RECONNAISSANCE GEOPHYSICAL METHODS IN LANDSLIDE INVESTIGATIONS

Landslides are a natural hazard in many countries and often affect civil engineering structures and projects. Three aspects in particular require examination in a geotechnical appraisal of a landslide's stability in engineering terms: (1) the definition of its three-dimensional shape with particular reference to shear surfaces and failure planes; (2) the definition of the hydrogeological regime with regard to water input to the landslide and its distribution within the slip mass; (3) the detection of movement by or within the slip mass and the characterisation of such movements. The site investigation costs may be very high since landslides may be extremely large, structurally complex and topographically severe. It is therefore advantageous in suitable circumstances to carry out reconnaissance geophysical surveys to define the structure and to guide optimum siting of boreholes and pits, and ultimately the installation of piezometers, inclinometers etc. Standard surface geophysical techniques including the seismic, electrical resistivity, acoustic emission and borehole methods have all been applied with varying success to look at a landslide before a major site investigation commences. In recent years electromagnetic methods have been the subject of considerable research in this field and significant advances have been made. In this paper, the application of the above geophysical methods at the reconnaissance stage in a landslide investigation has been reviewed and illustrated with several case histories taken from different geological settings. © 1990.