The Behaviour of Axially Loaded Piles Subjected to Lateral Soil Movements

Abstract

Many studies have been undertaken on piles subjected to vertical load, and on piles subjected to lateral soil movement. However, little information is available for evaluating the response of vertically loaded piles due to soil movement. In this thesis studies have been carried out to investigate the behaviour of axially loaded piles subjected to lateral soil movements. The main focus of the thesis was experimental, where a testing apparatus had been fabricated to perform laboratory model tests in either sand or clay. In each test, the apparatus had the ability to vary a number of parameters such as: the shape of the soil movement profile; the axial load; the ratio of the moving to the stable soil layers; the pile diameter; and the soil properties. In addition to these parameters, the pile group tests involved different pile spacing and various pile group arrangement. The pile response, in terms of bending strain and displacement at the pile head, was measured. The vast majority of tests were conducted on piles driven into sand. The results from the single pile tests show that, regardless of the shape of the soil movement profile, the maximum bending moment increases with the pile diameter, the sand density and the axial load. The ratio of the moving to the stable soil layers changed with the magnitude and the shape of the bending moment profiles. The pile group tests, apart from the abovementioned parameters, were found to have an influence on the piles; the pile spacing and the pile group arrangement also influenced the behaviour of the individual piles in a group. The testing apparatus was modified to conduct the tests in unconsolidated clay. The clay was very soft, which resulted a high relative stiffness between the pile and the clay. The results from a small number of tests showed that, in single pile tests, the piles behave like a rigid pile with the maximum bending moment increasing with the pile diameter. Numerical analyses with the three-dimensional finite difference method were performed to predict and compare the results from the single pile tests in sand. In parametric studies it was found that Young’s modulus, friction angle, dilation angle were among the parameters that had the greater effect on pile behaviour, in particular the maximum bending moment. Other less influential parameters were the interface properties between the pile and the soil, the density of the brick elements, and constitutive models. In all the predictions, the numerical analysis was shown to be able to predict the experimental results reasonably well. A further investigation into soil parameters (yet to be assessed in the experimental studies) was also carried out. These parameters included the ratio of the moving soil to the stable soil layers and the dilation angle of the sand. A simplified solution was proposed to analyse a rigid pile subjected to lateral soil movement by the mean of calculating the pressure distribution acting along the pile shaft. The simplified solution was able to predict the bending moment and shear force profiles from the calculated pressure distribution acting along the pile. A number of case studies were carried out to test the ability of the simplified solution. The experimental and numerical studies undertaken for this thesis have provided an important understanding of the behaviour of axially loaded piles subjected to lateral soil movement. In hope to benefit future research work, the limitations of the current studies and the areas for further research are outlined.