Identification of landslide slip-surface and its shear strength: A new application for shallow seismic refraction method

Traditional investigation methods for studying landslide and slope stability is concentrated on studying the present and original geometry of slope, geological cross-section, position of water table and shear strength parameters. It is of prime importance to determine the thickness of slipped ground and the slope of the slip surface. The depth is usually estimated from trial pitting, trenching and drilling boreholes. By using advanced non-invasive geophysical techniques engineers can get a representative picture of hidden subsurface condition with less disruption than using traditional investigation methods like coring, boring and sampling. In this reconnaissance study, seismic refraction survey using a hammer seismograph was conducted in order to determine the thickness of slip material and dip of the slip surface of a landslide. The results of seismic refraction surveys showed good correlation with borehole information. The thickness of the sliding material and the dip of the slip surface were well delineated. The results of the survey were then used to estimate the value of the shear strength parameter as a back value analysis technique. This value was then obtained by ring shear apparatus. The difference between the measured and calculated residual shear strength value was 2A degrees.