Developing an early warning system for a very slow landslide based on displacement monitoring

Abstract

The Ripley Landslide is a soil slide moving on a fully developed, sub-horizontal, shear surface. The landslide represents a hazard for two important railway lines across its toe. The landslide is being monitored by an array of displacement measurement systems including GPS units, a ShapeAccelArray (SAA), satellite InSAR, and crack extension metres, as well as an array of piezometers targeting pore water pressures in the vicinity of the shear surface. The displacement monitoring system shows an annual cycle of slope deformations most active between September and May. Annual horizontal displacements range between 60 and 100 mm. Vertical displacements range between 20 and 80 mm of settlement. The average horizontal velocities during the active displacement period are between 0.2 and 0.35 mm/day, with maximum velocities of up to 0.6 mm/day. This paper describes the development of an early warning system based on landslide displacement measurements. The system is based on GPS and SAA measurements, which provide near real-time displacement data. The early warning system focuses on detecting changes in landslide annual displacement cycles and potential accelerations, as well as the effects of slope deformation on the railway alignment. As such, the system monitors both the integrity and performance of the slope.