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Brittle failure, also known as rockburst, is a violent phenomenon that occurs during the excavation of hard rock in areas with high geostress, particularly at great depths. The induced hazards have been a global concern since the first half of the 20th century, leading to extensive efforts to understand the mechanisms and develop effective approaches to predict and control such rock mass failures. To understand the current state of research and future prospects of rockburst, a comprehensive review of past developments has been conducted. Firstly, we briefly summarize different definitions and types of rockburst. Next, we delve into the various technologies and methods employed in rockburst research and analyze the current knowledge on the mechanisms, classifications, and prediction of rockbursts. Then, we examine the existing methods for preventing and controlling these events. Despite the advancements made, the relationship between the behavior of rock masses at different scales, both in the laboratory and real-world conditions, remains an area of challenge. Additionally, the absence of rock mass classifications under high in-situ stress and lack of accuracy in rockburst prediction methods remain persistent issues that need to be addressed. This study delves into cutting-edge rockburst research, illuminating potential ground support strategies and empowering the mining industry in order to unleash innovative solutions for controlling these explosive phenomena. [ABSTRACT FROM AUTHOR]

One of the main causes for excessive deformation within a tunnel is due to the instability of the soil or soft rock ahead of the excavation face. Fiberglass bolts have been shown to be a useful advance reinforcement method for the excavation face. In this paper, an improved ADECO-RS (Analysis of controlled deformation in rock and soils) method had been proposed for soft rock mountain tunnels, in terms of the partial (mainly the upper bench) excavation face reinforcement and also for the bench excavation method. Strain gauges were used to test the micro-strain in the fiberglass bolt to investigate how the axial force of the fiberglass bolt varied during the tunnel excavation. In addition, combined with the field tunnel deformation monitoring data, the relationship between the reinforcement parameters of the fiberglass bolts and the tunnel construction phase were discussed. The research results show that: (1) The stress state of the anchor rod is related to the reinforcement length of the anchor rod; (2) Excavation within the lap area of the fiberglass bolt leads to an increase in the axial force of the bolt, while excavation outside the lap area of the fiberglass bolt has no effect on the anchor; (3) Reducing the reinforcement area of rock mass will affect the stability of the excavation. To ensure the stability of the excavation face, the initial support construction loop should be completed as soon as possible; (4) In a future project with similar conditions, the recommended lap length of the fiberglass bolt could be 3 m utilizing the fiberglass bolt grouting face reinforcement method. [ABSTRACT FROM AUTHOR]

Increasing demand for the use of different mechanized excavation systems in civil and mining projects has elevated the importance of understanding the wear process of rock-cutting tools. This requires proper measurement and analysis of rock abrasiveness and cuttability characteristics. Predicting the wear life of cutting tools, evaluating the required number of tools needed for excavating the desired structure in a given ground condition, and assessing the cost and time of tool replacements are among the most important topics for feasibility studies of any mechanized excavation project. Over the years, various testing methods have been developed and introduced to study and measure the abrasive and wear characteristics of rock materials. Several research centers throughout the world are working on experimental models for quantifying rock abrasiveness and to get more accurate and reliable measurements of this rock property. However, the majority of the testing methods focus on measuring abrasiveness as a rock-related characteristic rather than considering it as an interactive behavior. The ultimate use of the measured abrasive properties of rock is for estimating the tool life in drilling and excavation operations. Hence, many researchers are collecting field measurements and conducting various analyses to develop models for the prediction of tool life based on rock properties for a given application. This paper reviews the different rock abrasivity measurement and evaluation procedures. The effective factors on the measured abrasive characteristics of rock samples have been classified and discussed, and a critical review is offered to compare the performance and reliability of different testing methods for different applications. Highlights: A comprehensive review of the laboratory rock abrasiveness testing methods is offered. The effect of different test settings and parameters on the measured abrasiveness of rock is discussed. The suitability of different testing methods for wear prediction of hard rock cutting tools is evaluated. [ABSTRACT FROM AUTHOR]

Excavation of deep hard rock tunnels disturbs the initial stress imbalance, which can lead to rockburst, spalling and/or collapse. The disasters are related not only to the strength of the rock mass, but also to the excavation stress path. By analysing and summarizing a large number of engineering cases, the surrounding rock of a deep tunnel is divided into high-, medium- and low-risk fracture zones of disaster, and the excavation stress paths of the three risk fracture zones are generalized. Based on the true triaxial test system, the catastrophic failure mechanism of rock masses in high- and medium-risk fracture zones of hard rock tunnels in deep engineering under the excavation stress path is studied. It is revealed that the stress difference caused by the excavation stress path fundamentally determines the difference in the surrounding rock fracture degree. A method for evaluating the influence of the excavation stress path on the rock fracture anisotropy by using a three-dimensional stress difference coefficient is proposed. The results show that under the excavation stress path in the high-risk fracture zone, the energy stored in the rock is larger, the rock is more prone to failure, and the rock fracture is more violent. Under the excavation stress path of the medium-risk fracture zone, the rock is more prone to spalling failure. With the increase in the depth from the excavation boundary in the high-risk fracture zone, the stress difference decreases continuously, the rock bearing capacity increases, and the shear fracture component increases. The three-dimensional stress difference coefficient shows a linear positive correlation with the rock fracture anisotropy. The mechanism of the excavation stress path affecting rock burst disasters in deep hard rock tunnels is discussed from the perspective of energy storage and dissipation. This study also provides guidance for selecting a reasonable support scheme. Highlights: The excavation risk fracture zone of deep hard rock tunnel is divided, and its typical excavation stress path is summarized. The catastrophic failure mechanism of rock with different excavation stress paths under true triaxial stresses was investigated. A method for evaluating the influence of the excavation stress path on rock fracture anisotropy using a three-dimensional stress difference coefficient is proposed. The influence of the excavation stress path on field failure is discussed from the perspective of energy storage and dissipation. [ABSTRACT FROM AUTHOR]

Friction rock stabilizers (FRS) are routinely used to provide rock reinforcement to excavations in hard rock. Since the expiration of the original patent taken out in 1977, FRS are now available from multiple suppliers. The expectation that all FRS are equivalent, however, is not necessarily accurate. There are inherent variations in the design configuration, material chemistry/properties, and consequently in performance. In this context, a full traceability from steel grade and heat treatment to final product is critical. This paper reports the results of a QA/QC investigation aiming to identify the material properties for three equivalent FRS from the same supplier. A series of mechanical and accelerated corrosion tests highlighted the differences in these rockbolts. This work provides a template for a more comprehensive quality assurance programme to ensure compliance of FRS. This is critical when rockbolts, due to global supply chain constraints, are outsourced from multiple sources worldwide. [ABSTRACT FROM AUTHOR]

The strength, deformation characteristics and failure mechanism of tunnel surrounding rock are affected by the rock mass discontinuity. In order to explore the influence of the existence of rock mass discontinuity on the mechanical parameters and the instability mechanism of surrounding rock mass, the 3D digital photogrammetry system is used to measure the rock mass of Guangshan No. 1 tunnel to obtain the geometric information of discontinuities and its probability distribution model. Based on the information of rock mass discontinuity obtained by digital photography technology, the volumetric joint count (Jv) and joint roughness coefficient (JRC) are introduced to quantitatively study the geological strength index (GSI), and Hoek–Brown strength criterion is used to analyze the mechanical parameters of tunnel rock mass. According to the strength parameters of tunnel rock mass, the numerical simulation of excavation stability of the tunnel is carried out. The research results show that 3D digital photography can accurately locate the joints exposed by rock excavation in tunnel site, and the quantitative GSI method can accurately determine the rock strength parameters in Hoek–Brown strength criterion, which is conducive to the accurate simulation analysis of tunnel surrounding rock stability. The research realizes the digital identification of information of jointed rock mass, quantitative analysis of rock mass mechanical parameters and numerical simulation of tunnel stability, which provides a fast and practical method for stability analysis of tunnel with joint development. [ABSTRACT FROM AUTHOR]

Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank slope under freeze–thaw action, triaxial unloading tests were carried out on sandstone, freeze–thaw tests simulating freezing strength were conducted, and triaxial creep tests were implemented with graded incremental loading on unloaded specimens subjected to freeze–thaw action. The test results showed that the total deformation of the unloaded specimens is significantly increased compared with the conventional specimens, and the lateral direction is more likely to produce creep behaviour than the axial direction. The level of confining pressure determines the level of creep deformation of unloaded specimens and affects the variation law of creep rate. The creep behaviour of the unloaded specimens is aggravated by freeze–thaw action and, the longer the freezing period, the larger the creep strain share, and the creep rate increases significantly. The creep damage pattern of the unloaded specimens subjected to freeze–thaw action is mainly manifested as shear damage, and the creep process intensifies the derivation of tension-type cracks in the specimens. The higher the confining pressure of the unloaded specimen, the more obvious the plastic characteristics and the weaker the brittle characteristics during creep failure. The freeze–thaw action significantly reduces the long-term strength of the unloaded specimen, which is approximately 50~55% of the instantaneous strength. The long-term strength decays significantly with an increasing freezing period, and the research results can provide a theoretical reference for the evaluation of the long-term stability of excavated and unloaded rock masses in cold areas. [ABSTRACT FROM AUTHOR]

Rockburst is a kind of dynamic rock failure process that is easily induced by the excavation of a high-stress rock mass. However, from an energy perspective, the existing indexes for rockburst tendency have a limitation in that they do not consider the energy release speed. In this study, energy release effectiveness was proposed based on the local energy release rate while considering the influence of the energy release speed. The index can evaluate the stability of surrounding rock during the excavation of high-stress rock. The index can be obtained by recording the strain energy density of every element in the model during excavation and identifying the maximum strain energy density (Eimax), the minimum strain energy density (Eimin), the maximum time (timax), and the minimum time (timin) to calculate energy release speed and energy release effectiveness. A case study of the excavation of an experimental tunnel, namely, the URL of AECL, was adopted to validate the index. The results indicated that the proposed index can clearly identify the location and strength of the impact tendency area, and it can be effectively applied to the stability analysis during the excavation of deep tunnels. [ABSTRACT FROM AUTHOR]

The control difficulty of whole coal cavern groups is greatly increased due to the characteristics of soft rock with low strength, large sections, and the mutual influence of crossed cavern groups. The large section gas storage cavern group is taken as the research background. In this paper, the equivalent circle method is used to solve the loose circle of a rectangular roadway, and numerical calculation is used to obtain the deformation and stress distribution laws of the surrounding rock under the excavation conditions of large section whole coal cavern groups (WCCG). The deformation and failure mechanisms of the surrounding rock are revealed under the linkage impact between large section whole coal cavern groups. The stratified reinforcement ring concept of "long cable-bolt-grouting" (LBG) was proposed for the stability control of surrounding rock in the WCCG. On the roof of whole coal cavern groups, the supporting configuration of a high-strength bolt with a high pre-tightening force and the high-strength anchor with a high pre-tightening force were determined. On the two sides and floor of the WCCG, the grouting scheme was determined. These two supporting configurations in both the roof and sidewalls were applied to the large section gas storage cavern group. The results show that the surrounding rock presents asymmetric deformation and failure characteristics due to the large excavation area and complex structure. Tensile failure and mixed tensile-shear failure mainly occur in the shallow part of the surrounding rock, while shear failure mainly occurs in the deep part of the surrounding rock. The roof displacement curves show a symmetric distribution and saddle distribution in the low- and high-negative pressure caverns, respectively. The maximum displacements are on the left and right sides of the cavern roof. The range of the loose rings is 3.34 m and 2.54 m, respectively, on the roof and the two ribs. The stratified reinforcement ring support technology of LBG can effectively reduce the failure depth of surrounding rock, and the surrounding rock is in a stable state. The study can provide a theoretical basis for the layout of large section cavern groups and the stability control of surrounding rock. [ABSTRACT FROM AUTHOR]

Rock burst is a common hazard during tunnel excavation in high-stress and hard rock strata. Microwave-assisted breaking has a great potential application in hard rock tunnel excavation, reducing the possibility of rock burst, and how to reasonably make the application on the TBM cutterhead is one of the critical issues. The waveguide aperture and distance between the rock face and waveguide have serious effects on its performance. In this paper, based on the arrangement of the microwave waveguide of the TBM cutterhead and the actual excavation situation, considering the reflection of microwave energy by the metal cutterhead and the scattering state of electromagnetic waves at the rock surface irradiation, a 2D model of rock irradiated by microwaves is established. The effects of waveguide aperture and distance on microwave irradiation performance of rock are studied, considering three different waveguide types: convergent waveguide, rectangular waveguide, and horn waveguide. The results show that the maximum temperature is located on the rock irradiation surface, rather than inside the rock. The rock temperature decreases in a cosine pattern with irradiation distance, rather than in linearity, which is consistent with the characteristics of electromagnetic wave propagation. The interval of irradiation distance where the rock temperature local maximum value appears is 1/4 of the electromagnetic wavelength, corresponding to the crest and trough of the electromagnetic wave. The rock temperature at the wave trough distance is lower than that of the wave crest distance, but the high-temperature zone is wider. In the range of 50~200 mm waveguide apertures, the rock temperature and damage decrease with the increase in waveguide aperture when irradiated at the crest distance, while the valley distance is opposite. A convergent waveguide and short irradiation distance enhance the energy focusing performance, so the temperature rise characteristics and rock damage are more concentrated. A large-waveguide-aperture horn waveguide and long irradiation distance form a wide range of high-temperature zones and rock damages. [ABSTRACT FROM AUTHOR]

The existence of joints or other kinds of discontinuities has a dramatic effect on the stability of rock excavations and engineering. As a result, a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects. In recent years, 3D printing technology has become a promising tool in the field of rock mass mechanics and engineering. This study first reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects. Then, based on the comprehensive analysis of previous research, the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects. The first is the printing material. Although there are many materials for 3D printing, it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited. After research, we summarize and evaluate printing material that can be used for rock mass mechanics studies. The second is the printing methodology, which mainly introduces the current application forms of 3D printing technology in rock mass mechanics. This includes printed precise casting molds and one-time printed samples. The last one is the printing model, which includes small-scale samples for mechanical tests and large-scale physical models. Then, the benefits and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed. Compared with traditional rock samples collected in nature or synthetic rock-like samples, the samples made by 3D printing technology have unique advantages, such as higher test repeatability, visualization of rock internal structure and stress distribution. There is thus great potential for the use of 3D printing in the field of rock mass mechanics. However, 3D printing materials also have shortcomings, such as insufficient material strength and accuracy at this stage. Finally, the application prospect of 3D printing technology in rock mass mechanics research is proposed. [ABSTRACT FROM AUTHOR]

To investigate the effect of hydro-mechanical coupling characteristic in low-permeability hard rocks during the excavation of groundwater-sealed energy cavern and hydraulic engineering tunnels or chambers, triaxial compression tests were conducted on engineering granite under different confining and seepage pressures. The mechanical properties, such as the strength and deformation parameters, of granite under hydro-mechanical coupling condition were studied. The permeability of the granite under different stresses first decreases, then stabilizes, and then increases significantly until the final abrupt change, and the inflection point of the abrupt change in permeability tends to be in advance as the confining pressure increases or the seepage pressure decreases. Based on the statistical damage theory and test result, combined with the Mogi-Coulomb strength criterion, a hydro-mechanical coupling statistical damage constitutive model that considers the rock damage threshold and the initial compaction effect was proposed, and the proposed mechanical model was verified based on the test results under different confining and seepage pressures. The proposed mechanical model was further applied to predict permeability catastrophes during rock fracturing and achieves good results. This study provides a theoretical basis for the prevention and control of hydro-mechanical coupled disasters in rock engineering. [ABSTRACT FROM AUTHOR]

One of the main hazards during tunnel boring machine (TBM) excavation in hard rock is related to the occurrence of unforeseen adverse conditions, leading to unfavourable rock mass behaviour during tunnel boring. In this respect, the continuous analyses of TBM excavation parameters may represent an interesting tool for a continuous monitoring of geotechnical conditions at the tunnel face and for early detection of changing ground conditions in the rock mass. This work provides a back‐analysis of TBM data recorded during the excavation of the Frejus Safety Tunnel, bored across the French‐Italian border in the Western Alps. It is a 13 km‐long tunnel excavated by a 9.4 m diameter, single‐shield TBM through strongly anisotropic calcareous schist, with cover up to 1800 m. Main problems faced during TBM excavation were related to the local occurrence of buckling‐related convergence and consequent asymmetrical loading on the precast segment rings. Correlating TBM performance parameters to the encountered geological and geomechanical conditions provides the possibility to identify which parameters are most affected by geomechanical properties of the rock mass at the tunnel face and by rock mass behaviour. Conversely, the analysis indicates which parameters can be adopted as monitoring tool of ground conditions during TBM advance. In addition, this work highlights how buckling phenomena can be distinguished, in terms of TBM operation and performance, from other adverse conditions as, e.g., blocky ground or squeezing. [ABSTRACT FROM AUTHOR]

Joints have a significant influence on the deformation and failure mechanism of the surrounding rock. To reveal the influence of axial joint on mechanical response of the roadway surrounding rock after excavation unloading, the deformation and failure characteristics of cylindrical rock-like specimen (CRLS) with an axial joint was studied through laboratory tests and numerical simulation. Also, the influence of joint size and position on strain variation, secondary stress evolution and plastic zone distribution of the CRLS were analyzed. Results show that the axial joint can promote the deformation of the surrounding rock on the inner side of the joint, while hindering the deformation of the surrounding rock of the roadway on the outer side of the joint. In addition, the size and position of the axial joint have a significant influence on the distribution of secondary stress and plastic zone of the surrounding rock. The stress relief zone is mainly located between the joint and the excavation profile, whereas the plastic zone is mainly distributed at both ends of the joint and between the joint and the excavation profile. Finally, the tangential stress concentration can be alleviated by choosing proper distance between the joints and the roadway, and the failure mode of the surrounding rock between the joint and the excavation profile transmitted from tensile failure to shear failure with the axial joint moves away from the roadway. The research results could provide technical reference for roadway support and disaster prevention in a deep jointed rock mass. [ABSTRACT FROM AUTHOR]

Microwave irradiation on rocks before excavation is an effective method to reduce equipment wear and energy consumption during mechanical cutting. Rock mass excavation is usually carried out in a water-rich environment and exposed to dynamic loads, thus understanding the coupled effects of water content and loading rate on the mechanical behavior of rocks under microwave radiation is essential. In this study, sandstone samples with five levels of water content (from oven-dried to water-saturated) were exposed to microwave irradiation at a power of 700 W for 10 min. Brazilian disc tests were conducted on sandstone samples after microwave radiation under both quasi-static and dynamic loading conditions. Test results revealed that, with the increase of the initial water content, the microwave heating capacity of the rock is significantly improved. The surface temperature of the saturated samples is approximately 1.38 times higher than that of the dry ones. Moreover, weight, P-wave velocity, quasi-static and dynamic tensile strength of the rock decrease, while porosity and damage factor exhibit a similar growth law. Before microwave irradiation, the average value of the P-wave velocity and the quasi-static tensile strength of sandstone were about 2521.3 m·s−1 and 4.65 MPa. However, after microwave treatment, when the initial water content was 2%, 3%, 4% and 5.4%, the P-wave velocity decreased by 6.1%, 9.8%, 16.4% and 30.2%, while that quasi-static tensile strength reduced by 9.2%, 16.7%, 30.6% and 48.9%, respectively. For water-saturated samples under microwave irradiation, the porosity increases from 13.02% to 18.12% (showing an increase of 39.2%), and the damage value rises to 0.51. In addition, the dynamic tensile strength shows a significant loading rate dependence, and as the initial water content increases, also the dynamic increase factor (DIF) increases. At a given loading rate, the energy dissipation decreases with the increase of the initial water content, which indicates that the presence of water cause more significant damage to the rock when subjected to microwave radiation. Scanning electron microscopy (SEM) results indicate that the internal damage of the rock after microwave radiation is dominated by intergranular cracks, and crack density increases with increasing initial water content of the samples. The underlying damage mechanisms of microwave radiation on water-bearing sandstone were interpreted with the theory of pore water pressure and structural thermal stresses. [ABSTRACT FROM AUTHOR]

The excavation of hard rock roadways in coal mines is often in the environment of underground water and high ground temperature, and it is easy to be affected by the dynamic load, which leads to roadway destruction and increases the difficulty of roadway support. The ring sandstone specimens with different inner diameters (0~25 mm) were treated with temperature and water coupled, and the dynamic compression test was produced by the Hopkinson pressure rod device (SHPB). The experimental results indicate that the coupling effect of temperature and water reduces the dynamic performance of sandstone specimens. XRD test results showed that the composition of sandstone specimens did not change before and after warm water coupling, and no new substances were found. Dynamic properties of ring sandstone specimens with different inner diameters weaken with the increase in inner diameters. With the increasing inner diameter of ring sandstone specimens, the energy dissipation per unit volume increases the dynamic compressive strength decreases, and the degree of breakage increases. Fracture morphology, average strain rate, and dynamic peak strain of ring sandstone specimens increase with inner diameter. [ABSTRACT FROM AUTHOR]

A brief description of the agrochemical properties of the soils that make up the dumps of overburden rocks of quarries, sludge storage facilities of processing plants and waste rocks of mines is given. It was noted that the soils in the dumps and sludge dumps are represented predominantly by rocks of deep horizons, contain trace elements of many metals and have absolutely no organic components, nitrogen and phosphorus. A substantiation of plant species for biological reclamation (greening) of man-made objects consisting of iron ore mining and enrichment waste has been carried out. It is recommended to plant seedlings of poplars (Pópulus), maples (Acer), acacia (Robinia), pine (Pinus) as well as oleaster shrubs (Elaeagnus) and amorpha (Amorpha) directly on the rock with local excavation of holes on horizontal and slightly inclined areas of dumps. Landscaping of steep slopes (30-40°) and the surface of sludge storage facilities is proposed to be carried out by stimulating natural self-overgrowth by applying (including by hydraulic method) a mixture of seeds of perennial grasses, trees and shrubs along with mineral fertilizers and humus of organic substances. The surface of sludge storages, due to the high degree of salinity and "cementation" of the substrate, before planting plants, requires obligatory soiling with a layer of at least 200 mm of chernozem or a mixture of chernozem with loam, followed by planting of xerophyte plants: meadow brome (Lolium pratense), straight brome (Bromus erectus Huds)), rye - triticale (Triticosecale). [ABSTRACT FROM AUTHOR]

In the field of rock mechanics, the stress–seepage–damage coupling numerical simulation of rock has always been a hot topic but a difficult problem. Based on this background, we newly derive the smoothed particle hydrodynamics (SPH) form of the seepage equation and a two-dimensional (2D) stress–seepage–damage coupling constitutive model. The proposed coupling model considers the heterogeneity of the engineering rock mass and overcomes the difficulty of the conventional SPH algorithm in stress–seepage–damage calculation. Stable one-dimensional (1D) seepage is first simulated to verify the correctness of the seepage equation and that the simulation results coincide with traditional analytical solutions. Then two triaxial compression experiments considering seepage and no-seepage conditions are simulated to show that the coupled model can well simulate the progressive rock failure process and the change in permeability. The correctness of the coupling model is verified by comparing the simulated results with experimental results. The existence of a seepage field advances the initial cracking time and weakens the peak strength of the rock. Finally, the progressive damage processes of surrounding rock excavation under unloading action are simulated, showing that stress–seepage–damage coupling model has application prospects in rock engineering. The research results may provide some references for the application of the SPH method in the stress–seepage–damage coupling simulation of rock. [ABSTRACT FROM AUTHOR]

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This article provides the discussion on the evaluation of existing rock excavatability of tropical weathered rocks of granite and quartz type in Malaysia. To do this, a case study was conducted in Nilai, Negeri Sembilan, Malaysia. The rock mass at this site was divided into several subzones which had the same lithology and weathering grade. A scanline survey was conducted to obtain rock mass characteristics like type of discontinuity, dip, dip direction, persistence, nature of filling, surface roughness, surface shape, joint roughness, spacing, and water flow. Collected samples were determined for their moisture content, petrographic analysis, and slake durability. The existing excavatability assessment was made and critically reviewed. Performance for excavatability of rock mass was obtained by performing trial excavation on-site using available machinery. A trial excavation was carried out using an excavator EX200 and EX400. The excavation method was compared with rock mass classifications like rock mass rating (RMR) and Q system and other existing excavatability classification systems. The existing classification system was compared with the production rate of excavation methods used in surface excavation work at road construction sites. This paper presents findings from field work and laboratory tests to obtain rock mass and rock material properties in quartz and granite areas. Next, the parameters are compared to the existing excavatability assessment method, and the results are also presented. There is also an urgent need for an excavatability classification system that considers different rock types according to the geological parameters that are significant to surface excavation in tropical regions. [ABSTRACT FROM AUTHOR]

Due to the complexity of the talus-like rock mass with different values of volumetric block proportion (VPB), it is thus crucial to explore the VBP effect on the excavation-induced ground responses. We conduct a series of 2D DEM (discrete element method) simulations on a common circular tunnel excavation in the talus-like rock mass with different VBPs (0%, 15%, 50%, 85% and 100%). For each VBP, two support scenarios, i.e., unsupported and supported by a rigid lining, are considered. The micro characteristics of the excavation-induced ground responses, including the contact force, force chain, coordination number and shear-slip contact, and the stress distribution and ground settlement are elaborated in detail. Accordingly, three types of talus-like rock masses are identified as soil-, hybrid- and rock-types, corresponding to VBP = 0–15%, 50%, and 85–100%, respectively. It is found that the lining support is essential for maintaining the ground stability of a tunnel excavation in the soil- and hybrid-type talus-like rock masses while the backbones formed by rock blocks in the rock-type talus-like rock mass can provide a certain support for the surrounding ground. Our findings have important implications for optimizing the construction scheme of tunnel excavation in different types of talus-like rock masses. [ABSTRACT FROM AUTHOR]

The mining of deep coal resources occurs in a high-stress geological environment as well as an engineering environment of rock excavation and unloading. Research on the re-bearing capacity characteristics and damage mechanism of rock masses damaged by peak front unloading is critical in revealing the destabilization and rupture law of deep rock bodies. The triaxial pre-peak unloading point was controlled to prepare damaged sandstone specimens, and the RMT-150C rock mechanics test loading system and the AEwin USB-type acoustic emission monitor were used to perform uniaxial reloading tests on the pre-peak unloading-damaged sandstone and to monitor the acoustic emission signals during the rupture process. Among them, the peak front unloading point was set to 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90% of the peak strength at 10 MPa of the surrounding pressure for a total of 11 working conditions. The test results show that: (1) The degree of unloading before the peak controls the uniaxial reload deformation characteristics of sandstone. The higher the unloading point, the faster the deformation of the rock sample, even directly into the crack instability extension stage, and the sandstone deformation characteristics transform from plastic—elastic to elastic—viscous. (2) The cumulative energy characteristics of the 40% to 60% sandstone at the unloading point are comparable to those of the complete sandstone and are separated into smooth, steady growth, and secondary smooth phases. The acoustic emission energy characteristics of the 65% and 70% sandstone at the unloading point are mostly focused on during the crack expansion stage. The sandstone's acoustic emission energy characteristics exhibit a "double peak" occurrence at 75% of the unloading point. The cumulative energy characteristics of the 80% to 90% sandstone at the unloading point reveal a "stepped" rise. (3) Sandstone's pre-peak unloading rupture morphology influences the reload damage characteristics: 40% to 70% of the specimens at the unloading point exhibit "Y"-type double-slope shear damage features. The predominant cause of specimen damage in 75% of the specimens at the unloading point is secondary primary cracks based on the pre-peak tensile rupture pattern. The damage path of 80% to 90% of the specimens at the point of unloading occurs in shear damage along the pre-peak unloading rupture pattern. (4) A closed crack mechanics analysis model under uniaxial reload was established, and the basic solution of pseudo-force for fine microcracks subjected to far-field stress, the stress intensity factor at the crack tip, and the crack fracture angle were theoretically derived. Furthermore, the relationship between the fracture angle θ of rock compression-shear cracks, the crack angle β, and the friction coefficient f at the crack surface was clarified. [ABSTRACT FROM AUTHOR]

Blasting has been proven to be the most cost-effective method for rock excavation known to man. The cost-effectiveness advantage of blasting is overshadowed by its unpleasant environmental problems, particularly at construction sites close to human settlements and public utilities. Therefore, efforts are required to develop closed-form equations that can accurately predict environmental problems associated with blasting. This study proposes an ANN-based closed-form explicit equation for forecasting airblast overpressure (AOp) at multiple construction sites in South Korea. Nine important factors that affect AOp generation were used to develop the model. First, a stand-alone ANN was initiated, and the hyperparameters of the optimum ANN structure were tuned using two novel and robust metaheuristic algorithms: the slime mould algorithm (SMA) and multi-verse optimization (MVO). To appraise the predictive accuracy of the developed soft computing models, multilinear regression (MLR) and a generalized empirical predictor were developed for comparison. The analysis showed that the SMA-ANN and MVO-ANN models predicted AOp with the highest accuracy compared with the other models. The two hybrid ANN-based models were transformed into closed-form and explicit equations to aid in the easy forecasting of AOp when planning a blasting round at construction sites. The developed model equations were validated for practical engineering applications and a comprehensive relative importance analysis of the AOp input parameters was performed. The relevance importance analysis shows that the rock mass rating (RMR), charge per delay (Q), and monitoring distance (DIS) have the highest impacts on AOp. [ABSTRACT FROM AUTHOR]

Aiming at geological disasters triggered by fracture zones in the surrounding rock mass during the excavation of deep railway tunnels, deformation and failure of the surrounding rock mass triggered by sudden changes of rock quality encountered in a tunnel excavation project were investigated. This research conducted an analysis of a field case: the Daliang Tunnel on the Gansu–Qinghai section of the Lanzhou–Urumuqi second double-track railway in China. The deformation profiles of the surrounding rock mass at different distances from the fracture zone was evaluated. The deformation of the surrounding rock mass in and around the fracture zone was explored by combining in-situ measurement, theoretical research, and numerical simulation. Furthermore, relationships of deformation of the surrounding rock mass in the section of the fracture zone with the materials and length of advanced support as well as the excavation advance rate behind the fracture zone were elucidated. Analysis of the results indicated that there is an inflection point on the deformation curves of the surrounding rock mass far ahead of the fracture zone; however, it is difficult to observe the inflection point on deformation curves of the surrounding rock mass in engineering practice as the rocks have undergone substantial deformation before being exposed. A combination of material properties and length of advanced support is conducive to controlling the deformation of the surrounding rock mass in the fracture zone. Highlights: Deformation curves of surrounding rocks exposed ahead of a fracture zone have an inflection point. The efficiency is optimal when the length of advanced support is twice the width of the fracture zone. Fitted lines of deformation of support for surrounding rocks in the fracture zone pass through the origin. [ABSTRACT FROM AUTHOR]

To obtain time-dependent responses of rock in excavation engineering projects, a series of creep tests of dacite are conducted through stepwise unloading of confining pressure. Based on the test results, time-dependent behaviour and unloading failure mechanism of dacite are studied in terms of creep rate, failure mode, long-term strength, and time-dependent damage. According to the creep rate, creep deformation can be divided into decelerating creep stage, steady creep stage, and accelerating creep stage during the last unloading failure process. Time-dependent deformation exhibits an anisotropic characteristic. Local shear bands are found in failed samples, which is markedly different from tensile failure in a short-term unloading test. Time-dependent damage of dacite under unloading condition is the result of combined effects of cracks. Creep failure of dacite under unloading condition caused by concentrating in a local zone and coalescing to form one or more macroscopic shear bands. This study gives an insight to understand the mechanism of unloading creep failure of rock and provides an experimental foundation for developing a time-dependent constitutive model under unloading condition. [ABSTRACT FROM AUTHOR]

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The quality of excavated and unloaded rock masses on steep and high slopes in cold regions is prone to deterioration, which in turn affects the long-term stability and safety of excavated slopes. Based on a triaxial unloading-damage test of sandstone, the unloading quantity was used to analyze the evolution law of unloading damage; a freeze-thaw cycle test of the unloaded-damaged samples was carried out, and it was found that the average change in porosity and the reloading peak strength damage rate after freeze-thaw increased with the increase in the number of freeze-thaw cycles, and the porosity change characteristics were independent of the value of the confining pressure at the time of the unloading damage. An exponential decay model was used, and based on the average change in porosity after freeze-thaw, a freeze-thaw strength decay model that can take into account the effect of confining pressure was established, and its ability to predict the strength decay of unloaded-damaged rock samples after freeze-thaw was verified by experimental data. The research results provide a reference for the evaluation of freeze-thaw degradation of unloaded rock masses during slope excavation in cold regions. [ABSTRACT FROM AUTHOR]

Based on the actual engineering geological survey, the mechanical response mechanism and sliding surface characteristics of the interbedded slope containing six layers of soft and hard rock during excavation under heavy rain conditions are studied by numerical simulation, and the composite sliding surface stability algorithm of the layered slope is established by using the penalty function. The research shows that, during the excavation, the distribution characteristics of stress, strain, plastic zone, and horizontal displacement along the bedding plane are obvious; the stress is concentrated in the hard rock layer; however, the strain and plastic zone are concentrated in the soft rock layer. When the ratio of the maximum vertical displacement to the maximum horizontal displacement is less than 1.85, the slope will slide. According to the relative position of the soft rock layer and the toe of the slope, the sliding surface of soft and hard rock interbedded slope can be divided into two types, namely, circular-straight sliding surface and circular-straight-circular sliding surface. The verification shows that the composite sliding surface algorithm objectively reflects the destruction of the slope by bedding sliding and can reasonably evaluate the safety of soft and hard rock interbedded slope. [ABSTRACT FROM AUTHOR]

As the hydropower development strategies of China continue to be implemented, a host of large hydropower projects have been completed or are being constructed in southwest China. During construction of the Jinchuan hydropower station, this study examined the stability of the surrounding rock during the excavation and unloading of hydraulic tunnels under demanding geological conditions. Microseismic (MS) monitoring technology was employed to monitor the deformation and failure of the surrounding rock online and in real time, based on engineering geological data and site surveys. To analyze the stability of the surrounding rock in the spillway tunnel and to study the temporal and spatial evolution characteristics of MS events, source parameter analysis and numerical modeling were performed. The 3D finite-difference numerical modeling software FLAC3D was used to simulate the mechanical response of the surrounding rock during the excavation and unloading of the spillway tunnel and the diversion tunnel. The numerical modeling results were compared with the monitoring results and site surveys to determine the failure mechanisms of the surrounding rock during the construction and unloading of the hydraulic tunnels. The research results can serve as a guide for studying the stability of the surrounding rock in similar hydraulic tunnels. [ABSTRACT FROM AUTHOR]

Hard rock excavation affects excavation efficiency. During excavation, the cutoff teeth of the tunnel boring machine are severely worn or even fractured. However, the traditional blasting methods of excavation can lead to various safety problems. A new kind of stone crusher is urgently needed in practical engineering. In this study, the finite difference analysis software was employed to analyze the key drilling fracturing parameters (borehole diameter, borehole spacing, and borehole number) and discuss the effect of the rupture zone formed by multiple boreholes on the damage to the surrounding rock. The research results showed that the hard rock was more easily cracked with an increase in the diameter of the drilling hole. Decreasing the hole pitch strengthened the cracking effects, and increasing the number of drilling holes also increased the number of fracture zones. This study might be of great theoretical and practical significance in developing a new kind of stone crusher and enhancing the excavating efficiency. [ABSTRACT FROM AUTHOR]

A roof fall hazard is still one of the major threats in the underground mining industry. Each such type of event always brings great risk to miners and causes serious interruptions in the process of rock excavation. In general, the possibility of roof fall hazard occurrence is directly related to the local geology, the presence of horizontal stresses as well as the type of excavation method and the efficacy of the utilized roof support. Due to the complexity of this process, it is important to continuously evaluate the roof fall risk, especially in long life-time places where a mining crew is often present. Within this article, a detailed review of the current methods of monitoring and evaluating roof fall risk was presented. Based on the extensive literature survey, different types of devices were described, and their advantages and disadvantages were pointed out. Furthermore, new trends in the area of roof fall risk monitoring were described and discussed. [ABSTRACT FROM AUTHOR]

To solve the large deformation problem of foliated rock masses in the Changning Tunnel, rock mechanics experiments and discrete fracture numerical simulation calculations were carried out. The mechanical properties and large deformation mechanism of the foliated rock mass are analyzed. The results show a large strength dispersion in jointed rocks with different dip angles. Rock strata compression bending and shear slip caused by the rock strata structure and tectonic stress are found to be the main causes of large deformation in the Changning Tunnel. Five negative Poisson's ratio (NPR) anchor-cable support schemes were designed, and field experiments were carried out. The NPR anchor cable can maintain a constant support force to strengthen the surrounding rock and release the deformation energy by allowing the deformation of the surrounding rock through a sliding device. In the field test, the number of anchor cables in the five support schemes was gradually reduced. The reliability of these support schemes was evaluated by various monitoring methods, including surrounding rock displacement, pressure between the primary support and surrounding rock, pressure between the primary support and secondary lining, internal stress of the steel arch, and deep displacement and axial force of the NPR anchor cable. The monitoring results show that the five schemes can control the large deformation of the surrounding rock to varying degrees. The maximum deformation of the surrounding rock under the original support scheme was greater than 1 m, but the maximum deformation under the NPR anchor cable support was less than 150 mm, and the support structures were also within the safe range. Therefore, NPR anchor cable support can effectively control the large deformation of the surrounding rock in the Changning Tunnel. The research results can provide a reference for the prevention and control of large deformation in similar projects. Highlights: The mechanical and failure characteristics of rock samples under different joint angles have been analyzed by rock mechanics tests. A numerical model of the tunnel composed of triangular blocks was established, and the collapse characteristics and mechanical characteristics of the surrounding rock after excavation were analyzed. Five supporting schemes of "NPR long anchor cable + PR short anchor cable + W-shaped steel strip + polyester fiber mesh" were proposed and tested on site. The axial force of the NPR anchor cable, pressure on the primary support, pressure between the primary support and secondary lining, stress of the steel arch, deep displacement of the surrounding rock, and deformation of the initial support were monitored. The mechanical characteristics of the surrounding rock and supporting structure were analyzed, and the reasonably reserved deformation was determined. The supporting effect of the NPR anchor cable was evaluated. [ABSTRACT FROM AUTHOR]

For deep hard–brittle rock mass engineering in a complicated hydrogeological environment, deformation and damage of the surrounding rock during excavation are often driven by the combined action of the dynamic seepage water and the strong unloading effect. To investigate the failure mechanism of a deep-buried rock mass under high seepage water pressure and high unloading rate, a series of conventional triaxial and unloading triaxial compression tests at different seepage water pressures and unloading rates were conducted on Erlang Mountain granite. The results confirmed that the dynamic seepage water pressure has a great influence on the mechanical properties and failure mechanism of rock because its splitting and expanding effects could stimulate crack generation and accelerate fractures. As the water pressure increased, the granite entered the nonlinear growth phase of the permeability coefficient earlier and entered the energy softening stage later. While the compressive strength and energy storage capacity of the rock were weakened gradually by dynamic seepage water, the permeability, energy hardening properties, and brittle failure mechanism could be magnified. Moreover, the effect of the strong unloading on the mechanical properties and damage mechanism of deep-buried granite was similar to that of the dynamic water pressure. Although the peak stress, peak strain, and energy storage capacity were reduced under the strong unloading effect, the permeability, brittle fracture characteristics, energy hardening properties and energy release rate could be significantly enhanced. Under the combined action of high seepage pressure and high unloading rate, the rock gradually decreased in hardness and increased in brittleness, and these changes were conducive to the instantaneous release of elastic strain energy in the failure stage. [ABSTRACT FROM AUTHOR]

After the excavation of an underground cavern, how the surrounding rock and the support work together to bear the excavation load is an important prerequisite to correctly analyze the joint force characteristics; effectively play the role of support; and ensure the safety, efficiency, and economy of underground cavern construction. Starting from the elastic-plastic load release characteristics of surrounding rock, this paper proposes a calculation method of the elastic load coefficient of surrounding rock and a graded release method of plastic load, which ensures the actual effect of the synergistic action of the first support and surrounding rock. Based on the elastic-plastic damage evolution characteristics of surrounding rock, a weighted iterative calculation method of elastic-plastic damage is proposed, and an evaluation method of load release ultimate bearing capacity of surrounding rock is determined. By monitoring the change law of rock acoustic wave velocity with surrounding rock damage, the relationship between the wave velocity and the damage coefficient of the surrounding rock in the excavation process is deduced, and it is proposed to determine the latest support time for first support by using the measured rock damage wave velocity. Through the numerical simulation analysis of a diversion tunnel excavation and support, the damage evolution law of the surrounding rock with the release of the excavation load is studied. The ultimate bearing capacity of various surrounding rocks and supporting opportunity is determined. The results demonstrate the validity and practicality of the analysis and calculation methods in this paper, which provide a new idea and analysis method for quantifying the bearing capacity of surrounding rock and determining the support timing in the excavation and support design of underground caverns. [ABSTRACT FROM AUTHOR]

The safe and sustainable design of rock slopes, open-pit mines, tunnels, foundations, and underground excavations requires appropriate and reliable estimation of rock strength and deformation characteristics. Cohesion () and angle of internal friction () are the two key parameters widely used to characterize the shear strength of materials. Thus, the prediction of these parameters is essential to evaluate the deformation and stability of any rock formation. In this study, four advanced machine learning (ML)-based intelligent prediction models, namely Lasso regression (LR), ridge regression (RR), decision tree (DT), and support vector machine (SVM), were developed to predict in (MPa) and in (°), with P-wave velocity in (m/s), density in (gm/cc), UCS in (MPa), and tensile strength in (MPa) as input parameters. The actual dataset having 199 data points with no missing data was allocated identically for each model with 70% for training and 30% for testing purposes. To enhance the performance of the developed models, an iterative 5-fold cross-validation method was used. The coefficient of determination (R2), mean absolute error (MAE), mean square error (MSE), root mean square error (RMSE), and a10-index were used as performance metrics to evaluate the optimal prediction model. The results revealed the SVM to be a more efficient model in predicting (R2 = 0.977) and (R2 = 0.916) than LR (: R2 = 0.928 and : R2 = 0.606), RR (: R2 = 0.961 and : R2 = 0.822), and DT (: R2 = 0.934 and : R2 = 0.607) on the testing data. Furthermore, to check the level of accuracy of the SVM model, a sensitivity analysis was performed on the testing data. The results showed that UCS and tensile strength were the most influential parameters in predicting and. The findings of this study contribute to long-term stability and deformation evaluation of rock masses in surface and subsurface rock excavations. [ABSTRACT FROM AUTHOR]

In view of the limitations of several existing stress measurement methods under extremely high stress conditions (stress − strength ratio σ / R c > 0.5), this paper proposes a slot relief method based on partial deformation recovery to measure rock mass surface stress under extremely high stress conditions and justifies its viability with the help of an infinite element model. This method is then used to measure and study a research tunnel in West China's Jinping II Hydropower Station, where the maximum stress measured reached 80 MPa. In the process of measurement, this method needs neither complete borehole core nor ultrahigh pressure equipment. On the contrary, the test equipment is easy to carry and operate on, suitable for rock mass surface stress measurement under extremely high stress conditions, and able to provide in situ stress measurements for cavern rockburst prevention and slope management. [ABSTRACT FROM AUTHOR]

While drilling and blasting with explosives is widely used for rock fragmentation in mining and civil engineering, its use is associated with rigorous safety and environmental constraints as blasting creates toxic fumes, vibrations and dust. In recent years, there has been a growing interest in transitioning from blasting with explosives to rock fragmentation without explosives. In this study, the potential of expansive cement (EC), aka soundless chemical demolition agent (SCDA), as an alternative to explosives to break hard rock under confinement is explored through a comprehensive experimental and numerical modelling study. To do so, two large-scale tests have been designed and carried out on 1 m × 1 m × 0.25 m panels made from high-strength concrete and subjected to planar, biaxial loading conditions. Such test configuration is designed to mimic a mining front subjected to biaxial stresses. Different EC drill hole patterns were tested and compared. The fragmentation behaviour due to EC was first examined with five particle flow code (PFC2D) models simulating different EC drill hole patterns. Two panel designs were retained for the large-scale experiment. It is found that rock breakage with EC under confinement is feasible and promising, especially when the optimized drill pattern from numerical modelling is adopted. It is demonstrated that discrete element modeling with PFC2D can be used effectively to design and optimize the EC drill hole pattern under biaxial confinement. The findings of this study could set the stage for numerous future applications of EC for rock fragmentation of subsurface hard rock excavations such as shafts, tunnels, and mine openings. Highlights: PFC2D models are developed to examine the efficiency of expansive cement to fragment a panel under biaxial loading. Both modelling and large-scale test results indicate that panel breaks more effectively when relief holes are employed in both loading directions. Concrete panel #2 is successfully fractured using expansive cement while both in-plane and bulging failure mechanisms are observed during the test. [ABSTRACT FROM AUTHOR]

• The fractal characteristics of concrete fractures in blast tests are investigated. • An analysis of internal energy and kinetic energy of concrete is conducted. • The borehole wall pressure (BWP) distribution is theoretically analyzed. • A smooth blasting scheme to protect the stability of surrounding rock is proposed. The decoupled charge structure is often used in controlled blasting. However, in actual engineering scenarios, boreholes are typically horizontal or inclined. The explosive is close to the borehole wall because of gravity action, resulting in an eccentric charge structure. In this study, concentric and eccentric decoupled charge blasting tests were conducted on 250 mm × 250 mm × 150 mm cuboid concrete specimens. The blast-induced fracture propagation behavior was evaluated using digital image correlation (DIC) technology, and surface fracture networks were extracted by image processing to investigate the fractal characteristics. A three-dimensional finite element model was established and verified using experimental data to reveal the influencing mechanism of the coupling medium and eccentricity coefficient on concrete fractures from the energy perspective. Finally, the borehole wall pressure (BWP) and displacement distribution with different charge structures and coupling media are analyzed theoretically, and the application of an eccentric charge structure in smooth blasting is discussed. The results reveal that nonequivalent BWP and displacement are produced in eccentric charge blasting, with a more evident crushed zone appearing on the coupled side owing to the higher energy utilization efficiency of the explosive. Sand had the largest fracture volume fraction ratio between the coupled and decoupled sides, effectively controlling the damage level on the decoupled side. The proposed eccentric decoupled charge-blasting scheme produced directional damage effects in the field test, maximizing the failure of the excavation rock while reducing the damage level to the reserved rock. [ABSTRACT FROM AUTHOR]

Microwave-assisted rock-breaking is highly promising in the process of hard rock tunnel excavation due to its safety and high efficiency. Water plays a pivotal role in the microwave heating process, significantly impacting the effectiveness of microwave-assisted rock fragmentation. Nevertheless, there is a lack of comprehensive research on the influence of water in the process of microwave heating of rocks. This study investigated the influence of water on the response characteristics of granite under microwave irradiation by analyzing the changes in the real-time acoustic emission (AE) signals, porosity, wave velocity, and uniaxial compressive strength of samples with different levels of water saturation. The experimental results revealed the real-time AE characteristics of rock samples were categorized into three periods: a quiet period, a violent period, and an attenuation period. The maximum temperature in the quiet period was about 150 ℃, resulting in the proliferation of mineral crystal defects under the action of water, and the intensity of AE counts was positively correlated with water saturation. Simultaneously, the degree of thermal damage to porosity, wave velocity, and uniaxial compressive strength also increased with increasing water saturation. During the violent and attenuation periods, the activity of AE signals increased, yet remained largely unaffected by the the water saturation level. Moreover, the presence of water facilitated the transition of rock samples from elastic to ductile behavior under microwave irradiation. This investigation holds significant importance for the practical application and advancement of water utilization in microwave-assisted rock fragmentation technology. [ABSTRACT FROM AUTHOR]

The deep excavation unloading stress path and initial high stress difference (σ20-σ30\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\sigma_{2}^{0} - \sigma_{3}^{0}$$\end{document}) are distinctive features that differentiate deep engineering from shallow engineering. To investigate the mechanism of deep hard rock failure induced by initial stress differences under excavation unloading stress paths, a series of typical true triaxial unloading tests are conducted using a true triaxial experimental system. The results show that as the initial stress difference increases, there is a gradual enhancement in both the strength, brittleness and ultimate energy storage capacity of the rock. Additionally, the direction of rock fracture propagation gradually aligns with σ2, leading to an increase in the macroscopic failure angle of the rock. Moreover, the roughness of the rock fracture surface decreases, while transgranular and tensile fractures become more prevalent, often exhibiting sudden, high-energy fracture events. Building upon the non-uniform stress distribution characteristics induced by the initial stress difference, a principle governing the differential development of rock fractures is proposed. This principle underscores the pivotal role of the initial stress difference in triggering spalling of the surrounding rock parallel to the sidewall. Furthermore, a functional relationship between the initial stress difference and the propensity for rockburst events is established. These findings hold significant implications for understanding the failure mechanisms of surrounding rock in deep hard rock engineering excavations and for evaluating the risks associated with spalling and rockburst hazards. [ABSTRACT FROM AUTHOR]

• True triaxial loading tests were carried out on porous cubic specimens of five brittle rocks with and without prefabricated structural planes. • The presence of structural planes promoted the occurrence of rockbursts, changed the location of damage, and increased the destructiveness of rockbursts. Structural planes could effectively promote rockbursts in Marble and ineffectively promote rockbursts in Gray sandstone. • The presence of structural planes altered the acoustic emission processes and parameters. However, the degree and scale of damage derived from the rock were also altered. • In Marble, the rockburst modes of specimens with structural planes included flexural strain and slip strain. In Red sandstone, Gray sandstone, Granite, and Limestone, the rockburst modes of specimens with structural planes included compression shear strain and slip strain. The slip strain rockburst mode should be the final damage mode of a specimen with structural planes; this mode appears as a series of rockbursts. After deep rock excavation, rockbursts can easily occur. The structural plane and rock properties play important roles in controlling rockbursts. To study the role of structural planes and rock properties in controlling rockbursts in the peripheral rocks of tunnels, five different brittle and hard rocks (Red sandstone, Gray sandstone, Granite,Marble, and Limestone) were tested, and cubic specimens with round holes (100 mm*100 mm*100 mm, Φ = 50 mm) and prefabricated fissures were used to simulate the structural plane. A high-speed camera system and an acoustic emission system were used to monitor the damage and microfracture processes of the surrounding rock. The damage process, acoustic emission characteristics, and damage patterns of five brittle rocks with and without specimens with structural planes during loading were comparatively analyzed. The main conclusions were as follows. (1) The presence of structural planes in the rock mass changed the stress and energy propagation paths in the rock mass, resulting in stress concentration; the structural planes in the five brittle rocks could not store energy, hence increasing the propensity for rockbursts. Structural planes in the Marble had the most obvious effect on the promotion of rockbursts. However, structural planes in the Gray sandstone had the weakest effect on the promotion of rockbursts. (2) The presence of structural planes significantly increased the rockburst intensity. In the Marble, regardless of the presence of structural planes, the damage mode of the surrounding rock was mainly shear flexural damage. However, the fine particle contents of specimens with structural planes were significantly higher than those without structural planes. Thus, the rockburst intensities of specimens with structural planes were greater than those without structural planes. For the Red sandstone, Gray sandstone, Granite and Limestone, the surrounding rock specimens with structural planes experienced mainly violent shear ejection damage. (3) The distribution of RA and AF and the number of ruptures in the specimens with and without structural planes were obviously changed, and the numbers of rupture events in the Red sandstone, Gray sandstone, and Granite specimens obviously increased because of the presence of structural planes. The numbers of rupture events for Marble and Limestone specimens significantly decreased due to the presence of structural planes. Gray sandstone and Granite had the most rupture events. (4) Different brittle rock specimens with structural planes had different sizes. The degrees of damage were observed to significantly increase for a period. In addition, the rock body experienced additional internal shear rupture, which intensified due to the structural planes and the tunnels between the rock columns. The ruptures were caused by the destruction of the structural planes during rockburst, and they served as predictions and early warnings, thus providing a certain reference basis. (5) In the Marble during rockbursts, there were structural planes that underwent flexural strain and slip strain. In the Red sandstone, Gray sandstone, and Granite during rockbursts, there were structural planes that underwent compression shear strain and slip strain. The disaster chain was introduced to understand and discuss the mechanism of slip strain for the development of rockburst in structural planes, which should be the final damage form. The disaster chain was a series of rockbursts caused by compression shear and slip of specimens with structural planes. The development of rockbursts in specimens with structural planes occurred sequentially. The final damage pattern was the end result of the development of a series of rockbursts in specimens with structural planes. [ABSTRACT FROM AUTHOR]

• Developed a machine-learning model for predicting TBM disc cutter wear. • Incorporated individual disc cutter travel lengths, enhancing accuracy. • Model showcased an impressive RMSE of 0.049 mm per ring excavation length. • Utilized 17,947 datasets from the Daegok-Sosa TBM project for validation. Replacing damaged or worn disc cutters is costly and time-consuming, which can significantly reduce the utilization and advance rate of tunnel boring machines (TBMs). Accurate prediction of disc cutter life is crucial for optimizing TBM operation in tunneling projects. This study introduces a machine-learning-based prediction model designed to forecast disc cutter wear, incorporating the analysis of each cutter's travel length and the intervals between cutterhead interventions (CHI). The principle underlying the developed machine learning approach involves usage of multiple learning algorithms, ensemble learning methods, and a sophisticated analysis of these factors to identify patterns and relationships essential for effectively predicting wear rates. Employing CHI report data from the Daegok–Sosa tunneling project's hard rock excavation, the model evaluates 15 wear-influencing factors, providing precise wear predictions. This study proposes the ensemble machine learning (ML) methods, namely Random Forest (RF) and Extreme Gradient Boosting (XGB), for accurate wear rate predictions and discern influential factors. The proposed model demonstrated exceptional prediction accuracy, as evidenced by a root mean square error of 0.049 mm for a single-ring excavation length. Notably, this model innovatively accounts for variable wear rates of cutters based on the individual cutter travel lengths as well as other geological and operational parameters. Furthermore, the predicted cutter consumption rate showed reasonable correspondence when compared to the actual CHI records. The proposed model is expected to improve existing disc cutter life prediction methods and reduce the cost and time for replacing damaged or worn disc cutters. [ABSTRACT FROM AUTHOR]

In rock tunnel excavation using the drilling and blasting method, controlling overbreak and underbreak relies heavily on the careful selection and optimization of blasthole parameters, such as number and spacing. To achieve accurate blasting control, it is essential to automatically detect, acquire, and optimize the number and spacing of blastholes on the tunnel face. With the development of image recognition techniques based on convolutional neural networks (CNNs), there are new opportunities for blasthole detection. This study proposes an improved faster region-based CNN (Faster R-CNN) for blasthole detection and automatic acquisition of blasthole number and spacing. The proposed network adopts modular design concepts, including top-down feature fusion, two-stage training, false detection blasthole filtering, and blasthole parameter acquisition. These strategies enable efficient feature extraction, aggregation, filtering, and range finding, thereby significantly enhancing the intelligent acquisition ability of the overall blasthole parameters on the tunnel face. The improved CNNs are validated by an experimental study, and their precision, recall, and F1 score are superior to those of SqueezeNet, VGG-16, and ResNet-50. The distance data from the blasthole image-based detection results can effectively indicate the horizontal and vertical spacings of different types of blastholes on the tunnel face. [ABSTRACT FROM AUTHOR]

• A case of "closed-door" collapse is discussed, including the collapse phenomenon and collapse causes. • A new understanding, based on on-site surveys and monitoring, has been obtained: the "closed-door" collapse is a type of destruction that only occurs when both the surrounding rock and the support structure fail simultaneously. • The mechanism of the "closed-door" collapse was analyzed from the perspective of the surrounding rock and support. • The treatment method and prevention principles for the "closed-door" collapse were proposed. The prevention of "closed door" collapse is crucial for tunnel construction safety and progress assurance. To address the challenge of preventing "closed door" collapse, a study was conducted based on a case of tunnel collapse. This tunnel passes through sections of fractured rock with groundwater development. The main research methods are on-site monitoring and mechanical model calculations. The research findings indicate that weak fractured rock, groundwater, initial support quality issues, long trailing distances, and extensive excavation footage all contributed to the "closed door" collapse. On-site monitoring in the fractured rock section showed the tunnel deformation is high sensitivity to construction disturbances. Even without disturbances, tunnel deformation gradually increases. This contributes about 20% of the total deformation, worsening surrounding rock damage and loosening. Additionally, the initial support exhibits cantilever arch mechanical response characteristics due to excavation of the surrounding rock on one side of its lower part. The mechanical model calculation has verified that under a cantilever arch state, the initial support lacks the bearing capacity to withstand loose load. The continuous deformation of the surrounding rock damages the collapsed body, generating loose load. Excavation of the surrounding rock beneath the initial support arch foot changed the structure from a fixed arch to a cantilever arch, ultimately leading to the joint failure of the surrounding rock-support structure system. This is the mechanism behind the collapse. By combining the convergence confinement method, the influence mechanism of factors such as excavation footage and trailing distance on the "closed door" collapse was further elucidated. Finally, according to the stability evaluation of the collapsed cavity, a strategy of "supporting first and then grouting" is adopted for collapse treatment. Drawing from the understanding of the "closed door" collapse mechanism, the following principles for collapse prevention are proposed: "small excavation footage, ensuring the quality of initial support, short trailing distance, quick support, frequent measurement." [ABSTRACT FROM AUTHOR]

Due to the unique nature of the coal mining industry, safety is always one highly upheld premise of high production and high efficiency. According to the stress adjustment characteristics of the surrounding rocks in roadway excavation under a nondisruptive environment, the stress paths of unloading confining pressure and loading axial pressure were designed creatively and vividly, and the coal mechanical properties and energy evolution law under different loading axial pressure rates were studied through a series of experiments. As the loading axial pressure rate increases, the mechanical parameters at the time of coal failure show a nonlinear increase in the peak strength, the confining pressure, and the axial strain, while the variation laws of lateral strain and volumetric strain are not obvious. In addition, the failure mode transfers from the brittle failure to the ductile failure. In terms of energy, the positive work done by the axial pressure, the total work, and the elastic strain energy tend to increase nonlinearly, while the negative work done by the confining pressure and the plastic strain energy increase conversely. The elastic strain energy conversion rate increases logarithmically, indicating that a higher loading axial pressure rate tends to increase the probability and strength of coal instantaneous failure and subsequent dynamic behaviors. The research results reveal that providing an appropriate pressure relief and timely support after the roadway excavation in the actual production process can effectively reduce the energy level of the environment at the location of the surrounding rock support system, which is conducive to the roadway support and the surrounding rock stability control. Furtherly, it has important reference value for the roadway excavation and other underground engineering excavation and support operations and is of great significance to promote the development of deep resources. [ABSTRACT FROM AUTHOR]

In view of the geological environment, in which the upper part is the "soft" layer of completely weathered siliceous rock and the lower part is the "hard" layer of weakly weathered limestone, the rail surface line is designed to pass through the interface between the upper "soft" layer and lower "hard" layer. First, the MIDAS/GTS software was used to comprehensively simulate the stress and deformation law of surrounded rock under three excavation methods, which are the positive benching and retaining core soil method, CRD method, and double side drift method, for selecting the appropriate excavation method. After the excavation method was determined, the rule of change in the stress and deformation of the surrounded rock with time in the actual excavation process was analyzed by field monitoring means. Finally, on the basis of the findings in the numerical analysis as well as the field monitoring, the engineering characteristics, such as the stress and deformation of the surrounded rock during the excavation of deep buried tunnels in the upper-soft lower-hard ground, were analyzed. The results revealed the following: (1) Under all three excavation methods, the tunnel deformation was small and met the requirements for tunnel deformation control. (2) Due to the different excavation support sequence, the distribution of lining bending moment of the three excavation methods was widely different. The bending moment of the lining produced by the positive benching method was far less than that of the other two methods. (3) Due to the difference in lithology, the stress of the tunnel lining in the thick upper "soft" and "hard" strata was mainly concentrated on the upper soft rock area, while the stress in the lower hard rock area was relatively small, and the lining stress value generated using the three excavation methods was relatively large. In general, the deformation and stress in the positive benching method construction were less than those in the other two methods. In addition, the positive benching method was convenient for mechanized operation, the construction progress was fast, and the cost was relatively low. Therefore, the positive benching and retaining core soil method is adoptable for this kind of tunnel. (4) The measured stress and deformation at the rail surface line exhibited a change law of first increase, and subsequently, this tended to be stable. The change in stress-time can be expressed by the Boltzmann function, and the change in deformation with time can be well expressed by exponential functions. (5) The stress value and deformation value detected in the actual excavation were greater than the results of the theoretical numerical analysis. However, the findings in the theoretical numerical analysis still have certain guiding significance for actual excavation. [ABSTRACT FROM AUTHOR]