For the gob-side entry retained by roof cutting, the roof pre-splitting depth is directly related to its stability, especially under the condition of fully mechanized mining in 4.5 m thick coal seam underneath 13.7 m thick limestone roof. Due to insufficient investigation, the Yongning coal mine 10202 gob-side entry retained by roof cutting experienced large rock pressure, causing severe prop deformation and sharp reduction in the cross-section of the entry, which greatly affects its reuse. Extensive field measurements were conducted to analyze the severe rock pressure in the 10202 gob-side entry retained. Two typical models of overburden structure after roof pre-splitting were established, and they were used to study the effect of pre-splitting depth on the stability of gob-side entry retained in terms of the roof subsidence and the support resistance, respectively. A numerical investigation of the effect of roof pre-splitting depth on the stress distribution near the gob-side entry retained was carried out. Afterwards, the roof pre-splitting parameters for the 10204 gob-side entry retained were optimized, and they were validated through field experiments. The results indicated that insufficient pre-splitting depth is the main factor causing the severe rock pressure of the 10202 gob-side entry retained. The roof subsidence and support resistance after main roof pre-splitting were reduced by 35.2% and 24.8% compared with immediate roof pre-splitting, respectively. As pre-splitting depth increased, the stress-relaxation area expanded, but the pressure-relief effect weakened beyond 20 m. As the roof pre-splitting depth increased, the weighting interval increased, but the working resistance decreased, which indicates that the goaf is almost densely filled by the collapsed roof and the main roof has no space for subsidence movement. Thus, the rock pressure behaviors of the 10204 gob-side entry retained were milder than that of the 10202 gob-side entry retained.

In urban shield tunneling, reducing the disturbance of underground construction to the surrounding environment is important for both tunnel engineers and researchers. Among other factors, the quality of synchronous grouting is one of the crucial factors affecting the safe construction of shields. In order to determine a reasonable grouting pressure and grout amount during shield construction, the relationships among synchronous grouting pressure, grout amount and shield chamber pressure are analyzed using field monitoring data. Based on the tunnel face pressure and the ultimate yield conditions of the soil at the gap edge, a method for calculating the grouting pressure considering the overburdening load of the tunnel was proposed. Then, by linking the grout amount and the grouting pressure, an accurate calculation method for the simultaneous grout amount in shield construction was proposed. These methods were then used in the construction of the Jurong shield tunnel. The results show that the adopted grouting pressure and grout amount calculated by the proposed method, which considered the change of the overburdening load of the tunnel, can well control the ground deformation caused by the shield construction and significantly reduce the uneven settlement of the surface buildings. The proposed methods in this paper may provide a reference for other shield construction projects.

The great success of fully mechanized mining with a large mining height of 8 m and above in Mongolia and Shaanxi proves the feasibility of this technology. Although fully mechanized mining with a large mining height significantly increases the production capacity of mining areas, there are higher requirements for mining safety. Due to the special conditions of the 8 m coal seam in Huoxi Coalfield, the adoption of fully mechanized mining with a large mining height faces a serious problem of spalling. The key to whether complete equipment for fully mechanized mining with a large mining height can be adopted lies in the possibility to reduce such risks. In this paper, the mechanism of spalling on the 8 m fully mechanized mining face in Huoxi Coalfield is analyzed through theoretical analysis, numerical calculations and comparison of on-site data, and a “one point four zone” comprehensive evaluation method for coal seam at the front end of the working face is established based on the failure characteristics of the coal seam; according to the numerical simulation test results, it is believed that the presence of a dirt band in the middle and upper parts of the coal seam has a positive effect on the control of spalling; the overburden structure of Huoxi Coalfield exhibits the changes in “cantilever-instability-hinge”, and there is a risk of caving before the mining face, which exacerbates spalling; the advance blasting roof cutting of the working face has a significant effect on controlling the spalling of production coal faces. This research provides a theoretical basis and engineering reference for the treatment of spalling in fully mechanized mining with a large mining height in Huoxi Coalfield.

In order to alleviate the risk of landslides on high and steep slopes during excavation, slope protection coal pillars are commonly increased at the site to maintain slope stability, which causes a considerable waste of coal. In roof cutting for pressure relief at quarries, the movement of the overburden structure is artificially regulated by blasting. However, there is a lack of theoretical research on the impact on the slope movement. In order to explore how blasting roof cutting affects the deformation and fracture of slopes, a case study of the 10101 working face of Xinyuan Coal Mine was carried out. The particle flow code numerical simulation of the mining with different heights of roof cutting was performed to analyze the impact of the height of roof cutting on the movement of overlaying rock formation, the development of slope fractures, stress distribution, collapse angle, slope deformation and fracture, etc. The research results are as follows: the overlaying rock formation can be divided into the stable zone, the rotary zone and the subsidence area by displacement; a reasonable roof-cutting height allows the cutting and crushing of the overlaying rock formation, as a result of which the movement boundary is offset to cutting line and the slope is within the stable area; at the same time, the horizontal displacement of the rock formation in the rotary zone, the collapse angle and the stress at slope bottom are reduced, which controls the deformation and failure of slope by inhibiting the development of cracks at slope bottom and reducing the rotation of the rotary zone to the goaf zone. The research results provide certain references for controlling ground sedimentation and slopes in blasting roof cutting.