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By integrating an established rock damage model into the LS-DYNA computer code and using a widely used method for equivalently simulating multiple blastholes detonation, the damage processes of surrounding rock with different properties under the bench blasting of a large cross-section tunnel are comparatively studied. The damage distribution across the excavation cross-section is characterized by greater damage at the upper and lower ends, with lesser damage in the middle (junction between adjacent benches). For grade III surrounding rock excavated with two-bench blasting, the maximum damage depth of 3.6 m occurs in the middle floor. For grades IV and V surrounding rock excavated with three-bench blasting, the maximum damage depths both occur at the vault, with 3.6 m and 2.5 m, respectively. In bench blasting, the blasting of breaking holes closest to the excavation boundary significantly impacts surrounding rock, whereas the damage caused by smooth holes blasting is minor. The surrounding rock with poorer mechanical properties tends to exhibit greater damage under the same blasting operations. According to the proposed method, the critical Peak Particle Velocity (PPV) for cumulative damage in grades III, IV, and V surrounding rock of the Longnan tunnel is 16.8 cm/s, 13.7 cm/s, and 11.5 cm/s, respectively. [ABSTRACT FROM AUTHOR]

A reasonable support parameter design scheme is the key to ensuring the stability of the roadway. This study established 217 models using FLAC3D to analyze the evolution characteristics of elastic strain energy and plastic dissipation energy of surrounding rock under different shotcrete and rockbolt support structures. Additionally, five single models (BP, DT, ELM, RF, SVM) were introduced to explore the application of machine learning in predicting the stability of the roadway. The study found that in the parameters of the shotcrete layer support structure, the energy evolution of the surrounding rock is more sensitive to isotropic and thickness; in the parameters of the anchor rod support structure, the energy evolution of the surrounding rock is more sensitive to Young's modulus, cross-sectional area young, and grout stiffness. Additionally, the parameters of the shotcrete layer support structure are not necessarily the larger the better. When isotropic is 100 GPa, both the dissipated energy and the elastic strain energy are higher than that at 25 GPa. The results of the single model test indicate that machine learning is relatively accurate in predicting different shotcrete and anchor support structures. The runtime difference between traditional methods and machine learning models highlights the potential advantages of machine learning. [ABSTRACT FROM AUTHOR]

By integrating an established rock damage model into the LS-DYNA computer code and using a widely used method for equivalently simulating multiple blastholes detonation, the damage processes of surrounding rock with different properties under the bench blasting of a large cross-section tunnel are comparatively studied. The damage distribution across the excavation cross-section is characterized by greater damage at the upper and lower ends, with lesser damage in the middle (junction between adjacent benches). For grade III surrounding rock excavated with two-bench blasting, the maximum damage depth of 3.6 m occurs in the middle floor. For grades IV and V surrounding rock excavated with three-bench blasting, the maximum damage depths both occur at the vault, with 3.6 m and 2.5 m, respectively. In bench blasting, the blasting of breaking holes closest to the excavation boundary significantly impacts surrounding rock, whereas the damage caused by smooth holes blasting is minor. The surrounding rock with poorer mechanical properties tends to exhibit greater damage under the same blasting operations. According to the proposed method, the critical Peak Particle Velocity (PPV) for cumulative damage in grades III, IV, and V surrounding rock of the Longnan tunnel is 16.8 cm/s, 13.7 cm/s, and 11.5 cm/s, respectively.

Purpose – The wavelet neural network (WNN) has the drawbacks of slow convergence speed and easy falling into local optima in data prediction. Although the artificial bee colony (ABC) algorithm has strong global optimization ability and fast convergence speed, it also has the drawbacks of slow speed while finding the optimal solution and weak optimization ability in the later stage. Design/methodology/approach – This article uses an ABC algorithm to optimize the WNN and establishes an ABC-WNN analysis model. Based on the example of the Jinan Yuhan underground tunnel project, the deformation of the surrounding rock of the double-arch tunnel crossing the fault fracture zone is predicted and analyzed, and the analysis results are compared with the actual detection amount. Findings – The comparison results show that the predicted values of the ABC-WNN model have a high degree of fitting with the actual engineering data, with a maximum relative error of only 4.73%. On this basis, the results show that the statistical features of ABC-WNN are the lowest, with the errors at 0.566 and 0.573, compared with the single back propagation (BP) neural network model and WNN model. Therefore, it can be derived that the ABC-WNN model has higher prediction accuracy, better computational stability and faster convergence speed for deformation. Originality/value – This article uses firstly the ABC-WNN for the deformation analysis of double-arch tunnels. This attempt laid the foundation for artificial intelligence prediction in deformation analysis of multi-arch tunnels and small clearance tunnels. It can provide a new and effective way for deformation prediction in similar projects.

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]

The complex geological conditions in tunnels pose a huge challenge to the reliability of tunnel boring machine (TBM). However, existing reliability studies typically focus on core structures such as cutters and cutterheads, with less consideration given to the rest of the components that frequently fail. In this study, the reliability analysis and dynamic evaluation of TBM components with high failure rates are carried out relying on the Shanxi Central Yellow River Diversion Project. The life distribution and reliability variation characteristics of TBM components under different rock mass classes are investigated in terms of tunnelling time and tunnelling distance as two types of life data indexes. And the life index which is more suitable for the reliability evaluation of TBM components is identified by comparison. On this basis, a dynamic evaluation method for the reliability of TBM components under the condition of multi‐classes surrounding rock is proposed. This method can quickly evaluate the current reliability of TBM components and serve as the basis for preventive maintenance. The results of this study play a certain role in supplementing the reliability research of TBM and also provide a scientific basis for optimizing the design and maintenance strategy of TBM components. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southeast University / Dongnan Daxue Xuebao is the property of Journal of Southeast University 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.)

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]

Copyright of Railway Construction Technology is the property of Railway Construction Technology 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.)

This paper refines an optimized array lateral logging tool designed for small boreholes, leveraging existing technologies. The tool features four investigation depth curves, and resistivity response curves are derived through finite element model simulations considering variables such as borehole size, mud characteristics, invasion zone features, resistive annuli, formation rock properties, and formation resistivity anisotropy. The findings included the following: (1) Increasing the wellbore diameter uniformly decreased resistivity across all four investigation depths, positively correlating with borehole size. When mud resistivity (Rm) exceeded formation resistivity (Rt), resistivity curves became distorted. (2) For high- and low-invasion models, the ratio of the deepest to the shallowest investigation depth curves ranged from 1 to 8 and 0.6 to 0.9, respectively, with maximum separation at an invasion depth of 0.5–0.8 m. (3) Under invasion conditions with annuli, an invasion zone depth and annulus width around 0.4 m yield well separated the resistivity curves for all depths. Low- and high-resistivity annuli of 2 m and 0.7 m, respectively, can cause curve intersections. (4) When the formation thickness exceeded 0.2 m, the tool accurately reflected formation resistivity variations and demonstrated effective layer identification in multi-layer conditions. (5) In anisotropic formations, resistivity was negatively correlated with the anisotropy coefficient (λ) as it changed from 2 to 4. The instrument can be fully utilized in the exploration of thin interlayers in oil and gas, significantly enhancing the accuracy of resource identification and extraction technologies. [ABSTRACT FROM AUTHOR]

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]

Copyright of China Mining Magazine is the property of China Mining Magazine Co., Ltd. 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.)

Abstract 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.

A reasonable support parameter design scheme is the key to ensuring the stability of the roadway. This study established 217 models using FLAC3D to analyze the evolution characteristics of elastic strain energy and plastic dissipation energy of surrounding rock under different shotcrete and rockbolt support structures. Additionally, five single models (BP, DT, ELM, RF, SVM) were introduced to explore the application of machine learning in predicting the stability of the roadway. The study found that in the parameters of the shotcrete layer support structure, the energy evolution of the surrounding rock is more sensitive to isotropic and thickness; in the parameters of the anchor rod support structure, the energy evolution of the surrounding rock is more sensitive to Young’s modulus, cross-sectional area young, and grout stiffness. Additionally, the parameters of the shotcrete layer support structure are not necessarily the larger the better. When isotropic is 100 GPa, both the dissipated energy and the elastic strain energy are higher than that at 25 GPa. The results of the single model test indicate that machine learning is relatively accurate in predicting different shotcrete and anchor support structures. The runtime difference between traditional methods and machine learning models highlights the potential advantages of machine learning.

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 order to solve the problem of the poor adaptability of the TBM digging process to changes in geological conditions, a new TBM digging model is proposed. An ensemble learning prediction model based on XGBoost, combined with Optuna for hyperparameter optimization, enables the real-time identification of surrounding rock grades. Firstly, an original dataset was established based on the TBM tunneling parameters under different surrounding rock grades based on the KS tunnel. Subsequently, the RF–RFECV was employed for feature selection and six features were selected as the optimal feature subset according to the importance measure of random forest features and used to construct the XGBoost identification model. Furthermore, the Optuna framework was utilized to optimize the hyperparameters of XGBoost and validated by applying the established TBM dataset of the KS Tunnel. In order to verify the applicability and efficiency of the proposed model in surrounding rock grade identification, the prediction results of five commonly used machine learning models, Optuna–XGBoost, Random Forest (RF), Gradient Boosting Decision Tree (GBDT), Decision Tree (DT), XGBoost, and PSO–XGBoost, were compared and analyzed. The main conclusions are as follows: the feature selection method based on RF–RFECV improved the accuracy by 8.26%. Among the optimal feature subset, T was the most essential feature for the model's input, while PR was the least important. The Optuna–XGBoost model proposed in this paper had higher accuracy (0.9833), precision (0.9803), recall (0.9813), and F1 score (0.9807) than other models and could be used as an effective means for the lithological identification of surrounding rock grade. [ABSTRACT FROM AUTHOR]

• The large-strain approach with logarithmic plastic strain and elastic strain in plastic region is derived. • The failure of surrounding rock for circular opening as an unstable state driven by energy. • The energy support design of surrounding rock is obtained considering the effect of three-dimensional mechanical properties. This study analyzes the stability of surrounding rock for a circular opening based on the energy and cavity expansion theory, and regards the surrounding rock failure of circular opening as an unstable state driven by energy. Firstly, based on the large-strain cylindrical cavity contraction and energy dissipation method, the deformation caused by the excavation of surrounding rock is regarded as the cylindrical cavity contraction process. By introducing the energy dissipation mechanism, the energy dissipation solution of cylindrical cavity contraction is obtained. The energy dissipation process of surrounding rock is characterized by the strain energy changes in the elastic and elasto-plastic regions of this cavity contraction analysis. Secondly, the deformation control effect of support and surrounding rock parameters on the energy dissipation of surrounding rock is studied based on the energy dissipation solution of surrounding rock under support conditions. Finally, the effectiveness and reliability of the analytical approach was demonstrated by comparing the support design results with those in the literature. The research results indicate that the three-dimensional mechanical properties and dilatancy angle of rock and soil mass have a significant impact on the energy support design of surrounding rock. This study provides a general analysis method for the stability analysis of surrounding rock of deep buried tunnels and roadway. [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]

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.

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.

The damage and failure analysis of deep rock mass subjected to blasting under different crustal stress conditions is still insufficient at present. To explore the damage and failure law of surrounding rocks of deep tunnel during blasting excavation, based on the finite element software ANSYS/LS-DYNA, the Riedel-Hiermaier-Thoma constitutive model is adopted to carry out numerical analysis on the influencing factors of tunnel blasting effect and surrounding rock disturbance range under different crustal stress environments. The results show that the cross-section damage degree of the bidirectional isobaric tunnel is negatively correlated with the geostress level. With the increasing geostress, the damage of the tunnel floor is more significantly suppressed by geostress. The surrounding rocks at the waist of the tunnel is prominently disturbed by blasting, and its stress and vibration velocity increase significantly with the increasing lateral pressure coefficient, and the vibration velocity increases by more than 40%, much higher than that of the top surrounding rocks. Under the vertical stress of 20 MPa, the amplitudes of stress and vibration velocity at the waist measuring point increase slowly with the increasing lateral pressure coefficient. When the vertical stress rises to 60 MPa, the lateral pressure coefficient has a great influence on the disturbance of surrounding rocks. The relevant conclusions obtained are of important guiding significance for actual engineering construction, and are of certain reference value for monitoring the stability of tunnel surrounding rocks and optimizing support parameters.

The heat damage in a coal face of a high-temperature mine is a significant mine disaster owing to various heat sources. Understanding the influence of various heat sources on the air temperature distribution in the coal face can help us to determine reasonable working conditions. Therefore, it is necessary to take into account the coupling relationship of multiple heat sources and obtain accurate prediction results. In this paper, the finite volume calculation method is used to establish a numerical model of heat dissipation of surrounding rock considering the difference in thermal and physical properties of coal and rock in the coal face. And then, a high-temperature coal mine in the northeast of China is taken as an example to explore the airflow temperature distribution law of the coal face under the influence of the absolute heat source and the relative heat source via the finite difference method. Furthermore, an orthogonal test was performed to investigate the influence degree of major factors on heat exchange of the coal face through range analysis. This work supplements the existing numerical model and research, and provides a theoretical basis and more accurate practical methods for predicting the thermal environment of coal face, especially in high mining depth mines. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for analysing the state of an inclinometer tube used for in-situ monitoring of the relative slide between backfill and surrounding rock mass, based on the principles of elastic beam and elastic foundation beam theory. Through the utilisation of this approach, it becomes feasible to evaluate the appropriate depth for installation, the extent of measurement, and the operational state of the inclinometer tube. The mechanical response of the inclinometer tube was analysed using the new method and finite element method, with Longshou Mine serving as the background. The feasibility of the new method was subsequently confirmed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe 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.)

Abstract 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.

This paper refines an optimized array lateral logging tool designed for small boreholes, leveraging existing technologies. The tool features four investigation depth curves, and resistivity response curves are derived through finite element model simulations considering variables such as borehole size, mud characteristics, invasion zone features, resistive annuli, formation rock properties, and formation resistivity anisotropy. The findings included the following: (1) Increasing the wellbore diameter uniformly decreased resistivity across all four investigation depths, positively correlating with borehole size. When mud resistivity (Rm) exceeded formation resistivity (Rt), resistivity curves became distorted. (2) For high- and low-invasion models, the ratio of the deepest to the shallowest investigation depth curves ranged from 1 to 8 and 0.6 to 0.9, respectively, with maximum separation at an invasion depth of 0.5–0.8 m. (3) Under invasion conditions with annuli, an invasion zone depth and annulus width around 0.4 m yield well separated the resistivity curves for all depths. Low- and high-resistivity annuli of 2 m and 0.7 m, respectively, can cause curve intersections. (4) When the formation thickness exceeded 0.2 m, the tool accurately reflected formation resistivity variations and demonstrated effective layer identification in multi-layer conditions. (5) In anisotropic formations, resistivity was negatively correlated with the anisotropy coefficient (λ) as it changed from 2 to 4. The instrument can be fully utilized in the exploration of thin interlayers in oil and gas, significantly enhancing the accuracy of resource identification and extraction technologies.

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]

In underground coal mines, the stability of the retracement channel in the surrounding rock is crucial for the safe and efficient retracement of the equipment and to guarantee the continuity of the retracement work. To reveal the deformation and damage mechanism of the surrounding rock of an auxiliary retracement channel (ARC) and the determination method for the reasonable spacing of two retracement channels during the end of the mining period, the deviatoric stress field in front of the working face and the change in the shape characteristics of the plastic zone in the ARC are investigated in this paper. The formation of ultimate stress equilibrium, high deviatoric stress, decreasing deviatoric stress, and low deviatoric stress environments in front of the working face during the end of mining occur successively, and the different deviatoric stress environments are the main reasons for the different shape characteristics of the plastic zone in the surrounding rock. The changes in the shape characteristics of the plastic zone correspond to the changes in the shape characteristics in the zone with deviatoric stress and exhibit the following order: full plastic deformation zone, butterfly-shaped zone, elliptical zone, and circular plastic zone. A reasonable spacing determination method for the two retracement channels is proposed: the ARC is arranged in the decreasing deviatoric stress environment, where the surrounding rock plastic zone shape is elliptical, and the ARC is relatively stable. Based on this research result, the spacing of the double retracement channels at the Lijiahao 22-116 working face was determined to be 25 m, which achieved a positive application effect and allowed the safe and efficient retracement of the working face equipment. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology 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.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology 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.)

Purpose – The purpose of the study is to quickly identify significant heterogeneity of surrounding rock of tunnel face that generally occurs during the construction of large-section rock tunnels of high-speed railways. Design/methodology/approach – Relying on the support vector machine (SVM)-based classification model, the nominal classification of blastholes and nominal zoning and classification terms were used to demonstrate the heterogeneity identification method for the surrounding rock of tunnel face, and the identification calculation was carried out for the five test tunnels. Then, the suggestions for local optimization of the support structures of large-section rock tunnels were put forward. Findings – The results show that compared with the two classification models based on neural networks, the SVM-based classification model has a higher classification accuracy when the sample size is small, and the average accuracy can reach 87.9%. After the samples are replaced, the SVM-based classification model can still reach the same accuracy, whose generalization ability is stronger. Originality/value – By applying the identification method described in this paper, the significant heterogeneity characteristics of the surrounding rock in the process of two times of blasting were identified, and the identification results are basically consistent with the actual situation of the tunnel face at the end of blasting, and can provide a basis for local optimization of support parameters.

UGS (underground gas storage) is of great significance for ensuring emergent supply and CCUS (Carbon Capture, Utilization, and Storage). However, very different from gas reservoir development, some stress changes in reservoir, caprock, and bottom support rock may affect its operation. Sichuan Basin is rich in natural-gas resources and geological targets for the UGS rebuilt from fractured carbonate reservoirs. Moreover, gas storage is featured by rapid injection and production, and the change of in-situ stress affects intensively the permeability of reservoir fracture. However, most existing models on the fracture permeability assume that the surrounding-rock stress is constant. So, a new model has been established for the fracture permeability based on the Eshelby theory, considering the effect of both direct caprock and bottom support rock (also called surrounding rock) and the stress redistribution mechanism of the entire geological body during UGS injection and production. Results show that for the fracture, the permeability is related to not only its compressibility and orientation, but also reservoir shape and elastic property of the entire geological body including reservoir and surrounding rock. In most disk-shaped or elliptical reservoirs, vertical fracture is less susceptible to pore pressure than horizontal one. The surrounding-rock elastic property is also an important factor in the fracture-permeability model. Hard surrounding rock can reduce the stress sensitivity in fracture. When the elastic modulus ratio (elastic modulus of reservoir vs. that of surrounding rock) is 0.1, the fracture permeability decreases by only 15%. This model is also applicable to multiple fractures. Using the superposition principle, it is found that the main direction of permeability and the degree of permeability anisotropy may change when there are multiple fractures in the reservoir in spite of the same fracture compressibility.

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]

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]

The second invariant of deviatoric stress of the coal and rock mass is closely related to the distortion energy driving the deformation and failure of the surrounding rock. Based on the second invariant of deviatoric stress, this study built a global model of gob-side entry with different widths of the coal pillar through numerical analysis, and compared and analyzed the evolution law of the surrounding rock distortion energy, plastic location state, and roadway deformation with the width of the coal pillar. This study concluded that the peak distortion energy in the virgin coal rib and the roof and floor of the gob-side entry gradually increases with the reduction in the coal pillar width. When the coal pillar width is 5 m, the second invariant peak value of deviatoric stress in the virgin coal rib reaches the maximum of 294.8 MPa2. When the width of the coal pillar is reduced from 30 m to 5 m, the second invariant of the deviatoric stress in the side of the coal pillar and the roof and floor of the side presents the law of first increasing and then decreasing. The greater the damage degree of the coal pillar, the smaller the distortion energy it contains. The distortion energy is the key factor in driving the deformation and failure of the surrounding rock. The greater the distortion energy, the greater the deformation degree of the surrounding rock, the more vulnerable it is to external mining stress disturbance, and the greater the difficulty in controlling the stability of the roadway-surrounding rock. [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.)

Goaf-side entry with small coal pillars (GESCPs) has an intrinsic advantage of improving the coal recovery ratio by implementing drifts with a small pillar size next to previous goafs. This technology is increasingly gaining popularity in the longwall mining of underground coal mines in China. This study focuses on understanding the critical condition of the main roof failure above the solid coal side of the goaf-side entry and investigating the key parameters that affect the structural stability of the surrounding rocks for GESCP. Mechanical models of the main roof and multi-layer cracking structures of the side wall of GESCP were established and the limiting equilibrium equation for the structural stability of the surrounding rock was proposed. The characteristics affecting the main parameters of the structural stability of the surrounding rock were analyzed. The research findings suggest that the integrity of the coal side walls plays a major role in maintaining the structural stability of the surrounding rock for GESCP under the given cross-sectional dimensions. Other factors, including the uniform load of overburden, the width of the coal pillar, the length of the roof hanging along the goaf side, and the fracture length in the main roof of the entry side wall, are less important. The key to achieving structural stability of the surrounding rocks for GESCP is to enhance the strength of the supporting coal side walls and, especially, to ensure the integrity of the small coal pillars. These conclusions were verified by engineering practice at the 1252(1) haulage gateway in a Coal Mine in China. [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]

Copyright of Railway Construction Technology is the property of Railway Construction Technology 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.)

Copyright of Water Conservancy Science & Techonlogy & Economy is the property of Water Conservancy Science & Technology & Economy 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.)

In order to solve the problem of the poor adaptability of the TBM digging process to changes in geological conditions, a new TBM digging model is proposed. An ensemble learning prediction model based on XGBoost, combined with Optuna for hyperparameter optimization, enables the real-time identification of surrounding rock grades. Firstly, an original dataset was established based on the TBM tunneling parameters under different surrounding rock grades based on the KS tunnel. Subsequently, the RF–RFECV was employed for feature selection and six features were selected as the optimal feature subset according to the importance measure of random forest features and used to construct the XGBoost identification model. Furthermore, the Optuna framework was utilized to optimize the hyperparameters of XGBoost and validated by applying the established TBM dataset of the KS Tunnel. In order to verify the applicability and efficiency of the proposed model in surrounding rock grade identification, the prediction results of five commonly used machine learning models, Optuna–XGBoost, Random Forest (RF), Gradient Boosting Decision Tree (GBDT), Decision Tree (DT), XGBoost, and PSO–XGBoost, were compared and analyzed. The main conclusions are as follows: the feature selection method based on RF–RFECV improved the accuracy by 8.26%. Among the optimal feature subset, T was the most essential feature for the model’s input, while PR was the least important. The Optuna–XGBoost model proposed in this paper had higher accuracy (0.9833), precision (0.9803), recall (0.9813), and F1 score (0.9807) than other models and could be used as an effective means for the lithological identification of surrounding rock grade.

The destruction of the surrounding rock of underground projects is one of the pronounced problems which undermine the safety of the project and personnel. The evaluation of the stability of surrounding rocks of underground projects and its model of deformation and damage are the main issues to be addressed in underground exploration, which is also the main research target of underground projects. In recent years, it had achieved significant progress in underground project exploration and ways of evaluation of the stability of surrounding rocks. In the meantime, observation at the site and multiple in-situ geotechnical engineering experiments had disclosed respective physical and mechanical properties of many surrounding rocks, put in place the numerical evaluation models of the stability of surrounding rocks in different conditions and analyzed the deformation models of the rocks in a scientific manner. For the deep-buried long-water diversion tunnel, the high precision comprehensive geophysical prospecting method, rock and lithology characteristics, the combination of rock units had been systematically studied. In the underground engineering of ultra-deep mine, we had summarized the existing supporting system of mine roadway, provided the quantitative calculation and evaluation model and other software based on UDEC, FLAC3D through the field observation and evaluation of roadway deformation and support failure, which played key roles in the prevention and control of surrounding rock deformation and failure in underground projects. The future research will focus on the mechanical properties and deformation laws of 3D geological structure of surrounding rocks in underground projects. [ABSTRACT FROM AUTHOR]