ABSTRACT
This chapter discusses the various large-scale and small-scale stability problems that can occur when working in soil, including instability of excavation side slopes and bases. In the context of the design and implementation of groundwater control, the term ‘soil’ means uncemented deposits of mineral particles such as gravel, sand, silt and clay, where the flow of groundwater will be predominantly intergranular. The underlying Chalk Group is analysed as rock because of the more cemented nature of the dominant limestones and marls; groundwater flow is mainly via fractures. Inadequately controlled groundwater can cause stability problems on a large and a small scale via a variety of mechanisms; the problems likely to be prevalent at a given site and for a given excavation geometry will be largely controlled by ground conditions. Upward groundwater pressures act on the ‘plug’ of low-permeability soil beneath the excavation floor.
