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2025, 44 (6): 0-0
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Study on critical stress of circular chamber rockburst ^Hot!

PAN Yishan1, 2, GAO Xuepeng1

2025, 44 (6): 1363-1376 doi: 10.3724/1000-6915.jrme.2024.0965
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Rockburst is a dynamic disaster characterized by the sudden instability and violent fracturing of chambers under high-stress conditions, with the critical stress serving as the most pivotal indicator. In this study, the maximum load criterion and the maximum potential energy criterion for the occurrence of rockbursts in chambers were proposed, and the theoretical critical stress formulas for rockbursts in circular chambers under hydrostatic pressure were derived. The discrepancy in critical stress derived from the two discrimination criteria is less than 2%. This study indicated that the critical stress was mainly influenced by uniaxial compressive strength, rockburst energy index, internal friction angle, and support stress. The biaxial isobaric loading experiments were conducted on circular chamber specimens of granite gneiss and basalt with dimensions of 150 mm× 150 mm× 50 mm. The average error between the experimental and theoretical values of the critical stress was 2.53%. Comparative analysis with field cases revealed an average ratio of 0.55 between actual stress and critical stress, prompting subsequent refinement of the formula. The application of the critical stress formula was discussed from the aspects of hazard assessment, prevention design, and safety evaluation of chamber rockbursts.

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Research status and development trend of deep geological exploration techniques for hydraulic and hydropower engineering#br#

ZHANG Shishu

2025, 44 (6): 1377-1404 doi: 10.3724/1000-6915.jrme.2024.0921
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With the advancement of national infrastructure construction and energy resource development strategies, hydraulic and hydropower development in Western China has exhibited a deeper and larger-scale trend. However, due to the complexities of deep geological environments and limitations in exploration techniques, deep engineering often faces challenges posed by high-energy geological conditions, such as elevated in-situ stress, high ground temperatures, and significant hydraulic pressures. Consequently, these factors present a series of challenges for the planning and implementation of major national projects, underscoring the necessity for the development of exploration and testing techniques tailored to deep conditions. This paper summarizes the current state of research on deep geological exploration and testing techniques, including ultra-deep directional drilling methods, deep geophysical exploration techniques, detection methods during tunneling or drilling, in-situ testing techniques, and the classification and parameter values of deep rock masses. It also identifies existing challenges within these areas. Furthermore, the paper discusses the development trends in deep geological exploration and testing techniques. The research findings will provide a foundation for deep engineering construction and the exploitation and utilization of deep resources.

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Study on failure mechanism of slopes induced by the underground coal mining subsidence

SUN Shuwei1, YANG Zhaoxi1, JIA Peizhi1, WANG Xiaolong1, LI Guojun2

2025, 44 (6): 1405-1419 doi: 10.3724/1000-6915.jrme.2024.0671
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The underground mine workings induce movements in the overlying rock layers and alter stress fields, leading to the deterioration of rock properties in slopes, which can easily result in disasters such as slope landslides. This study compares the failure process of the underground mine-slope system under various underground mining conditions through bottom friction tests and numerical simulations. Consequently, the failure modes and deformation mechanisms of the slope influenced by underground coal mining subsidence were analyzed. The findings are as follows: (1) The effects of underground coal mining subsidence on slopes primarily include a reduction in the integrity and strength of the slope rock mass, a change in the inclination angle of the slope rock layer, an enhancement of the tensile effects on the slope surface resulting in cracking, and a modification of the geometric shape of the slope. (2) The fracture mechanism of the overlying rock strata involves the gradual bending and collapse of the strata towards the underground mine workings due to gravitational forces. The fracture surface of the rock strata develops in a geese-like pattern, with the centerline of the underground mine workings serving as the axis of symmetry in the deeper field, and is connected to the tensile fractures on the slope surface in the near-slope field. (3) The mechanisms of slope failure induced by underground mine workings can be categorized into two types: compression-type and traction-type. Compression-type slope failure typically occurs in the lower slope of mining subsidence, and the process can be divided into stages such as overlying rock collapse, subsidence compression, and slope sliding. Conversely, traction-type slope failure usually occurs on the upper slope of mining subsidence, with the process divided into stages including the collapse of overlying rock strata, traction and tearing, and slope sliding. (4) The geological structure significantly influences the instability and failure processes of the overlying slope. When the rock layers of the slope are oriented in a bedding fashion, the fracture surface patterns on both sides of the overlying rock layer rotate towards the dip direction, resulting in a relatively large deformation and failure range of the slope induced by mining subsidence. In contrast, when the rock strata are in a reverse inclined orientation, the effect of underground mine workings at the same position and burial depth on the slope displacement is significantly reduced. The research results provide valuable insights for identifying slope disasters in coal mining subsidence areas and for ensuring safety in open-pit to underground mining transition projects.

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Time-dependent analysis of bolt-grouting support structures in deep roadways

MENG Qingbin1, 2, ZHANG Xuan2, GE Zhengyu2, HAN Xu1, AN Gangjian1

2025, 44 (6): 1420-1437 doi: 10.3724/1000-6915.jrme.2024.0839
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To address critical engineering challenges such as high deformation rates, significant deformation magnitudes, and difficulties in stabilizing deep roadways, this study employs rock rheology theory to analyze the time-dependent characteristics of bolt-grouting support structures. A rheological model specifically designed to capture the deformation behavior of these structures was developed. By integrating deformation monitoring data from the surrounding rock at the Zhujixi Mine, this study elucidates the deformation mechanisms of a composite support system, comprising “bolt-shotcrete + prestressed cable/U-shaped steel + grouting” across various support stages. The findings indicate that single-component bolt-shotcrete support is insufficient for maintaining the stability of surrounding rocks in deep roadways. Conversely, a multi-component support approach effectively harnesses the load-bearing capacity of the support system to control severe deformations and mitigate catastrophic instabilities. Increasing the thickness of shotcrete significantly reduces deformation, while its compressive strength has a negligible effect. Similarly, enhancing the diameter and strength of anchor bolts, along with reducing their spacing, markedly improves deformation control. The increased material strength and decreased spacing of U-shaped steel also contribute to effective stabilization. Practical engineering applications confirm that a staged combined support strategy—comprising “bolt-net-shotcrete initial support + prestressed cable reinforcement support/U-shaped steel reinforced support + grouting reinforcement”—can effectively meet the safety requirements for large deformation control in the surrounding rock of deep roadways.

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Degradation mechanism and equivalent simulation method of shear strength of limestone stylolite under immersion

YANG Chao1, 2, LI Tianyi1, 2, WANG Jiao1, 2, JIANG Haonan2, XIONG Yun2, 3, PAN Huixiong3

2025, 44 (6): 1438-1449 doi: 10.3724/1000-6915.jrme.2024.0933
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Limestone is relatively dense and has low permeability. Its internal structural weak planes act as conduits for water within the rock mass, potentially leading to engineering instability and failure. To examine the degradation characteristics and mechanisms of the shear mechanical properties of limestone stylolite under immersion, the stylolite was categorized based on field investigations, and specimens were prepared for testing. The findings showed that stylolite with a width of b < 1 mm exhibited similar characteristics to limestone. The impact of immersion was primarily evident in the reduction of cohesion, though this decline was not substantial (approximately 11.0%). Stylolite with 1 mm ≤ b ≤ 5 mm and b > 5 mm predominantly demonstrated a decline in the internal friction angle after immersion. The reduction rates reached 21.2% and 30.9%, respectively. The stylolite is composed of suture membranes on both sides and metasomatic dolomite in the middle. Stylolite comprising metasomatic dolomite with a width of b < 1 mm is exceedingly rare. The infiltration of water primarily weakens the bonding force between the membrane and the bedrock. Stylolite with a width of 1 mm ≤ b ≤ 5 mm and b > 5 mm are more susceptible to sliding and a reduction in the internal friction angle after immersion, due to the dissolution of the dolomite at the edges. The analysis demonstrates that the solubility of metasomatic dolomite is closely related to the reduction in the internal friction angle, which can be employed to quantify the impact of immersion on the stylolite. Based on these findings, a simulation method for assessing the weakening of interface units due to changes in suture solubility was proposed. The deformation curve and failure process calculated by this method are in good agreement with the test results and effectively simulate the frictional sliding of particles during the shear process of the sample. This can serve as a reference and a source of guidance for the simulation of limestone sutures.

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Research on spatiotemporal characteristics perception and prediction methods of shallow buried coal seam mining pressure in valley areas

XU Huicong1, 2, LAI Xingping1, 2, SHAN Pengfei1, 2, GUO Zhong?an3, XUE Ke3, YAN Zhongming2, 4,WANG Huachuan1, 5, XU Gang2, MENG Zheng2

2025, 44 (6): 1450-1465 doi: 10.3724/1000-6915.jrme.2025.0057
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The Western mining area has emerged as a crucial “ballast stone” for ensuring China?s energy security. Accurately identifying and predicting the spatiotemporal characteristics of mining pressure is essential for the safe extraction of shallow coal seams in this region. The interplay between temporal stress evolution in the mining area and spatial differences in the support system, due to the absence of key layers in the uphill section, complicates the manifestation of mining pressure in shallow valley-buried working faces. To address the low predictive accuracy caused by the nonlinear and differentiated distribution of stope data in these shallow coal seam working faces, this paper proposes an intelligent prediction method for ground pressure in valley mining faces. This method factors in the physical constraints of the “inclined bench rock beam” type and the spatiotemporal characteristics of support pressure data, while also accounting for the absence of the main key stratum. Initially, a theoretical model of the “inclined step rock beam” with missing key stratum is established. The model integrates data analysis techniques such as principal component analysis, kernel density estimation, and the DBSCAN clustering algorithm to clarify the spatiotemporal correlation between complex static operating parameters—such as slope angle and working face location—and the local strengthening effect of support pressure. Subsequently, an improved TFT architecture deep learning prediction model for mining pressure is developed, incorporating spatiotemporal correlation features and static metadata. Results indicate that the absence of the main key stratum is the primary controlling factor for mining pressure manifestation in the uphill section of shallow buried working faces in valley areas. Stress concentration occurs in the middle of the working face during this process. By introducing static metadata such as slope angle and working face location, along with the spatiotemporal mechanism of differential support pressure, the prediction accuracy of mining pressure is significantly improved. Compared with particle swarm optimization support vector machine (PSO-SVM), LSTM, and other mining pressure prediction algorithms, the R² value increased by up to 28% and the RMSE decreased by up to 64.9%. This provides a valuable reference for recognizing spatiotemporal characteristics and issuing intelligent warnings for mining pressure in shallow buried working faces in western valley areas.

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The concept and technological implementation of active control for foot settlement of soft rock tunnels

CHEN Lijun, CHEN Jianxun, GUO Huijie, ZHANG Lixin, SUN Pengfei, LUO Hua

2025, 44 (6): 1466-1480 doi: 10.3724/1000-6915.jrme.2024.0860
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The arch foot of the initial support is a crucial component in the deformation control during the sequential excavation of soft rock tunnels. To address the issue of foot settlement control in the upper step of soft rock tunnels, this study first analyzed the settlement deformation mechanism of the arch foot and proposed an active control concept for foot settlement. Subsequently, the use of small-diameter prestressed feet-lock cables was suggested to control foot settlement. A second-generation support structure, combining steel-rib, steel mesh, shotcrete, and feet-lock pipes (cables) with both active and passive support functions, was established. The advantages of small-diameter prestressed feet-lock cables over traditional feet-lock pipes (bolts) were analyzed. Field tests verified the effectiveness of small-diameter prestressed feet-lock cables in controlling foot settlement of the initial support, and potential challenges in their future application were discussed comprehensively. The results indicated that: (1) The systematic bolts were generally short and ineffective in soft rock tunnels, leading to fewer installations and more focus on tunnel feet-lock pipes (bolts). (2) The upper step of the tunnel had limited space, making it difficult to install large-diameter feet-lock pipes, and increasing the number of small-diameter feet-lock pipes had limited control effect on foot settlement. (3) Small-diameter prestressed feet-lock cables provide suspension and active support functions for the arch foot of the initial support, offering significant advantages over feet-lock pipes (bolts) which rely on transverse bending stiffness to resist foot settlement deformation. (4) Prestressed feet-lock cables can also control foot convergence deformation of the initial support by adjusting installation angles and positions, showing promising application potential. (5) Foot deformation in sequential excavation of soft rock tunnels is persistent and sudden. For high strength and toughness structures, the concept of a third-generation support structure combining steel-rib, steel mesh, shotcrete, and feet-lock pipes (cables) is proposed, providing a direction for future research.

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Analysis of failure characteristics in delayed strain-type rock burst simulation test on granite

WANG Hongjian1, 2, ZHANG Jinran1, LIU Dongqiao3, ZHAO Fei1, 3, SHI Xiaoshan2, 4, REN Fuqiang5, WANG Chuang1

2025, 44 (6): 1481-1499 doi: 10.3724/1000-6915.jrme.2024.0601
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Strain-induced rock burst can be classified into instantaneous and delayed types according to rockburst causes. In this paper, a real three-axis unloading and delayed strain-induced rock burst simulation experiment was conducted on granite using a deep-seated rock burst simulation experimental system. Based on the signal collected by the acoustic emission system, quantitative analysis of parameters and waveform was performed. At the same time, high-speed photography was used to record the process of rock burst destruction, and the characteristics of rock surface failure were observed. The occurrence mechanism of delayed strain-induced burst in granite rock was revealed from multiple perspectives. The results indicate that granite occurred severe delayed type rock burst under the special stress loading condition which referred to loading in three directions, unloading one single face and then loading in vertical direction. Before the granite occurred rock burst, the AE ringing counts had an intensive and explosive growth while the AE b-value showed a sudden continuous decline. During the rock burst phase, the proportion of AE signals with high amplitude in low-frequency showed a growth trend, indicating there occurred rapid development of large-scale cracks with higher energy release in rock. Based on AE cluster analysis of RA-AF distribution division, it was found that there appeared tensile and shear composite failure, and both the amount of tensile and shear type cracks decreased at first and then had an obvious increase until final decreased. Tensile-shear crack ratio increased and then decreased, remained stable, rose and then dropped again to the lowest value. The fractal of AE ringing count rate presented dense distribution in a short period of time before burst, and had a sudden decrease sharply after the continuous vibration. Compared the warning information of rock burst determined by AE ringing count, b-value, major frequency, RA-AF distribution and AE fractal dimension, the average precursor response coefficients were 1.18%, 0.94%, 1.50%, 1.45% and 0.91% respectively. Hence, the response time for identifying precursors based on the AE major frequency-amplitude and tensile-shear crack amount and ratio were earlier. They could more finely characterize the complexity of AE signals and reveal the rock fracture mechanism. This study can provide reference for revealing the mechanism of delayed type rock burst occurrence and establishing disaster warning methods.

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Deformation characteristics of rock mass under dislocation of deep-buried strike-slip fault and its influence by geostress

ZHANG Ning1, 2, ZHOU Hui1, 2, GAO Yang1, 2, ZHU Yong1, 2, LU Jingjing1, 2, ZHAO Chengwei1, 2, CHENG Guangtan3

2025, 44 (6): 1500-1513 doi: 10.3724/1000-6915.jrme.2025.0056
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Fault dislocation leads to significant deformation in rock masses, resulting in the damage of deeply buried structures such as tunnels. This study aims to investigate the deformation characteristics of rock masses caused by fault dislocation and the influence of geostress under deep-buried conditions. Using the central Yunnan water diversion project as a case study, a physical model test of deep-buried strike-slip fault dislocation to examine the deformation characteristics of rock masses is first conducted. Subsequently, a nonlocal model for numerical simulation to analyze the impact of geostress on rock mass deformation is applied. The results are as follows: (1) Under fault dislocation, the main fracture develops within the fracture zone, and the fault undergoes shear movement along this main fracture. (2) Rock mass displacement decreases from the footwall to the hanging wall, with displacement distribution showing partitioning near the main fracture and exhibiting an S-shaped pattern. The equivalent strain localization band develops within the fracture zone, and the strain distribution curves exhibit a single-peak pattern. (3) Soil pressure decreases near the main fracture, increases on the footwall, and remains constant on the hanging wall. (4) The nonlocal model effectively reproduces the test results, showing that geostress affects the angle of the equivalent strain localization band and the peak strain. This research enhances the understanding of rock mass deformation under fault dislocation, provides a basis for analyzing the failure characteristics of deeply buried tunnels, and offers guidance for the construction design of cross-fault deep-buried tunnels.

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Physical simulation experiments on non-uniform extension of multi-cluster hydraulic fractures under complex fracturing conditions

TAN Peng1, 2, 3, XING Yuekun2, HAN Taisen2, CHEN Jinlong2, XU Hang2, CHEN Zhaowei1, 3

2025, 44 (6): 1514-1526 doi: 10.3724/1000-6915.jrme.2024.0823
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Achieving uniform propagation of multi-cluster hydraulic fractures within shale gas reservoirs containing natural fracture zones remains challenging. This study developed a physical simulation methodology to model multi-cluster fracturing in specimens containing prefabricated natural fracture zones. The experimental setup for sample preparation and pumping allows for the distribution of liquid into multiple cluster fractures according to a predetermined sequence of extension, with independent monitoring of flow rates for each cluster. Leveraging the engineering-experimental similarity in fracture propagation characteristics, in-situ stress, and geometry, analogous relationships were derived between experimental and engineering parameters. The effects of pumping rates (0.825 and 3.3 m³/min per cluster), cluster spacing (6 and 12 m), and spatial arrangement positions (middle and side clusters) of natural fracture zones on the propagation of multi-cluster hydraulic fractures in field applications were experimentally investigated. The results showed that: (1) Low pumping rates combined with large cluster spacing enhance the uniform propagation of multi-cluster hydraulic fractures in both samples with and without natural fracture zones. Fractures adjacent to natural fracture zones tend to propagate preferentially, thereby inhibiting uniform multi-fracture propagation. (2) High pumping rates and small cluster spacing facilitate the formation of single-cluster branch fractures and promote inter-cluster fracture connectivity. Conversely, low pumping rates and large cluster spacing result in simpler, non-interfering multi-cluster fracture morphologies. When the initiation cluster is adjacent to a natural fracture zone, the morphology of hydraulic fractures exhibits connectivity between hydraulic fractures and natural fracture zones. (3) During multi-fracture propagation, each cluster of fractures sequentially receives fluid inflow, indicating that multiple hydraulic fractures extend in an alternating sequence rather than simultaneously. Clusters situated within fracture zones tend to receive fluid inflow preferentially and connect with natural fracture zones. Consequently, the pump pressure curve exhibits fluctuations prior to reaching the break pressure. (4) Based on the theories of fracture instability extension and stress shadow, this study discusses the mechanisms of single-cluster fracture instability propagation and multi-fracture complexity enhancement. A high pumping rate increases the driving force for fracture propagation, while natural fracture zones decrease fracture resistance, thereby promoting single-cluster fracture instability. Namely, these factors inhibit the uniform extension of multi-cluster hydraulic fractures. Furthermore, a combination of high pumping rates and small cluster spacing intensifies interference between fractures, leading to the generation of complex fractures. Finally, optimization suggestions for the fracturing design were proposed, focusing on achieving uniform propagation of multiple hydraulic fractures near the wellbore while promoting the formation of complex hydraulic fractures in more distant regions.

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Research on rock strength prediction method based on rock fragment br upscaling theory

ZHAO Jianjian1, WANG Qian2, YANG Fujian3, CHEN Shi3, HU Dawei3, SHAO Jianfu4,

2025, 44 (6): 1527-1538 doi: 10.3724/1000-6915.jrme.2024.0886
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Rock mechanics parameters are crucial for the design and construction of deep underground engineering projects. However, their reliability is often compromised due to challenges in core extraction and in-situ testing. To tackle this issue, this study adopts a micro-scale perspective on rocks, introducing the Hill tensor to precisely describe the morphological distribution characteristics of different mineral components, as well as internal pores and fractures, at the micro-scale and their significant impact on the macro-scale physical and mechanical properties of rocks. Subsequently, upscaling theory is utilized to establish a functional relationship between the complex microstructure and macro-mechanical properties of rocks. Building on this foundation, a localized tensor is innovatively introduced to accurately represent the mathematical correlation between deformations at the micro-scale and the macro-scale. Throughout this process, the study thoroughly considers the damage mechanisms at the micro-scale, enhancing the model's predictive accuracy and applicability. Furthermore, the study fully accounts for the influence of confining pressure on rock mechanical behavior, aligning the model more closely with real-world engineering conditions. The results indicate that the model, based on the mineral content, mineral elastic parameters, and pore characteristics within the rock, can quantitatively characterize the macro-scale elastic modulus and rapidly predict both linear and nonlinear deformations, considering the effects of rock damage and confining pressure.

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Development and application of a real-time high-temperature and high-stress true triaxial fracturing test system

GUO Wuhao1, 2, GUO Yintong1, 2, CHANG Xin1, 2, WU Mingyang1, 2, HE Yuting1, 2, BI Zhenhui1, 2, ZHANG Xinao1, 2, TENG Shilong1, 2, WANG Lei1, 2, YANG Chunhe1, 2

2025, 44 (6): 1539-1552 doi: 10.3724/1000-6915.jrme.2024.0665
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To investigate the initiation and propagation of fractures in deep oil, gas, and geothermal energy reservoir stimulation, an independently developed real-time high-temperature and high-stress true triaxial fracturing test system was created. This system bridges the gap between laboratory fracturing simulations and actual deep reservoir conditions. It is designed to simulate the fracturing and fracture propagation behavior of 300 mm cubic rock samples under in-situ deep reservoir conditions. The system monitors and processes parameters such as stress, displacement, pump pressure, flow rate, and acoustic emission signals during fracture propagation. The maximum stress in the X, Y, and Z directions can reach 88 MPa, and the internal temperature of the sample can be heated to 350 ℃. The intelligent temperature control mode ensures uniform heating of the entire sample, and the maximum pump pressure is 210 MPa when slickwater is used as the fracturing medium (120 MPa with supercritical CO2). The system has successfully conducted hydraulic fracturing tests of shale and supercritical CO2 fracturing tests of granite under high-temperature and high-stress conditions. The test results demonstrate high accuracy and good stability. Under high-stress conditions, post-peak fluctuations in the pump pressure curve are intensified. High temperatures reduce breakdown pressure and increase fracture complexity. When supercritical CO2 is used as the fracturing medium, the breakdown pressure of granite significantly decreases, the number and energy level of acoustic emission signals weaken, and fracture complexity increases. These findings provide theoretical and technical support for optimizing deep reservoir reconstruction technology.

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Refined meteorological early warning for rainfall-induced landslide based on temporal probability model

SONG Yufei1, LI Xiang2, FAN Wen2, YU Ningyu2, CAO Yanbo2, DENG Longsheng2, TAO Hong3

2025, 44 (6): 1553-1568 doi: 10.3724/1000-6915.jrme.2024.0805
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The landslide meteorological early warning model based on empirical rainfall thresholds (ERT) often has a low warning accuracy, and the temporal probability model (TPM) is expected to address this shortcoming. To verify this hypothesis, a comparative experiment was conducted. First, we used accumulated effective rainfall-duration (EE-D) and same-day rainfall plus accumulated effective rainfall over the previous four days (R0-AE4) as variables to construct two sets of TPM models. The receiver operating characteristic (ROC) curve and correlation coefficient were then used to evaluate the discriminative and predictive abilities of ERT and TPM. Subsequently, the conditional probability formula was employed to couple the spatiotemporal probability of landslides, resulting in the proposal of a probabilistic landslide meteorological early warning model (P-LEWM). Finally, through simulated warnings, P-LEWM was compared with the matrix-based landslide early warning model (M-LEWM), which was constructed using ERT. The results indicate that: (1) The ERT/TPM constructed with R0-AE4 is more accurate in assessing the hazard level of rainfall-triggered landslides, with the area under the ROC curve increasing by 6.8% to 12.5% compared to EE-D. (2) The TPM proposed in this paper can accurately predict the probability of rainfall-triggered landslides, with a correlation coefficient between the predicted and recorded triggering-rainfall amounts exceeding 0.83. Additionally, the EE-D type TPM is more accurate for heavy rainfall prediction, while R0-AE4 is more suitable for regular rainfall events. (3) The EE-D type ERT tends to underestimate the hazard level of prolonged heavy rainfall in triggering landslides, causing M-LEWM to miss numerous landslides during two typical rainfall events in 2018, with a missed rate exceeding 50%, whereas P-LEWM constructed with TPM achieved a correct alert rate of over 90%. (4) Due to the accurate TPM and a reasonable spatiotemporal model coupling method, the correct alert rate of P-LEWM proposed in this paper has significantly improved compared to M-LEWM. The correct alert rate increased by 20.7% to 26.0%, the reasonable correct alert rate increased by 15.6% to 28.6%, and the missed alert rate decreased by more than 20.5%.

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Frost heave characteristics and in-situ testing analysis of carbonaceous slate tunnel surrounding rock in high-altitude cold regions

LU Hanqing, BAO Weixing, YIN Yan

2025, 44 (6): 1569-1584 doi: 10.3724/1000-6915.jrme.2024.0620
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To investigate the frost heave characteristics of transversely isotropic surrounding rock tunnels, we employed unidirectional freezing tests on saturated carbonaceous slate with varying bedding inclinations, theoretical modeling of uneven frost heave force, and in-situ testing. Our study focused on the frost heave characteristics of the carbonaceous slate tunnel surrounding rock, the tunnel temperature field, and the distribution characteristics of the surrounding rock frost heave force. The results revealed the following: (1) Under unidirectional freezing conditions, the uneven frost heave coefficient of slate increases progressively with the temperature gradient. The larger the freezing direction and bedding inclination angle, the stronger the uneven frost heave. (2) The envelope diagram of the freeze-thaw cycle of the surrounding rock at the entrance of the Heiqia Tunnel during the construction period shows a pear shape, with the lowest temperature and the highest freezing depth at the arch foot, reaching a maximum freezing depth of 2.97 m. (3) The measured frost heave force of the surrounding rock-structure ranged from 0.08 to 0.63 MPa, with the maximum at the left arch foot and the minimum at the left arch shoulder. (4) Considering the relationship between the freezing direction and the inclination angle of slate bedding, the theoretical model of uneven frost heave force in cold region tunnels elucidates the uneven frost heave characteristics of transversely isotropic surrounding rock. This model can serve as a reference for anti-freezing design in high-risk frost damage areas of transversely isotropic surrounding rock tunnels in cold regions.

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Research of rock blasting seismic energy radiation and its dependence on blasting source and free surfaces

LI Yongzhen1, 2, LU Wenbo1, 2, WANG Yang1, 2, CHEN Ming1, 2, YAN Peng1, 2

2025, 44 (6): 1585-1595 doi: 10.3724/1000-6915.jrme.2024.0862
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To examine the impact of blasting source and free surface conditions on the energy proportion of rock blasting seismic waves, this study conducted two field single-hole blasting tests and vibration monitoring. The measured energy proportion of blasting seismic waves under various conditions was then analyzed in detail. A calculation model for seismic energy radiation was developed based on the crack boundary of rock blasting. Using the number of initial free surfaces as a key variable, the influence of blasting source conditions on the blasting seismic energy proportion was further investigated through numerical simulations. The results show that the measured energy proportion of blasting seismic waves in the field tests ranges from 0.83% to 11.70%. Significant variations were observed among different monitoring points, influenced by factors such as distance, propagation path of seismic waves, and blasting source conditions. Adding an additional free surface to the bench blasting with two free surfaces reduced the measured energy proportion of seismic waves by an average of 19.02%. The blasting seismic energy proportion is closely related to the computational boundary and the loading process. By consistently selecting the crack boundary of rock blasting as the computational boundary, the actual proportion of blasting seismic energy radiated outward from the blasting source can be accurately determined. The number of initial free surfaces primarily affects the energy proportion by altering the crack boundary area, with the energy proportion decreasing as the number of free surfaces increases. Under conditions with one, two, and three initial free surfaces, the blasting seismic energy proportions were 9.47%, 7.82%, and 6.36%, respectively.

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Study on vertical cross-interface expansion and permeability characteristics of N2 foam fracturing cracks in coal measures reservoirs

CHAI Wangyang1, LI Wenda1, LIANG Weiguo1, 2, WANG Zaiyong1, REN Sentao1, LUO Hongye1

2025, 44 (6): 1596-1611 doi: 10.3724/1000-6915.jrme.2024.0967
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Indirect fracturing technology is frequently employed to enhance the exploitation of coalbed methane (CBM) in fractured, low-permeability coal seams. Investigating the vertical cross-interface propagation behavior of fracturing cracks in different fracturing media is crucial for improving vertical communication and permeability enhancement in reservoirs. This study conducted experimental research on the cross-interface propagation of true triaxial hydraulic fractures in coal-rock combinations, utilizing water, N2 gas, and N2 foam under varying vertical stress difference coefficients (Kv). The evolution law of injection pressure, dynamic response characteristics of acoustic emission (AE), fracture propagation morphology and fracture surface conductivity difference were compared and analysed, and the vertical communication and permeability enhancement effects of different fracturing media were comprehensively evaluated. The results indicate that: (1) Regarding the evolution of liquid injection and AE dynamic response, under identical Kv conditions, N2 foam fracturing exhibits characteristics of extended pressurization time, higher fracture pressure, greater AE energy, fewer cumulative ringing counts, and concentrated frequencies of fracture initiation and propagation events. (2) Concerning fracture network morphology, N2 foam fracturing tends to create a penetrating two-wing fracture network with extensive vertical extension and expansion. Compared to water and N2 gas, it facilitates better vertical communication and permeability enhancement in multi-layered reservoirs during indirect fracturing. (3) For vertical cross-interface expansion of fracturing cracks, the critical cross-layer Kv values for N2 foam, water, and N2 gas are 0.28, 0.39, and 0.50, respectively. N2 foam can achieve cross-interface expansion of coal and rock masses under lower Kv conditions, broadening the application range of indirect fracturing technology. (4) In terms of fracture network conductivity, at Kv = 0.50, the in-situ reinjection pressure for N2 foam fracturing is 9.14 and 10.19 MPa lower than that for water and N2 gas, respectively. Additionally, the fracture opening post-fracturing is 0.108 5 and 0.169 6 mm larger than those for water and N2 gas, respectively. The lower in-situ reinjection pressure and larger fracture opening suggest that the conductivity of the N2 foam fracture network is superior. (5) Regarding permeability characteristics, seepage simulation results reveal that the permeability of the fracture network post-N2 foam pressure is 2.95 and 11.86 times that of N2 gas and water, respectively. In summary, compared to water and N2 gas fracturing, N2 foam, with its high viscosity and low filtration properties, more effectively promotes fracture vertical cross-interface expansion and permeability enhancement, making it more suitable for the indirect fracturing of coal measure reservoirs.

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Study on the effect of rock mesoscopic heterogeneity on its compressive mechanical properties based on GB-DDA method

GAO Shanhua1, 2, ZHANG Kaiyu1, 2, 3, YANG Mei1, 2, LIU Feng4, ZHU Kanyuan5

2025, 44 (6): 1612-1623 doi: 10.3724/1000-6915.jrme.2024.0919
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Discontinuous deformation analysis (DDA) is an implicit discrete element method used to simulate the deformation of discrete block systems. To investigate the influence of mineral grains on the initiation, propagation, and coalescence of microcracks during rock loading, a Voronoi mineral grain model (GB-DDA) that adheres to statistical laws was established based on the DDA method. Compared to laboratory experiments, the GB-DDA, calibrated by meso parameters, can accurately simulate the mechanical response of Barre granite under tension and compression, enabling the quantitative analysis of intragranular and intergranular damage evolution processes. Using quasi-static uniaxial compression experiments, several GB-DDA numerical models with varying average grain sizes, grain roundness, and mineral content were developed to study the influence of mesoscopic heterogeneity on the compressive mechanical properties of Barre granite. Research findings indicate that during quasi-static uniaxial compression, the number of cracks in the numerical Barre granite samples, generated by different factors, follows the order: intergranular tensile cracks, transgranular tensile cracks, intergranular shear cracks, and transgranular shear cracks. The uniaxial compressive strength, elastic modulus, and Poisson's ratio of the rock are significantly affected by average grain size, grain roundness, and mineral content. An increase in average grain size and grain roundness promotes the initiation of shear cracks but has little effect on intergranular and transgranular cracks. Additionally, an increase in biotite content promotes the generation of intergranular cracks but has minimal impact on tensile and shear cracks.

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The bearing capacity and load transfer mechanism of GFRP bar micro uplift pile

BAI Xiaoyu, ZHANG Yingjie, WU Zekun, SUN Gan, LIU Junwei, YAN Nan

2025, 44 (6): 1624-1635 doi: 10.3724/1000-6915.jrme.2024.0952
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To investigate the load-carrying performance and load transfer mechanism of glass fiber reinforced polymer micro uplift piles (GFRP-MUP), field ultimate load tests were conducted on both GFRP-MUP and steel-bar micro uplift piles (SB-MUP). Based on the field tests and numerical simulations, the damage evolution characteristics of the anchored solid were revealed. The study demonstrates that: (1) The average destructive load of GFRP-MUP can reach up to 941.7 kN, approximately 1.73 times the bearing capacity of SB-MUP of the same specification, fully meeting the project’s flotation resistance requirements in terms of pullout bearing capacity. (2) Under extreme loading conditions, the GFRP-MUP anchorage body was pulled out with an average displacement of 26.1 mm, identifying the anchorage body-rock interface as the weak part of the anchoring system. (3) The shear stress of the anchor bars in both materials of micro uplift piles initially increases and then decreases, with the highest shear stress at the GFRP bar-anchorage body interface reaching 4.30 MPa. This indicates that GFRP bars can serve as a suitable substitute for steel bars in anti-buoyancy structures. (4) Damage to the GFRP-MUP anchorage body under extreme load is primarily concentrated within 2.7 meters below the orifice. Compared with SB-MUP, it is preferable to use micro uplift piles with shorter anchorage lengths and larger anchorage diameters to control the overall displacement of the anti-buoyancy structure and enhance anchorage efficiency.

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Large-scale shaking table test study on seismic performance of geocell retaining wall with tensioned tape

JIN Feifei1, 2, 3, SONG Fei1, 2, 3, HUANGFU Zhao1, 2, 3, SUN Chuandi1, 2, 3

2025, 44 (6): 1636-1648 doi: 10.3724/1000-6915.jrme.2024.0864
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A large-scale shaking table model test was conducted to investigate the seismic performance of geocell retaining walls with and without ribbed bands. This study analyzed the changes in confining pressure, acceleration amplification factor, and horizontal displacement of the wall under earthquake action for both models by applying seismic waves with varying amplitudes, frequencies, directions, wave types, and durations. The results indicate that as amplitude increases, both the confining pressure and horizontal displacement of the two models gradually increase. Additionally, the acceleration amplification factor shows an amplifying effect along the height of the wall. When the frequency is below 4 Hz, both cell confining pressure and acceleration amplification factors are relatively low for each model, moreover, displacement decreases with increasing frequency. Conversely, when the frequency exceeds 4 Hz, all three factors gradually increase. The dynamic response of the retaining walls to XZ-directional vibrations is significant. Different types of seismic waves have varying effects on wall displacement, emphasizing the importance of considering regional seismic wave characteristics in seismic design. Holding time has minimal impact on the dynamic response of retaining walls. The seismic performance of the two models differs, with the reinforced retaining wall demonstrating superior performance. To enhance top stability, reinforcement tape should be placed at the top of the wall. The residual displacements of the two models are 32.58 and 30.32 mm, respectively, equivalent to 2.04% and 1.89% of the wall height, which do not meet the displacement failure criteria. Tensile strips can effectively reduce residual displacement and improve seismic performance. At an amplitude of 1.0 g, potential slip surfaces are observed in the unreinforced retaining wall but not in the reinforced one. Unreinforced retaining walls are suitable for areas with seismic fortification intensity not exceeding IX, while reinforced retaining walls can be used in areas with higher seismic intensity. These findings provide a basis for the seismic design and engineering application of geocell retaining walls.

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Study on mechanical properties and compaction quality evaluation of gravel soil subgrade based on impact load method

LI Mengwei1, 2, LU Zheng1, TANG Chuxuan1, 2, HU Zhi3, CHAI Shaoqiang4, LIU Yong4

2025, 44 (6): 1649-1657 doi: 10.3724/1000-6915.jrme.2024.0641
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The impact loading method is a technique used to assess the compaction quality of subgrade by applying impact forces and analyzing the resulting response signals. Investigating the response mechanism of gravel soil subgrade under impact loading enhances our understanding of its mechanical properties and improves the evaluation principles of subgrade compaction quality using this method. The actual working conditions of gravel soil subgrade were fully considered, and a dynamic response model was established using the discrete element method. The model parameters were calibrated through triaxial tests, and its validity was verified by field experiments. Subsequently, the attenuation characteristics of dynamic stress in the subgrade under different compaction densities were explored and compared with results from continuum medium theory. A quantitative model relating porosity to the resilient modulus was further developed. The variations in surface response of the subgrade with changes in its properties were analyzed, and the effects of different impact load amplitudes and plate radii on the effective detection depth were discussed. The findings are as follows: (1) Porosity significantly affects the attenuation of internal dynamic stress in gravel soil subgrade, with faster attenuation observed at lower porosity levels; the dynamic stress obtained using continuum medium theory is generally lower, with a maximum difference exceeding 70%. (2) There is a strong linear relationship between porosity and resilient modulus of gravel soil subgrade, validating the feasibility of using the impact loading method to evaluate subgrade compaction quality. (3) The plate radius significantly impacts the effective detection depth of the impact loading method, with effective detection depths within 0.3 m for plate radii of 0.15 and 0.2 m, and between 0.3 and 0.4 m for a radius of 0.25 m.

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Study on static and dynamic shear characteristics of geotextile- residual soil interface considering wet-dry effect

FENG Yuquan1, ZHU Rui1, 2, 3, ZHOU Feng1, GUO Wanli3, ZHANG Lingka4, WANG Mengling1

2025, 44 (6): 1658-1670 doi: 10.3724/1000-6915.jrme.2025.0039
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Geotextiles are extensively employed for slope reinforcement in granite residual soil regions. However, the static and dynamic shear characteristics of geotextile-granite residual soil interfaces under wet-dry conditions remain inadequately understood. This study conducted monotonic and cyclic shear tests on the interface between geotextile and granite residual soil, considering wet-dry effects. The shear stress-displacement relationships, shear strength parameters, and shear stiffness variations were analyzed with respect to wet-dry cycles and amplitudes. The results indicate that during monotonic shear processes, interface roughness progressively increases with wet-dry cycles. The wet-dry cycle has a more pronounced impact on the strength parameters of the geotextile-soil interface compared to the wet-dry amplitude. With the increasing number of shear cycles, the hysteresis curve of the geotextile-soil interface expands outward, and the interface shear stiffness increases, while the damping ratio decreases. Cyclic shear cycles have a limited effect on strength parameters, whereas wet-dry cycles primarily influence the cyclic shear modulus. Cohesion is more significantly affected by cyclic shear history than the internal friction angle. Additionally, repeated wet-dry processes weaken the structural integrity of granite residual soil and enhance the interlocking action of the geotextile-soil interface. The cyclic shear process can reduce the roughness of the geotextile-soil interface, which explains the observed trend of initially increasing and subsequently decreasing interface shear characteristics under varying wet-dry histories.