Support technology faces challenges in view of the large deformation of surrounding rock in three-soft coal roadways under high horizontal stress in Zijin Coal Mine, China. Geostress near the tested working face of the mine was measured and its distribution law was analyzed through theoretical analysis, numerical simulation analysis, and field measurement. The original supporting scheme of the three-soft coal roadway on the tested working face was analyzed to discover the deformation and failure mechanism of the surrounding rock of the original supporting roadway and the control measures. An optimized support scheme of H-G (hollow grouting) anchor cables, high strength bolts, W-shaped steel belts, metal meshes, and sprayed concretes was proposed for field applications. Based on the roadway in the tested 3201 working face at Zijin Coal Mine, the technical parameters for optimizing the combined support of the roadway were determined. The following results were be obtained through field measurement. The roadway was kept intact after excavation and the optimized support scheme was adopted in the three-soft coal roadway. No obvious deformation in appearance existed in the roof, floor, and roadway coal sides. Compared with the original support scheme, the stability of the roadways was improved visibly. The displacement of the roadway roof decreased from 100 to 30 mm, and that of the roadway coal walls decreased from more than 100 mm to less than 50 mm. This work verifies the effectiveness of a combined support scheme of H-G anchor cables, high strength bolts, W-shaped steel belts, metal meshes, and sprayed concretes to control deformations of surrounding rock in three-soft coal roadways. The new support scheme has good social and economic benefits and can be used as a reference for other roadway supports under similar conditions.

Based on cohesive zone model (CZM), a simplified method for estimating the tensile softening curve of quasi-brittle materials is proposed. First, assume that the virtual crack opening displacement is linearly distributed. According to Castigliano's theorem, a cohesive displacement proportional function $fk(a_0,a)$ is proposed, which can obtain Crack Tip Opening Displacement (CTOD) directly from Crack Mouth Opening Displacement (CMOD). This simplifies the governing equations of CZM and the tensile softening curve can be obtained quickly. Finally, the effectiveness of the method is verified by experiment and finite element.

Four representative TS-RCR (three-soft rock-coal-rock) structural bodies were selected according to the lithofacies analysis of coal measures in the Xiangshui Coal Mine, Guizhou, China, to analyze the mechanical properties, internal structure damage characteristics, and crack evolution law of the TS-RCR structural body composed of a soft roof, a soft floor, and soft coal seams. The mechanical model of the TS-RCR structural body was proposed. (1) The stress-strain curves of TS-RCR structures with different lithologies under cyclic loading and unloading show a change rule of sparsity, density, and sparsity with the increased cycles. The deformation of TS-RCR structures under cyclic loading and unloading can be divided into four stages. When the height ratio of the TS-RCR structural body was the same, the higher the strength of the upper and lower rocks, the more cycles the TS-RCR structural body had, and the denser the cyclic loading and unloading curve. On the contrary, the fewer cycles the TS-RCR structural body had, the sparser the cyclic loading and unloading curve. (2) The T₂ (transverse relaxation time) spectrum curves of the structural bodies were monitored at about 1 and 10ms, and two obvious peaks were detected, indicating micropores and mesopores with a large volume in the structural body. Signal intensity increased at the relaxation time of 1ms, decreased at 10100ms, and increased slightly at 1001000ms. The pore structure of the structural body with different lithologies changed significantly with the increased cycle number. (3) The damage and failure process of the structural body was roughly divided into three periods according to the time-history analysis of acoustic-emission AF (the ratio of acoustic-emission ringing count to duration) of the structural body: the active period with a relatively low AF value (AF<60kHz) in the 1^st-2^nd cycles; the rising period with a relatively stable increase of the AF value in the 3^rd-4^th cycles; and the explosive period with a relatively high AF value (AF60kHz) in the 5^th cycles. According to the relationship between the RA (the ratio of the rise time to the amplitude of the acoustic-emission-detection wave) value and time, the evolution law of the RA value and AF value of structures with different lithologies is similar in different periods under cyclic loading and unloading.