Integration of Mechanical Properties and Stability Index for the Stability Analysis of Tunnel Surrounding Rocks in a Deep Coal Mining Environment

This study investigates the mechanical properties and stability classification of surrounding rock masses in deep coal mine roadways using the Guojiawan Coal Mine in Shanxi Province, China, as a case study. This study synthesized multiple parameters from laboratory testing, in situ stress measurements, and the Stability Index (SI) method to quantify stability by lithology type in a heterogeneous deep mining system. The study developed a procedure that involved collecting rock samples from the 51206 and 51207 return ventilation roadways that represented silty mudstone, fine sandstone, coarse sandstone, and coal, and utilizing the GB/T 23561.1-2009 specifications, the samples were tested using uniaxial compressive, Brazilian splitting, and triaxial compressive testing. Statistical analysis (n ≥ 3 for each test type) of the rock samples showed that coarse sandstone had the highest uniaxial compressive strength (UCS) (52.86 ± 1.85 MPa) and elastic modulus (13.11 ± 0.75 GPa), and coal had the lowest (UCS: 20.43 ± 2.15 MPa; E: 2.36 ± 0.22 GPa). In situ stress conditions were low to moderate (σH = 9.99 MPa at 270 m); however, localized stress concentrations were present next to lithologies. The SI classified coarse sandstone as stable (e = 0.30-0.44), silty mudstone as stable to moderately stable (e = 0.47-0.73), and coal seams as moderately stable (e = 0.31-0.46). The Guojiawan Coal Mine case study illustrates how using laboratory-derived parameters together with site-specific stress conditions can provide results to optimize roadway support design in deep and geologically heterogeneous mining environments, offering a transferable framework for similar underground excavations.