Failure mechanism of gob-side entry in weakly cemented soft rock and bolt-grouting collaborative control method: a case study.

Abstract

During coal mining in western China, soft rocks with low strength, poor cementation, and a tendency to disintegrate upon water exposure are often encountered. This makes bolt support unable to maintain long‑term roadway stability, resulting in severe roadway deformation and failure. To solve this challenge, this manuscript combines theoretical research, numerical simulation, and field measurements. Firstly, the characteristics of weak cementation and low strength of weakly cemented soft rock were obtained through experiments. Combined with the field‑monitored features of large‑scale roof fracturing and failure in gob‑side roadways, the support failure mechanism was revealed: poor support effectiveness caused by surrounding rock fracturing in the anchored section of roof bolts. Secondly, the tangential stress around the rectangular roadway was obtained through theoretical calculation, and it was found that roadway width and lateral pressure coefficient are the main factors affecting surrounding rock deformation. Numerical simulation revealed that as roadway width and lateral pressure coefficient increase, the plastic zone in the roof strata expands laterally and into deeper areas. Finally, the mechanical properties of different grout consolidation bodies were investigated, and the grouting effects under different grouting ranges were obtained. A bolt‑grouting collaborative support method was proposed. Field tests showed that the roof‑to‑floor convergence was reduced by more than 60%, indicating good support performance.