Application of Electrical Resistivity for Subsurface Characterization of Hattian Bala Landslide Dam

On Oct. 8, 2005, an earthquake triggered a landslide which blocked two tributaries of the Jhelum River, namely the Karli and Tang channels at their confluence, near Hattian Bala, Azad Kashmir, creating two lakes. Construction of spillways for the two lakes reduced the volume of water in Tang Lake. Karli Lake kept filling until April 2007, when its surface elevation reached its spillway level. Inundation upstream of this landslide dam can cause substantial downstream damage in case of failure. To assess this failure potential, different studies have been undertaken and developing scenarios monitored. Attempts have been made to visualize the subsurface conditions using various geotechnical investigation tools. Selected details of the electrical resistivity method of investigation are presented. These include resistivity imaging surveys in space as well as time. Spatial variations in the resistivity values enabled visualization of the subsurface profiles, while the temporal changes in resistivity values helped assessment of the tendency of water seepage into the dam body from Karli Lake. Laboratory resistivity tests were also conducted at different densities and saturation levels on the matrix material from the dam to calibrate the field resistivity values with the degrees of saturation.