Abstract
A considerable amount of slope stability analysis has been observed in jointed rock masses in which the Geological Strength Index (GSI) estimated at the outcropping level is considered input data to define the rock mass strength. However, this procedure is unsuitable when the rock outcrop and the slope scales are significantly different (e.g., open-pit slopes), resulting in an overestimated rock mass strength.
For this reason, and in the absence of any criteria to modify the GSI based on scale effects, a new GSI version called GSIe or "equivalent GSI" is proposed. To define an expression for obtaining the GSIe in terms of the rock mass properties, comparative stability analysis was conducted in a series of hypothetical slopes using two approaches: the first considers the rock mass as a discontinuous medium of rock blocks separated by discontinuities, and the second considers the rock mass as an equivalent continuous medium characterized by an “equivalent GSI”.
For the adequate equivalent GSI value, evaluated in each analyzed slope, the safety factor and the failure surface are similar in both approaches. In conformity with the results, a GSIe formulation in terms of the slope height, the joint spacing, the intact rock strength, the persistence, and the joint condition has been proposed.
Finally, the formulation was validated by applying it in five slopes where the failure occurred in four of them.
