ABSTRACT
The authors carried out an initial series of centrifuge tests using a 2 × 2 pile group with an instrumented pile leg. This pile group is described fully by Knappett & Madabhushi (2008). The instrumented pile was fitted with a pressure cell at the pile tip, and an axial load cell at the top of the pile. However, this configuration only allowed the average shaft friction along the length of the pile to be measured. It is therefore not possible to understand any differences in shaft friction behaviour occurring in different soil layers. Where a pile is embedded in both loose and dense soils, these differences could be significant. The instruments used in the pile were also of concern. The diaphragm of the pressure cell at the pile tip is not stiff enough to accurately measure the bearing pressure and its use is therefore restricted to measuring dynamic changes in bearing pressure. The axial load cell was also observed to be significantly affected by
1 INTRODUCTION
Piled foundations have become popular worldwide as a solution for transferring high structural loading through weak or compliant soil layers to stiffer or more competent soils below the surface. However, during earthquake events, liquefaction of surrounding soils has led to many failures, especially when lateral spreading occurs and soil flows past the piled foundation. In the case of bridges, the effects of failure are not limited to the damage caused to the bridge itself. After an earthquake, access to the affected areas is of great importance as it can often be a key factor in the event’s ultimate toll. The failure of piled foundations during earthquakes has therefore led to active research in this area. Much of the research carried out in this area has focussed on the bending moments exerted on the piles during lateral spreading, for example Abdoun et al. (2003) and Brandenberg et al. (2005). However, some research has been carried out to investigate modes of failure induced by axial loading. Bhattacharya et al. (2005) investigated the axial failure of single rock-socketed piles in liquefiable soils, finding that if sufficiently loaded, these pile foundations were prone to buckling as the lateral soil support reduced. This work was extended by Knappett and Madabhushi (2009), who showed that pile groups are also subject to unstable collapse if the axial load is sufficiently high. However, the preceding two works rely on the high vertical support provided by the base rock. In the case of most piles, the bedrock is located too deep for piles to be able to realise the rock-socketed condition. Knappett & Madabhushi (2008) carried out centrifuge tests to investigate the behaviour of pile groups which
bending moments, and therefore readings during dynamic loading will be affected.
