Deep Soft Rock Roadway Research Articles

Creep deformation characteristics and control technology in deep mine soft rock roadway

In order to control the strong ageing creep and large deformation of deep soft rock roadway effectively, with the 61–71 track on the uphill of the mining area in Suzhou, Anhui as the research background, the triaxial creep test of mudstone was conducted using the TYJ-1500 M rock mechanics testing system. The creep deformation and failure characteristics of mudstone were analyzed. Additionally, the creep deformation characteristics of deep soft rock roadways were obtained through FLAC3D numerical simulation experiment, and the control techniques for deep soft rock roadway was proposed. The results showed that the axial strain and lateral strain of the specimen were mainly instantaneous strain and creep strain under triaxial stress conditions, and the both confining pressure and the axial pressure have a significant impact on the deformation and creep failure strength of the specimen. Under the condition of high ground stress and complex geological structure, the high stress concentration of roadway roof and floor and two bottom angles is the main cause of creep failure of soft rock roadway, and the large degree of surrounding rock fragmentation and unreasonable support mode reduce the bearing capacity of surrounding rock and aggravate the creep failure of roadway. The 'anchor net cable shotcrete + floor and two corners in floor bolt-grouting + deep and shallow hole grouting + secondary reinforcement support' combined support method was proposed and industrially tested, with average deformation of the roof, floor, and two sidewalls being 111.9 and 62.5 mm, respectively, representing 13.2 and 10.3% of the deformation under the original support scheme.

Numerical experimental study on combined support of bolt-arch in circular roadway

The deep soft rock roadway is in high stress environment, and the surrounding rock is prone to large deformation. Appropriate roadway cross-section form and high-strength support are effective control methods for surrounding rock deformation. Circular roadway is widely used in mine engineering because of its uniform stress and deformation, which gives full play to the characteristics of rock compression and non-tension. With the advantages of high strength, high cost performance and stability, the application of arch frame in deep soft rock roadway is increasing day by day. Based on this, based on the engineering background of deep roadway in extremely soft rock in sea area, numerical experiments were carried out using the FLAC3D bolt-arch fine numerical simulation platform. The progressive failure characteristics of bolt-arch combined support in soft rock roadway are revealed. The influence law of roadway section form, geostress grade and lateral pressure coefficient on support effect is clarified. The results show that: (1) Under the condition of deep soft rock, the surrounding rock deformation of circular roadway is uniform. Compared with the straight wall semi-circular roadway, the deformation is reduced by about 86% at most. (2) The failure of arch frame in circular roadway has a significant influence on the final control effect of surrounding rock. When the ground stress exceeds 15 MPa, the loss of bearing capacity of arch frame is instantaneous, and the deformation of surrounding rock increases suddenly. (3) When the support of circular roadway in deep soft rock fails, the axial force of bolt is very small, and it basically does not play a supporting role. According to the research results, the support optimization design is carried out, and the field verification is obtained.

Research on crack distribution characteristics and control technology of surrounding rock in soft rock roadway under different lateral pressure coefficients

AbstractTo solve the problem of controlling large deformation of surrounding rock in deep soft rock roadway, the distribution characteristics and deformation mechanism of surrounding rock cracks in soft rock roadway under different lateral pressure coefficients are studied using numerical simulation, theoretical analysis, and field measurement. The results show that under different lateral pressure coefficients, the range of surrounding rock cracks shows three forms: round, oval, and butterfly. No matter what lateral pressure coefficient the roadway is in, the surrounding rock cracks always appear in the plastic zone, and there is a high correlation between the surrounding rock crack range and the plastic zone. The stress characteristics of the surrounding rock in the plastic zone include two main aspects. One is that the direction of the principal stress of the surrounding rock is deflected, which is manifested as an annular distribution of the direction of the maximum principal stress around the roadway. The direction of the minimum principal stress in the upper part of the roadway points to the center of the roadway, and the direction of the minimum principal stress in the lower part of the roadway deviates from the center of the roadway. Second, the ratio of the maximum to minimum principal stress in the surrounding rock is large. Under this stress characteristic, the surrounding rock in the plastic zone has strong shear dilation. The shear dilation makes the crack of the surrounding rock open so that the surrounding rock is squeezed into the roadway space, and then the roadway produces large deformation. Due to the large range of cracks in the butterfly‐shaped plastic zone, the shear dilation deformation produced by the butterfly‐shaped plastic zone is far more than that of the round/oval plastic zone. According to the crack range of roadway surrounding rock under different lateral pressure coefficients, the corresponding support scheme is put forward. Field experiments show that the support scheme can effectively control the deformation of surrounding rock and meet the requirements of roadway use.

Study on Support Technology of Truss Anchor Cable Beam in Deep Soft Rock Roadway Excavation

Aiming at the difficult problem of soft rock roadway support in deep mine, the support mode of "truss anchor beam" is proposed, and the support mode technology of truss anchor beam in deep soft rock roadway driving is studied by FLAC simulation software. Combined with the measured displacement of coal and rock around underground roadway under this support mode, it is concluded that the truss anchor beam support mode can introduce the high stress of shallow coal and rock around roadway into deep area, thus effectively controlling the deformation of coal and rock around roadway and ensuring safe and efficient production of mine.

Study on Pretightening Loss Effect of Bolt Support in Deep Soft Rock Roadway

The magnitude of pretension force serves as an important indicator of the effectiveness of anchor bolt active support and is one of the significant factors influencing the stability of tunnel surrounding rock. Therefore, in practical engineering, it is crucial to establish the relationship between pretension torque and pretension force. However, current research in this field has some limitations. With a specific mine in western China as the engineering background, this paper first analyzed the influence factors of surrounding rock deformation and failure, established a mechanical model for pretension structure of anchor bolt support, and derived the quantitative relationship between pretension torque and pretension force based on hypothetical conditions. Finally, it proposed the loss effect of anchor bolt support and modified the pretightening loss coefficient for engineering application. The research results show that the actual pretightening force of anchor support is lower due to the influence of deep soft coal seam, which leads to failure of coal pillar under mining stress. The loss effect of surrounding rock on pretightening force was represented by a coefficient k, and the modified value of the coefficient was calculated as 0.19∼0.43. By applying the modified relationship between pretightening torque and pretightening force, it was found that the actual pretightening torque of 300 Nm applied to 11307 return air roadway effectively controlled surrounding rock deformation and failure, with coal pillar displacement less than 120 mm.

Model test on failure mechanisms of deep high-stress soft rock roadways based on excavation compensation method

Traditional support (TS) is not sufficient to address the issue of large deformations in deep soft rock roadways with high stress. Based on model tests, this study considered the superposition effects of the evolution of tangential stress σ1 and radial stress σ3 on the crack propagation of excavated rock mass. Moreover, it explored the response characteristics and failure mechanisms of surrounding rock under different support modes. The results showed that, compared with the TS, the compensation support (CS) reduces the surrounding rock deformation, fracture and expansion area, and crack length by 73.7, 86.5, and 37.7%, respectively, while the roadway cross-sectional area increases by 36.8%. At 0.5R, σ3 of the shallow surrounding rock increases by 68.3%, and the peak value of σ1 at this location drops by 18.2%. The excavation effect causes σ3 and σ1 of the surrounding rock to decrease and increase, respectively. The decrease in σ3 leads to initiation of microcracks in the shallow surrounding rock, whereas the increase in σ1 causes the cracks to further open and propagate deeper. Finally, the dislocation, slippage and overturning of the fractured rock blocks along the structural planes result in bulking deformation of the shallow surrounding rock. The occurrence of microcracks in the deep surrounding rock leads to dilatation deformation. The CS strongly compensates for the stress of surrounding rock through negative Poisson’s ratio (NPR) cables, giving full play to the triaxial strength of the surrounding rock and mobilising the self-bearing capacity of the deep rock mass, thereby inhibiting the propagation and penetration of cracks. In contrast, the TS cables have a low prestress and weak excavation compensation effect, which makes it difficult to inhibit the evolution and coalescence of cracks, leading to large deformations in the surrounding rock.

Research and development of fully enclosed wire-shell support structure technology for deep soft rock roadway based on TRIZ theory

The TRIZ theory was used to accurately discover the problems to be solved in the design of roadway surrounding rock control technology. This paper tried to solve the complex issue of surrounding rock control in deep roadways from a new perspective. Based on the functional component analysis and causal axis analysis of the problem’s primary reason, simultaneously, the surrounding rock control technology was optimized through technical contradiction analysis, physical contradiction analysis, and substance and field model analysis. As a result, a fully enclosed wire-shell support technology was proposed. Finally, taking the typical soft rock roadway engineering of Pansan Coal Mine in Huainan Mining Area, Anhui Province, China, as the engineering background, the engineering application and effect evaluation were completed. This paper provides a reference for controlling the instability of deep soft rock roadways in coal mines. A new idea of optimizing roadway support engineering based on TRIZ theory was proposed.

Study on deformation and instability characteristics and control technology of deep soft rock roadway with strong mining

With the development of deep mining of coal resources, the problem of deep roadway management is becoming increasingly prominent. This study aims to analyze the deformation and failure mechanism of deep-buried soft rock roadway under the influence of mining. Taking the material roadway of 3205 working face in Xin’an Coal Mine as the engineering background, this study analyzed the characteristics of roadway deformation and failure and its influencing factors through field investigation. This study firstly expounded the principles of graded continuous anchorage for roadway roof and then proposed a new support scheme whose feasibility was verified by numerical simulation. Field verification shows that the optimized support scheme can effectively control the deformation of roadway surrounding rock. Specifically, the deformation of roof and two sides is reduced by 91% and 50% respectively; the maximum crack depth decreases from 9.56 to 3.26 m, indicating that the roof crack development has been significantly inhibited. The new support scheme builds a solid anchored rock beam structure with thick roof layer, which can maintain the long-term stable bearing capacity of deep-buried composite roof roadway. This study provides a solution for the surrounding rock control of deep soft rock roadway.

Failure mechanism and control technology of deep soft-rock roadways: Numerical simulation and field study

Large deformations such as roof subsidence, floor heave, and two-sided deformations occur frequently in deep soft-rock roadways. The deformation becomes more severe under the combined effect of high in-situ and mining-induced stresses, which detrimentally affect the safe mining of coal. Based on the geological conditions and roadway failure characteristics of the Nanyaotou coal mine in Shanxi province, China, we used comprehensive numerical simulations and field observations to study roadway deformation and failure. The deformation mechanism of deep soft-rock roadways under dynamic pressures is described, and the corresponding control measures are proposed. The deformation and fracture development characteristics of roadways surrounding rocks were explored with a primary support scheme, and its effects were evaluated. The radius of the plastic zone and the displacement deformation of the roadway were studied by using theoretical analysis, and a combined-support design of “anchor bolt + anchor cable + shotcrete + deep and shallow borehole grouting + inverted arch” was proposed to limit deformations and relieve the stress in the surrounding rocks. Numerical simulations and field monitoring showed that the combined support scheme can effectively mitigate the large deformations of ventilation roadways and provide guidance for the stable control of deep soft-rock roadways.

Mechanical behavior of soft rock roadway reinforced with NPR cables: A physical model test and case study

Deep soft rock roadways are prone to large deformations and failure when reinforced with traditional rockbolts owing to the stiffness mismatch between soft rocks and rockbolts. Thus, a novel rockbolt named “negative Poisson’s ratio (NPR) bolt/cable” that maintains a constant support force during loading is used to reinforce deep soft rock roadways to prevent large deformations. In this study, a large-scale physical model test was conducted to reveal the mechanical performance of NPR cables in soft rocks and obtain the mechanical properties of reinforced rock masses. The test results show that the rock mass reinforced with the NPR cable underwent progressive failure and exhibited the characteristics of a constant-resistance yielding-pressure under external loading, suggesting that NPR cables operate well with soft rock masses. Moreover, on-site investigations confirmed that the effective control of NPR cable supports slow and large deformations of soft rock roadways. An analytical model was developed to verify the physical model test results. The study findings can serve as a reference for theoretical model studies and field applications of NPR cables to prevent large deformations.

Mechanism of Time-Dependent Instability of Deep Soft-Rock Roadway and Crack-Filling Reinforcement Technology

Soft broken surrounding rock exhibits obvious rheological properties and time-dependent weakening effects under the action of deep high-ground stress, leading to the increasingly prominent problem of sustained large deformation in deep roadways. In this study, with the II5 Rail Rise in Zhuxianzhuang Coal Mine as an example, the mechanism and control technology of time-dependent damage and instability in a deep soft-rock roadway were explored through a field observation and numerical simulation. The research results show that the range of the loose circle in the deep fractured surrounding rock can reach 3.0 m. The expansion of shallow and deep cracks causes the primary plastic deformation and secondary rheological deformation of the surrounding rock, with the rheological deformation rate increasing by 21.4% every 55 days on average, which ultimately induces the instability and failure of the surrounding rock. Based on the mechanism of roadway instability, a control technology of high-preload bolt + deep- and shallow-borehole crack filling was proposed. The technology reduces deformation and ensures the stability of the roadway surrounding rock by inhibiting the propagation of deep and shallow cracks and reinforcing the surrounding rock.

Study on Stability Control Mechanism of Deep Soft Rock Roadway and Active Support Technology of Bolt-Grouting Flexible Bolt

In order to study the stability control mechanism of deep soft rock roadway and the active support technology of the anchor-grouting flexible bolt, this paper takes the west wing transportation roadway of Yuandian No. 2 Coal Mine of Huaibei Mining Co., Ltd., Huaibei, China as the research background. By analyzing the occurrence conditions and failure characteristics of the surrounding rock of the west wing transportation roadway and the structural characteristics and mechanical properties of the anchor-grouting flexible bolt, combined with the elastic–plastic and superimposed arch theory analysis, the superposition community theoretical model and the superposition joint support scheme of “bolt (cable) + anchor net + anchor-grouting flexible bolt + shotcrete support” are proposed. The reliability of the combined support scheme is analyzed by FLAC 3D numerical simulation software and field experiment. The results show that the maximum roof-to-floor convergence and two-side convergence of the west wing transportation roadway are only 30.7 mm and 27.1 mm after adopting the combined support scheme, and the deep displacement variation is within 7 mm, which can effectively maintain the stability of the roadway. The combined support scheme has a certain reference value for other similar roadways.

Study on Formation Mechanism of Pre-stressed Anchor Pressure Arch Based on Safe Co-Mining of Deep Coal and Gas

It is challenging to assure safe and effective gas mining due to the surrounding soft coal rock and rock roads in deep and high gas mines being extremely loose and broken. One of the effective ways is to arrange pre-stressed anchors in a certain area of the roadway surrounding rocks to form a compression arch with the joint action of anchors and surrounding rocks, but due to the lack of in-depth systematic research on the formation mechanism of the compression arch, the effect is difficult to give full play. The typical microstructure of deep soft coal and rock was observed by the borehole camera method, and the mechanical performance parameters were measured in the laboratory. The distribution characteristics of different bolt spacing, bolt pre-tightening force, and bolt length along the bolt arrangement direction and the additional compressive stress on the surface of the straight wall of a semi-circular arch deep soft coal and rock roadway were numerically simulated and analyzed. According to the uniform distribution range and size of the small fluctuation of the additional compressive stress inside the coal and rock, the distribution and size of the additional compressive stress on the surface of the straight wall and the effective superposition of the additional compressive stress, and the thickness and strength of the compression arch of the deep coal and rock preload bolt were analyzed, and the reasonable parameters of the pre-stressed bolt were determined. The results show that bolt spacing, pre-tightening force, and bolt length significantly affect the thickness and strength of the compression arch. The reasonable spacing of the pre-stressed bolt was a × b = 600 mm × 600 mm~400 mm × 400 mm, the pre-stressed bolt pre-tightening force was F = 50~90 kN, the length of the pre-stressed bolt was L = 1500~2000 mm, the strength of compression arch was Δσc = −1.480~−1.589 MPa, and the thickness of the compression arch was m = −266.67~−533.33 mm.

Study on the Constant Resistance Coupling Support Technology for Rock Column at the Intersection Point of Deep Soft Rock Large Section Roadway: A Case Study in China

In order to solve the problem on the serious deformation and failure of the rock column at the intersection of large cross sections in Shiyakou coal mine, based on field engineering geomechanics analysis, theoretical analysis, and three-dimensional numerical simulation, combined with the mutual coupling between the constant resistance coupling support cable and surrounding rock, a dual-control constant-resistance coupling control technology with high prestressed constant resistance coupling support cable as the core solution is proposed. The field engineering practice and field monitoring data show that the dual-control constant resistance coupling support control technology has a good control effect on the deformation of the rock column at the large cross section intersection of the deep soft rock roadway and can be effectively used in the engineering practice.

Study on failure mechanism of deep soft rock roadway and high prestress compensation support countermeasure

The problem of surrounding rock stability control of deep soft rock has become increasingly prominent. Taking Shiyakou Coal Mine as the engineering background, the deformation and failure characteristics of roadway is obtained through on-site investigation and drilling peep. X-ray diffraction and electron microscope scanning experiments analyze the mineral composition and microstructure of surrounding rock, and the microscopic mechanism of roadway failure is obtained. The relationship between roadway deformation, rock inclination and position of the weak layer was analyzed by the numerical simulation. And the deformation and failure mechanism of soft rock cross-cut roadway is obtained. By analyzing the action mechanism of the high-stress compensation support theory, the countermeasure of high prestress es compensation support based on Constant-resistance large deformation (CRLD) bolt was put forward. The analysis of field test and monitoring results show that the control effect of the new support scheme is good and has guiding for similar projects.

Space-Time Evolution Characteristics of Deformation and Failure of Surrounding Rock in Deep Soft Rock Roadway

In view of the problems of large deformation of surrounding rock, high in-situ stress, and serious soft fracture of rock stratum in deep soft rock roadway, the instability deformation failure mode of deep soft rock roadway is analyzed theoretically. The FLAC3D software is used to establish a three-dimensional numerical model of surrounding rock damage under load, and to study the displacement, stress, and plastic expansion process of damage and failure evolution in the surrounding rock of the roadway. The mechanical response mechanism of deep soft rock roadway surrounding rock bending deformation, elastoplastic transformation, and unloading failure is verified by MATLAB numerical analysis, and the space-time evolution characteristics of soft rock deformation and failure are revealed. The results show that the surrounding rock of deep soft rock roadway has many failure modes, such as obvious displacement and deformation, high stress concentration, and intensified plastic transformation in the surrounding rock. The vertical stress in the surrounding rock is concentrated at the direct top and bottom, and the horizontal stress is concentrated at the roadway side and bottom; plastic deformation and failure first appeared at the roadway side, and then extended to other parts. The research conclusion provides an important reference for surrounding rock control and roof management of high-stress soft rock roadway under deep excavation disturbance.

Deformation Prediction and Analysis of Soft Rock Roadway with High Altitude and Large Buried Depth Based on Particle Swarm Optimization LSTM Model

Deformation prediction is an important basis for roadway information construction, especially for soft rock roadway at high altitude and large buried depth, whether the deformation of roadway surrounding rock can be effectively and accurately predicted is an important basis for judging the stability of roadway surrounding rock. However, at present, the research on the informatization construction of the roadway is not in-depth, and the intelligent prediction technology for the deformation of the surrounding rock of the roadway is still in its infancy, and the accuracy of deformation prediction is also low. Therefore, based on the research of domestic and foreign researchers, in order to solve the breakthrough of related technology, this paper puts forward the deformation prediction and control technology of high altitude and deep buried soft rock roadway based on a neural network model. This method is based on the traditional prediction model and is replaced by the neural network, so as to improve the problems of low accuracy and large prediction deviation in the related deformation prediction of the traditional prediction model. At the same time, aiming at the problem of poor local weight and network search ability, an improved method using particle swarm optimization algorithm is proposed, which effectively considers the influence of local and global factors on the combined weight. Finally, the improved deformation prediction model of high altitude and deep buried soft rock roadway based on particle swarm optimization LSTM model is applied to an engineering example and compared with the traditional model to explore its feasibility and effectiveness. The results show that the prediction model has higher prediction accuracy than the traditional prediction model, and the relative deviation of the prediction results is controlled within 2%. At the same time, compared with other models (BP neural network model), it has relatively higher accuracy and stability. The research results can provide a new idea for the deformation prediction of soft rock roadway with high altitude and deep burial.

Research on Soft Rock Damage Softening Model and Roadway Deformation and Failure Characteristics.

To determine a reasonable control strategy for deep buried soft rock roadways, a study on deformation and failure characteristics was carried out. The Weibull distribution damage variable was introduced to construct a damage-softening model considering the lateral deformation of the rock mass, and the functional relationship between the model parameters F0 and m and the confining pressure were discussed. The nonlinear fitting method was used to correct the model parameters. Using the model, the failure characteristics of deep buried soft rock roadways were analyzed. A comprehensive and step-by-step joint support control strategy was proposed based on the numerical simulation results. The research results showed that the damage-softening model curve established could genuinely reflect the whole process of mudstone failure. The apparent stress concentration phenomenon occurred in the surrounding rock. The surrounding rock deformation showed that roadway floors had larger plastic failure areas than sides and vaults. The plastic failure depth could reach 2.45 m. After a comprehensive and step-by-step joint support control strategy was adopted, the deformation rate of the roadway at the section was less than 0.1 mm/d. The optimized support scheme can effectively improve the stability of the roadway.

True 3D geomechanical model test for research on rheological deformation and failure characteristics of deep soft rock roadways

Deep soft rock roadways generally present large deformation characteristics, and a vast number of workers attempt to repair them to no avail. A true 3D model test was performed based on the engineering background of the transportation roadway of the Huafeng coal mine in China. The selected analogous materials have a significant time similarity relationship with the surrounding rock, and a similar bolt-mesh-shotcrete support structure, according to the engineering background, was applied to the roadway. The test results showed that the evolution process of the rheological deformation of the roadway is two sidewalls → floor → vault → full-section convergence of the roadway. The large deformation zones of the surrounding rock are constantly transferred from the surface to the depth, and the bearing capacity of the bolts decreases rapidly after the deformation of the anchorage zones. The mechanical characteristics of the floor determine that the lower surrounding rock always repeats the failure process of the upper rock stratum, and the floor heave does not stop. The test results revealed the full-section convergence rheological deformation laws and migration laws of the internal key deformation locations of the surrounding rock and clarified the reasons for the floor heave. The model test results are verified through field monitoring, and opportunities and suggestions for secondary support are determined. These results could provide a reference for the failure process and control technology of the same type of deep soft rock roadway.

Seepage Law of Nearly Flat Coal Seam Based on Three-Dimensional Structure of Borehole and the Deep Soft Rock Roadway Intersection

Exploring the evolution characteristics of gas seepage between boreholes during the drainage process is critical for the borehole’s layout and high-efficiency gas drainage. Based on the dual-porous medium assumption and considering the effect of stress redistribution on coal seam gas seepage characteristics, a coal seam gas seepage model with a three-dimensional roadway and borehole crossing structure has been established and numerically calculated, concluding that the coal seam is between the drainage boreholes. The temporal and spatial evolution characteristics of gas pressure and permeability help elucidate the gas seepage law of the nearly flat coal seam associated with the deep soft rock roadway and borehole intersection model. The results indicate that: (1) The roadway excavation results in localized stress in some areas of the surrounding rock, reducing the strength of the coal body, increasing the expansion stress, and increasing the adsorption of gas by the coal body. (2) Along the direction of the coal seam, the permeability decreases initially and then increases. The gas pressure in the coal seam area in the middle of the borehole is higher than the pressure in the coal seam around the borehole, and the expansion stress and deformation increase, reducing the permeability of the coal body; when near the next borehole, the greater the negative pressure, the faster the desorption of the gas attracts the matrix shrinkage effect and causes the coal seam permeability rate to keep increasing. (3) The improvement of gas drainage with the overlapping arrangement of two boreholes firstly increases and then decreases as time goes on. (4) When the field test results and numerical simulation of the effective area of gas extraction are compared, the effectiveness of the model is verified. Taking the change of the porosity and the permeability into the model, it is able to calculate the radius of gas drainage more accurately.