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Zhang H.,Tongji University | Liu S.-G.,Tongji University | Han Z.,Central South University | Zheng L.,Hong Kong Polytechnic University | And 4 more authors.
Computers and Geotechnics

In the contact theory for three-dimensional discontinuous deformation analysis (3-D DDA), the first step is to identify the types of contacts between the blocks. This paper presents a new algorithm to identify contact types between arbitrarily shaped polyhedral blocks for 3-D DDA. First, pairs of neighbouring blocks that are close enough to possibly be in contact are recognized using their axis-aligned bounding boxes. Four types of dominant contacts (i.e., vertex-to-vertex, vertex-to-edge, vertex-to-face and crossing edge-to-edge contacts) that control the movements of blocks, especially rotations, are then identified using an extended hierarchy territory algorithm. Finally, using a new loop search procedure, face-to-face contacts in which the interface strength depends on the friction angle, cohesion and tensile strength rather than only the friction angle, are formed from several interdependent dominant contacts. The results of three numerical examples demonstrate the ability of the new algorithm to address the complex problem of contacts between arbitrarily shaped polyhedral blocks. © 2016 Elsevier Ltd Source

Zhang H.,Tongji University | Liu S.-G.,Tongji University | Zheng L.,Hong Kong Polytechnic University | Zhong G.-H.,Tongji University | And 3 more authors.
Computers and Geotechnics

This paper extends the edge-to-edge (E-E) contact model for three-dimensional discontinuous deformation analysis (3-D DDA) by addressing the difficulties in determining the contact point pairs, contact candidates and mechanical properties of the interface required for friction analysis. Contact candidates and mechanical properties of the interface are determined using new judgment criteria. Contact point pairs are evaluated using path-dependent analysis. Complete formulations for the new E-E contact model are derived from the auxiliary-simplex method. These extensions have been implemented in the 3-D DDA program. Numerical tests demonstrate that the extended 3-D DDA can accurately model the frictional behavior of a block system. © 2015 Elsevier Ltd. Source

Wang C.-H.,China Earthquake Administration | Song C.-K.,First Crust Deformation Monitoring and Application Center | Guo Q.-L.,China Earthquake Administration | Zhang Y.-S.,China Earthquake Administration | Ding J.-M.,China Earthquake Administration
Chinese Journal of Geophysics (Acta Geophysica Sinica)

The MS7.0 Lushan Earthquake in the southern segment of Longmenshan Fault has brought great loss to the local natives and societies. To analyze the earthquake from the viewpoint of stress buildup in the upper crust is helpful and meaningful to understand more about the seismogenic mechanism. In the past 21 years, the research group accumulated and collected lots of in-situ stress data from 22 boreholes. These in-situ stress data show that the stress regime is of reverse faulting, and that the orientation of the maximum horizontal principal stress is N44°-64°W. At the same time, the stress measurements indicate that the stress state in the research area is relatively stable. In this paper, the authors suggest adopting the ratio of half maximum differential stress to the mean effective stress, μm, to reflect the capability and stress level of the upper crust. According to the theoretical analysis, μm has similar physical meaning with μ, so we can replace μ with μm to do rock friction analysis. The μm based on all the stress measurements ranges from 0.39 to 0.56, approximately approaching the lower limit defined by the Byerlee law, μ=0.6, which also agrees well with the static friction coefficients of gouge specimen from the Longmenshan fault after Wenchuan Earthquake tested in the laboratory. Therefore, the occurrence of the Lushan Earthquake proves that the upper crust of the research area is in the critical frictional equilibrium state or sub-equilibrium state. The focal mechanism solution of Lushan Earthquake is reverse faulting, with the main P axis of 122°, which is consistent with the stress state defined by the in-situ stress measurements. Compared with the research findings made by other geoscientists, the Lushan Earthquake can be regarded as one induced earthquake due to the stress increase caused by the Wenchuan Earthquake on the southern segment of Longmenshan fault. Source

Wang W.,Kyushu University | Wang W.,Wuhan University | Chen G.-Q.,Kyushu University | Zhang H.,Tongji University | And 4 more authors.
Engineering Analysis with Boundary Elements

Large impulsive waves generated by slope failures and a subsequent landslide in a reservoir area may lead to serious damage to the dam, shoreline properties and lives. Therefore, analysis of landslide-generated impulsive waves is of significant importance for hazard prevention and reduction. There are three key points for analyzing this problem: (i) the landslide run-out, (ii) the free surface flow and (iii) the landslide-water interaction process. The Discontinuous Deformation Analysis (DDA) method was previously developed to investigate discontinuous block movements, while the Smoothed Particle Hydrodynamics (SPH) method was used mostly to model free surface flow. However, the solid-fluid interaction is seldom considered in the respective fields, which greatly restricts their applications. For this reason, the coupled DDA-SPH method was proposed in this study to solve the solid-fluid interaction problem. To validate this approach, this study considered a wedge sliding along an inclined plane and interacting with the water body. The corresponding Heinrich's experimental results were adopted to evaluate the accuracy of the coupled method in modeling the landslide movement and wave profile, proving that the landslide motion and wave profiles could be captured accurately by the coupled method. Finally, the effect of the governing parameters on the wave amplitude was discussed. © 2015 Elsevier Ltd. All rights reserved. Source

Wu Y.,Institute of Earthquake Science | Jiang Z.,Institute of Earthquake Science | Yang G.,First Crust Deformation Monitoring and Application Center | Zhao J.,Institute of Earthquake Science
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University

Based on the analysis of fitting residual errors of GPS velocity, the errors of deformation parameters, and the applicability of block model, we use GPS velocity fields, strain rate fields, slipping rate of faults and GPS profile results from 1999-2007 and from 2007-2009 to identify the deformation difference of principle faults on the north section of North-South Seismic Zone. The results show that the laevorotation deformation of Zhuanglanghe Fault has increased, which the dextrorotation deformation rate calculated from Eulerian model is about 1.5±0.3 mm·a -1 in the period 1999-2007, and the laevorotation deformation rate is about 5.3±0.4 mm·a -1 in the period 2007-2009. On the other hand, the laevorotation slipping rate of north boundary of Qilian block has increased from 2.5±0.2 mm·a -1 to 7.0±0.2 mm·a -1 in these two periods. Otherwise, the extrusion deformation of Liupanshan and Haiyuan Faults has strengthened too, but the deformation magnitude is not big. These above deformation characteristics illustrate that the region of east side of Zhuanglanghe Fault has accumulated high strain energy. Source

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