Toppling failure in the Marmot Vertical Limb at Quintette Coal Ltd., Tumbler Ridge, British Columbia

Two years in a row Quintette Coal Ltd. had a toppling failure occur on the North Wall in the Marmot Vertical Limb. The wall has an overall angle of approximately 50 degrees, and the stratigraphy, consisting of poor quality sandstone and shale, is dipping almost vertical. The July 27th bench scale toppling failure, was initiated by high pore pressures generated in tension cracks. The September 18th toppling failure was a multi-bench failure, which had been developing for over a year. Although water pressures did not initiate failure, transient water tables contributed to the overall instability. Both failures were the result of poor wall design and blasting damage. This thesis presents the background material, the mine and monitor method developed and the back analysis of the failure. The areas researched include: regional and local geology, structural geology in the Vertical Limb, mine development, the groundwater conditions encountered, the blasting practices used, the artificial support systems installed and the monitoring network established. The analysis of the failure used the Distinct Element Method developed by Peter Cundall. This method is a recognized discontinuum modelling approach, which is used to model jointed media subjected to quasi-static or dynamic loading. The method has been compared to the Limit Equilibrium Analysis proposed by Goodman and Bray in 1976, but most of the work involving UDEC (Universal Distinct Element Code) has centred around tunnel design and support requirements, rock reinforcement, fluid flow through a jointed media, dynamic loading and thermal-mechanical modelling. In this thesis the rock mass is analyzed as a series of rigid blocks, which are subjected to gravitational forces. The purpose of UDEC is not to design pit walls or better dams, but rather to be used as a tool to better understand how a jointed rock mass behaves under static and dynamic loads.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat