The mechanical properties of mortar materials in construction are influenced both by their own proportions and external loads. The trend of the stress–strain curve in cracks compaction stage has great influence on the relationship between the strength and deformation of cement mortar. Uniaxial compression tests of mortar specimens with different cement–sand ratios and loading rates were carried out, and the stored and dissipated energies were calculated. Results indicated that the elastic modulus and strength of mortar specimens increase with the cement–sand ratio and loading rate. The energy dissipation shows good consistency with the damage evolution. When the loading rate is less than 1.0 mm/min, most of the constitutive energy at the peak point is stored in the specimen and it increase with cement–sand ratio. A simple representation method of axial stress in cracks compaction stage was proposed and an energy-based damage constitutive model—which can describe well the whole process of cement mortar under uniaxial compression—was developed and verified.

Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads.

This study considered longwall working face No. 41101—located in a steeply inclined coal seam at the Awuzisu coal mine in Xinjiang, China—as an example in which macroscopic shear cracks had occurred in the cement-based filling body of the gob-side entry retention structure. A mechanical model of the support structure for the gob-side entry retention was first established. Then, field observations and laboratory tests were used to obtain the force exerted by the coal wall on the main roof, the relationship between the axial bearing capacity and compression ratio of the rubble inside the gob, the supporting force exerted by the rubble and filling body, and the thrust of the rubble on the filling body. The shear stress experienced by the roadside filling body of the gob-side entry retention in working face No. 41101 was calculated to be 15.89 MPa. To meet the needs of roadside support, an innovative roadside backfill–truss support structure was adopted, with a 60° angle of inclination used for the anchor bolts of the gob-side entry retention structure. In this way, the ultimate shear strength was improved by 107.54% in comparison with the cement-based filling body.

Mining of the coal seam adjacent to the extracted coal panel is widely practiced in China to improve coal resource recovery rates, but the energy change associated with longwall mining may present a new risk to ground stability and gateroad failure. To understand the energy change effectively, a meticulously validated numerical model, built using FLAC3D software, incorporating a double‐yield model for the gob materials and a strain‐softening model for the coal/rock masses, was developed to investigate the energy redistribution in coal seams and barrier pillars during the process of mining the coal seam adjacent to the extracted coal panel. The model results showed that the closer the region was to the LW 5301 gob, the higher the location and magnitude of the peak strain energy density. Consequently, the risk of rockburst in coal seams was greater than that in barrier pillars. Along the coal seam strike, with increasing advancing distance from the setup room, the magnitude of the peak strain energy density gradually increased to 1.88‐2.78 times the premining energy level. In addition, along the coal seam dip, the maximum distance from the peak strain energy density to the edge of the coal seam was approximately 16‐28 m, which is greater than that in the barrier pillar. The proposed numerical simulation procedure and calibrated method could be a viable alternative approach to evaluate longwall mining‐induced energy changes.

The Gaojialiang Coal Mine in Inner Mongolia in China was used as an example to investigate the process of chain pillar and gateroad failure in the lower coal seam under the effect of an irregular residual coal pillar in the upper close‐distance coal seam. The results indicated that after the longwall face in the lower coal seam retreated through the area under the large irregular residual coal pillar in the upper coal seam, the bearing area of the residual coal pillar decreased and the roof pressure continuously concentrated in the elastic core area of the residual coal pillar. Isolated triangular slab rock was formed above the triangular residual coal pillar, and the weight of the overlying strata was transferred downward through the triangular slab rock. When the chain pillar under the residual coal pillar was destroyed due to loading that exceeded its carrying capacity, the upper triangular slab rock rotated and sank, which resulted in the intensification of the concentrated stress in the solid rib of the gateroad in the lower coal seam. Based on the analysis, it is suggested that in the design of a longwall system, a gateroad under an isolated residual coal pillar in the upper coal seam should be avoided when mining in close‐distance coal seams.

Gobs and coal pillars left in the upper coal seam exploitation bring a series of changes to the surrounding rock structures and stress environment of the roadway in the lower coal seams, which leads to difficulties in roadway maintenance. Firstly, the deformation and failure laws of roadway surrounding rock during shallow-buried multi-seam mining are studied using UDEC simulation. The results show that the vertical-stress concentration of the roadway under the coal pillar is stronger than that under the gobs and solid coal. The roadway displacement mainly undergoes three stages, i.e. severe deformation, slow deformation and deformation stabilization. Each of the three stages has the critical deformation value. The roadway displacement under the coal pillar also is larger than that under the gobs and solid coal. Then, allowing for its location, the roadway can be divided into three subareas, including below solid coal, below gobs and below coal pillars. The roadway below gobs consist of two kinds of subareas, i.e. the interlayer spacing is 3.2–4 m and the other is larger than 4 m. The support schemes corresponding to the four subareas are put forward. Finally, these proposed support schemes are used in the subareas of No. 20314 auxiliary haulage roadway. The field monitoring results show that the roadway displacement is small and bolt (cable) forces are stable, and the support effect is excellent. This study can provide a reference for roadway support in shallow-buried coal seams under similar geological conditions.