10.5 Measurement of water level and pressure
The usual method of monitoring water levels in a slope is to drill and case a borehole. The water surface is located by dropping a measuring tape down the boring. It is more useful for simple water table situations. Other methods may be more desirable where monitoring is required on frequent basis. Under such cases, more sophisticated instruments like vibrating wire piezometers may be used.
Piezometers can be used to measure pore pressure of the groundwater within a geological structure. Differential pore pressure measurements allow the changing structural and rainfall conditions to be mapped. Common types of borehole piezometers are the vibrating wire, pneumatic and standpipe piezometers. The type of piezometer to be used depends on the level of permeability of the surrounding rock mass. Vibrating wire piezometers should be protected from electrical transients and must also compensate for local barometric pressure when used in wells that are open to the atmosphere.