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Wang L.,Xian University of Technology | Chen Z.,China Institute of Water Resources and Hydropower Research | Wang N.,China Institute of Water Resources and Hydropower Research | Sun P.,China Institute of Water Resources and Hydropower Research | And 3 more authors.
Engineering Geology | Year: 2016

Evaluation of breach flood of landslide or artificial dams is usually performed by combining the hydraulic modeling of the breach flow and geotechnical analysis of the breach channel stability. This paper is a continuation of the previous work, which mainly focused on the hydraulic aspects of a dam breach flood. Efforts have been made to improve the related slope stability analysis approach that traditionally adopts a simple wedge failure mode. The improvements includes a vertical cut at the slope toe due to soil erosion, an approach to determine the critical slip surface, the effective and total stress methods dealing with different dam materials, and a procedure to model the stepped failures of the breach bank due to continuous toe cutting. Using VBA programming, an Excel spreadsheet entitled DBS-IWHR has been developed to perform the stability analysis. This spreadsheet has been incorporated into another spreadsheet entitled DB-IWHR for the calculation of the flood hydrograph. The developed model has been tested by back analysis of the Yigong landslide dam breached at the Tibetan Plateau in China in 2000 with a flood peak of 94,013 m3/s. The calculated results of the final breach base level and the peak discharge are in good agreement with the field data. Further, the results are shown to be insensitive to the variations in the geotechnical parameters used in the model. © 2016 Elsevier B.V. Source

Niu X.,Tsinghua University | Yu J.,China Renewable Energy Engineering Institute
Procedia Engineering | Year: 2015

As a flexible Lagrangian particle method, smoothed particle hydrodynamics (SPH) can easily capture large interface deformation, breaking, merging and splashing, which is quite suitable for the simulation of water surface waves. The classic weakly compressible smoothed particle hydrodynamics (WCSPH) algorithm for incompressible fluid flow usually needs small time steps to ensure numerical stability, which makes it computational time consuming. The major reason is that the pressure is linked with the density deviation which should be zero everywhere in incompressible fluid flows. Generally, the equation of state for a weakly compressible fluid is adopted to simulate incompressible fluid. To enforce the incompressibility, the stiffness of fluid is set to be large enough to keep the density deviation less than an allowable error. That will lead to a problem that a tiny error of computed density will cause a large pressure error and further numerical instability. In order to obtain rational pressure distribution and good computational efficiency as well, a new algorithm is proposed considering that flow field is globally incompressible from the view of spatial averaged flow field and weakly compressible locally due to the computational error from the view of particles. The basic conception of the proposed modified SPH is to split the pressure into a global part and local fluctuating part. The global part of pressure or the spatial averaged pressure on the resolution of background mesh is obtained by solving the pressure Poisson equation based on the velocity divergence free condition. The local fluctuating pressure is related to the local particle density variation by solving the local pressure Poisson equation, which is applied to maintain particles' spacing in relative equilibrium. Based on this idea, formulas for the spatial averaged pressure and local fluctuating pressure are derived. The spatial averaged pressure is used as a primary estimation of the pressure gradient force and then the local fluctuating pressure is added as a correction of local density deviation. The proposed algorithm is verified by simulating the classic dam broken problem and then applied to simulate water wave breaking. A comparison of the particle configurations with previous studies at different times is shown. Good agreement between the present results and the previous results can be found. A discussion on computational efficiency is also carried out. The result shows that the proposed algorithm has better stability and can greatly reduce the computational time cost. © 2015 The Authors. Published by Elsevier Ltd. Source

Chen A.,China Institute of Water Resources and Hydropower Research | Sui X.,China Institute of Water Resources and Hydropower Research | Wang D.,China Institute of Water Resources and Hydropower Research | Liao W.,Beijing Institute of Water | And 2 more authors.
Ecological Engineering | Year: 2016

Wetlands are important habitats on biodiversity protection. In this study, the relationship between wetland and avifauna changes in the Yellow River Delta Wetland was studied. Remote sensing and geographic information system provided an advanced platform for the research. After the avifauna survey was performed from 2012 to 2013, the birds' variation and driving factors were analyzed. The results showed that the flow into the wetland increased continuously from 2000, and the increased of artificial wetland prevented the wetland degradation, although at the same time the total wetland area decreased. Medium grassland, tidal flat and pond are the three main landscapes which are beneficial for the habitation of birds. The migrating numbers of red-crowned crane increased significantly from 2005, and the overwintering numbers increased from 2009. The study results show that the key land use types for protecting endangered species of birds are medium grassland, tidal flat and pond landscapes. Wetland changes are sensitive to the birds and significantly affected by the flow. We suggest that the artificial wetland project should enhance the three land use type area to ensure the wetland restoration. © 2015 Elsevier B.V. Source

Wang Y.,Basin Water | Wang Y.,China Institute of Water Resources and Hydropower Research | Ren A.,China Renewable Energy Engineering Institute | Wang Y.,Chinese Academy of Geological Sciences | And 3 more authors.
Canadian Geotechnical Journal | Year: 2016

This paper presents the observed findings and laboratory test results of an anchor exhumed from Manwan Hydropower Station, China, that was installed 20 years ago. The prestressed cables are 25.6 m long with a working load of 1000 kN. It consists of eight strands, and each strand consists of seven wires. The anchor was installed using the “single protection” technique (i.e., the steel strands without greased sheath and were backfilled directly with cement mortar). The anchor was unearthed by excavating a 1.5 m × 1.7 m tunnel. Visual inspection shows that the steel strands in the free and fixed lengths are basically stainless except for a few places where the grout failed to cover the anchor completely, thereby allowing direct contact of the strands with air. The magnitude of rebound of the tendon during the advancement of the tunnel face was simultaneously measured indicating a gradual release of bonding force, which was up to 62% of the prestressed load. This shows that the existence of the bonding force is provided by the bonding between the strand and the grout, while this bonding does not exist in the “double protection” system. The results of the mechanical test confirm that the tensile strengths in all the 33 steel wires exceed the requirement as specified by a current Chinese Standard. The concentrations of various chemicals also satisfy the requirements as specified by the China State Bureau of Quality Technical Supervision. The results of the X-ray diffraction test show that the stains taken from the surface of the strand are composed of FeO and FeOOH, both being oxide products of iron. This shows that exposure of the material to air is an important condition to initiate corrosion. By following the ASTM International G1-03 test procedure, the average corrosion rate is found to be between 3 × 10−4 and 6 × 10−4 mm/year. This investigation generally supports the use of unprotected steel strands in rock anchor. © 2016, National Research Council of Canada. All rights reserved. Source

Zhang X.,China Renewable Energy Engineering Institute | Chen S.-H.,Hubei Engineering University
Yantu Lixue/Rock and Soil Mechanics | Year: 2015

Prestressed anchor technics is a primary measure to reinforce rock masses in geotechnical engineering. It plays an important role in mobilizing the self-bearing capacity of the rock masses and improving the strength and self-stability of the rock masses. Because of the complexity and diversity of anchoring engineering, anchoring mechanism has not been well understood, and the design theory and related computational method are insufficient for engineering applications. Two important problems remain to be addressed, which are related to the existing analytical solutions of the stress transfer along the anchored section of the prestressed anchor cable. Firstly the stress variation along the anchored section of prestressed anchor cable has not been well characterized,and secondly the stress singularity at the endpoint has not been considered in the existing analytical solutions. Through the analysis of applicability and limitation of the previous analytical solutions, it is shown that the stress distribution along the anchored section can be divided into three stages: elastic stage, plastic stage and failure stage. The stress distributions are different in different stages. Within this context, an expression is developed for calculating the transferred load in the above three stages. The shear stress and axial force distributions along the anchored section are determined. For a practical case, the critical anchorage length is determined by the proposed equation, and the result is compared to those of other methods, showing the validity and capability of the proposed procedure. ©, 2015, Academia Sinica. All right reserved. Source

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