ABSTRACT:

One of the common reasons for uneven settlement of existing structures, founded on pile foundations, is the negative skin friction (NF) developed along the piles. In the past, several experimental studies on negative friction have been carried out to understand the above mechanism. However, the mechanism of negative friction on a pile foundation has not been completely established so far. In the current investigation, the fundamental characteristics of negative friction development on a pile foundation constructed in soft ground were experimentally studied through a centrifuge model. The negative friction development due to a surface loading was studied including the influence of multi-layered soil strata. Theoretical formulations were derived to predict the negative friction development on a pile foundation, and the centrifuge results were compared with the theoretical predictions.

INTRODUCTION

Large-scale structures with long pile foundations have been constructed in Japan since 1960"s. In such constructions, uneven settlements of the foundation and bearing capacity failures due to negative friction are known to have occurred. As a result, many experimental studies were conducted (JSSMFE ed., 1969; Tsutsumi and Nei, 1975; Okabe, 1975) incorporating simple model tests satisfying similarity rules. Prototype tests needed large-scale testing facilities, long-term measurements and therefore there still remains uncertainty in rationally understanding the mechanism of negative skin development. In the current study, centrifuge model tests were carried out on typical pile foundations to evaluate the mechanism of the axial forces induced by negative friction. The several aspects examined during these tests are:

  • influence of shearing (slipping) along the pile-soil interface on the negative friction,

  • settlement characteristics of soft ground, and

  • mechanism of neutral point shifting due to ground conditions at the pile bearing end.

Theoretical formulations for predicting negative friction were developed including the bearing capacity estimates with the concurrent NF-induced forces.

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