Installation effects of a bored pile wall in overconsolidated clay

In situ embedded retaining walls are used to form basements and cuttings in urban areas throughout the world, particularly where space is restricted. It is generally accepted that the process of installing such a wall may influence the stress state of the soil and hence the post-construction displacements, wall bending moments and prop loads. However, wall installation is a complex three-dimensional problem, and its effects are not well understood. This paper describes a study carried out on a section of contiguous bored pile retaining wall in an overconsolidated clay in Kent, England, using instrumentation to monitor total horizontal stresses and pore water pressures before, during and after wall installation. Reductions in horizontal stress were recorded during wall installation, bringing the ratio of horizontal to vertical effective stress, K, from an initial value of about 1 to about 0·8. Following wall installation there was no further change in horizontal stress over an additional period of 10 months during which no further construction work took place.