Behaviour of axially loaded piles (1988)
AuthorsCheung, Ka-Chingshow all
This project may be described in three parts. The first part mainly involves the evaluation of existing soil models under undrained conditions. The second part of the project is to evaluate the currently used methods for representation of the pile installation process. The third part of the work involves the study of the axially loaded pile problem, and particular interest is paid to the investigation of pile load displacement, shear transfer and load diffusion along the pile. Three different soil model have been used to represent the soil for this problem. Theoretical solutions have been compared with field test results.
The modified Cam-clay model and the more advanced bounding surface model developed from classical plasticity theories, and the rate-type model founded upon hypoelasticity theory have been studied. Model predictions of these three models were compared and evaluated base on results of triaxial tests and direct simple shear tests under undrained conditions. Both the modified Cam-clay model and the rate-type model are closely related by the similarity of. their yield surfaces, but the rate type model requires only three soil parameters and provided reasonable agreement with test results on normally to heavily overconsolidated clay. The modified Cam-clay model is relatively restricted to the lightly overconsolidated clay. The sophisticated bounding surface model provides remarkable model prediction power to fit the test results, but numerous model parameters are required.
The cylindrical cavity expansion approach and the simple pile method, both of which may be used to simulate the pile installation process have been investigated. The rate-type model has been choosen to represent the soil. The simple pile method attempts to include the tip effect due to pile advancement which has been ignored in the cylindrical cavity expansion approach. The simple pile method approximates the strain field around the pile by an ideal fluid, but it is found that this method results in unrealistic pile-soil interaction. The predicted excess pore pressures from both methods were compared with field test results. This indicated that the simple pile method provided better agreement with test results than did the cylindrical cavity expansion approach.
An idealized one-dimensional pile model has been proposed. The modified Cam-clay model, bounding surface model and the rate-type model have all been used to simulated the soil response due to axial pile loading. Theoretical solutions were compared with three well documented pile test results. The pile tests were carried out in lightly to heavily overconsolidated clay deposits. The pile model predicted good agreement with test results, especially in regard to the pile load displacement response, shear transfer and load diffusion along the pile at low stress level.