A simple device for monitoring large pre-failure movements on a slope

Abstract

The level of sophistication required by a slope monitoring system should be related to the importance of the slope. Dam abutments, bridge foundations, slopes under expensive engineering installations and slopes which threaten people’s homes justify the installation of the more sophisticated monitoring systems mentioned in order to give the earliest possible warning of instability. Most highway slopes and mining slopes, on the other hand, are too extensive to monitor effectively in this way except at prohibitive cost. In such cases regular inspection of the slopes on a daily or weekly basis may be the most practical and effective method. The inspection should ideally be done by the same person who should note on a standard form the condition of the slopes (e.g. seepage, dangerously loose material) and the presence and extension of any tension cracks. Once instability has been detected a monitoring system should be designed and installed. In many cases an extended system of surface control points is probably the most effective method of monitoring for the money expended. In practice, control points are often lost due to interference, natural hazards or because it becomes dangerous to approach them, so that it is as well to allow for up to a 50 per cent casualty rate. In addition the mode of failure of a rock slope may change from that predicted (new cracks may open up) so that the original monitoring system could become ineffective. Until a specific problem is delineated, the principle should be to monitor a large