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17 pages, 4106 KiB

Open AccessArticle

Research and Application of the Synergistic Support System of “LDAGF” in an Extremely Soft and Fragile Fully Mechanized Caving Face Roadway

by Xianjie Ni, Yuan Yuan, Xinzhu Hua and Ke Ding

Appl. Sci. 2024, 14(18), 8485; https://doi.org/10.3390/app14188485 - 20 Sep 2024

Viewed by 452

Abstract

This study aims to alleviate the serious deformation of surrounding rock (SR) in an extremely soft and fragile fully mechanized caving face roadway (ESFFMCFR, the 8# coal seam, Huaibei mining area) under a conventional support. Laboratory tests of roadway SR were conducted. The [...] Read more.

This study aims to alleviate the serious deformation of surrounding rock (SR) in an extremely soft and fragile fully mechanized caving face roadway (ESFFMCFR, the 8# coal seam, Huaibei mining area) under a conventional support. Laboratory tests of roadway SR were conducted. The results show that in this coal seam, the extremely soft and fragile coal body has a high clay mineral content, so it is of low strength and breaks and softens easily. With reference to the mechanical tests on coal and rock mass around the coal seam and the monitoring results of roadway deformation, the roadway deformation is mainly caused by the development of fractures in the roadway SR, the separation of the support body and SR and the loose supporting structure. Considering the engineering environment and deformation characteristics of SR in the ESFFMCFR (the 8# coal seam, Huaibei mining area), this study proposed a synergistic support system of “lowering, drilling, anchoring, grouting and flatting (LDAGF)” for the ESFFMCFR based on the synergistic mechanism of support and SR under the basic principles of synergetics. Specifically, the synergistic support system of “LDAGF” includes the following measures: floor breaking and side lowering, bolt advance support, anchor cable support, advance water injection and grouting and flat-roof U-shaped steel shed support. Furthermore, this synergistic support system was applied on the ESFFMCFR in the 8# coal seam of Xinhu and Guobei coal mines, Huaibei mining area. The on-site application results reveal that when the synergistic support system is adopted, the maximum subsidence values in the above roadway roofs are 117 mm and 121 mm and the maximum displacement values of the two sides are 66 mm and 74 mm, respectively, which proves an excellent support effect. The synergistic support system, which can effectively control the serious deformation of the SR in ESFFMCFRs and ensure long-term stability and safety of the roadways, is suitable for the support of ESFFMCFRs and is of great guiding significance for roadways of the same type. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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21 pages, 9246 KiB

Open AccessArticle

Research on Key Roof-Cutting Parameters for Surrounding Rock Stability Control in Gob-Side Entry Retention without Coal Pillars in Karst Mountainous Area

by Yutao Liu, Wenhao Guo, Gangwei Fan, Wei Yu, Yujian Chai, Xin Yue and Xuesen Han

Appl. Sci. 2024, 14(18), 8118; https://doi.org/10.3390/app14188118 - 10 Sep 2024

Viewed by 459

Abstract

The differential distribution of original rock stress and stress concentration caused by the variation in coal seam depth in karst topography are critical factors influencing the selection of roof-cutting parameters. Based on this, this study explores a method to determine reasonable roof-cutting parameters [...] Read more.

The differential distribution of original rock stress and stress concentration caused by the variation in coal seam depth in karst topography are critical factors influencing the selection of roof-cutting parameters. Based on this, this study explores a method to determine reasonable roof-cutting parameters by incorporating the characteristics of coal seam depth variation in karst mountainous areas. A mechanical model of the cantilever beam structure for roof cutting in gob-side entry retention (GSER) is constructed, and the critical values and reasonable ranges of roof-cutting height and angle under different burial depths are derived. Furthermore, the displacement and stress evolution characteristics of surrounding rocks in gob-side entry retention under different coal seam burial depths, roof-cutting heights, and roof-cutting angles within the reasonable range of roof-cutting parameters are analyzed. The results show that there is a positive correlation between roof-cutting height and tensile stress in the uncut portion of the main roof, while roof-cutting angle and coal seam depth are negatively correlated with tensile stress. From the perspective of impact, roof-cutting height has a greater impact than roof-cutting angle, followed by coal seam depth. As for the distribution characteristics of the reasonable roof-cutting parameter range, the fan-shaped area of reasonable roof-cutting parameters gradually decreases with increasing coal seam depth. Taking the geological conditions of Anshun Coal Mine as an example, when the burial depth increases from 350 m to 550 m, adjusting the roof-cutting height to 6 m, 7 m, and 8 m, respectively, and setting the roof-cutting angle at 10° can effectively achieve the stability of the surrounding rock in the GSER. The research findings can provide a scientific basis and engineering references for selecting roof-cutting parameters in mines with similar geological conditions. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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13 pages, 1667 KiB

Open AccessArticle

Solution of Water Inflow and Water Level Outside the Curtain of Strip Foundation Pit with Suspended Waterproof Curtain in the Phreatic Aquifer

by Da Li, Ningyi Liu, Jiahe Han and Junhong Shen

Appl. Sci. 2024, 14(17), 7918; https://doi.org/10.3390/app14177918 - 5 Sep 2024

Viewed by 526

Abstract

The seepage field of a suspended waterproof curtain strip foundation pit in a deep phreatic aquifer is theoretically analyzed, and a calculation method for the foundation pit water inflow and water level outside the curtain is derived. In this paper, it is assumed [...] Read more.

The seepage field of a suspended waterproof curtain strip foundation pit in a deep phreatic aquifer is theoretically analyzed, and a calculation method for the foundation pit water inflow and water level outside the curtain is derived. In this paper, it is assumed that the horizontal hydraulic gradient of the seepage field above the aquiclude below the bottom of the waterproof curtain decreases linearly. The separation variable method is used to solve the seepage field in the regular area inside the foundation pit, and the hydraulic head distribution function inside the foundation pit is obtained. According to the hydraulic head distribution function inside the foundation pit, the calculation expression of the water inflow of the foundation pit is further deduced theoretically. On this basis, the improved resistance coefficient method is applied to link the water level outside the pit with the solved hydraulic head inside the pit and solved. In addition, the calculation results presented in this study are compared with the calculation results of the existing model and the measured data of the foundation pit project of Yangwan Station, which proves that the analytical method can effectively meet the requirements of engineering applications. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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13 pages, 5172 KiB

Open AccessArticle

Research on the Support Technology for Deep Large-Section Refuge Chambers in Broken Surrounding Rock in a Roadway

by Wenqing Peng and Shenghua Feng

Appl. Sci. 2024, 14(17), 7527; https://doi.org/10.3390/app14177527 - 26 Aug 2024

Viewed by 443

Abstract

The phenomenon of peripheral rock instability is more common in crushed bedrock roadways, and the fundamental reason for this lies in the significantly different characteristics of its peripheral rock stress field. Taking the newly dug belt inclined shaft of PingDingShan TianAn Coal Co., [...] Read more.

The phenomenon of peripheral rock instability is more common in crushed bedrock roadways, and the fundamental reason for this lies in the significantly different characteristics of its peripheral rock stress field. Taking the newly dug belt inclined shaft of PingDingShan TianAn Coal Co., Ltd. No. 6 Mine as the engineering background, a mechanical model of a broken perimeter rock roadway was established by using classical rock mechanics theory. Stress distribution around the roadway of the broken perimeter rock medium was systematically analyzed, and radial and tangential stress formulas of the broken perimeter rock were deduced. Through the formula calculation, it was deduced that there was a stress drop in the intact surrounding rock outside the disturbed zone, and the radial stress of the intact surrounding rock in its deep part was relatively increased, while the tangential stress was relatively decreased. The existence of crushed surrounding rock increased the minimum principal stress and decreased the maximum principal stress of the unfractured surrounding rock, which proves that a well-maintained disturbed zone can play a lining role. Thus, a “U-shaped steel + inverted arch + bottom arch linkage beam + floor bolt compensation” support program was proposed. This joint support program easily forms a closed support structure, which is more effective in controlling the deformation of tunnel perimeter rock. The support structure can effectively resist the deformation of the surrounding rock and enhance bottom drum resistance. Through numerical simulation, it was concluded that the horizontal displacement of the two gangs was reduced by 70%, and the displacement of the top and bottom plates was reduced by 77% after optimization of the support, which effectively controlled the stability of the broken surrounding rock. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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11 pages, 5070 KiB

Open AccessArticle

Fracture and Damage of Slit Charge Blasting in the Layered Rock Mass

by Chenxi Ding, Hong Su, Haitao Yang and Chenglong Xiao

Appl. Sci. 2024, 14(13), 5840; https://doi.org/10.3390/app14135840 - 4 Jul 2024

Cited by 1 | Viewed by 665

Abstract

Directional fracture blasting technology of the slit charge has broad application prospects in the drilling and blasting construction of the layered rock mass. In this paper, the method of model experiment and numerical simulation is used to preliminarily explore the fracture damage characteristics [...] Read more.

Directional fracture blasting technology of the slit charge has broad application prospects in the drilling and blasting construction of the layered rock mass. In this paper, the method of model experiment and numerical simulation is used to preliminarily explore the fracture damage characteristics of slit charge blasting in the layered rock mass. The results show that the blasting effect of the slit charge in the layered rock mass is significantly different from that of the unlayered rock mass, and the pressure relief of the blasting gas at the layer is the main factor affecting the blasting effect. The length of directional cracks in the slit direction is significantly larger than that in other directions, and the directional fracture effect of the slit charge in the layered rock mass can still be played well. However, both the directional crack length and the damage range of rock mass in the slit direction gradually decrease along the detonation direction. In addition, the damage value of a single-layer rock mass also decreases gradually along the detonation direction. In engineering practice, the directional fracture effect of the layered rock mass can be improved by detonating at both ends of the slit charge at the same time. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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19 pages, 22154 KiB

Open AccessArticle

Study on the Meso-Failure Mechanism of Granite under Real-Time High Temperature by Numerical Simulation

by Kangwen Li and Fan Zhang

Appl. Sci. 2024, 14(11), 4575; https://doi.org/10.3390/app14114575 - 27 May 2024

Cited by 1 | Viewed by 947

Abstract

In the development of geothermal resources in hot dry rocks, deep underground rock masses are typically subjected to real-time high-temperature environments. High temperatures alter the physical and mechanical properties of the rocks, directly affecting the safe and efficient utilization of hot dry rock [...] Read more.

In the development of geothermal resources in hot dry rocks, deep underground rock masses are typically subjected to real-time high-temperature environments. High temperatures alter the physical and mechanical properties of the rocks, directly affecting the safe and efficient utilization of hot dry rock resources. Therefore, a grain-based model (GBM) of particle flow code (PFC) was constructed based on uniaxial compression tests, and the model was verified according to macroscopic mechanical parameters and damage modes, in order to carry out the simulation study of the uniaxial compression of granite and explore the meso-failure mechanism of granite under real-time high temperature. The relationships between stress–strain curves and crack derivation, the evolution of microcracks, and the characteristics of acoustic emission activity and energy changes at different temperatures were investigated in conjunction with the results of laboratory tests. The results show that crack development, acoustic emission activity, and energy evolution during uniaxial compression include four main stages: initial compression, elasticity, plastic strengthening, and post-peak damage. The failure of granite is primarily controlled by mica and feldspar. During loading, intergranular tensile cracks first emerge within the granite, followed by intragranular tensile cracks, with shear cracks appearing last. As the temperature increases, the total number of microcracks continuously rises, the frequency of acoustic emission events increases, and both dissipated energy and boundary energy gradually decrease, showing an upward trend in the energy dissipation ratio, indicating an increase in thermal damage due to high temperatures. At 400 °C, the rate of microcrack formation increases significantly, with intergranular and intragranular cracks starting to coalesce into macroscopic cracks that extend outward. In the post-peak stage, the phenomenon of multiple peaks in acoustic emission events begins to appear. At 600 °C, the rate of microcrack formation reaches its maximum, with cracks extending throughout the sample to form a network of fractures, resulting in the granite exhibiting ductile failure characteristics. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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16 pages, 9316 KiB

Open AccessArticle

Effect Mechanism of Material Ratio on Ultrasonic P-wave Velocity in Coal Based Paste Fill Materials

by Baifu An, Jie Song, Jinfang Ren, Junmeng Li, Chenghao Cui, Jiale Wang and Wenting Bai

Appl. Sci. 2024, 14(9), 3668; https://doi.org/10.3390/app14093668 - 25 Apr 2024

Viewed by 664

Abstract

This research is designed to investigate the variations in ultrasonic p-wave velocity in various coal based paste fill materials used for recovering standing pillars in closed/closing coal mines, with consideration given to the effects of numerous material-related factors. For this purpose, orthogonal tests [...] Read more.

This research is designed to investigate the variations in ultrasonic p-wave velocity in various coal based paste fill materials used for recovering standing pillars in closed/closing coal mines, with consideration given to the effects of numerous material-related factors. For this purpose, orthogonal tests were designed. The evaluation was performed on the effects of four variables on the ultrasonic p-wave velocities in samples, using coal grains as the primary material. These variables consisted of the coal grains’ particle size (P_A), high-water material content (P_B), cement content (P_C), and water content (P_D). The experimental results show the following: (1) Ultrasonic p-wave velocity of coal based paste fill materials are measured within the range of 1.596 to 2.357 km/s, and these are classified (in descending order) as P_D, P_B, P_C, and then P_A, based on their effects on ultrasonic p-wave velocity. (2) Ultrasonic p-wave velocity is positively correlated with compressive strength and shear strength; the correlation coefficients are 0.82 and 0.69, respectively. (3) Changes in the ultrasonic p-wave velocity of coal based paste fill materials, when exposed to various factors, have been characterized by fitted formulae. It was observed that the velocity maintained a quadratic polynomial correlation with factor P_B and exponential correlations with factors P_A, P_C, and P_D. The comprehensive predictive model, reflecting the characteristics of the ultrasonic p-wave velocity in response to the combined influence of these four factors, was developed through the utilization of fitted equations pertaining to individual factor variations. Subsequently, this model underwent verification. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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16 pages, 8529 KiB

Open AccessArticle

Comparative Analysis of the Stability of Overlying Rock Mass for Two Types of Lined Rock Caverns Based on Rock Mass Classification

by Qi Yi, Zhen Shen, Guanhua Sun, Shan Lin and Hongming Luo

Appl. Sci. 2024, 14(8), 3525; https://doi.org/10.3390/app14083525 - 22 Apr 2024

Viewed by 1033

Abstract

Lined rock caverns (LRCs) are becoming the preferred option for air storage at sites where there are no natural cavities, such as salt caverns, and this storage technology is being developed and utilized in markets around the world. The stability of the overlying [...] Read more.

Lined rock caverns (LRCs) are becoming the preferred option for air storage at sites where there are no natural cavities, such as salt caverns, and this storage technology is being developed and utilized in markets around the world. The stability of the overlying rock mass is one of the key factors to ensure the successful operation of LRCs. In this paper, a stability assessment method is presented that first calculates the potential fracture surfaces of the surrounding rock based on the limiting stress field and the Mohr–Coulomb damage criterion, and then, based on these fracture surfaces, solves for the factor of safety defined on the basis of the concept of strength reserve. Using this method, this study evaluates the stability of two types of LRCs, tunnel- and silo-type, under three different geological conditions. The results of the analysis show that the silo-type LRCs are more economical for engineering purposes. Also, this paper provides some guidance for engineers in site selection and preliminary design. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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18 pages, 5510 KiB

Open AccessArticle

Analytical Solution of Ice–Rock-Model Stress Field and Stress Intensity Factors in Inhomogeneous Media

by Feifei Cao, Laiwang Jing and Shaochi Peng

Appl. Sci. 2024, 14(4), 1412; https://doi.org/10.3390/app14041412 - 8 Feb 2024

Viewed by 953

Abstract

The stress distribution and fracture parameter calibration of ice–rock models are important aspects of studying rock properties at high altitudes and latitudes. However, progress in ice–rock modeling has been slow and singular, and it is limited due to the discrete nature of rocks [...] Read more.

The stress distribution and fracture parameter calibration of ice–rock models are important aspects of studying rock properties at high altitudes and latitudes. However, progress in ice–rock modeling has been slow and singular, and it is limited due to the discrete nature of rocks and the applicability of fracture mechanics. In this study, a circular inhomogeneous ice–rock model is proposed for the first time, and a method is provided for calculating the stress field of the model under biaxial loading. A method for calculating the single-crack stress intensity factor of the model subjected to biaxial compressive loading is also provided. The novelty of this work is that the inhomogeneous ice–rock model is treated as a superposition of two models, namely, a circular pore plate and circular ice, according to the superposition principle. The key is that the stress field distribution law of the ice–rock model is obtained based on the basis of the displacement continuity of the ice–rock interface. The analytical and approximate solutions of the stress intensity factor of a single crack were also obtained by considering the normal phase effect of the crack surface and combining the stress distribution law of the ice–rock model. Comparison with the CAE method was made to verify the correctness of the stress field and stress intensity factor calculation methods. The evolution laws of lateral pressure coefficients, the elastic modulus ratio of ice and rock on the stress field, and the stress intensity factor were analyzed. The effects of lateral pressure coefficients, elastic modulus ratios, and crack distributions on the failure modes were investigated using the extended finite element method (XFEM). This study can provide a theoretical basis for the evaluation of mechanical properties and prediction of the failure modes of frozen rock bodies. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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21 pages, 8303 KiB

Open AccessArticle

Study on Voids and Seepage Characteristics within Rock Fracture after Shear Dislocation Viewing from CT Test and Numerical Modeling

by Tingfa Dong, Jian Zhou, Ziqian Yan, Yanfang Wu and Tianqiao Mao

Appl. Sci. 2024, 14(3), 1013; https://doi.org/10.3390/app14031013 - 24 Jan 2024

Cited by 2 | Viewed by 1089

Abstract

In rock mass engineering, stress balance changes often cause the relative slip of fractures along a wall surface, impacting the seepage behavior of fluid in the fractures. Using computer tomography (CT) scanning, spatial models of fractures with dislocations ranging from 0 to 10 [...] Read more.

In rock mass engineering, stress balance changes often cause the relative slip of fractures along a wall surface, impacting the seepage behavior of fluid in the fractures. Using computer tomography (CT) scanning, spatial models of fractures with dislocations ranging from 0 to 10 mm were created to explore the relationship between changes in fracture dislocation and changes in fluid flow behavior, respectively. The spatial fractal dimension of cavity distribution within the fractures was calculated using a thin-plate filling approach to characterize the complexity of the fracture cavity distribution. The fluid flow within the dislocation fractures was then simulated using COMSOL, and the effect of cavity alterations in the form of dislocation on the fluid seepage behavior was analyzed using the spatial fractal. The results show that the values of mechanical aperture after dislocation of the fracture obtained by a CT test are normally distributed, the distribution range of mechanical aperture gradually widens with an increase in the dislocation distance, and the average mechanical aperture increases on a logarithmic curve. The relative spatial fractal dimension decreases gradually with an increase in dislocation distance, and the interconnected pathways within the fracture decrease; in addition, it is observed that the change in the relative spatial fractal dimension is closely correlated with the change in the mean mechanical aperture. Numerical simulations of dislocation fracture seepage found that the permeability increases nonlinearly with increasing dislocation distance. When the dislocation distance reaches 5 mm, nonlinear behaviors such as eddy currents occur, and the influence range of eddy currents gradually expands with the increase in dislocation distance under the influence of the boundary. Moreover, the inertia coefficient B in the Forchheimer equation and the critical hydraulic gradient Jc, which can describe the nonlinear seepage characteristics, show a power function decreasing trend with increasing dislocation distance, and the fluid in the fracture is more likely to produce nonlinear flow. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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15 pages, 5019 KiB

Open AccessArticle

Novel Understandings of Biomineralization in Backfill Materials: A Fundamental Investigation of Coal Gangue and Fly Ash Impact on B. pasteurii to Enhance Material Properties

by Shijie Guo, Alessandro Pasquale Fantilli, Hao Yan, Kai Sun and Luwei Ding

Appl. Sci. 2024, 14(2), 799; https://doi.org/10.3390/app14020799 - 17 Jan 2024

Cited by 1 | Viewed by 1155

Abstract

This paper proposes a fundamental investigation of coal gangue and fly ash impact on B. pasteurii to enhance the properties of backfill materials. The goal is to obtain effective microbial mineralization and potential mechanical properties of coal gangue and fly ash as backfill [...] Read more.

This paper proposes a fundamental investigation of coal gangue and fly ash impact on B. pasteurii to enhance the properties of backfill materials. The goal is to obtain effective microbial mineralization and potential mechanical properties of coal gangue and fly ash as backfill materials and to mitigate the impact of the most common binders used in the backfill material of mines. Micro-scale mineralization was performed with B. pasteurii bacteria using microbially induced carbonate precipitation (MICP) technology to clarify solid waste impact on B. pasteurii and to bind coal gangue and fly ash. Several tests were carried out to analyze the behavior of B. pasteurii, especially when it coexists with these two waste materials separately. In such cases, it was possible to observe a reduction in mineralization initiation time with respect to the natural mineralization of the MICP technology. Moreover, at the macro-scale, the new mineralized backfilling material shows good workability in the fresh state, whereas the strength at 28 days is 5.34 times higher than that obtained with non-mineralized coal gangue and fly ash. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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20 pages, 4532 KiB

Open AccessArticle

Effect of Cyclic Loading on Mode I Fracture Toughness of Granite under Real-Time High-Temperature Conditions

by Fei Lv, Fan Zhang, Subiao Zhang, Kangwen Li and Shuangze Ma

Appl. Sci. 2024, 14(2), 755; https://doi.org/10.3390/app14020755 - 16 Jan 2024

Viewed by 1067

Abstract

Under hot dry rock development, rock formations undergo the combined challenges of cyclic loading and high temperatures, stemming from various sources such as cyclic hydraulic fracturing and mechanical excavation. Therefore, a fundamental understanding of how rocks fracture under these demanding conditions is fundamental [...] Read more.

Under hot dry rock development, rock formations undergo the combined challenges of cyclic loading and high temperatures, stemming from various sources such as cyclic hydraulic fracturing and mechanical excavation. Therefore, a fundamental understanding of how rocks fracture under these demanding conditions is fundamental for cyclic hydraulic fracturing technology. To this end, a series of three-point bending tests were conducted on granite samples. These tests entailed exposing the samples to cyclic loading under varying real-time high-temperature environments, ranging from 25 °C to 400 °C. Furthermore, different upper load limits (75%, 80%, 85%, and 90% of the peak load) obtained in monotonic three-point bending tests were used to explore the behavior of granite under these conditions. The analysis encompassed the study of load–displacement curves, elastic stiffness, and mode I fracture toughness under cyclic loading conditions. In addition, the microscopic features of the fracture surface were examined using a scanning electron microscope (SEM). The findings revealed notable patterns in the behavior of granite. Cumulative vertical displacement in granite increased with the growing number of cycles, especially at 25 °C, 200 °C, and 300 °C. This displacement exhibited a unique trend, initially decreasing before subsequently rising as the cycle count increased. Additionally, the critical damage threshold of granite exhibited a gradual decline as the temperature rose. As the temperature ascended from 25 °C to 200 °C, the damage threshold typically ranged between 80% and 85% of the peak load. At 300 °C, this threshold declined to approximately 75–80% of the peak load, and at 400 °C, it fell below 75% of the peak load. Within the temperature ranging from 25 °C to 300 °C, we noted a significant increase in the incidence of cracks, crystal microfracture zones, and the dislodging of mineral particles within the granite as the number of cycles increased. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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13 pages, 3180 KiB

Open AccessArticle

A Study of the Characteristics of Micro-Seismic (ME) and Electromagnetic Radiation (EMR) Signals under the Static Load Conditions of Rocks

by Liao He, Qingfeng Li and Baifu An

Appl. Sci. 2023, 13(23), 12910; https://doi.org/10.3390/app132312910 - 2 Dec 2023

Cited by 3 | Viewed by 1125

Abstract

Geological hazards, such as the frequent occurrence of rock bursts in deep mining, emphasize the critical necessity for the early warning and prediction of dynamic fractures in coal and rock masses, as well as the destabilization of the surrounding rock. This study delves [...] Read more.

Geological hazards, such as the frequent occurrence of rock bursts in deep mining, emphasize the critical necessity for the early warning and prediction of dynamic fractures in coal and rock masses, as well as the destabilization of the surrounding rock. This study delves into the mechanisms of electromagnetic radiation (EMR) signals and their synchronous coupling with micro-seismic (ME) signals. EMR and ME signals from rock specimens were systematically collected during the uniaxial compression fracture process using a dedicated monitoring and acquisition system. Employing the wavelet analysis method, the original data underwent reconstruction and denoising, while the EMR and ME spectra, derived through fast Fourier transform, were subjected to detailed scrutiny. The comprehensive analysis unveiled that EMR signals arising from rock fractures exhibited precise timing synchronization with ME signals. Moreover, the dominant frequencies of both signals are closely aligned within the low-frequency band, indicating a remarkable degree of similarity and homology. These findings establish an experimental basis for the development of monitoring and early warning systems geared toward assessing damage to coal and rock masses using EMR and ME signals. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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21 pages, 4559 KiB

Open AccessArticle

Evaluation of the Rock Mechanical Properties of Shale Oil Reservoirs: A Case Study of Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin

by Jian Xiong, Renzhong Gan, Xiangjun Liu, Lixi Liang and Xiucheng Guo

Appl. Sci. 2023, 13(23), 12851; https://doi.org/10.3390/app132312851 - 30 Nov 2023

Cited by 2 | Viewed by 1201

Abstract

Rock mechanical properties play an important role in the exploration and development of shale oil reservoirs. To study the rock mechanical properties continuously distributed along the longitudinal direction of the formation, physical and mechanical property data of shales from the Permian Lucaogou Formation [...] Read more.

Rock mechanical properties play an important role in the exploration and development of shale oil reservoirs. To study the rock mechanical properties continuously distributed along the longitudinal direction of the formation, physical and mechanical property data of shales from the Permian Lucaogou Formation of the Junggar Basin were gathered through experimental tests. The regression analysis method was applied to obtain relationships between physical properties and rock mechanical properties. Based on this, new empirical relationships between rock mechanical properties were established. The results show that the uniaxial compressive strength (UCS) ranged from 48.40 to 147.86 MPa, the Young’s modulus (E_s) was between 3.02 and 20.63 GPa, the Poisson’s ratio (ν_s) ranged from 0.13 to 0.36, the cohesive force (C) ranged from 14.65 to 34.60 MPa, and the internal friction angle (φ) was between 27.61 and 46.94°. The rock mechanical properties were more sensitive to the P-wave interval transit time (Δt_c) and bulk density (DEN). Among them, the UCS was more sensitive to Δt_c, while the C, E_s, and ν_s were more sensitive to Δt_c/DEN. For UCS and E_s, an exponential function correlation is more reliable than linear expression and power function, whereas for C and ν_s, power function and linear expression were adopted for higher accuracy, respectively. Compared with the empirical equations presented in the literature, the empirical equations established in the paper are more accurate and reliable, making them applicable to the Permian Lucaogou Formation shale oil reservoirs in the Jimusar Sag of the Junggar Basin. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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25 pages, 21086 KiB

Open AccessArticle

A Thorough Investigation of the Dynamic Properties of Granite under Cyclic Loading

by Xiaobin Ding, Junxing Zhao, Yaojun Dong and Mi Zhou

Appl. Sci. 2023, 13(22), 12514; https://doi.org/10.3390/app132212514 - 20 Nov 2023

Cited by 2 | Viewed by 1131

Abstract

We propose a novel inverse analysis method that utilizes shockwaves to detect the operational condition of tested rock. To achieve this back analysis, an in-depth investigation of the dynamic properties of granite specimens was conducted. The dynamic properties of the granite specimens were [...] Read more.

We propose a novel inverse analysis method that utilizes shockwaves to detect the operational condition of tested rock. To achieve this back analysis, an in-depth investigation of the dynamic properties of granite specimens was conducted. The dynamic properties of the granite specimens were investigated using a triaxial cyclic loading machine, under different confining pressures, loading frequencies, stress amplitudes, and numbers of cycles, and a dynamic response model was constructed from the test data. The results show that the dynamic elastic modulus increased with the increase in confining pressure, while its damping ratio decreased. The dynamic elastic modulus and damping ratio increased with the increase in loading frequency. As the dynamic stress amplitude increased, the dynamic elastic modulus of the granite increased, but the dynamic damping ratio decreased. As the number of cycles increased, the dynamic elastic modulus and dynamic damping ratio of the granite decreased and gradually stabilized. The modified Duncan–Chang model was used to construct the dynamic response model of the specimens. It is worth saying that the correlation coefficient of the model is low at a loading frequency of 20 Hz. This indicates that the frequency has a greater effect on the dynamic response of the specimen compared with the confining pressure. The conclusions obtained from these tests can be used to study more comprehensively the interaction and causal relationship between different factors, and to prepare for the next steps of tunnel rock stress-state prediction. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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13 pages, 2761 KiB

Open AccessArticle

Study on Experimental and Constitutive Model of Granite Gneiss under Hydro-Mechanical Properties

by Lin Liu and Bo Wen

Appl. Sci. 2023, 13(22), 12130; https://doi.org/10.3390/app132212130 - 8 Nov 2023

Cited by 1 | Viewed by 1001

Abstract

Permeability, as a critical element in making sure the underground facilities are secure, is a vital consideration in analyzing the rock material seepage. Selecting granite gneiss from underground oil storage as the research sample in this study. Triaxial mechanical property tests under different [...] Read more.

Permeability, as a critical element in making sure the underground facilities are secure, is a vital consideration in analyzing the rock material seepage. Selecting granite gneiss from underground oil storage as the research sample in this study. Triaxial mechanical property tests under different hydro-mechanical properties were carried out under the rock full-automatic triaxial servo system that controls the application of axial pressure, confining pressure, and seepage pressure. Through experiments carried out, we obtained the rock samples’ mechanical properties and permeability in three stages of the stress–strain process. The study shows that the seepage pressure considerably affects granite gneiss strength and deformation parameters under hydro-mechanical properties. On the basis of the same confining pressure, in pace with the growth in seepage pressure, elastic modulus, the deformation modulus, and the peak strength present a prominent decreasing inclination. The derived mechanical parameters are bound up with the stages we divided. This study analyzes and discusses the relationship among the strains and permeability, establishing the granite gneiss hydro-mechanical coupling constitutive model. Verification shows the results in numerical and experimental matches well, indicating that the rock hydro-mechanical properties could be effectively represented by the constitutive model. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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12 pages, 40464 KiB

Open AccessArticle

Mechanical and Acoustic Emission Characteristics of Grouted Reinforcement in Fissure-Containing Rock-like Specimens

by Zhonglin Yu and Chenchen Song

Appl. Sci. 2023, 13(21), 11661; https://doi.org/10.3390/app132111661 - 25 Oct 2023

Cited by 1 | Viewed by 949

Abstract

In order to study the reinforcing effect of the different grouting materials applied in fissure rock engineering, ultra-fine cement slurry, cement–silicate slurry, and MARITHAN^® were used to carry out grouting tests on specimens of fissure-containing rocks. With the help of a uniaxial [...] Read more.

In order to study the reinforcing effect of the different grouting materials applied in fissure rock engineering, ultra-fine cement slurry, cement–silicate slurry, and MARITHAN^® were used to carry out grouting tests on specimens of fissure-containing rocks. With the help of a uniaxial compression acoustic emission test system, the mechanical characteristics of the grouted specimens were obtained, and the damage process of the specimens was revealed by using the acoustic emission signals. The tested results showed the following: the residual strength of the grouted specimens using the three grouting materials increased by 16.931%, 13.075%, and 39.998%, respectively; the ultra-fine cement grouting and cement–silicate grouting specimens showed damage patterns of shear-slip damage along the original rupture surface; the specimens of MARITHAN^® grouting cracked from a position near the end of the specimen with no damage to the grouted body portion; the cumulative acoustic emission energy curves of the grouted specimens showed obvious stage characteristics; and the acoustic emission energy distribution characteristics of the grouted specimens differed depending on the grouting materials. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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25 pages, 19832 KiB

Open AccessArticle

Study on the Influence of Rock Shape on Rolling Distance

by Feng Liu, Ning Hu, Gangchen Sun and Bai Yang

Appl. Sci. 2023, 13(20), 11351; https://doi.org/10.3390/app132011351 - 16 Oct 2023

Viewed by 1117

Abstract

To explore the influence of rock shape on rolling distance and effectively mitigate rockfall hazards, the following research was conducted. Factors influencing the rolling distance of rocks were determined through model experiments, and the mechanics of rolling resistance were analyzed. The coefficient RF, [...] Read more.

To explore the influence of rock shape on rolling distance and effectively mitigate rockfall hazards, the following research was conducted. Factors influencing the rolling distance of rocks were determined through model experiments, and the mechanics of rolling resistance were analyzed. The coefficient RF, reflecting the ease of rock rolling, and the shape parameter ψ, quantifying the rolling distance, were proposed. By incorporating the shape parameter into kinematic equations, formulas for calculating the rolling distance of rocks with varying shapes on diverse ground characteristics were derived. These formulas underwent validation using data from model experiments, revealing minimal disparities between the experimental and calculated values. Irregularities on the rolling surface, commonly referred to as “steps” due to the differences in surface hardness among various materials, as well as deviations and shifts in the rolling axis during rock movement, were identified as the primary factors influencing rolling distance and contributing to calculation errors. Combining these deviations for rocks of distinct shapes with theoretical formulas enabled the determination of the range of influence of rock rolling at various velocities, offering valuable insights for assessing areas prone to rockfall hazards. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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18 pages, 23730 KiB

Open AccessArticle

Experimental Research into the Ultrasonic P-Wave Velocity of Coal Slime Based Backfill Material

by Baifu An, Chenghao Cui, Jinfang Ren, Dongda Wang, Jiale Wang and Qiaomei Yi

Appl. Sci. 2023, 13(19), 11043; https://doi.org/10.3390/app131911043 - 7 Oct 2023

Cited by 1 | Viewed by 1052

Abstract

To study the influences of different mix proportions of materials on the ultrasonic p-wave velocity of coal slime based backfill materials, influences of four factors on the p-wave velocity of specimens were investigated by designing orthogonal tests and taking coal slime as the [...] Read more.

To study the influences of different mix proportions of materials on the ultrasonic p-wave velocity of coal slime based backfill materials, influences of four factors on the p-wave velocity of specimens were investigated by designing orthogonal tests and taking coal slime as the principal raw material. The four factors included the following: (A) the mass concentration of coal slime, (B) the content of high-water-content material, (C) cement content, (D) and content of fly ash. Test results revealed the following: (1) the ultrasonic p-wave velocity is in the range of 3.916 to 8.319 km/s and various factors are listed in a descending order as A, D, B, and C according to their influences on the ultrasonic p-wave velocity; (2) the ultrasonic p-wave velocity is positively correlated with the compressive strength and shear strength, with correlation coefficients separately of 0.87 and 0.65; (3) the equations for variations in the ultrasonic p-wave velocity under influences of different factors are fitted. The ultrasonic p-wave velocity has a quadratic polynomial relationship with factor A, while following exponential relationships with factors B, C, and D. A predictive model for characteristic parameters of the ultrasonic p-wave velocity of coal slime based backfill materials jointly influenced by the four factors was established based on the fitting equation for variations of single factors and ultrasonic p-wave velocity. The predictive model was then verified. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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11 pages, 805 KiB

Open AccessArticle

Emphasizing the Creep Damage Constitutive Model of Hydro-Mechanical Properties of Rocks: A Case Study of Granite Gneiss

by Lin Liu and Bo Wen

Appl. Sci. 2023, 13(19), 10967; https://doi.org/10.3390/app131910967 - 4 Oct 2023

Viewed by 1039

Abstract

The constitutive model of rock materials can describe the mechanical behavior of rocks in creep tests. Also, it is one of the important means to study the deformation and strength characteristics of rocks in complex stress environments. This paper is based on the [...] Read more.

The constitutive model of rock materials can describe the mechanical behavior of rocks in creep tests. Also, it is one of the important means to study the deformation and strength characteristics of rocks in complex stress environments. This paper is based on the analysis of the porosity variation characteristics of the internal structure under the coupling effect of rock hydro-mechanical properties. The concept of the hydro-mechanical properties variable is proposed, and the relationship between the coupling variable, damage and plastic deformation is established. By introducing the coupling variable, instantaneous damage variable and time-dependent damage variable into the yield surface equation, as well as the plastic potential energy equation and the stiffness matrix of the elastic–plastic creep constitutive equation, a hydro-mechanical properties creep damage coupling model was established to simulate the creep mechanical properties of rock under coupling. Based on the triaxial creep test results of granite gneiss, the model parameters are determined. By comparing the test results with numerical results, it was revealed that the model can better describe the creep mechanical properties of rocks under the coupling effect of hydromechanical properties. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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12 pages, 6178 KiB

Open AccessArticle

Investigation of Rock Joint and Fracture Influence on Delayed Blasting Performance

by Pengfei Zhang, Runcai Bai, Xue Sun and Tianheng Wang

Appl. Sci. 2023, 13(18), 10275; https://doi.org/10.3390/app131810275 - 13 Sep 2023

Cited by 1 | Viewed by 1133

Abstract

Geological structures such as joints and faults in rock mass have a significant influence on open-pit mining. Hence, it is critical to develop an understanding of dynamic joint behavior under blasting loading. This, in turn, can provide both theoretical and practical guidance to [...] Read more.

Geological structures such as joints and faults in rock mass have a significant influence on open-pit mining. Hence, it is critical to develop an understanding of dynamic joint behavior under blasting loading. This, in turn, can provide both theoretical and practical guidance to improve blasting rock fragmentation and associated bucket excavating efficiency. In this paper, delayed blasting on a highwall bench at an open-pit mine is used as an example; a nonlinear joint blasting model is also constructed. By simplifying the blasting wave propagation velocity and combining the relevant stress and displacement theories of type I and II cracks, equipotential diagrams of the stress and displacement field with the vibration velocity of the particle are obtained. Additionally, ANSYS is used to analyze the distribution of the stress field. This is able to be visualized by the degree of color change post-processing. It is concluded that, with the attenuation of the detonation wave energy, the stress exhibited a decreasing trend in this process. According to the distribution of the peak effective stress, it is found that the peak value first increases to 10–12 MPa and then shows a downward trend. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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19 pages, 5324 KiB

Open AccessArticle

Research on Particle Size and Energy Consumption Law of Hard Coal Crushing under Impact Load Based on SHPB Test

by Haibo Wang, Wenqing Xu, Bing Cheng and Qi Zong

Appl. Sci. 2023, 13(5), 3298; https://doi.org/10.3390/app13053298 - 4 Mar 2023

Cited by 5 | Viewed by 1889

Abstract

To study the particle size distribution and energy variation law of hard coal under a load, an impact compression test of hard coal specimens under different impact loading conditions was carried out using a Φ50 mm diameter Separate Hopkinson Press Bar (SHPB) test [...] Read more.

To study the particle size distribution and energy variation law of hard coal under a load, an impact compression test of hard coal specimens under different impact loading conditions was carried out using a Φ50 mm diameter Separate Hopkinson Press Bar (SHPB) test system. We implemented the theory of dynamic impact energy of rock to establish the calculation expression of hard coal impact crushing energy dissipation, and we established the Weibull distribution model of a crushing body to analyze the impact velocity in relation to the particle size distribution of hard coal crushing and crushing energy consumption. The results demonstrate that due to the different original states of the specimens, the damage to the specimens under static action is in the mode of conjugate plane shear damage, single bevel shear damage, and tensile damage. The damage process of the specimen under impact load loading is divided into three stages: elastic deformation, elastic–plastic deformation, and plastic softening, while the increase in the strain rate caused the peak stress of the specimen to increase. The Weibull distribution can characterize the impact crushing size distribution of hard coal specimens very well. The parameter of coal rock crushing degree is a power function that is influenced by the impact velocity; the greater the impact velocity, the higher the coal rock crushing degree, but the characteristic index of coal rock crushing fluctuates with the increase in impact velocity. As the impact velocity increases, the incident energy and reflected energy increase linearly, while the transmitted energy increases first and then decreases. The dissipation energy of coal rock crushing also increases linearly with the impact velocity. There is no obvious regular change between the energy dissipation rate of coal rock and impact velocity during impact damage, and the dissipated energy of macroscopic crushing only accounts for 10~20% of the incident energy; most of the energy is used for damping loss and damage loss. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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16 pages, 14650 KiB

Open AccessArticle

Study on Characteristic Strength and Constitutive Model of Red Sandstone under Hydraulic Coupling

by Xinwei Li, Zhishu Yao, Xianwen Huang, Xiaohu Liu and Xuesong Wang

Appl. Sci. 2023, 13(1), 391; https://doi.org/10.3390/app13010391 - 28 Dec 2022

Cited by 1 | Viewed by 1530

Abstract

The newly built shaft in the western region needs to pass through the deep Cretaceous stratum, where the pores and fissures are developed, the cementation ability is poor, and the surrounding rock is rich in water. Under the coupling effect of the stress [...] Read more.

The newly built shaft in the western region needs to pass through the deep Cretaceous stratum, where the pores and fissures are developed, the cementation ability is poor, and the surrounding rock is rich in water. Under the coupling effect of the stress field and seepage field, the surrounding rock is easy to deteriorate and loses stability. The hydraulic coupling test of Cretaceous red sandstone was carried out by using the TAW-2000 rock mechanics testing system, and the characteristic strength evolution law of red sandstone was analyzed; Mohr’s circle and strength envelope were obtained by the M–C criterion, and the influence mechanism seepage pressure on red sandstone was explored; and combined with the effective stress principle and M–C strength criterion, a constitutive model under hydraulic coupling was established. Confining pressure limits the development of cracks and strengthens the mechanical properties. The results revealed that red sandstone has the characteristics of low less clay, loose particles, and weak cementation capacity; under the action of water pressure, the cement between particles disintegrates and loses the cementation strength, resulting in a significant decrease in cohesion, and the loss of cementation strength is the internal reason for the softening of red sandstone. The constitutive model based on the effective principle and M–C criterion can better reflect the mechanical behavior of red sandstone under hydraulic coupling. This paper provides a research basis for understanding the microscopic characteristics and hydraulic coupling characteristics of Cretaceous weakly cemented sandstone. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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Review

Jump to: Research

18 pages, 3401 KiB

Open AccessReview

Underground Disposal of Coal Gangue Backfill in China

by Weijian Song, Jixiong Zhang, Meng Li, Hao Yan, Nan Zhou, Yinan Yao and Yaben Guo

Appl. Sci. 2022, 12(23), 12060; https://doi.org/10.3390/app122312060 - 25 Nov 2022

Cited by 31 | Viewed by 4537

Abstract

China’s total coal production in 2021 exceeded 4.13 billion tons, 52% of the world’s total. Coal gangue, a solid waste of coal mining accounts for 15–20% of coal production, when directly discharged on the ground surface as waste heaps, it occupies large areas [...] Read more.

China’s total coal production in 2021 exceeded 4.13 billion tons, 52% of the world’s total. Coal gangue, a solid waste of coal mining accounts for 15–20% of coal production, when directly discharged on the ground surface as waste heaps, it occupies large areas of land and cause environmental pollution. This paper summarizes the existing gangue backfilling methods, their working principles, efficiency, and application status. The methods that are meeting Middle and Western China’s mining demands are discussed in detail. The state-of-the-art technologies that can realize high-efficiency, centralized, and large-scale underground backfilling of coal gangue are analyzed. This paper shows that the industrial implementation of these technologies can increase the current maximum disposal capacity of coal gangue by three times, reaching five million tons per year. The equipment innovation and automation are analyzed, and the environmental effect of coal gangue backfilling is discussed. This review offers inspirations and guidelines for coal gangue disposal and the environmental hazard reduction of coal mining. Full article

(This article belongs to the Special Issue Advances and Challenges in Rock Mechanics and Rock Engineering)

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