Life Cycle Changes in p-y Stiffness for a Conductor Pile Installed in Carbonate Silt

Abstract

Lateral soil stiffness has a strong influence on the overall strength and fatigue life of well conductors and piles. This paper reviews data from centrifuge testing of a short model pile embedded in carbonate silt, which was subjected to packets of cyclic lateral displacement. Key conclusions are that (i) cyclic lateral stiffness is significantly affected by prior loading history due to the generation and dissipation of pore pressure, (ii) the generation process leads to the wellrecognized softening of p-y curves, (iii) the dissipation process leads to a lessrecognised stiffening of the response, and (iv) carbonate silts show a different shape of cyclic lateral response compared to non-carbonate clays, meaning that existing 'fully degraded' steady state p-y models are not appropriate. Future ideas to capture these improvements in lateral response modelling are set out, with the aim of allowing more accurate and reliable design of conductors and piles.

A cyclic p-y model for the whole-life response of piles in soft clay

“…The net result is a rise in strength and stiffness, and a reduction in the sensitivity observed in each packet. This trend matches published results from various model testing studies of lateral pile behaviour (Zhang et al 2011, Doherty et al 2019, Guevara et al 2020, Lai et al 2020 as well as analogous studies of cyclic T-bar penetrometer tests (White & Hodder 2010) or plate anchor loading (Zhou et al 2020).…”

“…with sets of cycles interspersed by periods of consolidationby Zhang et al (2011) showed the pile head lateral stiffness fall to 40% of the initial value during an initial cyclic episode, but then rise by a factor of 2 following subsequent consolidation periods. Further results presented by Doherty et al (2019), Lai et al (2020) and Guevara et al (2020) show similar trends in more detail, illustrating the effects of cyclic amplitude, pile length and different patterns of cycling and waiting periods. The observed changes in p-y stiffness are significant and affect the stability, stiffness and fatigue rate of piles and well conductors.…”