QAJARAN OPEN-PIT OVERALL SLOPE STABILITY ASSESSMENT UNDER UNLOADING CONDITIONS BASED ON THE STRESS REDISTRIBUTION

Abstract

Under low - confinement conditions, the extension crack initiation lower and interaction upper bounds in the in-situ rock mass within the Qajaran open-pit South-West overall slope presented with hydrothermally altered and weathered monzonite and granodiorite is assessed. As an integral part of the large open pit projects, it is essential to estimate the in-situ rock mass strength and the expected failure mechanism as accurately as possible, taking into account the stress relaxation in near-surface rock mass. In an excavation-induced unloading condition, it has been shown that the extension crack propagation mechanism is a function of low confinement condition which, in turn, leads to low in-situ rock mass strength. The global failure mechanism in the fractured rock mass of the overall slope has been theoretically assessed, and a good agreement between the estimated global failure surface and failure surface obtained from the slope stability analysis has been found. The propagated extension cracks within the rock mass are considered to be ground water flow paths which is the second reason for the in-situ rock mass strength reduction due to the developed high pore water pressures in the toe rock mass of the overall slope. An in-situ rock mass strength reduction envelope in stability analysis to assess the rock mass strength of the Qajaran open-pit overall slope in low confinement geomechanical environment taking into account the high pore water pressures of the rock mass due to propagated extension cracks has been used. It has been found that there is nearly 20% difference when taking into account the extension crack interaction zones within a near-surface rock mass in low confinement conditions.