Hidden Degree Applied in the Research on Incipient Motion of Cohesionless Sediment Particles
MENG Zhen, YANG Wen-jun
(Key Laboratory of Management of Rivers and Lakes & Flood Control of Ministry of Water Resources, Yangtze River Scientific Research Institute, Wuhan 430010, China)
Abstract : Based on the results of sediment hidden degree research, an incipient velocity formula with hidden degree as its parameter was deduced in this paper using the rolling model of sediment incipient motion. The formula was applied in limit analysis and monotonicity analysis to theoretically expound the physical phenomena of incipient motion and to demonstrate the starting characteristic of broadly graded non uniform cohesionless sediment. The numerical relations between hidden degree and non-dimensional incipient shear stress were established via the analysis on incipient motion criterion and the characteristic of hidden degree distribution of cohesionless sediment particles. Finally, former research achievements are taken to manifest the applicability of this incipient velocity formula.
Key words: hidden degree; incipient motion; limit; monotonicity; incipient motion conditions
Issues on Water Quantity Operation of Large-Sized Reservoirs in the Yangtze River Basin
YIN Zheng-jie, HUANG Wei, CHEN Jin
(Yangtze River Scientific Research Institute, Wuhan 430010, China)
Abstract : In light of the changes of water resources and water engineering conditions, water quantity operation of large-sized reservoirs has become an important part of water resources management in the Yangtze River basin. In this paper, the demand for water quantity operation of large-sized reservoirs is put forward, and the status quo of the operating work and existing problems are presented. Moreover, the capacity of water quantity operation of large-sized reservoirs on different tributaries and mainstream sections are also evaluated. Based on the above understanding, an overall framework of reservoir operation for water quantity is proposed. The framework includes operation targets and principles, reservoir selection criteria, operation contents, management system and supporting conditions. The research will provide decision making reference for the future integrated operation of water quantity of large sized reservoirs in the Yangtze River basin.
Key words: water quantity operation; hydropower reservoir; river basin management; Yangtze River basin
HEC-RAS for Risk Analysis of Flood Overtopping Inundation in Huainan Reach of Huai River
XU Wei1,2 , LIU Mao1, YANG Jie1, LI Chun-zhi2 , SHANG Xiao-juan3
(1.Research Center on Urban Public Safety, Nankai University, Tianjin 300071, China; 2.No.2 Construction Company of China Petroleum Pipeline Bureau, Xuzhou 221008, China; 3. School of Life Sciences, Tianjin Normal University, Tianjin 300387, China)
Abstract : There are a large number of people, factories, farmlands and buildings in Huainan area, the south part of Huai River. Big floods will severely endanger people ' s life and property. In this paper, HEC---RAS software and HEC-GeoRAS module are employed in GIS to simulate the flood overtopping inundation in Huainan reach of Huai River under the existing flood protection works during floods once in 40, 60, and 100 years respectively. The designed water level of different cross-sections, the overtopping inundation area, and the inundation depth data are obtained. The simulation manifested that the flood protection works in this reach are capable of handling floods once in 40 and 60 years, and can generally withstand floods once in 100 years. The simulated water level is consistent with the designed level. Therefore it is concluded that it is reasonable and credible to use HEC-RAS to simulate flood overtopping, and thereby providing reference for the early warning, the population evacuation planning, as well as flood disaster risk analysis.
Key words : HEC-RAS; Huai River; flood; overtopping; risk analysis
Response Surface Optimization Design for Cutting Slope Anchoring Parameter
WANG Yu1 , WEI Xian-zhong2 , SHAO Lian-fen1,2
(1.School of Engineering, China University of Geosciences, Wuhan 430074, China; 2.Huanghuai University, Zhumadian 463000, China)
Abstract: Scientific and reasonable parameter selection for anchored protection structure of cutting slope is of great significance as it can directly affect the engineering design, and thereby affecting the stability of highway slope. A Response Surface Methodology (RSM) design is proposed and is applied to the parameter selection of anchoring protection structure. The impact of anchoring support parameters on slope stability factor is studied, and a quantitative relation model between the stability factor and influencing factors is established. The residual distribution of stability factor and the stability coefficient contour and response surface 3-D graph of different operation variables are also given. Meanwhile, the test conditions are optimized and the optimal value of each parameter is obtained. Moreover, the response surface optimization is compared with the computation result of limit equilibrium method, and the optimized slope stability is evaluated. It is concluded that the optimal response surface design is reasonable and reliable. As an applicable method for the study of cutting slope stability, it provides a scientific basis for the design and optimization of cutting slope anchored support parameters.
Key words: cutting slope; anchored protection; RSM analysis; optimized design; stability factor
Risk Assessment System for Environmental Slope Hazard at Hydropower Project
JI Feng1 , DENG Zhong-wen2
(1.State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China; 2.Chengdu Hydroelectric Investigation & Design Institute of State Power Corporation, Chengdu 610072, China)
Abstract : The construction of hydropower station in west China gave rise to an increasingly obvious problem of environmental slope hazard. The stability of slope within the opening line received sufficient attention and regulation by human engineering activities; whereas the environmental slope outside the opening line still keeps its natural stability. It is neither necessary nor possible to make comprehensive analysis or extensive regulation on its natural state and to impose the same safety control standard as with excavated slopes. In addition, the lack of standard guidance or research documents published for reference brings about neither systematic nor unified evaluation criteria and protective measures, which has become a potential safety hazard for the construction and operation of hydropower stations. In this paper, issues regarding the defining, classification, slope safety level, prevention and control criterion of environmental slope hazard are expounded, and a risk assessment system is proposed to provide basis for further research.
Key words : hydropower station; environmental slope; hazard; risk assessment system
Physical and Chemical Reaction Between River Water and Clayey Soil from Reservoir Landslide
BI Ren-neng1 , XIANG Wei2 , GUO Yi1 , LI Tao-tao1 , WANG Jing-e1
(1.Faculty of Engineering, China University of Geosciences, Wuhan 430074, China; 2.Three Gorges Research Center for Geohazard of Ministry of Education, China University of Geosciences, Wuhan 430074, China)
Abstract: Water level fluctuation in reservoir intensifies the water-soil interaction between river water and loose soil of landslide deposit, and thereby profoundly affecting the engineering properties of surface rock-soil. The impact of river water on the engineering property of clayey soil at the reservoir bank is studied from the perspective of water-soil interaction. Contrast tests including X-ray diffraction, Zeta electric potential, exchangeable cation types, shear test for consolidated samples, and SEM are performed to study the change of components, microstructure and shear strength of clayey soil from landslide before and after the interaction. It is concluded that Zeta electric potential at the surface of soil particle decreases under the combined effect of hydration and cation absorption. The thickness of absorbed water of soil grains decreases, and the microstructure and shear strength of remoulded soil are somewhat varied as the cations absorb divalent cations to soil grains. Moreover, dilatancy effect is generated due to the change of soil particle structure in the shear test of water-treated clayey soil. The mechanism of water-soil interaction affecting on the engineering properties of fine-grained soil is finally revealed.
Key words: water-soil interaction; cation absorption; Zeta potential; shear strength; microstructure
Research on Risk Probability Model and Calculation Method for River Closure System
HE Chang-hai1 , LIU Yong-yue2
(1.Experimental Research Center on Hydraulic Model, State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072 China; 2. Department of Power Generation, Heilongjiang Provincial Research Institute of Electric Power Exploration and Design, Harbin 150010 China)
Abstract : To make scientific decision on river closure for water conservancy and hydropower projects, this paper firstly makes a brief review on the research history of river closure risk. Based on the actual engineering, the random factors of river closure system are identified, and the resulting factors of possible risk events are analyzed. Taking the hydrological, hydraulic and construction uncertainties into consideration, a new mathematical model is proposed and the calculation of risk probability for river closure system is improved. The model uses average velocity, water depth and average dumping intensity at the closure gap axis as risk variables to assess the integrated risk of the river closure system. Furthermore, by comparing the defects and merits of different calculation methods, the Monte-Carlo method of calculating the risk probability based on complete hydraulic calculation is put forward. At last, problems including the correlation of risk variables, dynamic and static risk differentiation, sampling frequency, and sampling error are discussed and a specific numerical example is presented. The calculation results show that the integrated risk of the river closure system varies greatly with the change of designed discharge and is closely correlated with dumping intensity which indicates the organizing ability of the construction.
Key words : river closure system; risk probability; Monte-Carlo method; construction uncertainty; sampling error
Comparison of Numerical Approaches of Simulating Seepage Flow with Free Surface
JIANG Sheng-yin1 , LI Lian-xia1 , LIAO Hua-sheng1 , YANG Hua1 , ZOU Jun2
(1. State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Sichuan 610065, China; 2. Pearl River Hydraulics Research Institute, Guangzhou 510611, China)
Abstract : The fixed grid methods can be classified into initial flow method, variable seepage coefficient method, variational inequality method, node imaginary flow method, imaginary elements method and the water free surface adaptive grid method which was put forward recently. Each method has its advantages and disadvantages. To ultimately guide us to choose proper methods when processing the practical seepage problems in large scale, it is of great value to evaluate their applicability including flexibility, robustness, numerical stability, computational efficiency and reliability by comparing the accuracy, iterative steps, grid sensitivity, and initial free surface sensitivity of three different fixed grid methods. The results show that the water free surface adaptive grid method is of higher computing efficiency and accuracy than the other two methods in the same grid system. The initiative steps are less, and the accuracy of computing results is less sensitive to the initial free surface and grid density than the other two methods.
Key words: free surface of seepage flow; numerical simulation; fixed grid methods; method of water free surface adaptive grid
Critical Velocity and Seepage Discharge for Identifying Piping Risks below the Downstream Embankment and Its Application in Flood Control
MAO Ning, MAO Chang-xi
(Nanjing Hydraulic Research Institute, Nanjing 210024, China)
Abstract : During flood season, piping risk in the downstream of embankment is the most dangerous hidden trouble. The discrimination of piping in the past was generally based on seepage gradient which is not only limited theoretically by Darcy ' s flow but also inconvenient in practice. In view of this, a method of identifying piping below embankment, which can be called critical velocity or unit seepage discharge observation method, is suggested in this paper. It is based on the experimental curve of drag coefficients for single immersed spherical body moving steadily in water as well as the seepage experimental results for porosity relationship of grained soil mass. Furthermore, the empirical formulas for different flow patterns (Darcy and non-Darcy ' s flow) of the experimental curve are given to calculate the critical velocity. A table for the critical velocity and seepage discharge of different kinds of soil mass is also given. In practice, it only needs to measure the seepage discharge per unit by surrounding a suitable ring on the permeable surface to determine whether piping will happen or not.
Key words : piping; embankment; critical velocity; critical seepage discharge; non-Darcy’s flow; flood prevention during flood season
Slope-Angle-Increasing Method for Safety Factor Calculation and Its Application
CHEN Li-jie 1, CAI Xue-yan 1, WANG Zheng-zhong 2
(1. Institute of Agro-products Processing Science & Technology, Chinese Academy of Agricultural Sciences, Beijing 100193, China; 2.Research Center of Water Engineering Safety and Disaster Prevention, Northwest A&F University, Yangling 712100, China)
Abstract : Slope instability is a complex problem in road and bridge engineering, hydraulic engineering, and construction engineering. The mechanism of slope instability has long been an important content of geotechnical engineering research. Nonetheless, among various slope stability analysis methods, traditional limit equilibrium method is complicated, nonobjective, and cannot provide the only safety coefficient; while the convenient and practical strength reduction method can not reflect the mechanism of slope instability. In this paper, a simple and intuitive slope-angle-increasing method which reflects the slope instability mechanism is proposed. This method is based on the principle of geotechnical centrifuge and limit equilibrium and is demonstrated by example calculation. The method is to increase the slope angle gradually so that the sliding force is increased and the anti-sliding force is reduced until the slope instability reaches its limit and slope failure happens. In this way, the correlation between slope angle and safety factor can be deduced. The method is demonstrated by example calculation and the result is compared with that of traditional limit equilibrium method and finite element strength reduction method. The comparisons show that slope-angle-increasing method can be applied to slope projects of low groundwater level, and offers a new research idea for slope stability analysis.
Key words: slope; safety factor; geotechnical centrifuge model; limit equilibrium theory; slope-angle-increasing method
Determination of the Maximum Dynamic Shear Modulus Based on Improved RBF Neural Network
CHEN Zhi-qiang, WANG Liang-qing, LIU Shun-chang, FENG Guang-liang
(Faculty of Engineering, China University of Geo-sciences, Wuhan 430074 , China)
Abstract : To avoid the complicated work of searching for quantitative experiential formula, a nonlinear relationship between maximum dynamic shear modulus(Gmax) and the influence factors including void ratio(e), cell pressure(σ3), and consolidation ratio(kc) was built directly by using Radial Basis Function(RBF) neural network. In addition, the optimal value of spread speed(SPREAD) of RBF was calculated by pattern search method to minimize the prediction error. Taking standard sand in Fujian province as an example, the optimal value of SPREAD calculated by pattern search method equals to 2.287 , and the average relative error of Gmaxpredicted by RBF neural network is 0.931 6 % , which is quite small. It shows that RBF neural network can determine Gmax under different conditions conveniently and effectively. Besides, the relationship curve ofG-γcan also be simulated by this network. Therefore, the method of using RBF neural network to calculate the maximum dynamic shear modulus is recommended to be used widely.
Key words : radial basis function neural network; maximum dynamic shear modulus; Hardin formula; pattern search method
Mechanical Simulation of Freezing Method Applied to the Construction of Connected Aisle in a Cross River Tunnel
LI Kai-wen 1 , MAO Yong 1 , SUN Chuang 2 , ZHU Ze-qi 3
(1.Nonferrous Metals Industry Survey and Design Institute, Kunming 650000, China; 2.Liaoning Technology University, Fuxin 123000, China; 3.Institute of Rock and Soil Mechanics ,Chinese Academy of Sciences, Wuhan 430071, China)
Abstract : To ensure the safety of the excavation of connected aisle in a cross-river tunnel by directly looking into the mechanical features of freezing soil curtain and the impact of the excavation on the curtain, large finite difference software FLAC 3D is employed to numerically simulate the excavation process. Through the simulation, the stress and deformation of the freezing curtain are analyzed and its safety is evaluated. Moreover, the stress and displacement distributions of the curtain are further analyzed in detail. The designed thickness of the freezing soil curtain is determined to be safe at 2.5 m , which meets the construction requirements. It is also pointed out that the contact location between the freezing soil curtain and the tunnel should be given more concern as it is easy to see stress concentration because of quick heat dissipation during the freezing with unsatisfactory freezing effect. The study can serve as a reference for the artificial freezing technique and the numerical simulation of connected aisles.
Key words :connected aisle; freezing metho; numerical simulation; freezing soil curtain; FLAC 3D
Seepage Stability of Upstream Slope of Earth Dam During the Drawdown of Reservoir Water Level
ZHANG Da-wei 1, YAN Wen-qun 2
(1.Management Office of Lianyungang Shilianghe Reservoir, Lianyungang 222323, China; 2.College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou 225009, China)
Abstract : When reservoir water level drops sharply and rapidly from long-time high-level storage, the falling velocity of reservoir water level and soil property will exert adverse impact on the stability of upstream slope soil mass. The hazard of seepage on the upstream slope surface is demonstrated by seepage analysis softwares (Geoslope and unsst2). Fitted curves between k/μv and critical descent altitude of reservoir levels when flow with free surface does not appear are presented. Moreover, both the influence of soil anisotropy caused by various factors and the impact of substrate suction internal frictional angleφb on the stability of upstream slope seepage are also considered. The study reveals that all possible factors in practical projects and the results of seepage field calculation should be considered in the analysis of the seepage stability of upstream slope during the drawdown of reservoir level.
Key words: drawdown of reservoir water level; seepage stability; critical gradient of seepage from slope surface
Sensitivity Analysis on Influencing Factors of Shallow Landslide of Coal Measure Strata
ZHU Lei 1,2, HONG Bao-ning 3
(1.Water Resources Research Institute of the Huaihe River Commission of the Ministry of Water Resources, Bengbu 233000, China; 2.Construction Quality Supervision and Test Station of Anhui Province, Hefei 230088, China; 3.Geotechnical Research Institute of Hohai University, Nanjing 210098, China)
Abstract : Elasto-plastic contact FEM with strength reduction method is employed to study the sensitivity of main influencing factors of coal measure strata shallow landslides. The calculation indicates that the sensitivity of shallow landslide stability of coal measure strata ranges from maximum to minimum as follows: the slope degree, the cohesion of slip surface soil, the internal friction angle of slip surface soil, the weathering depth, and the slope height. Elastic modulus and Poisson’s ratio of rock-soil mass have less impact on the stability of shallow landslide of coal measure strata. The research results provide theoretical reference for the design, construction and treatment of coal measure strata slopes.
Key words : coal measure strata; shallow landslides; elastoplastic FEM; contact algorithm; sensitivity
Design and Implementation of Management Information System for the Administrative Enforcement of Water Law
WU Jie, LI Kai
(Nanjing Yangtze River Waterway Management Department, Nanjing 210011,China)
Abstract :Based on the analysis on the current situation of the administrative enforcement of water law in Nanjing waterway of the Yangtze River, the demands and targets of the management information system for the enforcement of water law are put forward. Basic information database of the waterway and the database of the departments which occupied the waterway are the core of this system. Technologies including WebGIS, computer network, and modern wireless communication are adopted to set up the enforcement system. The system is operated and managed on the basis of the administration department ' s intranet.
Key words: administrative enforcement of water law; information system; WebGIS
Impact of TGP Operation on the Hydrologic Regime in the Downstream Main Channel of the Dam
HUANG Yue, YAO Shi-ming, LU Jin-you
(Yangtze River Scientific Research Institute, Wuhan 430010, China)
Abstract : The operation of Three Gorges Project (TGP) changes the flow and sediment conditions in the downstream river channel of the dam, and will further affect the hydrologic regime of its downstream river channel. Using one dimensional mathematical models of flow and sediment, the changes of flow, water level and sediment load influenced by TGP operation along the downstream main river during high, average and low flow years are respectively calculated and analyzed. Results reveal that the flow increases during low-water and water-discharging seasons, and the downstream streamwise low water level of the dam rises accordingly. During storage period the discharge flow decreases and streamwise water level drops. During a low-flow year, the impoundment of the reservoir causes an excessively small inflow into the downstream river channel of the dam (with the average discharge at Datong hydrometric station less than 9 000m3/s in late October). Whereas during the storage period of an average flow year, the water level at middle and lower Yangtze River drops substantially with the streamwise water level drop in the range of 1.71 -3.68m , which influences the navigation and water supply in the downstream river channel of the TGP dam.
Key words: TGP; typical hydrological years; hydrologic regime; mathematical model
Changes of the Stage Discharge Relation in Jingjiang River after the Impoundment of Three Gorges Reservoir
GUO Xiao-hu, QU Geng, ZHU Yong-hui
(Laboratory of River Regulation and Flood Control of MWR, Yangtze River Scientific Research Institute, Wuhan 430010, China)
Abstract : The change of stage-discharge relation along the Jingjiang river is analyzed based on the field data before and after the impoundment of Three Gorges Reservoir. Results show that the water level during low flowrate at Zhicheng station decreased slightly. Apart from that, the water level during medium and low flowrate decreased to some extent at stations in the upper Jingjiang reach, among which Shashi station witnessed the largest decline of low water level. The water level in lower Jingjiang reach also decreased slightly under the same flowrate. Moreover, the change of stage-discharge relation in Jingjiang reach is mainly caused by the Jingjiang river erosion, in particular, the erosion in the low water river channel. In addition, the changes of low water level at Zhicheng station is caused by the sand hole and stone pond formed by the shallows of the Lujia River.
Key words: Jingjiang river; water level; scouring