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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.

In order to solve the problem of large deformation at the intersection of deep large section soft rock roadway, this paper takes the intersection of kilometer-deep roadway in the Wanfu Coal Mine as an engineering example and applies Negative Poisson's Ratio (NPR) steel anchor cable in roadway support for the first time. By combining numerical simulation indoor test, theoretical analysis and field test, the deformation mechanism of surrounding rock at the intersection of deep-buried roadway was analyzed, and the control strategy with micro NPR steel anchor cable as the core was put forward. Through numerical simulation, the numerical analysis model of roadway intersection with different intersection angles and excavation sequence was constructed, and the impact of two key variables of rake angle and excavation sequence on the stability of surrounding rock at roadway intersection was studied. The optimal dip angle is 90° and the optimal excavation sequence was determined as pump house -pump house passage - substation. The mechanical properties of the micro-NPR steel anchor cable were studied through the static tensile test in the laboratory. The results showed that the micro-NPR steel anchor cable showed high constant resistance, uniform tensile, no yield platform, and no obvious necking phenomenon during breaking. Through theoretical derivation, it was calculated that the vertical stress of roadway intersection is 45 MPa, and the bearing capacity of superposed arch composed of micro NPR steel anchor cable is 1257 kN, which is enough to guarantee the overall stability of intersection. Support application test and monitoring were carried out on site, and it was verified that the combined support strategy of short and long micro NPR steel anchor cable has a good control effect on large deformation of surrounding rock at intersection, which provides a new support material and support means for the safety and stabilization control of surrounding rock at intersection. [ABSTRACT FROM AUTHOR]

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.

Gob-side entry retaining (GER) has been widely used around the world. However, when the technology of gob-side filling and roadway retaining is applied to the mining of three-soft thick coal seam, large deformation of surrounding rock and failure of support structure are still unavoidable, especially the floor heave deformation, even the closure of the roadway section in serious cases. Taking 16,011 working face of Zhaogu No. 1 Coal Mine as the research object, mineral composition analysis showed that there are a lot of clay minerals in the surrounding rock, which shows strong swelling characteristics. The mechanical model of the overlying strata with long cantilever structure was constructed to explain the process of ground pressure transferring from two sides of roadway to the floor after retaining roadway, and then the variation and distribution law of stress on both sides of the floor with the working face promotion was obtained. With the aid of uncoupling support theory, this paper analyzed the floor heave mechanism of GER in three-soft thick coal seam, and pointed out that shear staggered floor heave was the main cause of floor heave deformation. Based on above analysis of large deformation mechanism of GER, the three-level control technology of surrounding rock in entry retaining in three-soft thick coal seam was put forward: directional pre-splitting decompression technology, constant resistance & large deformation anchor cable (CRLDAC) roof support technology and floor deformation control technology. The key parameters of the three-level control technology were determined by field industrial test. Monitoring data proved that the three-level control technology can effectively control the deformation of surrounding rock in retained roadway, in which roof-to-floor convergence had been reduced by 58%, and floor heave had been reduced by 65%, finally, the roadway had been retained successfully. [ABSTRACT FROM AUTHOR]

Taking the deep gob-side entry under the mined gob in the Nantun coal mine as the background, indoor physical mechanic property research, situ engineering geomechanics analysis, theoretical formula analysis and three-dimensional numerical simulation were adopted. The type of deformation mechanism of this roadway was confirmed. The coupling control technology of constant resistance was proposed and used in practice successfully in situ engineering. Practice was proved that the coupling technology of constant resistance based on NPR bolt could absorb the energy accumulated in surrounding rock and ensure the total safety of the roadway. [ABSTRACT FROM AUTHOR]

• 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]

Gob-side entry retaining technology is an effective method for sustainable exploitation of coal resources and has been widely used in China. However, there are a large surrounding rock deformation and hard support in the gob-side entry retaining. In this paper, take the gob-side entry retaining in thin coal seam from Jiyang Coal Mine as the engineering background. Firstly, using FLAC software to simulate and analyze the deformation and stress distribution of gob-side entry surrounding rock in different schemes. Secondly, a new coupling support method was put forward after taking full consideration of the simulation results and field engineering experiences, namely: "bolt-mesh-anchor" for basic support, single hydraulic props as reinforced support of gob-side entry, and reinforced filling wall with bolts. In-situ engineering practices showed that this method has a good effect on controlling the deformation of gob-side entry surrounding rock and creates the better conditions for normal production of the working face. [ABSTRACT FROM AUTHOR]

The roof and floor of transportation roadway of S2S2 working face of Xiaokang coal mine were oil shale and siltstone. The content of clay mineral in the surrounding rock was about 60-80%, which was easy to softening with water and weathering. The deformation of primary archy support roadway was serious and the repair rate was high. To control effectively the deformation of extremely soft rock roadway of Xiaokang coal mine, A combined support system of circular full closed section + high strength and pre-stress anchor + “W” strip + powerful anchor cable + shotcrete + 360U yieldable steel support + back wall filling support was suggested. By combining numerical calculation and field measurement, the convergence and convergence velocity of new circular support roadway were analyzed after excavating completion and compared with the value of primary archy support roadway. The convergence and convergence velocity of new circular support roadway significantly decreased. The deformation of surrounding rock tended to be convergent in a relatively short time. The new supporting technology was a kind of effective control method for the large deformation roadway of deep extremely soft rock. The experience for reference was provided for the support of roadway of other similar mine. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• 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]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

In order to solve the difficult support problem of No. 3 intersection of deep large cross section in Jiahe Mine, the paper analyzed the major causes of the deformation failure in No. 3 intersection were the high ground stress, mining and excavation turbulence and the uncoupling between the surrounding rock strength and structure. A coupling support technology of bolt/steel mesh/shotcreting + anchor + floor corner bolt + double control anchor in middle rock pillar was provided. The site application showed that after the coupling support applied, a max roof and floor convergence of No. 3 intersection was 69mm, a max convergence of the two sidewalls was 45 mm and the deformation of No. 3 intersection was effectively controlled. [ABSTRACT FROM AUTHOR]

• High geo-stress and soft rock mass are main reasons of large deformation in tunnel. • NPR anchor cable keeps constant resistance 350 kN and adapts to large deformation. • Energy absorbed by NPR anchor cables should been greater than releasing by rock mass. • The release of energy of the primary support ensures the safety of secondary lining. • NPR anchor cable can solve the large deformation and failure in soft rock tunnel. To solve the large deformation problem of thin-layered carbonaceous slate in Minxian Tunnel, the mechanical properties and large-deformation mechanism of carbonaceous slate are analyzed. A negative Poisson's ratio (NPR) anchor cable supporting solution was designed based on the principle of energy coupling support and field tests were carried out. Thin-layered low-strength jointed rock mass and extremely high geo-stress is found to be the main causes of large deformation in Minxian Tunnel. Dissolution of clay minerals in carbonaceous slate by fissure water accelerates softening of surrounding rocks, which is another reason for the large deformation. The adopted NPR anchor cable energy supporting system can maintain a constant support reaction force (350 ± 10kN) for the surrounding rock, releasing the deformation energy of the surrounding rock through conical body sliding. Evaluation study on NPR anchor cable support was performed including axial force of NPR anchor cable, convergence deformation of surrounding rock, pressure monitoring between steel arch with surrounding rock and pressure monitoring between primary support structure with secondary lining. Monitoring results demonstrate the effectiveness of the adopted NPR anchor cable (7.3 m and 12.3 m) supporting system in Minxian Tunnel. This report would be helpful for the construction of soft rock tunnel under high geo-stress conditions for the control of large deformation and failure. [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]