Slope movement is most common in open pit mines. Several mines continue to operate safely with moving slopes with the help of monitoring to enable timely warning against deteriorating stability conditions. Slopes are designed with a factor of safety to control the risk of injury and equipment damage due to likely danger of slope failures and rock falls. Geological structures, rock mass properties, and hydrologic conditions are important elements for design of safe and efficient slope structures. Groundwater, surface water, and precipitation runoff can be controlled to abate their deleterious effects on stability. Benches and berms are normally used to stop rocks before to fall prior and pose a significant hazard. Mechanical rock fall catchment systems or secondary supports may also be used to stabilize slopes in particular locations. However, even a carefully designed and constructed slope may fail because of unidentified geological structures, unexpected weather conditions, or seismic activities. For these reasons, regular examination and systematic monitoring of slopes are important for early detection of failure and associated hazard.
Slope never fails spontaneously. Prior to failure, slope provides indication in the form of measurable movement and/or the development of tension cracks. In contrast to this, landslide is a result of long-term movement of slopes creeping for hundreds of years resulting in accumulative movement of tens of meters. Such movement may be superimposed for a short period of more rapid movement resulting from major events like earthquakes. Undersuch conditions, monitoring of slope stability and landslides involve selection of certain parameters and observing their behaviour with respect to time. The two most important parameters are displacement and groundwater levels. Slope displacement can be characterized, in terms of depth of failure plane(s), direction, magnitude, and rate, using conventional slope monitoring, whereas, piezometers can be used for determination of water levels. Surveying of fixed surface movements deploying extensometers, inclinometers, and tiltmeters capture changes in direction and rate of slope movement depth and areal extent of the failure mass.
This chapter describes common methods of monitoring movement of slopes, and interpretation of the results. Here, it is considered that monitoring programs are most appropriate for active slopes such as open pit mines and quarries which have a limited operational life and where a carefully managed on-going surveying program can be set up. The survey will enable to identify accelerating movement of the slope and take measures to minimize the risk by moving operations away from the active slide.