Towards an improved geotechnical understanding of landslide hazard and slope stability from ground-based geophysical survey and monitoring

For slope-scale forecasting of moisture driven landslide events, the complex subsurface structure (materials, strata) and hydrogeology need to be characterized and understood in three-dimensions (3D), and at resolutions and timescales consistent with the processes driving slope failure. Recent years have seen key advances in several relevant and complementary areas including 3D geomechanical approaches to slope stability modelling and the 3D characterisation and 4D monitoring of slopes using geotechnical and geophysical approaches (e.g. geoelectrical, seismic). There is a growing interest in linking hydrogeological and geomechanical models to improve understanding of landslide failure processes, but progress has been limited by an inability to provide high spatial and temporal resolution input data on the physical properties of the subsurface (e.g. strength, composition) and changes associated with hydraulic processes (e.g. pore pressure, moisture content). The hypothesis that we are ultimately seeking to test is that recent advances in hydrogeophysical and geotechnical monitoring can now provide timely information to inform and update geomechanical models - thereby enabling spatial/volumetric near-real-time estimates of stability (e.g. slope factor of safety) to aid forecasting of landslide events at the slope scale.

Here we present results from a range of studies deploying geophysical approaches to characterise and monitor unstable natural and engineered slopes. We demonstrate the use of these approaches (supported by laboratory based determinations of geophysical-geotechnical property relationships) to provide an improved assessment of geological heterogeneity and the development of 3D ground models, and the long-term monitoring of moisture driven processes within the slopes. We conclude with an initial consideration of how geophysical monitoring results can directly inform geomechanical models of slope stability.