Water Pressure

Water Pressure can be accounted for on the joints, by defining the Water Pressure as a Joint Property in the Input Data dialog.

Generally a Water Pressure of zero is assumed, since underground excavations are usually free-draining. However, the influence of water pressure on the stability of a wedge may be important in some cases, for example, when the wedge has been supported with shotcrete and no allowance has been made for drainage.

There are two options available for defining water pressure in Unwedge: Constant or Elevation.

Constant

The Constant Water Pressure option assumes a constant (i.e. uniform) water pressure, over the entire joint plane. The units of pressure are determined by the Units selected in Project Settings.

Elevation

The Elevation Water Pressure option allows you to specify the y-coordinate of a water table. The value of Elevation must be consistent with the y-coordinates of the Opening Section. For example:

The water pressure will be calculated on each wedge face, based on the vertical distance from the wedge to the Elevation.

NOTE: the Elevation Water Pressure option is only strictly applicable for horizontal excavations (i.e. Plunge = 0). If the excavation is nearly horizontal (e.g. within a few degrees), then you may use the Elevation option, and the error should not be too significant. If the excavation is more than a few degrees from horizontal, or is vertical, then you should NOT use the Elevation option at all, because the water pressure will not be calculated correctly.