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© 2019 JETIR March 2019, Volume 6, Issue 3

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Variation of In-situ Properties with boredepth in alluvial deposits of ChuntKol Barbarshah Sgr 1

Sheikh Adnan Farooq, 2Obaid Qadir Jan 1 MTech Scholar, 2MTech Scholar 1 Geotechnical Engineering, 1 National Institute of Technology, Srinagar, India Abstract : After the recent devastating flood in Kashmir in 2014, a detailed geotechnical investigation has become imperative prior to construction of any structure. The detailed geotechnical investigation has to be kept in mind before suggesting any suitable foundation. The Net safe bearing/Pile capacity depends on soil parameters which include field & laboratory results. Considering lack of funds, a detailed investigation is not possible for every structure. As such a rough estimate of the field parameters may be of help in and around the area. N value being a reliable part of field investigation can be used as an indicative of engineering properties of soil and net safe bearing/Pile capacity. In this regard boring was carried out on alluvial deposits in the field at Barbarshah, Srinagar to ascertain the rough behaviour of the soil using shell and auger boring. Boring was carried in one boreholes (BH1) upto 15m depth. Standard Penetration Test (SPT) values were taken at different depths ranging from 1.5m to 3m. IndexTerms - geotechnical investigation, flood, N Value, SPT Values I. INTRODUCTION

A

LLUVIAL has very low bearing capacity. The site is proximate to a tributary of Jhelum River (Chunt Kol). This river is

flood prone and has a history of causing large scale damage to the adjoining structures. The site has plain topography and deposits consist of silt of medium to high plasticity upto full bore depth. The strata show low resistance and N–values are low. However, N values increase considerably from a depth of 13.5m. Seepage water was encountered from a depth of 0.75m. Ground water was encountered at a depth of 4.65m. Keeping in view the maximum credible earthquake magnitudes in the region, the site area is classified in zone 5 of B/S code of practice (IS-1893-2016) where earthquake magnitudes can exceed 7.5. The field work was started and completed on 28-10-2018. As per the stipulated proposal the bore depth is 15mtrs for BH1. The bore depth and number of boreholes was decided by the requisitioning agency. Standard Penetration Tests (SPT), Sampling have been carried out on the collected samples. The water table will be fluctuating depending upon the flood level in the river and it will be assumed at NSL for better safety. II. MATERIALS AND METHOD Alluvial soil of Barbarshah proximate to a tributary of River Jhelum (Chunt Kol) of Srinagar city was tested using Standard penetration test. The alluvial deposits were tested at intervals of 1.5 to 3m.. Virgin soil properties like SPT Values were taken. Density & In situ moisture content was recorded after sampling using split spoon sampler. III. RESULTS AND DISCUSSION Visual observation fully established the silty and clayey nature of strata barring 12m depth. During the process of boring N value were low upto a depth of 13.5m varying from 3 to 6.Beyond 13.5m, there is considerable resistance with N-values varying from 36 to 39. Samples obtained from the boreholes have been subjected to various laboratory tests. Standard Penetration tests (SPT) conducted at various depths show erratic N value. The recorded N-value have been corrected for over-burden and dilatancy and these corrected values have to be used for determining allowable pressure at the base of the foundation. The overall average observed N value is 16.0 and corrected value is 11.0. The bulk density is approximately 2.0T/m2 with an average moisture content of 28.07%. This will give the submerged density of 1.0 T/m3. Variation of N Value with bore depth During the process of boring there was very less resistance upto a depth of 13.5m where the N value varies from 3 to 6.Beyond 13.5m ,there is considerable increase in N values and the N-values vary from 36 to 39. The overall average observed N value is 16 and corrected N value after overburden & dilatancy is 11.0.

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TABLE 1. N Value

N-Value (Corrected) Overburden Dilatancy

Depth(m)

BH-1(Observed)

1.5 3 4.5 6 7.5 9 10.5 12 13.5 15

3 4 5 6 36 39

5 5 5 5 29 31

5 5 5 5 22 23

Average Values

16

-

11

Variation of dry density with bore depth The dry density of the material varies from 1.50T/m3 to 1.71T/m3 with an overall average of 1.60T/m3.The average bulk density is approximately about 2T/m3 which is very close to saturated density with an average moisture content of 28.07%. The dry density shows no definitive trend. However, maximum dry density is observed at 13.5m depth. Minimum dry density is observed at 6mtrs. Considering the split spoon sampler has a poor recovery ratio in this case i.e. thin walled sampler was not used. An accurate in situ dry density could not be derived as such. TABLE 2. Density (g/cc)

Depth(m)

BH-1

Avg Value

1.5 3 4.5 6 7.5 9 10.5 12 13.5 15

1.56 1.57 1.55 1.50 1.70 1.65 1.55 1.68 1.71 1.58 1.60

1.56 1.57 1.55 1.50 1.70 1.65 1.55 1.68 1.71 1.58 1.60

Average Values Variation of moisture content with bore depth

The moisture content of the soil varies from 20.34% to 37.58% with an overall average of 28.07%.

Depth(m)

BH-1

Avg Value

1.5 3 4.5 6 7.5 9 10.5 12 13.5

27.18 28.43 24.07 37.58 24.69 27.66 31.30 24.11 20.34

27.18 28.43 24.07 37.58 24.69 27.66 31.30 24.11 20.34

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35.38 28.07

Average Values

35.38 28.07

1.75

Dry Density (T/m2)

1.70 1.65 1.60 1.55 Dry Density (T/m2)

1.50

Linear (Dry Density (T/m2))

1.45 0

2

4

6

8 (m) Depth

10

12

14

16

Fig. 1. Variation of Dry Density (T/m2) with bore depth

40.00

Moisture Content (%)

35.00 30.00 25.00

20.00 15.00 Moisture Content

10.00

Linear (Moisture Content)

5.00 0.00 0

2

4

6

8 Depth (m)

10

12

14

16

Fig. 2. Variation of moisture content (%) with boredepth

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45 40

N obs N corr Linear (N obs) Linear (N corr)

35

N Value

30 25 20 15 10 5 0 0

2

4

6

8

10

12

14

16

Depth (m) Fig.3.Variation of N Value with depth

IV. CONCLUSION The study reveals that the soil has following parameters 1. Alluvial deposits in Barbarshah proximate to a tributary of Jhelum River have very low N value. 2. However, a detailed geotechnical investigation should be done as per the importance of the project. 3. There could be significant variation in the area and complete dependence on these results is not technically feasible. However, it can be used to get a preliminary idea of the geotechnical field parameters. Scope of future work  A detailed field investigation around the area can be carried out.  A detailed laboratory investigation should also be considered.

REFERENCES 1.

[1] Arora,K.R (2011). Soil Mechanics & foundation Engineering, Pg 427

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