Electrical resistivity tomography (ERT) based subsurface characterisation of Pakhi Landslide, Garhwal Himalayas, India

Pakhi landslide is one of the major debris slides of retrogressive nature along national highway (NH-58) corridor from Rishikesh to Badrinath in Garhwal Himalayas, India. The present work is the first such attempt in one of the landslides in Indian Himalayas and in the present case study, the subsurface characterization of the landslide was carried out with an aim to correlate the subsurface lithology, slip surface and geometry of the landslide using borehole investigation and electrical resistivity tomography (ERT) techniques. The results from ERT survey along and across the landslide could help to delineate different strata layers; thereby deciphering the probable slip surface of the landslide activity. Further, based on the landslide model drawn from the ERT interpretations, it can be stated that the crown portion of the right flank is more vulnerable to sliding phenomenon and that of the left flank is more prone to erosion. The results obtained from both the borehole investigation and ERT techniques are observed to be in great agreement and could complement each other for subsurface detailed investigation of landslide. The integration of both these techniques provides useful information about the landslide activities and defines the geometry of the landslide. Hence, it will be quite helpful in planning mitigation strategies as well as usefulness of each of these techniques.