Rock Pressure Research Articles

Top Coal Weakening by Pulse Hydraulic Fracturing and Roof Cutting by Directional Hydraulic Fracturing for Control of Hanging Roof in the Face End of Fully Mechanized Top Coal Caving

Abstract Due to the supporting effect of the coal pillar on the side of the roadway, there is often a problem of the top coal and roof in the working face end not collapsing in time. The single directional hydraulic fracturing method cannot directionally cut off the top coal of the working face end. To overcome the above shortcomings, this article first proposes a method of controlling top coal and roof in the working face end by pulse and directional hydraulic fracturing. The method of using pulse hydraulic fracturing to weaken the top coal and directional hydraulic fracturing to cut off the roof to induce rock pressure to break the coal is used to control the timely collapse of the top coal and roof in the working face end. When the vertical stress on the top coal is greater than the strength of the weakened top coal, the top coal and roof begin to collapse. The vertical displacement of the weakened top coal and the cut roof gradually decreases from low to high, and the caving top coal and roof finally fill the goaf. The maximum reduction in stress concentration of coal pillar is about 75%. Then, the principles for determining the parameters of this method were provided. Finally, the industrial experiment was conducted in the coal mine. The construction water pressure of the roof is between 30 and 40 MPa. The construction water pressure of top coal ranges from 8 to 16 MPa, with an amplitude of approximately 4 MPa. Directional crack is formed within an area of 3.3 m in the direction of the adjacent roof borehole. A crack network is formed within a 4 m area near the top coal borehole. After hydraulic fracturing, the top coal and roof in the working face end collapse with mining.

Model test of foundation pit excavation adjacent to the existing double-lane tunnel

Abstract To study the influence of foundation pit excavation on the adjacent existing double-track tunnel, a model box test with a similarity ratio of 1/50 was carried out. In this paper, the mechanical parameters of loess around the tunnel are determined through laboratory tests, and the miscellaneous fill, loess, sand, tunnel structure, support structure, and retaining wall are prepared by similar principles. The variation of the surface settlement, the deformation of the retaining wall, and the surrounding rock and soil pressure of the tunnel were analyzed by using equipment such as the miniature earth pressure box, dial gauge, and strain gauge. The results of the study showed that the existence of the supporting structure makes the bending moment of the retaining wall show the phenomenon of negative value first, then positive value, and finally negative value. In the process of foundation pit excavation, when the horizontal distance of the model surface is 4 times the excavation depth, the foundation pit excavation has little effect on the settlement of the model surface. The earth pressure value of the surrounding rock decreases with the increase of the excavation depth of the foundation pit. The earth pressure value of the surrounding rock is the right > the left > the lower part > the upper part and the excavation of the foundation pit has the greatest influence on the upper and left sides of the surrounding rock close to the side of the foundation pit, and the least impact on the right side of the surrounding rock.

Research on the failure mechanisms and preventive actions of tunnels under butterfly load in loess regions

The results of surrounding rock pressure measurements from numerous loess tunnels exhibit a butterfly distribution pattern, subsequently referred to as ’butterfly load’. This pattern significantly deviates from the load distribution and magnitude—referred to as ’specification load’—calculated by current Chinese tunnel design specifications. By means of model experimental and numerical simulation, the mechanical behavior, failure cause, failure mechanism and preventive actions of tunnel structure under different load distribution are studied. The experimental results indicate that the ultimate bearing capacity of the tunnel structure under the butterfly load is significantly lower than that under the specification load, with the ultimate bearing capacity decreasing as load unevenness increases. The butterfly load increases the unevenness of the axial force distribution throughout the annular structure and also causes the structure to produce reverse moments in the vault and arch shoulder. Similarly, the morphological characteristics of the cracks show that the butterfly load most significantly influences the tunnel vault and arch shoulder. Under the influence of the butterfly load, the lining structure is prone to developing cracks at the arch shoulder and arch foot positions, with tensile cracks located at the vault position. Aiming at the failure mechanism of tunnel structure under butterfly load, it is suggested to implement advanced small conduit grouting at the tunnel arch to suppress the dislocation of the formation and to lay root piles at the arch foot to improve the bearing capacity of the tunnel bottom. The prevention effect of this technology in different loess regions is sandy loess > general loess > clay loess.

Crack evolution and fractal characteristics of fractured red sandstone based on acoustic emission parameters

Rock is a widely used engineering material, and accurate understanding of its internal microcrack evolution process during loading can provide a theoretical basis for preventing instability and failure in rock engineering. The rock pressure test system and acoustic emission equipment were used to carry out uniaxial loading and acoustic emission monitoring tests on fractured red sandstone. Based on the RA and AF values of acoustic emission and the fractal theory, the internal crack patterns and evolution rules of red sandstone with different crack angles were explored. The results show that the compressive strength of red sandstone varies with the crack Angle in the shape of “U”, and there is an obvious stress drop after the elastic stage of 30° and 45° crack red sandstone, which has a good correspondence with the acoustic emission ringing count rate. During the loading process, the damage mainly caused by tension cracks first appears inside the rock, and then the tension cracks increase steadily and the shear cracks gradually increase, indicating that the rock enters the stage of fracture instability development. With the development of shear cracks, the peak strength is finally reached and the instability failure occurs. During the loading process of 30° fracture red sandstone, the corresponding stress drop phenomenon of “shear crack group” appears. According to the D/S statistical analysis of different crack samples based on acoustic emission ringing count, the fractal dimension presents a decreasing-rising-decreasing trend with the increase of crack inclination, which corresponds to the change of the complexity of crack development in rock.

Research on high‐pressure abrasive water jet slotting and pressure relief technology for hard rock roof

AbstractTo solve the problem of severe rock pressure near coal mining face tunnels, a high‐pressure abrasive water jet slotting and roof breaking pressure relief technology is proposed. First, the laneway deformation mechanism and the process of hard rock slotting using high‐pressure abrasive water jets under long‐distance cantilever conditions are analyzed, and the crack initiation conditions of roof strata are obtained. Second, slotting tests under different slotting pressures, nozzle diameters, abrasive particle sizes and slotting times were carried out, and the slotting parameters of a high‐pressure abrasive water jet on a typical roof rock were obtained. Finally, industrial application was carried out in the 81,403 working face of Huayang No.1 Mine. After the hydraulic roof slotting measures were implemented in the test area, the maximum axial force of the anchor cable was reduced to 67 kN, which was 35.5% lower than that of the comparison. The average stress of the coal seam was 15 MPa, which was approximately 25% lower than that of the comparison. The deformation of the tunnel in the experimental area was significantly controlled, with an average movement of 30.0% toward the roof and floor of the tunnel and an average movement of 23.2% toward the two sides of the tunnel. Compared with the movement in the comparison section, the movement toward the roof and floor of the laneway was 42.3% lower, and the movement toward the two sides was 38.2% lower. The industrial application results show that high‐pressure abrasive water jet roof slotting and pressure relief technology can cut off the stress transmission path between the roof rock on both sides, effectively improve the stress state of the surrounding rock of the laneway, reduce the deformation of the roof, floor and two sides of the working face in the later stage of the mining laneway.

Failure Mechanism and Control Technology of the Primary Support for Asymmetric Deformation Disaster of Deep Tunnel

Asymmetric large deformation disasters inevitably occur when highway tunnels cross active fault zones. Relying on the Nanlangshan No.1 Tunnel Project, the mechanism of asymmetric deformation is analyzed based on the in-situ engineering geology and tunnel monitoring data, and numerical calculations are used for verification. Based on the results of asymmetric large deformation disaster analysis, the control scheme of double-layer primary support is proposed, and the design is optimized with numerical calculation before engineering practice. The conclusions are as follows: 1. The original primary support program cannot withstand the asymmetric surrounding rock pressure, and the slip of the weak interlayer in the engineering geology is the main reason for the asymmetric deformation disaster in the tunnel. 2. According to the results of the numerical calculations, the tilted weak interlayer greatly reduces the stability of the surrounding rock, which leads to the local bending damage in the left shoulder of the tunnel, and the local shear deformation damage in the right arch girdle. 3. When using the double-layer primary support program, the appropriate delay of support timing for the second layer of primary support can effectively decrease the tunnel asymmetric deformation. However, if the second layer of primary support lag distance is too large, it will also lead to tunnel deformation convergence larger, or support failure and other issues. So, it is recommended that the second layer of primary support lags behind the first layer of primary support by 2 m to be applied.

Study on the Susceptibility of Steel Arches with Letting Pressure Nodes Based on Incremental Dynamic Analysis

When soft rock tunnels pass through fractured fault zones, they are particularly susceptible to extrusion and large-scale deformations, especially during seismic events. To address these challenges, this study introduces an innovative yield-support steel arch design featuring a circumferential letting pressure node at its core. This design delivers incremental support resistance within the deformation zone and a susceptibility curve is applied to evaluate the damage probability of the steel arch with a letting pressure node under seismic loading conditions. Measurements of the surrounding rock pressure and structural forces on the steel arch with the letting pressure node were conducted at the Baoshan Jewel Mountain Tunnel in China. The field experiment results revealed a 23% reduction in the surrounding rock pressure and an 11% decrease in the internal forces of the support structure. These findings demonstrate the successful application of the letting pressure node-supported steel arch in mitigating large deformations in soft rock environments. Additionally, using finite element software ANSYS 2022, a seismic time-history analysis was conducted, employing the relative deformation rate of the letting pressure node steel arch as the damage index and the peak ground acceleration (PGA) as the strength parameter to generate the incremental dynamic analysis (IDA) curve. According to the susceptibility curve derived from the incremental dynamic analysis, at the design ground motion level of 8 degrees, the letting pressure node steel arch has a 94% probability of exceeding its normal service life limit and experiencing damage. The findings of this study offer a novel approach to addressing large deformations in soft rock tunnels. The proposed susceptibility curves for steel arches with letting pressure nodes provide a robust foundation for predicting the damage probability of yielding support structures under seismic conditions.

Enrichment conditions and resource potential of coal-rock gas in Ordos Basin, NW China

To reveal the enrichment conditions and resource potential of coal-rock gas in the Ordos Basin, this paper presents a systematic research on the sedimentary environment, distribution, physical properties, reservoir characteristics, gas-bearing characteristics and gas accumulation play of deep coals. The results show that thick coals are widely distributed in the Carboniferous–Permian of the Ordos Basin. The main coal seams Carboniferous 5# and Permian 8# in the Carboniferous–Permian have strong hydrocarbon generation capacity and high thermal evolution degree, which provide abundant materials for the formation of coal-rock gas. Deep coal reservoirs have good physical properties, especially porosity and permeability. Coal seams Carboniferous 5# and Permian 8# exhibit the average porosity of 4.1% and 6.4%, and the average permeability of 8.7×10−3 μm2 and 15.7×10−3 μm2, respectively. Cleats and fissures are developed in the coals, and together with the micropores, constitute the main storage space. With the increase of evolution degree, the micropore volume tends to increase. The development degree of cleats and fissures has a great impact on permeability. The coal reservoirs and their industrial compositions exhibit significantly heterogeneous distribution in the vertical direction. The bright coal seam, which is in the middle and upper section, less affected by ash filling compared with the lower section, and contains well-developed pores and fissures, is a high-quality reservoir interval. The deep coals present good gas-bearing characteristics in Ordos Basin, with the gas content of 7.5–20.0 m3/t, and the proportion of free gas (greater than 10%, mostly 11.0%–55.1%) in coal-rock gas significantly higher than that in shallow coals. The enrichment degree of free gas in deep coals is controlled by the number of macropores and microfractures. The coal rock pressure testing shows that the coal-limestone and coal-mudstone combinations for gas accumulation have good sealing capacity, and the mudstone/limestone (roof)-coal-mudstone (floor) combination generally indicates high coal-rock gas values. The coal-rock gas resources in the Ordos Basin were preliminarily estimated by the volume method to be 22.38×1012 m3, and the main coal-rock gas prospects in the Ordos Basin were defined. In the central-east of the Ordos Basin, Wushenqi, Hengshan–Suide, Yan'an, Zichang, and Yichuan are coal-rock gas prospects for the coal seam #8 of the Benxi Formation, and Linxian West, Mizhi, Yichuan–Huangling, Yulin, and Wushenqi–Hengshan are coal-rock gas prospects for the coal seam #5 of the Shanxi Formation, which are expected to become new areas for increased gas reserves and production.

Оценка удароопасности массива горных пород Стрежанского месторождения

The article considers the aspects of assessment of the rock burst hazard of the rocks of the Strezhan deposit using various methods: visual inspection, fracturing of the massif, core disking, and lab tests for extreme deformation. In 2023, ore samples and host rocks were selected at the Strezhan deposit to determine their deformation and strength properties. The studies revealed their high strength. In the same year, the components of the stress tensor were measured at the mine using the well hydraulic fracturing method at two measuring stations at a horizon of +750 m (at a depth of approximately 240 m from the daytime surface). It has been established that the natural field of the Strezhan deposit is characterized by a tectonic regime with horizontal tectonic stresses as maximum stresses, whereas vertical stresses are minimal. The azimuth of the maximum horizontal stress was 140 ± 10° in the northwest-southeast direction. As a result of field measurements of the natural stress field at the horizon +750 m at the Strezhan deposit, the values of the highest horizontal stresses in the rock mass (ore) were established as equal to 15.2 MPa. This means that the level of stress of the rock mass at the horizon +750 m (mining horizon) is insufficient to destroy mine workings. Calculations established the critical depth of mining operations as 500 m for the rock burst condition. In addition, ores prone to rock bursts have been detected in the deposit: solid copper-zinc and sulfur-pyrite. The assessment of the structural disturbance of the deposit rocks via the rock quality index RQD = 60.26 % enabled the classification of the deposit rock mass mainly as moderately fractured, where dynamic manifestations of rock pressure are not registered and not forecasted within the designed mining depths. As a result of the studies, it has been established that the rock mass of the Strezhan deposit located at a depth of 500 m from the daytime surface can be classified as non-hazardous in terms of rock bursts on the condition of observation of the mining technology adopted in the design.

Wpływ niejednorodności skał na stabilność ściany odwiertu

"One of the complications that arise while drilling wells is hydraulic fracturing. Hydraulic fracturing pressure is the pressure at which the integrity of the rock in the walls of the well is compromised, leading to the formation of artificial cracks. Various authors have proposed formulas to determine the hydraulic fracturing pressure Phf in the absence of actual data. Рhf = 0.87 Рrock Рhf = 0.85 (Рrock – Рres) + Рres Phf = [μ/(1 – μ)] (Рrock – Рres) + Рres Рhf = [2μ/(1 – μ)] Рrock where: μ – Poisson's ratio, which takes values of 0.25–0.4 for dense clay, 0.33–0.4 for clay with sandstone interlayers, 0.1–0.2 for shales, 0.3–0.35 for sandstone, 0.28–0.33 for limestone; Рrock, Рres – rock and reservoir pressure, respectively. This study examines the problem of determining hydraulic fracturing pressure taking into account the heterogeneity of rocks. The work can be roughly divided into two parts. In the first part, the physical properties of porous bodies in contact with fluids are studied, treating them as a two-phase medium. When a porous body comes into contact with fluids, the fluids penetrate into them, transforming them into a two-phase medium. The term “fluids” refers to both liquids and gases, with real liquids considered incompressible and gases highly compressible. The remaining part of the porous body, excluding the pores, is called the skeleton. Pores in porous bodies are connected through capillary tubes. In the second part, the influence of the magnetic field and rock heterogeneity on the stability of the well wall is studied. Formulas are derived to determine hydraulic fracturing pressure, depending on the mechanical properties of the rocks and the reservoir pressure. Based on the theory of destruction, the critical value of excess pressure (or hydraulic fracturing pressure) is determined, which is necessary to ensure the safety of drilling oil and gas wells. The machines used in drilling operations in the oil and gas industry must be easy to operate, reliable, and capable of long-time use. When designing such machines, considerations such as being lightweight, economical, and quick and inexpensive to prepare should be taken into account from the outset.

Experimental study on the influence of extremely broken surrounding rock grade on the mechanical characteristics of tunnels

To study the significant deformation and distortion issues in certain sections of the Qinyu tunnel extremely fragmented surrounding rock under identical conditions, six tunnel sections with the same depth of burial and lithology were selected for on-site monitoring of stress. The experimental data were then used to explore the impact of gradation on the mechanical characteristics of the extremely fragmented surrounding rock tunnels. The results indicate that the tunnel experiences larger stresses at the crown and smaller stresses at the side walls and invert, showing the influence of gradation on the stress behavior of extremely fractured surrounding rock. A dual-fractal structure model was employed to quantitatively describe the gradation of the surrounding rock, yielding fitting coefficients above 0.9. The model demonstrated good applicability for extremely fractured rock with significant particle size differences. Additionally, the relationship between fractal model parameters and the maximum rock pressure at various tunnel sections was discussed, revealing an exponential correlation between the absolute difference in fractal dimensions of coarse and fine particles and the maximum rock pressure. To further understand the factors and the influence of gradation on tunnel rock pressure, indoor model tests were conducted using six different gradations. The experimental results once again confirmed the importance of gradation on the stress behavior of highly fragmented rock tunnels and validated the functional relationship between the absolute difference in fractal dimensions and rock pressure. The results can provide guidance for the design of tunnels with extremely fractured surrounding rocks in the future.

Safety and high-recovery mechanisms and application research for initial mining of thick-coal-seam with complex structure and thick-hard roof

Thick-coal-seam with complex structures and thick-hard roof in the initial mining phase pose various challenges, including a long weighting interval, strong rock pressure, poor top coal caving performance (TCCP), and significant coal loss. These problems directly affect the safety and efficiency of the mining operations. This study employs the principles of elastic thin plates and ellipsoidal bodies to unravel the formation mechanism of strong rock pressure in thick-hard roof and the influence of parting on the TCCP. In addition, a hydraulic fracturing technique is proposed for safe-efficient recovery during the initial mining phase. The reliability of this technique is verified through numerical simulations and field experiments. The research findings reveal the following. (1) The primary causes of strong rock pressure in the mining face are attributed to a long weighting interval and wide collapse range of the main roof, and the weighting interval is primarily influenced by the thickness and tensile strength of the main roof. (2)The key factor affecting the TCCP is the cantilever beam structure formed by the fracture of the thick-hard parting, as it intersects the ellipsoidal body during coal caving. The simultaneous fracturing of both the top coal and roof can reduce the weighting interval on the working face. This process effectively decreased the strength of the thick-hard parting within the top coal, while simultaneously enhancing its load strength and eliminating the cantilever structure resulting from the parting fracture. It not only reduces the first weighting intensity but also promotes the early and proper coal release, thereby enhancing the TCCP and ensuring safe-efficient mining during the initial mining phase. (3) Aiming at the difference in the strengths of the top coal and roof, a graded hydraulic fracturing technique and system were proposed. Fracturing boreholes with a diameter of 60 mm, spacing of 10 m, and height of 20.85 m, which can economically and effectively ensure the fracturing results. Field applications have demonstrated that fractured coal and rocks in fracturing areas exhibit well-developed fractures. During the initial mining phase, the weighting interval in the working face was reduced by 20 m, resulting in a decrease in the overburden pressure and 26.9% reduction in the lumpiness of the top coal. Additionally, the recovery rate increased by 31.19%.

A breakdown pressure model for supercritical CO2 fracturing considering fluid infiltration effect using the point stress criterion

Precisely predicting the breakdown pressure of rock fractured by supercritical CO2 (SC-CO2) is one of the major challenges for optimize in-situ fracturing schemes. However, the influence of the infiltration effect caused by the unique properties of SC-CO2 on the fracture mechanism remains unclear, which may lead to inaccurate prediction of breakdown pressure. In this work, a pressurization rate model considering the physical properties changes of SC-CO2 is proposed to describe the relationship between the pressurization rate and the injection pressure of the fracturing fluid in a wellbore. Ultimately, combined with the pressurization rate model and the point stress criterion, a breakdown pressure model is established by considering the changes in the in-situ stress of wellbore surrounding rock, the fluid injection pressure inside the wellbore, and the pore pressure distribution. The results show that for permeable reservoirs, the breakdown pressure increases as the viscosity and injection rate of fracturing fluid increase, but it decreases with increasing rock permeability. The low viscosity and pressurization rate of SC-CO2 effectively increase the stress generated by the infiltration effect, which is negatively correlated with the breakdown pressure. In addition, the unique pressurization rate of SC-CO2 is the key factor for the abnormal breakdown pressure at different injection rates.

Failure Mechanism and Structural Optimization of the Primary Support Structure for Expressway Tunnel in Soft Rock: A Case Study

When the highway tunnel crosses the soft rock, the primary support structure often fails and damages because it cannot withstand the excessive surrounding rock pressure. For the Magu tunnel in Yunnan Province, which is in the upper hard and lower soft stratum, the surrounding rock deformation is large, and the primary support structure occurs spray concrete cracking, steel arch frame twisting deformation. According to the convergence constraint curve, this paper proposes to adopt the primary support optimization design scheme of "shortening the bench length + optimizing the length and arrangement of anchor rods". According to the numerical simulation results of FLAC3D, the important indexes such as deformation convergence, surrounding rock stress, anchor axial force and thickness of plastic zone in different excavation support conditions are analyzed. The conclusions are as follows: 1. The soft rock at the foot of the benches does not provide sufficient support resistance, resulting in large settlement and convergence deformation that can cause the primary support structure to fail and become damaged. 2. The length of the middle bench and the primary support strength and stiffness contribute most to the deformation. 3. The deformation control effect of the short anchor rods on the surrounding rock is relatively weak. Increasing the length of anchor can better play the role of anchor suspension enhancement and give full play to the surrounding rock's own bearing capacity. Finally, the deformation of the tunnel is under control after adopting the optimized primary support structure, which ensures the smooth construction.

Analysis and Experimental Study on the Stability of Large-Span Caverns’ Surrounding Rock Based on the Progressive Collapse Mechanism

The collapse failure of rock surrounding caverns involves a progressive collapse process. Based on the nonlinear Hoek–Brown failure criterion and the upper limit theorem, the whole process curve of the progressive collapse of the surrounding rock of a large-span cavern is outlined in this paper. The progressive collapse process of the surrounding rock of the large-span cavern is experimentally studied using an independently developed visualized large-span-cavern geomechanical model test device with variable angles. The results show that, through theoretical calculation and model tests, the surrounding rock at the top of the large-span cavern undergoes three collapses. Under the condition of rock mass and the shape of the cavern, the larger the span of the cavern, the more times the surrounding rock collapses; with the increase in surrounding rock pressure, the first collapse occurs in the middle part of the arch roof. When the overlying load reaches a certain level, the arch foot becomes the weakest part, and the rock undergoes shear failure along the arch foot, gradually extending upwards, accompanied by multiple collapses, forming a progressive collapse process. The theoretical calculation results of this paper are basically consistent with the scope of the model test, and the research results can provide a basis for the construction and support design of the large-span cavern.

Surrounding rock pressure in the tunnel portal section through moraine under freeze-thaw action

Surrounding rock pressure in the tunnel portal section through moraine under freeze-thaw action

Модернизация технологий месторождений оловянных руд с учетом ретроспективной оценки опыта восстановления потенциала предприятий

The article describes the experience of restoring the potential of enterprises in the tin industry of the Khabarovsk Territory and the Chukotka Autonomous Okrug in difficult mining and geological conditions. The purpose of the study is a retrospective assessment of the experience of improving the technology of mining tin ores in stable rocks. Materials and methods. The goal is achieved through comprehensive research, including analysis and synthesis, comparison of calculated and experimental data, calculations of mass control parameters and measures to improve the quality of ores. Results. The characteristics of the deposits and the features of their location and ore extraction are given. The parameters of the applied development systems with differentiation into variants are detailed. A scheme of options is given with a critical analysis of their advantages and disadvantages so that they can be reproduced in similar conditions. Discussion. The effectiveness of the integration of ore mining processes and equipment for their implementation is shown. The experience of using an arsenal of systems for the development of shallow and inclined deposits in stable host rocks is described. The experimentally obtained dependences of the size of the pillars on the fall of the ore body and the spans of the mine are given. The variants of a promising chamber development system with the delivery of ore by the force of an explosion are detailed. Conclusion. It is shown that the development of tin deposits with the integration of the capabilities of technological processes and equipment ensures effective development of the field while improving the safety of mining operations and extraction of minerals from the subsurface. Resume. It is concluded that the integration of mining processes and equipment for their implementation is a reserve for the implementation of the production program, and the experience of developing tin deposits can be in demand when modernizing existing technologies and designing new deposits of solid minerals. Suggestions for practical applications and directions for future research. Future research will be aimed at addressing issues related to reducing ore losses and dilution, improving the rock pressure management system and increasing the environmental and economic efficiency of the enterprise.

Rationale and modeling of technology for complex bottom-hole zone de-stressing of gas-dynamically active rock mass

Purpose. The research aims to substantiate the geological principles and peculiarities of modeling complex de-stressing of a stressed bottom-hole mass during the construction of mine workings at depths of more than 1000 m. Methods. A comprehensive research methodology is proposed, which consists of conducting a computational experiment for calculating a complex de-stressing scheme and analyzing the stress-strain state (SSS) of the bottom-hole mass in the most informative mine working cross-sections, conducting experimental studies on the effectiveness of the method using the developed methodology for observing rock pressure manifestations and estimating energy consumption on the tunneling face rock destruction. Findings. A combination of two methods for de-stressing a rock mass adjacent to the tunneling face using advance slots has been substantiated. A geomechanical model has been created that takes into account the specifics of the proposed method. The stress-strain state of the rock mass adjacent to the tunneling face has been calculated in a series of cross-sections and longitudinal section of mine working. Originality. Three geotechnological principles of simultaneous de-stressing of both rocks adjacent to the face and rocks within the mass along the mine working route has been formulated and elaborated, embodied in the construction of a geomechanical model of complex adjacent rock mass de-stressing. Based on the obtained stress-strain state, five positions of have been developed for complex consideration of changes in the distribution fields of determining stress components. The methodological principle for assessing energy consumption for rock destruction has been substantiated, and an evidence base has been created to confirm the advantages of the proposed mine working construction technology at depths above 1000 m in a gas-dynamically active rock mass. Practical implications. The method for complex de-stressing the rock mass adjacent to the tunneling face, using pre-drilled wells and de-stressing slots, is proposed. Experimental studies confirm the proposed method feasibility in three directions for safe and resource-saving construction of mine workings in a gas-dynamically active rock mass at great depths. Calculations have proven that energy consumption for bottom-hole rock destruction has decreased in the range of 15-26%.

Inversion of fluid-release rates from episodic tremor and slip signals in subduction zones via a coarse-grained reaction diffusion model

Episodic Tremor and Slip (ETS) events showcase dynamic interactions of oscillatory slow slips and tremors deep within subduction zones and offer a window into Earth's internal dynamics. However, the exact mechanisms driving these events remain unresolved. This study proposes a novel approach that goes beyond traditional explanations focused on fluid pressure from mineral dehydration. Existing models often neglect the intricate interplay between fluid and rock pressures across various depths and potential fluid sources. This calls for a more comprehensive understanding of how fluid release from reactions interacts with rock deformation. The present formulation captures the interplay between fluid and solid pressures providing a more rigorous picture of ETS events. It employs a minimalistic and efficient approach based on integrating dehydration reactions. The model thereby develops a generic framework for mineral dehydration, offering an enhanced perspective of the underlying processes without the need to trace down to specific minerals. It allows a refined fit to GPS data by including high-frequency components from linear and nonlinear stability analyses, giving rise to improved correlation coefficients. Through the inclusion of the dynamic interplay between fluid and rock pressure diffusion within subduction zones, we propose a unified model of ETS events.

Displacement and pressure of surrounding rock during shield tunnelling and supporting in low water content loess

Using a self-developed micro shield machine, a laboratory-scale experimental scheme for shield tunnelling and supporting was designed, and the soil displacement law and earth pressure on the segments during tunnel construction were studied. Based on a nonlinear elastic constitutive model describing the characteristics of loess, the UMAT subroutine was redeveloped and verified by conventional triaxial tests. It was then applied to the numerical simulation of shield tunnelling and supporting. The following are the findings: 1) The disturbance modes of surrounding rock directly above the shield tunnel under different boundaries are similar. The main disturbances occur approximately 4 m above the shield tunnel, extending to a distance of one segment outer diameter on either side of the tunnel's central axis. 2) The pressures on the top and bottom of the segments can be divided into rapid increase, slow increase, and stable fluctuation. These stages correspond to the processes of the segments getting out of the shield shell and the soil collapsing. 3) The largest surrounding rock pressure is at the vault, followed by that at the arch bottom, and the smallest is at both sides of the arch waist, which is consistent with the law obtained based on laboratory-scale model tests. The surrounding rock pressure values of the vault in the numerical simulation are consistent with the laboratory-scale model test results. These verify the reliability of the laboratory-scale model test and the UMAT subroutine based on the nonlinear elastic constitutive model of loess in simulating the shield tunnel construction in loess strata.