A thesis submitted in the partial fulfilment of the requirement for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1980

A finite elements model, capable of predicting the load deformation and the load transfer characteristics of an isolated bored pile.in a cohesive soil profile is presented. The material properties for the pile and the soil were assumed to be linear-elastic, except at the pile soil interface where special elements were introduced whose behaviour was described by an elasto-plastic shear stress-displacement law. The elastic modulus of the soil was taken as a multiple of the undrained shear strength, whereas the shear stiffness of the interface elements was related to the undrained strength of the soil and the adhesion factor. The load was applied to the pile in small increments and the elastic properties of the soil medium were assumed to remain constant during each step of loading. The maximum shaft load an interface element could sustain was governed by the adhesion failure between pile and soil. The finite element model was applied to three large diameter bored piles in Bangkok subsoils consisting of soft and stiff clay underlain by a sand stratum. The bases of the piles were close to the sand layer. The necessary soil parameters were derived from vane shear tests.in the the soft clay and from unconfined compression tests in the ·stiff ·clay. One of the piles investigated was instrumented and fair agreement between predicted and observed load-settlement and load transfer behaviour could be obtained, particularly in the normal working region of applied loads. The results .showed that adhesion failure started at the base and at the head of the pile and propagated towards the centre. They further revealed that only a ·small fraction of the applied load was carried by the base, even at loads approaching the ultimate shaft capacity.