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Wen S.-L.,Yangtze River Scientific Research Institute
Yantu Lixue/Rock and Soil Mechanics

The bearing capacity of pile tip is the main component of the pedestal pile; so it is the key of the pedestal pile design that how to evaluate the bearing mechanism qualitatively and quantitavely. By the model test of pedestal pile, we've done some discussion and analysis of the pile-tip bearing mechanism of the pedestal pile, and drawn some conclusion as follows. The value of the pedestal pile bearing capacity is determined by the exerting level of the pile-tip bearing capacity. The unsynchronized level of the pile-tip bearing capacity and shaft resistance of pedestal pile is much more obvious than that of the non-pedestal pile. The limit equilibrium zone of the pedestal pile tip is different from that of the non-pedestal pile tip; but is similar to that of contrary anchor-slab foundation. Because of the enlarged part, the foundation bearing capacity at pile tip is lower in some extent; so during the design and calculation of the pedestal pile tip bearing capacity, it is necessary to modify the pile tip bearing capacity lowered by the enlarged bottom. Source

Su H.,Yangtze River Scientific Research Institute
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics

The numerical simulations of large deformations of continuums lead to the choice of an appropriate kinematical description. In classical viewpoints, Lagrangian and Eulerian description approaches are alternatives. Lagrangian approach tracks material particles, allowing for a clear delineation of boundaries of material. However, meshes that adhere to material are easy to be distorted, inducing a poor accuracy or even computation failure. On the other hand, Eulerian approach is very attractive in the point that fixed meshes will never be distorted, but it suffers from the complexities of handling moving boundaries and convective terms of Eulerian governing equations. Thus ALE (Arbitrary Lagrangian-Eulerian) method, which is reported to take advantages of Lagrangian and Eulerian approaches to a certain extent by allowing motions of meshes, is developed in recent years. Nevertheless, how to devise a good mesh motion algorithm is a great burden to the user, and convective terms are still involved. This paper presents a novel method, numerical manifold method (NMM) with fixed mathematical meshes, for short, fixed-mesh NMM, for analyzing pure geometric non-linear problems. Making well use of the fact that mathematical meshes are independent of material boundaries in NMM, this method is based on the Lagrangian description approach, but using fixed meshes. It has the virtues of both Lagrangian description approach and Eulerian description approach, avoiding mesh distortion of the former, and complexities of handling moving boundaries and convection items of the latter. Following the time steps, equations of NMM for large deformations are adopted in this paper, providing an easy way to implement fixed-mesh NMM. There are only two special factors to consider: after each time step is completed, deformed material boundaries are intersected with fixed mathematical meshes to generate new manifold elements; initial stress loads are handled in a proper way, which is most important to fixed-mesh NMM. Based on fixed rectangular mathematical meshes and one order polynomial cover functions, two methods are presented to compute initial stresses. Given results of large deflection of a cantilever beam show the feasibility of the fixed-mesh NMM, and indicate that more research should be further done on computational stability due to initial stress loads. Source

Zhang Q.-H.,Yangtze River Scientific Research Institute
Computers and Geotechnics

Locating all spatial blocks cut by an arbitrary three-dimensional discrete fracture network (DFN) within a rock mass volume is a basic issue in many research fields related to fractured rock masses. In this paper, analysis procedures based on both the oriented rule and the closed rule are described, followed by a description of a proposed method for block progressive failure analysis. Lastly, two engineering cases in which the proposed method is implemented are presented. The results show that the identified blocks may be extremely complicated and may even be composed of thousands of loops (block faces consist of loops); block progressive failure analysis is extremely useful and efficient in determining block-reinforcement measures. Overall, the 3-d block cutting analysis is important progress in block theory and has a large potential for application in fractured rock masses. © 2014 Elsevier Ltd. Source

Finite element generation of complicated fracture networks is the core issue and source of technical difficulty in three-dimensional (3-D) discrete fracture network (DFN) flow models. Due to the randomness and uncertainty in the configuration of a DFN, the intersection lines (traces) are arbitrarily distributed in each face (fracture and other surfaces). Hence, subdivision of the fractures is an issue relating to subdivision of two-dimensional (2-D) domains with arbitrarily-distributed constraints. When the DFN configuration is very complicated, the well-known approaches (e.g. Voronoi Delaunay-based methods and advancing-front techniques) cannot operate properly. This paper proposes an algorithm to implement end-to-end connection between traces to subdivide 2-D domains into closed loops. The compositions of the vertices in the common edges between adjacent loops (which may belong to a single fracture or two connected fractures) are thus ensured to be topologically identical. The paper then proposes an approach for triangulating arbitrary loops which does not add any nodes to ensure consistency of the meshes at the common edges. In addition, several techniques relating to tolerance control and improving code robustness are discussed. Finally, the equivalent permeability of the rock mass is calculated for some very complicated DFNs (the DFN may contain 1272 fractures, 633 connected fractures, and 16,270 closed loops). The results are compared with other approaches to demonstrate the veracity and efficiency of the approach proposed in this paper. © 2015 Elsevier B.V. Source

Shi X.,Yangtze River Scientific Research Institute | Cheng Z.,Yangtze River Scientific Research Institute
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering

Four groups of triaxial test with high confining pressure on Qipei hydropower station bedding material are carried out. Based on the test results of particle size distributions, the fractal model is established, and its fractal behavior in crushing is studied. The results show that particle size distributions after particle breakage of these two kinds of rockfills possess good fractal behavior; fractal dimensions vary from 2.6127 to 2.7232; and the fractal dimensions of bedding material after crushing are less than those of average line. The fractal dimensions increase with the increasing confining pressure in the same density. The increasing trend has stage characteristics: its growth rate keeps slow under low confining pressure; while the grain breakage increases with confining pressure, its growth rate becomes sharp under low confining pressure. The fractal dimensions increase with the density under the same confining pressure. The magnitude of fractal crushing dimensions reflects the particle sizes of breakage and the uniformity of the particle size distributions. The larger the fractal dimension is, the more the quantity of particle breakage is. Besides, there is a close relationship between fractal dimension and Marsal index of particle breakage. Source

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