Mark Bolton

Limiting Capacity of Piled Raft

The piled raft foundation is based on a skillful geotechnical concept wherein the pile group does not have any accountability for the safety and stability of the structure but performs the role of settlement reducer. In the design of piled raft, the capacity of the overall foundation system gains more importance than the capacity of individual constituting elements. Hence it becomes necessary to establish the limiting capacity of the piled raft so that the factor of safety for the overall system stability requirements can be assessed. The paper presents the details of the work done to establish a procedure to fix the limiting capacity of the piled raft based small scale 1g model tests and an independent numerical study.

Parametric Study on the Interaction Factor of Piled Raft

The performance of the piled raft foundation system depends upon the interaction level between the raft-soil-and the pile group. Understanding of this process is more complicates than the conventional pile group as the raft in contact with the ground influences the confining pressure, making the interaction behaviour more complicated. This paper presents a qualitative and a quantitative assessment of the interaction behaviour through a non dimensional interaction factor, through the results of a series of 1g model studies. The effect of various important parameters like pile length, pile raft area ratio and spacing on the interaction factor are discussed.

EXPERIMENTAL STUDY ON EFFECTIVENESS OF VERTICAL DRAINS BY MEANS OF ROWE CELL APPARATUS

Vertical drains have recently become a popular method of soil improvement in Australia as it provides a low-cost solution for improving the performance of thick deposits of soft clays. The successful application of this method typically depends on the validity of analytical solutions in which settlements of soft deposits are predicted utilizing classical consolidation theories from soil mechanics. However, little has been done to test such theoretical models in practice, where different soil conditions can be encountered, primarily because project deadlines typically do not allow for such time-consuming endeavours. However, lack of reliable field and laboratory data may lead to a situation in which the effectiveness of soil improvement can be significantly below expectations, as recorded in some recent case studies. This research seeks to fill this gap in scientific data by presenting the results of experimental tests in which the behaviour of vertical drains was studied by means of a Rowe Cell apparatus. These tests were designed to investigate the influence of the size of vertical drains, as well as the smear effect, on settlements of soil at different stress levels. It was found that the process of consolidation occurred more rapidly when a drain of a larger diameter was utilized. In addition, similar to the results from large-scale field trials, it was observed that the presence of smear zone can also slow down the rate of settlement in the laboratory tests. Comparisons were made between different laboratory studies in which the performance of sand drains was investigated in a series of Rowe Cell tests. Finally, an attempt was made to compare the performance of vertical drains obtained in the laboratory tests with that which was observed in large-scale field projects.