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1.
针对缺乏地形条件和工程处置措施对堰塞坝溃决过程影响研究的现状,采用4种河床坡度（0°、1°、2°、3°）和3种泄流槽横断面型式（三角形、梯形、复合型）,开展了堰塞坝溃决的模型试验。通过分析堰塞坝的溃决流量、溃决历时、溃口发展和坝体纵截面演变过程,研究了不同河床坡度和泄流槽横断面对堰塞坝溃决过程的影响规律。试验结果表明：... 相似文献
2.
为了解堰塞坝在不同沟床坡度地段的溃口展宽历程,进行了沟床坡度为7°~13°,间隔为1°的7组水槽试验。对比分析7组试验观测数据,评价不同沟床坡度对堰塞坝溃口展宽历程的影响。得到如下结果及结论:(1)漫顶破坏的堰塞坝在不同沟床坡度地段的溃口展宽历程是十分相似的,根据其溃决特征,可将其展宽历程划分为溃口贯通、突变和稳定边坡形成等3个阶段。(2)在突变阶段溃口边坡沿x轴方向会发生多次失稳,溃口顶部形态在背水坡呈“S”型,在坝顶呈“U”型,在迎水坡呈“弧”型。(3)不同沟床坡度条件会影响突变阶段的溃决特征,随沟床坡度的增加突变阶段溃口边坡单次失稳规模表现出先增大后减小的特征,溃口边坡失稳次数呈现出先减少后增加的特征。(4)溃口边坡的稳定性主要取决于溃口的侧蚀宽度和下蚀深度,其与溃口顶、底部侧蚀宽度之差呈负相关关系,与溃口下蚀深度呈正相关关系。(5)不同沟床坡度堰塞坝的溃决流量随溃决时间的延长具有相同的变化趋势,但不同沟床坡度堰塞坝的溃决峰值流量和峰值流量到达时间却不尽相同,随沟床坡度的增加峰值流量逐渐减小,峰值流量到达时间先提前后推迟。 相似文献
3.
A computational model system is proposed for the prediction of sea dike breaching initiated from the seaward side by breaking
wave impact with the focus on the application of the model system for the estimation failure probability of the defence structure.
The described model system is built using a number of existing models for the calculation of grass, clay, and sand erosion.
The parameters identified as those having the most significant influence on the estimation of the failure have been described
stochastically. Monte Carlo simulations to account for uncertainties of the relevant input parameters and the model itself
have been performed and the probabilities of the breach initiation and of the full dike breaching have been calculated. This
will form the basis to assess the coastal flood risk due to dike breaching. 相似文献
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5.
终碛坝广泛分布于世界各地的高山和极高山区。为了探究终碛坝的溃决过程,了解溃口的演变特征,文章以嘉龙错终碛坝的原位实验,模拟了终碛湖漫顶溃决过程。通过分析实验结果发现:（1）根据观察,将终碛坝溃决过程划分为坝体下游坡面冲刷、“溯源侵蚀”、出水口下切和溃口拓宽四个阶段。（2）上游湖区崩塌体激发的涌浪会造成溃口内的瞬时流量增加数倍,从而使得在有涌浪和无涌浪的条件下,“溯源侵蚀”过程出现陡坎和斜坡两种下切型。（3）通过分析溃口下切侵蚀过程,发现溃口的下切侵蚀发展过程主要受到坝体孔隙比和细粒含量的影响,并且溃口中点侵蚀率与水流剪应力存在一定的线性关系,符合线性侵蚀模型。通过分析发现,嘉龙错终碛坝的侵蚀系数为0.051,临界启动应力为237.64 Pa。与堰塞坝相比,可侵蚀系数比更小,而临界启动应力更大。 相似文献
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利用野外径流小区动态监测和人工模拟降雨试验,阐明了草被和灌木的减流减沙效应,从力学层面揭示了坡面侵蚀产沙的过程机理。结果表明,与裸地相比,野外坡面草地和灌木地径流量分别减少28.1%~56.5%和85.7%~100%、产沙量分别减少84.9%~90.7%和98.5%~100%;在人工模拟降雨强度下,草地和灌木地径流量分别减少51.9%~90.9%和61.7%~80.6%、产沙量分别减少93.6%~99.2%和95.5%~99.2%;植被具有明显的增强土壤抗剪强度的作用,不同植被坡面抗剪强度与剪切面上的法向压力成正比,且符合库仑定律;不同下垫面条件下土壤黏聚力与坡面径流量和侵蚀产沙量呈显著的负相关关系,随着黏聚力的增大,径流量和侵蚀产沙量呈下降趋势;草地和灌木地坡面侵蚀临界径流切应力分别为裸地的2.64~3.16倍和2.44~3.18倍,建立了不同被覆坡面临界径流切应力与土壤抗剪强度和黏聚力的关系。研究结果对定量评价植被减蚀作用和深化土壤侵蚀力学过程有一定的参考意义。 相似文献
7.
The breach of landslide dam often causes significant disaster in the inundated area; the prediction of breach hydrograph is in high demand for the dam breach risk evaluation. In this study, according to the model tests and Tangjiashan landslide dam breach case, the surface erosion accompanied by intermittent mass failure is known as the key breaching mechanism for landslide dam due to overtopping failure. The downstream slope angle would gradually decrease during the dam-breaching process, whereas a planar wedge failure occurs when the breach slopes at the dam crest and downstream breach channel fail. Based on the breach mechanism, a numerical model for landslide dam breach due to overtopping is developed to simulate the coupling process of water and soil. The model focuses on the breach morphology evolution during the breaching for the sake of the improvement of breach hydrograph prediction. Furthermore, the model can handle one- and two-sided breach, as well as incomplete and base erosion at the vertical direction. The case study of Tangjiashan landslide dam-breaching feedback analysis testifies the rationality of the present model with the relative errors less than 10% for peak discharge, final breach widths, and time to peak. The sensitivity analysis indicates that the final breach depth and soil erodibility affect the breach flow prediction of the landslide dam significantly, whereas the one- or two-sided breach mode is less sensitive. 相似文献
8.
Lin Li Yi Pan Farshad Amini Kuang Cuiping Jean-Louis Briaud 《Geotechnical and Geological Engineering》2014,32(4):847-857
Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and land-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. This study addresses erosion resistance performance of a levee strengthening technique—high performance turf reinforcement mat under combined wave and surge overtopping conditions using full-scale flume tests as well as erosion function apparatus (EFA) tests. Based on the results of full-scale flume tests, an “upper limit” of soil loss is observed for certain flow conditions. Erosion rate was presented as a function of velocity and freeboard. The effect of duration of overtopping on the erosion depth is also determined. The results of EFA tests indicate that the presence of grass roots substantially improve the critical velocity and soil erodibility. 相似文献
9.
堤防溃决时溃口附近水流形态及溃决流量变化过程的正确描述是指导溃口堵复及时避险、预测溃堤洪水演进并进一步评估淹没损失的前提条件.通过弯道水槽中的概化模型试验,根据无粘性土堤防漫顶溃决的溃口变化和水流运动特征,将无粘性土堤防溃决过程分为漫流、冲槽、展宽及稳定4个阶段.试验系统研究了堤防溃决后河道以及溃口附近水位的变化过程,研究了河道洪水流量、洪水位和筑堤材料对溃口处水位的影响.基于大量的试验资料,进一步归纳总结出溃决流量与溃口口门宽度及溃口处水头变化之间的关系. 相似文献
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Breaking tests on homogeneous earth-rock-fill dams destroyed by overtopping flow are presented. Two types of shear erosion are found: wetting shear erosion and quick shear erosion; the water level-discharge process is divided into “sharp rise and drop of flow” and “slow change of flow” types. Furthermore, overtopping break modes are divided into head-cut erosion and scour breaching mode (Mode 1), shear erosion and collapse breaching mode (Mode 2), and wetting shear erosion mode (Mode 3) based on the main failure types and their coupled mode during dam break. In Mode 1, the downstream slope encounters head-cut erosion at the onset of the breach and expands and undercuts gradually at the development stage; in Mode 2, the dam slope encounters rapid shear erosion and the downstream edge of the crest erodes quickly towards the upstream face at the onset of breach: the breach expands suddenly due to instability and collapse at both sides of the breach in its development stage; in Mode 3, the strength of the dam’s materials continuously decreases by wetting and erosion happens is localised at positions where wetting caused the most strength loss, no obvious breach was developed. Dam breaking time, dam-break flow process, and the maximum discharge flow varied for each breaking mode. Overtopping flow size, materials, height, and initial breach size of dam are important factors influencing breaking mode, by virtue of their changing the relative strength of the relationship between the critical shear stress of dam materials at the edge of the dam crest and the lower parts of its slope, and the given flow’s destruction capacity. Overtopping will cause different manifestations of damage to be exhibited, so modal classification is favourable for safety assessment and preparation of relevant protective measures for protection of earth-rock-fill dam against overtopping. 相似文献
12.
Field investigation of erosion resistance of common grass species for soil bioengineering in Hong Kong 总被引：1，自引：0，他引：1
Grass cover is considered as a sustainable means of controlling soil erosion and enhancing durability of soil slopes. A number of grass species are commonly available for soil bioengineering in Hong Kong, but their capacities to control soil erosion have not been characterized quantitatively. The main objectives of this paper are to study the influence of soil density on characteristics of grass roots, to measure the erodibility parameters of the root-permeated soils at two growth stages, and to select the proper Hong Kong grass species that effectively control soil erosion. Three types of Hong Kong turf grass including Cynodon Dactylon, Paspalum Notatum, and Zoysia Matrella were planted on three soil grounds with degrees of compaction of 80, 90, and 100 %, respectively. The featural parameters of grass roots on each compacted ground, including root mass density, root volume density, and root depth, were measured in two growth stages. A jet index apparatus was applied to measure two erodibility properties (i.e., coefficient of erodibility and critical shear stress) of these vegetated soils in the two test stages. Cynodon Dactylon and Zoysia Matrella have higher root mass density values than Paspalum Notatum does, and reduce the susceptibility of soil erosion more effectively. Therefore, the two grass species are suggested for soil bioengineering in Hong Kong. 相似文献
13.
Slope Stability Analysis of Earthen Levee Strengthened by High Performance Turf Reinforcement Mat under Hurricane Overtopping Flow Conditions 总被引：1，自引：0，他引：1
The slope stability of levees during hurricane overtopping conditions involving storm surge and wind generated wave action is an important aspect to assess the safety of earthen levees. A comprehensive slope stability investigation was conducted in this study for an earthen levee subjected to full-scale overtopping scenarios, including storm surge only overflow, wave only overtopping, and combined wave and surge overtopping conditions. The crest and the landside of the levee were strengthened by high performance turf reinforcement mat (HPTRM) to protect against overtopping erosion. A conceptual model for HPTRM strengthened levee as well as a methodology for analysis and incorporation of various overtopping flow conditions in levee slope stability is presented. The findings of this study indicate that HPTRM strengthening of the levee improves the stability of the levee significantly during wave only as well as combined storm surge and wave overtopping conditions. However, during the storm surge conditions, the factor of safety is only improved slightly as a result of strengthening of the levee by HPTRM. 相似文献
14.
为研究生产堤溃口横向展宽过程的发展规律,以黄河下游生产堤土体为材料,开展概化模型试验,分析溃口处水深、流速、流量以及溃口宽度的变化。试验结果显示,溃口横向展宽的机理主要表现为水流冲刷堤身下层土体伴随上层悬臂土体发生绕轴崩塌;随着溃口展宽,堤前水深持续下降但下降速率逐渐减小,溃口流速呈先增大后减小的趋势,流速峰值约为1.1 m/s;随着主槽流量增加,溃口宽度发展至0.7 m时,溃口的水深、泄流流量、流速、展宽速率均有所增加。基于对溃口展宽的影响因素分析,提出溃口横向展宽速率的计算关系式,计算溃口展宽过程与实测值符合较好。研究结果不仅有助于生产堤展宽机理及发展规律的研究,还可为数学模型的建立与验证提供参考资料。 相似文献
15.
为研究生产堤溃口横向展宽过程的发展规律,以黄河下游生产堤土体为材料,开展概化模型试验,分析溃口处水深、流速、流量以及溃口宽度的变化。试验结果显示,溃口横向展宽的机理主要表现为水流冲刷堤身下层土体伴随上层悬臂土体发生绕轴崩塌;随着溃口展宽,堤前水深持续下降但下降速率逐渐减小,溃口流速呈先增大后减小的趋势,流速峰值约为1.1 m/s;随着主槽流量增加,溃口宽度发展至0.7 m时,溃口的水深、泄流流量、流速、展宽速率均有所增加。基于对溃口展宽的影响因素分析,提出溃口横向展宽速率的计算关系式,计算溃口展宽过程与实测值符合较好。研究结果不仅有助于生产堤展宽机理及发展规律的研究,还可为数学模型的建立与验证提供参考资料。 相似文献
16.
Jiang Xiangang Huang Jiahua Wei Yunwei Niu Zhipan Chen Fenghui Zou Zuyin Zhu Zhanyuan 《Landslides》2018,15(2):243-255
In this study, a series of natural dam overtopping laboratory tests are reported. In these tests, the effect of seven different sediment mixtures on the breaching process was investigated. According to the test results, three stages of the breaching process of natural dams made of different materials were observed. Backward erosion was the primary cause for the incising slopes. The effects of backward erosion became stronger with the larger fines contents of the materials. With an increase in the median diameter (d 50) of particles, the breaching time became longer. However, the peak discharge became smaller. With an increase in the fines contents (p), the median diameter of the particles and the void ratio were changed, which resulted in a decrease in the breaching time and an increase in the peak discharge. The breaching time and peak discharge were more sensitive to the median diameter than to the fines contents. The relation between breach width and depth was found to follow a logistic function \( W\kern0.5em =\kern0.5em \frac{\zeta }{1\kern0.5em +\kern0.5em {e}^{\left(-k\left(D\kern0.5em -\kern0.5em {D}_0\right)\right)}} \). The parameters ζ, k, and D 0 are defined by a linear relationship with the median diameter and fines content. A breach of the side slope occurred as a tensile failure when the fines contents of the materials were large; otherwise, shear failure occurred. Furthermore, when the materials had fewer fines contents, the volume of the collapsed breach side slope became larger. 相似文献
17.
Quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope 总被引：2，自引：0，他引：2
Two-dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows. The results suggest that in natural flows, turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser-grained beds in the bottomsets of Gilbert-type fan deltas. Experimental flows were generated on 0°, 3°, 6° and 9° slopes of equal length which terminated abruptly on a horizontal bed. Two-component velocities were measured on the slope, at the slope break and downstream of the slope break. Flows were depositional and non-uniform, visibly slowing and thickening with distance downstream. One-dimensional continuous wavelet transforms of velocity time series were used to produce time-period variance maps. Peaks in variance were tested against a background red-noise spectrum at the 95% level; a significant period banding occurs in the cross-wavelet transform at the slope break, attributed to increased formation of coherent flow structures (Kelvin–Helmholtz billows). Variance becomes distributed at progressively longer periods and the shape of the bed-normal-velocity spectral energy distribution changes with distance downstream. This is attributed to a shift towards larger turbulent structures caused by wake stretching. Mean velocity, Reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents. A turbulent kinetic energy transfer balance shows that flow non-uniformity arises through the transfer of mean streamwise slowing to mean bed-normal motion through the action of Reynolds normal stresses. Net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed-normal motion is limited. At the slope break, an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free-shear boundaries at the bottom and top of the flows, respectively. A rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope. The increased turbulent kinetic energy, limited bed-normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period. Thus, mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break. The internal effects of flow non-uniformity therefore can be separated from the external influence of the slope break. 相似文献
18.
Effects of sheet flow rate and slope gradient on sediment load 总被引：2，自引：0，他引：2
Sheet erosion is known as one of the most important forms of erosion, particularly in agricultural land. The purpose of this study was to investigate the effect of flow rate and slope gradient on runoff and sediment discharges in two different soils. Experiments were conducted using a tilting flume facility with the test area of 0.2?×?1.0 m. Overall, 24 experiments on two soils (clay loam and sandy clay loam textures) including six flow rates (75, 100, 125, 150, 175, and 200 ml/s) and two slope gradients (1.5 and 2 %) were performed. The selected flow rates and flume slopes were generated to simulate sheet erosion. The results showed that for both soils and slopes, unit flow discharge (q) and sediment concentration increased with increasing flow rate; however, the effect of slope gradient on flow discharge depends on soil type. In addition, sandy clay loam exhibited higher values of q and sediment concentration and consequently, it showed greater amounts of sediment load. At the start of event, sediment concentration was high but it decreased to approach a steady state. In addition, the time needed to reach a steady state condition was shorter for sandy clay loam than that for clay loam soil and in lower flow rates than higher flow rates. For each soil and slope, there was a direct relationship between sediment load and flow rate. The result implied that the effect of slope gradient on sediment load was almost greater in sandy clay loam soil than clay loam soil. Moreover, the differences between sediment loads of two soils are enlarged at slope 2 %. 相似文献
19.
Generally, collapse and landslide are the main sources of granular deposits while the initiation of deposits is triggered by the tremendous runoff from steep longitudinal gully. Substance composition, topographic condition and catchment characteristics directly affect the models of deposits initiation, and larger longitudinal grade provides better topographic condition for the initiation. Several sets of experiments on model casing were designed to simulate the failure mode of slopes under the states of stable and unstable seepages according to catchment and penetration characteristics. It was revealed from the experiments that the initiation of granular deposits had two fundamental modes, that is, fire hose effect and static liquefaction. The former one generally happens at the unsaturated slope or the slope of high permeability while the latter case occurs at the soils containing fine particles. It was concluded that the fire hose effect could generate the deep and narrow eroded channel along with the runoff, the movement distance was related to the continuous hydrodynamic force, and the transporting capacity of solid substances was weak. In addition, slope fluidization was featured with slow seepage failure at the early stage, instantaneous shear failure at the late stage, and wider channel came out due to serious erosion. 相似文献
20.
On experimentally deposited kaolinite, illite, and Ca-bentonite consolidated under their own load or by additional vertical pressure, the progress of compaction in relation to excess pore water pressure, mass physical properties, gravitational mass movements in a tilted tank, and erodibility under running water in a flume were studied. The very low consolidated sediments near the mud/water interface do not obey the generally used theory in soil mechanics. They show a different, non-linear relationship between void ratio or water content and depth below the sedimentary surface on the one hand, or effective overburden pressure and shear strength on the other. The same is true of other physical properties such as permeability, which changes considerably with depth and time of consolidation. High sedimentation rates on slopes induce shallow sediment flow, whereas at low rates and critical slope angles different types of slope failures including the breaking up of water-rich sediment into sharp boundered blocks are observed. Flume studies on soft clay muds show three different types of erosion: continuously suspending, discontinuous erosion of crumbs or shreds, and wavy deformation of the clay surface with disintegration of particles from the crests. The critical tractive stress depends not only on clay type, void ratio, and shear strength, but significantly also on the ‘geologic history’of the clay (i.e. deposition from thin suspension or dense slurry, fabric, consolidation and swelling generating minute inhomogeneities etc.). The experiments may lead to a better understanding of all mechanical processe's including pore-water flow taking place near or not far below the sediment/ water interface. 相似文献