Estimating soil moduli from drilled pier load tests

Modulus of deformation, E_sa, of sandy soils is estimated from load tests of drilled piers assuming that only the active depth lying directly under the pier base undergoes compression. The active depth is defined as the depth of the layer in which the increment of stress produced by the transmitted load is greater than a certain given fraction of the effective geostatic stress. Instrumented load tests yield the conclusion that the modulus, E_sa, is equal to the secant modulus of deformation E_sa as obtained from triaxial tests. The proposed method makes it possible to predict the settlement of piers at limit load using laboratory moduli determined from samples extracted from the layer underlying the pier base. An example illustrates how the settlement of axially loaded drilled piers bearing on sand can be calculated by the proposed method using the linear elastic theory as outlined by Poulos. The variance of the estimated modulus is indicated. It appears that lengthy and costly load tests of drilled piers could be avoided if the proposed method is applied.