An innovative roadway layout in a Chinese colliery based on gob-side entry retaining (GER) with thick and hard roof (THR) was introduced. Suspended roof is left with a large area in GER with THR, which leads to large area roof weighting...

Gob-side entry retaining (GER) in filling working face promotes sustainable mining by preserving roadways for reuse, reducing resource consumption, and minimizing environmental disturbances. This study investigates the deformation mechanism and failure characteristic of the mining roadway during GER in filling working face, using the CT301 headgate at Chahasu Coal Mine as a case study. A UDEC Trigon numerical model was established, and uniaxial compression tests were conducted to calibrate the mechanical parameters of the rock mass and filling material. The deformation, crack distribution, overburden subsidence, and lateral stress were compared under four conditions: caving method and filling rates of 65%, 80%, and 95%. The results showed that compared to the caving method, the filling method can effectively control overburden movement and suppress roadway deformation. As the filling rate increases, the surrounding rock deformation, crack density, subsidence, and lateral stress all decrease. Overall, the 95% filling rate was the most effective, followed by 80% filling rate, 65% filling rate, and then the caving method. After adopting a 95% filling rate at CT301 panel, the maximum deformation of CT301 headgate was only 190 mm, meeting the mine’s production requirements.

To address the engineering challenges of asymmetric large surrounding rock deformation and roadway support failure of deep gob-side entry retaining (GER) in the top-coal roadway, the progressive surrounding rock instability mechanism and fracture spatiotemporal evolution characteristics are revealed via theoretical analysis and universal distinct element code (UDEC) Trigon discrete element simulation. Results show that the top coal first undergoes bed separation and tensile failure, followed by backfill corner crushing and bearing capacity loss, which ultimately induces roadway support failure. Using UDEC simulation and mechanical tests, the influences of top-coal thickness, key block B length, backfill performance, and roadway support mode on roadway support stability are systematically clarified. Results indicate that keeping full top coal within the reinforcement zone, reducing key block B length, adopting a backfill width-to-height ratio of 0.45–0.8, a water–cement ratio of 1.5:1, and combining synergistic anchoring with delayed reinforced support can reduce the risk of roadway support failure. An optimized support scheme for the entry is proposed and field-implemented. Monitoring shows that the backfill has a smooth surface; reinforcement ladder beams and steel mesh have no fracture; coal pillar peak stress reaches 5.95 MPa; coal rib bolt load (178 kN) is significantly higher than that in the backfill section (115 kN); and the backfill adapts well to roof rotation and subsidence. The results support the feasibility of the proposed control scheme under the studied geological and engineering conditions and may provide a useful reference for similar GER projects.

Currently, research on the stability of roadway-side supports in gob-side entry techniques primarily focuses on vertical stress, neglecting the lateral effects induced via roof collapse and waste rock compaction in the mined-out area. This paper systematically investigates the effect of roof rotation and the compression of waste gangue on the lateral load-bearing behavior of the roadway-side support system, combining theoretical analysis with FLAC3D numerical simulations. The results indicate that the lateral load-bearing capacity of the support system is positively correlated with both mining height and the width of the roadway-side support. When the mining height or the support width is small, the lateral load-bearing capacity of the support system is weaker, making it more prone to sliding failure. Furthermore, lateral load control technology for the roadway-side support system is proposed, which includes “roof cutting + increasing width”. When the stress transfer path of the roof is blocked, as the support system width increases from 1 m to 2 m, the lateral load-bearing capacity of the roadway-side support significantly increases and then stabilizes. This results in different extents of expansion in the elastic region within the support system, providing valuable insights for the design of roadway-side supports.

To investigate the degradation mechanisms of the surrounding rock in abandoned mine roadways used for oil storage, this study combined uniaxial compression tests with digital image correlation (DIC), scanning electron microscopy (SEM), and other techniques to analyze the evolution of the rock mechanical properties under the coupled effects of oil–water soaking and initial damage. The results indicate that oil–water soaking induces the loss of silicon elements and the deterioration of microstructure, leading to surface peeling, crack propagation, and increased porosity of the sample. The compressive strength decreases linearly with the soaking time. Acoustic emission (AE) monitoring showed that after 24 h of soaking, the maximum ringing count rate and cumulative count decreased by 81.7% and 80.4%, respectively, compared to the dry state. As the liquid saturation increases, the failure mode transitions from tension dominated to shear failure. The synergistic effect of initial damage and oil–water erosion weakens the rock’s energy storage capacity, with the energy storage limit decreasing by 45.6%, leading to reduced resistance to external forces.