Papers by Author: Shu Hong Wang

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Authors: Shu Hong Wang, Heek Wang Lee, Xing Dong Zhao, Ahmad Bashir
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.
Authors: Shu Hong Wang, Chun An Tang, Wan Cheng Zhu, Kai Zhang
Authors: Huo Ran Sun, Shu Hong Wang, Shuai Xu, Wen Lin Chen
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.
Authors: Lai Gui Wang, Chunbin Wu, Feng He, Shu Hong Wang
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.
Authors: Shu Hong Wang, Chun An Tang, Juan Xia Zhang, Wan Cheng Zhu
Abstract: This short paper will present a two-dimensional (2D) model of masonry material. This mesoscopic mechanical model is suitable to simulate the behavior of masonry. Considering the heterogeneity of masonry material, based on the damage mechanics and elastic-brittle theory, the new developed Material Failure Process Analysis (MFPA2D) system was brought out to simulate the cracking process of masonry, which was considered as a three-phase composite of the block phase, the mortar phase and the block-mortar interfaces. The crack propagation processes simulated with this model shows good agreement with those of experimental observations. It has been found that the shear fracture of masonry observed at the macroscopic level is predominantly caused by tensile damage at the mesoscopic level. Some brittle materials are so weak in tension relative to shear that tensile rather than shear fractures are generated in pure shear loading.
Authors: Ru Wang, Chun An Tang, Shu Hong Wang, Zhi Yuan Wang, Tian Hui Ma
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.
Authors: Shu Hong Wang, Deng Pan Qiao, Peng Jia, Nan Zhang
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.
Authors: Shu Hong Wang, Juan Xia Zhang, Chun An Tang, Shan Yong Wang
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.
Authors: Shu Hong Wang, Huo Ran Sun, Tao Xu, Tian Hong Yang, En'de Wang
Abstract: Rock failure analysis is an important research in investigating the behavior of rocks, especially its failure process. And a rock sample, which contains pre-existing cracks, is a typical sample to investigate the rock failure behavior which under tension or compression, because almost all the natural materials exist micro-flaws more or less. This mode is closed to the natural material character. By using Rock Failure Process Analysis code, RFPA2D, we present a numerical simulation and similar materials experiment on rock samples with two pre-existing cracks in uniaxial compression were conducted to investigate the initiation, propagation, coalescence of cracks and failure mechanism of rock. Numerical simulations visually reproduce the process of crack initiation, propagation and coalescence in rock, which are well tallied with experiments in laboratory.
Authors: Deng Pan Qiao, Zong Sheng Zhang, Shu Hong Wang, Ya Bin Zhang
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.
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