8.2.3 Deep wells

As shown in Figure 8.6，the deep well method is to drill a well near the excavation zone and pump water out of it to make groundwater around the well flow into it under the influence of gravity.As a result，the groundwater level in the vicinity of the well will decline.The deep well method is another gravity draining method.

The diameter of a deep well is about 150⁃200 mm.If the goal of pumping is confined to lowering groundwater level to keep the excavation bottom dry，the depth of the well could be set around 2.0⁃5.0 m below the excavation surface and not lower than the bottom of the retaining wall.The wells are to be located around the vicinity of the excavation zone.The pumps used in a deep well can be submerged pumps or centrifugal pumps.Concerning the design，functions，and application limits of various pumps，please consult related documents.According to the type and arrangement of pumps used in a deep well，the pumping depth can reach more than 30 m.These types of wells are typically not spaced closer than 15 m.Figure 8.7 is a photo of deep wells for a deep shaft excavation.

Figure 8.6 Dewatering via the deep well method

Figure 8.7 Application of deep wells