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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]

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]

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]

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.)

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.)

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]

To explore the comprehensive effects of fracture geometric characteristics (length, penetration, quantity and dip angle) on rock mass strength, the uniaxial compression experiments were conducted on rock samples containing prefabricated fractures, the influence of fracture geometric characteristics on the deformation and failure of rock mass and the evolution law of crack propagation are systematically studied from macroscopic and microscopic perspectives. The results show that the conditions of uniaxial compression, the initial damage caused by prefabricated fracture further degrades the strength of rock samples. The rock sample mechanics process can be divided into the consolidation, secondary microcracks and crack extension and sample destruction of four stages, the peak strength, elastic modulus and peak strain of rock samples increase with the decrease of relative geometric characteristics. The failure form of intact rock sample was mainly tensile failure, the fracture (length and quantity) rock samples were subject to shear failure, the failure mode of rock sample with fracture penetration was mainly shear and supplemented by tension, the 0°, 30° and 90° fracture rock samples are X-shaped conjugate inclined plane shear failure, while the 45° and 60° fracture rock samples are shear failure. [ABSTRACT FROM AUTHOR]

In this paper, hydromechanical coupling model is proposed to study the mechanical and hydraulic behavior of fractured rock mass in the framework of advanced general particle dynamics (GPD), and the relationship between stress and seepage is determined. Then, the proposed model is employed to investigate one‐dimensional seepage, and the numerical seepage field is in a good agreement with the analytical solution, implying the feasibility and accuracy of advanced GPD method. Finally, the proposed model is applied to analyze the mechanical and hydraulic behavior of surrounding rock mass around excavated tunnel under hydromechanical coupling conditions, and the numerical results obtained by the proposed model are in a good agreement with those obtained by PFC, which further verifies the correctness of the proposed model. [ABSTRACT FROM AUTHOR]

Reliable size-effect law for discontinuous rock mass is the premise of projection of the scale-down model test results to practical engineering applications. In this study, 3D printing technology is engaged to manufacture repeatable and scalable rock models in different scaling ratios. Compression tests show that the strength, modulus, and failure pattern will change with the variation of the model size. Currently derived fitting curves for the variable strength against different sizes for intact rock models are consistent to the prevailing size-effect models of natural rocks in open literature. But the influence of fractures on the size effect is underestimated in scale-down fractured rock models in the reported literature, resulting in the small discontinuous models showing overestimated strength and unreliable mechanical behaviour. The reliability of the current size effect for both the intact and fracture rock is attributed to the highly resolutive additive-subtract manufacturing procedure to produce repeatable and scalable samples to eliminate uncertainties. Highlights: In this study, 3D printing technology is engaged to manufacture repeatable and scalable rock models in different scaling ratios. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Earth Sciences & Environment is the property of Journal of Earth Sciences & Environment 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 stability of slope rock masses is influenced by freeze-thaw cycles in cold region, and the mechanism of stability deterioration is not clear. In order to understand the damage and progressive failure characteristics of rock masses under the action of freezing and thawing, a model test was conducted on slope with steep joint in this study. The temperature, frost heaving pressure and deformation of slope rock mass were monitored in real-time during the test and the progressive failure mode was studied. The experimental results show that the temperature variations of cracking and the rock mass of a slope are different. There are obvious latent heat stages in the temperature-change plot in the crack, but not in the slope rock masses. The frost heaving effect in the fracture is closely related to the constraint conditions, which change with the deformation of the fracture. The frost heaving pressure fluctuates periodically during freezing and continues to decrease during thawing. The surface deformation of the rock mass increases during freezing, and the deformation is restored when it thaws. Freeze-thaw cycling results in residual deformation of the rock mass which cannot be fully restored. Analysis shows that the rock mass at the free side of the steep-dip joint rotates slightly under the frost heaving effect, causing fracture propagation. The fracture propagation pattern is a circular arc at the beginning, then extends to the possible sliding direction of the rock mass. Frost heaving force and fracture water pressure are the key factors for the failure of the slope, which can cause the crack to penetrate the rock mass, and a landslide ensues when the overall anti-sliding resistance of the rock mass is overcome. [ABSTRACT FROM AUTHOR]

The size effect has a significant effect on the mechanical behavior of rock, thereby fundamentally influencing the stability of rock excavations. The main challenge associated with the experimental research on the size effect of fractured rock mass lies in the difficulty of specimen preparation to represent the influence of size and fracture on the mechanical behavior of the rock material. In order to preliminarily explore the feasibility of 3D printing technology in the field of rock mechanics, fractured rock specimens of different sizes and different fracture characteristics were produced using sand powder 3D printing technology. The uniaxial compression test was combined with the digital image correlation method (DIC) technology to study the influence of the size effect on the mechanical properties and deformation and failure of different fractured specimens. The research finds that: (1) The elastoplastic mechanical characteristics of the sand powder 3D printed specimens are similar to soft rock. Specimen size and fracture angle have significant effects on the mechanical properties of specimens. Under different fracture conditions, the uniaxial compressive strength (UCS) and Elasticity Modulus of sand powder 3D specimens should be decreased with the increase of the specimen size, and the size effect has different influences on the specimens with different fracture characteristics. (2) Under different fracture conditions, the crack initiation position and failure mode of specimens of various sizes are affected by the fracture inclination to varying degrees. (3) The size effect of fractured rock mass is closely related to the defect level inside the rock mass. The size effect originates from the heterogeneity inside the material. The research results verify the feasibility of applying sand powder 3D printing technology to study the size effect of fractured rock masses and provide an innovative test method for the size effect test study. Preliminary exploration of the size effect of fractured rock masses provides a powerful reference for related research in this field. The study proves the feasibility of applying sand powder 3D printing technology in similar rock mechanics tests and contributes to understanding the size effect of a fractured rock mass. [ABSTRACT FROM AUTHOR]

The existence of fractures has a significant influence on the mechanical properties of a rock mass. The sensitivity of the rock mass's mechanical properties to the fracture's geometric parameters is conducive to improving the measurement accuracy of fractured rock mass engineering. Firstly, the fracture geometric parameters in the dam site area of Lianghekou Hydropower Station were counted using the ShapeMetriX3D system. Then, the effect of the fracture's geometric parameters on the deformation characteristics, failure mode, and mechanical parameters of the rock mass were investigated based on the RFPA3D under the uniaxial compression test. The results showed that the stress–strain curves of the fractured rock mass mainly exhibited elastic-brittle characteristics. The failure pattern of the fractured rock mass was mainly defined by a compressive-shear composite. Additionally, the influence of the fracture's geometric parameters on the uniaxial compressive strength (UCS) was greater than that of elastic modulus. The sensitivity of the UCS to fracture trace length was more significant. [ABSTRACT FROM AUTHOR]

Intelligent monitoring and early warning of rock mass failure is vital. To realize the early intelligent identification of dynamic fractures in the failure process of complex fractured rocks, 3D printing of the fracture network model was used to produce rock-like specimens containing 20 random joints. An algorithm for the early intelligent identification of dynamic fractures was proposed based on the YOLOv5 deep learning network model and DIC cloud. The results demonstrate an important relationship between the overall strength of the specimen with complex fractures and dynamic fracture propagation, and the overall specimen strength can be judged semi-quantitatively by counting dynamic fracture propagation. Before the initiation of each primary fracture, a strain concentration area appears, which indicates new fracture initiation. The dynamic evolution of primary fractures can be divided into four types: primary fractures, stress concentration areas, new fractures, and cross fractures. The cross fractures have the greatest impact on the overall strength of the specimen. The overall identification accuracy of the four types of fractures identified by the algorithm reached 88%, which shows that the method is fast, accurate, and effective for fracture identification and location, and classification of complex fractured rock masses. [ABSTRACT FROM AUTHOR]

Due to the existence of tiny cracks in rock, underground engineering has begun to consider how to divert a large amount of groundwater. To divert groundwater more effectively, it is necessary to master the seepage characteristics of fluids in the micropores of rocks. Based on rock samples obtained from an underground engineering site, this paper analyzes the microscopic pore structure of the rock through a combination of laboratory tests and numerical simulations and inputs this information into a computer model. The fluid seepage state in the rock under different conditions is simulated in the computer model, and parameters such as the fluid seepage velocity in the rock are obtained. Afterwards, it has been verified by engineering practice that the smallest remaining water inflow can reach 0.06‰. The results of this paper can effectively guide the discharge of groundwater to better manage water resources, greatly reduce the pollution of groundwater in construction and production environments, and reduce the pollution caused by grouting projects. Furthermore, the cleanliness and safety of underground engineering construction and production could be ensured. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency 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 Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology 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 Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology 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 existence of fracture flow has an undesirable effect on the creation of the frozen wall. Brine and liquid nitrogen combined freezing technology can ensure the safety of freezing engineering, reduce the construction period and save cost. Considering the permeability of the rock matrix, fluid exchange and Darcy–Stokes coupling effect between the rock matrix and fracture, a thermo-hydraulic model of the fractured porous rock mass under water seepage is herein established. The interfacial seepage field characteristics of fractured rock mass under different fluid flow models and interface conditions are compared. The numerical simulations of the initial brine freezing and liquid nitrogen reinforcement freezing are carried out. The results show that the overall permeability of fractured rock mass computed by free flow considering the Darcy–Stokes effect is greater than that computed by the Cubic law. The limit seepage velocity of the intact rock mass in brine freezing is 2.5 m/d, and that of fractured rock mass decreases to 1 m/d. The fracture aperture and groundwater seepage velocity are directly proportional to the closure time of the frozen wall. Liquid nitrogen freezing can seal water quickly and shorten the closure time of the frozen wall when the seepage velocity of the fractured rock mass is greater than the limit seepage velocity, and the rapid cooling of the upstream region plays an important role in the formation of the frozen wall in fractured rock mass. [ABSTRACT FROM AUTHOR]

Engineering rock mass is normally subject to cyclic–dynamic disturbances from excavation, blasting, drilling, and earthquakes. Natural fractures in rock masses can be reactivated and propagated under dynamic and static loadings, which affects the stability of rock mass engineering. However, fractured rock mass failure induced by cyclic-impact disturbances is far from clear, especially considering varying angles between the rock mass and the direction of impact loadings. This work investigated rock deformation and failure characteristics through cyclic impact tests on granite samples with cracks of different angles. A Hopkinson bar was employed for uniaxial cyclic impact tests on granite samples with the crack inclination angles of 0–90°. The magnetic resonance imaging technique was used to determine rocks' porosity after cyclic impacts. The stress–strain curves, porosity, strength, deformation modulus, failure modes, and energy density of samples were obtained and discussed. Results showed that the crack inclination angles significantly affected the damage evolution and crack morphology of rocks. Under the constant cyclic impact, the dynamic deformation modulus and dynamic strength of rock samples first increased and then decreased with the increase in crack inclination angle. The failures of granite samples for inclination angles of 0 and 90° were dominated by tensile cracking, while those for the inclination angles of 30–60° were dominated by shear cracking. The energy density per unit time gradually decreased with the increase in impact cycles. The results can provide references for the stability analysis and cyclic-impact-induced failure prediction of fractured rock masses. [ABSTRACT FROM AUTHOR]

Rockbolting is the most common support system in both civil and mining engineering. The mechanics of ground support using rockbolt have yet not been very clear, especially in highly fractured rock mass conditions. In this study, large-scale physical models with full-scale rockbolts and rock blocks were constructed, aiming to evaluate the bearing capacity of incoherent rock blocks quantitatively. The effect of surface support was especially examined with the incorporation of different sizes of bearing plates and mesh in the models. It is found that lateral confinement plays an important role in the load bearing and deformation capacity of the incoherent rock blocks reinforced by rockbolts. High lateral confinement promotes the formation of a strong pressure arch. The installation of surface support can significantly increase the deformation capacity of incoherent rock blocks. The result provides insight into the mechanism of rockbolting and highlights the importance of surface support in highly fractured rock mass ground conditions. [ABSTRACT FROM AUTHOR]

In this study, the failure characteristics of self-made rock with internal flaws under shear were studied and a numerical simulation analysis was carried out. Firstly, based on basic physical and mechanical tests, the shear strength characteristics of rocks with built-in 3D defects were summarized. PFC3D simulation software was used to model the samples with flaws, and the microscopic parameters were calibrated according to the test results. From the simulation results, it was found that the generation mode of microcracks from the flaw tip was different. The microcracks of forward shear and reverse shear were mainly generated from the horizontal direction, while the microcracks of lateral shear gradually increased from the upper and lower ends of the flaw in the opposite direction. When the peak shear strength was reached, the total number of cracks was the largest in lateral shear and the smallest in forward shear. When studying the particle velocity vector field, it was found that when reaching the peak shear strength, the particles on both sides of the prefabricated flaw appeared to be in vortex motion. When α = 45° and σn = 2 MPa, the failure mode of forward shear and lateral shear was shear-tensile-shear (S-T-S), and that of reverse shear and the intact specimen was shear-shear-shear (S-S-S). The lateral shear tensile effect was the most obvious and was mainly concentrated in the middle part of the sample. [ABSTRACT FROM AUTHOR]

The representative element volume (REV) of the fractured rock mass is the basis for its homogenization, and is essential for the study of groundwater seepage. In order to determine a simple method for estimating REV, we studied the topological characteristics of the fractured network. We propose the concept of topological representative element volume (TREV) for estimating the fractured rock mass. The topological structure can reflect many properties of the fractured rock mass, to which a great deal of attention has been paid. We examine the applicability of eleven topological parameters as the equivalent parameters of the TREV. According to the selected equivalent parameter, the TREV of twenty-three kinds of fractured rock mass were calculated and then compared with the permeability representative element volume (PREV). The results show that the size of TREV and PREV are essentially the same for a given rock mass. In other words, the PREV can be estimated accurately using the TREV for the rock mass with orthogonal connected fracture networks. The advantage of using TREV to estimate PREV is that there is no need for complex seepage calculations, as the calculation of TREV only needs to account for the geometric characteristics of the fracture network. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model for quantifying the uncertainty of three-dimensional fracture intensity measurements (P32), which measure fracture area per sampling volume, and for determining the geometrical representative elementary volume (REV) of fractured rock. The analytical model for estimating the variance of P32 is derived from the probability of a given number of fractures in a sample of rock. This model is validated through numerical simulations of fractured rock masses based on the discrete fracture network method. A series of parametric studies are conducted considering the dip angle, dip direction, Fisher constant, size and shape of the rock mass space, specimen volume, fracture diameter, and P32. Based on the results of the analytical model and the parametric studies, a simple model to quantify the coefficient of variation (COV) of P32 is established, which requires only the data of specimen volume, fracture diameter, and P32. Four engineering applications of the proposed analytical model are presented, including two case studies of estimating the geometrical REV at a given COV, one of assessing the variation of mechanical properties, and another of determining the variation of permeability. [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.)

In this work, effective thermal conductivity (λEff) of fractured rock masses was numerically investigated. A two-dimensional Discrete Fracture Network (DFN) model of the fractured rock masses was established based on the statistic results of natural fracture development in a potential area for high level radioactive waste disposal in China. Steady state heat transfer processes in the fractured granite rock masses were numerically simulated using finite element method (FEM). The calculated λEff values of the fractured granite rock masses in dry and saturated conditions are 1.99 W/(m K) and 2.31 W/(m K), respectively. Compared with the thermal conductivity of intact granite [λIntact, 2.5 W/(m K)], the drop rates are 20.4% and 7.6%, respectively. Sensitivity analysis was conducted on the main model parameters including fracture density (FDensity), trace length (FLength), thermal contact resistance (FTCR), and λIntact. The results indicate the relation between λEff and three fracture parameters (FDensity, Flength and FTCR) can be fitted using power law or negative exponent functions with good consistency. When fracture network parameters remain unchanged, λEff is in linear positive correlation to λIntact. The slop of the fitted line is determined by the fracture network parameters. Due to the fact that distribution of generated fractures in different directions are quite uniform, λEff did not show significant difference in different directions. On the basis of the above-mentioned results, an estimation model was proposed for the determination of λEff of fractured rock masses using P21 (total length of fracture traces per unit area), FTCR, and λIntact. The proposed estimation model shows good consistency to the calculated results of FEM model. [ABSTRACT FROM AUTHOR]