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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]

Deep roadways within fractured rock mass present substantial challenges for mining and construction due to the risk of large deformations. This study focuses on investigating the formation and evolution of cracking zones in the surrounding rock, specifically analyzing the 790-m level segment within the Jinchuan Mine No. 2 Mining area. Our comprehensive approach integrates field investigations, laboratory tests, in-situ monitoring, and numerical simulations. The findings highlight the vulnerability of surface surrounding rock in the σ 3 direction, leading to spalling and failure after excavation, while shallow surrounding rock acts as a natural barrier against deeper crack propagation. Over time, the elliptical cracking zone, aligned with the σ 1 direction, expands, which progressively degrades the internal rock mass, ultimately resulting in support failure due to instability and increasing deformation pressures. To mitigate these challenges, strategies were proposed to minimize the initial cracking zone and halt its growth. The insights and guidance provided herein are invaluable for enhancing project safety and efficiency in designing and constructing roadways in similar geological settings. • Shallow rock, a barrier against deep cracks, shields excavation; surface rock in σ 3 is prone to spalling and failure. • Elliptical cracking zone along σ 1 grow, leading to rock degradation, support failure, and heightened deformation over time. • Controlling large deformation hinges on minimizing the initial cracking zone and halting its ongoing evolution. [ABSTRACT FROM AUTHOR]

As components of natural geological bodies, rock masses generally experience long-term endogenic and exogenic geological processes. Since the composition and structure of rock masses generally vary from one domain to another, it is necessary to divide rock masses into several approximately homogeneous domains before developing rock engineering designs. A progressive framework that integrates geological, geotechnical and structural aspects was proposed to demarcate homogeneous domains. The proposed framework was applied to identify the homogeneous domains along three exploration tunnels at the Xulong dam site. The demarcation of geological domains was mainly done by means of thin-section examination of rock specimens and outcrop investigation. Field observations and P wave velocity tests were used to distinguish the changes in the geotechnical properties of rock masses caused by rock unloading and weathering. The crack tensor, which can synthetically consider the orientation, dimension and volume density of discontinuities, was introduced to determine the structural similarity of rock masses based on in situ measurable quantities. The results show that the crack tensor can effectively distinguish structural differences and exhibits better performance than conventional orientation-based methods. A major advantage of the proposed progressive framework is that it provides a quantitative, logical and reasonable framework to delineate homogeneous domains based on the comprehensive utilization of available field data in a logical sequence. [ABSTRACT FROM AUTHOR]

• First hydrogeological model established for URL site of HLW disposal in China. • The effect of the hydraulic influence zones of faults is incorporated in the numerical model. • Different variations in the horizontal and vertical directions of hydraulic conductivity are considered. • A total of 120 stochastic parameterized models are presented. • Hydraulic conductivity < 10−9 m/s at high-level radioactive waste disposal depth. Deep geological disposal is internationally accepted as a feasible and safe approach for high-level radioactive waste (HLW) disposal. To evaluate hydrogeological conditions in support of safety assessments for HLW disposal at the Xinchang preselected site in China, stochastic inverse models of site-scale groundwater flow were developed in this study to generate highly parameterized hydraulic conductivity fields for the fractured medium by adopting pilot point and null-space Monte Carlo methods. The hydraulic influence zones of the faults were carefully considered to have homogenous parameter values across the zones. A total of 120 multiple random realizations were generated to characterize the 3D spatial variations in hydraulic conductivity by conditioning to 1218 fixed pilot points. The simulated hydraulic heads of the realizations were in good agreement with observational data. The hydraulic conductivity fields close to the boreholes could be characterized in detail and had relatively low uncertainties. Furthermore, the hydraulic conductivity (K) values around underground research laboratory (URL) at the HLW disposal zone depth were less than 10−9 m/s. The K values obtained for most of the influence zones of these faults at this depth were consistent with hydraulic test data and ranged from 10−10 to 10−9 m/s, thereby indicating that the surrounding rock has low permeability and is suitable for HLW disposal. These findings offer new insights into hydrogeological conditions by providing key information on the permeability characteristics that need further focus on HLW disposal. [ABSTRACT FROM AUTHOR]

The natural fracture system exerts a significant influence on the physical and mechanical properties of rock masses. The heat transfer in fractured rock masses is much more complicated than that of intact rock due to the thermal contact resistance induced by natural fractures with varying size, aperture, roughness, and orientation. This work describes a method for determining the representative element volume (REV) of heat transfer and the 3D thermal conductivity tensor of fractured rock masses. The method is based on the element-wise averaging of temperature and heat flux, which can be obtained from a finite element solution to a steady state heat transfer problem with specific boundary conditions. A case study was conducted based on the geological data of a potential area for high level radioactive waste disposal in China. The results indicate that the size of heat transfer REV of the rock masses in the study area is approximately 18 m × 18 m × 18 m. 3D thermal conductivity tensor, the magnitudes and directions of the three principal thermal conductivities, and anisotropy of the fractured rock masses were obtained. Influences of main fracture parameters including density, disc diameter, and thermal contact resistance on the heat transfer characteristics were investigated. The research results in this work can provide a better understanding of the discontinuous heat transfer processes in fractured rock masses and their homogenization methods. [ABSTRACT FROM AUTHOR]

The deep geological disposal is an internationally recognized method for the disposal of high level radioactive waste. As an essential facility, the construction safety of underground research laboratory (URL) is very important. Taking the China's first URL in Beishan, Gansu Province as engineering background, considering the influence of arranged joints in rock mass, an elastic–plastic damage numerical method for fractured rock mass is presented and the corresponding subprogram in Flac3D is developed. Based on the numerical calculation of underground research laboratory construction, the optimized excavation scheme of URL is obtained and the distribution rules of surrounding rock displacement field, stress field and plastic damage zone are studied. The research result can provide important guidance for the construction of Beishan URL. [ABSTRACT FROM AUTHOR]

The coastal Sanshandao mine is threatened by the overlying Quaternary water and seawater. Following an introduction to the geology and hydrogeological conditions in the mine area, a detailed hydrogeological survey and sampling were conducted and hydrochemical and stable isotopic (δ2H and δ18O) tests on various waters were carried out to characterize the origin of water in the mine tunnels. Investigation and statistical analysis indicated that the northwest-trending fractures with large dip angles and long trace lengths are well developed in the northeast compared with those in the southwest of the mine. The permeability coefficients of the rock masses are in the range 4.19 × 10-8-2.25 × 10-5 m/s, indicating that the fractured rock masses have generally low permeability. The seepage water had higher values of EC, total dissolved solids, and concentrations of most elements than the seawater and saline groundwater. Besides, the isotope composition of the waters indicated that the seepage water was more isotopically enriched than seawater but less than brine. The proportions of the three different sources were calculated based on hydrochemical and isotopic analyses. Overall, the mine water was composed of 72% seawater, 14.8% brine, and 13.2% atmospheric precipitation, respectively. Therefore, some preventive measures are essential to avoid the probability of seawater inrush. [ABSTRACT FROM AUTHOR]

This paper presents a case study investigation into the hydrogeological characteristics and permeability of rock mass in a seabed mine. Following an introduction to the geology and hydrogeological conditions in the Xinli mine area, we reveal the features of the preferred structural planes, dynamic characteristics of mine water seepage, and the permeability of the fractured rock mass in the pit. The permeability of the pit rock mass shows varied characteristics at different geotectonic locations because of the different degrees to which the structural planes developed. The fractured rock mass generally shows low permeability, and the main composition of water seepage is high-salinity brine. Future large-scale undersea mining may induce rock mass movement, destroy water-resistant layers, and enhance water transmissibility and the probability of water gushing into the pit. Thus, strengthening the quality of the filling mass, protecting the stope roof and the water-resistant layers, as well as regular monitoring of water seepage discharge and identification of water sources are critical to work safety and the prevention of seawater gushing in the mine. [ABSTRACT FROM AUTHOR]