Surrounding rock deformation and failure patterns in abandoned roadway groups and control strategies

During coal seam mining, many abandoned roadways will be generated. Complex and dense geological conditions of abandoned roadways can easily lead to instability of surrounding rock, empty top operation of supports, and bottom leakage of supports, affecting the safe and efficient production of the working face. Traditional methods, such as adjusting the inclination of the working face and strengthening support, are difficult to control the surrounding rock of the abandoned roadways effectively. This paper studies the mechanical properties and transportation performance testing of gangue high porosity cemented paste backfill (GHP-CPB) with gangue base under different ratios, gangue particle sizes, and curing times. A physical analog model is established, and the deformation and stress evolution laws of the surrounding rock in the same floor roadway, cross-layer roadway, and underlying roadway during the mining process of the working face are studied. Combined with on-site measurements, the mining pressure law and the control effect of the abandoned roadway surrounding rock are analyzed. The results showed that with the increase of foaming agent dosage and water cement ratio, the uniaxial compressive strength of the specimens continued to decrease, and the initial setting time of the specimens continued to increase; The strength of gangue particles in the range of 0.8 ~ 10 mm in GHP-CPB is significantly lower than that of cement high porosity cemented paste backfill (HP-CPB). At particle sizes 1.25 ~ 2.5 mm and the dosage of 30%, the uniaxial compressive strength exceeds 1 MPa. During the mining process of the working face, the following ranking by roadway damage degree is observed: same layer roadway > cross-layer roadway > underlying roadway. After using the filling method, the maximum subsidence value of the abandoned roadway is − 31.8 mm, with a maximum stress concentration factor of 2.43, indicating a good control effect. The measured stress value of the coal rock mass in the working face is about 11–17 MPa. The maximum displacement of the two sides of the roadway is 160 mm, and the maximum force on the roadway anchor rod is 190 kN, achieving effective control and safe mining of the surrounding rock in the abandoned roadways of the working face.