Rock Strength Research Articles

Measurement While Drilling Method for Estimating the Uniaxial Compressive Strength of Rocks Considering Frictional Dissipation Energy

Measurement While Drilling Method for Estimating the Uniaxial Compressive Strength of Rocks Considering Frictional Dissipation Energy

A comparative study of three types of strength criteria for rocks

Currently, the unified strength criterion (USC), the three-dimensional Hoek-Brown (3D H-B) criterion and the generalized unified strength theory (GUST) are the three types of typical rock strength criteria. In this paper, a comparative study of the three types of strength criteria is performed for rocks. Based on the nonlinear characteristics of rock strength on meridian and deviatoric planes, the USC can predict rock strength under triaxial stress state. The USC is composed of two failure functions on meridian and deviatoric planes. The failure surface of the USC in principal stress space satisfies smoothness and convexity. The predicted strength for five types of rock under the true triaxial tests were compared among the USC, the GUST, and the 3D H-B criterion. The results indicate that the USC can effectively reflect the influence of the intermediate principal stress on rock strength and accurately predict rock strength under both triaxial tension (σ1=σ2>σ3) and triaxial compression (σ1>σ2=σ3). Additionally, the conventional triaxial tests were conducted on other eight types of rock to measure the strength on meridian plane. The predicted strengths for the eight types of rock on meridian plane were compared between the USC and the original H-B, which suggests that the USC is suitable for various types of rock and provides higher accuracy.

Experimental study on optimization of abrasive water jet process parameters

Abstract In order to improve the mining speed of coal mine roadway and fundamentally solve the problem of mining imbalance, the abrasive water jet technology is used to cut rocks in front of mechanical tools to achieve efficient improvement of coal mine roadway mining efficiency. Based on the existing high pressure pure water jet test equipment, the abrasive water jet test platform was built, and the uniaxial compressive strength of soft and hard rock was obtained by testing the rock mechanical properties. The effect of jet pressure, target distance, transverse velocity and jet impact Angle on rock cutting is studied by using control variable method. According to the single factor test analysis, L16 (44) four-factor four-level orthogonal test analysis table is selected to carry out orthogonal tests on granite and sandstone respectively. The results of range analysis and variance analysis show that the main and secondary relationships of abrasive water jet factors are as follows: transverse velocity > jet pressure > jet inclination > target distance. The optimal jet parameters are when jet pressure is 40 MPa, target distance is 5mm, transverse velocity is 2mm/s and jet inclination is 10°.

Accuracy of Point Load Index and Brazilian Tensile Strength in Predicting the Uniaxial Compressive Strength of the Rocks: A Comparative Study

Uniaxial compressive strength (UCS) of rocks is one of the main parameters required in the design of geotechnical projects such as tunnels, dams, or rock slopes. According to the literature, there are a large number of predictive regression equations to evaluate the UCS from the point load index (PLI) and Brazilian tensile strength (BTS). However, the equations developed in previous studies have different accuracies in UCS prediction. A more accurate prediction of the UCS will result in a more appropriate design of the geotechnical project, and thus ensure its success during operation. In the present paper, a comparative study was conducted between the accuracy of PLI and BTS in predicting the UCS of the limestone and sandstone. Moreover, the role of porosity (n) on the accuracy of predicting the UCS from PLI and BTS was investigated. Some statistical indices were used to investigating the accuracy of predictive regression equations of UCS. The results revealed that the UCS of rocks can be predicted with a higher accuracy using BTS compared with PLI. Also, the findings showed that the n had a significant role in increasing the accuracy of PLI- and BTS-based regression equations of the UCS predictive. The predictive equations established in the present study can be used in practical applications for indirect evaluation of limestone and sandstone UCS in the site of a geotechnical project.

Enhancing weathered slope stability assessment through the integration of slake durability index, elastic modulus of knocking ball, and electrical resistivity tomography.

This research assesses the stability of sedimentary rock slopes in Teloi, Sik, Kedah, by focusing on the mechanical properties of the rock layers and their susceptibility to weathering. Key tests include the slake durability index (SDI), elastic modulus of knocking ball (Ekb), and electrical resistivity tomography (ERT). The incorporation of electrical resistivity tomography (ERT) data through the virtual reality platform facilitates the visualization of subsurface conditions. The variability of strength characteristic of interbedded sedimentary rocks leads to the differential weathering of rock layers, which causes deterioration on the slope structure. The testing revealed significant variability in rock strength, with sandstone displaying higher durability (Id > 17.1%) and elasticity (Ekb: 0.97 to 29.31 GPa) compared to shale and siltstone, which exhibited lower durability and elasticity (Id < 2.2%, Ekb: 0.2 to 2.2 GPa). Utilizing the Wenner array setup, three distinct electrical resistivity lines were established to evaluate subsurface anomalies. The ERT profiles revealed variations in electrical resistivity among different rock types, identifying areas of weaker material, which are siltstone and shale, while high resistivity areas indicate sandstone. Kinematic analysis through the stereonet process revealed direct toppling as the primary failure mechanism, driven by the critical orientations of joint sets J1, J2, and J3. This aligns with on-site observations of hanging sandstone blocks prone to toppling failure. The findings of this research show that the slake durability index (SDI) and the elastic modulus of the knocking ball (Ekb) enhance the assessment of mechanical properties and weathering resistance of interbedded sedimentary rocks. The virtual reality platform was particularly helpful in analyzing and visualizing the sub-surface conditions and enhancing the evaluation of complex geological data. As a conclusion, this integrated method was helpful in the comprehensive geotechnical evaluation of the slopes, enabling the selection of effective stabilization measures by assessing the differential weathering of interbedded sedimentary rock and identifying potential failure zones.

Statistical analysis of thermally induced pre-existing microcracks and their influence on fracture behaviours of granite rock

Rocks containing varying degrees of microcracks have a significant influence on their mechanical behavior. Understanding the effect of pre-existing microcracks (PEMs) on rock fracture mechanisms has scientific and practical value in areas such as geothermal energy, nuclear waste disposal and deep mining. We employed a thermally induced approach to create PEMs in granite rock, and quantified characteristic parameters of PEMs by visualization methods, focusing on the quantitative relationships between the PEMs and the mechanical strength and acoustic emission (AE) properties of the rock. We find that the distribution characteristics of thermally induced PEMs obey a lognormal distribution, and the length of individual thermally induced PEMs is almost independent of temperature. The density and orientation of PEMs together determine the variation of the longitudinal wave velocity and rock strength, with the effect of microcrack density dominating. The AE signal suggests that PEMs can affect the fracture behavior and fracture mechanism, depending on the relative dominance of pre-existing and stress-induced microcracks. The AF-RA values show that PEMs lead to an important shift in the fracture mechanism of the rock. When the microcrack density is low, tensile mode dominates the rock failure. Conversely, the shear mechanism dominates the rock fracture.

Prediction model for the compressive strength of rock based on stacking ensemble learning and shapley additive explanations

Prediction model for the compressive strength of rock based on stacking ensemble learning and shapley additive explanations

Development and mechanical properties of nano SiO2 modified photosensitive resin for high-strength and high-brittleness 3D printing in rock reconstruction

3D printing technology, as a rapid prototyping method, can accurately reconstruct the internal structural characteristics of samples, making it highly promising for rock engineering applications. However, current 3D printing materials used to reconstruct rocks suffer from low strength and high ductility, which is inconsistent with the high strength and brittleness of natural rocks. This paper explores the use of silane coupling agents KH550 (γ-aminopropyl triethoxysilane) and KH570 (γ-methacryloxypropyl trimethoxysilane) to modify nano SiO2 powder. Through sample preparation and uniaxial compression tests, the mechanical properties and failure characteristics of the modified nano SiO2 powder were analyzed. The results indicate that, using the preparation method with a mass ratio of E-44 epoxy resin, KH550 modified nano SiO2 powder, and 593 curing agent at 80:40:26, the samples achieved an uniaxial compressive strength of up to 30.55 MPa without enhanced brittle post-processing. The failure characteristics exhibited significant axial tensile damage. Additionally, combining CT scanning technology demonstrated that the structural and mechanical properties of the samples can be effectively reproduced. Therefore, the 3D printing materials discussed in this paper provide a viable reference for accurately reconstructing high-strength and high-brittleness rock masses.

Hard rock fragmentation by dynamic conical pick indentation under confining pressure

Mechanical mining and excavation in deep metal mines can be regarded as the process of crushing hard rock by conical pick indentation. In this study, a confining pressure loading device was designed and used to carry out dynamic conical pick indentation crushing tests under confining pressure conditions on three types of granite with varying strengths, using the Split Hopkinson Pressure Bar (SHPB). The objective was to quantitatively investigate the effect of confining pressure and rock strength on the indentation crushing characteristics of deep hard rocks. The results indicate that as the confining pressure increases from 5 MPa to 20 MPa, the dimensional parameters such as volume, diameter and depth of the impact groove decrease linearly, while parameters such as the specific energy, indentation force, indentation index and energy utilization rate progressively increase. The increase in the confining pressure inhibits the formation of internal cracks in the rock, enhancing its resistance to pick indentation, which in turn makes rock fragmentation more difficult. This creates unfavorable conditions for efficient rock breaking. Furthermore, rock strength plays a crucial role in the pick indentation process. The higher the rock strength, the greater its resistance to pick indentation, leading to increased energy consumption, accelerated wear of the conical picks, and reduced efficiency in rock breaking.

Mechanical and fracture characteristics of weak microwave-absorbing sandstone under microwave irradiation: influence of pore water

Microwave radiation is an effective method to weaken the strength of hard rock, but this weakening effect is not obvious enough for weak microwave-absorbing rocks. This work focuses on the role of water in amplifying the effect of microwaves on weak microwave-absorbing rocks, by examining the bursting characteristics of the rocks as well as their physical and mechanical properties before blasting. The experimental results show that when subjected to microwave irradiation, and the time taken for this bursting decreases with higher microwave power. In addition, the surface temperature of saturated sandstone gradually rises with increased irradiation power and duration. Under high microwave power, the uniaxial compressive strength (UCS) of heated saturated sandstone notably decreases within the same irradiation duration. When the microwave power is low, the UCS of saturated sandstone remains relatively unchanged over time. The UCS of dry sandstone exhibits no significant alteration under identical irradiation power and duration. In conclusion, sandstone shows no significant change in its physical and mechanical properties during brief exposure to low-power microwave irradiation in its dry state. As water within the sandstone undergoes a phase transition from liquid to gas due to microwave irradiation, the resulting steam pressure causes the sandstone to rupture.

Pushing boundaries in slurry microtunneling: Innovations in microtunnel boring machine design for hard rock conditions

AbstractFor microtunneling in hard rock, as it is encountered very often in alpine tunneling, the continuous further development of technologies plays a key role to overcome the limitations in drive length and to improve performance. During the last decades, the application range of slurry microtunneling has been considerably extended and more demanding projects have been designed for underground utilities installations worldwide, including many sewage tunnels and hydropower plants. The prevailing ground conditions still play a key role and determine the limits for alignment design and the possible use of trenchless construction methods. In hard rock conditions with high rock strength and/or abrasivity, the applicability of slurry microtunneling has been especially limited in the non‐accessible diameter range in the past. With the new AVN 800 HR for hard rock microtunneling, Herrenknecht has developed a machine concept, enabling drives of up to 200 m, with precise steering of the MTBM. Longer drives, even through hard rock, make microtunneling a more economic, flexible, and more environmentally friendly construction method. New opportunities for clients and consultants in the planning of tunnel routes in alpine environments for different infrastructure installations can be considered, making trenchless installations even more cost‐effective, while improving public acceptance.

Study on failure mechanism of cracked coal rock and law of gas migration

China possesses abundant coal resources and has extensive potential for exploitation. Nevertheless, the coal rock exhibits low strength, and the coal seam fractures due to mining activities, leading to an increased rate of gas emission from the coal seam. This poses significant obstacles to the exploration and development of the coal seam. This paper focuses on studying the failure mechanism of fractured coal rock by conducting uniaxial and triaxial compression experiments on the coal rock found at the Wangpo coal mine site. Simultaneously, in conjunction with the findings from the field experiment, a gas migration model of the mining fracture field is constructed to elucidate the pattern of coal seam gas distribution during mining-induced disturbances. The study structure reveals that coal rock exhibits three distinct failure modes: tensile failure, shear failure, and tension-shear failure. The intricate fissure in the rock layer will intensify the unpredictability of rock collapse patterns. The compressive strength of coal rock diminishes as the confining pressure drops. The coal rock in the working face area will collapse as a result of the lack of confining pressure. In the rock strata above the mining fracture zone, the gas pressure is first higher and then significantly falls with time. After 100 days of ventilation, the low gas pressure area changes little, so to ensure the safety of the project, the ventilation time of the fully mechanized mining surface is at least 100 days. The research results will help to establish the core technology system of coal seam development and improve the competitiveness of coal seam resources in China.

Evaluation of the water weakening coefficient of sandstones by using non-destructive physical parameters

IntroductionThe presence of water significantly reduces the mechanical strength of rocks and induces various engineering geological hazards. The water weakening coefficient Kp is used to quantify this effect, defined as the ratio of wet uniaxial compressive strength to the dry value.MethodsA comprehensive physico-mechanical test was conducted on fifteen sandstones under dry and saturated conditions to predict the water weakening coefficient using easily obtainable physical parameters. Multiple linear regression was employed to establish the relationship between these parameters and the saturated water weakening coefficient.ResultsThe saturated water weakening coefficient decreases with increasing porosity and increases with higher Primary wave velocity (P-wave velocity). Rocks with higher porosity but lower P-wave velocity typically absorb more water. The P-wave velocity and clay mineral content were identified as the best predictors of the saturated water weakening coefficient (R2 = 0.82). Unsaturated water weakening coefficients at any water saturation level were well estimated using a previous exponential function.DiscussionThe roles of different clay minerals and P-wave velocity in the water weakening process of rocks are comprehensively discussed. This study enhances the understanding of the water weakening mechanism and provides an improved evaluation model for the water weakening coefficient of sandstones using physical parameters.

Development of an Automatic Rock Mass Classification System Using Digital Tunnel Face Mapping

To mitigate unforeseen incidents, such as key block failure or tunnel collapse during excavation, an appropriate support pattern that correlates with the geological conditions of the rock mass at the tunnel face should be designed. Rock mass evaluations should be conducted through geological face mapping during the construction phase, alongside predictions based on field investigations during the design phase. When marked discrepancies are identified, it is customary to convene an on-site evaluation involving a committee of experts. This study develops a digital tunnel face mapping system that utilises mobile devices to facilitate online evaluations during the construction phase. This system effectively replaces the traditional on-site field evaluation method. Tunnel face mapping can be promptly accomplished using images captured at the excavation face, enabling rapid analysis. In conjunction with the mapping capabilities, the developed system was designed to digitally store geological information, which includes parameters such as rock strength distribution, the spacing and length of discontinuities observed during the mapping process, as well as data pertaining to weathering and the groundwater conditions of those discontinuities. This information was then correlated with the rock mass rating sheet to automate the determination of ratings for each parameter, ultimately leading to a conclusive classification of the rock mass quality. By employing this system for tunnel face mapping and rock quality evaluation, we significantly reduced the discrepancies in the evaluation results that often arise due to the subjective judgement of geologists, as well as human errors that can occur throughout the rating process.

Case study on the influence of rock brittleness on the TBM tunnelling performance

Brittleness is an important mechanical property of rock. Accurately evaluating rock brittleness and its influence on the TBM tunnelling performance is necessary. In this work, via two practical engineering cases, with the aim of overcoming the difficulty of penetrating extremely hard rock (breccia fused tuff) in the Zhuxi\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z{\ ext{huxi}}$$\\end{document} project, the influence of rock brittleness on the TBM tunnelling performance was studied via comparative analysis with that Nabang\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Nabang$$\\end{document} project. Seven commonly used rock brittleness indices based on stress‒strain curves were summarized, and a brittleness evaluation method suitable for extremely hard rock was determined by introducing the normalized specific energy to obtain brittleness indices for two lithologies (breccia fused tuff and biotite hornblende plagioclase gneiss) in two projects. The influences of rock brittleness on penetration and the specific energy were compared and analysed. The results showed that the brittleness indices B3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B3$$\\end{document} and B5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B5$$\\end{document} were more suitable for evaluating rock brittleness. Rock brittleness influenced the TBM tunnelling performance, but this influence gradually decreased with decreasing uniaxial compressive strength (UCS\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$UCS$$\\end{document}), which is obviously less than that of the rock strength. When the UCS\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$UCS$$\\end{document} was lower than 150 MPa, the TBM tunnelling parameters could be adjusted within a significant margin to eliminate the influence of rock brittleness, which could be ignored when predicting the tunnelling performance. When the UCS\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$UCS$$\\end{document} was greater than 150 MPa, rock brittleness imposed a notable influence on the tunnelling performance, which must be considered when predicting the tunnelling performance. This research could provide reference data for evaluating the hard rock brittleness index and accurately predicting the TBM tunnelling performance in engineering practice.

Thermomechanical response and crack evolution of sandstone at elevated temperatures

Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O2 due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.

A novel method for identifying rock interfaces and fragmentation zones based on drilling response characteristics

The rapid measurement and acquisition of the fracture characteristics and strength of the surrounding rock are crucial for evaluating the stability of underground engineering. In this study, a laboratory/coal mine universal drilling test platform was developed to enable real-time measurement of drilling parameters. The testing results demonstrate that under identical rotation speed conditions, both thrust force and torque increase exponentially with increasing drilling speed, while under identical drilling speed conditions, both thrust force and torque decrease linearly with increasing rotation speed. In intact rock layers, variations in torque, thrust force, and drilling speed with depth remain relatively stable, in rock layer interfaces and fragmentation zones, sudden changes occur within a drill displacement range of approximately 3–7 mm, which become more pronounced as strength differences between adjacent rock layers increase.Based on the cutting mechanics model of drill bit, the evaluation index of drilling energy consumption of unit rock mass (Eη) is derived. Subsequently, based on drilling speed, rotation speed, thrust force, torque and energy index, a machine learning model for predicting rock strength is established using the LS-SVM nonlinear regression approach. Field practice has shown that drilling platform can effectively identify both the rock interface and range of fragmentation areas. The experimental results are of great value to the selection of supporting types in the process of coal mine roadway excavation.

Experimental study on rock drilling vibration of PDC bit in interbedded formations

Mastering the vibration characteristics of PDC bit, especially in interbedded formations, can help to explore reasonable bit failure control measures, achieve bit optimization and drilling optimization. This work used single rocks to construct different types of vertical and horizontal interbedded rocks with different interbedded properties, the experimental study obtained the bit vibration characteristics under single rock, sudden-changed rock, and alternating rock conditions. The vibration acceleration of a single rock is consistent with the rock strength. The acceleration increases with the increase of weight-on-bit and rotary speed, the influence of weight-on-bit is greater than that of rotary speed. The maximum amplitude of accelerations always occurs in the low frequency range of 0∼300 Hz, the difference between rocks is mainly reflected in the high frequency range greater than 400 Hz. When the drill bit suddenly crosses from soft rock to hard rock in the vertical interbedded formation, the acceleration increases rapidly, causing direct impact. When the drill bit suddenly crosses from hard rock to soft rock, the impact and acceleration attenuates slowly, which could cause fatigue damage to the drill bit and induce high-frequency vibration. The rapid and significant change in depth-of-cut is the fundamental reason for the impact generated when the bit crosses through the interlayer, and both the maximum and minimum depth-of-cut occur in the transition region. PDC bit alternately encountered soft and hard rocks in the horizontal interbedded formation, causing intensified vibration. The acceleration is consistent with rock difference. The influence of weight-on-bit on acceleration increases with the increase of rotary speed for horizontal interbedded formation with small rock differences. However, with the increase of weight-on-bit, the influence trend and degree of rotary speed on acceleration remain basically unchanged. The increase in weight-on-bit /rotary speed weakens the effect of rotary speed/ weight-on-bit on acceleration in horizontal interbedded formations with significant rock differences. The research results illustrate that the reason for the abnormal bit failure in interbedded formations is the frequent changes in depth of cut caused by rock mutation and alternation, and the resulting impact. This provides theoretical guidance for the implementation of effective measures such as reasonable cutter arrangement design, pertinent setting of auxiliary structures, and appropriate adjustment of drilling parameters.

Similar simulation test of the mechanical properties of layered composite rock mass

AbstractMost of the mine roadways in China are located in layered rock mass. To study the mechanical properties of a layered rock mass, the uniaxial compression test was carried out on the layered composite rock mass composed of sand and paraffin. The results showed that the locations of the high‐ and low‐strength rocks were independent of the strength of the layered composite rock. The main failure site was not affected by the combination mode. Failure was mainly concentrated in the low‐strength rock. The strengths of low‐ and high‐strength rocks determined the lower and upper limits of the strength of the layered rock, respectively. When the thickness of the layered high‐strength composite rock was &gt;60%, the layered composite rock strength tended to be high; conversely, layered composite rock strength lowered the rock strength, and with increasing thickness, the layered composite rock strength was significantly enhanced. From the perspective of energy conversion, the effect of the thickness of the high‐strength rock mass on the strength of the layered composite rock mass was analyzed.

Experimental and simulation investigation on failure characteristic of granite considering the effect of intermediate principal stresses

This study performs one-sided lateral unloading- and three-way five-sided force-vertical continuous loading experiments with different intermediate principal stresses (IPS) to investigate the effect of the IPS on deformation, strength, failure modes, and acoustic emission (AE) signals of rock and to elucidate the role of the IPS on the rock strength. The inoculation, occurrence, development, and failure of rockburst as well as the AE evolution characteristics are discussed. The findings indicate that the rockburst ejection includes localized ejections of particles, spalling of rocks into plates, shearing of rocks into fragments, and ejections of rock fragments. The formation mechanism of rockburst involves three progressive processes, i.e., tensile, shear, and tensile-shear composite destruction. The peak stress of sample increases with increasing IPS, while the deformation modulus decreases exponentially as the unloading progresses. The sample properties under true triaxial unloading condition with different IPS can be described by the Mogi-Coulomb criterion. The evolution curves of ringing impact ratio (CH) and cumulative absolute energy can be divided into four stages. The crystal-scale refined model that considers mineral components efficiently simulate the rockburst. The simulated stress-strain (SS) curves of samples are in good agreement with those obtained from laboratory tests.