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The safe and secure supply of strategic mineral resources is an important strategic need of China, and the extraction of mineral resources from the deep earth is an irreplaceable strategy for a long time in the future. To ensure the demand for mineral resources, the safe and efficient mining of high-stress hard rock is a major problem that must be solved in deep mining. Firstly, the technical challenges of deep high-stress hard rock mining and the transformative mining philosophy of "turning harm into benefit" was delineated. And a key engineering countermeasure to weaken the high-stress hard rock before mechanical rock breaking to achieve commercial mining was proposed. Next, the mechanism, characteristics and development status of contact and non-contact rock weakening methods were summarized, and the potentiality of these two types of rock weakening methods in the field of assisting mechanical breaking of high-stress hard rock was compared and analyzed. Finally, the safe and efficient continuous mining technology represented by mechanical rock breaking with thermal exfoliation damage weakening of deep high-stress hard rock was prospected. It provides useful guidance for the safe and secure supply of deep strategic mineral resources and the development of deep earth engineering. [ABSTRACT FROM AUTHOR]

Aiming at the current groove blasting problems of additional damage, the feasibility of double base propellant for groove blasting was explored. Based on the propellant gas release behavior, the pressure change of the double base propellant in the closed hole was calculated. Combined with high-speed photography and digital image correlation (DIC) method, two groups of experiments were carried out with propellant loading density of 0.84 and 0.96 g/cm³ to investigate the dynmic destruction process of granite slabs under the action of propellant. The results show that the granite slabs in the two groups of experiments were cracked along the groove direction at 100 μs after ignition, and the cracks penetrated through the slabs at 200 μs; the specimen with a charge density of 0.96 g/cm³ had a larger separation speed between the upper and lower slabs after fracture, and the upper and lower slabs were cracked by the friction of the blocking rubber and the inertia of the specimen, and the cracks were in the vertical direction at 2 500 μs. The grooves around the blast hole provide space for the effect of the propellant gas, and the grooves can effectively guide the direction of crack propagation, no crushing zone formed around the hole wall. The quasi-static pressure generated by the combustion of double-base propellant is the main driving force for crack initiation and propagation. The experimental results have some implications for the use of double base propellant in controlled rock blasting projects. [ABSTRACT FROM AUTHOR]

The mining stress formed in the surrounding rock after coal seam mining is the root cause of the damage and fracture of the stope surrounding rock. In order to study the evolution characteristics of mining stress and the fracture process of overlying strata on the mining face, a numerical model was established to simulate the evolution law of stress field and fracture field in the mining process of the working face by taking the 40101 mining face of Gaoliang Coal Mine as an example. The results show that the relationship between rock collapse and failure can be judged by using Mohr-Coulomb criterion to analyze the variation law of the difference between maximum and minimum principal stresses. The correctness of the time-varying evolution of fracture field and stress field in working face mining can be verified by comparing the numerical simulation results with the field measured results.

In the process of rock excavation, cyclic loading may occur before or after the peak value. In order to obtain the fracture damage evolution characteristics of rock under the pre-peak and the post-peak cyclic loading condition, the fracture tests of three-point bending granite beams were conducted by using the digital image correlation method and the acoustic emission technology. Based on the secant modulus, the acoustic emission energy and effective crack length, the rock fracture damage indexes DE, DAE, and DL were constructed respectively, and the rock fracture damage process was quantitatively analyzed. The results show that the damage index of the rock sample has an obvious rate effect. At the same number of cycles, as the loading rate increases, the damage index decreases. For the pre-peak cyclic loading condition, the fracture process of rock from elastic stage to elastic-plastic stage can be well reflected by DE. Under the condition of post-peak cyclic loading, DL can better represent the fracture damage process of rock from step up to continuous failure.

The distribution law of fluid flow in natural fissures was obtained by simulating the fluid flow in the rock fissures of the fault fracture zone. Based on the theoretical analysis, the velocity distribution model of wedge-shaped flow field was established. It was found that the location of the fracture mainstream zone could be expressed by the maximum inscribed circle of the fracture section. Computed tomography (CT) was used to reconstruct the natural fracture of the dielectric skeleton of the fault, and the maximum inscribed circle of the fracture was calculated by MATLAB to estimate the permeability of the fracture. The correlation between the results to calculate the fracture permeability obtained by the maximum inscribed circle method and the hydraulic diameter method was 0.976, which indicated that it was feasible to calculate the fracture permeability by the maximum inscribed circle of the fracture section instead of the hydraulic diameter. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute 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 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 order to accurately measure unsaturated hydraulic parameters of rock fractures and find the characteristics and laws of unsaturated seepage flow in fractures, a set of fracture unsaturated seepage test systems was designed and developed. The composition and the main function of the test system were also presented. The test system is mainly composed of injection system, model system, confining pressure system, back pressure control system and measurement and data acquisition system. The unsaturated seepage flow of rock fracture can be realized by the test system. The selection of high-precision piston pump, pressure sensor, electronic balance and back pressure control system can ensure the test measurement and control accuracy. By rock single-fracture unsaturated seepage test, some hydraulic characteristics of single-fracture unsaturated seepage are clarified. Compared with the generalized model fracture, the actual rock mass fracture has a larger irreducible water saturation. The unsaturated permeability coefficient is larger than that of the generalized model fracture when the saturation is very low due to the existence of thin film water and pore corner capillary water. The test relationship between capillary pressure and unsaturated permeability coefficient is established. Through the analysis of test data capillary pressure and the fitting formula of unsaturated permeability coefficient are proposed. According to established and predecessors experience formula of fissure water and drainage process, the high precision fitting formula has reference for further study. The system is accurate and reliable. It can be used to measure unsaturated hydraulic parameters of rock fractures and unsaturated seepage flow characteristics. [ABSTRACT FROM AUTHOR]

Solute transport in rock fractures is controlled by three mechanisms of convection， diffusion， and water-rock chemical reactions. The characteristics of reactive solute transport during the dissolution of rough fractures under the dominance of different mechanisms were analyzed， and the effect of roughness on solute transport was analyzed. The research results showed that there are four types of rough fractures dissolution processes， viz. uniform， non-uniform， extremely non-uniform， and uniform-non-uniform dissolution. In convection-dominated conditions， the fractures are dissolved uniformly， in chemical reactions dominated conditions， the dissolution rate at upstream of the fluid is higher than that at downstream. The initial roughness also has an important effect on the rough fractures dissolution process. Increasing the initial roughness will increase the water-rock chemical reaction rate， and at the same time， as the water-rock chemical reaction progresses， the fractures roughness will increase after the fractures are dissolved. [ABSTRACT FROM AUTHOR]

To achieve the effective monitoring of rock failure events in the mine water inrush inoculation process, a moment tensor inversion method based on digital seismology was introduced to process abnormal microseismic events monitored in Hebei Fanshan Phosphate Mine. The vibration displacement field in the mine scale could be expressed as the convolution of moment tensor and Green's function. The moment tensor was linearly inversed through extracting displacement data from the microseismic events and calculating the Green's function (pulse response of transmission medium between the source and sensors). Then, the type of ruptures was distinguished by analyzing the fracture azimuth of microseismic events. As a result, a 3D effect picture of the microseismic monitoring area was built to fit the rock failure surface, predict its development trend, and demarcate the water inrush danger zone preliminarily. Research results show that the moment tensor inversion method can be used to calculate a series of focal mechanism solutions and can reflect the rock failure in the mine water inrush inoculation pocess and development trend effectively.

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology 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.)

Karst regions, which account for about 15% of the terrestrial surface area, are characte-rized by specific hydrogeological structure different from most non-karst regions. Thus, many research methods that are used in non-karst regions cannot be directly used in karst regions. This issue is especially relevant to research on plant water sources. In this paper, origins and possible solutions to the common problems associated with research on water sources used by karst plant species were reviewed. Four questions were addressed: 1) why is it important to determine plant water source in karst regions? 2) Why are stable isotopes used? 3) What are the challenges associated with using stable isotopes in karst regions? 4) What are the probable solutions for these challenges? This review emphasized the advantages of using stable isotope techniques to identify sources of water used by karst plant species and the challenges associated with satisfying the prerequisites of this method. It is suggested that sources of water used by plant species in karst regions need not to be divided into specific depths and the method of identifying sources of water used by plant species based on their hydrologic properties was much applicable.