Piezometers for Measuring the Water Table to Monitor Landslides

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Appropriate design of the drainage system is possible only if the water flow pattern within the rock mass is understood. and for this purpose, the measurement of hydraulic conductivity and water pressure is carried out.

Piezometers are used for measuring water pressure within a slope in order to control the stability of the slope by drainage. Piezometers are devices that are sealed within the ground, generally in boreholes. They respond only to groundwater pressure in the immediate vicinity and not to groundwater pressure at other locations. Piezometers can also be used to measure the in situ hydraulic conductivity of rock masses, using variable head tests (Wyllie et al, 2004: 120).
The purpose of this paper is to discuss the role of piezometers in preventing landslides, identify the different types of piezometers, examine the advantages and disadvantages of each type of piezometers, compare the type of soil that they can be used in, and their applications.

Piezometers measure groundwater pressures, which is useful for “effective stress stability analyses of landslides and to observe the variation of pore pressure vertically in the landslide” (Cornforth, 2005: 82). Certain factors have to be taken into consideration when planning a piezometer installation to measure water pressures on a rock slope. It is important that the drill hole should intersect the discontinuities in which the groundwater is likely to be flowing. For example, the hole should intersect the persistent beds in the sedimentary rock which has low persistence joints. Zones of fractured or sheared rock should be located for positioning the completion zone of the piezometer since the groundwater flow would be more concentrated in these areas. The length of the completion zone in rock is usually longer than in soil, because of the requirement to intersect discontinuities. Fault zones are geological features. if they contain crushed rock they act as conduits for groundwater, or if they contain clay gouge, they may act as barriers to groundwater flow (Wyllie et al, 2004: 120).