Stability Assessment of Siwalik Rock Slopes – A Case Study from Dehradun Area, Uttarakhand, India

Abstract

This study presents a slope stability assessment of Siwalik rocks formations along an old, unpaved road connecting Dehradun to Thangaon village via Dunga village located in the Himalayan foothills. This road is a part of the proposed major road connecting Dehradun-Mussoorie. Hard rocks in the study area are medium-grained, massive sandstones composed of ∼100% quartz and less prone to weathering, while soft rocks are quartz-rich with ∼10% micaceous/argillaceous minerals, fine-grained, relatively laminated sandstones that are more prone to weathering. Joints are prominent in the hard and massive sandstones. Joint openings range from 0.5–1 mm to 2–3 cm. Rock mass rating and slope mass rating criteria along with kinematic analysis reveal that bedding, natural joint, and excavation faces are oriented such that ∼50% of locations have chances of wedge failure. Roads oriented in the NNW-SSE directions with ridges to the left are the most vulnerable to rock slides as evidenced by slope assessment. Natural joint orientations with respect to bedding strikes are unpredictable, as bed strike-parallel, strike-perpendicular, and strike-oblique joints are present at various locations. Most rock fall incidents happening during the monsoon implies extra water from the rains acts as failure catalyst. Based on the field observations, select remedial measures were suggested.