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Effect of Water Table on Bearing Capacity

The theoretical equations developed for computing the ultimate bearing capacity qu of soil are based on the assumption that the water table lies at a depth below the base of the foundation equal to or greater than the width B of the foundation or otherwise the depth of the water table from ground surface is equal to or greater than (Df+ B). In case the water table lies at any intermediate depth less than the depth (Df+ B), the bearing capacity equations are affected due to the presence of the water table.
Two cases may be considered here.
Case 1. When the water table lies above the base of the foundation.
Case 2. When the water table lies within depth B below the base of the foundation.
We will consider the two methods for determining the effect of the water table on bearing capacity as given below.
Method 1
For any position of the water table within the depth (Df+ B), we may write Eq. (12.6) as
eq 11.23-24
Method 2: Equivalent effective unit weight method
Eq. (12.6) for the strip footing may be expressed as
eq 12.25
Figure 12.10 Effect of WT on bearing capacity
 
equation of Effect of Water Table on Bearing Capacity