To study the soft roof failure mechanism and the supporting method for a gateway in a gently inclined coal seam with a dip angle of 16° kept for gob-side entry retaining, and through the methodology of field investigation and numerical and analytical modeling, this paper analyzed the stress evolution law of roof strata at the working face end and determined that the sharp horizontal stress unloading phenomenon along the coal wall side did not appear after the working face advanced. Conversely, the horizontal stress along the gob side instantly decreased and the tensile stress produced, and the vertical stress in the central part of the roof had a higher reduction magnitude as well. An in-depth study indicates that the soft roof of the working face end subsided and seriously separated due to the effect of the front abutment pressure and the roof hanging length above the gob line, as well as certain other factors, including the rapid unloading of the lateral stress, tension and shear on the lower roof rock layer and dynamic disturbance. Those influencing factors also led to rapid crack propagation on a large scale and serious fracturing in the soft roof of the working face end. However, in the gob stress stabilized zone, the soft roof in the gob-side entry retaining has a shearing failure along the filling wall inside affected by the overburden pressure, rock bulking pressure, and roof gravity. To maintain the roof integrity, decrease the roof deformation, and enable the control of the working face end soft roof and the stabilization of the gob-side entry retaining roof, this study suggests that the preferred bolt installation angle for the soft roof situation is 70° based on the rock bolt extrusion strengthening theory.

Intermolecular forces that act between moisture and the atoms of the coal structure have a significant influence on methane adsorption- and desorption-induced deformation in coal. After analyzing the porous characteristics and existing forms of moisture in coal, both the adsorption-induced swelling and the desorption-induced shrinkage deformation experiments were carried out under the conditions of varying moisture content, constant temperature, and variable equilibrium pressure. Both the swelling and shrinkage volumetric strains with different coal moisture contents were fitted by Langmuir-type equations in which the fitting coefficients were functions of the moisture content. It was found that there is a lag between the swelling curve and the corresponding shrinkage curve, and a variable known as the hysteresis rate was defined to illustrate this characteristic. A mathematical model of swelling and shrinkage deformation that considers the effect of moisture content was established based on the experimental results and analysis.

The construction of urban underground cross‐interchange transfer subway stations often encounters the difficulties of shallow‐buried, different surrounding rock, large spans and heights, congested road traffic, and surrounding buildings sensitive to the construction sequence. Therefore, there is a need for an underground project that controls the stability of underground space and ground subsidence. Based on the construction difficulties of a certain station (the maximum excavation area over 760 m²), this paper conducts a comprehensive selection design of the structure, construction mechanics response, and control technology of this type of interchange station structure and construction excavation. First of all, based on the design experience of large‐scale underground transfer transportation engineering and taking full consideration of the stratum conditions, an “arch‐wall” cross transfer structure method is proposed. The refined numerical analysis shows that the structure can fully utilize the stratum conditions to reduce the ground surface settlement. Then, in view of the stability of surrounding rock during the construction of a large section, based on the traditional large section excavation method, a construction method of “cross rock beam + heading method” was proposed. In order to verify the effect of the construction method, the three‐dimensional detailed numerical model was used to simulate the construction conditions, and the mechanical response characteristics and displacement changes of surrounding rock under each excavation step are explored. Simultaneous interpreting with the traditional large section excavation method, the results show that the new method has advantages in controlling the stability of the surrounding rock. Meanwhile, in order to ensure the safe construction of the project, the self‐developed multifunctional engineering test system for traffic tunnels is used to carry out a large‐scale physical model experiment to simulate the entire process of the “arch‐wall” cross transfer structure construction response characteristics. By analyzing the data of measuring points, the results show that the structure form and the excavation method cause the ground surface settlement, stress, and structural forces meet the requirements for safe construction. Finally, the station can be safely constructed under the new structure form and construction method. Therefore, the structure form and method proposed in this paper can be adapted to the large‐scale underground structure under construction in complex environments.

To study common failure characteristics of gateways, a total of 55 typical gateways at coal mines, in Sichuan Province, China, were selected for investigating the rules of broken widths based on the ground-penetrating radar (GPR) technique and numerical model. Results indicated that the broken width values around the gateways were larger than 1.5 m, and those in the roof and high side wall were larger than those in the low side wall, as a whole. The width values had close relationships with the thickness of the coal seam and immediate roof, angle of the coal seam, and depth of the gateways. Furthermore, combined with the plastic zone of numerical models in 3-Dimensional Distinct Element Code (3DEC) and the broken width, we obtained the excavation broken zone (EBZ) cross-section diagram for each gateway and determined that the EBZ appeared to have a basically elliptical shape—with the long axis along the seam inclination direction and the short axis along the vertical direction of the rock layer—and that this elliptical shape was only slightly affected by the gateway cross-section shape. It was observed that the failure extent was greater in the seam inclination direction than in the vertical direction of the rock layer. Obviously, the gateways presented asymmetric failure characteristics and implied that an asymmetric support system should be provided when using bolts, cables, and shotcrete combined with steel mesh and steel belts. Such a support system could improve material parameters and form a combined arch structure in surrounding rocks, with arch crown and arch springing thicknesses that are larger in the roof and high side wall.