Stability assessment of obliquely-bedded rock cuts using multi-prong procedures – case study

Abstract

The stability of vertical cuts in rocky strata, associated with the provision of the transportation infrastructure through a mountainous terrain, is always a challenge for the geotechnical engineers. The problem becomes further complex if the cuts are parallel or near parallel to the bedding planes. Such a scenario results in all sorts of slope instability scenarios, including planar, wedge, rockfall, and toppling failure. A linear project was planned to pass through the mountainous stretches of western Saudi Arabia. The rock slopes exposed at the site after the excavations constitute igneous origin Granite/Granodiorite rock present in a moderately to highly weathered state and consist of two sets of discontinuities; one running almost parallel to slope faces and another nearly orthogonal to the major set of discontinuities. Based on the orientation of the discontinuities along the cuts on both the sides of the excavation, there is a high probability of all types of slope failures, including planar, wedge, toppling, or boulder/rockfall. This paper presents details of geologic field mapping, field and laboratory testing, and the software analysis of several modes of the possible slope failure modes. The study was carried out considering all the potential triggering factors, including rainfall, under both static and dynamic/seismic conditions. The paper also discusses the slope failure prevention measures recommended based on the interpretation of the field and laboratory data, software analysis, and the construction sequence.