From before blogs we talked about calculation of bearing capacities by using 4 equations. From this blog we will see the effect of water table for calculations and what are the variations if there are layered soil mediums under the footing.
Effect of the water table
For the calculations of ''qult" the water table will directly affect. Basically in bearing capacity equations "q" and " gamma b " will depend on the water table.Case 01 - B < dw
There are no changes in the equation
Case 02 - 0< dw < B
Gamma b will change
Case 03 - dw = 0
Gamma b will change
Case 04 - dw < Df
q and Gamma b will change
Case 05 - Df < dw
q and Gamma b will change
Actually no change but we need to use "gamma soil" as "gamma sub"
Note : Using this we can prove if the water level rise it will not affect to the foundation.
Layered soil medium
We consider "B" depth as effective depth for our calculations. For our calculations we need to consider average values for phi, C and gamma. There for we need to take weighted average (effective method)
Effective stress or total stress analysis
If the pore water pressure due to loading of the foundation is dissipated within a very short time period. The soil is in a drained condition, therefore effective soil strength parameters C' and phi' are used in the bearing capacity equation.If the soil is in the undrained condition need to use total strength parameters C and phi.
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