Monotonic and cyclic lateral loading of piles in low to medium density chalk

Abstract

Offshore and other structures often rely on driven piles to carry lateral loads. However, there is currently no established design method to cover lateral loading at chalk sites, which are widespread across NW Europe. This paper reports monotonic and cyclic lateral load tests on highly-instrumented 508mm and 1220mm diameter open steel piles driven at a well-characterised chalk test site in Kent, UK, for a recent Joint Industry Project (JIP) that developed new benchmark datasets and analyses, supported by high-quality testing. The ultimate lateral pressures mobilised in the chalk are shown to be relatively low compared to its UCS strengths due to pile-driving damage, natural fracturing, local yielding and brittleness. Significant gaps opened between the piles and chalk during loading, that led to a substantially softer response on unloading and subsequent reloading, as well as marked axial capacity losses. Reaction curves extracted from the field measurements and applied in a 1D numerical model perform well in reproducing the monotonic lateral tests. As with piles driven in other materials, one-way cyclic lateral loading led to permanent displacement accumulation and stiffness changes that were linked to the cyclic loading parameters. Both effects were more marked under bi-axial cyclic lateral loading.