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The mechanical and deformation behaviors of the surrounding rock play a crucial role in the structural safety and stability of tunnel shafts. During drilling and blasting construction, seepage failure and hard brittleness damage of the surrounding rock occur frequently. However, previous discussions on stress deformation in the surrounding rock did not consider these two factors. This paper adopts the theory of elastoplastic to analyze the effects of seepage and hard brittleness damage on the stress and deformation of the surrounding rock of a tunnel shaft. The seepage effect is equivalent to the volumetric force, and a mechanical model of the surrounding rock considering seepage and hard brittleness damage was established. An elastoplastic analytical formula for surrounding rock was derived, and its rationality was verified through numerical examples. Based on these findings, this study revealed the plastic zone as well as stress and deformation laws governing the behavior of surrounding rock. The results showed that the radius of a plastic zone had a significant increase under high geostress conditions, considering the hard brittleness damage characteristics of the surrounding rock. The radius of the plastic zone increased with an increase in the initial water pressure and pore pressure coefficient, and the radius of the plastic zone increased by 5.5% and 3.8% for each 0.2 MPa increase in initial water pressure and 0.2 increase in pore pressure coefficient, respectively. Comparing the significant effects of various factors on the radius of the plastic zone, the effect of support resistance inhibition was the most significant, the effect of the seepage parameter promotion was the second, and the effect of the hard brittleness index promotion was relatively poor. The hard brittleness index and water pressure parameters were positively correlated with the tangential and radial stresses in the surrounding rock, and the radial stresses were overall smaller than the tangential stresses. The deformation of the surrounding rock was twice as large as the initial one when hard brittleness damage and seepage acted together. These findings can provide a reference for the stability evaluation of the surrounding rock in tunnel shafts. [ABSTRACT FROM AUTHOR]

To ensure the construction and operational safety of tunnel undercrossing multi-situational goafs, the Huaying Mountain High-Speed Rail Tunnel, a critical section of the Xi'an-Chongqing High-Speed Railway, was taken as a case study. Based on a three-dimensional finite difference numerical simulation platform, twelve situations were established to analyze the effects of three factors: distance, scale, and angle. The stability analysis was conducted by examining the displacement and deformation characteristics of the surrounding rock, stress changes, and axial forces of the initial support for each situation. The results show that in tunnel undercrossing multi-situational goafs, the vertical deformation, horizontal convergence of the surrounding rock, and the maximum axial force of initial support are all affected. Within a certain range, changes in distance significantly impact subsidence and settlement deformation of the surrounding rock. However, as the distance increases, the horizontal and vertical displacements of the tunnel and the axial force of the initial support tend to decrease. Conversely, the scale and angle of the goaf have an opposite effect on the surrounding rock: as the scale and angle increase, the stability of the surrounding rock deteriorates. In this case study, when the distance exceeds 1.13 times the tunnel span, the influence of the goaf on the stability of the surrounding rock gradually decreases. When the angle exceeds 45°, vertical displacement decreases, and the increasing trend of horizontal displacement gradually diminishes. The conclusions of this paper can provide guidance for designing reinforcement schemes for tunnels crossing through multi-situational goafs. The findings provide valuable insights and guidance for similar engineering projects. [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]

The excessive destruction of surrounding rock in deep tunnel will change the original environmental state and destroy the natural ecological balance. Research on the dynamic response characteristics and damage thresholds of rock masses in deep environments plays a crucial role in determining the excavation range of blasted rock and establishing safety construction scheme. This study employs numerical simulation techniques to investigate the dynamic response characteristics of surrounding rock under different ground stress conditions. By introducing the dynamic ultimate tensile strength criterion, critical fracture stress threshold, and maximum damage radius of rock under coupled dynamic-static loading conditions are determined. The research shows that under uniaxial ground stress condition, increasing ground stress inhibits damage to the surrounding rock and the extension of cracks in the excavation area, while imposing restrictions on the attenuation rate of explosive stress. Under bidirectional equal ground stress condition, an increase in lateral pressure coefficient inhibits the development of damage zones along the excavation contour, yet enhances the extension of cracks in the maximum principal stress direction. Moreover, when lateral pressure coefficient becomes excessively large, the attenuation rate of explosive stress significantly increases. Based on the threshold values of peak particle velocity (PPV), the functional relationship is established to predict safety criteria for deep blasting excavation. [ABSTRACT FROM AUTHOR]

To explore the fracture characteristics and fracture mechanism of the surrounding rock of straight‐walled arched tunnels, this study first carried out biaxial compression tests on rock samples and analyzed the disaster evolution characteristics under loading. Then, a stress distribution function was established using a complex function, and the distribution characteristics of the surrounding rock stress field were determined. Finally, combining the stress field with results obtained by computational tomography and acoustic emission measurements, the dynamic evolution of the main fracture mechanism of the tunnel surrounding rock was comprehensively analyzed, and the fracture mechanism of the surrounding rock of the straight‐walled arched tunnel was elucidated. The research results strengthen the understanding of rock fracture evolution during tunnel construction and operation and provide a basis for tunnel construction and surrounding rock stability analysis. Highlights: The biaxial compression test was carried out on rock samples.The stress field of the surrounding rock is analyzed based on a complex function.The fracture characteristics of the tunnel surrounding rock are elucidated. [ABSTRACT FROM AUTHOR]

To solve these problems of poor supporting effect and serious deformation and failure of surrounding rock of mining roadway under deep mining stress, a FLAC-3D numerical calculation model is established with −800 m level no. 2424 upper roadway in the Suncun Coal Mine as the background to compare the stress, deformation, and failure law of surrounding rock of mining roadway under once support and multi-level support with the same support strength. It is found that the multi-level support technology has obvious advantages in the surrounding rock of the horizontal roadway on the 2424 working face. From this, the key parameters of multi-level support are determined, and the field industrial test is carried out. The results show that the overall deformation of the surrounding rock is obviously reduced after multi-level support. The displacement of the two sides is reduced by about 40%, the displacement of the roof and floor is reduced by about 30%, and the plastic zone of the roadway is reduced by about 75%. The peak value of concentrated stress decreases from 98.7 MPa to 95.8 MPa, which decreases slightly. The integrity and stability of the surrounding rock are excellent, and the support effect is satisfactory. The research can provide reference and technical support for surrounding rock control of deep high-stress mining roadways. [ABSTRACT FROM AUTHOR]

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

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]

Field practice shows that, joints have very adverse influence on crack formation in the protective layer of rock mass, during blasting excavation. To improve the crack formation in rock mass with filled joints, V-shaped notch blasting method is conducted in simulation and site. It can be seen from the calculation in dynamic finite element method that the V-shaped notch boreholes played a certain role of guiding energy in rock blasting excavation, the crack is generated along the hole attachment when the radial decoupling charging coefficient is.198. Studies show that, when a layer of filled joint is at the middle point of the attachment of notch borehole, the compressive stress at the middle point of filled joint will increase as the angle between the joint and the borehole attachment increases. When the angle is 15°, the damage depth of surrounding rock, d ≈ 3R; the angle is 30°and 45°, d > R; the angle is 60°, 75°and 90°, d ≤ R, the penetration crack between adjacent boreholes can be formed along the borehole attachment. [ABSTRACT FROM AUTHOR]

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

In this paper, the deformation and stress variation of tunnel lining are studied by using finite difference program FLAC3D, and the mechanical response characteristics of surrounding rock are explored. Besides, the sensitivity of stress field, plastic zone and deformation to different mechanical parameters of surrounding rock is analyzed. The results indicate that under different construction methods, the lining of drainage tunnel is safe according to the pressure and tensile calculation, and the maximum tensile stress is mainly concentrated on the bottom arch. The maximum vertical and horizontal displacements of surrounding rock are the smallest when constructed by full section method. Lining stress and surrounding rock deformation are most sensitive to elastic modulus, and the adhesion force and friction angle have great influence on plastic zone. [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]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Acceptable temperature is very important for mine refuge chamber (MRC) to ensure the safety of occupants. A novel temperature control scheme combining cold source storage with mine compressed air (MCA) was proposed for MRCs. An experiment was conducted to explore the characteristics of temperature controlling in a MRC via the MCA. Effects of several main factors such as initial surrounding rock temperature (ISRT), ventilation temperature (VT), ventilation rate (VR) and heat rate (HR) on the performance of temperature controlling in the MRC were numerically studied. Results show that: (1) In the MRC, the heat transfer process between the air and walls will reach a dynamic equilibrium within 0.5 h; (2) The ambient temperature in the MRC increases linearly with the square root of time from 1 h to 96 h, the gradient increases with VT and HR but decreases with ISRT and VR; (3) Ventilation with rate of 0.3 m3/min per capita and temperature of 20 °C can meet the temperature control requirements of a MRC located in the sandstone layer with the ISRT of 32.2 °C. An empirical formula for predicting ambient temperature and a ventilation parameter calculation method for meeting the temperature control goal of the MRC are obtained. [ABSTRACT FROM AUTHOR]

Reinforcement technology for semi coal-rock roadways with large deformations is one of the most challenging areas in underground engineering support. Based on the serious deformation problem that occurred in a semi coal-rock roadway in China's Meihuajing coal mine, this paper analyzes the characteristics of discontinuity in surrounding rock structure and incompatibility in surrounding rock deformation via means of geological investigation, mechanical experiments and numerical simulation. Then, a new kind of combined supporting system with filled-wall, shotcrete, grouting cable, prestressed anchor cable and U-shaped steel support for semi coal-rock roadway reinforcement is proposed. The width of the filled-wall is determined by parameterized numerical simulation method. Field application and deformation observation shows that the proposed combined supporting system is effective to control the large deformation of semi coal-rock roadways, which can provide certain references significance for similar engineering. [ABSTRACT FROM AUTHOR]

The problem of shaft instability has always been a major difficulty in deep mining practices. The shaft fracture has a high probability of being located near the aquifers and the soft–hard rock contact zone. This paper describes the deformation and stress characteristics of surrounding rock and the shaft lining under the interactive geological conditions under soft and hard rock strata in Anju coal mine, Shandong Province, China. Using the Method of Geological Strength Index (GSI) and considering the rock-softening characteristics of water, the parameters of rock mass are calibrated. By means of the 3DEC-trigon method, the variation characteristics of surrounding rock and the shaft lining are simulated. After shaft excavation, under the condition of no support, shear failure and tensile failure occur in shallow surrounding rock shafts, and a pressure relief zone is formed. Shear failure is the main destruction mode in deep surrounding rock. Because of the different strengths of the surrounding rock, the deformation of the surrounding rock is significantly different. After the surrounding rock is softened by water absorption, the difference is magnified. The maximum shear stress and plastic zone appear near the interface between soft and hard rock. Under the condition of shaft lining support, uneven deformation of surrounding rock surely leads to nonlinear variation of pressure on the shaft lining. Under the action of an inhomogeneous pressure field, partial shear failure occurs in the shaft lining, and the shear failure area increases after the surrounding rock is softened by water. Because of the nonlinear deformation of the shaft lining, it is easy to produce stress concentration and bending moment near the interface between hard and soft strata. The control methods of advance grouting and pressure relief excavation are proposed to improve the stability of the shaft, and a good effect is gained. [ABSTRACT FROM AUTHOR]