Search

The mechanical properties of fully-grouted bolt support are critical for the safety of support engineering works. To study the influences of factors including the bolt length and diameter, strength of the rock, and fracture angle on the mechanical properties of fully-grouted bolt support, compression tests were conducted on an anchored rock mass, considering the shortcomings of pullout tests on bolts. The discrete element software PFC2D (4.0) was adopted for numerical simulation and analysis from two aspects, namely, the stress distribution and anchorage force supplied by such bolts. The research found that by increasing the bolt diameter and length as well as the strength of the rock, the maximum anchorage force of bolts increases. Whereas the stress distribution of all bolts increases at first and then decreases along the bolts, and there is only one peak on the stress distribution curves, which also gradually shifts to a greater depth. In a fractured rock mass, the maximum anchorage force of bolts decreases, then increases (and is minimized at a fracture angle of 45°) with the decrease in fracture angle. The influence of fractures with different angles on the stress distribution of bolts is mainly reflected in the fracture zone. The bolt stress decreases abruptly in the zone with a fracture angle of 90°, forming a valley. The bolt stress increases suddenly in the zones with fracture angles of 60° and 45°, thus forming peaks. The bolt stress does not increase or decrease suddenly in the zone with a fracture angle of 30°. Therefore, it necessitates consideration of the influences of fractures on the anchorage force and the selection of bolts of appropriate size during anchorage design. After installation, the bolt stress should be monitored for stability and early warning of anchored rock mass according to changes in the stress provided. [ABSTRACT FROM AUTHOR]

With the increasing complexity of mining conditions, the high degree of development of fractures in roadway surrounding rock significantly affects the stability of the rock mass in space, leading to difficulties in maintaining numerous roadways. In response to the challenges posed by the development of fractures in deeply buried roadway surrounding rock under complex geological conditions, a novel method for scientifically and reasonably characterizing the complex fractures in surrounding rock stability analysis of roadways was proposed, which combines field measurements, numerical simulations, and physical experiments, providing strong capabilities for comprehensive analysis. The development of fractures in coal mine sites was investigated and statistically analyzed using the scanning survey method, on the basis of which the probability density model of various fracture parameters was established by computational analysis. The Monte Carlo stochastic simulation technique was used to reconstruct and recover the fractures obtained from the field investigation using a discrete fracture network (DFN), which realizes the characterization of complex fractures in engineering field conditions. On this basis, and in conjunction with the finite difference method (FDM), the FDM–DFN coupling model was implemented into FLAC3D (version 5.01). A parametric study of the proposed FDM–DFN coupling model was carried out, and the results were compared to Mohr–Coulomb and strain-softening models. It has been shown that the fracture density, which is a newly considered parameter in the proposed model, exhibits noticeable effects on the deformation and failure of the roadway rock mass. Thus, the FDM–DFN coupling model offers a more realistic simulation of the roadway behavior than Mohr–Coulomb and strain softening models. The proposed model can be utilized for other applications involving rock reinforcement of mine openings under similar geotechnical conditions. [ABSTRACT FROM AUTHOR]

Abstract With regard to deep mining in metal mines, an investigation into the failure mode of deep fractured rock masses and their corresponding acoustic emission signal characteristics is conducted via uniaxial compression tests. Subsequently, a fractal damage renormalization group mechanical model is developed to explain the behavior of those fractured rock masses. Employing the bonded block model (BBM) numerical simulation method, fracture process in synthetic rock samples is analyzed, thereby validating the efficacy of the mechanical model. The numerical simulations highlight the critical role of fractures expansion in underlying the deterioration of rock mass strength. As the peak load decreases, the fracture fractal dimension increases, leading to a significant 14.2% reduction in compressive strength accompanied by an approximate 8.7% rise in average fracture fractal dimension. A comparative analysis of tetrahedral and voronoi block synthetic rock samples reveals the tetrahedral block samples exhibit a superior ability to depict the fracture behavior of fractured rock masses. Specifically, they offer a more accurate simulation of acoustic emission characteristics and failure modes. Furthermore, variations in the fracture fractal dimension with respect to the hole defect’s position are observed, with the maximum value occurring along the vertical axis of the hole defect. This observation underscores the potential utility of visually monitoring deep rock fracture dynamics as an effective mean for quantitatively evaluating fracture damage and strength degradation in deep rock formations.

As a calculation method based on the Galerkin variation, the numerical manifold method (NMM) adopts a double covering system, which can easily deal with discontinuous deformation problems and has a high calculation accuracy. Aiming at the thermo-mechanical (TM) coupling problem of fractured rock masses, this study uses the NMM to simulate the processes of crack initiation and propagation in a rock mass under the influence of temperature field, deduces related system equations, and proposes a penalty function method to deal with boundary conditions. Numerical examples are employed to confirm the effectiveness and high accuracy of this method. By the thermal stress analysis of a thick-walled cylinder (TWC), the simulation of cracking in the TWC under heating and cooling conditions, and the simulation of thermal cracking of the Swedish Äspö Pillar Stability Experiment (APSE) rock column, the thermal stress, and TM coupling are obtained. The numerical simulation results are in good agreement with the test data and other numerical results, thus verifying the effectiveness of the NMM in dealing with thermal stress and crack propagation problems of fractured rock masses.

Determining the anisotropic permeability of rock masses plays an important role in various geoscience and engineering projects. Since hydraulic aperture is difficult to be measured directly, numerical or theoretical methods for calculating directional permeability are usually used for qualitative technical support, rather than quantitative analysis. A semi-theoretical method is proposed in this study to estimate the directional relationship based on average permeability, where the latter can be obtained through a relatively cheap single-borehole water pressure tests. In this method, hydraulic aperture is replaced by aperture ratio, which can be quickly determined through field investigation by experienced geologists. Compared to adopting multiple-borehole water pressure tests to determining the anisotropic permeability, the new developed method can significantly reduce the testing cost. Numerical experiments are conducted and validated our method, the results show that the mean error rates are generally below 20%. [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]

With regard to deep mining in metal mines, an investigation into the failure mode of deep fractured rock masses and their corresponding acoustic emission signal characteristics is conducted via uniaxial compression tests. Subsequently, a fractal damage renormalization group mechanical model is developed to explain the behavior of those fractured rock masses. Employing the bonded block model (BBM) numerical simulation method, fracture process in synthetic rock samples is analyzed, thereby validating the efficacy of the mechanical model. The numerical simulations highlight the critical role of fractures expansion in underlying the deterioration of rock mass strength. As the peak load decreases, the fracture fractal dimension increases, leading to a significant 14.2% reduction in compressive strength accompanied by an approximate 8.7% rise in average fracture fractal dimension. A comparative analysis of tetrahedral and voronoi block synthetic rock samples reveals the tetrahedral block samples exhibit a superior ability to depict the fracture behavior of fractured rock masses. Specifically, they offer a more accurate simulation of acoustic emission characteristics and failure modes. Furthermore, variations in the fracture fractal dimension with respect to the hole defect's position are observed, with the maximum value occurring along the vertical axis of the hole defect. This observation underscores the potential utility of visually monitoring deep rock fracture dynamics as an effective mean for quantitatively evaluating fracture damage and strength degradation in deep rock formations. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Deformation monitoring data provide a direct representation of the structural behavior of reservoir bank rock slopes, and accurate deformation prediction is pivotal for slope safety monitoring and disaster warning. Among various deformation prediction models, hybrid models that integrate field monitoring data and numerical simulations stand out due to their well-defined physical and mechanical concepts, and their ability to make effective predictions with limited monitoring data. The predictive accuracy of hybrid models is closely tied to the precise determination of rock mass mechanical parameters in structural numerical simulations. However, rock masses in rock slopes are characterized by intersecting geological structural planes, resulting in reduced strength and the creation of multiple fracture flow channels. These factors contribute to the heterogeneous, anisotropic, and size-dependent properties of the macroscopic deformation parameters of the rock mass, influenced by the coupling of seepage and stress. To improve the predictive accuracy of the hybrid model, this study introduces the theory of equivalent continuous media. It proposes a method for determining the equivalent deformation parameters of fractured rock mass considering the coupling of seepage and stress. This method, based on a discrete fracture network (DFN) model, is integrated into the hybrid prediction model for rock slope deformation. Engineering case studies demonstrate that this approach achieves a high level of prediction accuracy and holds significant practical value. [ABSTRACT FROM AUTHOR]

Fluid flow and evolution mechanisms in fractured rocks are fundamental tasks in engineering fields such as geohazards prediction, geothermal resource exploitation, oil and gas exploitation, and geological sequestration of carbon dioxide. This study employed an enhanced X-ray imaging digital radiography to investigate nonlinear flow model of fluid through different roughness fractures. The X-ray images of fluid flow during rock failure were analyzed using a multi-threshold segmentation method applied to the X-ray absorption dose. The result show that a proposed nonlinear flow equation considers the joint roughness coefficient and the uniaxial compressive strength of the jointed rock, enabling a better understanding of the nonlinear flow behavior in fractured rock masses. This modeling approach has important theoretical and practical implications. By accounting for key factors influencing fluid flow behavior, it can help guide monitoring efforts to support early warning of fractured rock mass instability. Additionally, a more mechanistic understanding of flow processes may inform strategies to prevent engineering geological hazards. [ABSTRACT FROM AUTHOR]

The aim of this paper is to explore hydrothermal transport in surrounding rocks during deep mining, focusing on the mechanisms and key factors influencing groundwater seepage and heat accumulation disasters. Stress–seepage coupling tests were conducted on fractured rock mass with varying roughness under constant-pressure loading/unloading conditions. Also, a permeability model considering joint roughness coefficient and confining pressure was established. The study further examined the evolution of heat transfer in rough fractured rock mass and variations in convective heat transfer characteristics. The heat transfer process was observed to progress through stages of surge, attenuation, and stabilization. Two calculation models were developed using multivariate linear regression and random forest regression to quantify how different factors influenced water–rock convective heat transfer in mining-induced fractured rock mass. The average correlation coefficient R2 of the proposed models exceeded 0.95. The importance scores of osmotic pressure, inlet water temperature, rock temperature, and permeability were 0.417, 0.296, 0.223, and 0.065, respectively. The flow rate and water–rock temperature difference were determined to be the key factors influencing hydrothermal transport. This study enhanced the understanding of the hydrothermal migration mechanisms in surrounding rocks during mining and provided insights into geothermal water control.

Numerical simulation of radon migration in fractured rock masses is crucial for environmental radon pollution protection, radon tracing technology and the co-exploitation of coal and uranium resources. This paper proposed a novel model based on a fractal discrete fracture network (DFN) to simulate radon migration in fractured rock masses. The paper provided a detailed method for determining the locations of three-dimensional fractures using the multiplicative cascade process. The governing equations for radon migration in fractures and the rock matrix were established and numerically solved using the finite element method. The study developed open-source software DFNRn (Discrete Fracture Network model for Radon migration), which was publicly available on GitHub. The software simulated radon migration in a fractured rock mass with a domain size of 100 m. The results demonstrate that fluid convection in fractures drives radon migration, which is dominant compared to the diffusion process. The accuracy of our proposed model was verified by comparing it with the measured data of the fractured rock. Furthermore, the study investigated the relationship between the percolation threshold of the fracture density P 32 ′ and the key parameters of the DFN. The results show that P 32 ′ decreased with the fractal dimension Df (1.4 ≤ Df ≤ 1.9) and normalization constant α (1.4 ≤ α ≤ 1.8) and is not correlated with the length exponent a (1.2 ≤ a ≤ 2.8). P 32 ′ decreased with the mean orientation angle and has no correlation with the Fisher constant. The radon source term of the rock matrix has the greatest impact on radon migration in fractured rock masses compared to the radon diffusion coefficient and permeability. Highlights: A new approach is proposed to model radon migration in fractured rock masses. An open-source software DFNRn was developed and is publicly available on GitHub. The procedure of the multiplicative cascade method in 3D space is given in detail. [ABSTRACT FROM AUTHOR]

This paper introduces the development of a dynamic seepage network method (DSN) within a two-dimensional discontinuous deformation analysis (2D-DDA) framework. The primary goal is to identify actual fractures and seepage spaces, establish a seepage network, and automatically compute hydraulic water pressure within blocky systems. In addition, a new coupled dynamic hydromechanical model (DDA–DSN) is proposed to investigate seepage behavior in time-varying fractured rock masses. The DSN method tracks fracture propagation between blocks during seepage flow, while the DDA component characterizes the translation, rotation, and deformation of arbitrarily formed blocks. The paper covers fundamental theories, the determination of neighboring non-contact block pairs, the creation of seepage networks, hydraulic pressure calculations, and the integration of DDA and DSN in detail. Furthermore, the validity of the coupled DDA–DSN hydromechanical model is confirmed by comparing numerical results with experimental measurements. These results highlight the model's effectiveness in capturing fluid flow behavior within fractured rock masses, emphasizing the exceptional capabilities of DSN in identifying seepage spaces, constructing seepage networks, and automatically computing hydraulic pressure. Overall, this proposed model holds significant promise for addressing engineering challenges related to seepage flow behavior inner the rock masses. Highlights: Developed a new algorithm for identifying the real fractures, forming the seepage pathways, and calculating the hydraulic water pressure on blocks automatically in 2D-DDA. Proposed a new coupled DDA–DSN model to investigate the seepage behavior in time-varying fractured rock mass systems. Checked validity of the DDA–DSN model by contrasting several numerical findings with experimental measurements. [ABSTRACT FROM AUTHOR]

Grouting reinforcement technology is a vital component of geotechnical engineering, which plays a crucial role in repairing surrounding rock that is damaged and improving its strength. To analyze the impact of grouting on the mechanical properties of rock fractures, specimens of mudstone fractures were selected before and after grouting reinforcement for direct shear tests. The purpose was to investigate the changes in mechanical properties under normal and tangential loading conditions. Furthermore, the microscopic–mesoscopic and macroscopic aspects of grouting reinforcement were discussed to explore its influence on the interface structure, deformation resistance, and strength of the fractured rock mass. By analyzing the test results of the fracture's mechanical properties before and after grouting, a constitutive model and strength criterion were proposed to accurately describe the mechanical behavior of the fracture surface. Building on a numerical software platform, the custom model was compiled with the VC++ integral programming environment and embedded in UDEC software. Finally, these findings were successfully applied to a typical deep roadway surrounding rock grouting reinforcement project, which showcased the practical implications of this paper. The results demonstrate that grouting reinforcement significantly impacts the normal and tangential mechanical properties of the fracture surface and the shrinkage and dilatation mechanical behaviors. The grout filling and cementation process enhances the rock mass fracture's resistance to deformation, effectively preventing the gradual weakening and slip in the fracture field. This improves the overall integrity and stability of the rock mass. The proposed mechanical model effectively captures the compression, shear, shrinkage, and dilatation mechanical behaviors before and after grouting. Similarly, the custom fracture grouting mechanical model could be a useful tool to simulate the behavior of grouting reinforcement in engineering rock masses. [ABSTRACT FROM AUTHOR]

The presence of fractures in rock masses plays a major role in its stress state and its variability. Each fracture potentially induces a stress perturbation, which is correlated to its geometrical and mechanical properties. This work aims to understand and quantitatively predict the relationship between fractured systems and the associated stress fluctuations distribution, considering any regional stress conditions. The approach considers the rock mass as an elastic rock matrix into which a population of discrete fractures is embedded—known as a Discrete Fracture Network (DFN) modeling approach. We develop relevant indicators and analytical solutions to quantify stress perturbations at the fracture network scale, supported by 3D numerical simulations, using various fracture size distributions. We show that stress fluctuations increase with fracture density and decrease as a function of the so-called stiffness length, a characteristic length that can be defined as the ratio between Young's modulus of the matrix and fracture stiffness. Based on these considerations we discuss, depending on DFN parameters, which range of fractures should be modeled explicitly to account for major stress perturbations in fractured rock masses. Highlights: Stress fluctuations in fractured rocks are predicted quantitatively from a tensorial approach. At the fracture scale, stress fluctuations depend on fracture size, orientation with respect to the applied remote stress field, and mechanical properties. At the network scale, stress fluctuations depend on fracture density, as well as size, orientation and mechanical property distributions. [ABSTRACT FROM AUTHOR]

In this study, a combined finite–discrete-element method (FDEM)-based grouting simulator, in which the effect of time-dependent rheological characteristic caused by grout hydration on grouting penetration is adequately considered, was developed for more accurately modeling the grouting penetration process in the fractured rock mass, especially for quick-setting grout. To implement the grouting penetration process, the time-dependent Bingham model for characterizing the time-dependent rheological characteristic of grout, the flow network searching algorithm combining with the grout flow solver for solving the grout flow, and the hydromechanical (HM) coupling algorithm for characterizing the grout–rock interaction were systematically integrated into the FDEM framework. After that, to validate the developed simulator for modeling the grouting penetration of time-dependent Bingham grout and the grout–rock interaction, two benchmark tests were conducted. Finally, to further demonstrate the capability of the developed simulator, the rheological model for characterizing the cement and sodium silicate (C–S) grout, a quick-setting grout, was embedded in the simulator to simulate the grouting penetration process in the discrete fracture network. The results indicated that the developed simulator can accurately capture the effect of time-dependent rheological characteristic caused by grout hydration on the grouting penetration process. As the water–cement ratio (W/C) increased or the cement–sodium silicate (C/S) ratio decreased, both the penetration rate and grouting ratio increased significantly. Increasing the W/C ratio was more effective than decreasing the C/S ratio to increase the penetration range. Decreasing the C/S ratio can increase the grouting penetration range more significantly than increasing the grouting pressure. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a hydro-thermo-mechanical coupling model based on the smoothed particle hydrodynamics with total Lagrangian formula (HTM-TLF-SPH) is proposed to simulate the crack propagation and instability process of fractured rock mass. TLF-SPH uses the Lagrangian kernel approximation, that is, the kernel function and its gradient need only be calculated once in the initial configuration, which is much more efficient than the smoothed particle hydrodynamics (SPH) based on the Euler kernel approximation. In TLF-SPH, particles interact with each other through virtual link, and the crack propagation path of rock mass is tracked dynamically by capturing the fracture of virtual link. Firstly, the accuracy and robustness of the HTM-TLF-SPH coupling model are verified by a reference example of drilling cold shock, and the simulation results agree well with the analytical solutions. Then, the crack propagation law of surrounding rock and the evolution characteristics of physical fields (displacement, seepage and temperature fields) after excavation and unloading of deep roadway under the coupling condition of hydro-thermo-mechanical are investigated. In addition, the seepage and heat transfer processes of the surrounding rock of Daqiang coal mine under different coupling conditions are successfully simulated. Meanwhile, the effect of the boundary water pressure difference on the temperature and seepage fields under the hydro-thermal coupling condition is quantitatively analyzed.

Abstract Laboratory tests are one of the most fundamental and crucial methods in rock mechanics and engineering research. Natural rock specimens are challenging to acquire, and traditional casting methods involve prolonged curing times and cannot produce rock-like specimens with complex internal fractures. Furthermore, 3D printing technologies such as SLA, SLS, and FDM possess inherent limitations. In this study, high-silica sand was used as the printing material, and sand powder 3D printing technology was harnessed to fabricate rock-like specimens. Uniaxial compression tests were performed on specimens with varying placement times, aimed at investigating the impact of placement time on the mechanical properties of sand 3D-printed rock-like specimens. Acoustic emission technology was used to explore the internal state changes during deformation and failure of specimens with different placement times. The findings indicate that the mechanical properties of sand powder 3DP rock-like specimens exhibited no deterioration over time after approximately 7 days of placement. The internal structure remained unchanged across different placement times. This study's outcomes underscore the superiority of sand powder 3D printing technology within the realm of rock mechanics and establish the groundwork for the accurate and efficient fabrication of rock-like specimens through sand powder 3D printing technology in the future.

The mechanical properties of fully-grouted bolt support are critical for the safety of support engineering works. To study the influences of factors including the bolt length and diameter, strength of the rock, and fracture angle on the mechanical properties of fully-grouted bolt support, compression tests were conducted on an anchored rock mass, considering the shortcomings of pullout tests on bolts. The discrete element software PFC2D (4.0) was adopted for numerical simulation and analysis from two aspects, namely, the stress distribution and anchorage force supplied by such bolts. The research found that by increasing the bolt diameter and length as well as the strength of the rock, the maximum anchorage force of bolts increases. Whereas the stress distribution of all bolts increases at first and then decreases along the bolts, and there is only one peak on the stress distribution curves, which also gradually shifts to a greater depth. In a fractured rock mass, the maximum anchorage force of bolts decreases, then increases (and is minimized at a fracture angle of 45°) with the decrease in fracture angle. The influence of fractures with different angles on the stress distribution of bolts is mainly reflected in the fracture zone. The bolt stress decreases abruptly in the zone with a fracture angle of 90°, forming a valley. The bolt stress increases suddenly in the zones with fracture angles of 60° and 45°, thus forming peaks. The bolt stress does not increase or decrease suddenly in the zone with a fracture angle of 30°. Therefore, it necessitates consideration of the influences of fractures on the anchorage force and the selection of bolts of appropriate size during anchorage design. After installation, the bolt stress should be monitored for stability and early warning of anchored rock mass according to changes in the stress provided.

The assessment of landslide hazard related to slopes in fractured rock masses is generally correlated with the probability of occurrence of potential rockfall phenomena. The propensity to detachment of rock blocks can be defined through direct or indirect approaches. The first, widely used for decades, is regulated by the International Society for Rock Mechanics recommendations, and provides for the definition of a series of parameters for discontinuities that cross a line designated by the operator, according to the so-called “scanline” methodology. The most applied indirect approaches are based on the construction of a 3D model of the studied front through input data acquired by a digital camera, laser scanner or radar. These two different approaches were used to analyze the discontinuities orientation of a rocky slope on the west side of Mt. Pellegrino (northern Sicily). In this context, it is essential to anticipate rockfall, given the presence of densely urbanized areas at the foot of the rocky slope. The main discontinuity sets were obtained from traditional geo-structural analysis and 3D Point Cloud model of the slope; the latter were derived by applying the Structure from Motion technique on frames captured during the surveys. The kinematic analysis applied to the obtained data allowed us to define from a geomechanical perspective, the main modes of failure. Moreover, back analyses were carried out on the already collapsed blocks to reveal the most likely rockfall volume and reached distance. [ABSTRACT FROM AUTHOR]

Due to the complex geometric distribution of discontinuities, the determination of the shear strength of rock masses has become a difficult task limiting the stability analysis of surrounding rock masses in underground tunnels. This problem might be attributed not only to the size effect of fractured rock masses but also due to the difficult quantification of the geometric distribution of fracture systems. To find a solution to this problem, a series of direct shear tests were numerically simulated by utilizing the synthetic rock mass method (SRM) in the PFC3D software to estimate the shear strength of a rock mass in Qingdao Metro tunnels, located in Shandong province, China. The numerical simulation results show that the shear strength parameters vary significantly with the orientation of the fracture network contained in the rock mass. Meanwhile, it was found that the fracture tensor component in the direction z, Fzz, which is in the perpendicular direction to the shearing plane (x–y plane) of the rock mass displayed an inversely varying trend with the shear strength parameters. Accordingly, a shear strength model was established for the rock mass by introducing Fzz to reflect the effect of the geometric distribution of the complex fracture system. The developed shear strength model was verified by conducting direct shear tests in the field, and a good agreement has been achieved. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the seepage process of fractured rock mass at a mesoscopic level, using the discrete element method. To this end, an improved pipe flow algorithm is proposed within the framework of particle flow code, including the heterogeneity of initial micro‐cracks and the deformation of solid skeleton. A series of numerical samples with a single non‐penetrating fracture are then studied. The relationships between the rock permeability and different properties of fracture (i.e., the aperture, dip angle and length) are investigated. The influence of fracture properties on the distribution of pore pressure in the rock mass is also analyzed. The obtained numerical results exhibit that the seepage properties of rock mass with non‐penetrating fracture depend strongly on the dip angle and length of fracture and are slightly disturbed by the fracture aperture. Moreover, its permeability is almost of the same order as that of non‐fractured rock. The numerical results and mesoscale analysis can help us understand the influence of fracture properties on the permeability of host rock and provide practical guidance for the prevention of hydraulic disasters and the development of mineral resources. [ABSTRACT FROM AUTHOR]

Exploitation of mineral resources and construction of traffic facilities have led to the destruction of a large number of mountains, resulting in the formation of high and steep rock slopes, which have caused serious geological safety hazards and ecological function degradation. The ecological restoration of high and steep rock slopes is imperative. The key of slope ecological restoration is vegetation reconstruction. At present, there are still many problems such as lack of restoration theory and unclear reconstruction conditions. In order to clarify the relationship between the temperature and humidity fields and the plant growth in the rock slope, this study established a test site near Xiaodongshan in the city of Zhangqiu in Shandong Province. Multi-period monitoring experiments on the temperature and humidity field in the rock slope were carried out, the distribution characteristics of the temperature and humidity field in the rock slope are examined, and their ecological significance is analyzed in detail. The results show that (1) the atmospheric temperature causes the difference of the temperature variation in the monitoring hole in different seasons. In winter, the heat in the unsaturated zone of fractured rock mass is transferred from deep layer to surface layer, but in spring and summer it is opposite, The depth of the variable temperature zone ranges from 0 − 467 cm, and the depth of the constant temperature zone is greater than 467 cm. (2) In winter, the relative humidity in the slope first increases and then decreases with the increasing depth. In spring and summer, the relative humidity in the slope increases gradually with the increasing depth. (3) The water vapor saturated zone appears near the depth of 20 cm in winter, and begins to appear at the depth of 20 − 40 cm in summer and extends deeper. (4) The temperature and humidity in the rock mass are suitable for the growth of plants, and the plants are easier to survive if they are planted near the depth of 20 cm in spring. The results are of has important theoretical significance and application value for guiding the ecological restoration of rock slopes.

Based on the self-stress slurry reinforcement method for fractured rock mass proposed by the authors, considering the influence of rock strength on the coupling effect of self-stress slurry and rock mass, the paper selected underground sandstone, carbonaceous mudstone, sandy mudstone, and coal as the research objects. Then, the comparative tests of reinforcing fractured rock mass with different strength by ordinary slurry and self-stress slurry were carried out to further analyze the influence of rock strength on grouting reinforcement effect. The composite reinforcement effect of restrained self-stress slurry on the rock mass fracture interface was investigated from multiple angles to reveal the reinforcement mechanism of slurry self-stress. Through several engineering cases of different rock strength, the macroscopic reinforcement effect of the self-stress slurry system on the engineering surrounding rock with different rock strength was analyzed. The results showed that the reinforcement effect of self-stress slurry on the fractured rock masses with different strength, such as soft and hard rock, was greater than that of ordinary slurry. As the strength of the rock mass became weaker, the repair degree of slurry to the fractured rock mass was gradually reduced, and the grouting reinforced rock mass specimens gradually transited from shear failure along the diagonal direction to splitting collapse failure. The self-stress of the slurry improved the restrained state of the slurry-rock interface, and then increased the shear strength of the interface by increasing the friction force. The contact connection effect of the two mediums of slurry and rock had been improved. The cementation density of self-stress slurry-rock interface was significantly higher than that of ordinary slurry-rock interface. The crystal particle distribution, compactness and mechanical properties of self-stress slurry stone were obviously better than those of ordinary slurry. The ultra-fine siliceous self-stress slurry system had achieved good results in the reinforcement of broken soft rock roadways, relatively hard rock roadways, and soft coal wall.

Deformation monitoring data provide a direct representation of the structural behavior of reservoir bank rock slopes, and accurate deformation prediction is pivotal for slope safety monitoring and disaster warning. Among various deformation prediction models, hybrid models that integrate field monitoring data and numerical simulations stand out due to their well-defined physical and mechanical concepts, and their ability to make effective predictions with limited monitoring data. The predictive accuracy of hybrid models is closely tied to the precise determination of rock mass mechanical parameters in structural numerical simulations. However, rock masses in rock slopes are characterized by intersecting geological structural planes, resulting in reduced strength and the creation of multiple fracture flow channels. These factors contribute to the heterogeneous, anisotropic, and size-dependent properties of the macroscopic deformation parameters of the rock mass, influenced by the coupling of seepage and stress. To improve the predictive accuracy of the hybrid model, this study introduces the theory of equivalent continuous media. It proposes a method for determining the equivalent deformation parameters of fractured rock mass considering the coupling of seepage and stress. This method, based on a discrete fracture network (DFN) model, is integrated into the hybrid prediction model for rock slope deformation. Engineering case studies demonstrate that this approach achieves a high level of prediction accuracy and holds significant practical value.

The objective phenomenon of seepage reduction and self-healing is easy to occur in the mining fractured rock mass after long-term evolution process of coal seam after mining. In survey of this phenomenon, taking the No. 12401 work face of Bulianta Coal Mine and the No. 52306 work face of Daliuta Coal Mine in Shendong as typical test areas, the engineering exploration and theoretical research on the self-healing law in different areas of overburden were carried out. The evolution law of long-term self-healing process of overburden after mining was revealed. The results show that the fractured overburden of the two coal mines had achieved good self-healing effects 15 years and 7.3 years after mining, respectively. The areas with water conduction within the original water-conducting fractured zone have been significantly reduced. Although the caved zone still conducts water, the height has also been reduced. By taking the ratio of the vertical length of the self-healing section in overburden from the original water diversion to the water isolation to the height of the water-conducting fractured zone as the self-healing recovery rate for statistics, it is obtained that the self-healing recovery rate of No. 12401 work face in the overburden near the mining boundary and in the middle of the dip has reached 59.5% and 53.5% respectively, and the self-healing recovery rate of 52306 work face in the corresponding area is 25.8% and 47.5% respectively. Due to that No. 12401 work face has mined for a longer time and has a larger coal seam burial depth, its self-healing effect of fractured overburden is obviously better. Affected by the occurrence difference of different strata in the vertical direction of the overburden and the initial damasge degree in different areas in the horizontal direction, the distribution of the self-healing area is often discrete and discontinuous, in which the interval of the unrepaired area generally corresponds to the position of the key stratum or thick and hard rock layer, and the shorter the post mining life and the closer to the mining boundary, the more significant the dispersion. The self-healing effect of mining fractured rock mass is actually a process of permeability reduction and evolution under the comprehensive influence of multiple factors. For the mining conditions in Shendong coalfield, the residual settlement caused by stress compaction plays a leading role in the initial process within 1.5 to 2 years after coal mining, which is relatively significant in the overburden in the middle of the mining area. Then, the self-healing process has been dominated by the water-rock or water-gas-rock interactions in goaf. That is, the filling and sealing effect of the derivatives produced in the relevant process on the fractures and the roughness reduction of the fracture surface induced by hydraulic erosion directly affect the self-healing results. Therefore, whether there is long-term water seepage in the overburden after mining determines the difficulty of self-healing of fractured rock mass. Water conducting fractures in the overburden of most mines in Shendong are generally directly connected to the Quaternary loose layer or surface, and in recent years, there is abundant rainfall, which provides superior conditions for the generation of water-rock or water-gas-rock interactions and the promotion of self-healing effect.

Abstract The energy replenishment and heat convection induced by fracture water flowing through the rock mass impact the shallow geothermal energy occurrence, transfer and storage mechanisms in it. In this article, a suitability evaluation and categorization system is proposed by including judgement indexes that are more closely aligned with the actual hydrogeological conditions in fracture developed regions; an assessment approach of regional shallow geothermal energy is proposed by coupling the influences of fracture water into the calculation methods of geothermal capacity, thermal balance and heat transfer rate. Finally, by taking two typical fracture aperture distributions as examples, the impacts of fracture water on the investigation and evaluation of shallow geothermal energy are quantitatively analyzed. Although the fracture apertures only share 1.68% and 0.98% of the total length of a borehole, respectively, in the two examples, the fracture water convection contributes up to 11.01% and 6.81% of the total heat transfer rate; and the energy replenishment potential brought by the fracture water is equivalent to the total heat extraction of 262 boreholes. A single wide aperture fracture can dominate the aforementioned impacts. The research results can support more accurate evaluation and efficient recovery of shallow geothermal energy in fracture developed regions.

Objective Groundwater flow in fractured rocks has strong heterogeneity and anisotropy. The discrete fracture network (DFN) method has been internationally considered as one of the most reasonable and effective methods to describe the fracture water transport. Methods In this work, we focused on granite rock from an underground research laboratory site for the geological disposal of high-level radioactive waste. In addition, a high-performance numerical computing system and parallel codes were employed to develop a groundwater flow simulation method in fractured rocks based on the DFN model. Results The results indicated that the proposed method could conduct the groundwater flow simulation of DFN with thousands of mesh elements. This improved the computational efficiency and ability of the parallel codes to deal with complex models. We established the DFN model structure optimization and parameter setting methods of boundary conditions in a complex condition. This could ensure that the hydraulic heads were continuous at different scale models. Furthermore, in the model area, the hydraulic head is distributed as a network structure along fractures. For the connected fractures, the water level was continuous and changed from high to low. However, the water level in the nonconnected fractures was discontinuous. Groundwater flows along the fracture from the high water level area to the low water level area. The connectivity and permeability of the fracture network have an obvious influence on the groundwater flow characteristics. Conclusion Therefore, we could conclude that the parallel groundwater flow simulation method based on the DFN model could more reasonably reflect the groundwater flow in a fractured rock mass. It was of great significance to further improve the simulated prediction ability and deepen the understanding of groundwater flow characteristics in a fractured medium.

AbstractThe surrounding rock control has been a difficult problem for fractured rock mass in hard rock mines. This article describes a case study of the failure mechanisms and the support design technology for fractured rock mass drifts in Xinli Gold Mine. Based on field investigation, the geology characteristics, failure types, influencing factors, support types, and their failure types were analyzed. The rock mass classification, rock mass physical and mechanical parameters were obtained by using Q, RMR, and GSI systems. The zoning of surrounding rock, stability analysis and zoning support schemes design were carried out based on rock mass classification results. The pretension is designed by China underground mine experiences and verified by numerical simulation. RS2 was used to compare the plastic zone under pre- and post-support conditions. The plastic zone is significantly reduced after support is installed, which indicates that the designed support schemes can effectively control the failure of surrounding rock. In view of difficulties in the excavation and support of fractured rock mass, the short excavation and short support technology was proposed to ensure the success excavation of the drift in fractured rock mass. The field application shows that the short excavation and support technology are effective.

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is inevitable to develop strata through cracks in the site selection of long-distance water transfer projects, and the cracks in the strata have an important effect on the see-through field of slope, which may induce the leakage failure of channels. In Laizhou and partial drainage period of Jiaodong Water Diversion Project as the research object, based on the measured fracture distribution of samples and the Monte Carlo Method to generate the random distribution of fracture network. Finite element numerical calculation software COMSOL model based on pore and fracture model are used to carry out the different rainfall channel fractured rock slope under the condition of seepage analysis. The results show that the migration speed of the wetting peak in the fracture model is faster than that in the pore model, and the pore water is easy to contact the groundwater in advance, resulting in the rise of the groundwater level at the slope location. Under the same rainfall intensity and groundwater level, the water head value at the foot of the channel slope of the crack model is more than that of the pore model, which is more likely to cause the failure of the channel lining plate. Under the same rainfall condition, the existence of cracks makes the failure time of the lining plate advance, and also expands the failure range. The greater the rainfall intensity, the greater the failure area. [ABSTRACT FROM AUTHOR]

Grouting reinforcement is an effective method for controlling the stability of engineering rock mass. The mechanism is mainly to inject or infiltrate the grout into the fracture of rock mass to form a grouting entity, and strengthen the stability of rock mass and the ability to resist failures. In order to realize the calculation of the whole process of grouting diffusion and consolidation in broken surrounding rock, a diffusion-consolidation mechanism of grouting based on discrete element method was proposed. Also, the model checking and example analysis were carried out, and the results show that: ① In the full-length grouting of single fracture scenario, the shear peak strength of the post-fractured rock mass is higher than that of the non-grouting fracture, which depends on the frictional resistance generated by the solidification and cohesion of the slurry. ② In the point grouting simulation experiment, as the grouting pressure increases, the grout continues to diffuse. Therefore, the pre-peak shear yielding and post-peak phases of the rock mass are strengthened. ③ For the engineering-scale simulation test, as the grouting pressure increases, the diffusion radius increases in two stages. When the grout expands to the high-stress area, it needs to overcome a greater compressive stress to achieve flow. After reaching a relative higher grouting pressure, the diffusion area of adjacent boreholes is superimposed to form a grouting whole body that surrounds the roadway. When the solidification bond strength of the grout is low, the failure of contact is still the main controlling factor to determine the failure and instability of the roadway.

Enhanced geothermal system (EGS) is a primary method to develop geothermal resources stored in hot dry rock (HDR), but it faces several key problems, such as unreasonable hydraulic fracture networks at high reservoir temperature, unclear multi-scale and multi-field coupling regularity, low heat extraction efficiency caused by the flashing flow in geothermal wells, and low thermoelectric conversion efficiency of geothermal fluid, which restricts the large-scale commercial development of geothermal resources. To resolve these major bottleneck problems, systematically reviews and analysis of the research progress and development trend of EGS are conducted in this paper. Particular attentions are devoted to four key technologies involved in the development of HDR geothermal resource by EGS: (1) the hydraulic fracturing technology for HDR reservoirs, including reservoir reconstruction methods, hydraulic fracturing network forming mechanisms and fracture propagation prediction models is illustrated in detail; (2) the fracture characterization methods, mathematical models and solution methods are described from three aspects including pore-scale multi-field coupled models, reservoir-scale multi-field coupled models and upscaling methods; (3) the efficient extraction technology of wellbore thermal fluid, involving the mechanism of flashing flows in geothermal wells and the experimental and numerical methods for investigating the characteristics offlashing flows are discussed; (4) the HDR geothermal power generation technologies, considering the principles of geothermal power generation, the types of power generation systems and the main application markets are introduced. In conclusion, EGS is a technology-intensive system, however, due to the complex working conditions of the underground reservoirs and the instability of the ground equipment, theoretical research tends to be separated from the practice. For the purpose of promoting the applicability of EGS, intimate combination and mutual guidance with the pilot tests are necessary to develop a production-research combined mode, and to raise the awareness and break through the key points in a constant back-and-forth.

During the excavation process in fractured rock masses in underground mines, blasting excavation can cause dangerous block collapses on surrounding rock. The applicable blasting method can effectively reduce the damage of surrounding rock caused by blasting disturbance. In order to investigate the impact of blasting disturbances of dangerous blocks in fractured rock mass drift, this study focuses on the instability characteristics of dangerous blocks during the excavation process in a mine located in Jilin Province. Based on detailed detection of discontinuities characteristics in the study area, the damage effects of shaped charge hydraulic blasting and conventional blasting on surrounding rock structure are analyzed and compared by using equivalent static method. The 3DEC discrete element software was used to analyze the instability characteristics of surrounding rock dangerous blocks under these two different blasting methods. The results indicate that using shaped charge hydraulic blasting can effectively reduce the impact of blasting disturbances on the excavated rock mass and minimize dangerous block collapses during drift excavation.

The energy replenishment and heat convection induced by fracture water flowing through the rock mass impact the shallow geothermal energy occurrence, transfer and storage mechanisms in it. In this article, a suitability evaluation and categorization system is proposed by including judgement indexes that are more closely aligned with the actual hydrogeological conditions in fracture developed regions; an assessment approach of regional shallow geothermal energy is proposed by coupling the influences of fracture water into the calculation methods of geothermal capacity, thermal balance and heat transfer rate. Finally, by taking two typical fracture aperture distributions as examples, the impacts of fracture water on the investigation and evaluation of shallow geothermal energy are quantitatively analyzed. Although the fracture apertures only share 1.68% and 0.98% of the total length of a borehole, respectively, in the two examples, the fracture water convection contributes up to 11.01% and 6.81% of the total heat transfer rate; and the energy replenishment potential brought by the fracture water is equivalent to the total heat extraction of 262 boreholes. A single wide aperture fracture can dominate the aforementioned impacts. The research results can support more accurate evaluation and efficient recovery of shallow geothermal energy in fracture developed regions. [ABSTRACT FROM AUTHOR]

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of different shapes and distribution forms of fractures on rock mass failure behavior has been extensively studied. However, the influence of the matrix arrangement and non-through-boundary distribution of fractures has not been fully reported. In this paper, four failure modes are determined by physical experiments, and then the local tensile shear failure characteristics are obtained by disassembly along the fracture surface. Discrete element (PFC2D) was used to study the local mechanical behavior and stress field evolution of specimens. The results show that the existence of fracture groups obviously weakens the compressive capacity of the specimens. As the dip angle increases, the weakening degree decreases gradually. The failure modes can be divided into diagonal inclined fracture plane, Y-shaped fracture plane, inclined axial tensile shear fracture plane, and axial split fracture plane. The mixed failure area of local tensile and shear is concentrated in the small dip fault group, while the local failure mode of the large dip joint group tends to be tensile. Influenced by the dip angle of joint group, the regional distribution patterns of tension, and pressure chains at local rock bridge are different obviously, and the transmission paths are curved chain and X-shaped connection respectively. In general, a matrix joint group is conducive to partition failure of rock mass, large dip angle is more conducive to compression, and the failure mode is more inclined to block. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock fractures have a significant impact on the stability of geotechnical engineering, and grouting is currently the most commonly used reinforcement method to address this issue. To ensure the stability of grouted rock mass, it is necessary to study its deformation law and mechanical properties. In this study, theoretical analyses and laboratory experiments were conducted, and the fracture width, Weibull model and effective bearing area were introduced to improve the applicability and accuracy of the original damage constitutive model. Moreover, the constitutive model of grouted rock mass was derived by combining it with the mixing law of composite materials. The main conclusions are summarized as follows: (1) Based on macroscopic damage tensor theory, the fracture width parameter was introduced, which effectively described the variation law of macroscopic damage with fracture width to improve the accuracy of the original damage constitutive model. (2) The effective bearing area was used to optimize the original Weibull model to match the stress-strain curve of the rock mass with fractures. (3) The grouting-reinforced rock mass was considered to be a composite material, the original equivalent elastic modulus model was improved by combining macroscopic damage with the Reuss model, and the constitutive damage model of the grouted rock mass was deduced. [ABSTRACT FROM AUTHOR]

Fracture characteristics have a significant effect on the mechanical and hydraulic properties of rock mass. In this paper, before modeling a discrete fracture network, the fracture is simplified as a non-similar ellipse. First, the multifactor coupling stereological relationship of the sampling trace length distribution is established, which proves that the trace length distribution is independent of the fracture occurrence distribution. Using the Volterra integral equation method, the stereological formula of the trace length is inversely solved to obtain the distribution expressions of the major axis and axial ratio of the elliptical fractures. The analytical solutions of the probability density function (PDF) of the characteristic size of the elliptical fractures are derived for cases in which the trace length follows a uniform distribution, fractal distribution, and polynomial distribution. Second, for cases in which the trace length conforms to a negative exponential distribution, gamma distribution, chi-square distribution, and lognormal distribution, the statistical eigenvalues of the major axis and axial ratio of the elliptical fractures are deduced. Finally, a Monte Carlo statistical simulation is performed using the Rock Mass Joint Network Simulation (RJNS3D) toolkit to verify the applicability of the derivation process and the correctness of fitting a polynomial function to the trace length distribution to solve the PDF of the characteristic size of the elliptical fractures. The proposed method can better predict the distribution of the required parameters, such as the major axis and axial ratio of the elliptical fractures, according to the typical two-dimensional data in the sampling windows. This method can be further applied to reconstruct fracture networks in practical engineering tasks and lay a foundation for the analysis of rock mass strength and deformation, representative elementary volume (REV), seepage, and surrounding rock stability. Highlights: A non-similar elliptical model is developed to simulate a fracture network in rock mass. The multifactor coupling stereological relationship of the sampling trace length distribution is established. The correct analytical solutions of the probability density function of the characteristic size of elliptical fractures are derived. Trace sampling in the sampling window is simulated by the Monte Carlo method. [ABSTRACT FROM AUTHOR]

Abstract The existence of joints or other kinds of discontinuities has a dramatic effect on the stability of rock excavations and engineering. As a result, a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects. In recent years, 3D printing technology has become a promising tool in the field of rock mass mechanics and engineering. This study first reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects. Then, based on the comprehensive analysis of previous research, the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects. The first is the printing material. Although there are many materials for 3D printing, it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited. After research, we summarize and evaluate printing material that can be used for rock mass mechanics studies. The second is the printing methodology, which mainly introduces the current application forms of 3D printing technology in rock mass mechanics. This includes printed precise casting molds and one-time printed samples. The last one is the printing model, which includes small-scale samples for mechanical tests and large-scale physical models. Then, the benefits and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed. Compared with traditional rock samples collected in nature or synthetic rock-like samples, the samples made by 3D printing technology have unique advantages, such as higher test repeatability, visualization of rock internal structure and stress distribution. There is thus great potential for the use of 3D printing in the field of rock mass mechanics. However, 3D printing materials also have shortcomings, such as insufficient material strength and accuracy at this stage. Finally, the application prospect of 3D printing technology in rock mass mechanics research is proposed.

Abstract Complex weak structural planes and fault zones induce significant heterogeneity, discontinuity, and nonlinear characteristics of a rock mass. When an earthquake occurs, these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels. To investigate the wave propagation in a rock mass with different structural planes and fault zones, this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly. Then, a physical wave propagation model was constructed to investigate seismic waves passing through a fault, and dynamic damage was analyzed by using shaking table tests. Finally, stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored. The results indicate that under the action of weak structural planes, stress waves appear as a complex wave field decomposition phenomenon. When a stress wave spreads to a weak structural plane, its scattering may transform into a tensile wave, generating tensile stress and destabilizing the rock mass; wave dynamic energy is absorbed by a low‐strength rock through wave scattering, which significantly weakens the seismic load. Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation. This is one of the main causes for large deformation and even instability within rock masses. These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

Particle flow numerical simulation was used to reproduce the transient unloading process of a deep-buried single fracture tunnel. The influence of fracture characteristics on the transient unloading effect was analyzed from the aspects of stress state, deformation characteristics, fracture propagation, and energy conversion. The results shows that the surrounding rock stress field of the deep-buried tunnel is divided into four areas: weak stress area I, strong stress area II, stress adjustment area III, and initial stress area IV. The fracture has an important impact on the stress adjustment process of transient unloading of the deep-buried tunnel, and the stress concentration area will be transferred from the bottom corner of the chamber and the vault to the fracture tip. With the increase in the fracture length, the distance from the stress concentration area at the fracture tip to the free surface gradually increases, and the damage area of the surrounding rock gradually migrates to the deep area of the rock mass. At this time, the release amount of strain energy gradually decreases and tends to be stable, while the dissipation energy shows a near 'U' shape change trend of decreasing first and then increasing. Under different fracture angles, the number of mesocracks is significantly different. Among them, the number of mesocracks in the 60° and 30° fractured surrounding rocks is greater followed by the 0° fractured surrounding rock, and the number of mesocracks in the 45° and 90° fractured surrounding rocks is relatively less. In addition, the proportion of compression-shear cracks shows a change trend of increasing first and then decreasing with the increase in the fracture angle, and it reaches the maximum value in the 45° fractured surrounding rock. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simulations of tunnel excavations have to take into account the natural occurrence of joints and faults in the surrounding rock mass, which dominantly control its mechanical response. In this paper, we present work in progress toward 3D finite element analysis of excavation using equivalent rock-mass properties derived from stochastically generated discrete fracture networks (DFNs). The equivalent stiffness is determined by volume averaging. Presently, we solve the problem linearly for an incremental change of the stress state. The fracture’s stiffness is assumed to depend on the initial normal stress acting in direction normal to it. However, within the solved incremental step, we assume the fracture’s stiffness to be constant. This assumption is acceptable for small stress changes. Since the fractures represented in the DFN model have preferred directions, the equivalent stiffness is anisotropic.

The existence of joints or other kinds of discontinuities has a dramatic effect on the stability of rock excavations and engineering. As a result, a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects. In recent years, 3D printing technology has become a promising tool in the field of rock mass mechanics and engineering. This study first reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects. Then, based on the comprehensive analysis of previous research, the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects. The first is the printing material. Although there are many materials for 3D printing, it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited. After research, we summarize and evaluate printing material that can be used for rock mass mechanics studies. The second is the printing methodology, which mainly introduces the current application forms of 3D printing technology in rock mass mechanics. This includes printed precise casting molds and one-time printed samples. The last one is the printing model, which includes small-scale samples for mechanical tests and large-scale physical models. Then, the benefits and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed. Compared with traditional rock samples collected in nature or synthetic rock-like samples, the samples made by 3D printing technology have unique advantages, such as higher test repeatability, visualization of rock internal structure and stress distribution. There is thus great potential for the use of 3D printing in the field of rock mass mechanics. However, 3D printing materials also have shortcomings, such as insufficient material strength and accuracy at this stage. Finally, the application prospect of 3D printing technology in rock mass mechanics research is proposed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simulations of tunnel excavations have to take into account the natural occurrence of joints and faults in the surrounding rock mass, which dominantly control its mechanical response. In this paper, we present work in progress toward 3D finite element analysis of excavation using equivalent rock-mass properties derived from stochastically generated discrete fracture networks (DFNs). The equivalent stiffness is determined by volume averaging. Presently, we solve the problem linearly for an incremental change of the stress state. The fracture's stiffness is assumed to depend on the initial normal stress acting in direction normal to it. However, within the solved incremental step, we assume the fracture's stiffness to be constant. This assumption is acceptable for small stress changes. Since the fractures represented in the DFN model have preferred directions, the equivalent stiffness is anisotropic. [ABSTRACT FROM AUTHOR]