Appraisal of Rock Mass Properties and Their Influence on Probabilistic Slope Stability Analysis for a Hydroelectric Project

Hydroelectric projects in the Himalayas typically feature high slopes composed of geological materials such as rock, soil, or debris deposits. Rocks encountered in this region are generally jointed, making it a challenging task to assess their engineering properties. The present article presents an appraisal of rock mass properties for analyzing and designing a high rock slope for a hydroelectric project located in the higher Himalayas. The rocks encountered are predominantly mica schists with bands of quartzites. A concrete gravity dam was constructed at the site. The excavation was done to accommodate the dam. The height of the slope was more than 70m. Instabilities were observed after excavating to a depth of about 15m from the top. Immediate support measures were required to keep the slope stable. Detailed analysis of the slope is done, and the probability of unsatisfactory performance of the slope is evaluated. Rock mass properties for the slope section were derived from the outcome of field and laboratory investigations. The rock failure was found to be governed by joints. Non-linear shear strength criterion was considered for simulating shear strength behavior of the joints. Since uncertainties are involved in the properties, a probabilistic framework was adopted using statistical distributions.

Results demonstrate that incorporating statistical evaluation of joint shear strength behavior results in more realistic behavior of unsatisfactory behavior of compared the slope. The study also demonstrates the importance of non-linear failure criteria in assessing rock-slope stability.