Monitoring Of Face Dams

The term Face Dam is used to mean a fill dam having an impervious membrane on the upstream face. The membrane may be of reinforced concrete, bituminous concrete, timber, steel or any other suitable material.

The overall performance of this type of dam depends almost entirely on the compressibility of the embankment material and the ability of the membrane and its joints to withstand the deformation to which they are subjected. The fill material will normally be non-cohesive and relatively pervious and may be a sandy gravel or, more commonly, a quarried rockfill. If the the fill is highly compressible large deflections of the membrane will result leading to large strains in the membrane and the likelihood, in the case of a high dam, of rupture and consequent leakage. This is what occurred at such dams as Dix River (275ft. – 1925), Salt Springs (328 ft. – 1931), Paradela (355 ft. – 1958), Wishon (290 ft. – 1958) and Courtright (310 ft. – 1959). Leakage flow at these dams has been in the range 20 to 130 cusecs. All were constructed of quarried rockfill placed by dumping it in high lifts.

In recent years the trend has been towards improving the deformation properties of the fill and this has been achieved by placing rockfill in thin layers and compacting with heavy vibratory rollers.

This paper presents details of various types of instrumentation used to monitor the behaviour of several rolled rockfill face dams recently completed by the Hydro-Electric Commission, Tasmania. Measurements from different types of instrument are compared and the results of some observations are given.