Brosur Tensar Ground Stabilisation With Geogrid Biaxial

Contact Tensar International or your local distributor to receive further literature covering Tensar products and applications. Also available on request are product specifications, installation guides and specification notes. The complete range of Tensar literature consists of: • Tensar Geosynthetics in Civil Engineering A guide to the products and their applications

Reinforcing unbound layers in roads and trafficked areas

• Ground Stabilisation Reinforcing unbound layers in roads and trafficked areas • Steep Slopes Constructing embankments with steep slopes • Retaining Walls Constructing retaining walls in reinforced soil • Foundations over Piles Constructing over weak ground without settlement • Basal Reinforcement Constructing embankments over weak ground • Railways Reinforcing ballast under railway track • Asphalt Pavements Reinforcing asphalt layers in roads and trafficked areas • Erosion Controlling erosion on soil and rock slopes

Your local distributor is:

Tensar International Limited

Tel: +44 (0)1254 262431

New Wellington Street

Fax: +44 (0)1254 266868

Blackburn BB2 4PJ United Kingdom

Ground Stabilisation

E-mail: [email protected] www.tensar-international.com

Tensar geogrids are manufactured under tightly controlled conditions. The quality assurance procedures covering design and application and the manufacturing process have been certified by the British Standards Institution as a Registered Firm in accordance with BS EN ISO 9001:2000 Q05288

Tensar is a registered trade mark. ©Copyright Tensar International Limited Printed February 2003 Issue 4, 79010035

The information provided verbally, or in this document or as a Free Application Suggestion is of an illustrative nature and is supplied without charge. It does not form any contract or intended contract with the user. No liability in negligence will arise from the construction of any project based on such information or material. Final determination of the suitability of any information or material for the use contemplated and the manner of use is the sole responsibility of the user and the user must assume all risk and liability in connection therewith.

Tensar biaxial geogrids work by interlocking with aggregates

Road construction problems 2

Construction of road pavements is expensive and time consuming. Difficult access conditions can become impossible, especially in wet weather. Soft sensitive subgrades frequently require large thicknesses of aggregate, much of which is lost due to deep rutting. Aggregates are expensive and scarce, and their extraction damages the environment. They must be transported, placed and compacted.

Very difficult access.

The interlock mechanism.

Road building aggregates are becoming scarce and expensive - they must be transported, placed and compacted.

Wet weather conditions.

Soft sensitive subgrades.

• Helps control differential settlement over variable soils and spans voids or soft spots

• Reinforcement benefit is localised and can be generated within the loaded area This mechanism is also referred to as “confinement”, because interlock effectively immobilises and confines the aggregate particles.

e rc fo

• Reduces granular thickness by up to 40%, thereby conserving valuable aggregate resources and the environment

• Tensile load in the grid is generated at very small deflections of an applied vertical load

d

• Reduces excavation, disturbance and subsequent disposal of subgrade soils

The Tensar manufacturing process produces a unique grid structure, consisting of full strength junctions and stiff ribs, which present a thick square leading edge to the aggregate. This allows the aggregate particles to get a good “grip” on the geogrid, and results in effective mechanical interlock. Interlock helps prevent lateral movement and dilation of aggregate particles, so that a very high effective angle of

lie

Using Tensar biaxial geogrids in road construction can solve or reduce the problems described above. Designers can optimise their pavement design, especially when conditions are challenging. Contractors can reduce cost and save time. Including Tensar biaxial geogrids in a pavement:

shearing resistance is mobilised. Vertical load applied through aggregate particles above the grid can generate tensile resistance in the ribs with very small deflection. The combination of these features ensures that, in Tensar geogrid reinforced granular layers:

p ap

Tensar geogrids reduce cost and save time in road construction

Tensar biaxial geogrids can solve pavement problems because they interlock very efficiently with granular materials. When granular particles are compacted over these grids, they partially penetrate and project through the apertures to create a strong and positive interlock.

• Improves fill compaction • Increases design life and improves life-cycle management

The unique cross-sectional shape of Tensar ribs provides bearing points for aggregate particles and works like the triangular rack supporting a pyramid of snooker balls.

Building a pavement over Tensar geogrids (UK).

Tensar. The value engineered solution In Tensar you’ll find a partner with the experience and flexibility to respond to your project requirements. From design to completion, we’ll make sure you always benefit from a practical, costeffective solution to your specific need.

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The interlocking between the geogrid and the aggregates particles limits lateral movement when dynamic loading is applied.

Do geotexiles work in the same way? 4

This is a common question when considering using a geogrid in a road pavement. The answer is: NO. Geotextiles cannot interlock with aggregate particles, so they cannot generate the same very efficient interaction and confinement of the aggregate. Geotextiles are normally used as separators only, but if they

Designing pavements with Tensar geogrid

are designed to reinforce a pavement by developing tension, then they must form a “tensioned membrane” which requires large deformations, and fixed wheel paths. It is not suitable for use in the design of normal surfaced or permanent pavements. The difference is illustrated on the diagrams below.

Design of road pavements depends on: • Subgrade strength (CBR) • The properties of the fill/aggregates • The number and loading of the axles • The maximum rut depth or bearing capacity

Designing with Tensar geogrids results in reduced layer thickness.

Designs are carried out using sophisticated software.

Tensar International provides a full design service and has developed sophisticated computer software based on a number of different national pavement design guidelines. The reinforcing benefit of Tensar geogrids is incorporated in the design methods, using data from independent pavement tests and trafficking trials. These methods of designing reinforced pavements are reliable and have been in use for many years. Detailed test and trial data are given in “Properties and Performance of Tensar Biaxial Geogrids”, available from Tensar International. Tensar SS biaxial geogrids are manufactured in three grades (SS20, SS30 and SS40) with apertures suited to

typical sub-base gradings (75mm maximum particle size). Tensar SSLA biaxial geogrids have larger apertures making them suitable for aggregates of larger particle size. Two grades are available SSLA20 and SSLA30. Choice of grade depends principally on subgrade condition and strength, but axle load and service life are also taken into account. In addition, Tensar SS-G and SSLA-G are geocomposite products comprising a Tensar biaxial geogrid laminated to a non-woven geotextile. The products are particularly suited for use with uniformly sized aggregates. Documents giving detailed recommendations for choice of grid type are available from Tensar International. No responsibility is accepted by Tensar International for any project which does not involve the use of Tensar biaxial geogrids installed pursuant to Tensar International’s full design service.

Installation of Tensar biaxial grids TENSAR GEOGRID REINFORCED PAVEMENT

TENSIONED MEMBRANE REINFORCED PAVEMENT

• • • •

• • • •

Interlock stiffens the aggregate layer Load spread is increased Aggregate transfers the load Performance is improved

Geotextile is anchored at edges Load is transferred to geotextile Geotextile and subgrade deform Negligible performance gain

Installing Tensar biaxial geogrids using an overlap between adjacent rolls.

This difference in performance is emphasised by the rut profiles shown above, measured as part of a detailed pavement trial carried out by TRL (Transport Research Laboratory, UK). These are cross-sections of the trial pavement, showing both the top of the sub-base (320 mm thick) and the top of the subgrade (CBR = 1.5%), before and after completion of trafficking. After 5000 passes a deep rut has formed in the geotextile reinforced sub-base with a considerable amount of heave, and

a similar rut has developed at the top of the subgrade. This results in remoulding and softening of the subgrade. For the Tensar SS30 section, after 10,000 passes the rut in the subbase is much smaller with little heave, and the rut in the subgrade is negligible with no heave (mainly consolidation settlement of the clay subsoil). The strength of the woven geotextile is slightly higher than that of Tensar SS30, yet performance is quite different.

No special plant, equipment or techniques are required to install Tensar biaxial geogrids. Site formation should be prepared in the normal way, and any large obstructions, tree stumps and other protrusions should be removed. On very soft wet subgrades, biaxial geogrid is often used as a method of getting access onto the site, to allow initial layers of fill to be placed.

between 300 and 600mm depending on the condition of the underlying material. The larger overlaps are required over softer subgrades, whereas minimum overlap may be used over competent subgrades or for second layers. An alternative to a full overlap is to use a smaller overlap of two to three apertures, then join the rolls together using HDPE braid.

Rolls of Tensar biaxial geogrid are light and stiff, and do not require a core. They can easily be lifted and rolled out by two workers. Special lifting frames and cranes are not required. They are normally held in position by small piles of fill.

It is important that fill is placed correctly for maximum benefit. It should be tipped onto stockpiles on top of the existing placed material, then a mechanical excavator or bulldozer should lift and cascade the material onto the grid. If the material is pushed forwards from a stockpile, then it can create a bow wave, and over soft soils it will tend to push the grid into the subgrade soils. This will diminish the interlocking effect.

Adjacent rolls are usually overlapped to give continuity of the reinforcing function. The required overlap is Adjacent rolls may be joined together using HDPE braid.

If the fill grading requires a geotextile separator as well as geogrid reinforcement, both functions can be served by a single Tensar SS-G composite.

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Correct method of placement and spreading of granular material is important.

Tensar SS-G composite.

AIRPORT PAVEMENTS Loadings on airport pavements are very high, and frequently lead to multi-layer reinforced construction. The US Army Corps of Engineers carried out some special pavement trials in the early 1990’s to examine the benefit of geogrid reinforcement in aircraft pavements. These well documented comparative trials showed that Tensar biaxial geogrids were the only materials used which gave a significant improvement in performance.

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New taxiway at Adelaide Airport (Australia).

Road widening, Auckland (New Zealand).

Versatility of Tensar biaxial geogrids Since the early 1980’s several hundred million square metres of Tensar biaxial geogrids have been used in tens of thousands of projects. They have been used in most countries in the world, under a wide variety of climates and soil conditions, and frequently they have been used to solve difficult design or construction problems. Getting access over very soft subgrade.

Temporary access road across peat swamp, Machap (Malaysia).

ACCESS OVER VERY SOFT SUBGRADE Some subgrades are so soft or waterlogged that the main problem is to get access to place fill or sub-base material. These include very soft mud, peat and tailings deposits. Tensar biaxial geogrids act like a “snowshoe”, providing immediate support to workers and the initial fill layers. In addition, the interlocking effect allows some compaction to be achieved, even in the fill directly above the soft subgrade. TEMPORARY ACCESS ROADS

Construction of major highway (Oman).

Tensar biaxial geogrids are excellent for helping to build temporary access roads, especially when the subgrade is soft, trucks are heavy and good fill is scarce. The wide rolls are ideal for a single track road to carry typical construction vehicles, and they are easily transported and deployed.

Container yards, logging areas and fabrication sites frequently require vehicles with very high track or axle loads, and the pavements are often

MAJOR HIGHWAYS Major highways require large investment, and the cost of pavement building materials is normally a significant proportion. Also, costing of this type of pavement must take into account future maintenance, in terms of overlays and possible reconstruction. Using Tensar biaxial geogrids can reduce the cost of capital investment and future maintenance.

Widening existing roads is common due to increasing traffic and requirements for higher standards. Generally the existing road must be kept open, and there are frequently services already in place. Using Tensar geogrids can reduce the thickness of the new pavement, thereby minimising disruption. This can also help avoid relocation of existing services if they are shallow. Linking the geogrid into the existing pavement can help minimise differential settlement between the old and new sections.

Heavy Duty Pavements

WHARF AND PORT AREAS Wharf and port areas are subject to heavy loads from cranes and transport vehicles, as well as from the goods being handled. The subgrades are frequently poor marginal soils or fills. Tensar biaxial geogrids improve bearing capacity and help to create high quality pavements.

Wharf area (Latvia).

Tensar SS geogrid properties Property

Units

Tensar geogrid

*SS-G & SSLA-G

SS20*

SS30*

SS40*

SS2

SSLA20*

SSLA30*

PP

PP

PP

PP

PP

PP

All of the geogrids marked * are also available as a geocomposite. The geocomposite comprises

Polymer (1)

Geocomposite properties

Minimum carbon black (2)

%

2

2

2

2

2

2

Roll width

m

4.0 & 3.8

4.0 & 3.8

4.0 & 3.8

4.0

3.8

3.8

the geogrid heat bonded to a geotextile

Roll length

m

50

50

30

50

50

50

separator. The properties of the geotextile are

Unit weight

kg/m2

0.22

0.33

0.53

0.29

0.22

0.32

Roll weight

kg

46 & 44

67 & 64

65 & 62

60

43

65

AL

mm

39

39

33

28

65

65

Effective opening size (6)

µm

125

AT

mm

39

39

33

40

65

65

Permeability (7)

m/s

0.135

Unit weight (8)

kg/m2

0.16

ROAD WIDENING

When axle or vehicle loads become very heavy, number of axle passes becomes very great or the subgrade is very soft, granular layer thickness increases to an extent where more than one layer of biaxial geogrid is required to maintain continuity of the reinforcing function. In such cases two or possibly three layers of geogrid are required. Heavy duty pavements may require two or three geogrid layers.

HEAVY DUTY HANDLING AREAS

unsurfaced. Tensar biaxial geogrids have been used in many such applications, frequently with multiple layer construction. Performance of these types of pavement in service has shown that reinforcement improves traffickability and reduces maintenance and regrading.

Dimensions

given in the following table. Geotextile component Puncture resistance (CBR) (5)

WLR

mm

2.2

2.3

2.2

3.0

4.0

4.0

WTR

mm

2.4

2.8

2.5

3.0

4.0

4.0 7.0

tJ

mm

4.1

5.0

5.8

3.8

4.4

tLR

mm

1.1

2.2

2.2

1.2

0.8

1.7

tTR

mm

0.8

1.3

1.4

0.9

0.8

1.5

Rib shape

N

>1500

Roll Width (Transverse)

Roll Length (Longitudinal)

tJ

Rectangular with square edges

tTR

Ribs

Quality Control Strength (longitudinal) Tult(3)

kN/m

20.0

30.0

40.0

17.5

20.0

30.0

Load at 2% strain (3)

kN/m

7.0

10.5

14.0

7.0

7.0

11.0

Load at 5% strain (3)

kN/m

14.0

21.0

28.0

14.0

14.0

22.0

Approx strain at Tult

%

11.0

11.0

11.0

12.0

10.0

9.0

tLR Junctions

AL

WLR

AT

WTR

Quality Control Strength (transverse) Tult (3)

kN/m

20.0

30.0

40.0

31.5

20.0

30.0

Load at 2% strain (3)

kN/m

7.0

10.5

14.0

12.0

8.0

12.0

Load at 5% strain (3)

kN/m

14.0

21.0

28.0

23.0

15.0

25.0

Approx strain at Tult

%

10.0

10.0

10.0

10.0

10.0

9.0

95

95

90

95

95

Junction strength as % of QC strength (4) Minimum junction strength

%

95

(1) PP denotes polypropylene. (2) Carbon black inhibits attack by UV light. Determined in accordance with BS 2782:Part 4: Method 452B:1993. (3) Determined in accordance with BS EN ISO 10319:1996 and as a lower 95% confidence limit in accordance with ISO 2602:1980 (BS 2846:Part 2:1981). (4) Determined in accordance with GRI GG2-87 and expressed as a percentage of the quality control strength. (5) Determined in accordance with BS EN ISO 12236:1996. (6) Mean value of O90 determined in accordance with wet sieving test to BS EN ISO 12596:1999. (7) Mean value expressed as velocity index VIH50 determined in accordance with BS EN ISO 11058:1999. (8) Mean value determined in accordance with BS EN 965:1995. (9) All quoted dimensions and values are typical unless stated otherwise.

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