Limiting values of retaining wall displacements and impact to the adjacent structures

摘要

Support systems for deep excavations are designed to ensure safety of the works and to limit deformations in the ground to acceptable levels. BS 8002 recommends the use of mobilisation factors, M, if wall displacements are required to be less than 0.5% of wall height for medium dense or firm soils. This paper article presents the author's view on this requirement of the BS 8002. The measured displacements from the published data will also be reviewed in this article to demonstrate that there are considerable numbers of cases where measured wall displacements exceeded the limit of 0.5% of excavated depth and the excavations were carried out successfully. This article will also present a study on the variation of the ratio of wall displacement to excavation depth at various stages of a deep excavation and highlight that it is not appropriate to use a limit on maximum wall displacement of 0.5% of the excavated depth as a governing criterion for safety of the works and adjacent structures. Instead of using wall displacement limit based on excavation depth, a separate assessment on the impact of the deep excavation to the adjacent structures should be carried out irrespective of wall displacements which can be higher or lower than 0.5% of the excavated depth.