Deep Roadway Research Articles

A viscoelastic–plastic constitutive model incorporating creep initiation stress for surrounding rock in deep roadways and its practical application

AbstractWith the increasing depth of engineering in rock masses, the issue of significant rheological deformation becomes notably prominent. To accurately characterize the deformation and failure behavior of the surrounding rock near the goaf in deep small coal pillars, we have developed a viscoelastic–plastic constitutive model that takes into account the initial stress associated with creep. This model builds upon an existing viscoelastic–plastic constitutive framework and is implemented numerically using C++ in the FLAC3D. The Oedometer test method is used to check the creep components and the calculated parameter (η/G) ensure convergence of numerical operations. We conducted both pre‐improvement and post‐improvement tests of the constitutive model in a simple numerical analysis of roadways. The enhanced model demonstrates improved accuracy in deviational stress calculations and proves suitable for modeling deep, soft roadways. Furthermore, we applied the improved model to simulate actual working conditions at Zhaozhuang Mine, where mining operations near the working face induce a fracture zone of approximately 3 m in the small coal pillar located at the goaf's edge. The new model closely aligns with the observed results, further validating its suitability for tunneling along the goaf. Tunneling and mining activities result in significant deformation at various locations, including the shoulder socket of the working face, the top angle of the coal pillar, and the bottom angle of the floor. The crushing zone at the working face extends up to 4 m. Rheological effects transform the triangular elastic core, from its original high‐pressure elastic state to a fracture and plastic zone in the deep coal. Stress in deep coal is transmitted along the triangular elastic core. Numerical simulation results closely match the excavation profile of the tunneling, providing valuable insights into the impact of mining activities. This study can provide reference for deformation of similar geological conditions and engineering situation.

Retracted: Deformation Analysis of Surrounding Rock of Deep Roadway by the Fluid Structure Coupling Model with MIDAS-GTS

Retracted: Deformation Analysis of Surrounding Rock of Deep Roadway by the Fluid Structure Coupling Model with MIDAS-GTS

Monitoring Technology of Surrounding Rock Deformation Based on IWFBG Sensing Principle and Its Application

Abstract To address the challenge of achieving precise real-time monitoring of significant deformation in deep roadway surrounding rock, a quasi-distributed strain-sensing cable (SSC), which has a spatial resolution of 1 m, was developed based on the principle of Identical Weak Fiber Bragg Gratings. The performance of SSC has been evaluated through a series of calibration tests, revealing a range of 0%–3%, an accuracy level of 0.5%, a strain sensitivity measuring at 1.23 pm/με, and a temperature sensitivity recorded as 10.78 pm/℃. Furthermore, a real-time deformation monitoring system has been established to monitor rock deformation, consisting of SSC, supporting installation equipment, demodulation equipment, and monitoring software. Moreover, the proposed methodology was applied in the deep roadway of Guqiao coal mine. The results showed that the maximum surface displacement of the roadway is 103.47 mm, while the lateral contrast error stands at 5%. The maximum strain value of the surrounding rock measures 27,095 με. The depth of rock rupture zone is about 3 m, while the boundary of rock damage zone extends up to 6 m. This information serves as the foundation for determining the parameters of the roadway reinforcement support design.

Mechanism and key parameters of stress load-off by innovative asymmetric hole-constructing on the two sides of deep roadway

Traditional dense large-diameter borehole stress load-off techniques reduce the stress levels in the shallow surrounding rock, weaken the bearing capacity of the shallow surrounding rock, and greatly deteriorate the shallow surrounding rock strength and supporting structure, which is not conducive to maintaining the long-term stability of the roadway. Therefore, to address the control problem for the pronounced extrusion deformation in the two sides of a roadway and the overall outward movement of the shallow surrounding rock supported by the sides bolts and anchor cables, as well as to comprehensively consider the on-site construction conditions of the two sides of a test roadway, stress load-off technology for asymmetric hole construction on the two sides of a roadway is proposed. The asymmetric stress load-off technique is a new method; while the shallow surrounding rock of the roadway sides is strongly anchored via a full anchor cable support form, a group of large stress load-off holes near the deep stress peak line of the roadway sides is excavated to relieve pressure and protect the roadway. This technology can transfer the peak stress area of the roadway side deeper into f the surrounding rock without deteriorating the shallow surrounding rock strength and damaging the supporting structure. A numerical simulation analysis of asymmetric stress load-off on the two sides of the roadway was performed, the stress load-off effect evaluation index was established, and the optimal field construction parameters were obtained. The stress load-off parameters obtained from the study are applicable to field engineering practice. Mine pressure data reveal that the test roadway remains intact and stable during the use period when the asymmetric stress load-off technique is adopted.

Energy evolution mechanism during rockburst development in structures of surrounding rocks of deep rockburst-prone roadways in coal mines

Influenced by the deep high-stress environment, geological structures, and mining disturbance in coal mines, the frequency of rockburst disasters in roadways is increasing. This research analyzed energy evolution characteristics during rockburst development in the elastic bearing zone and energy conversion in the plastic failure zone. The critical energy criteria for structural instability of roadway surrounding rocks were deduced. Numerical software was also applied to simulate the energy evolution during rockburst development in surrounding rocks of rockburst-prone roadways under conditions of different mining depths and coal pillar widths. The occurrence mechanism of rockburst deep in coal mines was analyzed from the perspective of energy in structures of deep roadway surrounding rock in coal mines. The research results show that the critical energy criteria are closely related to the elastic strain energy stored in deep roadway surrounding rocks and the energy absorbed by support systems. The impact energy in roadways is directly proportional to the square of the stress concentration factor k. Moreover, as the mining depth increases, the location of the peak point of maximum energy density gradually shifts to coal ahead of the working face. The larger the mining depth is, the more significantly the energy density is influenced by advanced abutment pressure of the working face and the wider the affected area is. With the increment of the coal pillar width, the distance from the peak point of energy density to the roadway boundary enlarges abruptly at first and then slowly, and the critical coal pillar width for gentle change in the distance is 30 m. Changes in the peak elastic energy density in coal pillars with the coal pillar width can be divided into four stages: the slow increase stage, abrupt increase stage, abrupt decrease stage, and slow decrease stage. The elastic energy density is distributed asymmetrically in deep roadway surrounding rocks in coal mines. Under the action of structures of roadway surrounding rocks, energy evolution in these structures differs greatly during rockburst development under conditions of different coal pillar widths. This research provides an important theoretical basis for the support of rockburst-prone roadways during deep coal mining.

Research on application of annular concrete-filled steel tube support in deep roadway

In this paper, through on-site investigation and monitoring, the characteristics of roadway deformation and the causes of deformation and damage are analyzed. Among them, the unreasonable support system is an external factor, and the nature of rock mass, deterioration degree of surrounding rock, and high ground stress are internal factors. A simulation method of CFST considering initial defects in core concrete is proposed and utilized to analyze the mechanical properties of CFST supports. Building upon numerical simulation results, we introduce an optimized support scheme comprising annular CFST support, segmental fissure surrounding rock grouting, and bolts. Field comparison tests demonstrate that the application of the new repair technology yields remarkable enhancements in the bearing capacity of surrounding rock and supporting structures while ensuring a more uniform stress distribution within the rock mass.

Experimental and Numerical Study of Water–Rock Coupling Creep under Uniaxial Compression

In order to study the influence of the long-term strength of the rock surrounding deep roadways under the action of groundwater on surrounding rock stability, taking the rock surrounding the deep roadway of the Wanfu Coal Mine as the main research object, uniaxial compression and uniaxial creep tests were carried out on sandstone samples under different water-content states. It was found that the water content had an obvious softening effect on short-term and long-term strength, and both strengths showed a negative exponentially declining relationship. The viscosity modulus (E¯v) was put forward to describe viscoelastic creep deformation. And damage variables corresponding to E (the instantaneous elastic modulus) and E¯v were proposed. A sticky element that can describe the accelerated creep behavior was also established to improve the Nishihara model, based on the experimental results and damage theory. A comparison of the identified parameters and the experimental curves showed that the model can describe the mechanical behavior of various creep stages well. The model was developed using the ABAQUS user subroutine function, and the uniaxial compression creep experiment was simulated. The simulation results were basically consistent with the experimental results, which provide a basis for the further long-term stable use of roadway and creep failure simulation and have important practical and guiding significance.

Deformation characteristics and failure evolution in deep high-stress roadways under creep action

As geotechnical engineering continues to expand into deep underground environments, it is common for creep effects to cause large deformations of roadways and damage to supporting structures. For this purpose, a large-scale model experiment is conducted with a 1300 m deep roadway as the engineering background. Creep-similar materials for prototype rock and construction specifications, as well as designed supporting components and work processes, were developed. Pressure-preserved loading is applied for physical models. The results indicate that the sequence of roadway failure is “floor-heave induced roadway-foot deformation → roadway-foot levered sidewall-bulge → sidewall-bulge driven roof-sink → full-section convergence”. The strain of the roadway changes from compressive to tensile, and it fails when the ultimate tensile strain is reached. The surrounding rock within 0.2 times the width of the roadway is extremely fractured and stripped. Multiple intersecting fissures are visible near the roadway and extend from the surface to the deep interior. The integrity reduction coefficient of the surrounding rock in the original support anchorage zone is greater than 80%, and the rockbolts along with the surrounding rock are deformed toward the center of the roadway. The numerical simulation and field test can verify the authenticity of the model experiments. Finally, the countermeasures of “ floor protection and sidewall control” and “surface-shallow-deep” triple-bearing structures are proposed. The research results can guide the control of creep deformations in deep high-stress roadways.

Experimental study on combined load-bearing instability of filling body and roadway surrounding rock in original roadway filling without coal pillar excavation

Under the influence of deep high ground stress and strong mining, stress of surrounding rock of gob-side entry increases. The original roadway filling without coal pillar excavation is proposed to cope with the difficult problem of surrounding rock control in deep roadway. In the technology, filling body and surrounding rock form a variety of combined structures, and these structures stability is closely related to roadway control. In this paper, theoretical analysis and mechanical test are used to analyze the strength characteristics of single lithology and bearing capacity deterioration characteristics of multi-lithology combination. The results show that the long-term strength of filling body is greatly affected by water-cement ratio, and the water-cement ratio of 2:1 has characteristics of high long-term residual strength and small residual strain. When analyzing the strength of the contact surface of the combined body, the D-P criterion is closer to test results than M-C. The strength of combinations is determined by the minimum value of the strength of the contact surface between filling body and other lithology and the strength of the non-standard sample of each lithology. And stress-strain curves of the combined body are elastic-plastic, and all belong to the shear tension composite failure. The UCS of combinations of two lithologies decreases with the increase of the volume ratio of filling body. When volume ratio of filling body is constant, the UCS of the three and four lithologic combinations increases with the increase of volume ratio of sandy mudstone to mudstone. The test results play a theoretical and reference role for the application of original roadway filling without coal pillar excavation in different geological conditions.

Mechanical properties and meso-structure of concrete under the interaction between basalt fiber and polymer

Insufficient adhesion of the fibers to the concrete matrix causes the fibers to be pulled out under load, making the fiber concrete unable to meet the support requirements of deep roadways. Basalt fiber (BF) and polymers were selected for the design of mechanical experiments and studied using CT scanning, scanning electron microscopy (SEM) and discrete element simulation. The results show that the fiber mainly affects the compressive and flexural strength of concrete, and the polymer has an effect on the splitting tensile strength of the fibers. From the fine viewpoint, the increase in BF admixture resulted in the conversion of medium pores to small pores within the concrete. Incorporation of polymers results in a smooth polymer film inside the concrete matrix and more hydration products on the surface of the BF to enhance the adhesion of the BF to the concrete matrix. In the discrete element simulation, the fracture evolution can be divided into three stages and the angle of the microscopic fracture is mainly distributed in the range of 60°∼130°. Under loading, BF shares the stress of the matrix and presents itself as a tensile force at its tip, and the increase in BF doping improves the integrity of the specimen at damage.

Stress-Relief–Anchor-Grouting, a Collaborative Control Technology for Severe Extrusion Floor Heave in a Deep Roadway: A Case Study

Severe extrusion floor heave is the most common type of failure of floors in deep roadways, and it is also a major problem restricting the safe and efficient mining of deep coal resources. In deep roadways, reducing floor stress is an effective means to control floor heave. In this study, the method of creating directional stress-relief zones by constructing stress-relief boreholes is applied; while the stress is released, the path of stress from the ribs transferred to the floor and to the extrusion failure path is cut off, and floor heave control is achieved. Therefore, based on the stress-boundary and rock-mass parameters of the roadway, the control effects of the borehole angle, length, diameter, and row spacing on the extrusion floor heave were studied, and the reasonable thresholds of borehole parameters were shown to ensure the stress-relief effect on the roadway. In addition, the bolt-grouting technology was used to strengthen the floor of the roadway, the broken surrounding rock was modified via grouting consolidation, the support strength of the floor was increased using high-tension bolts (cable), and there was a good floor heave control effect in the field application. On the basis of traditional floor reinforcement, the control effect of stress regulation on floor heave is fully considered in this study, and stress-relief–anchor-grouting, a collaborative control technology for floor heave in deep roadways, is developed. Based on the three factors affecting the stability of deep roadways (stress, lithology, and support), the collaborative prevention and control of severe extrusion floor heave were realized, which provides a new method for deep roadway floor heave control and has good application value.

Prediction of fractured zones in deep roadway of coal mine excavated via TBM based on Measurement While Drilling method

Prediction of fractured zones in deep roadway of coal mine excavated via TBM based on Measurement While Drilling method

Mechanical responses of anchoring structure under triaxial cyclic loading

Dynamic load on anchoring structures (AS) within deep roadways can result in cumulative damage and failure. This study develops an experimental device designed to test AS under triaxial loads. The device enables the investigation of the mechanical response, failure mode, instability assessment criteria, and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths. The results show that the peak bearing strength is positively correlated with the anchoring matrix strength, anchorage length, and edgewise compressive strength. The bearing capacity decreases significantly when the anchorage direction is severely inclined. The free face failure modes are typically transverse cracking, concave fracturing, V-shaped slipping and detachment, and spallation detachment. Besides, when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength, loading rate, and anchorage inclination angle increase, the failure intensity rises. Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend. Under cyclic loads, the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability. Finally, a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.

Thickness and Strength Analysis of Prestressed Anchor (Cable) Compression Arch Based on Safe Co-Mining of Deep Coal and Gas

The stability of the gas extraction roadway is very important for the safe mining of coal and gas. The compression arch formed by the combined action of the prestressed bolt (cable) support and surrounding rock has been widely used in the engineering practice of the gas extraction roadway. It is of great engineering application value to analyze the influence of prestressed bolt (cable) parameters on the compression arch. In this paper, combined with the engineering practice of the deep roadway in Huainan and Huaibei mining area of Anhui Province, the mechanical parameters of surrounding rock are measured via field coring and the laboratory. The numerical simulation software FLAC3D is used to analyze the typical position of fractured mudstone, mudstone, sandy mudstone and muddy sandstone under the bolt pre-tightening force of F = 50 kN, 70 kN and 100 kN; the bolt spacing of a × b = 400 mm × 400 mm, 500 mm × 500 mm and 600 mm × 600 mm; the bolt length of L = 1500 mm, 2000 mm, 2600 mm and 3000 mm; and the distribution characteristics of additional compressive stress on the surface of the side. The influence of the different lithology and bolt parameters on the thickness and strength of the compression arch was analyzed, and on this basis, prestressed anchor cables with a pre-tightening force of F = 80 kN, 100 kN and 120 kN and length of L = 3000 mm, 4000 mm and 6000 mm were applied, and their influence on the thickness and strength of the compression arch was analyzed. The results show that the bolt pre-tightening force (F) and the bolt length (L) have a significant effect on the thickness of the compression arch, while the surrounding rock lithology, the bolt spacing (a × b), the anchor cable pre-tightening force (F) and the anchor cable length (L) have no obvious effect on the thickness of the compression arch. The surrounding rock lithology, the bolt pre-tightening force (F), the bolt length (L), the bolt spacing (a × b), the anchor cable pre-tightening force (F) and the anchor cable length (L) have a significant effect on the strength of the compression arch.

Analysis of an improved Nishihara creep model considering plastic strain accumulation

Rock-engineering structures, particularly subway excavation rock-engineering structures, are subjected to the long-term effects of external loading that may gradually damage and cause creep and severe plastic deformations or even progressive failure. The traditional Nishihara creep model cannot accurately describe the accelerated creep stage of rock with particularly obvious nonlinear characteristics. Based on this model, a damage variable that can consider the plastic strain accumulation is introduced in this study to replace the viscoplastic body in the traditional model with a damaged viscoplastic body and establish an improved Nishihara creep model. Using the superposition principle, the creep equations of the improved model in the one- and three-dimensional stress states are derived. The accuracy and rationality of the improved model are verified using uniaxial and conventional triaxial creep tests of mudstone and sandstone under different confining pressures. The improved model can not only accurately reflect the nonlinear characteristics of the creep curve in the decay and constant velocity stages but also describe the accelerated creep characteristics of mudstone and sandstone in a high-stress state. Its applicability and accuracy are superior to those of the traditional model. This study can provide a theoretical reference for subway tunnel excavation and stability analysis of deep roadway surrounding rocks.

Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway

In order to solve the support problem of deep soft crushed coal roadway, a concentrated cavern in a mining station of a mine is taken as the test object. Based on the analysis and summary of the field observation data and the law of rock pressure appearance, a new technology of pressure relief anchoring with the main body of “initiative support + borehole pressure relief” is proposed. This new technology will carry out strong active support in the shallow part of the surrounding rock and excavate a row of low-density large-diameter pressure relief boreholes in the deep coal body of the roadway ribs. The numerical analysis model is established by FLAC3D, and the second invariant of deviatoric stress (J2) is used as the analysis index to elaborate the influence of different borehole parameters on the pressure relief effect of roadway surrounding rock. The results show that different borehole parameters have different effects on roadway pressure relief, that is, borehole depth > borehole length > borehole spacing. After the borehole process is used to relieve the pressure of the surrounding rock, the deformation of the mining roadway side in the subsequent observation process is always controlled within the range of 100 mm, and the shallow surrounding rock support system is effectively protected. The comprehensive control effect is very obvious. Therefore, the field practice proves that the supporting technology can effectively solve the problem of large deformation support of similar roadway surrounding rock.

Study on Slurry Flow Characteristics and Diffusion Law of Superfine Cement-Based Composite Grouting Material

The soft surrounding rock of deep roadways is in the state of “micro-fracture and low permeability”. In order to solve the problem of grouting reinforcement of micro-fractures surrounding rock in deep roadways, the influence characteristics of auxiliary materials and additives on slurry flow were analyzed, and the composition and proportion of superfine cement-based composite grouting materials were determined: superfine cement accounted for 89.4%, superfine coal ash accounted for 5%, ultrafine mineral powder accounted for 5%, naphthalene water reducing agent accounted for 3~5‰, and lignin sulfonate calcium accounted for 1~3‰. The effects of water–cement ratio and water reducer content on slurry viscosity and water bleeding rate were tested by laboratory experiments. Based on the fracture characteristics of surrounding rock and the “Liu Jiacai Formula”, the influence law of fracture opening, grouting pressure and slurry viscosity on the slurry diffusion radius was analyzed. The results show that the slurry viscosity decreases with the increase of water–cement ratio and water reducer content, but the bleeding rate increases obviously with the increase of the two factors; when the water–cement ratio is 1.0 and the water reducer content is 3‰, the slurry has the advantages of “strong permeability, strong flow and low water bleeding rate”; the smaller the fracture opening is, the greater the required grouting pressure and the lower the required slurry viscosity. Aiming at the “micro-fracture zone” of surrounding rock in deep roadways, when the dynamic viscosity of the slurry is 2.0 mPa·s, the reasonable grouting pressure should be 12 MPa to meet the needs of grouting reinforcement engineering. The high-pressure grouting test of surrounding rock in the “micro-fracture zone” was successfully carried out by using the superfine cement-based composite grouting material.

Mechanistic formulation and validation of cutting seam by energy-focusing blast for pressure relief of deep roadway

Coal sources still comprise a significant proportion of the global energy supply, especially for developing countries. As mining depth increases, roadway instability, failure, and burst become increasing concerns over deep resource utilization and mining safety. Cutting seam by energy-focusing blast (CSEFB) technique is a novel approach to mitigate the problems. Driven by the demand for further understanding and application, this study discusses the mechanistic formulation of CSEFB through theoretical analysis, numerical simulation, and field experiments. Results show that CSEFB uses the broken-expansion rock and roof-cutting effect to relieve mining stresses. The CSEFB angle and length are two critical technical parameters. The angle is the prerequisite for validating pressure relief, and the length is the condition for determining the relief degree. The formulas are given for determining the range of angle and length. Within the range, the pressure-relief effect decreases modestly with increasing angle and increases significantly with increasing length. The standard length is proposed to use the support by bulking rock fully. An increase in the length can provide an additional effect by roof cutting itself, but this effect is limited as the length increases. This mechanism helps the formulation of CSEFB in the application. A bigger angle and the standard length are primary considerations. If requiring additional pressure-relief effect, a moderate increase in the length can add to pressure-relief effect by improving the stress field. Combined numerical simulation and field experiment with a typical high-stress deep mine, CSEFB exhibits good adaptability. Apart from relieving the high vertical stress, CSEFB avoids bad influences by the great horizontal stresses. The floor heave is exploited to facilitate the pressure-relief process. Research results have importance to the CSEFB application and promotion, thus contributing to the safety of deep mining.

“Migrate-Transfer-Control” Support System of Surrounding Rock in the Deep Roadway and Its Application

After coal mining enters the deep, the mining environment changes dramatically, and engineering disasters become increasingly prominent, which are mostly related to rock instability and failure. As traditional support is difficult to meet production needs, it is necessary to improve the support system. Based on the engineering background of the Pinggang mining roadway, this work studies the migration law of overlying strata in deep goaf by theoretical analysis and numerical simulation. The results show that the vertical stress and plastic failure range of the surrounding rock in front of the working face increase with the advance distance and when the working face advances to the first square, reaching the maximum. A stope spatial model considering the influence of horizontal stress is established. Combined with the theory of key strata, the stress transfer characteristics of overlying strata are analyzed. It can be seen that 0~30 m in front of the coal wall of the working face is the influence range of advanced abutment pressure, and the dynamic mining pressure in this range has a great influence. The inclined direction of the working face, 0~20 m away from the coal wall of the roadway, is the influence range of the solid coal abutment pressure. On this basis, the “migration- transfer- control” technical system of surrounding rock in deep stope face is put forward, i.e., the stress transfer of surrounding rock is caused by overlying rock migration, and the large deformation of surrounding rock is controlled by supporting means. Based on the original support scheme of the roadway, three reinforcement schemes are designed for the roof, the sidewalls, and both the roof and sides. The deformation control effect of the reinforcement scheme is far greater than that of the single factor, and the field monitoring effect is good. The research results aim to provide theoretical and technical support for the deformation control of mining roadways in the deep mining process.

Study of Bearing Characteristics and Damage Law of Grouting-Reinforced Bodies

To explore solutions for reinforcement problems of broken rock masses in deep roadways, it is necessary to study the performance of cement-based grout and its reinforcement effect. In this study, grouting-reinforced specimens with different particle sizes of broken coal were made, which revealed the reinforcement effect of grouting on the bearing capacity of broken coal and the mechanism for secondary bearing damage and the instability of the reinforced specimens. First, it was determined that the appropriate water–cement ratio (W/C) to meet the field grouting conditions is 0.45. Second, the uniaxial compression of the grouting-reinforced specimens with 0.45 W/C was carried out, and acoustic emission equipment was used to detect it. Finally, through indoor experiments, this study investigated the differences in failure modes, stress–strain curves, and acoustic emission signal characteristics among intact coal samples, grouting-reinforced bodies with different particle sizes, and grouting-reinforced bodies after anchoring. The deformation and failure patterns of grouting-reinforced bodies were revealed, and the failure mechanisms of grouting-reinforced bodies with different particle sizes were elucidated.