Reliability of Shear Strength Parameters for a Safe Slope Design in Highly Jointed Rock Mass

Abstract

Shear strength parameters of a slope mass are of utmost concern in stability analyses. However, due to sampling difficulties, it is quite challenging to retrieve precise design parameters particularly for the slopes excavated in heavily jointed rock masses. As a matter of fact, a rough estimation of shear strength may lead to slope failures causing catastrophic events. In this paper, a repeating slope failure in highly jointed and deformed metamorphic rock mass threatening the safety of a large-scale reinforced concrete water storage tank in western Turkey is evaluated considering the reliability of shear strength parameters. On site, a series of slope stabilization works were carried out to protect the stability of existing water storage tank on the upper level. Slope stabilization by retaining pile wall failed to stop the failure at first as a consequence of poor structural design and improper assignment of shear strength parameters. Final slope stability was achieved after the placement of a permanent granular buttress. Back analyses using linear Mohr-Coulomb and non-linear Hoek-Brown failure criterion were executed to reveal the shear strength parameters of the chaotic rock mass. The maximum normal stress acting on the sliding surface was found to be around 130 kPa. Non-linear back analyses proposed a GSI value of 21 indicating a blocky and highly disturbed material. High shear strength parameters were found for the highly fractured rock mass after back analysis by the linear Mohr-Coulomb failure criterion. Eventually, it is noteworthy to mention that the shear strength parameters of a failure surface in heavily jointed rock mass are normal stress-dependent and well defined by the non-linear failure criterion.