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HYDROLOGICALLY DRIVEN MECHANISMS OF headcut DEVELOPMENT

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International Journal of Sediment Research 2005年第3期20卷 22-30页

作者： M. J. M. RMKENS,S. N. PRASAD USDA-ARS National Sedimentation Laboratory Oxford MS 38655 USA Department of Civil Engineering University of Mississippi University MS 38677 USA

An analytic investigation of the effect of surface seal mechanical properties, overland flow, and subsurface hydrology was performed on headcut development. headcut growth rates on upland areas have been observed to be quite small (less than 0.00015 meter per second) and that they occur in increments in which chips break off at points where cracks have developed in surface seals. The substrate soil under the seal collapses and is removed by the flow. This mode of headcut development is the result of a strong interaction between the surface and the subsurface processes. The surface process is energetically controlled by the mechanical features of the seal whereas the subsurface process is hydrologically controlled. The analysis yields estimates of the temporal scale of headcut velocities. In cases of infiltration from the vertical gully wall into the substrate, the flexural wave velocity (seismic sound velocity) was found to inversely affect headcut velocity.

关键词： Surface seal Subsurface headcut Soil erosion Overland flow

Overtopping breaching of cohesive homogeneous earth dam with different cohesive strength

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Science China(Technological Sciences) 2009年第10期52卷 3024-3029页

作者： ZHANG JianYun LI Yun XUAN GuoXiang WANG XiaoGang LI Jun Nanjing Hydraulic Research Institute Nanjing 210029China State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Nanjing 210029China

In consideration of the range of clay content of Chinese earth dams, the world's highest prototype tests have been made to research on the effects of cohesive strength of filling of cohesive homogeneous earth dam on breach formation. Three breach mechanisms were presented, they were the source-tracing erosion of dam body with the form of "multilevel headcut", "two-helix flow" erosion of dam crest and collapse of breach sidewalls due to instability. It can be concluded that the cohesive strength of filling of earth dam has great effect on breach formation. When the cohesive strength is bigger, the breach process becomes slower, and the peak outflow and the final width and depth of breach become smaller. The main character of the breach formation is head cutting and dumping collapse. When the cohesive strength is smaller, the breach process becomes faster, and the peak outflow, the final width and depth of breach become bigger. The main character of the breach formation is single level head cutting and shearing collapse.

关键词： earth dam breach mechanism headcut two-helix flow

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Numerical model for homogeneous cohesive dam breaching due to overtopping failure

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Journal of Mountain Science 2017年第3期14卷 571-580页

作者： ZHONG Qi-ming CHEN Sheng-shui DENG Zhao Department of Geotechnical Engineering Nanjing Hgdraulic Research InstituteNanjing 210024China Nanjing Hgdraulic Research Institute Nanjing 210029China Key Laboratory of Failure Mechanism and Safety Control Techniques of Earth-rock Dam of the Ministry of Water Resources Nanjing 210029China

Based on the large-scale model tests, a simplified dam breach model for homogeneous cohesive dam due to overtopping failure is put forward. The model considers headcut erosion as one of the key homogeneous cohesive dam breaching mechanisms and we calculate the time-averaged headcut migration rate using an energy-based empirical formula. A numerical method is adopted to determine the initial scour position at the downstream slope in terms of the water head and dam height, and the broad-crested weir equation is utilized to simulate the breach flow. The limit equilibrium method is used to analyze the stability of breach slope during the breach process. An iterative method is developed to simulate the coupling process of soil and water at each time step. The calculated results of three dam breach cases testify the reasonability of the model, and the sensitivity studies of soil erodibility show that sensitivity is dependent on each test case's soil conditions. In addition, three typical dam breach models, NWS BREACH, WinDAM B, and HR BREACH, are also chosen to compare with the proposed model. It is found that NWS BREACH may have large errors for cohesive dams, since it uses a noncohesive sediment transport model and does notconsider headcut erosion, WinDAM B and HR BREACH consider headcut erosion as the breaching mechanism and handle well homogeneous cohesive dam overtopping failure, but overall, the proposed model has the best performance.

关键词： KeHomogeneous cohesive dam Overtopping headcut Initial scour position Sensitivity analysis Models comparison

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Experimental investigation on breaching of embankments

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Science China(Technological Sciences) 2011年第2期54卷 148-155页

作者： ZHU YongHui VISSER P J VRIJLING J K WANG GuangQian State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China Changjiang River Scientific Research Institute Changjiang Water Resources Commission Wuhan 430010 China Faculty of Civil Engineering and Geosciences Delft University of Technology Delft 2600 GA Netherlands

Breaching of embankments has recently drawn more and more attention due to its importance in the development of early warning systems for embankment failures,in the evacuation plans of people at risk,in the design method of embankments based on a risk-approach,etc. The erosion process observed during embankment breaching tests in the laboratory and the analysis of the results are described in this paper. Five embankments,one constructed with pure sand,four with different sand-silt-clay mixtures were tested. The height of the embankments was 75 cm and the width at the crest was 60 cm. Examination of the data from these tests indicated that headcut erosion played an important role in the process of breach growth in the embankments made of cohesive soil mixtures. Flow shear erosion,fluidization of the headcut slope surface,undermining of the headcut due to impinging jet scour and discrete soil mechanical slope mass failure from the headcut were all observed during these tests. For the embankment constructed with pure sand,the breach erosion process was dominated by shear erosion,which led to a gradual and relatively uniform retreat of the downstream slope. The cohesive proportion in the sand-silt-clay mixtures strongly slowed down the erosion process.

关键词： embankments breaching experiments headcut erosion

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OVERVIEW OF DAM GULLY EROSION RESEARCH

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International Journal of Sediment Research 2005年第3期20卷 105-115页

作者： G. J. HANSON,D. M. TEMPLE,K. M. ROBINSON,K. R. COOK USDA-ARS HERU Stillwater USDA-ARS HERU Stillwater USDA-NRCS ENTSC Greensboro USDA-NRCS State Office Stillwater

Traditionally gully erosion has been identified with the dissection of the landscape in agricultural settings but it is also recognized as a prevalent erosion feature in earthen dam auxiliary spillways and embankments. Flows through earthen spillways and over dam embankments, due to large rainfall events, have the potential to erode and breach the dam or spillway and result in catastrophic releases from the reservoir. The gully erosion process in an earthen spillway or on an embankment can be characterized by stages of initiation, development, and migration of a headcut. A headcut is defined as a near vertical drop at the upstream end of a gully. The rate of headcut migration is important in determining the breach potential of an earthen spillway and dam embankment. A research program is being conducted to examine the gully erosion processes of earthen dam auxiliary spillways and embankments. This paper describes: 1) the unique test facilities constructed to examine the dominant factors affecting the erosion of earthen spillways and embankments; 2) the observations of the erosion processes and results to date; and 3) the predictive relationships that have been developed for dam gully erosion research at the ARS Hydraulic Engineering Research Unit laboratory in Stillwater, OK.

关键词： Dams Erosion Spillways Embankments Gullies headcut Breach

A Study on the impact of sand extraction on riverbed evolution in lower reaches and delta of the Dongjiang River

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A Study on the impact of sand extraction on riverbed evoluti...