Installation of bored piles in stiff clays: An experimental study of local changes in soil conditions.

This thesis attempts to identify some of the fundamental mechanisms involved in the modification of soil properties and conditions due to pile installation. Pile behaviour is dependent on soil conditions during pile loading, and at that stage the soil properties existing prior to pile installation have experienced some important changes. Pile design methods, pile installation and the effects of pile installation are critically reviewed with a summary of all factors controlling the behaviour of bored piles. Different experimental techniques are used to study local changes in soil conditions. Both laboratory and field studies of moisture content and undrained shear strength variation due to the contact of soil with fresh concrete are presented. A fall cone test was used to study the variation in strength. A method involving the use of a radioactive labelling procedure to study the migration of water from fresh concrete to the surrounding soil is proposed, with a detailed description of the testing procedures. Results obtained when using such a technique are presented for specimens of London Clay in contact with a concrete mix containing labelled water. The pore water pressure regime in the fresh concrete is studied and some new facts concerning the boundary conditions at the interface between the fresh concrete and the surrounding soil emerge , leading to the study of the variation in pore water pressure at different distances inside clay specimens in contact with fresh concrete. A field experiment, involving the design of instrumentation to study the horizontal stress regime variation during and after the installation of a model bored pile, is presented. Suggestions for further research are made, including laboratory model studies, with the presentation of the proposed apparatus