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Deep coal resources are the crucial backup for China's energy security in the future. However, large deformation and instability of rock mass in deep roadway engineering still poses serious problems in the deep "three high and one complex" geomechanical environment. Therefore, this study departed from the support surrounding rock interaction and developed a series of NPR anchor bolts/cables with high strength, high constant resistance and large deformation mechanical properties. It constructed the constitutive equation of NPR anchor bolts, and carried out comprehensive mechanical tests indoor and on-site to verify the unique mechanical properties of NPR anchor bolts/cables. This study analyzed the interaction relationship between NPR support and surrounding rock, derived the constitutive relationship of rock mass supported by NPR, and elucidated the excavation compensation mechanical effect after adopting NPR coupling support, which revealed the high pre-stress NPR coupling support mechanism. By drawing on the actual working conditions of Daqiang Coal Mine, this study proposed the NPR support technology for intensive chambers group of deep pump house suction well with NPR bolt /cable as the core. The numerical analysis and field monitoring data show that the high prestress NPR coupling support technology can significantly improve the bearing characteristics of the support surrounding rock, effectively reduce the distribution and development range of the plastic zone of the rock mass in the roadway engineering, homogenize the support surrounding rock stress field, and reduce the overall deformation of the surrounding rock by more than 68 %, ensuring the long-term stability of the rock mass in the deep roadway engineering. The research results can provide reference for stability control of deep roadway engineering under similar conditions.

Abstract The advanced hydraulic support group combined with bolts (cables) constitutes the advanced coupling support system, which can ensure the stability of coal mine roadway safely and effectively. To explore the influence of the initial bearing capacity of the advanced hydraulic support on roadway roof deformation under anchor bar (cable) action. According to the actual geological conditions and roadway support of the 15106 working faces in Pingshuo Coal Mine, Yangquan, and Shanxi. Based on the change in the stress and displacement of the half‐space body under normal force in elastic theory and combined with the linear superposition principle, the contact mechanics model of the advanced hydraulic support group and roadway roof under anchorage is established. Selecting the measured anchor bar (cable) preload in the coal mine as the input load of the model, the stress and displacement distribution of the roadway roof under different initial bearing capacities are calculated. The calculation results show that the stress and displacement of the roadway roof along the axis exhibit a “symmetrical distribution” and the whole roadway exhibits a “saddle surface” gradient distribution during the active support of advanced hydraulic support under anchorage. The increase in the initial bearing capacity of the advanced hydraulic support has a great influence on the support effect in the middle area of the roadway and has a relatively small influence on the support effect in the surrounding area of the roof. With an increase in an initial support capacity, the stress gradient changes violently but substantially less than it would under the crushing strength of the surrounding rock. Using the similar simulation experiment theory, a similar simulation experiment roadway was established at 1:40, and the simulation experiment of an advanced hydraulic support coupling active support under anchor protection was carried out. The maximum error percentage of the theoretical calculation and experimental results of roof deformation under different initial bearing capacities is 19.51%, and the maximum error percentage of stress is 13.77%. The accuracy of the distribution law of roof stress and displacement under the initial bearing capacity in the process of active support obtained by theoretical calculation is verified. The research results provide a theoretical basis for advanced coupling adaptive support and the control of fully mechanized mining faces.

The advanced hydraulic support group combined with bolts (cables) constitutes the advanced coupling support system, which can ensure the stability of coal mine roadway safely and effectively. To explore the influence of the initial bearing capacity of the advanced hydraulic support on roadway roof deformation under anchor bar (cable) action. According to the actual geological conditions and roadway support of the 15106 working faces in Pingshuo Coal Mine, Yangquan, and Shanxi. Based on the change in the stress and displacement of the half‐space body under normal force in elastic theory and combined with the linear superposition principle, the contact mechanics model of the advanced hydraulic support group and roadway roof under anchorage is established. Selecting the measured anchor bar (cable) preload in the coal mine as the input load of the model, the stress and displacement distribution of the roadway roof under different initial bearing capacities are calculated. The calculation results show that the stress and displacement of the roadway roof along the axis exhibit a "symmetrical distribution" and the whole roadway exhibits a "saddle surface" gradient distribution during the active support of advanced hydraulic support under anchorage. The increase in the initial bearing capacity of the advanced hydraulic support has a great influence on the support effect in the middle area of the roadway and has a relatively small influence on the support effect in the surrounding area of the roof. With an increase in an initial support capacity, the stress gradient changes violently but substantially less than it would under the crushing strength of the surrounding rock. Using the similar simulation experiment theory, a similar simulation experiment roadway was established at 1:40, and the simulation experiment of an advanced hydraulic support coupling active support under anchor protection was carried out. The maximum error percentage of the theoretical calculation and experimental results of roof deformation under different initial bearing capacities is 19.51%, and the maximum error percentage of stress is 13.77%. The accuracy of the distribution law of roof stress and displacement under the initial bearing capacity in the process of active support obtained by theoretical calculation is verified. The research results provide a theoretical basis for advanced coupling adaptive support and the control of fully mechanized mining faces. [ABSTRACT FROM AUTHOR]

The control method of deformation of large sections of soft rock formations in coal mines is a major problem in mining practice. Taking Wangzhuang Coal Mine in Shanxi Province, China, for example, the support method of large sections of soft rock formations was studied to control the deformation of the top and bottom plates and two gangs, and to obtain the damage of the surrounding rocks at different depths through drilling imaging. In addition, the displacement, plastic area and stress field distribution patterns of surrounding rocks are obtained by simulating in FLAC3D. Coupling support for broken, plastic and elastic zones is achieved using bolts, grout anchors, and long anchor cables. The bottom of the road is effectively controlled by floor grout and concrete reverse arches. The results show that under the combination of anchorage and grout, the fault depth and degree of the surrounding rocks are less than the original support method, which can effectively reduce the subsidon of the roof and the deformation of the two gangs. It is important to note that anchorage cable set support can effectively reduce shear fault areas in floor and two gang plastic areas, and reduce the weight of the pavement floor. This study provides a technical reference for the support of large sections of soft rock roadways in coal mines.

• The deformation failure mechanism of soft rock roadways in strong wind oxidation zones was studied by analyzing the macroscopic and microscopic variability of the coal and rock. • The "pregrouting + anchor net and sprayed concrete + inverted arch structure + U-shaped steel + high and low-pressure, deep and shallow-hole reinforcement grouting" coupling support scheme was proposed. • The coupling support scheme was used to strengthen the soft rock roadway, which proved that the technology can effectively strengthen the surrounding rock. Due to the influence of sedimentary environment, the coal seams and overlying rocks in the wind oxidation zone exhibit developed fractures, high rock porosity, strength attenuation, and poor self-stability. It leads to the large deformation of the surrounding rock and managing the roof of roadways difficultly. This made the roadway excavation extremely difficult. And the rendering conventional "bolt-cable-mesh (belt)-shotcrete" combined support system was not applicable. In this paper, the No. 49,104 air return roadway in the strong wind oxidation zone of the Shuiquan Coal Mine was selected as the engineering background. The change trends of the coal and rock in the strong wind oxidation zone physical and mechanical properties were revealed, and the deformation and failure mechanism was analyzed. According to the deformation and failure characteristics of the roadway in the wind oxidation surrounding rock with engineering practice, a coupling support scheme "pregrouting + anchor net and sprayed concrete + inverted arch structure + U-shaped steel + high and low-pressure, deep and shallow-hole reinforcement grouting" was proposed. A roadway grouting reinforcement diffusion range model was established in COMSOL Multiphysics, and the grouting diffusion range was then imported into FLAC3D to compare and analyze the coupling support scheme reinforcement effect of roadway in the strong wind oxidation zone. And the coupling support scheme was used to reinforce the No. 49,104 air return roadway, and the reinforcement effect was monitored in situ. Results showed that the proposed coupling support and reinforcement scheme can be employed to effectively control the deformation of the surrounding rock and the expansion of plastic zone damage. And the stability and safety of the roadway were significantly improved. This coupling support scheme was reasonably designed, and it could provide an engineering reference for the support and reinforcement of roadways in weak and crushed surrounding rocks under similar geological conditions. [ABSTRACT FROM AUTHOR]

Monitoring analysis was performed for the deformation characteristics of a deep roadway in soft rock masses in a certain mine by the convergence instrument. It was indicated that shotcrete and bolt support for the surrounding rock deformation under forces produced a poor effect so that a shotcrete rockbolt mesh coupling support pattern was put forward and four coupling support schemes were designed to carry out field monitoring for surrounding rock deformations on the basis of above schemes. According to the research, we could summarize as follows. Firstly, when load in floor strata reached a certain value, shear failure took place on the edge of floor; then, with the continuous increase of such a load, shear zones were subsequently expanded and connected together into one big region; at that time, as the load on floor strata had been up to its limit, the floor could be settled sharply as long as this load went up slightly so that the uplift of rock mass gave rise to floor heave. Secondly, bearing capacity of floor rocks was dependent on the average binding force, internal friction angle and unit weight of floor rocks as well as the concentrated stress action width of lateral wall and the average pressure value borne by the roadway floor. Thirdly, after the shotcrete rockbolt mesh coupling support was adopted, two-sided displacement dropped 80% and above, roof subsidence decreased more than 70% and the capacity of floor heave falls by over 90%; as a result, stability of the roadway could be significantly improved.

• The highly prestressed NPR cable coupling support technology is proposed. • The numerical model of the second-generation NPR cable is established. • The NPR cable support scheme can effectively control the deep roadway. The stability control of deep roadways has always been a difficult problem related to the safe production of mines. This study took the -950 level substation roadway of the Wanfu Coal Mine in China as the project background to study a new support technology with negative Poisson's ratio (NPR) cables as the core. Firstly, based on the mechanical properties of the NPR cable with a large constant resistance, a high elongation, and uniform full-length energy absorption, the highly prestressed NPR cable coupling support technology was proposed. Its mechanism was revealed, i.e., by strengthening the surrounding rock with a high prestress and releasing its deformation energy with a large constant resistance and a large deformation, the "stress compensation" effect of the NPR cables can be brought into full play so that coupling of the "support-surrounding rock" can be achieved. Secondly, the numerical model of the second-generation NPR cable was established by FLAC3D, which can realise the constant resistance and large deformation of the NPR cable and achieve the sequential breaking of the NPR steel strands during the deformation of the NPR cable. Numerical tensile tests verified its effectiveness. Finally, the NPR cable support scheme was designed through theoretical calculations and numerical simulations. After field application, the roadway deformation was constrained within 80 mm, effectively preventing engineering failures. This study may serve as guidance for similar projects. [ABSTRACT FROM AUTHOR]

Highly stressed soft rock subject to expansion deformation is particularly difficult to control. Field observations and experiments analysis show that an exhaust air roadway, level 100 of the Xiajing Coal Mine in Guangxi, China, is located in an intumescing rock with high in situ stress. Then we designed a bolt-mesh-anchor coupling support for the roadway repair and reinforcement, which consists of a first coupling support with bolt-mesh and secondary reinforcement with anchor cables. Field monitoring results show that bolt-mesh -cable coupling support has guaranteed the stabilization of the roadway and reduced the deformation of the surrounding rock considerably. [ABSTRACT FROM AUTHOR]

Improving the safety and stability of soft surrounding rock with nonlinear large deformation gives a strong guarantee for the safe mining and sustainable development of deep coal mines. In order to control the nonlinear large deformation of the surrounding rock in a deep soft rock roadway, this paper discusses the nonlinear large deformation mechanism and coupling support countermeasures of a typical engineering application at Xin'an coal mine in Gansu province, China. The series of experiments and theoretical analysis described in this paper reveal the phenomena, properties, and reasons for the nonlinear large deformation of soft surrounding rock in detail. Then, the type of nonlinear large deformation mechanism is determined and transformed from a composite one to a simple one. Based on experimental results and mechanism transformation, a suitable coupling support countermeasure, which contains the Constant Resistance Large Deformation (CRLD) bolt, steel mesh, floor hollow grouting cable, and steel fiber concrete, is proposed to reduce the nonlinear large deformation and the potential risk during mining. The application shows that the coupling support countermeasure can effectively reduce the nonlinear large deformation of the surrounding rock and help to maintain the stability of the deep soft rock roadway at Xin'an coal mine. [ABSTRACT FROM AUTHOR]

Monitoring analysis was performed for the deformation characteristics of a deep roadway in soft rock masses in a certain mine by the convergence instrument. It was indicated that shotcrete and bolt support for the surrounding rock deformation under forces produced a poor effect so that a shotcrete rockbolt mesh coupling support pattern was put forward and four coupling support schemes were designed to carry out field monitoring for surrounding rock deformations on the basis of above schemes. According to the research, we could summarize as follows. Firstly, when load in floor strata reached a certain value, shear failure took place on the edge of floor; then, with the continuous increase of such a load, shear zones were subsequently expanded and connected together into one big region; at that time, as the load on floor strata had been up to its limit, the floor could be settled sharply as long as this load went up slightly so that the uplift of rock mass gave rise to floor heave. Secondly, bearing capacity of floor rocks was dependent on the average binding force, internal friction angle and unit weight of floor rocks as well as the concentrated stress action width of lateral wall and the average pressure value borne by the roadway floor. Thirdly, after the shotcrete rockbolt mesh coupling support was adopted, two-sided displacement dropped 80% and above, roof subsidence decreased more than 70% and the capacity of floor heave falls by over 90%; as a result, stability of the roadway could be significantly improved. [ABSTRACT FROM AUTHOR]