Maximum width of undercut slope with planes of discontinuity studied by 1G physical models

Abstract

Physical models of undercut slope have been successively studied in order to cope with the mining problem at the Mae Moh open-pit coal mine in Lampang province of Thailand, where the layers of coal working as counterweight along to toe of the slope are excavated without prior removal of unstable rock masses. Previous research has convinced the mechanical idealization by validating with the results of physical models with sufficient reliability for practical designs. However, the effects of faults existing at the actual site have not included in the previous study. Therefore, undercut slope models were improved by inserting faults to the physical model in the present study. This paper focuses on the maximum undercut width of physical models in regard to both symmetrical and unsymmetrical discontinuous planes. Experimental procedures and controlled conditions were clarified including water content and bulk density as well as construction sequences of the modeled slope. The results observed from the experiments were compared with the theoretical idealizations based on the beam failure assumptions and the existing arch failure assumptions which are strip arch with soil slip, segmented arch with stable scarp, and circular arch with upheaval buckling. Formulation of the derived equations for predicting the maximum width were explained and discussed with an aim to identify the factors causing agreement and disagreement with the experimental results.