Conditions of stability in a marl and limestone opencast mine

摘要

The objective of the work was to check the slope stability in marl and limestone mine in the city of Opole. In this mine, due to its location, blasting exploitation method was abandoned. The medium hardness rocks allowed operating the mine only by the excavators without the use of explosives. However these required the control of slope stability and the recognition of safety of exploitation processes. The scope of performed work included study of documentation, field observations, detailed engineering geology mapping and numerical analysis. In order to determine the rock strength properties, field mapping, Hoek-Brown Classification and uniaxial compression tests were used. Based on obtained data geotechnical conditions within the pit were characterized. The description of rock profiles and new cross-sections contained important information for slope stability. The field observation and mapping detected risk of displacements in strongly weathered limestone deposits to depth of 6-8 m, especially in wet conditions. The slope stability modelling included LEM analysis by Janbu and Fellenius Methods. They took into account the conditions resulting from the mining method and weather. The calculations detected that the slope was stable in dry conditions (Fs = 1.19-2.45). In the wet conditions, slope stability was reduced (Fs = 1.01-1.65). In two investigated profiles the values of relative factor of safety was very low (Fs = 0.76-1.1). Results of slope stability analysis included loads caused by the mining excavator and weather conditions. It was recommended that for mining operations at the top part of the deposit to the depth of 6-8 m, the excavator should be located at least 3 m from the slope edge. The other recommendations concerning the geotechnical instructions for mining operations were presented in the conclusions.