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Based on uniaxial compression laboratory results, the failure process of marble with a single hole was simulated using the particle flow code PFC2D under uniaxial and biaxial compressions. The influence of the pre-existing hole shape, confining pressure and the rock heterogeneity on the mechanical properties of marble and the coalescence of cracks was analyzed. Numerical results show that compared to an intact marble specimen, the peak strength of a specimen containing a single hole reduces significantly, and the extent of reduction is related to the hole shape. The confining pressure has a significant effect on the mechanical properties of marble and the coalescence of cracks. The peak strength increases with the increase of confining pressure, while the peak deviator stress increases first and then decreases with the confining pressure increasing. Specimens containing circular holes exhibit X-type shear failure, while specimens containing rectangular or U-shaped holes exhibit diagonal shear failure. The mineral nodules in the rock specimen significantly affect the propagation of cracks leading to a change in the failure mode of marble specimen. Analysis results of the microscopic mechanisms show that the initiation and propagation of cracks around the hole is always accompanied by the release and transfer of stress from a concentrated zone. Three types of macroscopic cracks can be classified in specimen containing a single hole as hole surface spalling, tensile crack, and compressive shear crack.

Rock-mass unloading often occurs during underground and slope engineering excavations. Here, rock-mass crack initiation and propagation during the excavation unloading progress was simulated using the extended finite element method (XFEM) in ABAQUS. Crack propagation and its influencing factors were studied and discussed after calculating the stress intensity factors at the crack tips, and by recording the crack's shape a dynamic evolution model was produced. The results show that the faster the unloading rate,the longer the crack,and the greater the crack dip angle, the easier the crack initiates. The normal stress on a crack surface decreases while shear stress increases during unloading, and that crack propagation is mainly controlled by shear stress. This is consistent with the theoretical analysis. The final shape of the modeled crack was also close to the result of the physical experiments, indicating the reliability of this study.

A series of Brazilian split tests on rock-cement interface considering the effect of interface orientations were conducted to investigate the influence of hard rock-soft rock interface direction on failure behavior. The tensile strength for different interface orientations was obtained and failure mechanism of the interface was analyzed by the particle flow code PFC2D. The measured tensile strength increases as the interface-loading angle increases. The measured tensile strength can be considered to be equivalent to that of the interface if the interface orientation is parallel to the loading direction, because tensile failures occur along the interface. Mixedmode failures occur if the interface is not parallel to the loading line. In addition, another series of Brazilian tests were conducted to investigate the influence of the interface tensile strength on failures by increasing the cement dosage and roughening the rock surface. Based on the results, a diagram of the failure mode distribution marked with the typical failure patterns from the Brazilian test results for the rock-cement interface was developed. These findings provide a better understanding of the failure modes of the hard rock-soft rock interface.

To solve the problems of the precontrol roof sublevel filling method in deep mining, such as the complexity of the excavation process of precontrol roadway roofs and the suseeptibility of precontrol roofs to blasting vibration, this article introduces a collaborative stoping based sublevel filling method which utilizes horizontal and vertical holes at the same time. The sublevel filling method can effectively solve the roof stability problem of surrounding rock through changing the precontrol roof into a rear control[roof by altering the support order. Furthermore, optimization research is performed on the sublevel filling method based on collaborative stoping:firstly, the structural parameters are optimized by stability analysis using SURPAC and ANSYS; then, the partition drawing and supporting method is applied to solve the problems of the poor support quality of the two sides and the inefficient ore-drawing. A case study of Xincheng Gold Mine shows that the displacement of the roof significantly decreases and the economic indicators:improve, indicating safe and high-efficient mining of the thick and large orebody under high geostress.

A space-time unified distribution model of ground fracture ratio caused by mining-induced underground coal fire was proposed based on the theory of random medium movement. The distribution and dynamic change laws of ground line (tension) fracture ratio, areal fracture ratio and shear fracture ratio were revealed through the analysis of an example. The maximum values of these three categories of ground fracture ratio respectively distribute in the ground surface region corresponding to the 20-m inner side from the surrounding boundary, the 4 midpoints of the surrounding boundary, and the 4 marginal endpoints of goaf. With combustion of the coal seam, the line fracture ratio perpendicular to the fire development direction and the areal fracture ratio corresponding to the boundary of goal change according to the half normal curve and stable at the maximum, while the shear fracture ratio, line fracture ratio along the fire development direction and the areal fracture ratio corresponding to the interior of goaf change according to the normal curve.

Through statistical analysis of random experiments, there is a function of porosity 3lnφ-2ln(1-φ) that approximately follows a normal distribution. In the test particle size range of 30 to 180 ram, the expectation and variance of this function value increase with an increase in grain size of rock blocks. On the basis of deriving the subsidence hypersurface equation of a basic roof, a continuous inhomogeneous distribution model and a random inhomogeneous distribution model of porosity in the combustion space area (CSA) are deduced. For a rectangular coal fire space, the porosity in the shallow and edge side of CSA is large, but in the middle region is small. In the x-y plane, the porosity contour appears a side lying U-shaped distribution, and the porosity presents negative exponent attenuation with an increase in distance entering CSA along the x axis. In addition, the overall trend of the porosity of continuous distribution and random distribution is the same, but the difference is that the porosity described by the random distribution model has a certain stochastic volatility. The random distribution model of porosity has been used in a numerical simulation of the temperature field in a fire zone, and the accuracy of simulation and the applicability of this porosity model are verified by infrared temperature measurements.

The characteristics of dynamic strength and deformation on rock with different axial pre-compressions under cyclic impacts were conducted with modified split Hopkinson pressure bar (SHPB). Firstly, the different axial pre-compression stresses were loaded on sandstone specimens before the cyclic impact loadings were carried on. And then, the typical dynamic stress-strain curve of specimen under cyclic impacts was investigated. Finally, the characteristics of dynamic strength and deformation of rock with different axial pre-compressions were studied during cyclic impacts. The results show that, with the increase of number of cycle impacts, the deformation modulus of loading stage and the first unloading stage, transmitted wave and peak stress, the ratio of recovered strain and peak strain, the ratio of recovered stress and critical unloading stress reduce gradually. While, the average strain rate, peak strain, the deformation modulus of the first unloading stage, and specific energy absorbency increase gradually. When the axial compression of rock is 22%, 51% and 65% of its uniaxial compressive strength, the relation between the ability of resistance against cyclic impacts and the cycle-index is from slow development to sharp decline. When the axial compression of rock is 0 or 65% or 87% of its uniaxial compressive strength, the ability of resistance against cyclic impacts drops constantly during the whole cycle. The rock's ability of resistance against the cyclic impacts is highest when the axial compression of rock is 22% of its uniaxial compressive strength. [ABSTRACT FROM AUTHOR]