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Microwave assistance has the potential to reduce the energy input required for mechanical rock breaking. This study systematically investigated the changes in electrical properties (specifically resistivity, capacitance, and impedance) of gabbro after microwave heating during the graded loading process, as well as its internal fracture mechanism. The findings indicate that the variations in resistivity, impedance, and capacitance of gabbro can be divided into three stages during the graded loading process: the compaction stage, elastic-steady cracking stage, and nonlinear crack propagation stage. When the strain level exceeds 70%, the resistivity and impedance start to increase, and the capacitance begins to decrease. The study also identifies a significant positive correlation between microwave power and the rate of temperature increase on the rock surface. A critical power threshold of approximately 2 kW is observed, below which achieving rapid temperature rise becomes challenging, but beyond which the temperature escalates swiftly with the energy input. Once the temperature exceeds 350 °C, rupturing mineral inclusions generate numerous microcracks, causing resistivity and impedance to exponentially increase. Furthermore, microwave heating induces a temperature differential exceeding 200 °C between the internal and external regions of the rock. Under the same radiation energy, high-power short-duration radiation is more likely to generate thermally induced cracks within the rock. The rapid expansion and heating of absorbent minerals, as well as the rupture of inclusions, further intensify the propagation of microcracks, greatly reducing the mechanical properties of the rock. This study will provide theoretical guidance for microwave-assisted mechanical rock excavation. [ABSTRACT FROM AUTHOR]

In response to a series of engineering disasters encountered during the excavation and support construction of loess tunnels, considering the issues of water enrichment in surrounding rock induced by excavation disturbance and system bolt failure, drawing on the concepts of lime pile composite foundation and composite bearing arch, and based on the principle of the New Austrian Tunneling Method (NATM) that fully mobilizes and leverages the self-supporting capacity of surrounding rock, this study comprehensively considers the wetting and stress adjustment processes of the surrounding rock after excavation disturbance in loess tunnels. By adopting the technical principle of "water absorption and densification of shallow surrounding rock, suspension and anchoring of deep surrounding rock, and composite arch bearing", a new type of water-absorbing, densifying, and anchoring bolt was developed that can reduce the water content of surrounding rock while enhancing its resistance. To further investigate the water absorption, densification effect, and pull-out bearing characteristics of this new bolt, laboratory model tests were conducted, examining the temperature, pore water pressure, densification stress of the soil around the bolt, as well as the physical properties of the soil in the consolidation zone. The test results indicate that a cylindrical heat source forms around the water-absorbing, densifying, and anchoring bolt, significantly inducing the thermal consolidation of the surrounding soil. The variations in temperature, pore water pressure, and densification stress of the soil around the bolt truly reflect the qualitative patterns of hydro-thermal–mechanical changes during the water absorption, curing, and exothermic reaction processes. The water absorption and densification segment of the bolt effectively enhances the density of the soil in the water absorption, densification, and consolidation zone, improving soil strength parameters. Compared to traditional mortar-bonded bolts, the water-absorbing, densifying, and anchoring bolt exhibits a greater pull-out bearing capacity. The research findings provide important guidance for the theoretical design and engineering application of this new type of bolt. [ABSTRACT FROM AUTHOR]

Excavation in deep weak rock engineering can significantly alter the stress state in the surrounding rock, often leading to varying degrees of floor heave. The excavation stress paths from the immediate floor to the interior floor were determined by simulating tunnel excavation and monitoring stress changes at fixed points on the floor. The characteristic stresses, failure modes, acoustic emission and deformation features of three types of clastic rock under excavation stress paths were experimentally investigated to reveal the floor heave mechanism. The study found that as the distance from the excavation boundary increased, the bearing capacity of the clastic rock gradually enhanced, and the risk of macroscopic failure decreased, transitioning from tensile failure to tensile–shear mixed failure. Simultaneously, the excavation-induced dilational deformation rapidly decreased. A novel method was proposed to evaluate the dilational deformation of surrounding rock induced by excavation based on the strain features of the samples under the different stress paths. The results demonstrated a rapid decrease in dilational deformation from the immediate floor to the interior floor for the three types of surrounding rock, with the maximum total dilation and the greatest risk of floor heave observed in contact cementation surrounding rock. Finally, the floor heave mechanisms of three types of clastic rock were summarized as follows: unloading dilation combined with macroscopic failure; slight rebound of the immediate floor coupled with multiple microcracks; notable rebound of the immediate floor accompanied by few microcracks. This study provides new insights into the mechanics disasters and selection of support measures for deep-buried tunnels. Highlights: Experiments were conducted on three types of clastic rock under excavation stress paths from the immediate floor to the interior floor. The characteristic stress, failure mode, AE characteristics and deformation behavior induced by excavation of three types of clastic rock were studied. A method was proposed to evaluate the dilational deformation of surrounding rock induced by tunneling. The floor heave mechanisms of three types of clastic rock were revealed. [ABSTRACT FROM AUTHOR]

Blasting excavation of rock masses under high in-situ stress often encounters difficulties in rock fragmentation and a high boulder rate. To gain a deeper understanding of this issue, the stress distribution of rock masses under dynamic and static loads was first studied through theoretical analysis. Then, the ANSYS/LS-DYNA software was employed to simulate the blasting crack propagation in rock masses under various in-situ stress conditions. The fractal dimension was introduced to quantitatively analyze the influence of in-situ stress on the distribution of blasting cracks. The results indicate that in-situ stress primarily affects crack propagation in the later stages of the explosion, while crack initiation and propagation in the early stages are mainly driven by the explosion load. In-situ stress significantly influences the damage area and fractal dimension of cut blasting. Under hydrostatic in-situ stress, as the in-situ stress increases, the damage area and fractal dimension of blasting cracks gradually decrease. Under non-hydrostatic in-situ stress, when the principal stress difference is small, in-situ stress promotes the damage area and fractal dimension of the surrounding rock, enhancing rock fragmentation. However, when the principal stress difference is large, in-situ stress inhibits the damage area and fractal dimension of the surrounding rock, hindering effective rock breaking. [ABSTRACT FROM AUTHOR]

This research examines the relationship between excavations and tunnel responses, emphasizing the influence of geometric factors on tunnel heave. Utilizing an exponential correlation between heave and unloading ratio, the study investigates into stress changes with increasing excavation depth. Maintaining a constant axial horizontal distance proves crucial for stable tunnel responses. FLAC3D numerical modeling highlights increased stress-strength ratios near excavations, impacting the tunnel crown. Water ingress induces soil consolidation, leading to additional deformations, while adverse excavation conditions can cause leaks, dislocations, and cracks in the tunnel lining. The study also analyzes rock behavior under diverse loading and excavation conditions, revealing stress point relationships with the yield surface in principal stress space. [ABSTRACT FROM AUTHOR]

Aiming at the stability problem in the surrounding rock of the adjacent layered staggered vertical mining conditions during the downward layered filling mining, a stress model of the surrounding rock structure of the excavation was established, and the influence characteristics of the backfill roof on the stability of the surrounding rock under different mining conditions were analyzed, then the mechanical state of the backfill roof under the third-stage excavation was obtained. Using FLAC3D numerical simulation, the stress evolution characteristics of the surrounding rock under the "third-stage" tunneling mining in the lower layer were analyzed. The results show that during the backfilling process of the first and second stages of the lower layer, the horizontal stress on the side walls of the two ore bodies is distributed in a camel hump shape in the direction of advancement. In the first stage, the vertical displacement of the two sides of the roadway shows symmetrical positive and negative values. During the third stage of the excavation process, the unmined ore body carries increasing overlying loads, and the risk factor gradually increases. Due to the impact of mining, the stability of the lower layer edge access is poor, especially for the mining of edge accesses without backfill roofs. The rock mass stability is poor and the risk factor is high, so it is necessary to strengthen support during backfilling. [ABSTRACT FROM AUTHOR]

Hard rock tunnel boring machines (TBMs) are increasingly widely used in tunnel construction today; however, TBMs are deeply buried underground and have a low perception of the underground surrounding rock conditions and excavation parameters. In order to ensure the safety of TBM digging, this paper describes the research carried out relating to the accurate prediction of TBM digging parameters and the precise prediction of tunnel surrounding rock grades. Based on the on-site excavation parameters and geological data of a certain water diversion project in Xinjiang, the thrust, torque, rotational speed, net excavation speed, construction speed, and excavation specific energy of the stable section of TBM excavation are selected as the input parameters for the model. A convolutional neural network optimized–long short-term time series prediction model (CNN-LSTM model) is established to predict the excavation parameters under various levels of surrounding rock conditions. The research results indicate that the CNN-LSTM model has a high prediction accuracy, with most data having a relative prediction error rate (Er) within 10%, root mean square error (RMSE) within 5%, mean absolute percentage error (MAPE) within 10%, and goodness of fit (R2) above 0.9. The model can assist in parameter setting, engineering planning and disposal of high-risk holes in the TBM digging process, and improve the safety level of TBM digging. [ABSTRACT FROM AUTHOR]

Discontinuities largely influence the mechanical properties of rock joints. However, traditional discontinuity recognition methods often require manual intervention during processing. This paper proposes a new deep-learning-based method for discontinuity recognition using 3D point clouds. A neighborhood PCA-weighted oriented contraction method is proposed to extract point cloud skeletons as discontinuity intersection lines. Then an optimal color mapping (OCM) method is proposed to establish the optimal mapping relationship between 3D normal vectors and RGB, converting 3D point clouds to 2D OCM images for discontinuity segmentation. The convolutional neural network of Mask R-CNN is adopted to segment discontinuities from OCM images. Finally, 3D discontinuities can be generated from discontinuity-segmented OCM images. Forty-two rock slope image sequences and a rock slope point cloud are collected and labeled, generating 4632 OCM images including 430,613 discontinuity planes after data augmentation for training. Three cases of rock slopes and rock tunnel excavation faces are adopted for testing. The average recognition time per 3D point cloud model is approximately 12 s due to the high recognition efficiency of Mask R-CNN for 2D images. The results show the proposed method can recognize discontinuities close to manual judgements with high accuracy, good robustness to point cloud density variations, and good adaptability to different rock engineering scenarios. Highlights: An NPW-OC method is proposed to extract point cloud skeletons. An OCM method is proposed to assign 3D normal vectors with optimal RGB. OCM images are generated to assign discontinuities with different and uniform color. Deep-learning-based method is used for intelligent recognition of discontinuities. Conversion of discontinuity recognition from 3D point clouds to 2D OCM images. The results show good efficiency, accuracy, robustness, and adaptability. [ABSTRACT FROM AUTHOR]

The developing trend in tunnel engineering is toward the expansion of the tunnel's inner diameter, which is bound to affect the deformation of the tunnel surrounding rock. To address this problem, transient and slow unloading tests of small thick-walled cylindrical surrounding rock specimens made of natural sandstone with different inner diameters are performed. The influence of the tunnel excavation inner diameter on the deformation and failure characteristics of the surrounding rock under the two unloading rates is studied, and numerical simulations under the same conditions are performed using FLAC3D. The results show the following. (1) Under transient and slow unloading, the strain on the inside and outside of the surrounding rock specimen increases with increasing inner excavation diameter, and under the same conditions, the inner strain on the surrounding rock specimen is greater than the outer strain. (2) When the excavation diameter is small, the inner deformation of the surrounding rock specimen experiences partial rebound, and when the excavation diameter is large, the surrounding rock specimen is damaged. (3) The surrounding rock specimen shows obvious brittle characteristics when damaged. The specimens expand significantly along the radial direction, bulge and drop blocks in the direction of unloading, and are accompanied by circumferential cracks. (4) Comparison and analysis of the numerical simulation results with the test results indicate that the test values are 2–3 times larger than the numerical values but that the presented deformation laws are consistent. Highlights: Transient and slow unloading tests of thick-walled cylindrical surrounding rock specimens made of natural sandstone with different inner diameters were carried out using the self-developed roadway surrounding rock excavation unloading model test system. The deformation law of the tunnel surrounding rock with the increase of excavation diameter under different unloading rates was obtained. The characteristics of unloading failure of tunnel surrounding rock were monitored and observed. [ABSTRACT FROM AUTHOR]

Viscoelastic plastic solutions for tunnel excavation in strain-softening rock mass and tunnel-rock interaction are proposed based on the Mohr-Coulomb and the Generalized Zhang-Zhu (GZZ) strength criterion considering stress path. The solutions are verified by numerical simulations, results show that the theoretical solutions are close to the simulated data. The evolutions of rock stresses, strains, displacements and support pressure were investigated and the influences of residual strength parameter, support stiffness, support timing, initial support pressure and viscosity coefficient on the rock deformation and the support pressure are discussed by proposed solution. It is found that strain-softening results in large deformation and high support pressure, with stiffer support and a larger viscosity coefficient contributing to even greater support pressure. Ductile support is recommended at the first stage to release the energy and reduce the support pressure by allowing a relatively large deformation. The support pressure, especially the additional support pressure at the second stage will be much smaller if a higher initial support pressure is applied at the first stage. This can not only control the displacement rate of surrounding rock and improve the tunnel stability at the first stage by exerting sufficient support pressure immediately after tunnel excavation, but also greatly reduce the pressure acted on permanent support and improve the structure stability at the second stage. Therefore, to avoid the instability of support structure, ductile support, which could not only deform continuously but also provide sufficient high support pressure, is recommended at the first stage. [ABSTRACT FROM AUTHOR]

During tunnel excavation, stress redistribution is caused by disturbance of the surrounding rock; when the stress exceeds the strength of rock mass, the surrounding rock enters the postpeak deformation stage and then produces the strain-softening effect. This effect will lead to a decrease in rock mass strength, the expansion of the fracture zone, and a decrease in stability. To further study the influence of strain-softening effect on the loose circle of the surrounding rock, the strain-softening factor is introduced into the unified strength criterion. On this basis, the triaxial test with elastic–plastic theoretical analysis is combined, and the strain-softening model based on the unified strength criterion is proposed. Based on this strain-softening model, the stress state of the postpeak plastic zone of the surrounding rock after excavation is studied and analyzed, and the theoretical calculation formula of the loose circle radius considering the strain-softening effect is obtained. Through theoretical calculations and engineering examples, the influence of strain-softening effect and support reaction force on the radius of the surrounding rock loose circle is compared and analyzed. The results show that: (1) the strain-softening effect further deteriorates the mechanical properties of the surrounding rock in the plastic zone, the stability of the surrounding rock is reduced, and the radius of the loose circle is increased, but closer to the measured values; and (2) with the increase of supporting reaction force, the constraint ability of surrounding rock deformation increases and the radius of the loose circle gradually reduces. Therefore, by enhancing the residual strength of the surrounding rock, controlling the radius of the loose circle of the surrounding rock by improving the strength of the supporting structure, and performing primary support on time, the stability of the surrounding rock can be increased. Practical Applications: During tunnel excavation, the process disrupts the surrounding rock, causing stress redistribution. When the local stress surpasses the strength of the rock, it results in damage, forming a loose circle and triggering strain softening. At the same time, both contribute to the expansion of the loose circle, further compromising the stability of the surrounding rock. Analyzing the distribution pattern of loose circles in the tunnel-surrounding rock considering the strain-softening effect, enhancing the residual strength of the surrounding rock, and improving the strength of the supporting structure while implementing the initial support in time can effectively control the expansion of the loose circle and improve the stability of the surrounding rock. This research provides an important theoretical basis and engineering experience for tunnel engineering to ensure construction safety and reduce construction costs. [ABSTRACT FROM AUTHOR]

Microseismic (MS) source location is an integral component of MS technology and essential to understanding the rock failure mechanism and avoiding potential geological hazards in underground rock excavation. However, accurate location remains challenging owing to the complex geological conditions and unknown rock failure mechanisms. In this study, a novel location framework was developed to locate the MS source positions and their uncertainties based on probabilistic programming. Probabilistic programming was utilized to determine the coordinates of the MS source and its variation using the Markov Chain Monte Carlo (MCMC) method based on the waveform equation. A classical benchmark problem was utilized to verify and illustrate the developed framework. The developed framework can not only locate the position of the MS source but also determine its variation due to the uncertainty during the monitoring and excavation. The located MS source is in agreement with the actual positions. The results show that the developed framework is a scientific, accurate, reasonable, and promising tool for the location of MS sources. Then, the developed framework was applied to locate the position of the blasting in a practical mine. This further proved that the developed framework could locate the MS source, providing an excellent uncertainty analysis tool for underground rock excavation. [ABSTRACT FROM AUTHOR]

The excavation of rock, whether in mining, petroleum, or civil engineering projects, predominantly relies on traditional drilling techniques. Across these applications, drilling bit wear considered as a primary factor impacting the overall cost of rock excavation projects. This wear of drill bits is directly linked to the properties of the rock being drilled. In this study, an investigated relations between drilling bit wear and geomechanical properties have been investigated. To measure drill bit wear, a laboratory-scale drilling rig was employed, based on 30 selected rock units. A comprehensive laboratory testing plan was executed on these rock units, encompassing various rock characteristics such as uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), Cerchar abrasivity index (CAI), equivalent quartz content (EQC), grain size of minerals (GS), and Schmidt rebound number (SRN). Nonlinear regression techniques were employed to predict bit wear based on geomechanical rock properties. Performance evaluation criteria were used to validate the regression models. The results revealed an exponential increase in bit wear values with rising UCS, BTS, CAI, EQC, GS, and SRN. The statistical analysis indicated a strong correlation between rock characteristics and drill bit wear, with CAI emerging as the most influential parameter, having a correlation coefficient of R2 = 0.954. The regression models developed in this study are primarily intended for rock engineers engaged in rock drilling projects. [ABSTRACT FROM AUTHOR]

Excavation‐induced rock failure and deformation near an underground opening boundary is closely associated with the intermediate principal stress, strain softening and rock mass dilation. By combining theoretical analysis and numerical simulation to explore the mechanical evolution of the roadway surrounding rock during excavation. The elastic–plastic criterion solutions for surrounding rock stress, displacement, and the plastic zone of a circular roadway were deduced by including the intermediate principal stress, strain softening and rock mass dilation, based on the Drucker–Prager criterion and the nonassociated flow rule. Furthermore, ABAQUS finite element software was utilized for numerical simulations to scrutinize the influence of mechanical parameters on stress redistribution, surface displacement, and plastic range. The results of the numerical simulations verify the reliability of the theoretical analysis and affirm the high consistency of the results with the theoretical solution. The research findings indicate that the strength of surrounding rock is significantly influenced by the intermediate principal stress, and the deformation and failure of rock mass are primarily impacted by rock mass dilation, while strain softening mainly affects the thickness of the fractured zone. Moreover, the study reveals that enhancing the residual strength of the surrounding rock can improve its resistance to deformation and failure. Furthermore, the excavation of the roadway is observed to increase the original rock stress in the surrounding rock, but increasing the ground support strength effectively controls the deformation and failure of surrounding rock. Ultimately, the research outcomes offer valuable references for engineering calculations and ground support design of surrounding rock in deep roadways. [ABSTRACT FROM AUTHOR]

According to various human needs, such as mineral supply, transportation, and underground storage, tunnel excavation has become commonplace today. However, one of the undesirable phenomena encountered during tunnel excavating, particularly when employing drilling and blasting techniques, is the overbreak phenomenon (OBP). This phenomenon not only compromises the safety of the work environment but also leads to increased operating costs. Therefore, accurately predicting the occurrence of OBP in tunnel excavation is of utmost importance. Due to the numerous uncertainties and complexities associated with rock formations, traditional methods have limited accuracy in predicting OBP. Consequently, this research used the rock engineering system (RES) method to comprehensively understand the physical and mechanical characteristics of the rock mass at any given point. By employing the RES method, accurate modeling of the OBP can be achieved in a time- and cost-efficient manner without requiring extensive and complicated coding. To construct the model using the RES method, 217 data points from three case studies were utilized: the Tarzeh underground coal mine in Iran, the Azad tunnel on the Tehran-North road in Alborz, Iran, and an Indian mine. The parameters considered in this study that affect the OBP (%) included perimeter hole powder factor (PPF, kg/m3), spacing-to-burden ratio of contour holes (S/B, kg), tunnel section area (A, m2), specific drilling (SD, m/m3), and rock mass rating (RMR, %). To compare and evaluate the RES method, various regression methods were also employed. Statistical criteria revealed that the RES method (RMSE = 0.0046, MSE = 0.068, R2 = 0.945) demonstrated high accuracy compared to other regression methods. Consequently, it can be concluded that the RES is a highly valuable and essential tool for rock engineers. [ABSTRACT FROM AUTHOR]

Steep fill–bedrock interfaces usually appear in many filling soil infrastructures, such as airports, houses, and road embankments in mountainous areas, when the excavation of rock slopes is constrained. These interfaces are prone to be tensioned up to failure, which easily triggers landslides of fill slopes. The anchor system buried in the fill soil, named radial cable system, was proposed for effectively enhancing the stability of steep fill–bedrock interfaces. At the interface, the steel ropes of the anchor section cable were equally divided into three subcables with a radial distribution. The pullout performance, failure evolution, and branching effect of the radial cable coupled with anchor plates were studied by a pullout test (in a laboratory setup) and a numerical simulation. The results showed that (1) the ultimate pullout capacities (Pu) of the radial cables were 193.53%–312.94% (for the 7 mm diameter of the anchor plate) and 141.25%–247.50% (for the 10 mm diameter of the anchor plate) greater than those of the single cables; (2) the pullout performance of the radial cable was significantly improved with an increase in the diameter of the anchor plate, and the optimal radial inclined angle of subcables coupled with anchor plates was 15°; (3) the soil surrounding the radial cable showed a progressive failure pattern, and its failure area was basically a symmetric conical; and (4) the radial cable can better reinforce the steep fill–rock interface than the conventional cable, as verified by a hill-fill project. The results of this study provide some new and important guidelines for the design and application of the radial cable system. [ABSTRACT FROM AUTHOR]

The design of anchor bolt in tunnel engineering mostly depends on empirical method and analogy method. In order to study the mechanical effect of surrounding rock in prestressed anchor bolt support system, a mechanical coupling model of prestressed anchor bolt and surrounding rock is established. Considering the damage effect of surrounding rock excavation, the analytical expressions of stress distribution and radial displacement of surrounding rock after tunnel excavation are derived by elastic-plastic mechanics theory. The finite difference software FLAC3D is used to verify and analyze the influence of prestressed anchor parameters on the state of surrounding rock. The results show that the maximum tangential stress and the radius of plastic zone of surrounding rock in theoretical analysis and numerical simulation are 4.77 MPa, 15 m and 4.49 MPa, 15.86 m respectively. The stress distribution and displacement of tunnel surrounding rock calculated by theoretical analysis and numerical simulation are basically the same. The rationality of theoretical analytical solution is verified in IV and V grade surrounding rock strata. With the increase of pre-tightening force, the radial displacement of surrounding rock in plastic zone and the radius of plastic zone gradually decrease, while the elastic zone is basically unaffected. When the length of the free section of the bolt is located in the plastic zone, the radial displacement of the plastic zone and the radius of the plastic zone of the surrounding rock gradually decrease with the increase of the length of the bolt. In practical engineering, the pre-tightening force of bolt should be increased as much as possible. The increase of bolt length has limited control effect on the displacement of surrounding rock and the development of plastic zone. The length of free section of bolt should be controlled in plastic zone. [ABSTRACT FROM AUTHOR]

Blasting is a prevalent technique in deep rock excavation, with the state of rock fragmentation under high in-situ stress conditions being distinct from that under low in-situ stress conditions. A new material point method framework utilizing the generalized interpolated material point and convective particle domain interpolation functions was implemented to simulate the single-hole blasting process, analyze the stress distribution around the blasting hole, and elucidate the mechanism of how ground stress influences the expansion of blasting cracks through the interaction with the blasting load. In addition, the dynamic relaxation method realizes the stress's initialization. It was concluded that the in-situ stress can increase the compressive stress induced by blasting load, whereas it decreases the caused tensile stress. With the increase in the ground stress, the scale of the cracks decreases. Under the non-isobaric condition, the blast-induced cracks preferentially expand along the high stress with the increase in the stress difference between the horizontal direction and the vertical direction, and the blast-induced cracks are suppressed to the greatest extent in the direction of the minimum ground stress. [ABSTRACT FROM AUTHOR]

To enhance comprehension of the improved arch cover construction method for underground metro stations and provide guidance for future construction techniques and programs, the paper examines the indoor improved arch cover method of construction in the underground concealed excavation station of Tianhe Road Station of Guangzhou Metro Line 10, China. It includes a similar model test of the key technology and an analysis of the evolution law of the surrounding rock stress, the law of the ground settlement, and the law of the arch top deformation after the tunnel excavation. The study found that increased over-support can decrease arch settlement, with the maximum settlement occurring near the arch. Ground settlement typically occurs in the same areas as arch settlement, but arch settlement may occur earlier. The excavation of the arch cover has little impact on the overlying soil pressure, and the supporting structure is more effective in controlling soil deformation. The upper part of the arch cap experiences mainly extrusion stress, with the maximum stress occurring near the middle of the arch. The stresses in the arch's base decrease significantly during the excavation of the side drifts but show an increasing trend during the excavation of the lower rock mass. The presence of the central column significantly affects both the settlement of the arch and the ground, as it bears most of the compressive stress of the arch. This stress decreases initially and then increases. The amplitude of deformation is more pronounced when the dismantled central column is closer to the middle of the arch. [ABSTRACT FROM AUTHOR]

Engineering rockmass classifications are an integral part of design, support and excavation procedures of tunnels, mines, and other underground structures. These classifications are directly linked to ground reaction and support requirements. Various classification systems are in practice and are still evolving. As different classifications serve different purposes, it is imperative to establish inter-correlatability between them. The rating systems and engineering judgements influence the assignment of ratings owing to cognition. To understand the existing correlation between different classification systems, the existing correlations were evaluated with the help of data of 34 locations along a 618-m-long railway tunnel in the Garhwal Himalaya of India and new correlations were developed between different rock classifications. The analysis indicates that certain correlations, such as RMR-Q, RMR-RMi, RMi-Q, and RSR-Q, are comparable to the previously established relationships, while others, such as RSR-RMR, RCR-Qn, and GSI-RMR, show weak correlations. These deviations in published correlations may be due to individual parameters of estimation or measurement errors. Further, incompatible classification systems exhibited low correlations. Thus, the study highlights a need to revisit existing correlations, particularly for rockmass conditions that are extremely complex, and the predictability of existing correlations exhibit high variations. In addition to augmenting the existing database, new correlations for metamorphic rocks in the Himalayan region have been developed and presented that can serve as a guide for future rock engineering projects in such formations and aid in developing appropriate excavation and rock support methodologies. [ABSTRACT FROM AUTHOR]

To elucidate the deformation characteristics during excavation of high rock slopes with oblique intersecting faults and the subsequent time-dependent behaviour after slope treatment, the comprehensive case study on a high rock slope with faults in the southern Shaanxi was conducted. The on-site surveys, numerical simulations, and multi-point displacement monitoring methods were employed to analyze the failure mechanisms inherent to high rock slopes with oblique intersecting faults, the primary disaster-inducing factors associated with these slopes were summarized, and the deformation characteristics during excavation process were analyzed, and the effectiveness of remedial measures for mitigating issues in high rock slopes with oblique intersecting faults was discussed. The results show that the study area has steep terrain and is influenced by faults and excavation at the foot of the slope, exhibiting typical overhanging terrain features, and geological structure affects the degree of exposed rock breakage and joint development. Numerical simulation demonstrates the feasibility of using an "anchor cable reinforces the upper slope + brushing the middle slope + anchor cable and anti-slide pile reinforces the slope foot" plan for high rock slopes with oblique intersecting faults. Combined with on-site surveys and monitoring data, it is evident that the slope stabilization treatment has a significant effect. The soil erosion effect at the fault site is substantial, and heavy rainfall has initiated a collapse issue on the platform near back edge fault of high rock slope. However, by implementing drainage measures near the fault and the base of the slope, the slope disaster are effectively mitigated while overall deformation rates are effectively contained. The research results have important reference value for the treatment of high rock slopes with oblique intersecting faults and the analysis of their failure mechanisms [ABSTRACT FROM AUTHOR]

In the past, the number of CPU cores/threads was usually less than 8/16; now, the maximum number is 128/256. As a CPU-based parallel method, OpenMP has an increasing advantage with the increase in CPU cores and threads. A parallel combined finite-discrete element method (FDEM) for modeling underground excavation and rock reinforcement using OpenMP is implemented. Its computational performance is validated in the two advanced CPUs: AMD Ryzen Threadripper PRO 5995WX (64/128 cores/threads); and 2 × AMD EPYC 7T83 (128/256 cores/threads). Then, its ability in simulating tunnel excavation under rockbolt-shotcrete-grouting support is implemented using the novel solid bolt model, which can explicitly capture the interaction between bolt, grout, and rock. The parallel performance validation of the uniaxial compression test shows: (i) for the speedup ratio, the OpenMP-based parallel FDEM obtains maximum speedup ratios of 30 (33 k elements) and 41 (3304 k elements) on the Threadripper, and 31 and 43 on the 2 × EPYC, respectively; (ii) for the scalability of speedup ratio, when the number of threads used is less than 128, the speedup ratio is always increasing with the increase of the number of threads; (iii) for the stability of speedup ratio, it has a stable speedup ratio, regardless of whether the rock is pre- or post-fractured. Highlights: A parallel FDEM for modeling underground excavation and rock reinforcement using OpenMP is implemented. Its computational efficiency is validated in the two advanced CPUs: AMD Ryzen Threadripper PRO 5995WX; and 2 × AMD EPYC 7T83 (128/256 cores/threads). Its ability in simulating rockbolt-shotcrete-grouting support is implemented using the novel solid bolt model. It obtains maximum speedup ratios of 30 (33 k elements) and 41 (3304 k elements) on the Threadripper, and 31 and 43 on the 2 × EPYC. It has good scalability and stability of speedup ratio, regardless of whether the rock is pre- or post-fractured. [ABSTRACT FROM AUTHOR]

To improve the extraction of coal resources, gob‐side entry driving is gradually being promoted and applied. However, as the thickness of the coal seam increases, the deformation control of the roadway becomes more difficult. Aiming at this problem, a combination of theoretical calculation, numerical simulation, and field test was used to analyze the aspects of the stress environment, surrounding rock properties, and support forms. The phenomenon and mechanization of intensified deformation and failure of roadway with increasing coal seam thickness were revealed. The specific results include: (1) The ratio of principal stress at the excavation position controls the maximum failure depth of roadway, and the direction of principal stress determines the location of the maximum failure depth; (2) As the thickness of the coal seam increases, the properties of the surrounding rock at the excavation position decrease, the principal stress ratio increases, and the deflection angle of the principal stress increases, which lead to an intensification of the deformation and failure of the roadway. Based on the deformation and failure characteristics of the roadway and the shortcomings of the original support form, a control strategy and support scheme based on a new support structure called "Anchor Cable with C‐shaped Tube" is proposed, which has achieved better deformation control effect in on‐site application. [ABSTRACT FROM AUTHOR]

For underground deep mines, mining activities often cause mining disasters such as rock burst, roof fall and water inrush. Especially for underwater mines in the fault zone, surrounding rock instability and water inrush are the main threats to mining safely and efficiently. This paper briefly reviews the research progress and development trend of deformation law and failure mechanism of jointed rock mass specimens, multi-field coupling numerical simulation method of rock mass with faults, prevention of water inrush. Geological tectonic movement and rock mass excavation destroy the integrity and continuity of rock, break the in-situ stress field of rock mass, and lead to weak structural planes such as joints, cracks, and faults. The stress and strain properties of rock mass reflects the mechanical effects of rock mass and joints comprehensively. The physical, chemical, and stress environments of rock masses in deep mines are more complex. The mechanism of rock failure and water inrush disaster under the coupling effect of THMC multiple fields is worth further research. By combining CT scanning technology, digital core construction, and 3D printing technology, a digital core model and repeatable rock specimens can be constructed to study the mechanical properties and permeability evolution mechanism of jointed rock masses. According to the development of 5G technology and artificial intelligence technology, 5G technology is integrated into the monitoring, early warning, and emergency disposal of water inrush disaster. [ABSTRACT FROM AUTHOR]

Numerical calculations are a standard part of modern structural design. Engineers remain particularly interested in real problems where analytical and numerical solutions can be compared with experimental results. Such cases are typical examples of benchmarks because they are used to verify the assumptions introduced. This study shows in detail how shear stresses affect the deflection of a relatively short and high cantilever when the span-to-height ratio of the cross-section is less than five. Such models are frequently used in the design of cantilevers that support heavily loaded beams, for example in the cement industry (e.g., often as structural elements for a heat exchanger system) or for the assessment of short cantilever limit states that appear during excavation in rock sediments. The models are also suitable for designing the various details and joints in the industry of prefabricated elements. This work analyzes in depth the analytical solutions for the displacement field of the linear elastic plane stress theory with two displacement boundary conditions. Also, the solutions were compared with the beam, two-, and three-dimensional numerical models using SAP2000. The results highlight the fundamental principles and solutions behind plane stress and beam theories, with an insight into the advantages and limitations of such models. [ABSTRACT FROM AUTHOR]

The primary factor restricting the construction of deeply buried underground projects is the imprecise identification of the surrounding rock damage zone. This study examines the Shuangjiangkou underground powerhouse to investigate damage zoning in the surrounding rock mass. The temporal and spatial characteristics of deep rock mass deformation evolution are studied by multipoint extensometers, microseismic (MS) monitoring, acoustic wave testing and borehole TV. Subsequently, a quantitative analysis delineating damage zones is executed by evaluating alterations in displacement, wave velocity volatility, and the distribution of MS events within the surrounding rock mass. The excavation zone of the surrounding rock mass is segmented into distinct sectors: highly damaged zones (HDZs), excavation-damaged zones (EDZs) and excavation-disturbed zones (EdZs). Additionally, the energy ratio of S-waves to P-waves (Es/Ep) and the moment tensor inversion (MTI) are introduced to reveal the failure mechanism of the surrounding rock mass in each damage zone. The results show that the rock mass fracture around the Shuangjiangkou underground powerhouse presents remarkable zonation characteristics. The spatial depth ranges for the HDZs, EDZs, and EdZs, determined quantitatively based on multivariate monitoring data, are 0–5 m, 5–10 m, and 10–20 m, respectively. The failure mechanisms of surrounding rock mass differ across various damage zones: the HDZ primarily exhibits tensile failure, while the EDZ is mainly characterized by shear failure. The research provides a valuable reference for evaluating the stability of surrounding rock during the excavation of underground caverns of Shuangjiangkou hydropower station. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of moisture absorption and swelling in soft rock during tunnel excavation, emphasizing the response to support resistance. Utilizing COMSOL numerical simulations, we conduct a comparative analysis of various strength criteria and non-associated flow rules. The results demonstrate that the Mohr–Coulomb criterion combined with the Drucker–Prager model under compressive loads imposes stricter limitations on water absorption and expansion than when paired with the Drucker–Prager model under tensile loads. Restricted rock expansion leads to decreased horizontal displacement and ground uplift, increased displacement in the tunnel's bottom arch, and significantly reduced displacement in the top arch. The study also considers the effects of shear dilation, burial depth, and support resistance on the stress and displacement of the surrounding rock. Increased shear dilation angles correlate with greater rock expansion, resulting in increased horizontal displacement and ground uplift. The research study concludes that support resistance is critical in limiting the movement of the tunnel's bottom arch and impacting the stability of the surrounding rock. Additionally, the extent of rock damage during the excavation of expansive soft rock tunnels is found to be minimal. Overall, this study provides valuable insights into the processes of soft rock tunnel excavation and contributes to the development of more efficient support systems. [ABSTRACT FROM AUTHOR]

Rock excavation by disc cutters is widely employed in tunnel boring machine (TBM). Rock-breaking impact load acted on disc cutters especially when cutting heterogeneous rock, which if not properly dealt with, may induce cracking of disc cutters. The impact load is excitation source of the TBM dynamic response and it is feasible to analyze the law of impact load based on dynamic response. In this study, a set of real-time dynamic response monitoring and analysis system was installed in a slurry TBM of a water delivery tunnel in Beijing to analyze the impact load action law that induced cracking of the cutter ring, and a series of in-situ tunneling experiments were carried out. The time-domain and frequency-domain characteristics of acceleration response were deeply investigated. The results show that compared with the static parameters, such as thrust and torque of the TBM, the acceleration response is extremely sensitive to changes of the driving parameters (advance speed, cutterhead rotating speed and penetration rate) and rapidly attenuates from the cutterhead to the shield tail of the machine. In the full section quartzy sandstone stratum, the acceleration response of the cutterhead is significantly increased with the slight improve of the penetration rate and the rotating speed and the effect of the penetration rate is larger. The acceleration response is small during the TBM tunneling with low penetration rate–high rotating speed, which is also applicable to the broken stratum. The results of dynamic response test indicate that the impact load resulting in cracking of cutter ring can be effectively reduced by three methods: reducing penetration rate, reducing rotating speed and tunneling with low penetration rate–high rotating speed. The statistical data of cutter wear validate this conclusion. The findings in the engineering practice can provide valuable references for similar TBM construction. Highlights: In situ tests were conducted to analyze the effect of driving parameters on TBM dynamic response. The dynamic load of disc cutters was investigated from the perspective of TBM dynamic response. Three measures were proposed to reduce the cracking of disc cutter ring. The measures were verified by the statistical analysis data of cutter failure. [ABSTRACT FROM AUTHOR]

This paper focuses on investigating the stability of a deep foundation pit with hard surrounding rocks at different excavation stages with different supporting schemes by means of numerical calculations. The supporting schemes in question were combinations of one fixed vertical support and four varied transverse supports. Drilled grouting piles were used as vertical supports, and the commonly used steel bracings and prestressed anchorages served as transverse supports. The parameters used to evaluate the stability of the foundation pit at different excavation stages included the lateral displacements of the surrounding rocks, the settlement of the surrounding ground, the axial forces of steel bracings, and displacements at the tops of the drilled grouting piles. Simulation results showed that when a transverse supporting scheme consisting of one-layer steel bracings and prestressed anchorages set at 9 m and 22.5 m underground, respectively, was adopted, the lateral displacements of the surrounding rocks and settlement of the surrounding ground at different excavation stages were the largest compared to those under the other three transverse supporting schemes, while the corresponding values were lower compared to those allowed in Chinese standard GB50007-2011, demonstrating that this kind of supporting scheme is effective in terms of ensuring the safety of the foundation pit at different excavation stages. Moreover, the setting techniques for this kind of supporting scheme were relatively simple, and the corresponding influences of supporting element arrangements on excavation techniques were the lowest. Therefore, one-layer steel bracings and one-layer prestressed anchorages constituted the most suitable transverse supporting scheme for excavating a deep foundation pit with hard surrounding rocks. [ABSTRACT FROM AUTHOR]

The crack initiation stress threshold is widely used in excavation industries as rock spalling strength when designing deep underground structures to avoid unwanted brittle failures. While various strain-based methods have been developed for the estimation of this critical design parameter, such methods are destructive and often requires subjective interpretations of the stress–strain curves, particularly in rocks with pre-existing microcracks or high porosity. This study explore the applicability of non-destructive ultrasonic through-transmission methods for determining rock damage levels by assessing the changes in transmitted signal characteristics during loading. The change in velocity, amplitude, dominant frequency, and root-mean-square voltage are investigated with four different rock types including marble, sandstone, granite, and basalt under various stress levels. Results suggest the rate of signal variations can be reliably used to estimate crack closure and crack initiation stress levels across the tested rocks before failure. Comparison of the results between the conventional techniques and the new proposed methods based on ultrasonic monitoring are further discussed. [ABSTRACT FROM AUTHOR]

Block theory, which successfully applies the geometric topology method to the field of rock mass stability analysis, is very suitable for analyzing the problem of local block stability caused by the cutting of structural planes (discontinuities) in engineering rock mass. It is a rare original theory in rock mechanics and engineering. However, compared with the completeness, progressiveness, and originality of the theory, the application of block theory in engineering is not widespread enough. Combining the authors' long-term experience in fundamental research and engineering applications of block theory, this work first clarifies the differences in the connotation of block analysis before and after the excavation of rock masses. This difference reflects the main ideas of using block theory for engineering applications and also reflects the different focuses of block theory application at different construction stages. Furthermore, it is pointed out that before and after excavation, the core tasks are "block prediction-support drafting" and "block determination-support verification", respectively. Before the excavation of the rock mass, the main tasks are to group and combine discontinuities, distinguish removable blocks and key blocks based on the whole-space stereographic projection (WSSP) for different discontinuity combinations, estimate the size and shape of unlocated blocks, analyze block stability, and draft support design parameters. After the excavation of the rock mass, the main tasks include analyzing the shape of the located block, analyzing the stability of the block, and verifying the support design parameters for rock blocks. Finally, combined with engineering cases, the key technical issues and work ideas in engineering applications were analyzed, such as how to estimate the size of the unlocated blocks, how to sort out the support-required blocks from key blocks, and how to draft or verify support parameters. The work is of great significance for the application and promotion of block theory in engineering. Highlights: Different connotations of block analysis before and after rock excavation are clarified. Before rock excavation, the core tasks are "block prediction-support drafting". After excavation, the core tasks are "block determination-support verification". Some key issues are discussed, such as distinguishing the support-required block. [ABSTRACT FROM AUTHOR]

Discontinuities largely influence the mechanical properties of rock joints. However, discontinuity orientation clustering methods often rely on the aggregation and separation of orientation data without full consideration of the prior probability structure of orientation data. This paper proposes a method of optimal clustering by Fisher mixed distribution (OCFMD) for automatic grouping of discontinuity orientation. Based on the Fisher prior probability structure of orientation data, OCFMD can identify optimal group centers and group numbers by balancing the fitting accuracy and dominance of Fisher mixed distributions, and optimal grouping results can be generated by membership calculation. A Newton–Raphson expectation maximization (NR-EM) algorithm is derived for the parameter fitting of Fisher mixed distributions. The Fibonacci sequence is used to generate sample points. In addition, the neighbor probability and density of sample points based on Fisher mixed distributions is derived for fitting accuracy calculation. Several cases of rock slopes and rock tunnel excavation faces are adopted for analyzation. Three clustering algorithms combined with four clustering validity indexes of discontinuity grouping are used for comparison. The results show that OCFMD is more accurate and robust than the other automatic grouping methods in optimal grouping result generation. Highlights: An automatic optimal clustering method of discontinuity orientation is proposed based on Fisher mixed distributions. The balance between fitting accuracy and dominance of Fisher mixed distributions is derived for the selection of optimal grouping results. The grouping results of several traditional clustering algorithms combined with clustering validity indexes are observed to be inconsistent with manual results. The proposed method is more accurate and robust than the compared traditional methods in optimal grouping result generation. The convergence effectiveness, sensitivity of neighbor angle selection and robustness to normal vector variations are validated. [ABSTRACT FROM AUTHOR]

Rock abrasivity is an important parameter that influences tool design and wear, the efficiency of tools, and cost during rock excavation. Generally, the abrasiveness of rocks is measured with the Cerchar abrasivity index (CAI). In this research, several Cerchar abrasivity parameters such as penetration of stylus (Ps), the volume of material scratched in the groove (Vm), scratching force (SF), scratching energy (SE), and Cerchar scratching specific energy (CSSE) were determined using an Cerchar device. For evaluating Cerchar abrasivity parameters, 24 rock samples were used comprising igneous, metamorphic, and sedimentary rocks. The new classification was presented based on the Cerchar abrasivity index and Cerchar abrasivity parameters. In this research, the specific energy of the Sievers J miniature drill test (SJ) was calculated for comparison with the specific energy of the Cerchar abrasivity test. Then, the relationship between Cerchar abrasivity parameters with SJ was investigated, new relationships between Cerchar abrasivity parameters and SJ with accurately acceptable presented. The results indicated that the Cerchar abrasion ratio (CAR) is a good parameter for measuring rock abrasivity and cutting. The SJ exhibited a good relation (R2 = 0.78) with CAR. In addition, CAR showed a good correlation (R2 = 0.97) with the specific energy of the rock cutting test (SEcut). The CAR can be used to evaluate abrasivity laboratory tools and the specific energy of a rock cutting test. [ABSTRACT FROM AUTHOR]

As a widely used rock excavation method in civil and mining construction works, the blasting operations and the induced side effects are always investigated by the existing studies. The occurrence of flyrock is regarded as one of the most important issues induced by blasting operations, since the accurate prediction of which is crucial for delineating safety zone. For this purpose, this study developed a flyrock prediction model based on 234 sets of blasting data collected from Sugun Copper Mine site. A stacked multiple kernel support vector machine (stacked MK-SVM) model was proposed for flyrock prediction. The proposed stacked structure can effectively improve the model performance by addressing the importance level of different features. For comparison purpose, 6 other machine learning models were developed, including SVM, MK-SVM, Lagragian Twin SVM (LTSVM), Artificial Neural Network (ANN), Random Forest (RF) and M5 Tree. This study implemented a 5-fold cross validation process for hyperparameters tuning purpose. According to the evaluation results, the proposed stacked MK-SVM model achieved the best overall performance, with RMSE of 1.73 and 1.74, MAE of 0.58 and 1.08, VAF of 98.95 and 99.25 in training and testing phase, respectively. [ABSTRACT FROM AUTHOR]

Purpose. To justify and develop the theoretical bases of the formation and operation of the container technology for moving mining mass from quarries, which ensures a reduction of economic and energy costs, as well as damage to the environment during the extraction of mineral resources. Methodology. The work used complex research methods, including analysis and scientific synthesis of scientific and technical information; theoretical research; methods of mathematical and computer modeling, and design developments. Findings. The analysis of existing technologies for open-pit mining and the current state of mining indicates an urgent need to develop new resource-saving technology and environmentally friendly technologies for moving rock mass for open-pit mining. A new technology for container transportation of rock mass in containers is proposed without the construction of additional transport communications in the quarry and has technological and energy-saving advantages. Originality. The scientific novelty of the research consists of an integrated and systematic approach to assessing the energy efficiency and environmental safety of the proposed set of equipment for container technology for transporting rock mass. Practical value. In this work, special attention is paid to the problem of the formation and effective use of a new resource-saving and environmentally friendly container technology for moving rock mass from deep quarries. These advantages are simultaneous excavation of rocks, transportation of rocks over the shortest distance, low container packing ratio, and mobility of a complex of lifting machines, which will reduce energy consumption and the cost of transporting rock mass. A transport complex has been developed to ensure the reliable operation of lifting and transport machines. [ABSTRACT FROM AUTHOR]

Because the urban tunnel is an essential knot of urban traffic and an easy blocking point in busy hours, upgrading the urban tunnel was necessary for the city after the tunnel being in service for a long time. However, to demolish the existing tunnel, some problems may be encountered, and these problems include occurrence of longitudinal cracks at the tunnel vault, increase of load due to infrastructure construction over the tunnel, unloading due to excavation of the rock over the tunnel, and uneven load due to asymmetric excavation or construction. To reinforce a cracked tunnel in Chongqing City, China, steel arches were installed to improve its bearing capacity, but some steel arches failed during the excavation of ground over the tunnel. Therefore, the scheme of "steel arch + shotcrete + tube column + transversal horizontal bracing" (hereinafter referred to as SASTCT) was proposed to ensure tunnel safety due to unloading and uneven load during the subsequent construction procedures. Numerical analysis indicated that the SASTCT measure can ensure the safety of the traffic and subsequent construction, which can provide some suggestions for similar tunnel upgrades in the future. [ABSTRACT FROM AUTHOR]

Non‐uniformly distributed in‐situ stress around the tunnel is a significant factor inducing various geohazards during tunnel excavation in the rock mass, and the anisotropy of the rock mass would further differentiate the in‐situ stress state around the tunnel. To ensure the safety of tunnel construction and operation, it is necessary to deeply analyze the stress distribution law and mechanical mechanism of the orthogonally anisotropic elastic media the around tunnel. This paper presents a complex variable function method for the elliptical tunnel in an orthogonally anisotropic elastic full‐space under non‐uniform in‐situ stress. To obtain the analytical solution, the affine transform and conformal mapping are applied to consider the orthogonal anisotropy of material and the ellipticity of the tunnel. A numerical series fitting method is introduced to describe the non‐uniformly distributed load, and then the stress solution around tunnel is further obtained. The comparisons with the existing literature, numerical solutions and model tests are provided to verify the correctness of the proposed method. Finally, the convergence study and the numerical analysis on the stress distribution are given graphically. [ABSTRACT FROM AUTHOR]

The high water content of the surrounding rock in loess tunnels will lead to the deterioration of rock strength, causing deformation and damage to the initial support structure and thereby affecting safety during construction and operation. This article first analyzes the strength characteristics of loess under different water contents through indoor physical and mechanical tests. Secondly, based on numerical simulation results, the ecological environment, and design requirements, the water content threshold is determined. Finally, a reinforcement scheme combining surface precipitation measures and curtain grouting measures is proposed, and the reinforcement effect is analyzed based on on-site monitoring data. The results show that as the water content of loess increases, the cohesion, internal friction angle, and elastic modulus of the surrounding rock all decrease, leading to an increase in the sensitivity of the surrounding rock to excavation disturbances and a deterioration in strength. During the construction process, it shows an increase in the vault settlement and sidewalls' convergence. During the process of increasing the distance between the monitoring section and the palm face, the settlement and convergence of the tunnel show a rapid growth stage, slow growth stage, and stable stage. The water content threshold is determined to be 22%. The reinforcement scheme of combining surface precipitation measures with curtain grouting measures not only meets the requirements of the ecological environment but also makes the settlement and convergence values lower than the yellow warning deformation values required by the design. [ABSTRACT FROM AUTHOR]

In order to clarify the impact mechanism of shallow buried soft rock tunnel excavation on the upper existing highway, as well as the mechanism of pipe shed reinforcement, a combination of theoretical analysis and on-site monitoring was used to conduct in-depth research on the Diantou Tunnel Crossing the existing highway project of Dayong Expressway. The impact of shallow buried soft rock tunnel crossing construction on the existing highway and safety control issues were studied, a new deformation control index, namely deformation difference rate, was introduced. The results show that the main lateral area of influence of rock deformation is within a distance of one diameter, and the overall area of influence is within a distance of twice the diameter. From the perspective of axial tunnel deformation, the deformation of surrounding rock tends to be stable when the excavation face passes through the monitoring section about twice the tunnel diameter. Effectively controlling rock deformation depends on the total amount of settlement deformation, the change rate of deformation, and the difference rate of deformation. For V-class shallow buried tunnel surrounding rock, in order to prevent cracks on the surface, the cumulative deformation of the surrounding rock needs to be less than 50 mm, the change rate needs to be less than 3 mm/day, and the difference rate needs to be less than 5 mm/m. Finally, the proposed control standard for surface subsidence is given for similar engineering reference. [ABSTRACT FROM AUTHOR]

Rapid, precise and frugal surveying is a strategic factor in the present mechanized mining environment owing to rapid surface profile transformation in a short period. Determination of global coordinates with high accuracy using the satellite-based global navigation satellite system (GNSS) has been studied in the mining arena and is gradually becoming an essential component. A case study of Khanak Stone Mine, Haryana, India, is discussed here, highlighting the combination of GNSS system and terrestrial laser scanner for the preparation of a surface profile of a rugged terrain with the key objective to determine the precise in situ rock excavation in periodical phases. The actual tonnage of rock produced/transported from the mine has been calculated by determining the in situ density and bulk density in the laboratory. The study reveals that this survey of approach is apt to achieve quality plan and to obtain the goal of actual tonnage of rocks excavated. [ABSTRACT FROM AUTHOR]

To investigate the asymmetric failure mechanism and failure mode of layered rock tunnels, a novel mixed-mode power exponent cohesive zone model (M-PECZM) is proposed in this paper, which can capture the crack propagation process under single-mode loading, tension-shear loading, and compression-shear loading conditions. The parameters in the formula can be obtained from pure tensile and shear tests, and the introduction of the post-peak characteristic parameter α makes the M-PECZM suitable for post-peak softening curves of different kinds of rocks. The proposed M-PECZM is embedded in FDEM to carry out uniaxial compression, direct tension, and triaxial compression simulations. By comparison, the numerical and experimental results show a good agreement, which verifies the reliability and effectiveness of the M-PECZM. Besides, the FDEM is adopted to simulate the excavation of gently inclined layered surrounding rock tunnel, and the influence of shear stress field and buried depth on the EDZ evolution process and convergence displacement is studied. Highlights: A novel mixed-mode power exponent cohesive zone model (M-PECZM) for FDEM is proposed. The introduction of the post-peak characteristic parameter α makes the M-PECZM suitable for various rocks. Comparisons with experiments verify the accuracy and completeness of the M-PECZM. The influence of shear stress field and buried depth on the EDZ evolution process and convergence displacement is analyzed particularly. The asymmetrical deformation mechanisms of the tunnel resulted from the coupling action between the layered soft rock and tectonic shear stress. [ABSTRACT FROM AUTHOR]

As the global push towards clean energy intensifies, the demand for critical minerals has driven deep excavation in hard rock formations, posing significant challenges related to rockburst and spalling. Spalling refers to explosion-like rock fractures under high geo-stresses. Despite several successful studies and practical models, the mechanisms governing spalling propagation under polyaxial stress states remain inadequately understood, particularly in weaker and high-porosity rocks. This study introduces a novel Crack Mode-Changing Stress (CMCS) concept, which defines the minimum principal stress required to change the crack mode from shear to tensile failures when rock spalls. The concept was validated using cubed sandstone samples containing centric circular holes subjected to a range of loading conditions including uniaxial, biaxial, generalized triaxial compression, generalized triaxial tensile, and true triaxial loading stress states. Our results highlight the significance of the out-of-plane minor principal stress on the crack initiation threshold and the CMCS, emphasizing the need for careful consideration when designing openings in highly stressed environments. [ABSTRACT FROM AUTHOR]

For the soft-plastic loess tunnel engineering, collapse and damage of the surrounding rock during excavation are often driven by the combined action of the seepage water and the unloading effect. Under water pressure and unloading, the soil suffers complex stress-seepage coupling action causing the inevitable change of permeability and mechanical properties. In this paper, seepage control devices were added to the GDS test device, and a new triaxial permeability measurement system was developed. Triaxial unloading–seepage tests were conducted on soft-plastic loess under the effect of hydraulic coupling. The variation of permeability characteristics of Q2 type soft-plastic loess under lateral unloading and the soil mechanical characteristics under different seepage pressure were analyzed. Meanwhile, microstructure characteristics of soft-plastic loess during the triaxial test were obtained by scanning electron microscope to clarify the deformation and seepage mechanism. The results show that the strength of soft-plastic loess decreases significantly with the increase of osmotic pressure. Under the condition of 50 and 100 kPa osmotic pressure, the cohesive force of soft-plastic loess decreases by 15.5% and 39.0% and the friction angle decreases by 9.4% and 22.6%, respectively. The permeability coefficient of loess increases slowly at first and then increases rapidly during the unloading process. The main reason for the significant increase of permeability coefficient is the penetration of soil fissures and the formation of shear bands after entering the plastic deformation stage. [ABSTRACT FROM AUTHOR]

The shear mechanical behavior of discontinuities under unloading conditions induced by intensive rock mass excavation differs from that under loading conditions. Therefore, the mechanical parameters obtained from the conventional direct shear test cannot effectively be used to assess the stability of excavated rock masses. To solve this problem, we conducted a series of experiments on saw-toothed discontinuities with different undulating angles and initial shear stresses under unloading normal stress with constant shear stress. The test results showed that the shear pattern transformed from climbing to climbing-gnawing and then to gnawing patterns as the undulating angle and initial shear stress increased. The shear stress remained stable with increasing shear displacement after instability in the climbing pattern, decreased with fluctuations in the climbing–gnawing pattern, and dropped steeply in the gnawing pattern. A negative linear correlation exists between the unloading magnitude and the initial shear stress. Unloading normal stress promoted deformation rebound and sawtooth damage, reducing the mobilizing shear strength. Modified Patton and Barton shear strength criteria considering the undulating angle, initial stress, and failure pattern under unloading normal stress were proposed. Highlights: The shear mechanical behavior of saw-toothed discontinuities with different undulating angles and initial shear stresses under unloading normal stress with constant shear stress are investigated. The failure pattern changes from the climbing pattern to the climbing–gnawing pattern and then to the gnawing pattern as the undulating angle and the initial shear stress increase. Unloading promotes the increase in rebound deformation and the area of the damage zone, leading to the decrease in shear strength of saw-toothed discontinuities. The modified Patton criterion and the Barton criterion are proposed for unloading normal stress considering the undulating angle, initial stress state, and failure pattern. [ABSTRACT FROM AUTHOR]

The strength and hardness of rock are much higher at freezing temperatures than at room temperature. This results in high excavation costs and low excavation efficiency in frozen rock layers. This study proposes a novel way to thaw porous and water-bearing rock by microwave irradiation. It is applicable to a wide range of strata and is not dependent on whether the rock contains wave-absorbing minerals. Quartz sandstone specimens free from absorbing minerals and of different saturation levels were used in an investigation of thawing and softening behaviors under microwave irradiation. The rock pore structures were observed before and after irradiation. The results show that (1) frozen quartz sandstone irradiated by microwaves undergoes three stages: (i) rapid melting of pore ice, (ii) intense vaporization of meltwater, and (iii) drying. (2) Microwave irradiation significantly reduces the strength of frozen quartz sandstone. (3) The mechanisms are vaporization expansion, which causes the propagation of intergranular cracks, and thermal expansion, which induces trans-granular cracking. (4) Softening of 40–100%-saturated frozen quartz sandstone is caused by both vapor and thermal expansion, while 0–40%-saturated sandstone is mainly affected by thermal expansion. This study provides theoretical and experimental support for microwave-assisted breakage of frozen porous and water-bearing rock. Highlights: Microwave irradiation is a promising auxiliary method in excavation of frozen rock. Microwave irradiation heating melts frozen sandstone completely within only 40 s. Unfrozen water in frozen sandstone is the fundamental cause of the rapid melting. Softening effect on frozen sandstone is enhanced by increasing saturation degree. [ABSTRACT FROM AUTHOR]

To investigate crack propagation and the coalescence mechanism of a rock bridge under unloading condition induced by intensive excavation of rock mass, the direct shear test with unloading normal stress and corresponding particle flow code (PFC) simulation were conducted on the sandstone specimen containing a parallel fissure pair considering different fissure inclinations (varied from 0° to 90°) and initial shear stresses (varied from 4 to 7 MPa). Three failure patterns (i.e., shear failure, tensile failure, and tensile–shear mixed failure) are identified as experimental and numerical results. The failure pattern transforms in the order of a shear, tensile, and tensile–shear mixed failure pattern as the fissure inclination increases. Three displacement field types are summarized and correspond to different failure patterns. Comparing the shear strength, cracking process, and microscopic displacement field in the direct shear test with unloading normal stress and the conventional direct shear test, normal unloading weakens the shear strength of the specimen under the selected stress conditions (initial normal stress is 20 MPa, initial shear stress ranges from 4 to 7 MPa). Rebound deformation in the process of unloading promotes the high proportion of tensile cracks for the tested fissure inclinations. [ABSTRACT FROM AUTHOR]

The utilization of auxiliary tools employing ultrasonic high-frequency vibration to enhance rock breaking efficiency holds significant potential for application in underground hard rock excavation engineering. To investigate the failure mechanism of rocks under high frequency ultrasonic vibration load, this study employs particle flow software PFC2D for numerical simulation. By incorporating boundary conditions from actual ultrasonic vibration rock breaking experiments and utilizing a parallel bond model to construct the rock, we analyze the deformation, damage, fracture, and energy evolution process of hard rocks subjected to vibrational loads. The results demonstrate that the maximum displacement in hard rocks increases nearly linearly with vibrations until reaching 5.0199 × 10−3 m, after which it plateaus. Additionally, macroscopic fissures formed during rock failure exhibit an X-shaped pattern. Furthermore, based on our model, we examine the impact of amplitude variation on hard rocks with an equal number of cycles (5,000,000 cycles). Under ultrasonic vibration loads, amplitude influences the total input energy within the rock system. While increasing amplitude does not alter maximum deformation in rocks, it enhances fragmentation degree, fracture degree and energy dissipation coefficient—thereby improving rock breaking efficiency. [ABSTRACT FROM AUTHOR]

Strainburst often occurs in the loading process of tangential stress concentration from surrounding rocks after excavation and unloading of deep rock mass. The concentrated tangential stress is relatively larger on the tunnel walls, which decreases towards the interior of surrounding rocks with a certain gradient. To explore the fracture evolution characteristics of surrounding rocks under different tangential gradient stresses and understand various phenomena in the strainburst process, a large‐scale true‐triaxial gradient and hydraulic‐pneumatic composite loading rockburst test device was adopted to carry out the strainburst tests under four different gradient stresses. Based on the macroscopic failure phenomena, distribution of rockburst debris, macro‐micro morphology of failure cross section, and monitored data of acoustic emission (AE), the fracture evolution of rockburst specimens was analyzed under different stress gradient loadings. The results indicate that the stress gradient has an obvious influence on the fracture characteristics, resulting in different rockburst phenomena. With the increase of stress gradient, the failure stress of rockburst decreases, while the dynamic failure characteristics of rockburst trends to be significant. The increase of stress gradient contributes to higher fragmentation degree of debris, more uniform distribution and better continuity. The total number of cracks in the model decreases with the rise of the stress gradient, and the proportion of shear failure increases, which is the main reason for the enhancement of the rockburst intensity. [ABSTRACT FROM AUTHOR]

This paper presents a system for measuring the geometry of powered roof support sections (Shield Support Monitoring System, SSMS). The problem of measuring the geometry of powered roof support sections for the purpose of predicting geological hazards during the rock excavation process is presented. Information on the construction and implementation of the SSMS and research at the Budryk Mine is included. The research aimed to evaluate both the precision and accuracy of the measurement apparatus created, as well as to examine how operating conditions affect the system's usability. An analysis of inclinometer measurement errors in the prototype system was conducted during in situ tests, demonstrating minimal scattering and high sensor accuracy according to the provided data. [ABSTRACT FROM AUTHOR]