Project Dewatering Limited

Pressure relief wells are a method of controlling excess pore water pressures in confined aquifers. The artesian or sub-artesian head within a confined aquifer can be dangerous if the overburden pressure is equal or less than that of the confined pore water pressure, and if not dealt with it will result in piping or heaving of the base of the excavation.

There are two basic means of relieving this pressure

1. The use of Passive Pressure Relief Wells ; and
2. The use of active pumping pressure relief wells, which can consist of either Deep Wells or Wellpoints.

The recommended solution is to adopt an active pumping pressure relief system. The reason is that this system gives you greater control over the problem area. While passive relief systems can be a more economical solution, they can lead to difficult working conditions with groundwater seepage onto the excavation floor, necessitating a progressive sumping arrangement to remedy. Passive relief systems can also prove difficult to seal effectively upon completion of the project.

Drilling Pressure Relief Wells

A variation of a passive well is Sand drains, which is provides a drainage path between two aquifers. Typically, they are used to drain a perched aquifer, which cannot dewater by gravity drainage into a dewatered lower aquifer. They are effective, in particular where the perched water would cause stability problems to an open-cut excavation, or to speed up the consolidation of Silts and soft Clays.