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The deterioration of the mechanical properties of gypsum due to water–rock reactions has attracted extensive attention in the areas of structural geology and civil engineering, and accurately predicting variations in the mechanical behavior of gypsum under different engineering conditions presents a challenging yet intriguing endeavor. In our study, we conducted experimental investigations of the influence of water–rock reactions on the mechanical behavior and mechanisms of gypsum-bearing mudstone. Subsequently, we constructed a mechanical damage model to predict the behavior under varying dissolution times. During the water–rock reaction, water dissolves substances along crystal interfaces and mineral joint surfaces, changing the way particles contact each other, weakening the contact strength, creating intergranular solubility pores, and causing an increase in porosity, all of which lead to a decrease in the mechanical strength of gypsum–containing rocks. The experimental results showed that the maximum decrease in peak strength and cohesion of the samples with the increase in porosity was 69.68% and 79.02% after the water–rock reaction, respectively, and the internal friction angle showed a small fluctuation change with increasing porosity. The maximum increase in elastic modulus and peak strength with increase in confining pressure was 34.21% and 37.10%, respectively. In addition, for samples with different shapes and spatial locations of weak zones due to water–rock reactions, there is no clear relationship between the change of elastic modulus and the porosity of the samples. By constraining the peak strength and peak deformation, the established gypsum-bearing mudstone constitutive model was accurate and flexible. Comparing the established damage constitutive model with measurements, we found that the developed damage constitutive model is compatible with the measured data during the damage evolution process of water–rock reactions over long periods and can play a predictive role. This study has laid an important foundation for research on the evolution of gypsum mechanical properties and model construction under water–rock reactions. Highlights: Extensive indoor dissolution tests and mechanical tests are conducted. The damage mechanism of gypsum-bearing mudstone under water–rock reactions is explored. The variation of rock mechanical parameters under water–rock reactions is obtained. A widely applicable constitutive model is developed [ABSTRACT FROM AUTHOR]

Flawed rocks subjected to hydrostatic confinements in deep underground engineering are vulnerable to dynamic disturbances. Understanding the dynamic mechanical responses and fracture characteristics of flawed rocks is crucial for the design and construction safety of deep underground structures. In this research, using a triaxial split Hopkinson pressure bar device, the dynamic triaxial compression tests are performed on multi-flawed sandstone specimens containing different flaw angles and distances. The experimental results revealed the influence of the flaw angle, flaw distance, and hydrostatic confining pressure on the dynamic strength characteristics, deformation properties, failure modes and fracture mechanisms of rocks. Both the dynamic strength and elastic modulus increase with rising hydrostatic confining pressure, while the dynamic strength depicts a positive correlation with strain rate. The dynamic strength fluctuates zigzag with the flaw angle, and decreases first and then increases slightly with flaw distances. Specimens with different flaw angles all demonstrate conjugated "X" shape failure, while the single shear band failure is shown for certain flaw distances. Seven crack categories are identified based on the basis of different trajectories and the fracture characteristics of new cracks are analyzed in multiscale perspective. The scanning electron microscope observation indicates numerous shear traces on the fracture surface while brittle fracture features are relatively few. Furthermore, the fracture surface roughness is quantified by the 3D scanning technique and fractal dimension. Rocks containing higher flaw distance or under higher hydrostatic confining pressure are featured by lower fractal dimension and smoother fracture surfaces. Highlights: Dynamic impacting tests on hydrostatically confined rocks containing multiple flaws were conducted. The influence of hydrostatic confining pressure and flaw configuration on the dynamic strength, deformation properties, and failure characteristics of rocks were investigated. The fracture mechanism of flawed rocks under hydrostatic confinements by the scanning electron microscope and 3D scanning technique was analyzed. [ABSTRACT FROM AUTHOR]

The deformation of surrounding rock in the withdrawal roadways of fully mechanized working faces is a critical factor affecting the safe and efficient withdrawal of mining equipment. In order to address this issue, an experimental study was conducted on an innovative method for pre-split blasting to protect withdrawal roadways, using a working face in Shaanxi Province, China, as the engineering background. Firstly, research was conducted using physical model experiments to study the protection of the withdrawal roadway through pre-split blasting. The results indicate that at a certain distance ahead of the working face, the use of pre-split blasting technology on the roof of the withdrawal roadway leads to a significant reduction in both surrounding rock deformation and stress in the blasted side Withdrawal Roadway (I) compared to the unblasted side Withdrawal Roadway (II). The effective blocking of the stress transmission path caused by mining-induced stress leads to substantial relief of stress concentration in the withdrawal roadway's surrounding rock. This demonstrates that pre-split blasting technology can effectively reduce the advance mining stress on the withdrawal roadway, achieving the goal of protecting the withdrawal roadway. Subsequently, numerical simulation experiments were conducted to further investigate the patterns of surrounding rock stress and displacement in the withdrawal roadway under the influence of advance mining stress during the excavation of the working face. Furthermore, the numerical simulation results closely match the data from the model experiments, confirming the accuracy of the model experiments. Finally, this technology was applied to an engineering site. Monitoring results show that when pre-split blasting technology is employed at the advance working face, the deformation of the surrounding rock in the withdrawal roadway is effectively controlled. The research findings provide valuable insights for the protection of similar withdrawal roadways. [ABSTRACT FROM AUTHOR]

In the geomechanical characterisation practice of jointed rock masses, the volumetric fracture intensity P32, defined as the total area of discontinuities per unit volume, is becoming increasingly popular as one of the most suitable three-dimensional estimators of the fracture abundance. 3D discrete fracture network (DFN) modelling is currently the most rigorous approach to estimate P32. However, considering the practical difficulties of many practitioners in using DFN technology routinely, it seemed advantageous to search for alternative methods suitable to assess this parameter from common discontinuity measures of rock mass exposures. In order to address this practical need, the paper presents a new analytical approach based on the Monte Carlo method that can be used, with acceptable accuracy, to estimate P32 of fractured rock masses. The computational strategy developed requires the knowledge of few orientation bias-free measures of the fracture abundance, namely the "true" (orthogonal) spacing distribution and persistence of each relevant fracture set comprised in the rock mass. Key advantages of the proposed methodology are the mathematical simplicity with which it can be implemented in standard spreadsheet and its applicability to rock masses with both persistent and non-persistent discontinuities. These features make the new analytical approach a valuable practical tool to complement the existing P32 estimation methods in different rock engineering and geological applications. Highlights: A new analytical approach based on the Monte Carlo stochastic simulations is proposed to predict the volumetric fracture intensity of a rock mass. Volumetric fracture intensity is increasingly used in the geomechanical practice as an orientation bias-free three-dimensional measure of the fracture abundance. The new approach has proven to be a valid tool for estimating fracture intensity of persistently and non-persistently jointed rock masses. The methodology has been validated through Discrete Fracture Network modelling. [ABSTRACT FROM AUTHOR]

Energy drives the large deformation of soft rock tunnels, which is a nonlinear mechanical behavior of surrounding rock. This study aims to develop an analytical model for analyzing the energy conversion and absorption processes involved in tunneling. First, an analytical approach is presented for analyzing the energy conversion of the surrounding rock and energy absorption properties of the yielding support system during tunnel excavation. Subsequently, a comprehensive parametric investigation is conducted using the analytical model to investigate the impact of support pressure, tunnel radius, and initial stress on the energy conversion and dissipation of the surrounding rock. Similarly, the effect of support installation time, tunnel radius, and initial stress on the energy absorption properties of the yielding support system is explored. The results reveal that energy is input into the surrounding rock at the outer boundary through radial stress work. A portion of the energy is converted into elastic strain energy of the surrounding rock. Simultaneously, the plastic deformation of the surrounding rock consumes some of the input energy. Subsequently, the remaining energy flows from the excavation boundary as rock pressure work. Installing yielding components in the support system significantly enhances its maximum energy absorption capacity, which may be raised by up to 30 times. Moreover, the earlier the support installation time, the larger the tunnel radius, and the higher the initial stress, the more energy the yielding elements of the support system absorb. Highlights: Proposed an analytical model to characterize energy conversion in large deformation tunnels with yielding support. Quantitatively analyzed the energy conversion and dissipation properties in the surrounding rock. Explored the energy absorption characteristics of yielding support in large deformation tunnels. [ABSTRACT FROM AUTHOR]

Excavation in deep weak rock engineering can significantly alter the stress state in the surrounding rock, often leading to varying degrees of floor heave. The excavation stress paths from the immediate floor to the interior floor were determined by simulating tunnel excavation and monitoring stress changes at fixed points on the floor. The characteristic stresses, failure modes, acoustic emission and deformation features of three types of clastic rock under excavation stress paths were experimentally investigated to reveal the floor heave mechanism. The study found that as the distance from the excavation boundary increased, the bearing capacity of the clastic rock gradually enhanced, and the risk of macroscopic failure decreased, transitioning from tensile failure to tensile–shear mixed failure. Simultaneously, the excavation-induced dilational deformation rapidly decreased. A novel method was proposed to evaluate the dilational deformation of surrounding rock induced by excavation based on the strain features of the samples under the different stress paths. The results demonstrated a rapid decrease in dilational deformation from the immediate floor to the interior floor for the three types of surrounding rock, with the maximum total dilation and the greatest risk of floor heave observed in contact cementation surrounding rock. Finally, the floor heave mechanisms of three types of clastic rock were summarized as follows: unloading dilation combined with macroscopic failure; slight rebound of the immediate floor coupled with multiple microcracks; notable rebound of the immediate floor accompanied by few microcracks. This study provides new insights into the mechanics disasters and selection of support measures for deep-buried tunnels. Highlights: Experiments were conducted on three types of clastic rock under excavation stress paths from the immediate floor to the interior floor. The characteristic stress, failure mode, AE characteristics and deformation behavior induced by excavation of three types of clastic rock were studied. A method was proposed to evaluate the dilational deformation of surrounding rock induced by tunneling. The floor heave mechanisms of three types of clastic rock were revealed. [ABSTRACT FROM AUTHOR]

Although squeezing ground may undergo rapid convergences following tunnel excavation, its behaviour is often markedly time dependent due to creep or consolidation. The effects of creep and consolidation on shield tunnelling are comparatively evaluated in two companion papers, with the aim of demonstrating their qualitative similarities and distinctive features. The present, first paper investigates the basic time effects, placing focus on the time development of ground deformations and the complex interaction between ground, tunnel boring machine (TBM) and tunnel support during excavation and during construction standstills. The presented numerical simulations indicate several qualitative similarities between the two mechanisms of time dependency, in respect of the time development of ground deformations, the counter-intuitive behaviour of increasing shield loading with increasing rate of advance under certain conditions, as well as the thoroughly adverse effect of the additional time-dependent deformations taking place during construction standstills on the shield loading. However, they also underscore two prominent differences resulting from the fundamentally different nature of creep (a purely mechanical rheological process) and consolidation (a coupled hydromechanical process): first, the consistently more extensive plastic yielding in consolidating ground, which is partially associated with the seepage forces exerted by the pore water on the solid rock constituents. Second, the role of seepage forces as a potential destabilising agent, particularly for the tunnel face, which does not happen in the case of creep and may be critical for shield and cutterhead jamming. Building upon these investigations, the companion paper compares creep and consolidation with respect to the transferability of experiences about the required thrust force to tunnels of different diameter or to adjacent tunnels. Highlights: Analysis of similarities and differences between the effects of creep and consolidation on mechanised shield tunnelling through squeezing ground. Similar time development of rock deformations and shield loading during advance and during standstills in creep and consolidation. Similar counter-intuitive behaviour of increasing shield loading with increasing advance rate under certain conditions in creep and consolidation. More extensive ground plastification in consolidation than in creep, partially due to the effect of seepage forces on the solid rock constituents. Potential instability due to seepage forces may induce excessive convergences or face extrusion and render shield or cutterhead jamming critical. [ABSTRACT FROM AUTHOR]

Coupled thermo-hydro-mechanical (THM) processes in fractured rocks have been a topic of intense scientific research for more than 30 years. The present paper takes a look into the past and highlights some scientific advances which are of an unusual "out-of-the-box" nature, and then looks forward and discusses possible directions of future research in this interesting field of study. Concerning future research directions, we see a trend from a focus on coupled THM processes in single fractures or a few interacting fractures, to the study of coupled THM behavior in complex fracture network systems where the fractures act collectively giving rise to local stress concentration points and points of large pressure gradients. Three examples of future research directions are presented. First is an effort towards identifying characterizing parameters of a fracture network that play a direct controlling role in major coupled THM phenomena (such as induced seismicity and flow channeling), rather than parameters of stochastic distributions of fractures in the network. The second example of research direction is accounting for the heterogeneity and hierarchy of fractures in a fault or fracture zone which has been associated with major THM events in a number of geo-energy projects. The third example is at the opposite end of the first; here it is recognized that in some cases, the coupled THM processes in fractured rocks may be controlled dominantly by only a few key bridges. Identification, characterization, and evaluation of these key bridges should be one of the important research directions in the coming days. Highlights: The research into coupled thermo-hydro-mechanical processes in fractured rock over the last thirty years is reviewed. Three past scientific advances of an "out-of-box" nature are highlighted. Future research directions are discussed with three examples of potentially fruitful research directions. [ABSTRACT FROM AUTHOR]

In natural rock masses, joints or fractures usually occur at different penetrations. To study the deformation and failure behavior of rock mass with different fracture penetrations, a series of triaxial compression experiments were conducted on rock specimens containing prefabricated fracture at penetrations of 0%, 25%, 50%, 75% and 100%. The results show that the greater the fracture penetration and the smaller the strength of the rock sample, the more obvious the plastic deformation section of the stress–strain curve. Confining pressure can greatly improve the compressive strength of rock samples. For intact rock samples, confining pressure will change the failure mode from tensile failure to shear failure. For fractured rock samples, the confining pressure will aggravate the degree of damage to the rock sample. PFC 3D simulation shows that the failure process of rock samples is accompanied by the transformation of strain energy to damping energy and particle sliding energy, which can quantitatively characterise the damage process of rock. The increasing trend of crack number is slow-steep-slow, which is the 'S' type. It began to grow rapidly after reaching peak strength and gradually stabilised after reaching residual strength. It is consistent with the trend of energy change. The article carried out multi-scale experimental study of fractured rock mass with the same length and different penetration. The larger the fracture penetration, the lower the strength of the rock sample, and the more complex the crack when it is destroyed. The article analysed and summarised the mechanical properties and failure modes of rock samples with different fissures under different confining pressures and clearly recognised the deterioration effect of fissure penetration on rock samples. PFC 3D was used to simulate the test, which clearly showed the crack propagation process of fractured rock samples under triaxial compression, quantitatively characterised the damage law and revealed the failure mechanism. [ABSTRACT FROM AUTHOR]

SUMMARY: The amplitude, frequency and polarization of ground motion at the surface can be affected by the local geology. While low-velocity sediments and fill can amplify ground motions in certain frequency ranges, the low velocities found in fault zones can also produce prominent wavelets. In this paper, we provide further evidence that polarization of ground motion can be affected by the geological fabric in fault zones that have sustained significant brittle deformation. Aside from the well-known effect of fault-trapped waves in the low-velocity zone with polarization azimuths parallel to the fault strike, the effect of stiffness anisotropy was recently recognized with polarization azimuths at high-angle to the fault strike and orthogonal to the locally predominant fracture field in the fault damage zone. To clarify further such features, we investigate directional amplification effects across the San Jacinto fault zone in Southern California using seismic data recorded by permanent seismic stations and dense across-fault arrays. We observe three main polarization trends. The first trend parallel to the fault strike is ascribed to fault-trapped waves along the low-velocity zone, in agreement with several studies in the last decade in the same region. The second and third trends are orthogonal to the orientation of R and T Riedel planes, respectively. They are related to the stiffness anisotropy in densely fractured rocks in the damage zone, which are more compliant orthogonal to their fractures. At some locations the two effects are superimposed, occurring in different and distinct frequency ranges. Directional amplification at rock sites can be important for expected ground motion and seismic hazard. However, in seismic engineering the current prescriptions of seismic codes do not account for amplification effects at rock sites at frequencies of engineering interest. [ABSTRACT FROM AUTHOR]

Numerical modelling has became one of the most widely used design tools for evaluation of engineering responses in ground and support measures around excavations. Proper model setup for numerical analysis is important, especially for excavations created in blocky and massive rockmasses by including rock joints network in the model. Characterisation of rock joint such as spacing, length, persistent and shear strength may have a large influence on the mechanical behaviours of rockmass in terms of strength and deformation in rock engineering problems. Overview the current practice, no appropriate guidance is given assistant in setting up rock joints network in model for jointed rockmass analysis. To fill this gap, a recommended rock joints setting for a range of rockmass qualities in model analysis is proposed based on a comprehensive literature review on rock joints studies. Verification of the recommended rock joints setting is performed that two published case examples are used to examine the disparity in rock joints setting in the model and checked against the difference between the modelled results and as-constructed monitoring records. The verification demonstrates that a close agreement between the model result and as-constructed monitoring record could be obtained to minimise any potential over- or under-design practice. [ABSTRACT FROM AUTHOR]

The slope on the left side of the spillway tunnel at Wudongde Hydropower Station's water cushion pool exhibited significant deformation during excavation. Based on long-term monitoring data, an analysis was conducted on the deformation mechanism of the stratified rock and soil slope. A geological model of a high and very steep slope was established using FLAC3D to evaluate its stability. It was observed that the left stratified rock and slope at the spillway tunnel is prone to deformation due to long-term construction disturbance and fissure water seepage. Construction disturbance strongly impacts the artificially excavated area below 1070 m, while it has limited influence on the mountain above 1070 m. The maximum rock deformation and surface displacement reached 92.2 mm and 312.5 mm, respectively. After water filling, there will be a significant increase in deformation for the natural mountain on the left bank at the outlet of the spillway tunnel; however, deformations in unexcavated parts of this natural mountain remain below 20 mm. Furthermore, deformation of the left bank was higher compared to those observed in the right bank. Numerical simulation indicates that once the excavation is complete, fundamental safety factor of approximately 1.3 can be achieved for the left bank slope at the exit from the spillway tunnel. The rate of increase in deformation for the water cushion pond behind the dam is slight over time, and the trend of displacement change in-situ monitoring is mostly consistent without numerical calculation, eventually showing a convergence trend. [ABSTRACT FROM AUTHOR]

Pulsating hydraulic fracturing (PHF) is a promising fracturing method and can generate a dynamic periodic pressure. The periodic pressure can induce fatigue failure of rocks and decrease initiation pressure of fracture. If the frequency of periodic pressure exceeds 10 Hz, the distribution of pressure along the main fracture will be heterogeneous, which is much different from the one induced by the common fracturing method. In this study, the impact of this special spatial feature of pressure on hydraulic fracture is mainly investigated. A coupled numerical simulation model is first proposed and verified through experimental and theoretical solutions. The mechanism of secondary fracture initiation around the main fracture is then discovered. In addition, sensitivity studies are conducted to find out the application potential of this new method. The results show that (1) this coupled numerical simulation model is accurate. Through comparison with experimental and theoretical data, the average error of this coupled model is less than 1.01%. (2) Even if a reservoir has no natural fracture, this heterogeneous distribution pressure can also cause many secondary fractures around the main fracture. (3) The mechanism of secondary fracture initiation is that this heterogeneous distribution pressure causes tensile stress at many locations along the main fracture. (4) Through adjusting the stimulation parameters, the stimulation efficiency can be improved. The average and amplitude of pressure can increase possibility of secondary fracture initiation. The frequency of this periodic pressure can increase number of secondary fractures. Even 6 secondary fractures along a 100 m-length main fracture can be generated. (5) The influence magnitudes of stimulation parameters are larger than ones of geomechanical properties, therefore, this new fracturing method has a wide application potential. [ABSTRACT FROM AUTHOR]

Rock fractures are an important indicator for assessing the quality of rock masses. The significant differences in the color and texture distributions of rock mass exposures lead to great challenges in the automated extraction of fractures from various low-contrast images. To address these issues, an adaptive generalized gamma correction enhancement algorithm for rock fracture images is proposed. First, the entire gray level is divided into three regions, namely, the fracture region, transition region, and rock mass exposure region, through piecewise linear fitting of the prepeak gray histogram and a designed evaluation function. Subsequently, a generalized gamma transform curve with dynamic nonlinear variation of the gamma factor is proposed, enabling more flexible transitions between compression and expansion effects at different grayscale levels, and its parameters are automatically determined by fitting the histogram partition data. Ten representative rock fracture images and five well-known crack datasets are used for quantitative assessment and visual analysis, with the pixel response intensity ratio introduced as the quantitative metric. The experimental results demonstrate that compared to several traditional and state-of-the-art enhancement algorithms, the proposed method exhibits stronger targeting and adaptability in enhancing fractures while effectively suppressing rock mass exposure noise, with excellent performance. [ABSTRACT FROM AUTHOR]

Cobalt-rich ferromanganese crusts (CRC) are potential resources for Co, Ni, Pt, and other strategic metals. The CRC thickness varies from a few mm to more than 100 mm at various distance scales over the rock outcrops in the seamounts. However, their variation patterns and controlling factors are not well understood. We conducted a comprehensive small-scale survey, including shipboard acoustic measurements, seafloor observations, and rock drilling over the Xufu Guyot of the Marcus-Wake seamounts in the Northwestern Pacific to characterize the thickness variations on a scale of several kilometers with the topography and geological evolution of the guyot. Rock drilling revealed that thicker CRC (>100 mm) tend to occur on the margins and flat areas on the guyot, while thinner CRC are associated with carbonate reef mounds over the volcanic pinnacles and seamount slopes. The microstratigraphic description indicated that the CRC thickness is strongly related to the geological evolution of the guyot, mainly the stability of the substrate rocks and coverage with calcareous pelagic sedimentation. [ABSTRACT FROM AUTHOR]

The permeability of a rock mass is an indispensable and significant parameter for the construction of rock engineering. Since most fractures are buried in the rock mass, accurately assessing the permeability of the rock mass has posed a challenge to scholars in the field. The discrete fracture network (DFN) is recognized as an effective method for calculating the permeability of rock masses. However, the impact of the fracture model on permeability calculations is neglected during the construction of DFNs. This study uses the FracMan software to conduct a series of numerical simulation experiments, demonstrating that the selection of the fracture model significantly influences permeability calculations. Furthermore, we investigate the effects of constructing different circular DFNs based on trace information from various sampling windows. The results indicate that relying solely on a circular DFN derived from a single sampling window to calculate permeability is unreliable, and we reveal the fundamental laws of how DFNs constructed based on different fracture models influence the permeability assessment of rock masses. Therefore, integrating multi-source information from rock mass outcrops and boreholes, in conjunction with selecting an appropriate fracture model for constructing DFNs, is crucial for accurate permeability calculations of rock masses. [ABSTRACT FROM AUTHOR]

The simulation of a two-phase acidizing process coupled with thermal–chemical–fracturing is a complex task, given the presence of natural fractures in carbonate rocks and the influence of temperature on the acid–rock reaction. In this work, we introduce a mixed computational strategy combining the operator splitting and the Newton iteration built upon the embedded discrete fracture model. This innovative strategy is designed to tackle nonlinear problems arising from the coupling of multiphysics fields. The porosity improved region within rock is divided into three parts: the high (H), medium (M), and low (L) efficiency regions, aimed at clearly assessing the impact of various physical fields on acidizing efficiency. The results show that the wormhole morphology is determined by the H and M regions, and the L region determines the acidizing efficiency. The oil in the rock can have a "sealing effect" on the acid, improving the acidizing efficiency. For the large fracture aperture, the wormhole morphology is predominantly influenced by fractures, with the influence diminishing as the aperture decreases. At small apertures, fractures exhibit minimal impact on the morphology. While increasing injection temperature may not significantly alter the wormhole morphology, it can enhance acidizing efficiency. The morphology of wormholes is highly sensitive to multiphase interactions, fractures, and temperature variations. The proposed hybrid computational strategy effectively addresses multiphysics field challenges in two-phase acidizing. [ABSTRACT FROM AUTHOR]

Radial injection of shear-thinning fluids into rock fractures is ubiquitous in subsurface engineering practices, including drilling, hydraulic fracturing, and rock grouting. Yet, the effect of injection-induced fracture deformation on radial displacement behavior of shear-thinning fluids remains unclear. Through radial injection experiments of shear-thinning fluids displacing an immiscible Newtonian fluid in a Hele–Shaw cell, we investigate the fracture deformation behavior during injection and the fluid–fluid displacement patterns under this impact. A mixed displacement pattern is observed where the invasion front gradually evolves from unstable (viscous fingering) to stable (compact displacement) as the injection proceeds. We demonstrate that the combined effect of shear-thinning property and radial flow geometry plays a controlling role in the evolution of the patterns. At high flow rates, the fracture dilation induced by high injection pressure tends to reduce the displacement efficiency in stages. Based on linear stability analysis, we propose a theoretical criterion for the transition of interfacial stability considering the viscosity of injected fluids and fracture deformation, which agrees well with the experimental observations. This research underscores the importance of rock deformation on two-phase flow dynamics in fractured media. [ABSTRACT FROM AUTHOR]

Fracture is an early symptom of ground movement related to the physical properties of soil, including permeability, porosity, density, cohesion and internal friction angle, where these physical properties affect the stability of the soil. This research aims to identify soil fracture in landslide-prone areas using the values of water saturation and soil pressure based on electrical resistivity tomography (ERT) data. Water saturation values are obtained using the Waxman-Smits model based on the relationship between porosity and resistivity. The advantage of this model is its ability to apply correction due to clay-containing soil layers found in the research area. Another parameter used to determine soil fracture is the soil stress value. In this study, the Rankine method is used to calculate soil stress, and this method can be applied to the soil conditions that experienced deformation, caused by weathering of breccia and tuff rocks, allowing water to penetrate the rock medium. Consequently, the weathered layers of breccia and tuff act as slip planes. The presence of water on the slip planes leads to soil movement. Based on the analysis results, soil fractures are correlated with low water saturation values and contrast in soil stress values. A profound contrast in water saturation and soil stress values appears only at fractured slopes. Based on our analysis, soil fractures correlate with low water saturation values (5 - 15 %) accompanied by apparent contrast of soil stress values, i.e. the fractured soil is having lower soil stress (< 15 KN/m²) in comparison to the surrounding. Such a contrast was not found in slopes without fractures. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

Rock slope landslides and underground construction destabilization are frequently attributed to shear impairment by intermittent joints, and the support by bolts represents an indispensable technique for reinforcing jointed rocks. Therefore, we conducted laboratory experiments on intermittently jointed rock-like materials that were anchored, employing various anchoring inclination angles and methods, to investigate the influence of bolt anchoring on the shear properties and acoustic emission characteristics of intermittently jointed rock-like materials. Experimental results revealed that the peak shear strength of the anchored intermittently jointed rock-like materials is proportional to the bolt inclination angle. The strain on the joint is inversely related to the peak shear strength and the bolt inclination angle. The full-length anchorage and end anchorage can drastically enhance the mechanical traits of intermittently jointed rock-like materials, effectively impeding the proliferation of shear cracks after reaching the peak shear strength. The anchorage inclination exhibits a positive correlation with the accumulative acoustic emission (AE) energy and, conversely, a negative correlation with the peak AE count. In geotechnical engineering, the anchoring effect of anchor bolts can enhance the integrity of fractured rock masses and improve overall stability. [ABSTRACT FROM AUTHOR]

The technology of combining a negative Poisson's ratio (NPR) anchor cable with a double-layer truss support technology (N-DTST) is a new support technology for deeply buried tunnels. To evaluate the stability of the surrounding rock support after the application of this new support technology in the Sichuan–Tibet Railway tunnels, geomechanical model tests were conducted for the first time. A model test loading system with intelligent numerical control and automated analysis was developed to reveal the changing patterns of displacement and stress in the surrounding rock of tunnels. The test results revealed the following: (1) After the burial depth exceeds 800 m, the tunnel undergoes large deformations with displacements greater than 37.5 mm, and the traditional anchor cable support fails; (2) In the burial depth range of 800–2,000 m, the new support technology can control the surrounding rock deformation, and the surrounding rock displacement is less than 10 mm; (3) After the tunnel excavation, the radial stress decreases and the tangential stress concentrates. When the burial depth is greater than 800 m, the radial stress compensation provided by the anchor cable no longer meets the stability of the tunnel surrounding rock, and the new support technology can provide high stress to support the deeply buried tunnel; (4) After the burial depth exceeds 2,000 m, butterfly-shaped damage occurs on the tunnel surface, the truss structure inside the tunnel is damaged, and the support structure fails, so it is recommended to carry out reinforcement support at the arch shoulder. The research results verify the effectiveness of the new support technology and provide an important reference for the support of the surrounding rock in deeply buried tunnels. Practical Applications: Common Poisson's ratio anchors/ropes or shotcrete are widely used in tunnels as the core support structure. They often fail to meet the requirements of fractured rock, expansive rock, and high-ground-stress soft rock tunnels because they cannot adapt to the large deformation characteristics of the catastrophic rock mass. Based on this, this paper proposed a new support technology: an anchor rod/rope with a negative Poisson's ratio material combined with a double-layer three-dimensional truss for joint support of the tunnel. To verify the feasibility of this technology, the research and development team developed a new design for the structure. To verify the feasibility of this technology, a large-scale geomechanical model test system was developed, and a comparative model test was conducted using this test system in combination with the ground stress environment of the Sichuan–Tibet Railway to verify the effectiveness of the new support technology proposed in this paper, which provides a reference for the world's deep buried tunnel support technology. [ABSTRACT FROM AUTHOR]

The morphological characteristics of the fracture surface play a crucial role in determining its shear strength and deformation. Additionally, the fracture surface undergoes varying degrees of damage at different positions during the experimental process. This study aims to investigate the local damage mechanism of the fracture surface post-experiment, as it is essential for understanding the size effect and anisotropy of mechanical properties in rock masses. To achieve this, 3D scanning and 3D printing technologies were employed to create molds of rough fracture surfaces, and rock-like material mortar was used to cast samples of these rough fractures. The direct shear tests were successfully conducted on two rough rock fracture surfaces under varying normal pressures and shear directions. The analysis of the fracture surface's shear stress law indicates the presence of apparent anisotropy and varying damage modes in response to changes in normal pressure. Following the experiment, it was observed that the damage is localized on specific areas of the fracture surface, and its distribution characteristics are significantly influenced by the shear direction and normal pressure. Using 3D scanning technology, the JRC2D of various profiles and JRC3D of fracture surfaces are determined through the utilization of the geometric index WPA. Both local and overall roughness of the fracture surface were weakened after the shearing. Notably, the degree of local damage was found to be significantly related to the roughness feature at the corresponding position. [ABSTRACT FROM AUTHOR]

The mechanical and hydraulic behaviors of rock fractures are strongly dependent on the properties of the surface morphology. In this study, a sandstone fracture surface is taken as the research object. The morphological properties of the fracture surface characterized by parameters Z2s, Z2, and SRv are analyzed under the different sampling windows and profile lines. The results show that the large sampling window is more conducive to obtaining stable values of the morphology parameter Z2s. The coefficient of variation (CV) and the percentage of variation (PV) are proposed to determine the stable values of the morphology parameter Z2s, which is defined as a representative elementary surface (RES). It is confirmed that there is a RES with a size of 220 mm in the study region. The large sampling window generates a long correlation length of the morphology parameter Z2s. The differential sensitivities of the morphology parameters Z2 and SRv are compared under the different profile lines. It is found that the parameter Z2 can better describe the random variation properties of the surface morphology, while the parameter SRv is more suitable for describing the spatial structural variation properties of the surface morphology. The findings of this work are of great significance for investigating the size effect and anisotropy of rock fracture permeability. [ABSTRACT FROM AUTHOR]

The seepage-stress coupling characteristics of fractured rock mass were studied theoretically in this paper. Based on the cubic law and the equivalent circuit principle, a modified multi-parallel plate equivalent model (MPPEM) for seepage analysis of a rough single-fracture and a modified equivalent seepage resistance model (ESRM) for seepage analysis of a fracture networks consisting of rough single-fracture combined in series and parallel were proposed. On this basis, the equation for the variation of fracture aperture of fractured rock masses under the action of the three-direction principal stresses and pore water pressure was derived, and the discrete element calculations of the seepage-stress coupling of the two-dimensional fractured rock mass were carried out under different ground stress coefficients. The results show that the error of the modified MPPEM characterizing the seepage in a rough single-fracture in a rock mass does not exceed 7%. The modified ESRM can better characterize the seepage in T-shaped combined fracture and × -shaped combined fracture. With the increase of normal stress applied to the fracture surface, the fracture aperture and seepage flow rate of the fractured rock mass decrease. The above study is of great theoretical significance for the analysis of the seepage evolution law of the fractured rock mass under the action of geostress. [ABSTRACT FROM AUTHOR]

The deformation, strength, and failure characteristics of layered composite sandstones (LCSs) are critical issues in a stability evaluation in underground engineering. These issues were examined in this study using true triaxial experiments, with the main focus being on the influences of mechanical contrast (MC) between the layers in a three-dimensional (3D) restricted stress state. The overall strength of LCSs is mainly controlled by the strength of the weaker sandstone when MC exists between the layers. Failure under true triaxial stress results in σ2-oriented fractures coexisting with σ3-oriented fractures within LCSs. The overall failure of an LCS test specimen exhibits the σ3-transverse symmetric fracture mode, i.e., σ3-transverse symmetric tension near the σ3-loading surface and σ3-transverse symmetric shear in the middle of the specimen. A new strength criterion is proposed to predict the true triaxial strength of LCSs effectively. The study results provide insights into the cracking morphologies of LCSs with mechanical property changes in individual layers under true triaxial stress. [ABSTRACT FROM AUTHOR]

The quantification microstructural parameters has gained significant attention to estimate the strength of rock materials. Some researchers have qualitatively explained the influence of microstructural parameters on rock mechanical properties and many developed empirical relations between various microstructural indices and engineering properties of different rock types. A comprehensive review on the relation between microstructure and strength of rock materials has been carried out in this study based on the available literature and the tests performed on granite and sandstone from Malanjkhand and Kothagudem respectively. It has been observed that the correlation of rock strength with mineral content, textural parameters and micro-crack patterns does not signifies any perceptible correlation or any definite trend. This is attributed to the fact that rock strength is a manifestation of cumulative responses of a number of microstructural parameters and thus, correlating rock strength with any single parameter would overlook the impact of others. The study also discusses the challenges and potential benefits of both quantitative and qualitative analysis of microstructure in rock mechanics, providing a way forward for future research in the field. It is ascertained that microstructural studies are time consuming approach and involve significant limitations when quantifying the parameters from the microscopical images and relating them individually with strength of the rocks. However, they might be an important aspect in comprehending the variation in strength and deformation of rock materials and in this respect the implication of modern technological setups would be efficient over the conventional methods. [ABSTRACT FROM AUTHOR]

Understanding the time-dependent behavior of the rock mass is crucial to improve the reliability of underground structure design, particularly for projects with longer lifespans, such as nuclear waste repositories and hydrocarbon storage tanks. Creep is a time-dependent mechanism that plays a significant role in such designs but is often overlooked. Hence, a comprehensive study of the non-linear viscoelastic response of caverns over extended periods is needed to assess cavern closure under various scenarios. Therefore, this study investigates the time-dependent behavior of caverns constructed in rock-salt and shale rock using a finite element (FE) approach. The analysis was performed by the ABAQUS CAE tool, focusing on an axisymmetric approach. The time-dependent deformation behavior of the rocks was simulated using the Power-Law creep model. Furthermore, a parametric study was carried out to evaluate the influence of overburden depth, shape, volume, and time on the long-term behavior of caverns. The analysis revealed that the excavation of caverns in rock salt resulted in minimal displacements compared to that of shale rock. The results suggested inward displacement at the crown and wall of the cavern, with uplift found at the heel. Furthermore, the augmentation in the volume of the cavern and the depth of the overburden resulted in an enhanced displacement at the wall, crown, and heel of the cavern. Further, the examination of several cavern shapes revealed that spherical caverns show the least displacement compared to cylindrical and horseshoe-shaped caverns. Additionally, the normalized graphs were developed using normalized displacement, rock mass density, overburden depth, and Young's modulus as the basis. Engineers and designers can use these graphs as a useful tool to evaluate the long-term behavior of caverns and make well-informed judgments during the planning stage. Overall, this study contributes to safer and more reliable engineering practices in cavern construction and maintenance by offering insightful information about the time-dependent behavior of rock mass and useful suggestions for enhancing the stability and design of underground structures. [ABSTRACT FROM AUTHOR]

In sandy cobble stratum, the contents of rock blocks along the tunnel line present to be different. The tunneling-induced ground deformation under different rock contents is perceived as a main concern. Considering the heterogeneity of ground material, the meso-scale numerical models of sandy cobble strata were used to simulate tunnel excavation, in which the rock blocks and soil matrix were treated as separated constituents. By comparing the ground stress of simulation results with that of theoretical values, the applicability of meso-scale models was verified. The simulation results show that the rock content has a significant effect on the ground deformation performance. With the increase of rock content from 0 to 50%, the maximum ground settlement and the expansion of plastic zone gradually decreases, and the variation rule of the maximum ground settlement with rock content can be described by a normal distribution function. Meanwhile, the tunnel deformation pattern changes from non-uniform convergence to uniform convergence. It is also found that the relationship between the maximum subsurface settlement or the width coefficient of subsurface settlement trough and subsurface depth can be described by a power function, respectively. [ABSTRACT FROM AUTHOR]

Reasonable retention of safe coal and rock pillars is significant for safe mining and liberating coal resources under thick loose aquifers. The 18,041 working face of Chengcun Mine is taken as the research background. The elastic foundation model of the rock-clay synergistic aquiclude was creatively constructed, and the structural instability criterion was derived. The dynamic evolution law of thin bedrock failure and the vertical settlement law of clay layer are studied by numerical simulation test. A similar material simulation test is used to simulate the development law of water flowing fractured zone and the evolution law of vertical displacement of rock strata under the condition of fluid–solid coupling and to verify the stability of rock-clay synergistic water-resisting structure. The research shows that: (1) The maximum tensile stress in the middle of the long side of the rock stratum at the top of the bedrock is 0.652 MPa, less than its tensile strength threshold. (2) The clay and rock layers at the top of the bedrock have a synergistic settlement. The vertical settlement distribution transitions from a 'concentric circle' to a 'concentric ellipse'. The maximum deformation value in the central area is 0.5 m. (3) The development of water-conducting fractures under the thick loose layer and thin bedrock presents a 'double peak and one valley' shape, with a maximum height of 45.2 m. The rock-clay synergistic water-resisting structure maintains the effective water-resisting property, thus verifying the feasibility of the 4 m mining scheme. [ABSTRACT FROM AUTHOR]

To study the influence of interface angle on the tensile properties of rock-concrete composite specimens, Brazilian splitting tests of rock-concrete composite specimens under different loading angles were carried out by using the RMT-150B rock mechanics test system. The angle between the rock-concrete interface and the loading direction is 0°–90°. It is found that the tensile strength of rock-concrete composite specimens is greater than that of rock, and increases first and then decreases with the increase of loading angle. When the loading angle is 45°, the tensile strength reaches the maximum. The average splitting energy rate increases first and then decreases with the increase of loading angle and changes synchronously with the average tensile strength. Because the rock-concrete is bonded by grooves, the shear strength of the interface is large, and the specimen only exhibits tensile failure along the loading direction. By measuring the macroscopic crack length of the sample, it is found that the crack length decreases first and then increases with the increase of the loading angle. Finally, based on the plane stress problem in elastic mechanics, the stress analysis of the rock-concrete interface is carried out. [ABSTRACT FROM AUTHOR]

The Sarıçay Dam project in southwestern Türkiye integrates advanced geotechnical evaluation methods for building dams in areas with challenging geology and seismic activity. This study foregrounds an in-depth analysis of deformation modulus, the efficacy of consolidation grouting and shear strength parameters. It addresses critical issues such as encountering faults during construction and their mitigation, with the 'observational approach' being adopted to inform strategies and solutions and/or any modifications to these, including any design aspects. The appropriate selection of the deformation modulus and understanding its enhancement through consolidation grouting remain long-standing issues in geotechnical engineering. The comprehensive analyses of the deformation modulus revealed that certain empirical equations yield results comparable to those from in situ tests, although some may significantly overestimate; hence, correlating these tests with geophysical methods is crucial for accurate evaluation. Moreover, the deformation modulus results, derived from both rock pressuremeter and dilatometer tests on similarly characterized rock masses, displayed a notable comparability, despite the inherent scatter attributed to rock masses' heterogeneity and anisotropy. The findings revealed that consolidation grouting, despite its minimal effect on increasing the deformation modulus (4–18%), plays a role in reinforcing the foundation by filling joints and fractures. The research experiences and outcomes on this project will contribute to the knowledge base for future dam projects. [ABSTRACT FROM AUTHOR]

Middle-deep geothermal reservoirs, rich in energy, experience deep burial, high temperature, and intense three-dimensional stresses, causing noticeable elastic–plastic rock deformation under high confining pressure. However, existing researches primarily focused on elastic–plastic properties under various confining pressures, overlooking the impact of high temperature on granite's behavior. To address this, we conducted compression experiments at seven temperature points (25–600 °C) under varying confining pressures (0–15 MPa). The results reveal that increasing confining pressure prolongs the plastic yielding stage, linearly enhances compressive strength, and shifts rupture mode from brittle to expansion shear damage. Conversely, under constant confining pressure, compressive strength decreases with rising temperature, accompanied by more intricate artificial cracks. Rock cohesion, internal friction angle, and wave velocity decrease due to increased thermal damage micro-cracks. Heat treatment over 500 °C significantly increases porosity and pore throat radius, explaining heightened plasticity in hot dry rocks. These findings offer theoretical and technical insights for understanding elastic–plastic fracture mechanisms during hydraulic fracturing in middle-deep geothermal reservoirs and enhancing heat recovery efficiency. [ABSTRACT FROM AUTHOR]

The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw (FT) conditions. However, the unidirectional FT condition, which is also prevalent in engineering practice, has received limited attention. Therefore, a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed. Firstly, frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action, respectively. Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles, while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction. Moreover, the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions. Subsequently, the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured. Under uniform FT cycles, newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale, and thus the frost deformation shows isotropic characteristics in macro scale. Under unidirectional FT cycles, micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction, and rock structure gradually becomes anisotropic in micro scale, resulting in the anisotropic characteristics of frost deformation in macro scale. [ABSTRACT FROM AUTHOR]

As a widely recognized and effective roadway support method, the top-cutting pressure relief technology, plays a positive role in improving the stress distribution inside the roadway and reducing the deformation of surrounding rock. To address the stress issues faced by the 1123 transportation roadway in Xichuan Coal Mine and reduce the deformation of surrounding rock, a drilling into joint and top-cutting pressure relief technology has been proposed. This technology can drill deeply into high-pressure zones, has a good pressure relief effect, and is flexible reliable, which is suitable for harder rocks in coal seams, and has high reliability and practicality. Through precise calculations using the stress function method, the upper and lower thresholds suitable for the drilling of the coal mine were determined, which are 14.14 and 6.32, respectively. The collapse state of the roof under different hole spacing was analyzed in depth using the numerical simulation method, and the stress distribution properties of solid coal before and after roof cutting were studied. The results show that the top cutting and pressure relief technology significantly improves the roof caving performance and can effectively prevent the occurrence of rockburst. At the same time, this technology can effectively reduce the stress transfer ratio, reducing the peak stress values in solid coal by 25.44% and pushing the peak point inward by 179.18%. The research results can providea reference for the selection of small coal pillar retention and support methods in the future. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of pre-tension on the anchoring and crack-arresting effect of rockbolts, a theoretical model of stress intensity factor at the crack tip in anchored surrounding rock was established using fracture mechanics theory. An expression for the difference in stress intensity factor due to axial force on the rockbolt was derived, exploring the influence of pre-tension on the stress intensity factor of cracks. A numerical model of anchored crack specimens was developed using UDEC (V6.0) software to simulate and analyze the mechanical performance and damage characteristics of specimens anchored with different pre-tension. The results indicate that the difference in stress intensity factor of cracks is positively correlated with pre-tension. High-pre-tensioned rockbolts can effectively reduce the stress intensity factor of cracks. Prestressed rockbolts can alter the failure mode of rock masses from shear failure along pre-existing cracks to tensile splitting failure. The application of high pre-tension significantly enhances the strength of the rock mass, reducing both the damage degree and the number of internal cracks. After anchoring with high-pre-tensioned rockbolts, the peak strength and elastic modulus of the crack specimens increased by 22.5% and 31.9%, respectively, while damage degree decreased by 17.4%, the number of shear cracks decreased by 22.6%, and the number of tensile cracks decreased by 42.9%. The pre-tensioned rockbolt method proposed in this study was applied to the support of roadway widening. Field monitoring data indicated that the axial force of the rockbolts in the test section generally exceeded 60 kN, effectively controlling the deformation of the roadway surrounding the rock. The convergence of the two sides decreased by 22%, and borehole inspections showed a significant reduction in internal cracks. The research results provide a theoretical basis for controlling the discontinuous deformation of deep broken surrounding rock roadways. [ABSTRACT FROM AUTHOR]

To investigate how bedding planes affect the energy evolution and failure characteristics of transversely isotropic rock, uniaxial compression tests were conducted on soft–hard interbedded rock-like specimens with varying bedding angles (α) using the RMT-150B rock mechanics loading system. The test results indicate that throughout the loading process, the energy evolution shows obvious stage characteristics, and the change of α mainly affects the accelerating energy dissipation stage and the full energy release stage. With the increase of α, the ability of rock to resist deformation under the action of energy shows the characteristics of "strong–weak–strong". The energy dissipation process is accelerated by medium angle bedding planes (α = 45°~60°). The precursor points of the ratios of dissipation energy to total energy (RDT) and elastic energy to dissipation energy (RED) can be used to effectively predict early failure. With the gradual increase of α, the difficulty of crack development is gradually reduced. The changes of energy storage limitation and release rate of releasable elastic energy are the immanent cause of different macroscopic failure modes of specimens with varying α. [ABSTRACT FROM AUTHOR]

Theoretical analysis and numerical simulation are used to study the influence of different parameters of variable diameter borehole pressure relief technology on the surrounding rock and support. A strain-softening model was established to analyze the intrinsic connection between the parameters of variable diameter boreholes and the evolution of surrounding rock stress, deformation law, and support strength. The results show that: (1) With the increase in shallow borehole diameter, it is easy to cause anchor de-anchoring phenomenon. (2) After the deep borehole diameter is more than 250 mm, it transfers the peak of the shallow vertical stress to the deep surrounding rock (about 16 m away from the coal wall). (3) If the position of the variable borehole aperture is set between the anchorage zone and the stress peak of the roadway, the stress transfer effect is better, and the influence and effective binding force on the surrounding rock is smaller. (4) When the spacing is 1.0 m~2.0 m, the vertical stress starts to transfer to the deep surrounding rock, the deformation of the surrounding rock is smaller, and the reduction in the effective binding force of the anchors is smaller. The result can provide a reference for similar production conditions. [ABSTRACT FROM AUTHOR]

In this paper, based on smoothed‐particle hydrodynamics‐finite element method, numerical models of plunger squeezing water at a sinusoidal velocity were established to simulate self‐excited pulse water jet (SEPWJ). RHT constitutive model was adopted to describe the damage and failure of coal rock impacted by water jet. The morphological evolutions of broken pits and timeliness of rock‐breaking efficiency of SEPWJ and continuous water jet (CWJ) under the conditions with and without stress loadings were obtained and compared. The evolution laws of damage and stress inner coal rock induced by jet impact, and the failure mechanism were revealed. And the influences of different stress loading magnitudes on the fracture characteristics of coal rock were investigated. The results show that the morphologies of broken pits formed by self‐excited pulse jet undergo changes in a semi‐circular, U‐shaped, V‐shaped, and bullet shaped in sequence under the stress‐free loading condition. When applying one‐dimensional (1D) and 2D stress loadings, the shallow but wide broken pits with laminar main cracks along the stress loading direction and the inverted trapezoidal bowl broken pits are formed, respectively. With the increase of 1D stress, the depth and width of broken pits slightly decrease as a quadratic parabolic function and linearly increase, respectively. And the broken pit width and area both show an exponential slow decreasing trends with the increasing 2D stress. SEPWJ can induce higher stresses to cause the earlier occurrence of initial damage and the shorter duration of damage accumulation to coal rock than CWJ, which leads to a better rock‐breaking effect. The surface and deeper coal rock elements are broken mainly due to compressive shear stresses. The 2D stress loading delays the initial damage occurrence and prolongs the damage accumulation duration due to inhibitory effect of stress loading on jet impact. [ABSTRACT FROM AUTHOR]

In the rate‐state friction law framework, the transition from velocity weakening (V‐W) to velocity strengthening (V‐S) behavior marks the base of the seismogenic crust. Here we investigate the role of fault slip displacement under hydrothermal conditions in controlling the V‐W to V‐S transition. We shear simulated gabbro gouges at slip velocities ranging from 16 nm/s (∼50 cm/year) to 10 μm/s (∼8 cm/day) under hydrothermal conditions (300–400°C temperature; 30 MPa pore fluid pressure). We observe that cumulative fault slip increases the critical velocity for the V‐W to V‐S transition. The transition is accompanied by localized to distributed deformation mode, the formation of smectite‐type clays and occurrence of intergranular mass transfer. Our results provide insights into understanding the deepening and shallowing of V‐W/V‐S boundary (lower limit of the seismogenic zone) following a mainshock. Besides strain rate effects, slip‐enhanced chemical alteration and grain size‐sensitive deformation may temporarily contribute to the shallowing process. Plain Language Summary: According to the standard model of earthquake nucleation, earthquakes are the result of frictional instabilities along faults. The necessary condition for earthquake nucleation is that the frictional strength of a fault decreases with fault slip velocity ("velocity‐weakening" behavior) or slip distance ("slip‐weakening" behavior). Although extensive laboratory studies have been conducted to investigate the velocity‐dependence of friction in rocks, less attention was paid to the role of slip displacement on fault frictional stability, especially in the presence of hot and pressurized fluids. The latter, difficult to reproduce in the laboratory, is a common condition at seismogenic depths. In this study, we examine how the frictional stability evolves with slip velocity and displacement on simulated faults made of powders of gabbro (a common rock of the oceanic crust) under hydrothermal conditions up to 400°C. We find that the critical velocity for the transition from velocity‐weakening to velocity‐strengthening increases with cumulative slip displacement. In nature, the increase of this critical velocity may result in the uplift, during seismic sequences, of the base of the seismogenic crust (i.e., aftershock hypocenters will be shallower). Our findings suggest that, slip displacement, accompanied by fault mineralogical‐structural evolution, can influence fault frictional stability and earthquake nucleation. Key Points: The role of slip displacement in controlling fault stability under hydrothermal conditions is investigatedThe critical velocity for transition in friction from velocity‐weakening to velocity‐strengthening increases with slip displacementThis frictional transition, attributed to chemical alteration, is accompanied by the transition from localized to delocalized deformation [ABSTRACT FROM AUTHOR]

Complex natural fracture networks typically consist of multiple clusters, whose connectivity is rarely quantified. Therefore, for each identified fracture network, we propose a connectivity metric that accounts for individual fracture clusters and their interactions. This metric evaluates contributions from all fracture clusters, considering their relative sizes and interactions among the isolated clusters, which in turn depend on the hydraulic conductance of the interconnecting rock matrix. Furthermore, we investigate how the system connectivity depends on fracture sealing, alterations of central clusters, and cluster linkage. Fracture sealing strongly impacts overall fracture connectivity, with 5 percent of sealed fractures reducing connectivity by 20 percent. The connectivity reduction is small when transitioning the central cluster from the largest to the smallest one. However, the largest cluster significantly contributes to overall connectivity, while the smallest one contributes minimally. Natural fracture networks increase connectivity by linking more clusters, with heterogeneity and anisotropy playing pivotal roles. Plain Language Summary: Natural fractures are typical multi‐cluster systems found in many places, not just in crustal rocks but also in construction materials, human bones, and other areas. Multi‐cluster systems are even more widespread, including in biological systems and materials science. In crustal rocks, natural fractures are crucial for assessing rock stability and flow processes because they control the mechanical and hydrological properties of the rocks. Thus, fractures are important in many engineering fields, such as oil and gas production and underground hydrogen or CO2 storage. The connectivity of these multi‐cluster systems is essential as it directly impacts their mechanical and hydrological properties. Here, we propose a new metric to measure the connectivity of complex fracture networks. This method explains how individual fracture clusters contribute and interact based on their sizes and hydraulic conductance. Applying this to outcrop fracture maps shows significant changes in network connectivity due to factors like fracture sealing, changes in central clusters, and cluster linkage. This method can also be applied to 3D fracture systems and other multi‐cluster systems. These findings improve our understanding of how fractured formations evolve and how fluids flow through them, offering practical insights for better engineering practices. Key Points: Fracture sealing significantly impacts overall connectivity, with 5% of sealed fractures reducing it by about 20%Altering the central cluster insignificantly affects connectivity but significantly influences productionNatural fractures enhance connectivity by linking clusters, with heterogeneity and anisotropy playing a pivotal role [ABSTRACT FROM AUTHOR]

AbstractTo ensure the safety of subsea tunnel construction, it is crucial to prevent extreme deformation of the surrounding rock. An assessment and prediction study on the surrounding rock deformation induced by the excavation of the subsea tunnel using the three-bench method was conducted, based on Haicang Subsea Tunnel in Xiamen, China. A series of numerical simulations and on-site monitoring were conducted to reveal the evolution of the displacement field of the surrounding rock. The influences of various factors on the settlement trough of the surrounding rock above the subsea tunnel were also investigated, including seawater, bench length, and bench spacing. The rapid ring closure of the primary support by adopting short benches is imperative to control the arch settlement and settlement trough width. The settlement resulting from the excavation of the upper and middle benches contributed to 90% of the total deformation, as revealed by both numerical simulation and in-situ monitoring. Subsequently, an empirical formula was proposed to predict the settlement trough curves of surrounding rock at different depths above the seabed tunnel. [ABSTRACT FROM AUTHOR]

To solve the problem of controlling large deformation of surrounding rock in deep soft rock roadway, the distribution characteristics and deformation mechanism of surrounding rock cracks in soft rock roadway under different lateral pressure coefficients are studied using numerical simulation, theoretical analysis, and field measurement. The results show that under different lateral pressure coefficients, the range of surrounding rock cracks shows three forms: round, oval, and butterfly. No matter what lateral pressure coefficient the roadway is in, the surrounding rock cracks always appear in the plastic zone, and there is a high correlation between the surrounding rock crack range and the plastic zone. The stress characteristics of the surrounding rock in the plastic zone include two main aspects. One is that the direction of the principal stress of the surrounding rock is deflected, which is manifested as an annular distribution of the direction of the maximum principal stress around the roadway. The direction of the minimum principal stress in the upper part of the roadway points to the center of the roadway, and the direction of the minimum principal stress in the lower part of the roadway deviates from the center of the roadway. Second, the ratio of the maximum to minimum principal stress in the surrounding rock is large. Under this stress characteristic, the surrounding rock in the plastic zone has strong shear dilation. The shear dilation makes the crack of the surrounding rock open so that the surrounding rock is squeezed into the roadway space, and then the roadway produces large deformation. Due to the large range of cracks in the butterfly‐shaped plastic zone, the shear dilation deformation produced by the butterfly‐shaped plastic zone is far more than that of the round/oval plastic zone. According to the crack range of roadway surrounding rock under different lateral pressure coefficients, the corresponding support scheme is put forward. Field experiments show that the support scheme can effectively control the deformation of surrounding rock and meet the requirements of roadway use. [ABSTRACT FROM AUTHOR]

In order to analyze the stability of the bridge above the goaf, the disturbance influence of goaf residual deformation on the bridge is studied. Firstly, an equivalent numerical simulation method of goaf residual deformation evolution process is studied by quantitative analysis the sensitivity of residual subsidence to the rock parameters using the OAT (one-variable-at-a-time). Then, the collaborative deformation of ground, pile, and bridge floor is studied under the condition of a simply-supported beam bridge above the goaf center. Finally, the mechanism of collaborative deformation of ground, pile, and bridge floor is revealed. The results show that the goaf residual deformation process can be obtained by weakening the elastic modulus of fractured rock in the caving zone. At the final residual deformation stage, the subsidence ratio of ground to pile is about 10, and the subsidence ratio of pile to bridge floor is about 2, while the ground horizontal movement ratio of ground to pile is about 7, and the bridge floor horizontal movement can be ignored. The bridge floor is always in the positive curvature influence zone, and the pile has an inhibitory effect on the curvature deformation of the bridge floor. The compression deformation occurs between the piles locations, while the tensile deformation occurs at the pile location. The evolution of negative frictional resistance derived from goaf residual deformation is the main reason for the change in the collaborative deformation law among the ground, pile and bridge floor. This research can provide scientific support and theoretical basis for the design, construction, and protection of the bridge above the goaf center, and can also provide reference for the stability evaluation of bridge above goaf under other conditions. [ABSTRACT FROM AUTHOR]

To investigate the damage mechanisms in granite's physical and mechanical properties after high-temperature water quenching, this study employed MTS815.04 for uniaxial compression tests on thermally treated specimens, with concurrent acoustic emission monitoring, and utilized nanoindentation for micromechanical analysis. The results show that with increasing temperature, granite's peak strength and elastic modulus decrease, with a sharp decline after 400–500 °C, corresponding to a significant increase in the internal damage, which can be detected by acoustic emission monitoring. Below 500 °C, macroscopic mechanical degradation is due to mineral thermophysical property differences, while above 500 °C, microcrack development is the main deterioration factor. The failure mode shifts from tensile to tensile-shear complex to shear failure, with transition points at 400 °C and 800 °C. The results of this study are of certain reference value for improving the efficiency of extracting thermal energy from dry-hot rocks and providing security guidance for the tunnel restoration process following fire damage. [ABSTRACT FROM AUTHOR]

During rock drilling, a drill bit will wear as it breaks the rock. However, there is no uniform grading standard for rock abrasiveness. To solve this problem, the wear mechanisms of a polycrystalline diamond compact (PDC) bit and the formation it is drilling into are analyzed in depth, and an abrasiveness evaluation method based on the fractal dimension of the rock surface topography is established. Initially, a three-dimensional digital model is generated from a scanning electron microscope image of the rock after drilling; next, an evaluation of the irregularities on the rock surface is performed using an adapted Weierstrass–Mandelbrot (W-M) function to ascertain the fractal dimensionality. Then, the microcontact characteristics of the contact surface between the formation and the PDC bit are analyzed, and the distribution of the microconvex contact points of the two-body friction pair in a region is obtained. Because the sliding friction between the drill bit and the rock produces a large amount of heat, according to the contact area formula of the friction surface and heat conduction theory, the temperature rise and overall temperature distribution of the formation and PDC bit under the condition of sliding friction are revealed, and the real contact area between the formation and the drill bit within a certain temperature range is obtained. Finally, the evaluation index of rock abrasiveness under sliding conditions is established by adopting the wear weight loss of the rock cutting tool per unit volume as the index of rock abrasiveness, and the model is verified by a microdrilling experiment. The research in this paper is highly important for improving the rock-breaking efficiency and bit service life during drilling. [ABSTRACT FROM AUTHOR]

The study of rock burst tendency of rock masses with different sizes plays a key role in the prevention of rock burst. Through theoretical analysis, it is proposed that uniaxial compressive strength and deformation modulus ratio are the key mechanical parameters affecting rock burst occurrence. In order to find out the size effect of uniaxial compressive strength and deformation modulus ratio, theoretical analysis and uniaxial compression experiment are carried out on rock samples with different heights, different cross-sectional areas and different volumes. The results show that the smaller the uniaxial compressive strength is, the larger the deformation modulus ratio is, and the more likely rock burst are to occur. On the contrary, rock burst is still not easy to generate. The uniaxial compressive strength of rock samples with different heights, different cross-sectional areas and different volumes increases with the increase of rock sample size. The deformation modulus ratio of rock samples with different heights and different volumes shows an upward trend on the whole, while that of rock samples with different cross-sectional areas shows a downward trend on the whole. The fracture forms of rock are analyzed using the energy conversion law in the process of deformation and failure for three kinds of rock with different shapes and sizes. [ABSTRACT FROM AUTHOR]

The creation of fractures in bedrock dictates water movement through the critical zone, controlling weathering, vadose zone water storage, and groundwater recharge. However, quantifying connections between fracturing, water flow, and chemical weathering remains challenging because of limited access to the deep critical zone. Here we overcome this challenge by coupling measurements from borehole drilling, groundwater monitoring, and seismic refraction surveys in the central California Coast Range. Our results show that the subsurface is highly fractured, which may be driven by the regional geologic and tectonic setting. The pervasively fractured rock facilitates infiltration of meteoric water down to a water table that aligns with oxidation in exhumed rock cores and is coincident with the adjacent intermittent first‐order stream channel. This work highlights the need to incorporate deep water flow and weathering due to pervasive fracturing into models of catchment water balances and critical zone weathering, especially in tectonically active landscapes. Plain Language Summary: The creation of fractures in bedrock facilitates water movement through the subsurface which breaks down rock creating porous soil and weathered bedrock. Water movement is vital for important processes like plant growth, streamflow, and groundwater recharge. However, understanding how fracturing, water flow, and rock weathering interact is challenging because the subsurface is difficult and expensive to measure. Here we use observations from drilling, water level monitoring, and geophysics to understand these interactions. Our results indicate that the subsurface is highly fractured due to the geologic and tectonic setting. The large number of fractures makes it easier for water to flow through the subsurface and causes chemical alteration of bedrock. This may cause water to flow outside of the catchment through the subsurface. This work highlights the role of geologic and tectonic processes in driving fracturing, which dictates the movement of water and subsurface weathering beneath Earth's surface. Key Points: Deep weathering may be due to enhanced permeability and surface area from inherited rock damage from local geologic and tectonic conditionsWeathering and water flow extend to the elevation of the adjacent first‐order intermittent stream channelThe deep weathering and fracturing front may allow for inter‐basin water flow in headwater catchments [ABSTRACT FROM AUTHOR]

Flaw length has a significant effect on the cracking behaviour of fractured rock. PFC2D was used to simulate the uniaxial compression of red sandstone samples with secondary flaw lengths L2 of 0 mm, 5 mm, 10 mm, 15 and 20 mm under different primary flaw angles α(α = 0°, 15°, 30°, 45°, 60°, 75°, and 90°). Based on the simulation results, the effects of the secondary flaw length on the mechanical parameters, crack initiation location and crack evolution process of the fractured rock were analysed. Then, a method for judging the initiation location of the first cracks was proposed. Finally, the characteristics of the particle displacement field at preexisting flaw tips during first and secondary crack initiation were analysed. The results of this study are helpful for more deeply understanding the cracking behaviour of fractured rock. [ABSTRACT FROM AUTHOR]

There are fewer studies on the width of coal pillar retaining under a thick, hard roof. This paper takes the thick limestone roof in the 10110 working face of Jinniu Coal Mine as the background, taking the reasonable coal pillar width and its stability control technology as research objectives. Taking the theoretical analysis and calculation, numerical simulation to study the stress distribution along goaf under different parameters of the roof cutting, the stress distribution of the roadway, and displacement of the surrounding rock under different coal pillar widths, finally examined through on-site industrial experiments. The results show that (1) the vertical stress along goaf shows a gradual decrease with the increase of the roof cutting height and angle; after considering the cost and the difficulty, the optimal height and angle are chosen to be 21 m and 15°; (2) the vertical peak stress of coal pillar decreases with the increase of the width, coal pillar is gradually transformed from the crushed state to the elastic state, the displacement of the roadway also decreases with the increase of the width of the pillar, and the width of the coal pillar is chosen to be 8.0 m after comprehensive analysis; (3) during the roadway excavation and working face mining, the deformation of the surrounding rock is in a reasonable range, and the anchors and bolts are in a good state of stress, which indicates that retaining 8 m coal pillar is a success. This paper also provides theoretical references and implications for coal pillar retaining in similar geological mining conditions. [ABSTRACT FROM AUTHOR]