EFFECT OF WATER TABLE ON BEARING CAPACITY OF THE SOIL

PREPERED BY:- Davra Jaydip 14soecv11011 Dobariya anil 14soecv11015

Gajera kishan 14soecv11017 Goti prashant 14soecv11019 GUIDED BY :- Prof. Pandey sir

INTRODUCTION

The position of ground water has a significant effect on the bearing capacity of soil.

Presence of water table at a depth less than the width of the foundation from the foundation bottom will reduce the bearing capacity of the soil.

Lesser the depth, harder it is to build a strong foundation as the soil will have low bearing capacity. As speaking of bearing capacity, it is the maximum stress which a particular soil can withstand without failing.

EFFECT OF WATER TABLE ON BEARING CAPACITY

The change in moisture content of the soil affects the properties of the soil. Similarly, if soil gets submerged its ability to support the load coming over its unit area is reduced when the water table is above the base of the footing.

the submerged weight is used for the soil below the water table for computing the surcharge.

The water table corrections are applied to determine the ultimate bearing capacity of the soil.

The bearing capacity equation incorporating the ground water table correction factors is given below.

Where qu = Ultimate bearing capacity of soil in c = Cohesion of soil in Nc, Nq, N? are Therzaghi’s bearing capacity constants. Df= depth of foundation in meters B = Width of the foundation in meters Rw1 and Rw2 are water table correction factors The water table correction factors can be obtained from the equations given

below.

Case 1Water table located above the base of footing.

Zw

Rw1=0.5[1+Zw1/D] Rw2=0.5

Case 2If the water table located at a depth below base

of footing

Zw2

Zw

Rw1=1Rw2=0.5[1+Zw2/b]

Case 3Water table located at a depth equal to or

greater than width (D1>=B) OF footing below the base of footing

D1

Rw1=Rw2=1

IN THIS CASE NO EFFECT OF WATER TABLE ON BEARING CAPACITY OF SOIL

IS CODE METHOD

IS :6403-1981 gives the equation for the net ultimate bearing capacity which is similar to one proposed by vesic

Qnu = c Nc Sc Dc Ic +q(Nq-1)Sq Dq Iq + 0.5B ý N ý s ý d ý i ý w

Where D=effective pressure at the base Qnu =Qu – ýDf The factor w takes into account the effect of the water

table. If the water table is at or below a depth of (Df +B ) measured from the ground surface w =1

If the water table is likely to rise to the base of the footing or above the value of w is taken at 0.50

Case study

Project :- determination depth of foundation Location :- tramba village depth of water table Dw= 3.8m depth of foundation Df= 1.2mHere , Dw>DfSo we conclude,For this depth of foundation no effect on bearing capacity of soil due to water table level.

CONCLUSIONS At sites where construction on soils of low bearing

capacity is inevitable, then excess ground water should be pumped out as required to get the desired bearing capacity .

Higher the water table, lesser is the bearing capacity and strength of the soil.

REFERENCES

Soil mechanics and foundation engineering by Dr. K.R.Arora. By the site NPTEL

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