Cyclic loading effect on pile P-y curves : centrifuge modelling

摘要

A series of centrifuge model tests has been carried out to study the effect of cyclic loads on horizontally loaded piles in dense sand. From the collected data, the P-y reaction curves at different depths are obtained during both the first monotonic loading (reference P-y curve) and during the following cyclic loading sequences. The study focuses on the effect of cyclic loads on the P-y curves. A reduction coefficient r_c (P-multiplier) is determined experimentally. It may be applied to the P reaction of the reference P-y curve to obtained the cyclic loading P-y curves. The cyclic loading sequences are characterised by the number of cycles n, maximum applied load F and the cycles amplitude DF. Several combinations of F and DF have been investigated and the following results have been obtained: 1. the effect of cycle on the P-y curve is concentrated in the first 15 cycles 2. large hysteresis is observed on the cyclic P-y curve 3. depending on depth, the cyclic loads may either decrease or increase the soil resistance 4. a reduction coefficient r_c of the soil reaction P (or P-multiplier) has been determined to be applied to the monotonic P-y curve to take into account the cyclic loading effects 5. in the upper soil layers that governs the flexible pile response to horizontal loads, the value of r_c range from 0.5 to 1 depending on the cycle characteristics (F, DF). Simple relationships giving the r_c values as function of depth and of number and characteristic of cycles will be proposed to account for cyclic loading effects when designing horizontally loaded piles in practice.