Determination of possible failure surfaces in an open-pit slope caused by underground production

Assessment of open-pit slopes is important for identifying failure mechanisms and taking precautions before a serious slope failure. Especially in simultaneous underground and open-pit mining activities, unstable slopes are expected under the subsidence effect of underground production, independently of the current kinematical conditions of the pit slope. In these circumstances, the stability assessments must consider the effect of underground operation. The present study monitors the stability in an open-pit slope located above an underground mine by a terrestrial laser scanner (TLS), and compares the results with those of kinematical analyses. Although no failure was predicted in the kinematical analyses, significant deformation rates were detected by TLS. Depending on the subsidence effect of underground production, the minimum angle of open-pit slopes that cause the instability was determined, and the locations of possible failure were determined by a model created from the TLS measurements. The updated analyses revealed the possibility of plane, wedge, and block-toppling failures.