Papers by Author: Shu Hong Wang

Abstract: Study of mechanical characteristics of structural planes has been significant issue in engineering rock mass stability analysis. The factors that affect the mechanical behavior of structural planes are so complicated that it is quite essential to take an efficient method to quantificationally analyze these factors. Based on the basic principals of analytic hierarchy process (AHP), a structural plane classification method-CSPC method is proposed. It can conduct weight distribution in terms of the complicated factors, assess the structural planes comprehensively and also forecast the planes intensity parameters semiquantitatively. The classification and forecast parameters of structural planes appropriately fit the cases in engineering. Furthermore, the method is easy to master for the engineers and the application can be of great prospect.

Abstract: A series of numerical model tests were performed to investigate the behaviour of the anisotropic rock surrounding circular excavations under high confining pressures. The aim was to provide information on the formation of fractures and failure around deep level rock tunnels under controlled conditions. Solid cubes containing a circular hole were confined to a vertical pressure with same as the confinement in the horizontal directions. In this modeling, the inhomogeneous rock is generated by using Weibull parameters which are related to the microstructural properties determined by crack size distribution and grain size. The fracture angle is assumed to be 45o. The observed failure zone around the excavation was simulated using both the maximum tensile strain criterion and Mohr-Coulomb criterion respectively (as the damage threshold). And RFPA (Realistic Failure Process Analysis) code was used as the calculating tool in this modelling, three opening modes are simulated and compared. Computational model predictions that include crack propagation and failure modes of rock show a good agreement with those of the observation in site. It is pointed out that the damage evolution of EDZ strongly depends on the inhomogeneous, the excavation mode, anisotropic property, and the various loading conditions. Concerning the existence of a weak plane, the amount of displacement at the side wall of the tunnel was quite large, since the shear deformation occurred in EDZ. The model is implemented in RFPA code and is able to represent the change in fracture patterns between the solid and jointed parts. This provides confidence for the application of the numerical model to the design of rock tunnels at great depth.

Abstract: A typical mechanical character of rock is that the tensile strength is far less than the compressive strength. Meanwhile, the test data of tensile strength is very dispersive. Because the direct tensile tests always result in failure due to the difficulty in clamping the rock sample, the splitting test is used to determine the tensile strength of rock. There are four kinds of loading modes in the splitting test in actual laboratory test: angle pad splitting, round pad splitting, aclinic loading platen splitting, arc loading platen splitting. In this paper, the direct tensile test, the splitting test and the influence of different loading modes on rock tensile strength were studied. In order to study the stress distribution, the progressive splitting failure process was numerically modeled under the four kinds of loading cases by the Realistic Failure Process Analysis code (RFPA2D). Results show that the stress states under angle pad splitting, round pad splitting are similar to the stress states under diametrical compressive state. Regarding that the round pad splitting test is easy to implement, and its numerical results are also stable relatively, the round pad loading mode was suggested to be adopted.

Abstract: The periodically distributed fracture spacing phenomenon exists in the failure process of the reinforced concrete prism under uniaxial tension. In this paper, A numerical code RFPA3D (3D Realistic Failure Process Analysis) is used to simulate the three-dimensional failure process of plain concrete prism specimen and reinforced concrete prism specimen under uniaxial tension. The reinforced concrete is represented by a set of elements with same size and different mechanical properties. They are uniform cubic elements and their mechanical properties, including elastic modulus and peak strength, are distributed through the specimens according to a certain statistical distribution. The elastic modulus and other mechanical properties are weakened gradually when the stresses in the elements meet the specific failure criterion. The displacement-controlled loading scheme is used to simulate the complete failure process of reinforced concrete. The analyses focus on the failure mechanisms of the concrete and reinforcement. The complete process of the fracture for the plain concrete prism and the fracture initiation, infilling and saturation of the reinforced concrete prism is reproduced. It agrees well with the theoretical analysis. Through 3D numerical tests for the specimen, it can be investigated the interaction between the reinforcement and concrete mechanical properties in meso-level and the numerical code is proved to be an effective way to help thoroughly understand the rule of the reinforcement and concrete and also help the design of the structural concrete components and systems.

Abstract: The failure of rock mass under loading is resulting from preexisting flaws, such as cracks, pores and other defects. However, the propagation and coalescence mechanism among multi-group cracks is still a puzzle, especially to the engineering rocks in site. In this study, the failure of rock samples with two groups of preexisting parallel cracks under the axial load were numerically investigated by the Rock Failure Process Analysis code (RFPA) from a mechanics point of view. The simulated results reproduce the rock failure process: at the first loading stage, the particle is stressed and energy is stored as elastic strain energy with a few randomly isolated fractures. As the load increases, the isolated fractures are localized to form a macroscopic crack. At the peak load, the isolated fractures unstably propagate in a direction parallel to the loading direction following tortuous paths and with numerous crack branches. Finally, the major crack passes through the rock sample and several coarse progeny cracks are formed. Moreover, in the vicinity of the contacting zone the local crushing is always induced to cause fines. On the base of the simulated results, it is found that the dominant breakage mechanisms are catastrophic splitting and progressive crushing. It is pointed out that the particle breakage behavior strongly depends on the heterogeneous material property, the irregular shape and size, and the various loading conditions. Because of heterogeneity, the crack propagates in tortuous path and crack branching becomes a usual phenomenon. The failure process of rock sample demonstrated that due to the high stress concentration at the cracks tip or some weaker strength elements which are not on the cracks surface initiate some micro-fractures, those cracks and fractures may gradually become larger and larger, more and more with the progress of loading so that join into the branch cracks leading to the rock failure in the end. Not only did the output of the numerical simulation study compare well with the experiment results, but also the further insights of the mechanism of cracks propagation and coalescence process in rock mass were obtained.

Abstract: When a tunnel or an underground structure is excavated in rock mass, rock disturbed or damaged zone (EDZ) is formed around the excavation due to the stress concentration resulting from stress redistribution. Recent studies on the rock EDZ revealed it’s important to structural stability around underground opening. In this study, the fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by AE tests. The results of the experiments showed that tensile failure was the major microscopic failure mechanism of rock in excavation damaged and disturbed zone. The expression of the damage magnitudes in each AE source leads to accurate prediction of macroscopic failure mechanisms. In addition, the orientation of the macroscopic failure plane could be estimated by the orientational distribution of microcracks.

Abstract: The 290 level cave is situated in Nanfen Surface Mine, Liaoning, China. Nanfen surface mine is one of the biggest iron ore in Benxi Iron Company. The base line of the pit bottom has reached 346m level in Nanfen surface mine. The importance of in situ assessment of stability of the 290 level cave for next mining design and construction has been met. Investigation at the Nanfen Surface Mine has shown that damage exists around 290 level cave and that the damage develops from the energy imparted to the rock by the excavation method and by redistribution of the in situ stress field around the 290 level cave. Subsequent near-by excavations, removal of loose material from the existing cave and pore pressure changes will all influence the development and extent of rock damage, as does the rock type and its fabric. Based on the engineering characters and rock mechanics, the main characteristics of stress induced brittle failure of the site are introduced. Various evaluation and measures are sought to stabilize the over-stressed rock mass. The induced anisotropic damage process was modeled. The major results from numerical analysis of the cavern are presented and validated by direct comparison with actual monitoring data. Next, an optimization study was conducted with the experimentally validated and adjusted mathematical model, measured with a recorder within such a cave. And the stability of the 290 level cave in Nanfen Surface Mine was analysis. As a result, the model is expected to be a useful tool for simulation, design, and optimization of pasteurization tunnels. A suitable support measure was proposed and taken.

Abstract: Rock is a heterogeneous and anisotropic compound material, containing many shear surfaces, cracks, weak surfaces and faults. Damage and failure in a rock mass can occur through sliding along persistent discontinuities, or fractures. A new micromechanical approach to modeling the mechanical behavior of excavation damaged or disturbed zone (EDZ) of anisotropic rock is presented based on knowledge of the inhomogeneity of rock. In this numerical model, damage is analyzed as a direct consequence of microcracks growth. A study of the effect of elastic and failure anisotropy plus inhomogeneity on the underground excavations reveals that the modes of failure can be significantly influenced by the rock structure on the small and large scales. Fractures that develop progressively around underground excavations can be simulated using a numerical code called RFPA (Realistic Failure Process Analysis). This code incorporates the microscopic inhomogeneity in Young’s modulus and strength characteristic of rock. In the numerical models of a rock mass, values of Young’s modulus and rock strength are realized according to a Weibull distribution in which the distribution parameters represent the level of inhomogeneity of the medium. Another notable feature of this code is that no a priori assumptions need to be made about where and how fracture and failure will occur – cracking can occur spontaneously and can exhibit a variety of mechanisms when certain local stress conditions are met. These unique features have made RFPA capable of simulating the whole fracturing process of initiation, propagation and coalescence of fractures around excavations under a variety of loading conditions. The results of the simulations show that the code can be used not only to produce fracturing patterns similar to those reported in previous studies, but also to predict fracturing patterns under a variety of loading conditions. The numerical model was able to reproduce the associated complex stress patterns and the microseismic emission distribution for a variety of rock structural conditions.

Abstract: This paper presents a study on the quantification of the degree of damage from the microseismic event data, for assessment of excavation damaged zone of anisotropic rock in Jinchuan mine and presents numerical simulation and prediction on the deformation and failure of the rock masses surrounding laneway under rock mass properties and excavating conditions. Following an introduction to the engineering geology and mechanical properties of the rock mass in the Jinchuan mine areas, this paper reveals the features of the measured in situ stresses and puts emphasis on an analysis of the mechanism of underground opening and damage induced by the underground mining. Stress and AE redistribution induced by excavation of underground engineering results in the unloading zone in parts of surrounding rock masses. A micromechanics-based model has been proposed for brittle rock material undergoing irreversible changes of their microscopic structures due to microcrack growth. A systematical numerical modeling analysis method was completed. Based on numerical modelling, a series of predicting curves for rock mass response and deformation are obtained, which provides the basis of guiding the design and construction of anisotropic rock cave in Jinchuan mine. The use of the in situ stress field results in enhanced modeling of the stress concentrations and potential failures at the mines has also been reviewed. Knowledge of the prevailing rock stress field at the mines is a critical component for such modeling which has led to improved rock mechanics understanding and operations at Jinchuan mines.

Abstract: Metal materials especially steel or cast iron are used extensively in many types of construction such as buildings, bridges, cranes, vehicles and so on, so detection or prediction of metal failure is very important, but deformation of metal material often deliveries heat energy which can be detected by infrared imager. The test specimen is installed between the two grips of the testing machine and then loaded in tension and in compression. The IR913A infrared imager is used to observe the deformation of metal specimen. The high-sensitive infrared thermal images of metal specimen in the different phase of deformation are obtained. The paper theoretically analyzes the reason from the thermodynamics and plastic mechanics, the conclusions are drawn as follows: 1) When applying loads, temperature field on the surface of metal specimen is changing, the local rise of temperature is remarkable, this can be observed from the infrared thermal images. 2) From the infrared thermal images, rising temperatures are found in the regions of stress concentrations. 3) When the test specimen approaches to failure or appears fracture, there is a remarkable change that can be shown from the infrared thermal images with remarkable colors.