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Seismic dynamic stability is a critical problem in crossing-fault tunnels. A three-dimensional model with a crossing-fault tunnel and infinite boundaries is established based on the finite-element method. By combing the results in time and frequency domains, a time–frequency conjoint analysis method is proposed to systematically investigate the seismic response characteristics of the surrounding rock and tunnel structures in the crossing-fault tunnel. The propagation of waves in the crossing-fault tunnel and its seismic amplification effect are clarified in time domains. In frequency domain analysis, the analysis results of Fourier spectrum and modal analysis are integrated to reveal the correlation of the predominant frequency of seismic waves, the natural frequency, and the characteristics of dynamic response in the surrounding rock. The results show that, as the main wave propagation channel, the fault controls the wave propagation characteristics in the surrounding rock. In the crossing-fault section, the dynamic amplification effect of the surrounding rock is significant, and instability deformation is most likely to occur. Furthermore, the influences of tunnels on the dynamic response in the surrounding rock and crossing-fault are different. In the frequency domain, as a result of the first-order and higher-order natural frequency, the overall and local deformation caused have a combined effect on the surrounding rock. This work can be a reference for the assessment and prevention of damage in the tunnel under earthquake. [ABSTRACT FROM AUTHOR]

In this study, a new type of multi-arch tunnel construction method is proposed. This effort is undertaken due to the many disadvantages of the traditional multi-arch tunnel construction method. Furthermore, this method omits the construction of a middle pilot tunnel, and it has the advantages of safety, high efficiency, and being economical. When using the method of continuous arch tunneling without a middle pilot tunnel, the blasting of the first tunnel and the following tunnel has a greater impact on the surrounding rock damage, as well as on the supporting structure of the same cross-section. Therefore, this study uses LS-DYNA finite element software to construct a three-dimensional numerical model. In addition, the perimeter rock damage law and mechanical response characteristics of the supporting structure in the same cross-section of the first tunnel, as well as the following tunnel after blasting without a middle pilot tunnel, are analyzed. At the same time, the results of the study are based on optimizing the blasting program, and these are then applied to the field. Through the results, it is found that, after blasting a continuous arch tunnel without a medial pilot tunnel, the surrounding rock damage in the arch cross-region of the double-arch tunnel (where the arch top and the arch shoulder are more significant) and the effective stress of the supporting structure exceed the strength design value. In addition, the maximum adequate pressure is distributed in the medial diaphragm wall. With the optimized blasting scheme, the range of the peripheral rock damage is reduced by a maximum of 67%, and the effective stress in the supporting structure is reduced by 25.9–64.8%. The research results are of great significance in terms of improving construction safety, economic efficiency, and project quality, as well as in promoting the research and development of new work methods for double-arch tunnels. [ABSTRACT FROM AUTHOR]

High-pressure air storage is an important part of a gas storage system. Abandoned coal mine roadways can provide a large number of air storage spaces. The geological conditions of coal mines in different areas vary, such as depth, surrounding rock grade, in situ stress state, and surrounding rock permeability, which directly affect the mechanical behavior and air tightness of roadway surrounding rock under high internal pressure. Therefore, the suitable internal pressure must be selected for abandoned roadways with different geological conditions. In this study, the numerical simulation software FLAC3D was used to calculate the stress, deformation, plastic zone volume, and pore pressure of surrounding rock of an abandoned roadway under 5–10 MPa internal pressure. Results show that some differences exist in the suitable internal pressure of the abandoned roadway under different geological conditions. When the in situ stress state was σH > σh > σv or σH > σv > σh, the suitable internal pressure of grade I, II, and III surrounding rocks was 5–7 and 8–10 MPa at the depth greater than 200 and 300 m, respectively; the suitable internal pressure of grade IV and V surrounding rocks was 5–6, 7–9, and 10 MPa at the depth greater than 200, 300, and 400 m, respectively. When the in situ stress state was σv > σH > σh, the suitable internal pressure of grade I, II, III, IV, and V surrounding rocks was 5–7 and 8–10 MPa at the depth greater than 300 and 400 m, respectively. Surrounding rock permeability can be used to evaluate the air tightness of roadway surrounding rock under high-pressure air. The surrounding rock permeability that can meet the sealing requirements of compressed air energy storage (CAES) caverns is less than 1 × 10−14 m2, which are low-permeability strata. Low-permeability hard rock should be selected as much as possible. The research results provide a theoretical basis for the determination of internal pressure and the sealing evaluation of an abandoned coal mine roadway used for gas storage cavern. [ABSTRACT FROM AUTHOR]

In recent decades, the permanent single-layer tunnel lining has been developed to meet the requirements of the deep-buried and over-long tunnel projects. In this study, macro-synthetic polypropylene (PP) fiber-reinforced shotcrete was designed for the permanent single-layer tunnel lining. Uniaxial compressive tests were carried out on the three rock–shotcrete composites (G-NSC, S-NSC and S-FSC) with two types of rocks [granite (G) and sandstone (S)] and two types of shotcretes [normal shotcrete (NSC) and fiber-reinforced shotcrete (FSC)] to investigate the failure mechanism of the composites. Combined with X-ray computed tomography (X-CT) and digital image correlation (DIC) technologies, the meso-structures of shotcrete, the strain development, crack propagation and damage evolution laws of different composites were analyzed. The results showed that macro-synthetic PP fiber increased the porosity and the volume of large-diameter pores of the shotcrete. The microcracks mainly emerged and propagated in the shotcrete for G-NSC, but occurred and gathered near the rock–shotcrete interface of sandstone-based composites. Besides, macro-synthetic PP fibers can greatly increase the ductility of the composite, and cracks tended to propagate along with the interface between aggregates and mortar in FSC. Finally, damage calculation model based on the dissipated energy was proposed for the rock–shotcrete composites. [ABSTRACT FROM AUTHOR]

Background: The mining-induced stress in the surrounding rock after coal seam mining is the primary cause of damage and failure of the surrounding rock in the mining area. However, the magnitude and direction of the stress field induced by mining in the overburden strata during the excavation process of deep and adjacent coal seams are not yet clear, and it is difficult to determine how adjacent working faces interact with each other. Results: In this study, a large-scale numerical model was built using FLAC3D (Fast Lagrange Analysis Continua) to simulate the sequential mining process of three adjacent working faces (No.1, No.2, and No.3) in Liuzhuang Coal Mine located in southern China. The results showed that the maximum height of plastic zone development after mining in the No.1 working face was 41 m, and the maximum height of plastic zone development was 33.8 m away from the 13 coal seam. It did not affect the top and bottom of the No.3 working face. The development height of the plastic zone on the roof of the No.2 working face after mining was 52m, and the top and bottom plates of the No.3 working face remained intact. The plastic zone of the floor of the No.3 working face after mining was not communicated with the plastic zone of the roof of the No.1 and No.2 working faces. There was a complete rock layer between the two coal seams, and there was not the mutual influence of the mining activities. During the mining process of working faces No.1 and No.2, the range of dynamic pressure influence was extended up to 100m ahead of the working face. During the mining process of the No.3 working face, the range of dynamic pressure influence was 120 m ahead of the working face. The No.1 working face goaf and the mining of No.2 working face had not disturbance to the No.3 working face. Conclusions: After the mining of No.1 and No.2 working faces, the stress in the goaf significantly decreased, and the lateral support stress concentration area of No.1 and No.2 working faces had a relatively small impact on the 13 coal seam. Therefore, the No.1 goaf and mining of No.2 working faces had not disturbance to No.3 working face. [ABSTRACT FROM AUTHOR]

The MTS815.02 rock test system is used for performing triaxial compression creep experiments on sandstone to reveal the rheological properties of the rock in deep roadways. Instantaneous elastic, viscoelastic, and viscoplastic strains are separated, and the relationship between the model parameters and the stress and time is established by combining the characteristics of the creep curve. According to non-linear rheological theory, the constitutive equation of a creep model of the rock under a three-dimensional stress state is deduced, and the validity of the model is verified by the experimental data. Results show that the improved creep model comprehensively considers instantaneous elastic, non-linear viscoelastic, and viscoplastic strains, making the theoretical curve of the model highly consistent with the experimental curve. The model can describe the non-linear creep during the loading of sandstone. It can also reflect the creep parameters during the deformation. The correlation coefficients of the experimental curve and the theoretical curve under the same stress are both greater than 0.90. The comparison results verify the validity and feasibility of the creep model. Highlights: According to the characteristics of creep curve, the instantaneous strain, viscoelastic strain and viscoplastic strain are separated. The creep model based on viscoelastic-plastic strain separation can well describe the accelerated creep characteristics of rock creep process. The variation of creep parameters also reflects the evolution process of damage accumulation and deterioration of material properties. [ABSTRACT FROM AUTHOR]

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The cumulative damage effects of surrounding rock under single full-face blasting and multiple full-face blasting of a large cross-section tunnel are comparatively studied in this paper. The damage processes of the single and multiple full-face blasting of the tunnel are simulated by the established rock damage model embedded into the LS-DYNA computer code through its user subroutines and a cumulative damage simulation technology in the LS-DYNA. The simulation results are verified against field test data. The results demonstrate that the numerically predicted peak particle velocity (PPV) of the surrounding rock under multiple full-face blasting is more consistent with field test data than that under single full-face blasting, which indicates the advantages of multiple full-face blasting in comparison to single full-face blasting in simulating the blasting process of a tunnel. The maximum damage depth in the middle of the tunnel invert is mostly affected by multiple full-face blasting. Both the maximum damage depth and the maximum PPV occur in the middle of the tunnel invert under single and multiple full-face blasting. Based on the defined damage threshold Dcr and the modeled maximum damage depth of the surrounding rock, the influence of initiation sequence on the critical PPV for rock damage is analyzed, and a critical PPV of rock damage is proposed to provide a safety criterion for tunnel blasting excavation. [ABSTRACT FROM AUTHOR]

A study of the deformation of the surrounding rock and coal pillars near a fault under the influence of mining is conducted on a physical model for the design of coal pillars to support and maintain the roofs of adjacent fault roadways. This research is based on the 15101 mining face in the Baiyangling Coal Mine, Shanxi, China, and uses simulation tests similar to digital speckle test technology to analyse the displacement, strain and vertical stress fields of surrounding rocks near faults to determine the influence of the coal pillar width. The results are as follows. The surrounding rock of the roadway roof fails to form a balance hinge for the massive rock mass. The vertical displacement, vertical strain and other deformation of the surrounding rock near the fault increase steeply as the coal pillar width decreases. The steep increase in deformation corresponds to a coal pillar width of 10 m. When the coal pillar width is 7.5 m, the pressure on the surrounding rock near the footwall of the fault suddenly increases, while the pressure on the hanging wall near the fault increases by only 0.35 MPa. The stress of the rock mass of the hanging wall is not completely shielded by the fault, and part of the load disturbance is still transmitted to the hanging wall via friction. The width of the fault coal pillars at the 15101 working face is determined to be 7.5 m, and the monitoring data verify the rationality of the fault coal pillars. [ABSTRACT FROM AUTHOR]

The failure of surrounding rock in tunnel crossing water-rich fault is a sudden damage phenomenon with obvious nonlinear and abrupt characteristics, which is characterized by the uncertainty of deformation, the nonlinearity of constitutive relation and the mutation of failure process. Based on the mechanical model of tunnel-fault system, the cusp catastrophe model of the failure of surrounding rock in tunnel crossing water-rich fault is established. Combining with the field monitoring data, the model is employed to judge the stability of surrounding rock. Results show that the deformation curve of tunnel vault has a good correlation to the cusp catastrophe model, and the results for stability analysis is consistent with the actual situation. The influences that the strength of rock mass, groundwater and fault width have on the failure of tunnel are further discussed, which provides scientific guidelines to the construction of tunnel. [ABSTRACT FROM AUTHOR]

The demand for gob-side entry retaining (GSER) technology is extensive in Chinese coal mines because of its outstanding advantages. However, due to the occurrence of long-term roof movement disturbances, maintaining the conventional GSER over long distances is difficult. The urgent demand for this technology and its difficult maintenance are prominent contradictions faced in its application. In this paper, two characteristics of strata movement after mining that have great influence on GSER are determined in a physical simulation experiment. One is that the roof layers, which are dominated by the key strata (KS), collapse in multiple groups to form two-directional periodic pressures and superposed disturbances. The other is that the movement of the main roof will experience three stages of deformation, as follows: bending subsidence before collapse, sinking deformation at collapse and compressive deformation after collapse. In particular, the gradual compression of the bulging gangue in the gob extends the disturbance cycle. Therefore, it is difficult to maintain the GSER over long distances because of the long-term and multiple breaking disturbances of the roof layers. Mechanical models of KS breaking and GSER are established, and a method to determine the timing and strength of KS disturbances are proposed. Making use of the characteristics of staged collapse and fluctuating weighting of the overlying strata, an innovative technology named short-staged GSER is proposed. This technology maintains the maximum length of GSER within the optimal length, which ensures that the entry avoids superposed disturbances, and reduces the maintenance difficulty. The method for determining the key technical parameters is discussed, and an engineering case in panel 24202 of the Shaqu Mine in China is presented. From a back-calculation of measurements, the engineering practice demonstrates that the surrounding rock mass is stable, and the deformed entry size is safe when the length of the short-staged GSER does not exceed 100 m. [ABSTRACT FROM AUTHOR]

Deformation and destruction of roadway surrounding rock is one of the main causes of coal mine accidents. In this paper, the horseshoe-shaped roadway model was established by particle flow code firstly and then analyzed the roadway damage process through the contact force chain, deformation displacement and distribution of micro-cracks. The research result show that the parallel bond model can well simulate the damage process of the coal mine roadway. The surrounding rock can be divided into four zones from the roadway side to the deep rock mass. The micro-contact force chain is the force transmission path and the principal stress is the macroscopic reflection of the micro-contact force chain. [ABSTRACT FROM AUTHOR]

The effect of blasting vibration waves on surrounding rock and supporting structures is an important field in underground engineering. In this paper, the separation variable method is used to solve the displacement potential function for the propagation of the blasting vibration waves. In the axis coordinate system, the particle motion and stress change with axial distance, radial distance and time is obtained in surrounding rock. The peak particle velocity law in surrounding rock under different blast loads and surrounding rock parameters is discussed. In addition, the particle vibration characteristics in the surrounding rock are studied using numerical simulations method. The results shows that the peak particle velocity in surrounding rock appears negative exponent attenuation with the increase of axial distance, but it appears positive and negative fluctuations in radial direction. This phenomenon is a new discovery and it has been rarely investigated before. Moreover, the peak particle velocity attenuates more quickly and intensely in the near blasting field, which means that the supporting structure in a shorter distance away from the heading face is vulnerable to the impact of blasting vibration. The attenuation of blasting vibration velocity is closely related to charge length, blasting load amplitude, attenuation index and rock elastic modulus. The numerical simulation accomplishes the same results and then demonstrates the validity of theoretical results. [ABSTRACT FROM AUTHOR]

The huge plastic deformation is the characteristic of the underground roadways in coal mine. Therefore, to compute the stability of underground roadways, a elastic-plastic constitutive model of surrounding rock must be obtained. Many elastic-plastic constitutive models for rock mass have been proposed. In this study, a generalized constitutive law for an elastic-plastic constitutive model is applied. Using this generalized constitutive law, the problem of model identification is transformed to a problem of parameter back analysis, which is a typical and complicated optimization. To improve the efficiency of the traditional optimization method, a black hole algorithm is applied in this study. Combining the generalized constitutive law for an elastic-plastic constitutive model and black hole algorithm, a new back analysis method for model identification of rocks surrounding underground roadways in coal mine is proposed. Using this new method, the elastic-plastic constitutive models for two underground roadways in Huainan coal mine has been back-calculated. The results are compared with those of traditional genetic algorithm, fast genetic algorithm and immune continuous ant colony algorithm, that proposed in previous studies. The results show that the new model back analysis algorithm can significantly improve the computation efficiency and the computation effect, and is a very good method for back analysis the rock model surrounding underground roadways in coal mine. [ABSTRACT FROM AUTHOR]

To compute the stability of underground engineering, a constitutive model of surrounding rock must be identified. Many constitutive models for rock mass have been proposed. In this model identification study, a generalized constitutive law for an elastic-plastic constitutive model is applied. Using the generalized constitutive law, the problem of model identification is transformed to a problem of parameter identification, which is a typical and complicated optimization. To improve the efficiency of the traditional optimization method, an immunized genetic algorithm that is proposed by the author is applied in this study. In this new algorithm, the principle of artificial immune algorithm is combined with the genetic algorithm. Therefore, the entire computation efficiency of model identification will be improved. Using this new model identification method, a numerical example and an engineering example are used to verify the computing ability of the algorithm. The results show that this new model identification algorithm can significantly improve the computation efficiency and the computation effect. [ABSTRACT FROM AUTHOR]

Roadways supported by bolts contain support structures that are built into the rock surrounding the roadway, referred to as reinforced rocks in this paper. Using physical model simulation, the paper investigates the bearing characteristics of the reinforced rock under different bolt parameters with incrementally increased load. The experimental results show that the stress at the measurement point inside the structure varies with the kinetic pressure. The stress increases slowly as the load is initially applied, displays accelerated growth in the middle of the loading application, and decreases or remains constant in the later stage of the loading application. The change in displacement of the surrounding rock exhibits the following characteristics: a slow increase when the load is first applied, accelerated growth in the middle stage, and violent growth in the later stage. There is a good correlation between the change in the measured stress and the change in the surrounding rock displacement. Increasing the density of the bolt support and the length and diameter of the bolt improves the load-bearing performance of the reinforced rock, including its strength, internal peak stress, and residual stress. Bolting improves the internal structure of the surrounding rocks, and the deterioration of the surrounding rock decreases with the distance between the bolt supports. [ABSTRACT FROM AUTHOR]

Pingxiang Mining Area in Jiangxi Province is one of the major coal-producing areas and is prone to serious coal and gas outburst, therefore, it is of significance to research on gas geological features and its controlling factors. Based on the analysis of gas data collected from geological exploration and coal mining, the research reveals that the features of gas geology vary significantly between west part and east part of Pingxiang Mining Area, and it is characterized by high gas mines with serious coal and gas outburst in the west part and low gas mines with no coal and gas outburst in the east part. The main controlling factors to gas geology are discussed, and the great difference of gas geology between west part and east part is the result of comprehensive effect by geological factors. Concerning the gas generation, the coal rank in the west part is higher than that in the east part, which is favorable to generate more gas in the west part than in the east part. Concerning the gas preservation, the structures are characterized by gliding nappe in the west part and by tectonic window in the east part, the surrounding rocks are characterized by poor permeability in the west part and comparatively good permeability in the east part, and the characteristics of coal rank and coal body structure are favorable to gas preservation in the west part and favorable to gas emission in the east part. [ABSTRACT FROM AUTHOR]

Numerical simulations of the deep roadway were carried out through application of the strain-softening constitutive model. Differences between the deep and shallow roadway of the rock bearing structure were analyzed. Influences of the supporting resistance on the rock bearing structure at the deep roadway were discussed. The results show that there is alternation of strong and weak strength-softening region in the surrounding rock of deep roadway. However, the increase in the supporting resistance cuts down the size of strength-softening region of surrounding rock, decreases its strength-softening degree, and improves the stress distribution condition of the surrounding rock mass. It is concluded that the supporting resistance can raise the self-supporting ability of surrounding rock through controlling its strength-softening so as to make the rock bearing structure of deep roadway stable. [ABSTRACT FROM AUTHOR]

Numerical simulation-FLAC3D and equivalent material simulation were carried out to analyze the damaged patterns and lows, distribution of plastic width of face, and surrounding rock of FMTC during the advance of work face with different thick coal seams based on engineering geology and exploitation technology of 1151(3) fully mechanized top-coal caving (FMTC) face in Xieqiao Colliery. The results show that there is damage, and the destruction characteristics of surrounding rock and coal mass are different obviously in asymmetric exploitation layout. The damaged zone in surrounding rock and the coal of the return airway is larger than that of the intake airway. Moreover, the retained coal pillars are all damaged by tension and shear fracture, and plastic zone in coal mass in the dip direction ahead of Face is nonuniform. There are large damage zones in roof and floor strata, surrounding rock, and coal of return and intake airways near work face. The damaged zone in the upper part of Face is larger than that in middle and lower parts. The fruits of this paper are of guiding significance for engineering practices, such as support design and choice, roadway supporting and maintaining, rock pressure control of FMTC face, etc. [ABSTRACT FROM AUTHOR]

Discussed advantages of improved Monte-Carlo method and feasibility about proposed approach applying in reliability analysis for tunnel surrounding rock stability. On the basis of deterministic parsing for tunnel surrounding rock, reliability computing method of surrounding rock stability was derived from improved Monte-Carlo method. The computing method considered random of related parameters, and therefore satisfies relativity among parameters. The proposed method can reasonably determine reliability of surrounding rock stability. Calculation results show that this method is a scientific method in discriminating and checking surrounding rock stability. [ABSTRACT FROM AUTHOR]

Based on the measured displacements, the change laws of the effect of distance in phase space on the deformation of mine lane were analyzed and the chaotic time series model to predict the surrounding rocks deformation of deep mine lane in soft rock by nonlinear theory and methods was established. The chaotic attractor dimension( D) and the largest Lyapunov index( E max) were put forward to determine whether the deformation process of mine lane is chaotic and the degree of chaos. The analysis of examples indicates that when D > 2 and E max>0, the surrounding rock’s deformation of deep mine lane in soft rock is the chaotic process and the laws of the deformation can still be well demonstrated by the method of the reconstructive state space. Comparing with the prediction of linear time series and grey prediction, the chaotic time series prediction has higher accuracy and the prediction results can provide theoretical basis for reasonable support of mine lane in soft rock. The time of the second support in Maluping Mine of Guizhou, China, is determined to arrange at about 40 d after the initial support according to the prediction results. [ABSTRACT FROM AUTHOR]

The mechanical design parameters of surrounding rock and primary support of weathered rock tunnel are difficult to obtain by experiments. In this paper, taking the ratio of vault settlement to flank wall horizontal displacement as an investigation variable, we proposed the displacement ratio dichotomy numerical back analysis method (DDNBAM) to calculate the physical–mechanical parameters of tunnel surrounding rock-initial support system. Based on the DDNBAM, we presented a new method to evaluate the rationality of primary support design parameters by the ratio of the equivalent lateral pressure coefficient to the equivalent Young's modulus with time for weathered rock tunnel in construction. The results are shown as follows: the results calculated by the DDNBAM may reasonably reflect the dynamic variations of tunnel surrounding rock-primary support system using the center cross disphragm (CRD) method; the higher calculation precision may be obtained using the DDNBAM, comparing with the parabolic-apex back analysis method previously proposed by Xu (2012); and adopting the DDNBAM may obtain more reasonable and reliable physical–mechanical parameters of surrounding rock-initial support system. [ABSTRACT FROM AUTHOR]