OGI can identify if a structure is at risk from artesian groundwater pressure, and if required, can design a pressure relief system to safeguard against potential heave.
Artesian Pressure beneath an excavation is sometimes referred to as the silent enemy. During the construction period there can often be no apparent issue with groundwater, then with little or no warning, the base of the excavation can fail, with water flooding the structure.
It is, therefore, essential to establish if artesian conditions are present, before any deep excavation is carried out. If artesian conditions are anticipated, then a system of either active or passive pressure relief wells can be designed and installed in order to prevent heave.
Before the ground is reduced and the water pumped out, the upward water pressure is less than the downward weight of soil.
To prevent heave it is necessary to reduce the uplift pressure to below the weight of the overlying soil (in the temporary works condition) or structure (in the permanent works condition). This can be achieved by one of two methods:
- actively pumping from below the confining layer
(installation of active pumping wells)
- by providing a pathway through the confining layer allowing water to bleed into the excavation when artesian pressure rises
(installation of passive bleed wells)