Pile response in sand: experimental development and study

Pile response in sand remains an important issue in the field of foundations. The influence of such parameters as the consolidation stress, the density ratio, the direction of loading (tension or compression) and the installation method significantly affects pile behaviour. As part of the Forever research project on micropiles in France, a parametric study was undertaken in a calibration chamber to analyse the influence of these parameters on pile response. A pile was designed with specific instruments independently to measure the tip resistance and shaft friction for a given pile segment. Two installation methods were tested: displacement piles (DPs) and non-displacement piles (NDPs). Significant differences in tip resistance were associated with the two installation methods. The shaft friction exhibited a stiffer response during the compression tests of the NDP, but the difference in capacity was less distinct. The effect of loading was highly symmetrical for the NDP, but for the jacked pile the shaft friction was smaller under tension loading. A comparison of the results with data presented in the literature (laboratory and field tests) showed satisfactory agreement. In addition, hyperbolic transfer laws were proposed for the tip resistance and the shaft friction and validated for the experimental results.