Numerical study on stability of retained roadway in non-pillar mining at Nam Mau coal mine

Abstract

By using numerical modelling method, the study aims to better understand the geomechanical behaviours of roof strata and stability of retained roadway in the non-pillar mining method at Nam Mau coal mine. The analysis of numerical model shows that when the face is far away from the retained roadway, the mining does not cause significant impact on roadway stability. When the face approaches the roadway, the vertical stress gradually increases around the roadway. The stress reaches a peak value when the face is from 10 to 20 m away and then rapidly decreases when the roadway complete falls within the stress relief zone of longwall. In combination with the insignificant concentration of horizontal stress, the surrounding stress condition induces the roadway to deform and fail when the face approaches roadway. The study finds that the roadway is significantly affected when the face is adjacent to it. The rock mass around roadway fails up to 25 m towards the unmined area. At the end of the upper panel mining, only immediate roof caves that form a caving line of less than 70 degrees to seam floor. The strong main roof does not cave but sag downwards, causing significant load on roadway. The results in this paper can serve as fundamental knowledge for efficient design of roof cutting techniques, contributing to reducing the cost of using non-pillar mining method into Vietnam coal industry.