Jo mvA(Ti dH

If mv and A are assumed constant with depth the equation for p reduces to: ¿x = A + (l-A)a (4)

1" Jo


Act, dH

Poisson's ratio for a saturated soil is generally taken as 0.5 at the stage when the load is applied so a is a geometrical parameter which can be determined, various values for a that were obtained by Skempton and Bjerrum are given in Table 9.4.

Table 9.4

Circular footing Strip footing

The value of the pore pressure coefficient A can now be substituted in Equation (4) and a value for /i obtained, typical results being:

Soft sensitive clays... possibly greater than 1.0

Normally consolidated clays... generally less than 1.0 Average overconsolidated clays... approximately 0.5 Heavily overconsolidated clays... perhaps as little as 0.25

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