A new assessment of ultimate unit friction for driven piles in low to medium density chalk

摘要

A number of methods currently exist for the assessment of ultimate long term static axial pile capacity for driven piles installed in chalk stratum. In each of these methods the derivation of shaft resistance is based upon estimation of the in-situ horizontal stress and the pile interface friction angle (8) and it is conventional to impose arbitrary limits upon the ultimate unit friction to account for reduction in particle cohesion due to remoulding during pile driving. This paper presents the results of preliminary laboratory testing undertaken to examine the effects of driven pile installation on the static simple shear strength mobilised in low to medium density chalk after remoulding during high intensity pile driving. Data from the tests are interpreted with reference to the stress state behaviour of the chalk and show consistent trends which allow a more accurate, and less conservative, assessment of ultimate unit friction compared to current design methods.