Analysis of Roof Failure at the Intersections in a Coal Mine

摘要

The objective of this paper is to understand the behavior of the roof, and the cause of roof failure in intersections in a coal mine. Eleven roof falls occurred in a mine section in sequence. All the roof falls were surveyed, and the geological features were determined (rock type, mechanical properties, thickness, and excavation method). The immediate roof thickness was interpolated to determine that the cause of the roof failures was the inappropriate roof support where the immediate roof is thicker. The average thickness of the immediate roof was determined from the drilling log in 1.2-m (3.9-ft) deep holes. The roof support design was based on the average thickness of the immediate roof. A bolt length of 1.5 m (4.9 ft) used in suspension was selected. The challenge was to estimate where the immediate roof gets thicker and to design the support which would maintain the regular bolt length. This is because the cost and productivity of support operation could increase if the bolt length needs increased as the roof thickness changes. The concept was to adjust the support for beam building with fully grouted bolts and rearrange the bolt geometry to maintain a stable roof. It means, with the same bolt length, the type of roof support would change from suspension to beam building, depending on the thickness of the immediate roof. Two empirical approaches were considered to design the roof support: (1) the coal mine roof rating (CMRR) and (2) rock mass rating (RMR). The entry width is 5 m (16 ft), and the roof support was designed with four bolts per row. Where the roof support must change to beam building, the number of bolts per row was changed to five or six. The results of the design and application on underground performance showed that the approach will keep the immediate roof stable.