Some considerations with regard to the bearing capacity of foundation piles

Abstract

A practical approach is made to analyse the stresses and deformations in the ground before, during and after installation of foundation piles of various types. This exercise leads to the following conclusions: (1) Displacement type of piles improve the stress state in the surrounding soil during installation, while non-displacement type of piles will have an adverse effect. (2) A foundation on many small diameter piles will show less deformation than an alternative foundation on a small number of large-diametre piles. When an equal deformation is aimed at, the factor of safety to be applied to the large-diametre piles, should be substantially larger. (3) Driven piles improve the stress-state in the soil around their lower ends most, but increasing pile penetration during installation deteriorate this good result progressively. (4) There seems to be room for increasing the stress [eve[ around the pile section in the bearing stratum after pile installation. Such an approach would enable pile-installation techniques, which are more friendly to the pile and its environment than the techniques applied nowadays. (5) Theories for the prediction of pile capacity do not take into consideration, in a sufficient manner, the way piles are installed. (6) Pile-installation techniques do not exploit the possibilities to improve pile capacities. (7) Researchers approach the problem of pile capacities as if this is a matter of arithmetics without studying in detail what really happens with the pile and the ground. (8) The predetermination of pile capacities will require a lot more attention in the future. Using our knowledge about the geology of the underground, about the installation techniques to be applied and about the pile-shape and the pile-material needs more attention than hitherto.