Rock Crack Research Articles

Effect of high-temperature and strain rate on the mechanical and cracking behaviors of flawed sandstone under dynamic impact loading

A deep understanding of how flawed rock cracks under high temperatures and dynamic impacts is crucial for safe deep rock engineering design and operation. Dynamic impact tests were conducted on sandstones with various flaw inclinations using a Split Hopkinson Press bar (SHPB) system at room temperature and after high-temperature treatment at 600 °C. The results show that the dynamic peak stress and energy consumption of rock were reduced by thermal treatment. The study identified the circular tensile- and compressive-tangential stress zones around the flaw boundary using elastic theory. The strain accumulation zones gradually shift from the tensile- to the compressive-tangential stress zones as the flaw inclination increases, resulting in a larger crack initiation angle and opening displacement, while also constraining the propagation path. Additionally, the high-temperature treatment strengthened the deformation in the circular tensile-tangential stress zone. In contrast to the severe failure of specimens at room temperature, the clear failure pattern of the specimens after high-temperature treatment merely consists of wing cracks. Finally, this study presents a detailed theoretical explanation of the cracking behavior under various conditions, which is consistent with the experimental results. This research enhances the understanding of dynamic crack propagation in deep high-temperature rocks and provides scientific references for engineering safety design and protection.

Multiphysics phase-field modeling for thermal cracking and permeability evolution in oil shale matrix during in-situ conversion process

In-situ conversion process (ICP) is a promising recovery technology for economically effective exploitation of unmatured oil shale. High temperature treatment during ICP facilitates the chemical conversion of kerogen content in oil shale, while markedly improving the accessibility of pyrolyzed fluid through thermally-induced microcracks. Although extensively studied experimentally, the microstructure development in shale is not fully understood due to the lack of consideration for multiphysics effects during ICP at the mineral scale. This paper presents a numerical study on thermal cracking and permeability evolution in oil shale matrix during in-situ conversion process. To this end, a multiphysics phase-field model for investigating thermo-mechanical response, chemical reaction, and seepage behavior is developed, while arbitrary crack growth in heterogeneous shale matrix is naturally predicted using the phase-field method for fracture. Implementing the proposed numerical model, thermal cracking of heterogeneous granodiorite is first simulated, from which the numerical outcome regarding crack morphology is reasonably consistent with experimental data. Permeability evolution of oil shale matrix is found to be attributed to early-stage thermal crack propagation and late-stage kerogen decomposition by correlating multiple variables. Anisotropic permeability is also observed and investigated by examining crack morphology, pore-space interconnectivity and fluid permeation. Further analysis reveals that the shale matrix microstructure, in-situ stress and heating temperatures play vital roles in influencing thermal cracking and permeation behaviors of the shale matrix. The results provide a unique perspective to understanding thermal cracking and permeability augmentation of heterogeneous rocks.

Species distribution and habitat attributes guide translocation planning of a threatened short-range endemic plant

The success of plant translocations depends on defining habitat attributes critical for establishment and survival, and on locating this habitat in the landscape. We used species distribution modelling, coupled with fine-scale characterisation of local habitat attributes to characterise and identify potential sites for translocation of Tetratheca erubescens J.P.Bull (Elaeocarpaceae), a threatened shrub restricted to cliff faces on one banded ironstone range in semi-arid south-west Western Australia. Here, we 1) constructed a maximum entropy species distribution model (SDM) from known occurrence locations and environmental data, and projected this onto a broader surrounding landscape to seek suitable unoccupied habitat; 2) characterised the local habitat attributes (LHA) of both occupied and predicted but unoccupied habitat (locality types), determining potential characteristics of habitat suitability at the scale of individual plants (microsites) not captured by the landscape-scale models and; 3) assessed unoccupied areas of modelled high habitat suitability to identify ‘potential translocation sites’ that may have the characteristics to support T. erubescens. The SDM resolved two management considerations by identifying suitable habitat outside the known extent of threatened species to locate areas to search for additional natural populations (none found) or to verify as ‘potential translocation sites’ (24 sites identified). Using field surveys to assess LHA at a finer-scale, we detected differences between plant microsites and other random points in occupied habitat. As such, T. erubescens was more likely to grow in wider rock cracks, located in relatively water gaining points in the cliff profile, in soils with organic (rather than mineral) content. Our approach systematically addressed the complex challenges involved in identifying and selecting sites for translocation of a threatened plant species, a first for a semi-arid environment. We used the outcomes of this study to present a conceptual model for practitioners and regulators that outlines our approach for identifying ‘potential translocation sites’ and ranking their suitability within the context of three assessment filters: species requirements; management-operational constraints and regulatory considerations. This application is relevant to translocation programs that seek to return plant species into natural habitat areas.

Determining rock crack stress thresholds using ultrasonic through-transmission measurements

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

Investigation of the influence of pre-crack number on acoustic emission characterization of red-sandstone short-term creep damage and failure precursors

Rock crack is one of the main factors responsible for rock failure. Uniaxial compression creep tests are performed using acoustic emission techniques, a high-sensitivity, non-radiative, non-destructive testing method to understand the influence of crack number on the precursor characteristics of short-term creep damage in the fractured rock mass. Based on the Grassberger-Procaccia (G-P) algorithm, the calculation step size for the correlation dimension value (D 2) of the acoustic emission ringing count rate is consistent with that for the acoustic emission b-value. The influence of the number of pre-cracks on the Acoustic emission precursor characteristics of red sandstone creep is analyzed. The results show that near the destabilization of the specimen, the Acoustic emission accumulative ringing count surges in a stepwise manner, the Acoustic emission b-value decreases, the D 2-value increases, the Acoustic emission amplitude shows high intensity and high frequency, and the ringing count increases sharply, all with the characteristics of failure precursors. During the accelerated creep stage of the specimens, with the increase of pre-cracks number, the precursory time points of acoustic emission b-value and D 2-value advance, and their acoustic emission ringing counts increase sharply.

Formation of coronae topography and fractures via plume buoyancy and melting

Coronae are volcanic-tectonic features seemingly unique to the surface of Venus. As such they offer potential insights into differences in geodynamic processes on Venus and Earth. Largely due to limitations in processing power and computational complexity, models of corona formation generally ignore the effect of melt and magmatism despite the presence of volcanic features like domes and lava flows. Here we present a new model of corona formation integrating visco-plastic rheology with two-phase flow melt migration. Additionally, we model brittle failure of surface material, viscous flow of partially molten material at depth, and cracking of solid rock from fluid pressure in one model. The model consists of a two-dimensional half space with a round plume body ascending through an asthenosphere and interacting with a Venusian lithosphere and crust. The size and temperature of the plume body, lithosphere thickness, crustal thickness, and regional strain rate are all varied over 20 model runs. Most models show deflection of the plume as it rises due to the increased viscosity of the base of the lithosphere. As the plume spreads and rises against the base of the lithosphere, melting occurs. Melt rises and accumulates in the lithosphere which supports surface topography. Brittle failure occurs at the surface due to the induced stress of the migrating plume body and rising melt. Increased temperatures and sizes of initial plumes result in larger topographies occurring over smaller timescales. Decreased temperatures and sizes of initial plumes result in smaller topographies over larger timescales. Increased lithosphere thickness generates smaller topographies. Thinner crusts result in more viscous lithosphere and more strain accumulation, creating surface depressions seen in approximately half of real corona. Both thicker crusts and increased regional strain result in lower viscosities at the base of the lithosphere, preventing the deflection of the plume body, which instead rises through the lithosphere relatively unimpeded. The varied model parameters generally result in an evolutionary sequence of topographies and fracture patterns which resemble actual corona, without requiring a collapsing dome to create outer rims, as is often invoked for corona formation via upwelling plumes. Corona rim topography is generally created within 105 and 106 year timescales, while multiple rims or central depressions are generally observed over 106 year timescales. Observed topography is actively supported by partially molten regions in the lithosphere, supporting the notion of an active squishy-lid Venus. These partially molten regions are not centrally located and may provide a source for observed lava flows away from corona centers.

Study on rock-breaking mechanism and bit adaptive characteristics under the action of claw-toe impregnated diamond bit

In order to overcome the ingrained belief that the impregnated diamond bit primarily achieves rock-breaking via grinding and micro-cutting and to have a better understanding of the drilling mechanism of the bit, in this work, aiming at the inherent weakness of rock cracks, a claw-toe impregnated diamond bit (CTB) with a self-regenerative structure is innovatively designed. The concept is that the structure of the bit can actively induce the development of cracks inside the rock or create cracks in the dense rock. Through simulation, the differences in hole bottom morphology, drilling efficiency, rotational speed, torque and rock-breaking vibration between conventional bit (CB) and CTB (CTB with two sets of tooth units (CTB-2) and CTB with three sets of tooth units (CTB-3)) are analyzed, and the crack propagation and stress-strain field distribution characteristics of rock are compared when the tooth units of bit (TUBs) press into rock and cause initial damage to rock. Through field tests, the superiority of the claw-toe impregnated diamond bit (CTB) and its rock-breaking mechanism is verified. Compared with the conventional bit (CB), the simulation results show that the claw-toe impregnated diamond bit (CTB) can achieve efficient drilling with smaller rock-breaking torque, more stable rotational speed, and a more apparent shear effect on rock. The mean vibration reaction force of the claw-toe impregnated diamond bit with two sets of tooth units (CTB-2) and claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) increases by 0.78 times and 0.43 times, respectively, and the mean rock-breaking torque decreases by 10.66% and 21.81%, respectively. The structure of the claw-toe impregnated diamond bit (CTB) can force rock to produce more tensile stress concentration areas, induce rock crack initiation, and accelerate rock failure. Field tests show that the service life of the claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) is 1.9 times longer than the mean service life of the conventional bit (CB). Furthermore, the claw-toe impregnated diamond bit (CTB) has obvious structural advantages: it will self-sharpen its structure, maintain its best drilling structure in subsequent drilling, and tear up rock, resulting in better drilling performance.

A macro-mesoscopic constitutive model for porous and cracked rock under true triaxial conditions

The complex mechanical and damage mechanisms of rocks are intricately tied to their diverse mineral compositions and the formation of pores and cracks under external loads. Numerous rock tests reveal a complex interplay between the closure of porous defects and the propagation of induced cracks, presenting challenges in accurately representing their mechanical properties, especially under true triaxial stress conditions. This paper proposes a conceptualization of rock at the mesoscopic level as a two-phase composite, consisting of a bonded medium matrix and frictional medium inclusions. The bonded medium is characterized as a mesoscopic elastic material, encompassing various minerals surrounding porous defects. Its mechanical properties are determined using the mixed multi-inclusion method. Transformation of the bonded medium into the frictional medium occurs through crack extension, with its elastoplastic properties defined by the Drucker–Prager yield criterion, accounting for hardening, softening, and extension. Mori–Tanaka and Eshelby’s equivalent inclusion methods are applied to the bonded and frictional media, respectively. The macroscopic mechanical properties of the rock are derived from these mesoscopic media. Consequently, a True Triaxial Macro-Mesoscopic (TTMM) constitutive model is developed. This model effectively captures the competitive effect and accurately describes the stress-deformation characteristics of granite. Utilizing the TTMM model, the strains resulting from porous defect closure and induced crack extension are differentiated, enabling quantitative determination of the associated damage evolution.

ВИНИКНЕННЯ І РОЗВИТОК ТРІЩИНОУТВОРЕННЯ В ГІРСЬКИХ ПОРОДАХ ПРИ СТАТИЧНОМУ НАВАНТАЖЕННІ

The paper examines the occurrence and development of cracks in rocks under static loads, various conditions and factors of crack initiation and development. For comparison, such rocks as concrete, granite, sandstone, plasterboard are taken. This is said to help the cracks in the rock spread in the right direction. The technology of crack formation with the help of insert plates under the action of non-explosive mixtures is considered. When modeling, the minor and major axes of the ellipse around the insert of the plate with holes are taken. Construct isolines of rock destruction at a point in the form of ellipses. Determine the most likely direction of cracks during rock destruction. The conditions for the development of cleavage cracks relative to the axes of anisotropy with maximum and minimum strength are considered. The theoretical and experimental justifications of the rational technological parameters of mining stone blocks by the hole method by the formation of a separation crack in the rock in a given direction have been studied. The determination of the plane stress state around a hole with a 5- and 8-mm-thick insert plate is studied, and equivalent stress diagrams are given. The methods of directional destruction and the occurrence of cracks in rocks when pouring non-explosive mixtures into wells and inserting cartridges with a destructive substance into wells are considered. It clearly shows the greater efficiency of using cartridges that guarantee the appearance of cracks in a precisely specified direction. The influence of the load scheme on the development of a splitting crack in holes with stress concentrators is presented. The model for the analysis of crack formation at the tops of stress concentrators is considered. Non-explosive methods of directional destruction of monoliths using special structures are described. Considered patents for static rock splitting. The results of destruction over a certain time are given. In addition, non-explosive mining of gabbroid rock blocks using destructive mixtures together with surface-active substances is considered.

Repairing Performance of Polymer-Modified Cement-Based Thin Spray-On Liners on Pre-Cracked Rock-like Specimens

With the development of coal mining and the increase in excavation depth, the stress on roadway surrounding rock is also increasing. This creates conditions for crack development in the roadway, so it is urgent to develop rock repair materials with excellent performance. The ability of thin spray-on liner (TSL) to repair rock and concrete opens up the possibility of reusing abandoned roadways. The ability of TSL to support the surrounding rock is also important in preventing the generation of roadway waste. In this paper, styrene–acrylic emulsion (SAE), vinyl acetate–ethylene copolymer emulsion (VAE), and polyvinyl alcohol powder (PVA) were used to prepare three TSLs. Rock-like materials were configured using cement mortar according to similar principles. Three types of TSLs were tested for basic properties such as viscosity and mechanical strength, which provided data to support the explanation of the repair performance of TSLs. Three TSLs were used to repair pre-cracked rock-like specimens (PR). The number of brushing times and the angle of PR’s cracks were regarded as test variables. Changes in the mechanical strength of repaired PRs were tested by compressive and flexural tests. TSL repair performance was evaluated with the help of mechanical strength changes. Results show that polyvinyl alcohol powder modified cement-based thin spray-on liner is most suitable for repairing rock cracks; as the thickness of the brush slurry increases, its repair performance continues to improve. This paper can provide experience and a theoretical basis for the research of other rock repair materials, and it is also instructive for repairing shotcrete in the roadway.

Local adaptation in parapatric and sympatric mosaic coastal habitats through trait divergence of Setaria viridis

Abstract Maritime plants contain dwarf ecotypes that are adapted to exposure to strong winds transporting salt spray. When variants differentiated from local populations are well‐adapted and reproductively isolated, they become forerunners of ecotypes. This study aimed to determine how coastal variants arise from local populations under natural selection by studying phenotypic variations and survival of self‐fertilising Setaria viridis populations inhabiting pebble and sandy seashores in Japan. To identify adaptive traits characterising variants, common garden experiments were performed for determining the variation in morphology, salt spray tolerance and flowering time among populations in four adjacent habitats at two localities. To determine selective agents and their adaptation, field transplant experiments were performed, flowering phenology was monitored, and artificial crossing was conducted for F2 segregation. S. viridis populations comprised five coastal variants showing significantly higher salt spray tolerance than the inland variant. The most common of these was a short and tolerant variant adapted to cliff and pebble shore under intensive salt spray from the Pacific ocean. Three others were a tall and mid‐tolerant variant that endured mild breezes off the Seto inland sea, a tall and tolerant variant that survived sea splash from sporadic storms, and a prostrate and tolerant variant specialised for rock cracks exposed to strong sea winds. These variants imply that maritime plants first acquired salt spray tolerance for survival, after which compact plants evolved in habitats where strong winds caused damage from salt spray. Flowering in a fifth variant was delayed to avoid the fatal risk of reproducing during the mid‐summer drought. Although salt spray tolerance and late‐flowering were partially recessive, self‐fertilisation of S. viridis may have increased the homozygosity of recessive genes to generate novel variants. Synthesis. Diverse intensities of salt spray and wind as well as summer drought generated various coastal variants in parapatry and sympatry. This was partially attributable to self‐fertilisation. Among these, a compact variant adapted to common local seashores may become the forerunner of an ecotype. This study on the local adaptation in mosaic habitats will assist in determining adaptation modes of plants and the beginning of ecotype formation.

Experimental study of precursory features of CO2 blasting-induced coal rock fracture based on grayscale and texture analysis.

CO2 blasting has been identified as a potent method for enhancing the permeability of coal seams and improving gas drainage efficiency. This study is focused on elucidating the deformation and fracture mechanisms of coal and rock during CO2 blasting and on identifying the precursor characteristics of these processes. To this end, a CO2 blasting-induced coal rock fracture pressure model and a gas pressure distribution model were developed. The research utilized a self-developed CO2 blasting test platform along with a non-contact full-strain field measurement analysis system. Briquette samples were subjected to CO2 blasting tests under controlled experimental conditions, which included an axial pressure of 1.0 MPa and variable gas pressures of 0.5, 1.0, and 1.5 MPa. This methodology enabled the capture of the principal strain field on the surface of the samples. The Gray Level Co-occurrence Matrix (GLCM) was employed to extract and analyze the grayscale and texture features of the strain cloud maps, facilitating a quantitative assessment of their evolution. The aim was to pinpoint the precursor characteristics associated with coal rock cracking and crack propagation. The results revealed that: (1) During the cracking and subsequent propagation of samples, the strain field's grayscale histogram underwent a transformation from a "broad and low" to a "narrow and high" configuration, with a consistent increase in peak frequency. Specifically, at 3 ms, a primary crack was observed in the sample, evidenced by a grayscale peak frequency of 0.0846. By 9 ms, as the crack propagated, the grayscale peak frequency escalated to 0.1626. (2) The texture feature parameters experienced their initial abrupt change at 3ms. Correlation with the gas pressure distribution model indicated that this was the crack initiation moment in the sample. (3) A secondary abrupt shift in the texture feature parameters occurred at 9ms, in conjunction with experimental phenomena, was identified as the crack propagation phase. Monitoring the grayscale and texture features of the principal strain field on the coal rock surface proved effective in recognizing the precursor characteristics of crack initiation and propagation. This research has the potential to reduce blasting costs in coal mines, optimize blasting effects, and provided theoretical guidance for enhancing gas extraction efficiency from deep and low permeability coal seams.

Mapping Underground River Flows in karst Areas with the VLF-EM Method (Case Study of the Krawak Region, Singgahan Tuban)

The Krawak Springs is a source of springs from the cracks of river rocks in the middle of a teak forest in Guwoterus Village, Montong District, Tuban. This spring is a source of irrigation water for agricultural land in the District of Montong. Based on its urgency, it is necessary maintaining its sustainability by identifying recharge areas and underground river flows. VLF is quite advantageous for use in the regional mapping underground rivers in karst areas because can describe the structure of the karst environment and predict interconnected pathways in karst. Data acquisition uses four tracks with an average length of about 300 m. Data processing was made qualitatively using MATLAB software and quantitatively using Inv2DVLF software. Qualitative results show that the conductive zone is identified as a subsurface river flow. From the processing results, it is known that the subsurface river flow zone can be identified as a zone that is conductive or has low resistivity. The underground river flow is interpreted to be located on Track 3 and Track 4 and has a direction of continuity to the southwest

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Study on rock fracturing in smooth blasting under initial stress

In practical smooth blasting, rock fracturing is influenced by in-situ stress, which frequently leads to underbreak/overbreak and excavation damaged zone and consequently poses a serious threat to the safety of the excavated structure. This study systematically investigates the behaviour and mechanism of rock cracking under coupled initial stress and smooth blast utilizing experimental, theoretical, and numerical methods. Model experiments involving three-hole smooth blasting on 200 × 200 × 50 mm granite specimens are conducted under various static stresses. The resulting fracturing patterns are identified using the digital image correlation technique. The model testing examines rock cracking behaviours, fractal characteristics of rock fractures, and underbreak/overbreak. Experimental results indicate that the extents of rock fracturing and the fractal dimension in both the excavation and reserved zones show an overall decreasing trend as the static stress increases. Meanwhile, the area and depth of underbreak/overbreak also present a decreasing trend, suggesting that static stress is beneficial to the performance of smooth blasting. Then, the variations of crack patterns in model tests are theoretically analysed based on the transmission and superimposition of detonation stress waves combined with the static stress distribution near perimeter holes. Theoretical results emphasize the crucial role of the second hole and indicate no evidence of the third hole influencing the generation of connection fractures. The initial stress induces hoop tensile stress concentration on borehole-wall and generates the smallest hoop compression stress distributed vertically to the excavation line, which controls the initiation and extension of fractures in smooth blasting along the connection line of boreholes. Subsequently, the fracture evolution under coupled initial stress and smooth blast is numerically modelled using LS-DYNA. The numerical results vividly illustrate the necessity of a small burden to efficiently fragment the rock within the excavation zone when smooth blasting is applied to rock excavation under high in-situ stress.

Understanding the evolution mechanism and classification criteria of tensile -shear cracks in rock failure process from acoustic emission (AE) characteristics

This study aimed to investigate the crack evolution and failure mechanism of rocks by conducting uniaxial compression tests (UCT) and Brazilian indirect tension tests (BITT) using four categories of rock specimens. Real-time acoustic emission (AE) signals were detected and recorded during rock failure processes by an AE monitoring system. The study focused on the accumulative AE hits curves, stress–strain curves, and other AE energy characteristics to divide the failure process into five stages, and determine the stress thresholds. Furthermore, the transition trend of rock crack types was analyzed based on RA-AF data. A novel classification criterion of crack types based on clustering and statistical theory was proposed, and the crack boundaries of the four rocks were determined. Additionally, the tension to shear ratios of the rocks in descending order were fine-grained granite, granite, yellow sandstone, and white sandstone. Finally, the crack development trend and failure characteristics of the rock were analyzed using the crack scale and crack dividing line. The study found that the failure mode of the rock could be predicted accurately by AE parameter analysis at Unstable Crack Growth (Stage-IV).

Investigation of fracture geometry

This article presents a study on hydraulic fracturing as one of the most effective methods of increasing the flow rate of wells, namely, the importance of evaluating the geometry of a hydraulic fracturing fracture when designing in difficult geological conditions is considered. The quality and success of the event depends on the correct assessment of the predicted crack geometry and the volume of the injected proppant. The fracture geometry is influenced by the mechanical properties of the rock, so, in the article, the results of a study of the mechanical properties of the core by dynamic and static methods are presented, and the main characteristics of the dependence are given. The results of modeling the fracture geometry of hydraulic fracturing at the stage of analysis of mini hydraulic fracturing are also presented. The findings indicate the need to use data on the mechanical properties of core samples with a high clay content to achieve more accurate predictions of the crack geometry. It is recommended to use a correlation model of the mechanical properties of rocks to account for various factors such as horizontal stress and poroelasticity coefficient. The development of new approaches to the analysis and modeling of these parameters will allow us to create more reliable tools for predicting the behavior of cracks in rocks and effectively managing the process of hydraulic fracturing.

Machine Learning–Enhanced Microseismic Analysis for Evaluating Rock Crack Trajectory

Machine Learning–Enhanced Microseismic Analysis for Evaluating Rock Crack Trajectory

Material point method to simulate the evolution characteristics of loading damage in fractured sandstone

Cracks in rocks can lead to different load responses and mechanical properties. Primary and secondary cracks are altered during loading, with varying degrees of impact on the failure of underground engineering rock masses. However, the precise modeling of fracture initiation and propagation resulting in failure remains challenging, and the macroscopic evolution characteristics of cracks and stress fields have not been accurately described. In this study, a numerical simulation tool based on the material point method (MPM) and a strain softening model were used to establish a plane loading model with different cutting angles. A simulation of the damage evolution of fractured sandstone under constant-rate loading was conducted for different confining pressures and cutting angles. The results show the following. 1) A comparison of the simulation and experimental results indicates that the proposed numerical method accurately simulates the macroscopic crack generation and the complex physical processes of fractured sandstone during loading. 2) The stress concentration area originates from both ends of the crack and extends toward the edge in a diagonal direction until the crack has penetrated the rock. 3) The ranking of the cutting angle based on the sandstone strength is 0° > 90° > 60° > 30°. The cumulative dissipated energy exhibits an inflection point near the peak stress, and the increase after this point is primarily attributed to friction at the crack surface. The damage degree and dissipated energy of the rock in different stages correspond to the rock’s strength.

Numerical study on migration of overlying strata and propogation of cracks during multi-coal seams mining

The surface subsidence caused by the coal seam mining seriously affects the ecology of the mining area. Compared with the single-coal seam mining, the mechanism of the overburden fracture and crack propagation caused by multi-coal seams mining is more complex, which has not been fully understood. Taking the 22,108 and 42,108 working faces of Buertai Coal Mine as a research object, the discrete element method is used to simulate the migration and failure characteristics of overlying strata, and the propogation of cracks in the process of multi-coal seams mining is also been investigated. So many cracks develop in the soft strata overlying the coal seam, and they cross each other and form a complex fracture system. The hard layer produces staggered cracks with a large size, mainly high-angle longitudinal cracks. The surface subsidence curve of the single coal seam mining shows a wide and slow “bowl” type, and the surface subsidence curve of the double coal seams mining show a “funnel” type with only one inflection point. The overburden structure disturbance caused by the previous coal seam and rock cracking—settlement have great influence on the mining of the latter coal seam. The research results are basically consistent with the field data comparison, which could provide a reference for the related research and engineering practice of shallow-buried double coal seam mining.