Soil nail wall design optimization by geotechnical applications and geophysical techniques

Abstract

Soil nailing is a soil reinforcement technique which is used to stabilize slopes by insertion of slender elements, called nails. When steep slopes are to be stabilized by soil nailing, practical problems are encountered related to subsurface investigations, as drilling machines cannot be placed on such slopes. Hence, bedrock levels cannot be determined in advance, which is disadvantageous to produce cost effective designs. This research was focused on studying the methods that can be used for soil nail wall design optimization by applying geotechnical and geophysical techniques. The study was based on an unstable slope situated near Victoria dam. The physical properties of soil were determined by direct shear tests, and stability analysis was done by means of “Slope-W” software. Determination of the profile of weathered quartzite layer, inter-beded with Charnokite bands was the major emphasis of this research. Three techniques were used: Ground Penetration Radar (GPR), Earth Resistivity Measurements and Geological Mapping. This investigation scientifically showed that the existing slope is unstable, and to be protected. Further, it was identified in advance that the basement rock cannot be encountered at designed depths of the soil nails, which was subcequently proven as correct by the ongoing drilling for soil nail installations.