Q. Influence of Pressure in the Soil?

Figure shows the stress state beneath a footing. The steady state situation prior to footing as well as qualitative variation of pressure are also shown. From this Figure it can be seen that the strain E occurs in a zone directly beneath the footing of about 0.3 to 0.5 where the increase in pressure from the footing is greatest. These profiles also show that depth 'L' producing a significant strain contribution is between 2 and 4B. The correct estimate of strain is rather difficult since E, varies with depth. The other earth pressure coefficient will also vary and probably larger than KO. The value of Poisson's ratio is assumed to be in the range of 0.3 to 0.4.

In such condition, the trapezoidal formula can be used to obtain average value of E,. Alternately, one may subdivide the stratum into several increments and compute the settlement of the increment. Total settlement can be computed as the summation of the several layer.