Field tests on the lateral capacity of poles embedded in Auckland residual clay

The purpose of this paper is to present results of field testing to evaluate the lateral capacity of timber poles embedded in Auckland residual clay. The work was undertaken because the commonly used relation by Broms seems to predict lateral capacities for embedded poles used in construction of pole retaining walls that are too conservative. The reason for this is thediscounting of the lateral resistance contribution from the soil over then initial 1.5 embedment diameters. In all 16 poles were installed in residual clay at a site in Albany, thirteen of them concreted into bored holes with an embedment diameter of 0.45 m and three of them driven. A total of 14 poles were tested. The conclusion from interpretation of the results is that a very good match is achieved between measured and predicted capacity if a modified version of the pole capacity equation is used which is based on lateral reaction present over the full embedded depth of the pole of 3s_u. The paper describes the test method, the interpretation of the results, and verifies that a modified lateral capacity equation gives very good matching of the measured results.