Wall installation effects - preliminary findings from a field study at the CTRL, Ashford

In situ embedded retaining walls are used to form basements and cuttings in urban areas throughout the world. It is generally accepted that the effects of installing such a wall will influence its subsequent behaviour in terms of loads and bending moments. However, wall installation is a complex three-dimensional problem and its effects are not well understood. To obtain comprehensive field data on wall installation effects, a section of an in situ retaining wall formed from contiguously bored piles on part of the Channel Tunnel Rail Link in Kent has been instrumented and monitored. Push-in spade-shaped pressure cells were used to measure the horizontal stresses and pore water pressures at different depths and at different distances from the wall before, during and after wall installation. Significant reductions in horizontal stress were recorded, bringing the ratio of horizontal to vertical effective stress, K, close to the active condition. Following wall installation there was a further slight reduction over a period of about 10 months, during which time no further construction activities took place in the area. In this paper data which show how the reduction in horizontal earth pressure varies with distance from the wall are presented. Additionally, a study undertaken to evaluate the over-reading known to be exhibited by spade-shaped push-in pressure cells installed in overconsolidated deposits is briefly described. For the covering abstract see ITRD E128041.