Critical issues for the ground control of shallow roadways in weak ground: a case study

The roadways located in weak ground experience strong and cyclic dynamic loading induced by the thick coal seam extraction, which caused costly support and delay of normal production. This paper discusses the critical issues and support strategy for such roadways through a case study on a roof collapsed roadway which was excavated in a coal stratum at a depth of 120 m in Shanxi Province, China. A 2-m-high void between the concrete support and the exposed roof strata was left untreated due to poor roadway construction. The roadway collapse reached up to approximately 6 m in the roof strata, which was attributed to the large untreated void as well as the highly fractured rock mass. A combination support method of the void filling, the fracture grouting, and rock bolting was proposed to rebuild and reinforce the roadway. The deformation of the roadway was effectively controlled, and the maximum roof displacement reached 135 mm. The failure mechanism of the roadway was numerically investigated using discontinuous deformation analysis (DDA) based on specific geological conditions. The numerical findings suggested that the void above the roadway could significantly impact on the stability of the overlying strata.