Identification of soil/rock interface using GPR technique for soil nail wall design

Abstract

Soil nailing is one of the common slope stabilization techniques which has been used in Sri Lanka during the past decade. Due to the advantages of this method, its applications are growing rapidly around the landslide hazard areas in Sri Lanka. Applications of subsurface investigation methods which are used to identify soil/rock interface are limited due to steepness of the slope areas. Since lesser information available about the bed rock geometry, this leads to generate a low cost effective design for soil nailing. The aim of this research is to demonstrate applicability of GPR for optimizing soil nail length. The study area is located near the Nursing Training School Kandy, that has been proposed to be stabilized by using soil nailing technique. GPR readings were taken on the pre-determined traverse lines. Soil/Rock interface identification was done by using survey results together with their interpretation, and geological cross section was produced. GPR imaging indicated that the bed rock level variation at this location is from 15 m to 18 m. It was identified that design length of the soil nail is shorter than depth to the bed rock on the slope with the aid of the diagram. Therefore, it was identified that soil nail length cannot be optimized for the location. The scope of the GPR survey was to find the depth to the bed rock. By using that, length of the soil nail can be optimized and soil nailing process can be performed more efficiently. However, the depth to bed rock level on the slope has to be less than the design length of the soil nail to optimize the soil nail length by means of this technique. This research illustrates the benefits of using GPR to provide understanding about the soil/rock interface in a slope area for the optimization of soil nail length.