ABSTRACT
This chapter discusses the objectives of groundwater control and introduces the two principal approaches – pumping and exclusion – that can be used. It also discusses the potential for inadequately controlled groundwater to cause unstable ground conditions. To avoid troublesome conditions during excavation and construction, measures must be taken to control groundwater flows and pore water pressures in water-bearing soils and rocks. The concept of effective stress is fundamental to understanding the interrelation between groundwater and the stability of excavations in soil and rock. Drained conditions in highly permeable water-bearing soils are easy to understand. Essentially, groundwater will flow into an excavation at the same time as the excavation is dug. The reduced pore water pressures will create hydraulic gradients towards the excavation, which will draw groundwater in from the surrounding soil. The vast majority of cases where groundwater control is required are in relatively permeable strata – such as sands, gravels and highly fractured rock.
