coordinate System..................................................................................................... 6 5.7. Map production (projection, co-ordinate system and datum) ...................................... 6 5.8. Hazard Characterisation Procedure ........................................................................... 6 5.9. Dolomite Area Designation ........................................................................................11 5.10. Monitoring Designations ............................................................................................12 5.11. SANS 1936-1: Table 1, SANS 1936 Part 1 (2012) ....................................................14 GEOLOGY AND GEOHYDROLOGY ...................................................................................17 6.1. General Geology .......................................................................................................17 6.2. Local Geology ...........................................................................................................17 6.3. Geohydrology............................................................................................................18 6.4. Past Sinkholes and Subsidences ..............................................................................19 DOLOMITE HAZARD CHARACTERISATION .....................................................................19 7.1. Site investigation and Dolomite Hazard Assessment Procedures ..............................19 7.2. Hazard Characterisation of the site ...........................................................................19 CONCLUSIONS ...................................................................................................................21 8.1. Results of the borehole drilling programme ...............................................................21 8.2. Dolomite Hazard Characterisation and Suitability of the site for the current land use 22 RECOMMENDATIONS ........................................................................................................22 9.1. Rehabilitation of Sinkhole Area and related wet services ..........................................22 9.2. Precautionary measures ...........................................................................................25 9.3. Stormwater Management ..........................................................................................25 9.4. Monitoring Actions.....................................................................................................25 9.5. Database of ground movement and stability conditions .............................................27 GENERAL ............................................................................................................................27

TABLES SUMMARISED BOREHOLE INFORMATION AND INHERENT HAZARD CHARACTERISATION

TABLE 1

FIGURES LOCALITY PLAN TOPOGRAPHICAL SHEET LEGEND SITE LAYOUT WITH GROUND ELEVATION CONTOURS REGIONAL GEOLOGY GEOLOGY LEGEND REGIONAL GEOHYDROLOGY

FIGURE 1 FIGURE 1A FIGURE 2 FIGURE 3 FIGURE 3A FIGURE 4

DRAWINGS RESIDUAL GRAVITY, BOREHOLE POSITIONS AND DOLOMITE HAZARD ZONATION PROPOSED REHABILITATION AREA

VGI3737 S12/1 VGI3737 S12/2

APPENDICES BOREHOLE PROFILES

APPENDIX 1

1

1.

INTRODUCTION This report presents the results of a dolomite stability investigation carried out in the area where the outfall sewer pipeline, south of Khutsong Extension 3, collapsed into a sinkhole, within the Merafong City Local Municipality. A 5m diameter size sinkhole extending to a depth of approximately 4m occurred on 21 July 2016. The purpose of the investigation is to determine the extent of poor subsoil conditions or erosion and to provide recommendations and procedures on subsurface and wet service improvements. It is presumed that subsurface erosion of highly erodible dolomite residuum (wad) material was initially triggered by a leak on the outfall sewer line over an extended period of time. As a result of the initial leak, the sewer line settled and failure of the wet services occurred, leading to the formation of a sinkhole. These investigations involved field inspections, evaluation of existing gravity data, borehole drilling programme, analysis, reporting and recommendations on subsurface soil improvements and wet services and stabilisation procedures to be followed.

2.

TERMS OF REFERENCE AND SCOPE OF WORK VGIconsult was appointed by the Merafong City Local Municipality to conduct a dolomite stability investigation for the sinkhole on the outfall sewer line south of Khutsong Extension 3, as part of an Emergency investigation programme of five sinkhole areas in the Merafong City Local Municipality, under Reference Letter ID (WS), dated August 2016. VGIconsult presented technical and budget cost proposals on the investigation of the sinkhole in letter reference VGI3737 S12, dated 27 July 2016.

3.

AVAILABLE INFORMATION Information sources include: 3.1.

Topographic Data Topographic Map, 1: 50 000 Scale Series: issued by the Chief Directorate: Surveys and Mapping, Department of Land Affairs: Sheet Name Carletonville

3.2.

Reference 2627AD

Geological Information Geological Map, 1: 250 000 Scale Series: issued by the Geological Survey of South Africa (Council for Geoscience): Sheet Name West Rand

3.3.

Reference 2626

Industry Standards o

South African National Standard SANS 1936 Parts 1 ± 4 (2012).

o

South African National Standard SANS 2001-BE3: 2012 (DSS), Construction works Part BE3: Repair of sinkholes and subsidences in dolomite land.

o

South African National Standard SANS 633: 2012 (DSS), Soil profiling and rotary

2

percussion borehole logging on dolomite land in Southern Africa for engineering purposes.

3.4.

o

Environmental Earth Sciences, Springer-5HSRUW³A Performance Based Approach to Dolomite Risk Management´E\'%XWWULFN17UROOLS5:DWHrmeyer, N Pieterse, A Gerber, Volume 64, Issue 4, p1127 ± p1138, dated 2011.

o

South African National Standards: The Application of the National Building Code: SANS 10400, Part A: General principles and requirements and Part B: Structural Design, (2004).

o

Council for Geoscience/South African Institute of Engineering and Environmental Geologists (2003): Guideline for engineering-geological characterisation and development of dolomitic land.

o

Council for Geoscience (2007): Consultants Guide: Approach to Site on Dolomite Land.

o

Department of Public Works (PW344), September 2010: Development of Infrastructure on Dolomite. Manual for Consultants.

o

$QQDOV RI WKH *HRORJLFDO 6XUYH\ RI 6RXWK $IULFD ³6XEVXUIDFH VXEVLGHQFHV DQG sinkholes caused by lowering of the dolomitic water-table on the Far West Rand Gold Field of South $IULFD´E\5-.OH\ZHJWDQG'53LNH9ROXPHS ± p105, dated 1982.

Appropriate

Geotechnical Reports Geotechnical data pertaining to the Merafong City Local Municipality area of jurisdiction is housed at the West Rand District Municipality (WRDM) offices and/or the Council for Geoscience (CGS). o

3.5.

VGIconsult report, referenced VGI3606, dated October 2013³Khutsong Proper and Extensions 1-6: Feasibility Stage Dolomite Stability Investigation´

Geohydrological Information Groundwater information is made available by the Department of Water Affairs through theNational Groundwater Information System (NGIS) which offers read-only access to data from: o o o

National Groundwater Archive (NGA); Water Management System (WMS); and Hydstra [http://www.dwa.gov.za/chart/]).

,QDGGLWLRQWKHUHSRUW³*HRK\GURORJ\*XLGHOLQH'HYHORSPHQW,PSOHPHQWDWLRQRI'RORPLWH Guideline ± Phase 1, Activities 19 & 28: Desktop development of a Dolomite Hydrogeological Compartment Map and explanation booklet (Report), dated November 2009, Project Number: 14/14/5/2, Authors: Martin Holland: Water Geosciences Consulting, Frans :LHJPDQV*ROGHU$VVRFLDWHV´ZDVFRQVXOWHG 4.

DESCRIPTION OF THE STUDY AREA The sinkhole under investigation occurred on a northwest to southeast aligned outfall sewer line (unknown diameter and material type) located approximately 370m south of Mzwanzwa Street, Khutsong Extension 3 and 600m north of the Mooirivierloop, within the Merafong City Local

3

Municipality. The location of the site is displayed on Figure 1, super imposed on the topographic map. The site layout and ground elevation contours are displayed on Figure 2. The investigation area covers approximately 2800m2 (70m by 40m). The regional topography of the area falls from 1480m AMSL in the north to 1479m AMSL in the south. Locally surface water runoff takes place as sheetwash down the gradient in a southerly direction towards the Mooirivierloop. Existing subsurface services located in the affected area including the affected sewer line. Existing wet service and electrical site layout plans was not made available from the Merafong City Local Municipality for the area under investigation. A 5m diameter size sinkhole extending to a depth of approximately 4m occurred on 21 July 2016. It is presumed that subsurface erosion of highly erodible dolomite residuum (wad) material was initially triggered by a leak on the sewer line over an extended period of time. As a result of the initial leak, the sewer line settled and failure of the wet service occurred, leading to the formation of a sinkhole. 5.

PROCEDURES USED IN THIS STUDY 5.1.

Site Inspection by VGIconsult VGIconsult (Mr Jacques Meintjes) inspected the above mentioned site on 12th January 2016 and a second time on 26 July 2016. The following was observed and recommended on 12th January 2016: ‰ ‰

A blockage on the sewer line was reported. At that stage no evidence of a sinkhole could be observed. An onsite instruction was given by Mr Jacques Meintjes of VGIconsult to the MeUDIRQJ 2IILFLDOV GXULQJ WKH LQVSHFWLRQ ³0HUDIRQJ VKRXOG XQGHUWDNH D &&79camera inspection on the sewer line from manhole to manhole to determine the integrity of the sewer line and the position of the leak or blockage. If the CCTVcamera inspection reveal any damage or broken section on the sewer line, that VHFWLRQRIWKHSLSHVKRXOGLPPHGLDWHO\EHUHSDLUHGRUUHSODFHG´

VGIconsult (Mr Jacques Meintjes) inspected the above mentioned site for a second time on 26 July 2016 after a sinkhole was reported to Ms B. Ndiki of Merafong City Local Municipality. The following was observed on 26 July 2016: ‰

A 5m diameter size sinkhole extending to an anticipated maximum depth of approximately 4m below ground surface, with a 1m diameter size erosion tunnel at the observed base of the sinkhole extending in a southerly direction to an unknown depth.

‰

A broken sewer line with strong flowing sewage at the observed sinkhole base floor.

It is presumed that subsurface erosion of highly erodible dolomite residuum (wad) material was initially triggered by a leak on the sewer line over an extended period of time. As a result of the initial leak, the sewer line settled and failure of the wet service occurred, leading to the formation of a sinkhole. The following recommendations were given in the Interim Report VGI 3737 S12, dated 26 July 2016, documenting the site inspection:

4

5.2.

‰

The affected area should be fenced off immediately and a soil berm placed around the affected area to prevent any run-off surface water entering the affected area causing additional subsurface soil erosion.

‰

The broken sewer line section (with sewage flowing into the sinkhole) should immediately be diverted around the sinkhole area by means of a pipe system, approximately 30m away from the sinkhole.

‰

A detailed dolomite stability investigation including a gravity survey and the drilling of percussion boreholes is urgently required to evaluate subsurface conditions, determine the extent of the affected area and to provide recommendations in terms of appropriate rehabilitation.

Assimilation of Available Data -Information sources This investigation is initiated by gathering, assimilating and reviewing existing, available geological, geotechnical, geophysical and geohydrological data pertaining to the site.

5.3.

Gravity Surveys The existing residual gravity survey for Khutsong was obtained from VGIconsult Report No. VGI3606 dated October 2013 and was used during this investigation. The residual gravity is displayed on Drawing 3737 S12/1. The gravity survey revealed a gravity low field (deep dolomite bedrock) to the southeast of the sinkhole, with the sinkhole located on a gradual gravity gradient field.

5.4.

Rotary Percussion Boreholes A total of eleven percussion boreholes (3737 S12-01 to 3737 S12-11) were drilled in the area surrounding the sinkhole. The eleven boreholes were drilled on 15 and 21 September 2016 by JK Developments Drilling Contractor. The positions of the boreholes are displayed on Drawing VGI3737 S12/1. The borehole logs are presented in Appendix 1 and summarised in Table 1. 5.4.1. Borehole Information JK Developments Drilling Contractor was instructed by VGIconsult to undertake the drilling programme. Current practice requires that a number of rotary percussion boreholes should be drilled according to set specifications as outlined below: 5.4.2. Drilling equipment should comprise of the following mobile unit: a)

b)

compressor unit with measured and calibrated constant air delivery rating at (21,2m³/s (750 cfm) and 1600KPa (16 Bar) minimum or 26,9m³/s (950 cfm) with 2100KPa (21 Bar) maximum; and pneumatic percussion drilling rig with 165mm nominal diameter button bit capable of drilling in all soil and rock types.

5.4.3. Drilling a) b) c)

Representative samples shall be retrieved for every 1m drilled. Boreholes shall be drilled to 60m or 6m into dolomite bedrock, whichever occurs first. The depth of groundwater strikes shall be recorded.

5

d)

Hammer rate, sample and air recovery must be recorded, as well as hardness of the formations drilled.

5.4.4. Sampling a) b)

c)

Samples should be taken representatively and sufficiently to allow appropriate visual and tactile analysis. Tags should be included in every bag, recording depth of sample, penetration time and borehole number. Metres drilled where no sample return is recorded should also be tagged and bagged. Samples should be filed sequentially in plastic sleeves, with the borehole number clearly marked on the sleeve.

5.4.5. Drilling depths Current practice requires that: a) b) c)

d)

Boreholes be drilled at least 6 meters into hard rock dolomite; Boreholes be drilled to at least 60m if dolomite bedrock is not confirmed at shallower depth; A selection of boreholes are to be drilled into dolomite bedrock on gravity high anomalies to determine the shallowest bedrock depth (in instances where dolomite bedrock is anticipated to be very deep (deeper than 60m), In de-watered areas, a representative selection of boreholes shall be drilled to 100m or into dolomite bedrock to obtain a perspective of subsurface conditions below the OWL.

5.4.6. Drill contract details Drilling work is undertaken using a down-the-hole rotary percussion rig. The drilling machine is a Thor 5000. The compressor used is an Atlas COPCO (XRVS 476 CD) and delivers 27,7 m³/min at a pressure of 1900 kPa to a 165 mm diameter hammer (button bit). The drill operator was J.G. Maluleke. The boreholes drilled during this investigation were terminated 6m into dolomite bedrock. The boreholes were backfilled according to industry guidelines. 5.5.

Thickness and depth concepts In the context of this report the concepts of thickness and depths are used as follows: Depths Range in m 0-2/4 2/4-8/12 8/12-16/24 16/24-36/44 More than 40

Appellation Near-surface Shallow Intermediate Great Depth Very Great Depth Thicknesses

Range in m 0-8/12 8/12-16/24 16/24-36/44 36/44 and greater

Appellation Thin Intermediate Thick Very Thick

6

5.6.

Coordinate System The X-and Y-coordinates (values) for the boreholes, as reflected in Appendix 2, conform to the South African Coordinate System as set in the national control survey network maintained by the Chief Directorate: Surveys and Mapping of the Department of Land Affairs. The X-and Y-values are given in metres latitude (7 digit value) and longitude (5 or 6 digit value). These coordinates are projected using the Gauss Conform Projection which is the Transverse aspect of the Mercator projection. The reference ellipsoid is the WGS84 (Hartebeeshoek 1994) ellipsoid. The Central Meridian (longitude of origin or Lo) for this site is 27ºE, with the site as a whole located west of the Central Meridian. In the South African coordinate system the X coordinates are measured southwards from the equator (where x = 0) towards the South Pole which is positive. Y coordinates are measured from the Central Meridian (CM), increasing from the CM in a westerly direction so that Y is positive west of the CM and negative east of the CM.

5.7.

Map production (projection, co-ordinate system and datum) The projection information of the figures and drawings in this report are reflected on each individual figure and drawing and listed below: Projection surface:

Mercator (cylinder)

Projection orientation:

Transverse aspect

Datum or reference ellipsoid (model for the shape of the earth):

World Geodetic System 84 (as updated in 2004 and valid to 2010)

Central Meridian:

In degrees (29 for this study)

False easting and northing:

Zero degrees

Scale factor:

1

A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). Latitude and longitude values are traditionally measured either in decimal degrees or in degrees, minutes, and seconds (DMS). Latitude values are measured relative to the equator. Longitude values are measured relative to the prime meridian. Data defined on a geographic coordinate system is displayed as if a degree is a linear unit of measure. Although longitude and latitude can locate exact positions on the surface of the globe, it is not a uniform unit of measure. The drawings and figures are therefore presented (coordinated) in metres latitude (7 digit value) and longitude (5 or 6 digit value). 5.8.

Hazard Characterisation Procedure New national standards (Draft SANS 1936) require use of internationally accepted terminology. The applicable terminology and its definition (with previous term used) are given below:

7

1.

Hazard Source of potential harm. Hazard is the function of magnitude (of the events), area, and frequency.

2.

Inherent hazard (Inherent Risk) A reflection of the geological susceptibility of a karst area to an event (sinkhole or subsidence). Inherent Hazard is expressed in terms of three broad categories, namely low, medium and high, typically, but not exclusively, denoting anticipated number of events per area over time.

3.

Inherent hazard class (Inherent Risk Class) A site is characterised in terms of eight standard inherent hazard classes, denoting the likelihood of an event (sinkhole or subsidence) occurring as well as its likely size (diameter). The larger the Inherent Hazard Class (IHC) number, the greater the likelihood of the event occurring and the larger its potential size should it occur.

4.

Hazard rating The number of events that have occurred over a 20 year period due to human impact.

5.

Tolerable hazard rating The hazard rating is expressed as tolerable where the number of events experienced is less than and including 0.1 events per hectare per 20 years (preferably tending to 0 per hectare) that is exceeding the return period of 200 years and intolerable where the number of events experienced exceeds 0.1 events per hectare per 20 years (return period less than 200 years).

6.

Return period Known as a recurrence interval and is an estimate of the interval of time between events of a certain size.

7.

Subsidence Shallow, enclosed depression. In past South African literature subsidence, as defined above, is synonymous with doline. The term subsidence is substituted to prevent contradiction with international literature.

8.

Sinkhole A feature that occurs suddenly and manifests itself as a hole in the ground. In international literature the term sinkhole is often synonymous with doline.

9.

Dolomite land Land underlain by dolomite or limestone rock directly or at a shallow depth, typically no more than: a)

60m in areas where no de-watering has taken place and the local authority has jurisdiction, is monitoring and has control over the groundwater levels over the areas under consideration; or

8

b)

10.

100m in areas where de-watering has taken place or where the local authority has no jurisdiction or control over groundwater levels

Event Occurrence [or change of a particular set of circumstances], in the context of this standard referring to a sinkhole or subsidence. An event can be one or more occurrences, and can have several causes. An event can consist of something not KDSSHQLQJ$QHYHQWFDQVRPHWLPHVEHUHIHUUHGWRDVDQ³LQFLGHQW´RU³DFFLGHQW´

11.

Potential loss of support Refers to the removal of support below the foundation due to a nominal sinkhole or subsidence event. In proposing suitable foundation types in D3 areas, consideration should be given to the potential loss of support which could be anticipated for the designated Inherent Hazard Class based on the nascent1 sinkhole size. The philosophy to be applied to the design of the foundations is that in the event of catastrophic loss of support, there is sufficient time for occupants to safely escape after the occurrence of the sinkhole, and the level of expected damage associated with soil movements unrelated to sinkhole formation in near surface horizons is kept within reasonable limits.

7KH KD]DUG FKDUDFWHULVDWLRQ SURFHGXUH SUHYLRXVO\ UHIHUUHG WR DV ³ULVN characterisation procedure in South African literature) is in accordance with the peer reviewed paper referenced in Section 3.3 of this report:

The available information, geophysical data, borehole data and geohydrological information gathered during the investigation has been pooled and reviewed permitting the formulation of a perspective concerning the characterisation of the stability of the site. The predominant mobilising agencies considered in this investigation are major groundwater level fluctuations (>6m), ingress water, ground vibrations and gravity. Use is made of a generalised list of evaluation factors to evaluate the hazard. These factors are as follows: -

Receptacle development; Mobilising agencies, particularly ingress water from leaking services; Potential sinkhole development space; Nature of the blanketing layer; Mobilisation potential of the blanketing layer; Bedrock morphology.

Receptacles or disseminated receptacles refer to any voids or cavities in the dolomite bedrock or in the overburden capable of receiving mobilised materials. Receptacles are assumed to be present as no reliable geophysical tool exists to determine the location of these features. Consequently the information gathered from boreholes, including penetration times, air loss, hammer action, etc., combined with geophysical and geological information are used to formulate an impression of the degree of voids. The potential sinkhole development space, where used, refers to the expected maximum size sinkhole that conservatively may be anticipated to be generated if sustained ingress of water were to occur. This factor is related to the depth of the receptacles or disseminated receptacles. The gravity survey combined with borehole information strongly 1

Adj. beginning to develop

9

guides the appraisal of this factor. The nature of the material covering the receptacles, be they above or in the bedrock, determines the susceptibility of the subsurface material to erosion by ingress water. The presence of materials such as shales or intrusives, which can act as aquitards, serve to reduce the mobilisation potential and enhance the stability. In the case of dramatic groundwater level fluctuations the susceptibility of the soil material to mobilisation (i.e. consolidation settlement -subsidence formation, or ravelling and archfailure -sinkhole formation, due to pore pressure changes in soils), is strongly influenced by the position of the original groundwater level in the subsurface profile. In assessing the susceptibility of a subsurface profile to sinkholes and subsidences due to groundwater level drawdown, attention is given to the nature and extent of the material below the groundwater level. For example in the case of compressible dolomite residuum, as the groundwater recedes, pore pressures in the residual dolomite soils, typically characterised by high void ratios, gradually dissipate and the effective stress on the soil increases causing consolidation of the compressible material. A surface depression may occur gradually due to the load of the near-surface materials on the deeper lower density materials that settle into a denser state. The general maximum magnitude of natural groundwater fluctuation in the Gauteng dolomites is in the order of 5m (Hobbs, 2004; Holland, 2007). Hence artificial groundwater level drawdown is generally defined as drawdown exceeding 6m. Experience shows that groundwater level drawdown (beyond seasonal variations) has the greatest negative impact on dolomite stability in areas of shallow groundwater levels (30m or shallower) i.e. deeper (>30m) groundwater levels, pose less of a negative impact on stability, in the event of groundwater level drawdown or dewatering. However, where groundwater drawdown occurs in areas of deeper groundwater, the size of instability is typically anticipated to be large to very large. In view of the factors discussed above the following characteristics have been extracted from the gathered information during the assessment process: -

borehole position relative to the gravity data. collar elevation. depth to dolomite bedrock. depth to potential receptacles. depth to present groundwater level. nature and thickness of blanketing layer i.e. material type, penetration times, etc. position of the bedrock with respect to the present and original groundwater level. thickness and nature of the soil materials above and below the present and originalgroundwater level.

Inherent hazard is a reflection of the geological susceptibility of karst area to an event (sinkhole or subsidence formation) and is expressed in three broad categories, namely low, medium and high. The following reference to incidences, gives a perspective of the magnitude of problems encountered in each of the of hazard zones in research areas. It is important to note that these figures are largely derived from developments not effectively and appropriately designed or maintained. Inherent Hazard

Anticipated events per hectare over time (magnitude of problem)*

LOW

0 up to and including 0.1 events per hectare anticipated but occurrence of events cannot be excluded. Return Period is greater than 200 years.

10 MEDIUM

Greater than 0.1 and less than and equal to 1.0 events per hectare. Return period is between 200 and 20 years.

HIGH

Greater than 1.0 events anticipated per hectare. Return period is less than 20 years.

* that have occurred per hectare in a 20 year period in the "type" areas (statistics based on poor service design and maintenance)

The study area is characterised in terms of eight standard Inherent Hazard Classes. These classes denote the chance of a sinkhole or subsidence occurring as well as its likely size (diameter). The terminology used in terms of likely size of an event (sinkhole or subsidence) is defined as follows: Maximum diameter of surface manifestation (in metres) <2 2-5 5-15 > 15

Terminology Small-size Medium-size Large-size Very large-size

The larger the Inherent Hazard Class number, the greater the chance of a sinkhole or subsidence occurring and the larger its potential size should it occur. The meaning/definition of each Inherent Hazard Class is as follows: Inherent Hazard Class

Characterisation of Area

Areas characterised as reflecting a low inherent susceptibility of all sizes of events occurring. Areas characterised as reflecting a medium inherent susceptibility of Class 2 Areas small-size events occurring. Areas characterised as reflecting a medium inherent susceptibility of Class 3 Areas medium-size events occurring. Areas characterised as reflecting a medium inherent susceptibility of Class 4 Areas large-size events occurring. Areas characterised as reflecting a high inherent susceptibility of Class 5 Areas small-size events occurring. Areas characterised as reflecting a high inherent susceptibility of Class 6 Areas medium-size events. Areas characterised as reflecting a high inherent susceptibility of Class 7 Areas large-size events occurring. Areas characterised as reflecting a high inherent susceptibility of very Class 8 Areas large-size events occurring. NOTE: The event size reflects the predominant anticipated nascent event size. Class 1 Areas

The definitions above are summaries of the Inherent Hazard Class table presented in the 2001 paper referenced in Section 3. Inherent Hazard is defined in terms of ingress water and groundwater level drawdown reflected by two Inherent Hazard Class designations separated by a double forward slash, i.e.-Inherent Hazard Class (Ingress water) // Inherent Hazard Class (groundwater level drawdown). As an example, a designation of 1//8 indicates that the zone displays a low Inherent Hazard with respect to water ingress but a high Inherent Hazard with respect to groundwater level drawdown.

11

Further combinations may be appropriate: As an example, a designation of Inherent Hazard Class 1//1/4/8 indicates that the zone displays a low Inherent Hazard with respect to water ingress but a low to high Inherent Hazard with respect to groundwater level drawdown. This definition may, for example, be necessary in cases where groundwater was not encountered or the original groundwater level is not known and dolomite bedrock could not be confirmed. Zones delineated on a site may be combinations of the above. In some instances, the Inherent Hazard Classes are indicated with the primary zone description given first followed by a suffix in brackets. The primary Inherent Hazard Class describes the predominant characterisation of the zone and the suffix describes the characterisation of anticipated pockets or small subareas within the zone: As an example, a designation of Inherent Hazard Class 8(4) indicates that the zone predominantly displays a high Inherent Hazard for up to very large-size sinkhole and subsidence formation with anticipated pockets or small sub-areas of Class 4 i.e. displaying a medium hazard for up to large-size sinkhole and subsidence formation. Specific commentary should be provided on the impact that the action of ingress water may have on the soil profile upon lowering of the ground water level or base level of erosion. Does the susceptibility of the subsurface profile remain unchanged from an ingress of water perspective or not, as the the groundwater level is lowered and the previously ³SURWHFWHG´ SURILOH LV H[SRVHG ([DPSOH 7KH lowering of the groundwater level and exposure of a poor subsurface profile in an area of previously shallow groundwater level designated as Inherent Hazard Class 3//7, results in a change in susceptibility from medium to high and the Inherent Hazard Class from 3 to 6 i.e. the Inherent Hazard Class 3//7 will change to Inherent Hazard Class 6//7 once groundwater level drawdown has occurred. 5.9.

Dolomite Area Designation Dolomite Area Designations must be identified on sites located on or near dolomite land (land where dolomite is located at or near [less than 100m] ground surface). The definitions of the Dolomite Area Designations as defined in SANS 1936 Part 1 (2012) are as follows: Dolomite area designation

Description

D1

No precautionary measures are required.

D2

General precautionary measures, in accordance with the requirements of SANS 1936-3, that are intended to prevent the concentrated ingress of water into the ground, are required.

D3

Precautionary measures in addition to those pertaining to the prevention of concentrated ingress of water into the ground, in accordance with the relevant requirements of SANS 1936-3, are required.

D4

Development may only be considered provided the following requirements are met: Involvement of Competence Level 4 geo-practitioner in all the categories of the geotechnical engineering work, i.e. site characterization, analysis and design, supervision and review, supervision of execution and management (primary geo-practitioner). Review and acceptance of all the categories of the geotechnical engineering work by a Competence Level 4 peer. This peer reviewer may not be a business associate of the primary geo-practitioner(s) and

12 Dolomite area designation

Description may not have a vested interest in the project. All the categories of the geotechnical engineering work to be reviewed and accepted by the Authority who may request a further review by an Authority designated Competence Level 4 peer, if required. The responsible Local Authority must indicate its commitment to maintain dolomite risk management principles in accordance with SANS 1936-4.

5.10. Monitoring Designations According to SANS 1936 Part 4 (2012) Monitoring Designations must be identified and delineated according to the Inherent Hazard characterisation of the site and knowledge of problems which could impact on the infrastructure on site.The generic Monitoring Activities considered appropriate for dolomite site are as follows: Annotation

A

B

C

Activity* Visual inspections of ground, structures and above ground infrastructure(e.g. buildings, taps, gardens, private and public open space etc.): Examine buildings for cracks. Visual checks for outside dripping taps and pressure valves. Visual checks for damp or moss grown areas. Visual check for over-wetting of gardens. Visual check for blocked drainage ports in garden walls. Visual check for cracks in the ground. Visual inspection of stormwater systems: Visual checks for debris in open storm water channels at, for example, the start of the rainy season and after heavy storms. Visual checks for water flowing out of stormwater manholes at the start of the rainy season and after heavy storms. Search for ground cracks and cracks in lined and unlined channels. Testing of wet-services for leaks: Regular air and water tests on wetservices. In waste water and stormwater pipes with a diameter greater than 100mm wet-services to be inspected by camera.

Reaction

Any evidence of cracking or ground settlement should immediately be reported and investigated. Any evidence of blockages should be reported and cleared immediately.

Any leaks to be reported and repaired immediately.

Purpose

Monitor, control and prevention of concentrated ingress of water

13 Annotation

D

E

Activity* Monitoring of structures and ground levels: In many instances visual inspections may not be sufficient: It may be necessary to undertake precision ground-surface levelling, particularly in areas that have been rehabilitated after a sinkhole or subsidence event. Such levelling must be undertaken by a surveyor, recorded and stored in the databank and appropriate actions taken when excessive settlement continues. Monitoring of the groundwater level: This activity not only entails the measuring and recording of the groundwater level, but also the analysis and understanding of groundwater level trends over time and the control of excessive [beyond seasonal fluctuations] groundwater level drawdown: Drill and equip strategic boreholes with the necessary equipment to measure the groundwater level. Recorded groundwater level, monitoring well number, date and other relevant observations. Analyse groundwater level trend over time on a regular basis. Report artificial/excessive groundwater level drawdown to Council and the Department of Water Affairs. Investigate cause of artificial/excessive groundwater level drawdown. Arrest artificial/excessive groundwater level drawdown.

Reaction

Purpose

Any evidence of movement must be reported and investigated.

Monitor the effects of concentrated ingress of water or groundwater level drawdown

Evidence of lowering must be reported to Council and the Department of Water Affairs.

Monitor, control and prevention of groundwater level drawdown

*If there is no evidence of a particular problem, this result should be recorded.

The Frequency with which each Activity is to be performed is selected from the following categories: Annotation ()DAILY ()WEEKLY ()¹ ()³ ()6 ()¹² ()24 ()NA ()tbd

Frequency Activities to be undertaken daily. Activities to be undertaken weekly. Activities to be undertaken once a month. Activities to be undertaken quarterly. Activities to be undertaken bi-annually. Activities to be undertaken annually. Activities to be undertaken once every two years. NO ACTION REQUIRED TO BE DETERMINED

Areas of µQR GRORPLWHKD]DUG¶ require no monitoring from a dolomite risk management perspective. No action is required to lower the risk of dolomite-related instability, as these areas are not located on dolomite land. For example, portions of sites located on granite rock or Witwatersrand Supergroup rocks. Such areas may be designated as (ABCDE)0.

14

Areas of µORZ KD]DUG¶ for example Inherent Hazard Class 1 areas, are assigned a low priority and require basic monitoring and maintenance activities at long intervals, for example, where a site straddles very thick Karoo Supergroup rocks (in excess of 40 metres). The site or portion thereof may, for example, be designated as (ABC)24D0E12 indicating that all identified activities which control ingress water need only be undertaken once every two years, precision structure-and ground levelling not being required and groundwater level monitoring being required at long intervals. However, where such rocks overlie dolomite residuum below the original groundwater level a designation of (ABC)24D0E3 may apply, indicating that activities which control the ingress of concentrated water remain necessary once every two years but groundwater level monitoring is critical and should be undertaken quarterly. Areas of µKLJK KD]DUG¶for example Inherent Hazard Class 5, 3(5), 3/6 and therefore high priority in terms of monitoring and maintenance, should receive attention more frequently. These areas require stringent monitoring and maintenance activities at short intervals. Such areas are typically characterised by: o o o o o o o o o o

Metastable subsurface conditions or latent sinkhole formation. High Inherent Hazard conditions. Poor subsurface conditions e.g. cavities, cavernous conditions, sample or air loss. Previous sinkhole or subsidence formation. Palaeo-sinkhole or palaeo-subsidence structures. Geological contact areas. Fault zones. Shallow dolomite groundwater above dolomite bedrock. Anticipated ground settlement or Ponding of water, etc.

For example, an area in which various sinkholes have already been reported and where the area is designated as high hazard or even medium to high hazard from an ingress of water perspective a ABC3 or even (AB)daily (D)3 designation may apply, indicating the need to undertake activities controlling ingress of water quarterly, or even daily. A further example may be, an area in which various sinkholes have already been reported and where the area is designated as high hazard from a groundwater level drawdown perspective. In such a case a (ABC)12D0E3 designation may apply, indicating the need to undertake activities to monitor groundwater fluctuations and drawdown quarterly. 5.11. SANS 1936-1: Table 1, SANS 1936 Part 1 (2012) According to SANS 1936 Part 1 (2012) the development types suitable for the eight standard Inherent Hazard Classes are summarised as follows: Inherent Hazard Class

Land Usage Type

Commercial and miscellaneous non-residential usage 1

2

High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage

Land Usage Permitted with Dolomite Area Designation and footprint investigation requirement in terms of Deemed-To-Satisfy C1 (D3 + FPI), C2 (D3 + FPI), C3 (D2 + FPI), C4 (D2 + FPI), C5 (D2 + DLI), C6 (D2 + DLI), C7 (D2), C8 (D2) RH2 (D2 + FPI), RH3 (D2 + FPI) RL1 (D2 + FPI), RL2 (D2 + FPI) RN1 (D2), RN2 (D2), RN3 (D2) C1 (D3 + FPI), C2 (D3 + FPI), C3 (D3 + FPI), C4(D3 + FPI), C5 (D3 + DLI), C6 (D3 + DLI), C7 (D3+ FPI), C8 (D3)

15 Inherent Hazard Class

3

4

5

6

7

8

Land Usage Type High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses Commercial and miscellaneous non-residential usage High rise dwelling units Low rise dwelling units Dwelling houses

Land Use Class

Land Usage Permitted with Dolomite Area Designation and footprint investigation requirement in terms of Deemed-To-Satisfy RH3 (D3 + FPI) RL1 (D2 + FPI), RL2 (D2 + FPI) RN1 (D3), RN2 (D3), RN3 (D3) C1 (D3 + FPI), C2 (D3 + FPI), C3 (D3 + FPI), C5 (D3 + DLI), C6 (D3 + DLI), C7 (D3 + FPI), C8 (D3) RH3 (D3 + FPI) RL2 (D3 + FPI) RN2 (D3), RN3 (D3) C1 (D3 + FPI), C2 (D3 + FPI), C3 (D3 + FPI), C5 (D3 + DLI), C6 (D3 + DLI), C7 (D3 + FPI), C8 (D3) RH3 (D3 + FPI) RL2 (D3 + FPI) RN2 (D3), RN3 (D3) C1 (D3 + FPI), C2 (D3 + FPI), C3 (D3 + FPI), C5 (D3 + DLI), C6 (D3 + DLI), C7 (D3 + FPI), C8 (D3) RH3 (D3 + FPI) RL2 (D3 + FPI) RN3 (D3 + FPI) C2 (D3 + FPI), C3 (D3 + FPI), C6 (D3 + DLI) , C7 (D3 + FPI), C8 (D3) NA NA NA C6 (D3 + DLI) NA NA NA NA NA NA NA

Definitions Commercial and miscellaneous non-residential usage

C1

Places of detention, police stations, and institutional homes for the handicapped or aged

C2

Hospitals, hostels, hotels

C3

&RPPHUFLDO GHYHORSPHQWV ”  VWRUH\V LQFOXGLQJ UDLOZD\ VWDWLRQV VKRSV ZKROHVDOH stores, offices, places of worship, theatrical, indoor sports or public assembly venues, other institutional land uses, such as universities, schools, colleges, libraries, exhibition halls and museums, light (dry) industrial developments, dry manufacturing, commercial uses such as warehousing, packaging, electrical sub-stations, filling stations

C4

Commercial developments > 3 storeys, including railway stations, shops, wholesale stores, offices, places of worship, theatrical, indoor sports or public assembly venues, other institutional land uses, such as universities, schools, colleges, libraries, exhibition halls and museums, light (dry) industrial developments, dry manufacturing, commercial uses such as warehousing, packaging, electrical sub-stations

16 Land Use Class C5 C6 C7 C8

Definitions Fuel depots, processing plants or any other areas for the storage of liquids, waste sites Outdoor storage facilities, stock yards, container depots Parking garages Parking areas High rise dwelling units

RH1 RH2

> 10 storeys !VWRUH\VZLWKDSRSXODWLRQRI”SHRSOHSHUKHFWDUH

RH3

!VWRUH\VZLWKDUHVLGHQWLDOFRYHUDJHUDWLRRI” 0,4, no higher than 10 storeys, and a SRSXODWLRQRI”SHRSOHSHUKHFWDUH Low rise dwelling units

RL1

”VWRUH\VZLWKWRXQLWVSHUKHFWDUHDQGDSRSXODWLRQQRWH[FHHGLQJSHRSOH per hectare

RL2

”VWRUH\VZLWKXSWRXQLWVSHUKHFWDUHDQGDSRSXODWLRQQRW exceeding 400 people per hectare Dwelling houses 2

RN1

Up to 60 dwelling houses per hectare with stands larger than 150m , and a population of ”SHRSOHSHUKHFWDUH

RN2

Up to 25 dwelling houses per hectare with stands no smaller than 300m , and a SRSXODWLRQRI”SHRSOHSHUKHFWDUH

RN3

Up to 10 dwelling houses per hectare with 1 000 to 4 000m stands, and a population of ” 60 people per hectare

2

2

Infrastructure and social facilities Designation IN1

IN2

Description

Inherent hazard class determined in accordance with the requirements of SANS 1936-2 1

D2

Reservoirs and public swimming pools, water care works, attenuation and retention ponds for stormwater management and artificial lakes

D2

Cemeteries

IN4

Dams, slimes dams

IN5

Solid waste disposal facilities

3

4

5

6

7

8

Dolomite area designation

Trunk roads (national and regional roads which facilitate intercity travel) and primary distributor roads (major arterial roads forming the primary network for an urban area as a whole), railway lines, power lines, runways, bulk pipelines, including water, sewer, fuel and gas lines, pump stations

IN3

2

D3

D4

D3

D4

D3

D4

D3

D4 D3

D4

17

GEOLOGY AND GEOHYDROLOGY 6.1.

General Geology The site is underlain by chert and dolomite of the Malmani Subgroup of the Chuniespoort Group, Transvaal Supergroup with the possibility of intrusive materials in the form of dykes. The various lithological units and their weathered derivatives, recorded on the site are as follows: Lithostratigraphic Unit

Lithology

Intrusive

Syenite and associated soil derivatives.

Malmani Subgroup, Chuniespoort Group, Transvaal Supergroup

Dolomite, chert and associated soil derivatives.

Unconsolidated materials deemed to be various recent deposits (most likely 24 Ma [Miocene Epoch] and younger) are anticipated to mantle the hard rock geology (and residual product thereof). The material varies in thickness, sedimentological- and geotechnical properties: Post-Gondwana Deposits Colluvium

Local Geology A summary of the material intercepted in boreholes drilled on the site is reported here for ease of reference (explanations of letters, symbols and abbreviations are given in Table 1): Blanketing Layer (m) ± (m) Dolomite Residuum

Chert Residuum BH No. (Collar Elev. m AMSL) Fines dominant

3737 S12/1 (1480) 3737 S12/2 (1480) 3737 S12/3 (1480) 3737 S12/4 (1480) 3737 S12/5 (1480) 3737 S12/6 (1480) 3737 S12/7 (1480) 3737 S12/8 (1480) 3737 S12/9 (1480) 3737 S12/10 (1480) 3737 S12/11 (1480)

Fines subordinate

Manganiferous Soils

6.2.

Soils of sandy, silty or clayey composition or gravels

Ferroan Soils

6.

Highly weathered dolomite (m) ± (m)

Dolomite Bedrock (m) ± (m) (mAMSL)

32-38 (1448) 24-30 (1456) 34-40 (1446) 24-30 (1456) 24-30 (1456)

0-3

3-6

6-9

9-24

24-32

0-2

2-4

4-12

12-20

20-24

0-2

2-4

-

4-23

23-34

0-6

-

6-10

10-21

21-24

0-3

-

3-9

9-15

15-24

0-4

-

-

12-18

4-12 18-24

24-30 (1456)

0-3

3-5

5-8

12-22

8-12 22-24

0-6

-

6-10

10-22

22-24

0-6

-

6-9

9-28

28-38

0-6

6-18

-

-

18-24

0-6

6-13

-

13-30

30-39

24-30 (1456) 24-30 (1456) 38-44 (1442) 24-30 (1456) 39-45 (1441)

18

o

Chert residuum Chert residuum is typically intercepted from near surface. The horizons are thin (2m to 6m), the exceptions are Boreholes 3737 S12-10 and 3737 S12-11 comprising of an intermediate thick (13m to 18m) horizon.

o

Dolomite residuum (ferroan and manganiferous material) Dolomite residuum (ferroan material) is intercepted from near surface to a shallow depth or absent. The horizons are thin (3m to 8m). Dolomite residuum (manganiferous material /wad) is intercepted from a shallow to intermediate depth. The horizons are thin to intermediate thick (6m to 19m).

o

Problematic conditions in the overburden above the groundwater level: The OWL of 56m (or 1424m AMSL) is located within dolomite bedrock. Problematic conditions (sample and/or air loss) were encountered during the drilling programme within the chert residuum, dolomite residuum, highly weathered dolomite and dolomite bedrock. Cavernous conditions including disseminated voids are intercepted in nine of the boreholes drilled, i.e. 3737 S12/01 (9m to 18m), 3737 S12/03 (4m to 18m), 3737 S12/04 (10m to 17m), 3737 S12/05 (9m to 12m), 3737 S12/06 (12m to 18m), 3737 S12/07 (12m to 20m), 3737 S12/08 (20m to 22m), 3737 S12/09 (9m to 24m) and 3737 S12/11 (13m to 23m) all within dolomite residuum (manganiferous soils).

o

Dolomite bedrock conditions: Dolomite bedrock is considered to be the depth at which hard, unweathered dolomite rock is confirmed (i.e. no less than 6m of unweathered rock). Dolomite bedrock is confirmed at intermediate to great depths (24m to 39m). Highly weathered soft rock dolomite is intercepted from near surface to great depths (from 4m to 30m) typically above hard rock dolomite. The horizons are thin (2m to 11m).

6.3.

Geohydrology A desktop hydrogeological investigation and situation assessment was undertaken by Water Geoscience Consulting (WGC) on a number of dolomitic areas in 2009. According to the WGC Dolomite Hydrogeological Compartment Map (2009) the site is located in the Boskop-Turffontein Dolomite Groundwater Management Area. The regional groundwater level (OWL), as recorded in the SCTC archives, is anticipated at a depth of 1424m AMSL to 1425m AMSL (or 56m) within this portion of the BoskopTurffontein Dolomite Groundwater Compartment, taking the average ground elevation on the site as 1480m AMSL. The regional dolomite groundwater information is presented in Figure 4. A groundwater level of 1424m AMSL (or 56m) is considered for the dolomite hazard DVVHVVPHQWRIWKHVLWH$OOWKHERUHKROHVZHUHUHFRUGHGDV³GU\´KRXUVDIWHUGULOOLQJDQG the groundwater level is located within dolomite bedrock (1441m ASML to 1456m AMSL).

19

6.4.

Past Sinkholes and Subsidences No past sinkholes or subsidences are indicated in a radius of 50m around the current sinkhole.

7.

DOLOMITE HAZARD CHARACTERISATION 7.1.

Site investigation and Dolomite Hazard Assessment Procedures The site investigation procedures are presented in Sections 5.1 to 5.4 of this report. The dolomite hazard assessment procedures are presented in Section 5.8. Summarised information concerning the hazard characterisation of the site is provided in Table 1 of this report and the dolomite hazard zonation is displayed on Drawing VGI3737 S12/1.

7.2.

Hazard Characterisation of the site Based on the current data gathered, the site is characterised in terms of one primary Inherent Hazard Class area, namely: ‰

Dolomite Inherent Hazard Class 7/8(4)//1 defined as an area characterised as largely reflecting a high susceptibility of large to very large-size (with sub-areas reflecting a medium susceptibility of large-size) sinkhole and subsidence formation with respect to ingress water and a low susceptibility of all-size sinkhole and subsidence formation with respect to groundwater drawdown. In the event of groundwater level drawdown the Inherent Hazard Class remains unchanged.

a)

Blanketing layer Refer to Section 6.2.

b)

Dolomite Bedrock Dolomite bedrock is considered to be the depth at which hard, unweathered dolomite rock is confirmed (i.e. no less than 6m of unweathered rock). Dolomite bedrock is confirmed at intermediate to great depths (24m to 39m). Highly weathered soft rock dolomite is intercepted from near surface to great depths (from 4m to 30m) typically above hard rock dolomite. The horizons are thin (2m to 11m).

c)

Hazard Characterisation The site is characterized by the following conditions: i.

Blanketing layer The blanketing layer consists typically of chert residuum underlain by dolomite residuum (ferroan and manganiferous soils) and highly weathered soft rock dolomite. The chert residuum and dolomite residuum horizons exhibit rapid penetration times during drilling and a high manganese content (wad) within the dolomite residuum horizon with sample and air loss. Disseminated receptacles are recorded above the OWL within dolomite residuum in Boreholes 3737 S12/01 (9m to 18m), 3737 S12/03 (4m to 18m), 3737 S12/04 (10m to 17m), 3737 S12/05 (9m to 12m), 3737 S12/06 (12m to 18m), 3737 S12/07 (12m to 20m), 3737 S12/08 (20m to 22m), 3737 S12/09 (9m to 24m)

20

and 3737 S12/11 (13m to 23m). Prolonged ingress of water (leaking wet services) did lead to subsurface erosion and the formation of a 5m diameter size sinkhole extending to a depth of 4m. Groundwater drawdown will occur at a great depth (56m below ground surface or 1424m AMSL) within dolomite bedrock (24m to 39m depth). ii.

Potential Development Space The depth to the groundwater level (56m) and potential receptacles characterises the Potential Development Space (PDS) as mainly large to very large.

iii.

Hazard Classification (with Ingress of Water as a Triggering Mechanism) The typical subsurface profile consists of a thin to intermediate thick (2m to 18m) horizon of chert residuum, typically characterised by moderate to good internal drainage characteristics. The thin (3m to 8m) dolomite residuum (ferroan soils) horizon intercepted from near surface to shallow depth (absent in Boreholes 3737 S12/03, 3737 S12/06, 3737 S12/10 and 3737 S12/11) and the underlying thin to intermediate thick (6m to 19m) dolomite residuum (manganiferous soils) horizon intercepted from shallow to intermediate depths (absent in Borehole 3737 S12/10) is anticipated to have a high mobilization potential. Cavernous conditions including disseminated voids are intercepted within the blanketing layer dolomite residuum (manganiferous soils) in nine of the eleven boreholes drilled, sample and air losses were recorded. The subsurface conditions are characterised as largely reflecting a high susceptibility of large to very large-size (with sub-areas reflecting a medium susceptibility of large-size) sinkhole and subsidence formation with respect to ingress water, i.e. Inherent Hazard Class 7/8(4).

iv.

Hazard Classification (with Groundwater Drawdown as a Triggering Mechanism) Groundwater is anticipated at a depth of 56m or an elevation of 1424m AMSL. The groundwater level is therefore confirmed within dolomite bedrock within all the boreholes drilled. The susceptibility to sinkhole and subsidence formation with respect to groundwater level drawdown is therefore considered to be low as the groundwater level is within dolomite bedrock. Consequently the study area is designated as an Inherent Hazard Class 1 with respect groundwater level drawdown.

v.

Impact of Lowering of the Groundwater Level/Base of Erosion on the Action of Water Ingress In the event of groundwater level drawdown the Inherent Hazard Class remains unchanged i.e. IHC 7/8(4).

vi.

Composite Hazard Classification The composite hazard classification is Inherent Hazard Class 7/8(4)//1, defined as an area characterised as largely reflecting a high susceptibility of large to very large-size (with sub-areas reflecting a medium susceptibility of large-size) sinkhole and subsidence formation with respect to ingress water and a low susceptibility of all-size sinkhole and subsidence formation with

21

respect to groundwater drawdown. In the event that the groundwater level is drawdown significantly (6m or more), the hazard classification with respect to ingress of water remains the same i.e. Inherent Hazard Class 7/8(4). d) Design Hazard Class for rehabilitation works The provisional Design Hazard Class is 7.

8.

CONCLUSIONS 8.1.

Results of the borehole drilling programme The boreholes drilled on site intercept thin to intermediate thick (2m to 18m) horizons of chert residuum, thin horizons (3m to 8m) dolomite residuum (ferroan soils) intercepted from near surface to shallow depth (absent in Boreholes 3737 S12/03, 3737 S12/06, 3737 S12/10 and 3737 S12/11) underlying by thin to intermediate thick horizons (6m to 19m) dolomite residuum (manganiferous soils) intercepted from shallow to intermediate depths (absent in Borehole 3737 S12/10) and anticipated to have a high mobilization potential. Disseminated voids are intercepted within the blanketing layer dolomite residuum (manganiferous soils) in nine of the eleven boreholes drilled. Sample and air losses are recorded in the chert residuum, dolomite residuum, highly weathered dolomite rock and in dolomite bedrock. Disseminated receptacles and cavernous conditions are recorded above the OWL within dolomite residuum (wad) in Boreholes 3737 S12/01 (9m to 18m), 3737 S12/03 (4m to 18m), 3737 S12/04 (10m to 17m), 3737 S12/05 (9m to 12m), 3737 S12/06 (12m to 18m), 3737 S12/07 (12m to 20m), 3737 S12/08 (20m to 22m), 3737 S12/09 (9m to 24m) and 3737 S12/11 (13m to 23m). Dolomite bedrock is intercepted at 24m to the east and west of the sinkhole, at 24m to 39m to the north of the sinkhole and at 24m to 38m to the south of the sinkhole. The dolomite groundwater level at 56m (or 1424m AMSL) is within dolomite bedrock. A 5m diameter size sinkhole extending to a depth of approximately 4m occurred on the outfall sewer line south of Mzwanzwa Street, Khutsong Extension 3, on 21 July 2016. It is anticipated that subsurface erosion of highly erodible dolomite residuum (wad) material was initially triggered by a leak on the sewer line over an extended period of time (6 months). As a result of the initial leak, the sewer line settled and failure of the wet service occurred, leading to the formation of a medium to large size sinkhole. Sewage expelled from a leaking sewer line over a prolonged period of time will typically cause the erosion of highly erodible and compressible dolomite residuum (wad) and the formation of a cavity or erosion tunnel. Disseminated voids were intercepted in nine of the eleven boreholes during the drilling programme. An additional contributing factor is run-off surface water originating during heavy rains entering the sinkhole area further eroding subsurface materials. It should be noted that continuous and prolonged leaking wet services and surface water run-off water into the highly susceptible sinkhole area will aggravate the situation, including the enlargement of the sinkhole laterally and vertically potentially affecting a larger portion of the outfall sewer line.

22

8.2.

Dolomite Hazard Characterisation and Suitability of the site for the current land use The geotechnical data gathered during this investigation permits the dolomite hazard characterisation of the site in accordance with SANS 1936 (2012). Accordingly, the following Inherent Hazard Class area had been identified on the site: Area characterised as largely reflecting a high susceptibility of large to very large-size (with sub-areas reflecting a medium susceptibility of large-size) sinkhole and subsidence formation with respect to ingress water, and a low susceptibility of all-size sinkhole and subsidence formation with respect to groundwater drawdown. Composite Inherent Hazard Class 7/8(4)//1. In the event of groundwater level drawdown the Inherent Hazard Class remains unchanged.

9.

RECOMMENDATIONS The measures and recommendations outlined below are aimed at reducing the likelihood of a re-occurrence of a sinkhole or a subsidence in the affected area. Recommendations are based on experience gained during the investigation and rehabilitation of more than 100 instability features (sinkholes and subsidences) in the Ekurhuleni Metropolitan Municipality (EMM), City of Tshwane and West Rand District Area. 9.1.

Rehabilitation of Sinkhole Area and related wet services Based on the problematic profile intercepted during these investigations, improvement of the subsurface conditions will require the use of the Inverted Filter Method and a limited Compaction Grouting (i.e. backfilling) programme to rehabilitate the affected area, including a sinkhole and erosion voids at depth. The proposed rehabilitation area is displayed on Drawing VGI3737 S12/2. All services, including wet services (sewer, water) and electrical will need to be located prior to commencement of works. These services will need to be relocated beyond the area of works. 9.1.1. Safety precautions and site establishment The following procedures are recommended: ‰

Construct a temporary 1,8m high diamond fence around the proposed rehabilitation site and construction camp. Provide lockable access gates for each. The site shall be safe guarded by a 24-hour security service.

‰

Establish base camp and security services.

‰

Provide temporary chemical toilets for workers.

‰

Determine the locality, depth, diameter and material type of all affected services (i.e. sewer and possibly water). Relocate affected services to outside the area of works if practically feasible. The affected sewer line will need to be diverted above ground via a pipe system, pumping sewage from manhole to manhole before and during the period of rehabilitation.

‰

Obtain wet services layout plans from Merafong Local Municipality for the proposed rehabilitation area. Obtain way leaves from the various service providers for the affected area, before any work commence (if applicable).

23 ‰

Ensure that the safety file is in order before any work commences. The Safety Officer will be permanently on site during the period of rehabilitation. Personnel and construction crews are to be informed of the hazardous conditions pertaining to working in and around the sinkhole area.

‰

The personnel and construction crews are to be made aware of the need to report new surface cracks, voids, any ground movement or sudden changes in soil conditions. If such features are reported, the Resident Engineer should immediately clear the site and inspect the conditions. If uncertain of the implications of the reported conditions the Engineer should request inspection by a dolomite specialist.

‰

Personnel and construction workers executing work in and around the sinkhole are to be strapped in harnesses and safety ropes secured away from the sinkhole and excavation area or suspended from a crane or excavator parked in a safe position away from the feature.

‰

All mandatory safety procedures and requirements pertaining to working in excavations are to be applied. Use of independently attached harnesses is mandatory when workers are in the excavation. The Engineer is to as certain the need for shoring and identify those areas of the Works where shoring is to be provided to ensure the safety of workers and equipment. An inspection of the bulk excavated area shall be conducted by the Engineer each day before workers enters the excavated area as part of the safety precautionary measures.

‰

Place a soil berm around proposed area of rehabilitation to the north and east to prevent any surface runoff water entering the sinkhole area.

9.1.2. Soil improvements Improvement of subsoil conditions by means of the Inverted Filter Method and replacement of sub-surface services (sewer) Improvement of the affected area (sinkhole) will require the use of the Inverted Filter Method. The recommended rehabilitation procedure will be to remove all material to a maximum depth of 6m below ground surface, covering a surface area of 25m by 25m. Over-excavate a 5m by 5m area, with the sinkhole central to the overexcavated area down to a depth of 10m. Benching may be required at a depth of 6m creating a 2m wide terrace. Create a lip or bench 1m wide and 1m deep around the margin of the final excavation to create a protective umbrella over the contact zone between made earth and the virgin soil during backfilling. Excavation should start from the west of the sinkhole area extending towards the east. Excavation slopes from ground surface to 6m depth should be 1:1 (V:H) and from 6m to 10m vertical. An access ramp should be provided from the west. All mandatory safety procedures and requirements pertaining to working in excavations are to be applied as outlined in Section 9.1.1 7KH &RQWUDFWRU¶V Engineer must be satisfied with safety at all times. Backfilling of the excavation should involve blocking of the throats (if intercepted) with large boulders and stones filled with soilcrete compacted with an impact roller in 1m lifts up to 6m from ground surface. This should be followed by backfilling with low plasticity material: Cobbles/sandy gravels in 300mm thick layers up to a depth of 1,5m below ground surface (the first three layers should be stabilized with 3%

24

cement), followed with silty/gravely sand (G5-quality material) in 150mm thick layers up to ground level. Compaction should at least be 95% of Modified AASHTO maximum dry density at optimum moisture. The upper two 150mm layers should be compacted at least to 98% of Modified AASHTO maximum dry density at optimum moisture content and extending 1m beyond the excavated area. Provision should be made in the bill of quantities for testing of layer works to determine if the required compaction has been reached. Replace the existing broken sewer line from manhole to manhole with a butt welded HDPE pipe. All subsurface services can be placed during the backfilling of the excavation. A trench excavation (unknown depth, as no information on the depth of the affected sewer line was made available) will however be required from manhole to manhole and backfilled at 93% of Modified AASHTO maximum dry density at optimum moisture content. Reconnect all new wet services. Landscape the area to promote surface water runoff. Improvement of subsoil conditions by means of a backfill grouting programme The dolomite bedrock is encountered at a depth of 24m to 39m below natural ground level around the sinkhole. Disseminated receptacles and cavernous conditions are recorded above the OWL within dolomite residuum (wad) in Boreholes 3737 S12/01 (9m to 18m), 3737 S12/03 (4m to 18m), 3737 S12/04 (10m to 17m), 3737 S12/05 (9m to 12m), 3737 S12/06 (12m to 18m), 3737 S12/07 (12m to 20m), 3737 S12/08 (20m to 22m), 3737 S12/09 (9m to 24m) and 3737 S12/11 (13m to 23m). Based on the above findings, improvement of the subsurface conditions will require a limited grouting programme aimed at ensuring that voids intercepted in the above mentioned nine boreholes and immediate surrounds are backfilled. It is recommended that four boreholes be drilled around the position of each of the nine boreholes where voids were encountered i.e. within 3m and to the east, west, north and south. The position of the nine problematic boreholes should also be re-drilled RQLW¶VRULJLQDOSRVLWLRQ The grouting of each point will be carried out from the bottom up, which is referred to as upstage grouting, or a combination of methods may be required also including downstage grouting. The pumping rates and pressure induced to inject the grout should be selected carefully and monitored throughout the grouting process as excessive pressure will cause fracturing of the overburden resulting in ground heave and potentially more damage. The grouting mixture generally used with a slump of between 25mm and 75mm, does not need to meet any strength requirements as the objective is not to form a structural element in the ground but to backfill voids and compact problematic zones. As a point of departure provision should be made for 45 grouting points extending to a depth of 28m to 43m below ground surface, in the bill of quantities. It should be noted that the recommended grouting depths are an estimate based on existing borehole information. All the grouting boreholes should be drilled into at least 4m of solid dolomite bedrock. The injection of grout should not exceed 0,1 MPa (or 10 Bar). Provision should be made in the bill of quantities for 1m3 per meter drilling 2MPa strength grout. Clear and landscape (contouring) of the site will be required after completion

25

of the grouting programme. Provision should be made in the bill of quantities for 1 concrete cube test per day. The field report on the grouting programme, should include the applied pressure per meter (bar) and volume of grout (litre/metre) pumped at each grouting point. Also record any voids and their height. Care should be taken during the grouting programme to ensure that no damage is caused to surrounding structures. A crack survey is recommended before grouting work commences (both of the structures and the ground). 9.1.3. Monitoring of rehabilitated area Monitoring of the rehabilitated area is required on a daily basis the first three months after completion of works and thereafter on a monthly basis for the period three to six months after rehabilitation; and after six months on a three month interval to record any stability problems. These visual inspections and observations should be recorded in a log book and signed by the inspecting official. Any deterioration must immediately be reported to the City Engineer for appropriate action. 9.2.

Precautionary measures Water is a triggering mechanism, in the majority of cases, of distress in dolomitic/limestone areas. It is therefore imperative that the concentrated ingress of water into the ground be avoided at all times. 6$16  3DUW    ³'HVLJQ DQG FRQVWUXFWLRQ RI EXLOGLQJV VWUXFWXUes and LQIUDVWUXFWXUH´ LV LQ WKH SXEOLF GRPDLQ 7KH FRQWHQWV RI 6$16  VKRXOG EH DSSOLHG except where more stringent requirements are specifically required by the local authority. In accordance with SANS 1936, Part 3 (2012) all subsurface wet services should comprise of HDPE butt-welded pipes. It is recommended that all subsurface sewer lines (including manholes) around the affected sinkhole area be replaced with HDPE butt-welded pipes as specified by SANS 1936 Part 3 for areas underlain by dolomite. All subsurface stormwater pipes should also be HDPE butt-welded pipes.

9.3.

Stormwater Management Absolutely no ponding of water should be permitted on the site. An essential component of risk management is ensuring that stormwater is efficiently and effectively removed from the proximity of infrastructure and safely distributed or deposited into either the municipal stormwater system or natural river courses. Where stormwater canals are proposed on the site and carry large quantities of water, the canal should be lined.

9.4.

Monitoring Actions Immediate Monitoring Actions before rehabilitation takes place The procedure in the designation of monitoring activities and frequencies on site is described in Section 5. During the period before rehabilitation the designation for the site is as follows:

26

Inherent HazardClass Area

Monitoring Designation

7/8(4)//1

(ABC)Daily DDailyE0 Explanation

A B

Visual inspections of ground, structures and above ground infrastructure (e.g. roads, storm water canals, ditches) daily. Visual inspection of stormwater systems crossing the site for blockages daily.

C

Testing of wet-services for leaks daily.

D

Monitoring of structures and ground levels required daily. * Although not applicable to the site, any substantial lowering of the groundwater level may induce ground subsidence events in the general area. The groundwater level should be maintained within natural seasonal fluctuation limits i.e. dewatering resulting from the artificial drawdown of the groundwater level cannot be permitted.

E The Department of Water Affairs should be notified if monitoring detects groundwater level drawdown beyond that which represents natural seasonal fluctuations. In such an instance the Department of Water Affairs should immediately be requested to investigate the cause and every effort made to cease further lowering of the groundwater level. Long Term Monitoring Actions The long term designation for the site is presented as follows: Inherent HazardClass Area

Monitoring Designation

7/8(4)//1

(ABC)3 D3E0 Explanation

A B

Visual inspections of ground, structures and above ground infrastructure (e.g. roads, water supply lines, storm water canals, ditches) quarterly. Visual inspection of stormwater systems crossing the site for blockages quarterly.

C

Testing of wet-services for leaks quarterly.

D

Monitoring of structures and ground levels required quarterly. * Although not applicable to the site, any substantial lowering of the groundwater level may induce ground subsidence events in the general area. The groundwater level should be maintained within natural seasonal fluctuation limits i.e. dewatering resulting from the artificial drawdown of the groundwater level cannot be permitted.

E The Department of Water Affairs should be notified if monitoring detects groundwater level drawdown beyond that which represents natural seasonal fluctuations. In such an instance the Department of Water Affairs should immediately be requested to investigate the cause and every effort made to cease further lowering of the groundwater level. The rehabilitation works proposed are only an element of the mitigation and risk management measures required on the site. Ongoing risk management (SANS1936 (2012) Part 4) is essential.

27

9.5.

Database of ground movement and stability conditions It is recommended that the sinkhole that occurred on the outfall sewer line south of Mzwanzwa Street, Khutsong Extension 3 and all repair, upgrade and soil improvement work conducted is added to the 0XQLFLSDO¶V database of ground movement events. Detailed historical records of this nature are most useful in developing a clearer perspective on the stability situation on site and management of a pro-active maintenance strategy.

10.

GENERAL These findings are based upon our interpretation of the data recovered during these investigations. While every effort has been made, within the limits of the project budget, time and present-day insight, to determine overall ground conditions on this site, poorer sub-areas may have been missed.

VGIconsult Projects (Pty.) Ltd. P.O. BOX 604 FOURWAYS 2055 TEL : (011) 469 0854 FAX : (011) 469 0961 FAX : 0866892847 e-mail: [email protected]

TABLES SUMMARISED BOREHOLE INFORMATION AND INHERENT HAZARD CHARACTERISATION

TABLE 1

0-3

0-2

0-2

0-6

0-3

0-4

0-3

0-6

0-6

0-6

0-6

3737 S12/2 (1480)

3737 S12/3 (1480)

3737 S12/4 (1480)

3737 S12/5 (1480)

3737 S12/6 (1480)

3737 S12/7 (1480)

3737 S12/8 (1480)

3737 S12/9 (1480)

3737 S12/10 (1480)

3737 S12/11 (1480)

Fines dominant

3737 S12/1 (1480)

BH No. (Collar Elev. m AMSL)

6-13

6-18

-

-

3-5

-

-

-

2-4

2-4

3-6

Fines subordinate

-

-

6-9

6-10

5-8

-

3-9

6-10

-

4-12

6-9

Ferroan Soils

Blanketing Layer (m) ± (m) Chert Residuum Dolomite Residuum

13-30

-

9-28

10-22

12-22

12-18

9-15

10-21

4-23

12-20

9-24

30-39

18-24

28-38

22-24

8-12 22-24

4-12 18-24

15-24

21-24

23-34

20-24

24-32

(m) ± (m)

Highly weathered dolomite

39-45 (1441)

24-30 (1456)

38-44 (1442)

24-30 (1456)

24-30 (1456)

24-30 (1456)

24-30 (1456)

24-30 (1456)

34-40 (1446)

24-30 (1456)

32-38 (1448)

(m) ± (m) (mAMSL)

Dolomite Bedrock

Dry 56 1424 Dry 56 1424 Dry 56 1424 Dry 56 1424 Dry 56 1424

Dry 56 1424

OWL (m AMSL) Dry 56 1424 Dry 56 1424 Dry 56 1424 Dry 56 1424 Dry 56 1424

(m) (m AMSL)

Groundwater Rest Level

13-45

-

6-44

10-30

12-30

12-30

6-30

6-30

0-40

12-30

9-38

(m)±(m)

Air & Sample Losses

TABLE 1: BOREHOLE DATA AND DOLOMITE INHERENT HAZARD CHARACTERISATION

Manganiferrous Soils

13-23

-

9-24

20-22

12-20

12-18

9-12

10-17

4-18

-

9-18

(m)±(m)

Cavernous Conditions

High

Medium

High

High

High

High

High

High

High

High

High

Subsidence Formation

High

Medium

High

High

High

High

High

High

High

High

High

Sinkhole Formation

Low

Low

Low

Low

Low

Low

Low

Low

Low

Low

Low

Subsidence Formation

Low

Low

Low

Low

Low

Low

Low

Low

Low

Low

Low

Sinkhole Formation

Groundwater Drawdown

Hazard Characterisation Ingress Water

FIGURES LOCALITY PLAN TOPOGRAPHICAL SHEET LEGEND SITE LAYOUT WITH GROUND ELEVATION CONTOURS REGIONAL GEOLOGY GEOLOGY LEGEND REGIONAL GEOHYDROLOGY

FIGURE 1 FIGURE 1A FIGURE 2 FIGURE 3 FIGURE 3A FIGURE 4

-2908500

-2911000

-2913500

-2916000

-2918500

-2921000

! (

23500

GROUND MOVEMENT INCIDENTS

LEGEND

±

23500

26000

26000

28500

28500

31000

! (

VGI3737: S12.1

31000

33500

33500

36000

0

36000

1 000

1 500

Welverdiend

500

. !

! (

2 000

38500

2 500 metres

38500 -2908500 -2911000 -2913500 -2916000 -2918500 -2921000

GEOTECHNICAL

VGI3737

OCTOBER 2016

date

FIGURE 1

Drawing number

1:50 000

scale

checked

designed drawn

ref.no.VGI3737

N.T.

AR.G.

N.T.

LOCALITY PLAN (REF.: MAP 2627AD CARLETONVILLE 1:25 000)

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

name:

A3

page type

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

D.P.W.

False Northing = 0° Scale Factor = 1 Datum = WGS 84

AMENDMENT

Transverse Mercator Central Meridian = 27° False Easting = 0°

co-ordinate system

No. DATE

name:

GEOTECHNICAL

VGI3737

checked

scale date

FIGURE 1A

Drawing number

OCTOBER 2016

designed drawn

ref.no.VGI3737

N.T.

AR.G.

N.T.

TOPOGRAPHICAL SHEET LEGEND (REF.: MAP 2627AD CARLETONVILLE 1:25 000)

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

AMENDMENT

D.P.W.

A3

page type

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

co-ordinate system

No. DATE

-2914600

-2914625

-2914650

-2914675

-2914700

! (

Oberholzer NU

31025

31000

AREA OF INVESTIGATION

FARMS

SUBURBS

STANDS

31025

VGI5066 MERAFONG SINKHOLES AND SUBSIDENCES

GROUND MOVEMENT INCIDENTS: SINKHOLES

GROUND MOVEMENT INCIDENTS

ROADS

GROUND ELEVATION CONTOURS (mAMSL)

LEGEND

±

31000

31075

31050

VGI3737: S12 CAVITY 2016/01/12

31075

ID: T0IQ00000000009700052

VGI3737: S12.1 SINKHOLE 2016/09 WELVERDIENDSUB DIVISION NR. 00052

31050

31100

0

31100

5

10

15

20

31125

25 metres

31125

31150

-2914600 -2914625 -2914650 -2914675

31150

-2914700

8 14

0 GEOTECHNICAL

VGI3737

OCTOBER 2016

FIGURE 2

Drawing number

date

checked

designed drawn

scale

1:500

ref.no.VGI3737

N.T.

AR.G.

N.T.

SITE LAYOUT WITH GROUND ELEVATION CONTOURS

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

name:

A3

page type

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

D.P.W.

False Northing = 0° Scale Factor = 1 Datum = WGS 84

AMENDMENT

Transverse Mercator Central Meridian = 27° False Easting = 0°

co-ordinate system

No. DATE

-2906000

-2911000

LEGEND

±

16000

21000

26000

26000

31000

! (

VGI3737: S12.1

31000

36000

36000

0

41000

1 000

2 000

3 000

4 000

5 000 metres

46000

! (

16000

21000

GROUND MOVEMENT INCIDENTS

41000

46000

-2921000

-2926000

-2916000

-2906000 -2911000 -2916000 -2921000 -2926000

GEOTECHNICAL

VGI3737

page type

A3

OCTOBER 2016

FIGURE 3

Drawing number

date

checked

designed drawn

scale

1:100 000

ref.no.VGI3737

N.T.

AR.G.

N.T.

REGIONAL GEOLOGY (REF.: MAP 2626 WEST RAND 1:250 000 GEOLOGICAL SERIES)

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

name:

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

D.P.W.

False Northing = 0° Scale Factor = 1 Datum = WGS 84

AMENDMENT

Transverse Mercator Central Meridian = 27° False Easting = 0°

co-ordinate system

No. DATE

name:

GEOTECHNICAL

D.P.W.

VGI3737

page type

A3

checked

scale date

FIGURE 3A

Drawing number

OCTOBER 2016

designed drawn

ref.no.VGI3737

N.T.

AR.G.

N.T.

GEOLOGY LEGEND (REF.: MAP 2626 WEST RAND 1:250 000 GEOLOGICAL SERIES)

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

AMENDMENT

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

co-ordinate system

No. DATE

-2906000

-2916000

-2926000

-2936000

-2911000

-2913500

-2916000

-2918500

±

28500

28500

Mooirivierloop

C23K

C23G

R501

o Lo

C23J

C23E

! (

31000

36000

u pr ps

it

31000

46000

33500

46000

pruit

1:200 000

Loop s

QUATERNARY CATCHMENTS

LEGEND

MARSH VLEI

LARGE RESERVOIR

DAM

INLAND WATER AREAS

33500

1:50 000

DOLOMITE GROUNDWATER MANAGEMENT UNITS (GMU)

LEGEND

QUATERNARY CATCHMENTS

2 N1

! (

R50 0

GROUNDWATER MANAGEMENT UNITS (GMU)

C23F

26000

N14

36000

-2906000 -2916000

28500

Mooirivierloop

28500

26000

2 N1

! (

R501

36000

o Lo

u pr ps

it

31000

33500

46000

pruit

1:200 000

Loop s

MARSH VLEI

LARGE RESERVOIR

DAM

INLAND WATER AREAS

33500

1:50 000

DOLOMITE GROUNDWATER RESOURCE UNITS (GRU)

LEGEND

GROUNDWATER RESOURCE UNITS (GRU)

! (

31000

36000

46000

GROUNDWATER MANAGEMENT AREAS (WMA)

LEGEND

GROUNDWATER MANAGEMENT AREAS (WMA)

Upper Vaal

N14

26000

0 R50

26000

-2906000 -2916000 -2926000 -2936000 -2911000

-2926000 -2936000 -2911000 -2913500 -2916000 -2918500

-2913500 -2916000 -2918500

-2913500 -2916000 -2911000

-2906000 -2916000 -2926000 -2936000 -2911000 -2913500 -2916000 -2918500

-2913500 -2916000 -2918500

C2N0107

! (

W298

! (

BOSKOP - TURFFONTEIN OWL: 1424 - 1425m AMSL

BOSKOP - TURFFONTEIN

DOLOMITE GROUNDWATER COMPARTMENTS

! (

28500

C2N0103

W266

Mooirivierloop

28500

! ?

MMW1 IR863MW

! ?

MMW2 IR863MW

! ?

! ( ! (

31000

33500

33500

! ?

1:50 000

MMW4 IR863MW

MONITORING BOREHOLES (IR863 MW)

NGIS HYDSTRA: DISCONTINUED

NGIS HYDSTRA: STATUS UNKNOWN

LEGEND

NATIONAL GROUNDWATER INFORMATION SYSTEM

! (

W180 C2N0188

! ?

! (

31000

31000

1:24 000

DOLOMITE GROUNDWATER MANAGEMENT AREAS

LEGEND

DOLOMITE GROUNDWATER MANAGEMENT AREAS AND DWA REPORTS

Turffontein

31000

-2913500 -2916000 -2911000 -2913500 -2916000

00 R5

-2918500

00 R5

AMENDMENT

! (

name:

GEOTECHNICAL

VGI3737

A2

page type

OCTOBER 2016

FIGURE 4

Drawing number

date

scale

ref.no. VGI3737

checked

drawn

designed

I.K.

AR.G.

I.K.

REGIONAL GEOHYDROLOGY (REF.: MAP 2627AD CARLETONVILLE 1:25 000)

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

False Northing = 0° Scale Factor = 1 Datum = WGS 84

D.P.W.

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

Transverse Mercator Central Meridian = 27° False Easting = 0°

RIVERS

GROUND MOVEMENT INCIDENTS

GENERAL LEGEND

co-ordinate system

No. DATE

DRAWINGS RESIDUAL GRAVITY, BOREHOLE POSITIONS AND DOLOMITE HAZARD ZONATION

VGI3737 S12/1

PROPOSED REHABILITATION AREA

VGI3737 S12/2

-2914600

-2914625

-2914650

-2914675

31000

! (

-0.2

31025

AREA OF INVESTIGATION

DOLOMITE STABILITY ZONATION

31025

VGI5066 MERAFONG SINKHOLES AND SUBSIDENCES

GROUND MOVEMENT INCIDENTS: SINKHOLES

REGIONAL RESIDUAL GRAVITY (mGals)

BOREHOLES

LEGEND

±

31000

-0.3

31050

3737 S12.1-11

! (

! (

! ( ! (

! (

! (

3737 S12.1-03

3737 S12.1-07

! (

2016/09

! (

! (

31075

! (

3737 S12.1-09

3737 S12.1-04

! (

3737 S12.1-05

3737 S12.1-08

VGI3737:S12.1

3737 S12.1-02

31075

3737 S12.1-06

7/8(4)//1 5m x 5m DIA, 4m DEEP

3737 S12.1-01

3737 S12.1-10

31050

31100

0

31100

5

10

15

20

31125

25 metres

-0.4

31125

-2914600 -2914625 -2914650 -2914675

GEOTECHNICAL

VGI3737

page type

A3

OCTOBER 2016

checked

N.T.

AR.G.

N.T.

DRAWING VGI3737 S12.1/01

Drawing number

date

designed drawn

scale

1:400

ref.no.VGI3737

REGIONAL RESIDUAL GRAVITY WITH BOREHOLE POSITIONS AND DOLOMITE HAZARD ZONATION

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

name:

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

D.P.W.

False Northing = 0° Scale Factor = 1 Datum = WGS 84

AMENDMENT

Transverse Mercator Central Meridian = 27° False Easting = 0°

co-ordinate system

No. DATE

-2914625

-2914650

-2914675

BOREHOLES

! (

31025

AREA OF INVESTIGATION

VGI5066 MERAFONG SINKHOLES AND SUBSIDENCES

GROUND MOVEMENT INCIDENTS: SINKHOLES

AREA OF REHABILITATION

GROUTING POSITIONS

D

LEGEND

±

31025

! (

31050

3737 S12.1-11

D ! ( D D D D D

D 3737 S12.1-07 ! ( D D D D

! (

D ! ( D DD D

3737 S12.1-03

31075

0

D ! ( D D D D 3737 S12.1-08

5

D ! ( D D D D 3737 S12.1-09

! ( D

3737 S12.1-04

D 3737 S12.1-05 D D !( D D

D ! ( D D D D

31075

3737 S12.1-06

VGI3737:S12.1 5m x 5m DIA, 4m DEEP 2016/09 3737 S12.1-02

3737 S12.1-01

D D ! ( D D

3737 S12.1-10

31050

10

15

20

31100

25 metres

31100

-2914625 -2914650 -2914675

GEOTECHNICAL

VGI3737

OCTOBER 2016

checked

N.T.

AR.G.

N.T.

DRAWING VGI3737 S12.1/02

Drawing number

date

designed drawn

scale

1:300

ref.no.VGI3737

PROPOSED REHABILITATION AREA

drawing title

Project Number

VGI3737 S12.1 KHUTSONG EXT 3: OUTFALL SEWER SINKHOLE

service

discipline

2 MULBERRY HILL OFFICE PARK BROADACRES DRIVE DAINFERN VALLEY PO BOX 604 FOURWAYS 2055 TEL: (011) 469 0854 FAX: (011) 469 0961 E-mail: [email protected]

VGIconsult

consultant

cad file name

professional registration no.:

date:

name:

A3

page type

certified as-built drawings as per Centralised Drawing Archive AS-BUILT DRAWING REQUIREMENTS

as-built drawings

D.P.W.

False Northing = 0° Scale Factor = 1 Datum = WGS 84

AMENDMENT

Transverse Mercator Central Meridian = 27° False Easting = 0°

co-ordinate system

No. DATE

APPENDICES BOREHOLE PROFILES APPENDIX 1

APPENDIX 1 BOREHOLE PROFILES

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

1 23.02 3 Penetr Air SampleHammer time return recov rate min:s/m

3.09

2.44

2.40

2.07

1.55

1.46

1.33

1.02

0.59

0.46

0.37

0.42

0.23

0.19

0.15

0.04

0.02

0.03

0.05

0.03

0.06

0.03

0.05

0.03

0.59

0.50

0.46

0.24

0.22

0.26

0.23

0.25

0.27

30

25

20

15

10

5

Scale 1:150

32.00

25.00

9.00

6.00

3.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-01 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Brown clayey SILT with minor subangular brown grey highly weathered dolomite fragments; DOLOMITE RESIDUUM

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.05

3.00

3.07

3.04 35

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

1445

3.02

S12.1

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

S12.1-01 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914635 Y-COORD : -31057

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 20m to 38m, medium air loss between 18 m to 20 m, total air loss between 9 m to 18 m and total sample loss from 9 m to 38 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 32 m to 38 m

NOTES

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

38.00

JOB NUMBER: 3737

HOLE No: 3737 S12.1-01 Sheet 2 of 2

NO SAMPLE RETURN; interpreted as hard rock dolomite

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.01

3.07

3.02

3.08

3.06

3.04

1.56

1.43

1.37

1.25

0.43

0.19

0.10

0.13

0.10

0.11

0.12

0.10

0.20

0.21

0.27

0.31

0.53

0.46

0.24

0.21

0.26

0.20

0.22

0.25

30

25

20

15

10

5

Scale 1:150

30.00

24.00

20.00

12.00

4.00

2.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-02 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Brown clayey SILT with minor subangular brown grey highly weathered dolomite fragments; DOLOMITE RESIDUUM

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-02 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-02 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914646 Y-COORD : -31060

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 19m to 30m, medium air loss between 12 m to 19 m and total sample loss from 12 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

as

NO SAMPLE RETURN; interpreted as soft rock dolomite

interpreted

REDUCED LEVEL

1440

1445

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.05

3.00

3.08

3.11

3.06

3.10

2.13

40

35

40.00

34.00

1 22.13 3 Penetr Air SampleHammer time return recov rate min:s/m

2.00

1.56

1.49

1.40

1.36

1.43

1.40

1.35

1.27

0.58

0.47

0.41

0.35

0.20

0.16

30

25

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-03 Sheet 2 of 2

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-03 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914653 Y-COORD : -31066

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 19m to 40m, medium air loss between 0 m to 4 m, 12 m to 15 m, 18 m to 19 m, total air loss between 4 m to 12 m, 15 m to 18 m and total sample loss from 4 m to 40 m.

Groundwater

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 34 m to 40 m.

NOTES

NO SAMPLE RETURN; interpreted as hard rock dolomite

6) No water added

24.00

NO SAMPLE RETURN; dolomite residuum

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

0.02

0.02

20

4.00

2.00

0.00

S12.1

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

5) Boskop-Turffontein Compartment

15

10

5

Scale 1:150

JOB NUMBER: 3737

HOLE No: 3737 S12.1-03 Sheet 1 of 2

0.03

0.12

0.10

0.13

0.03

0.02

0.03

0.06

0.05

0.07

0.02

0.03

0.16

0.14

0.15

0.16

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.06

3.02

3.00

3.05

3.08

3.01

1.46

1.50

1.09

0.53

0.43

0.17

0.15

0.06

0.05

0.02

0.03

0.09

0.05

0.03

0.14

0.15

0.13

0.15

0.25

0.23

0.25

0.29

0.26

0.21

30

25

20

15

10

5

Scale 1:150

30.00

24.00

21.00

10.00

6.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-04 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Dark brown clayey SILT with minor translucent blue grey highly weathered chert fragments and black silt ( WAD); DOLOMITE RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-04 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-04 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914646 Y-COORD : -31078

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 19m to 30m, medium air loss between 6 m to 10 m, 17 m to 19 m, total air loss between 10 m to 17 m and medium sample recovery between 6 m to 7 m, 8 m to 10 m, poor sample recovery between 7 m to 8 m, total sample loss from 10 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m.

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.10

3.06

3.05

3.03

3.00

3.02

1.33

1.44

1.40

1.39

1.26

1.22

1.20

1.16

1.06

0.55

0.47

0.21

0.04

0.02

0.05

0.17

0.16

0.18

0.21

0.22

0.24

0.34

0.31

0.28

30

25

20

15

10

5

Scale 1:150

30.00

24.00

15.00

9.00

6.00

3.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-05 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Brown clayey SILT with minor subangular brown grey highly weathered dolomite fragments; DOLOMITE RESIDUUM

Dark brown clayey SILT with minor translucent blue grey highly weathered chert fragments and black silt ( WAD); DOLOMITE RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-05 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-05 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914641 Y-COORD : -31077

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 12m to 30m, medium air loss between 6 m to 9 m, total air loss between 9 m to 12 m and total sample loss from 9 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m.

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.07

3.03

3.00

3.04

3.01

3.05

1.56

1.53

1.42

1.49

1.01

0.56

0.06

0.08

0.05

0.07

0.03

0.09

1.20

1.18

1.13

1.10

1.15

1.00

1.02

0.56

0.28

0.25

0.27

0.3

30

25

20

15

10

5

Scale 1:150

30.00

24.00

19.00

12.00

4.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-06 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Subangular brown grey highly weathered soft rock DOLOMITE.

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-06 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-06 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914635 Y-COORD : -31072

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 18m to 30m, total air loss between 12 m to 18 m and total sample loss from 12 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.17

3.15

3.09

3.10

3.08

3.03

1.56

1.50

0.10

0.09

0.07

0.06

0.09

0.07

0.04

0.05

0.06

0.07

1.20

1.23

1.31

1.40

0.42

0.34

0.46

0.50

0.47

0.40

0.31

0.34

30

25

20

15

10

5

Scale 1:150

30.00

24.00

22.00

12.00

8.00

5.00

3.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-07 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Subangular brown grey highly weathered soft rock DOLOMITE.

Dark brown clayey SILT with minor translucent blue grey highly weathered chert fragments and black silt ( WAD); DOLOMITE RESIDUUM

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-07 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-07 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914659 Y-COORD : -31059

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 22m to 30m, medium air loss between 21 m to 22 m, total air loss between 12 m to 21 m and total sample loss from 12 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.10

3.03

3.08

3.14

3.11

3.04

1.40

1.07

0.06

0.07

0.13

0.17

0.15

0.10

0.09

0.08

0.07

0.09

0.13

0.10

0.25

0.23

0.22

0.24

0.29

0.31

0.36

0.30

0.28

0.25

30

25

20

15

10

5

Scale 1:150

30.00

24.00

22.00

10.00

6.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-08 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as hard rock dolomite

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Dark brown clayey SILT with minor translucent blue grey highly weathered chert fragments and black silt ( WAD); DOLOMITE RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-08 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/15 DATE : 2016/09/21

S12.1-08 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914661 Y-COORD : -31074

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 22 m to 30 m, medium air loss between 10 m to 12 m, 16 m to 20 m, total air loss between 12 m to 16 m, 20 m to 22 m and total sample loss from 10 m to 30 m.

6) No water added

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/16

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

interpreted

as 3.16

3.11

3.09

3.06

3.02

3.05

2.15

2.00

1.56

1.50

12 3 REDUCED Penetr Air SampleHammer LEVEL time return recov rate min:s/m

1440

1445

1.49

40

35

44.00

38.00

NOTES

NO SAMPLE RETURN; interpreted as hard rock dolomite

S12.1

1 21.49 3 Penetr Air SampleHammer time return recov rate min:s/m

1.43

1.39

1.35

1.00

0.56

0.48

0.30

0.25

0.16

0.07

0.03

0.09

0.09

30

25

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

DATE : 11/10/16 14:24 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/21 DATE : 2016/09/30

S12.1-09 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914656 Y-COORD : -31081

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 25 m to 44 m, medium air loss between 6 m to 9 m, 24 m to 25 m, total air loss between 9 m to 23 m and medium sample recovery between 7 m to 9 m, total sample loss from 9 m to 44 m.

6) Water added between 6 m to 9 m, 21 m to 22 m, 23 m to 24 m, 25 m to 26 m, 27 m to 28 m, 29 m to 31 m, 32 m to 34 m, 35 m to 36 m, 37 m to 38 m, 39 m to 40 m, 41 m to 42 m and 43 m to 44 m

Groundwater

5) Boskop-Turffontein Compartment

20

0.07

0.09

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/22

0.03

0.05

0.04

0.03

2) No groundwater intercepted

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Dark brown clayey SILT with minor translucent blue grey highly weathered chert fragments and black silt ( WAD); DOLOMITE RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

JOB NUMBER: 3737

HOLE No: 3737 S12.1-09 Sheet 2 of 2

0.05

29.00

9.00

6.00

0.00

S12.1

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

1) Driller reports solid conditions between 38 m to 44 m

15

10

5

Scale 1:150

JOB NUMBER: 3737

HOLE No: 3737 S12.1-09 Sheet 1 of 2

0.06

0.02

0.05

0.03

0.15

0.15

0.16

0.53

0.45

0.47

0.31

0.30

0.36

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

12 3 Penetr Air SampleHammer time return recov rate min:s/m

3.13

3.15

3.11

3.09

3.00

3.07

1.13

1.15

1.11

1.07

1.09

1.05

1.00

1.01

1.03

1.00

1.02

0.59

0.56

0.58

0.55

0.53

0.48

0.44

0.24

0.40

0.25

0.23

0.28

0.25

30

25

20

15

10

5

Scale 1:150

30.00

24.00

18.00

6.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-10 Sheet 1 of 2

Subangular blue grey unweathered hard rock DOLOMITE.

Subangular brown grey highly weathered soft rock DOLOMITE.

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

12 3 Penetr Air SampleHammer time return recov rate min:s/m

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

REDUCED LEVEL

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-10 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:25 TEXT : ..C:\DOTFILES\201610~1.TXT

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/21 DATE : 2016/09/30

S12.1-10 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914625 Y-COORD : -31052

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports no air or sample loss

6) Water added between 13 m to 15 m, 24 m to 25 m, 26 m to 27 m and 28 m to 30 m

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/22

2) No groundwater intercepted

1) Driller reports solid conditions between 24 m to 30 m

NOTES

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

REDUCED LEVEL

1450

1455

1460

1465

1470

1475

1 21.36 3 Penetr Air SampleHammer time return recov rate min:s/m

1.29

1.25

0.57

0.16

0.10

0.13

0.11

0.12

0.10

0.09

0.07

0.05

0.08

0.03

0.06

0.02

0.02

0.02

0.02

0.05

0.39

0.40

0.43

0.32

0.40

0.38

0.30

0.25

0.22

0.23

0.21

0.20

0.23

30

25

20

15

10

5

Scale 1:150

31.00

13.00

6.00

0.00

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-11 Sheet 1 of 2

interpreted

as

NO SAMPLE RETURN; interpreted as soft rock dolomite

NO SAMPLE RETURN; dolomite residuum

Angular translucent blue grey highly weathered CHERT fragments with minor silty sand; CHERT RESIDUUM

Brown silty SAND minor angular white to brown and translucent blue grey highly weathered chert fragments; CHERT RESIDUUM

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

3.06

3.05

3.00

3.04

3.11

3.15

2.43

2.33

2.15

1.53

1.42

45

40

35

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : J.K. DEVELOPMENTS MACHINE : THOR 5000 DRILLED BY : J.G MALULEKE PROFILED BY : J.MEINTJES

12 3 REDUCED Penetr Air SampleHammer LEVEL time return recov rate min:s/m

1435

1440

1445

1.36

JOB NUMBER: 3737

S12.1

HOLE No: 3737 S12.1-11 Sheet 2 of 2

Groundwater

DATE : 11/10/16 14:25 TEXT : ..C:\DOTFILES\201610~1.TXT

S12.1-11 dot.PLOT 5006 J&W

HOLE No: 3737

ELEVATION : 1480 m AMSL X-COORD : 2914634 Y-COORD : -31047

8) Projection Information: CM 27 degrees, Transverse Mercator, WGS 84

7) Driller reports slight air loss between 30m to 45m, medium air loss between 24 m to 30 m, total air loss between 13 m to 24 m and total sample loss from 13 m to 45 m.

6) Water added between 4 m to 5 m, 6 m to 7 m, 8 m to 9 m, 10 m to 11 m, 12 m to 13 m, 25 m to 27 m, 28 m to 29 m, 30 m to 31 m, 32 m to 33 m, 35 m to 36 m, 37 m to 38 m and 39 m to 45 m

5) Boskop-Turffontein Compartment

4) Original Dolomite Aquifer Groundwater Level (OWL) 1424m AMSL

3) Groundwater rest level recorded as Dry on 2016/09/22

2) No groundwater intercepted

1) Driller reports solid conditions between 39 m to 45 m

NOTES

NO SAMPLE RETURN; interpreted as hard rock dolomite

INCLINATION : 90 DEGREES DIAM : 165mm DATE : 2016/09/21 DATE : 2016/09/30

45.00

39.00

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION

D055 DBB

TYPE SET BY : J.MEINTJES SETUP FILE : SETUP.SET

CONTRACTOR : MACHINE : DRILLED BY : PROFILED BY :

{SA13} {SA21} {SA22}

DOLOMITE

CHERT

WAD

DATE : 11/10/16 14:25 TEXT : ..C:\DOTFILES\201610~1.TXT

dot.PLOT 5006 J&W

SUMMARY OF SYMBOLS

LEGEND

{SA09}

CLAYEY

ELEVATION : X-COORD : Y-COORD :

{SA07}

SILTY

INCLINATION : DIAM : DATE : DATE :

{SA06}

SILT

S12.1

{SA04}

JOB NUMBER: 3737

Sheet 1 of 1

LEGEND

SAND

MERAFONG CITY LOCAL MUNICIPALITY KHUTSONG: OUTFALL SEWER LINE SINKHOLE INVESTIGATION