Papers by Author: Wan Cheng Zhu

Abstract: In order to study the supporting of deep surrounding rock with zonal disintegration tendency, the zonal disintegration phenomenon of deep surrounding rock under three supporting forms is analyzed by the ABAQUS finite element software in this paper, and three supporting forms are un-supporting, bolting and grouting, and combined “Bolting and grouting plus Anchor rope” supporting. The results show that the different effects to zonal disintegration under different supporting forms will occur. Supporting can help to restrain the zonal disintegration of the reinforcement part advantageously, and also lower rupture degree of zonal disintegration and reduce the size of rupture zone. Meanwhile, the stability of surrounding rock is improved. But zonal disintegration may occur outside reinforcement part under greater ground stress. The results are great importance to a better understanding of the deep roadway supporting.

Abstract: Based on extensive literature review, the state of the art of coupled hydromechanical models and in-situ monitoring for groundwater inrush predictions are summarized in detail, based on which, it is proposed that the key issues for describing the seepage characteristics during groundwater inrush are to calibrate the equations for damage-induced evolution of permeability and of effective stress. Depending on in-situ experiments and numerical simulations, a new academic idea, i.e.“the rock micro seismicity induced by mining processes and water pressure disturbance is in essence the index of groundwater inrush” is put forward based on case studies, coupled hydro-mechanical theory, high-performance computing technology and microseismic monitoring. The authors propose that the tendency for analyzing and predicting the groundwater inrush is to synthetically inverse the inrush pathway formation, strata microseismic precursor and high performance computing results. And relying on the microseismic monitoring events, the groundwater inrush models are calibrated, which could be used to clarify the precursory characteristics and to locate the inrush pathway. This study will lay theoretical basis for establishing the models to predict the groundwater inrush in underground mining. Key words：rock mechanics, groundwater inrush models, calibrating, numerical simulation, microseismic monitoring

Abstract: Concrete is a heterogeneous composite material. The heterogeneity consists of the distribution and shape of aggregate, interfacial transition zone (ITZ) and the inhomogeneity of each component materials. The key in numerical models for simulating the fracture behaviors is how to describe the heterogeneity actually. In this paper, at meso-scale level general-purposed digital image processing technologies are utilized to characterize the heterogeneity resulting from the shape and distribution of aggregates and ITZ, and at micro-scale level, a statistical method (e.g. Weibull distribution) is used to describe the heterogeneity of each phase. And then a multi-scale numerical model based on digital image is proposed to simulate fracturing process of concrete under loading condition. The proposed model can take the actual distribution and shape of aggregate into account. The fracturing process of concrete in uniaxial compressive tests is simulated by using the model. The results show that the shape of aggregates plays an important role in stress distributions to influence the damage evolution during loading. The proposed model is capable of capturing the complete failure process of concrete materials that includes the initiation, propagation and coalescence of microcracks as well as cracking pattern associated with different loading stages, which is a new tool to study the fracturing behaviors of concrete in more detail. Key words: digital image; heterogeneity characterization; fracturing process; concrete

Abstract: The changing behavior for infrared thermal image omen of the rock with fracture is essential for the geotechnical engineering. In order to study the behavior, the infrared thermal images for the failure process of rock with hole are carried out. The size of the rock sample is 20cm×10cm×2cm with hole at the center of the sample and the diameter of the hole is 1cm. Considering the fact that sample will effect the results of the observation for infrared thermal image during the experiment, the laminated granite sample was used to replace the cylinder or cuboid sample. The achieved results under uniaxial compression indicate that intensity of the micro ruptures have a close relation with the thermal effects. When the main fractures happen, there is a strip of high temperature that will appear at the destructed local area. During loading process, the abnormity of infrared temperature has two kinds of behaviors as follows: (1) temperature rises and falls alternately, rises before the fracture; (2) temperature falls slowly at beginning, and then rises slowly, then rises quickly before the fracture appears. Even for the same rock sample, the behaviors of the infrared phenomenon may be different during failure.

Abstract: In this paper, a Material Failure Process Analysis code (MFPA2D) was employed to investigate the interaction of end effect zone of specimen with the wing crack propagation inside the brittle specimen containing pre-existing flaws under uniaxial compression comparing with the experimental results. The numerical results show that the shorter the distance between the pre-existing flaw and the specimen's end , the slower the crack propagation process and the shorter wing propagation length is , and vice versa. In addition, the end effect zone was also influenced by the wing crack propagation.

Abstract: In this paper, some numerical tests on the fracture process zone (FPZ) in concrete tension specimen were carried out with Material Failure Process Analysis code (MFPA2D) to investigate the behavior of the FPZ and the effect of the meso-scale heterogeneity of concrete on fracture process. The numerical results provide a clear indicator of the FPZ of concrete. The numerical results show that the FPZ accompanied by AE events gradually develops ahead of the notch tip with the increase of the loading in the concrete tension specimen. Moreover, many of the AE events bring about very small energy at the beginning of loading stage. Zones of higher energy events demonstrate a localization zone around the notch tip. The zones of AE events progresses forward gradually, and much densely distributed AE events can be observed in the FPZ. Moreover, the numerical simulations about AE events agreed well with those of the microcracks obtained by laboratory findings.

Abstract: Based on mesoscopic damage mechanics, a numerical code RFPA2D (dynamic version) is developed to simulate the spallation process of inhomogeneous medium induced by reflection of stress wave, and the influence of duration of stress wave on spallation is discussed. For convenience of description and discussion, the failure area in the immediate vicinity of loading position of model is divided into two zones, i.e. comminution zone and fracture zone; and the failure area caused by spalling in model is defined as spalling zone. The comminution zone is affected little by the duration of stress wave, but the fracture zone and the spalling zone are affected to a greater extent by duration, also, the stability of specimen is affected by the duration of stress wave. Furthermore, if the duration becomes significantly long, the fracture zone corresponding to the maximum extension of the radial tensile cracks will be dominant in specimen. If the duration of stress wave becomes short to some extent, the spalling zone corresponding to the maximum extension of the tangential tensile cracks will be dominant in specimen. In addition, if the duration of stress wave is long enough, the specimen may lose stability.

Abstract: A numerical code RFPA3D (Realistic Failure Process Analysis) is used to simulate the crack initiation and propagation in FRP-strengthened concrete beam under external loading. In our model, the FRP-strengthened concrete is assumed to be a three-phase composite composed of concrete, FRP, and interface between them. The displacement-controlled loading scheme is used to simulate the complete failure process of FRP-strengthened concrete the numerical simulation of failure process of the specimens. It is found that the main failure mode is the interfacial debonding and the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. The simulation results agree well with the experiment observations. The width of the FRP sheet is considered an important factor not only to significantly influence the debonding propagation type and crack distribution but also to control the ultimate load-capacity and ultimate strain. This study is focused on the failure process of the FRP-strengthened concrete beam and the effects of the width of FRP sheet on the failure mode and on the structural load-carrying capacity of concrete structures.

Abstract: Rock and concrete are typical heterogeneous material that the meso-scale heterogeneity may have a significant effect on their macro-scale mechanical responses. In this work, a digital image-based (DIB) technique is employed to characterize and quantify the heterogeneity of concrete, and the obtained data is directly imported into a numerical code named RFPA (Rock Failure Process Analysis) to study the effect of heterogeneity on the failure process of concrete. The upgraded RFPA is capable to simulate the progressive failure of brittle materials such as rock and concrete, representing both the growth of existing fractures and the formation of new fractures, obviating the need to identify crack tips and their interaction explicitly. The simulated results are in reasonable agreement with experimental measurements and phenomenological observations reported in previous studies.

Abstract: Many stiff clays forming part of natural slopes and earth dams exist in the fissured state. When these cracks are subjected to gravity induced normal and shear stresses they may propagate. The present discussion presents a numerical method to study the propagation direction of cracks under stress fields similar to those found in the field. Not only did the results on one crack propagation direction obtained from the numerical method and the analytical results agree well, but numerical results have been used to investigate the mechanisms of the whole process of two horizontal cracks initiation and propagation and coalescence in stiff soils.