Stability of slopes in a fire-prone mine in Jharia Coalfield, India

Stability of slope in an opencast mine is always associated with safety and economics. The steeper slope is always preferred from economic point of view but prone to failure, whereas flatter slopes are uneconomical. A proper understanding of slope which will be a steep enough to be stable is required for safety, economy, and stability of men and machineries. The Rajapur opencast mine is one of the important mines in terms of good quality coal but has problems of water seepage, fire, and weak overburden materials. The existing coal mine has three working seams which are mostly thick and occur at shallow depths of about 50–60 m. Overall slope angle of the working faces as well as final pit is very steep which leads to failures. In the present paper, an attempt has been made to characterize the materials of the mine for simulation of existing slopes. The rock samples from the coal measures were collected to determine the petrophysical characteristics of various rock units. All the pertinent geological parameters from the exposed face were also collected during field visit to assess the slope mass rating (SMR). A two-dimensional finite difference tool was employed to simulate the existing slope geometry as well as relevant parameters of the rock units. The numerical simulation indicates various vulnerable points which are prone to failure as well as displacements at various points along the slope. The results of simulations are corroborated with the SMR value. The results are well matching with the field condition.