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1.
Abdolreza Osouli Parham Safarian Bahri 《Geotechnical and Geological Engineering》2018,36(5):2823-2838
Characterizing soil erosion and predicting levee erosion rates for various levee soils and storm conditions during floodwall overtopping events is necessary in designing levee-floodwall systems. In this study, a series of laboratory scaled levee-floodwall erosion tests were conducted to determine erosion characteristics of fine grained soils subject to overtopping from different floodwall heights with variable flow-rates. A decreasing rate of erosion was observed as a pool of water was generated in the created scour hole at the crest of the levee model. The erosion rates were also assessed using jet erosion test (JET) and erosion function apparatus (EFA) tests. The results of levee-floodwall overtopping along with soil geotechnical characteristics such as plasticity index, compaction level, and saturation level of the levee soils as well as hydraulic parameters such as water overtopping velocity were used to develop a levee-floodwall erosion rate prediction model. Then, the results of JET and EFA were integrated to develop another prediction model for levee-floodwall erosion rate estimation. Consequently, the prediction models were evaluated by conducting additional tests and comparing the prediction results with the actual measured erosion rates. 相似文献
2.
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
3.
《Geomechanics and Geoengineering》2013,8(2):76-85
Although an important aspect of the assessment of safety of earthen levees is the consideration for its global stability, little is known regarding the slope stability of levees during hurricane overtopping conditions involving storm surge and wind generated wave action. In this study, a comprehensive slope stability investigation was undertaken where an earthen levee, representing full-scale overtopping conditions, was subjected to 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 roller-compacted concrete (RCC) to protect against overtopping. This paper presents a conceptual model for an RCC strengthened levee as well as a methodology for analysis and incorporation of various overtopping flow conditions in levee slope stability. The findings of this study indicate that RCC 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, strengthening of the levee by RCC does not increase the factor of safety during the storm surge conditions. 相似文献
4.
为防治漫顶引起侵蚀造成堤坝破坏,将微生物诱导碳酸钙沉淀即MICP技术应用于加固堤坝表层。通过向堤坝表层喷洒微生物细胞以及营养盐,最终在砂土孔隙中快速析出碳酸钙胶凝结晶,以改善堤坝表层砂的力学性能。首先,采用喷洒法处理堤坝表层;其次,对处理好的堤坝模型进行水槽试验,研究其抗侵蚀性;最后,对堤坝表层的试样进行强度与渗透试验。试验结果表明,采用MICP技术加固堤坝模型表层可有效提高其抗侵蚀力,防治由漫顶引起的堤坝破坏。对加固后的表层取样进行测试,结果表明：无侧限抗压强度可高达9 MPa,渗透系数从4×10?4 m/s 降低至7.2×10?7 m/s。试验说明,微生物胶结技术在加固堤坝表层方面具有潜在的工程实用价值和广阔的应用前景。 相似文献
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6.
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
7.
Ty V. Wamsley Mary A. Cialone Jane M. Smith Bruce A. Ebersole Alison S. Grzegorzewski 《Natural Hazards》2009,51(1):207-224
The purpose of this investigation was to examine storm surge and wave reduction benefits of different environmental restoration
features (marsh restoration and barrier island changes), as well as the impact of future wetland degradation on local surge
and wave conditions. Storm surge simulations of two representative hurricanes were performed using the ADCIRC storm surge
model with the inclusion of radiation stress gradients from the STWAVE nearshore wave model. Coupled model simulations were
made for a number of landscape configurations that involved both restored and degraded wetland features. The impact of barrier
island condition on hurricane surge and waves was also evaluated. Effects of landscape features were represented by changes
in elevation and frictional resistance. Restoration and degradation of marsh resulted in decreases (for restoration cases)
and increases (for degradation cases) in both surge and waves. The magnitude of change was correlated with the magnitude of
the horizontal extent and elevation changes in the marsh. In general, the wave change patterns are consistent with the water
level changes. Deflation of the Chandeleur Islands (barrier island chain) resulted in slightly increased surge. Results suggest
that coastal marsh does have surge and wave reduction potential. Results also indicate that the impact of the landscape features
is amplified in areas where there are levee “pockets.” Barrier islands and coastal ridges reduce wave heights, even if in
a degraded condition and thus can reduce wave energy in wetland areas, protecting them from erosion. 相似文献
8.
Landslides are recurring phenomena causing damages to private property, public facilities, and human lives. The need for an affordable instrumentation that can be used to provide an early warning of slope instability to enable the evacuation of vulnerable people, and timely repair and maintenance of critical infrastructure is self-evident. A new emerging technique that correlates soil moisture changes and deformations in slope surface by means of elastic wave propagation in soil was developed. This approach quantifies elastic wave propagation as wave velocity. To verify its applicability, a series of fixed and varied slope model tests, as well as a large scale model test, were conducted. Analysis of the results has established that the elastic wave velocity continuously decreases in response of moisture content and deformation, and there was a distinct surge in the decrease rate of wave velocity with failure initiation, soil deformation was thus envisaged to have more significant effect on elastic wave velocity than water content. It is proposed that a warning be issued at switch of wave velocity decrease rate. Based on these observations, expected operation of the elastic wave velocity monitoring system for landslide prediction in the field application is presented. Consequently, we conclude that the elastic wave velocity monitoring technique has the potential to contribute to landslide prediction. 相似文献
9.
Risk analysis for flood-control structure under consideration of uncertainties in design flood 总被引：1，自引：0，他引：1
This study presents a risk analysis model to evaluate the failure risk for the flood-control structures in the Keelung River
due to the uncertainties in the hydrological and hydraulic analysis, including hydrologic, hydraulic, and geomorphologic uncertainty
factors. This study defines failure risk as the overtopping probability of the maximum water level exceeding the levee crown,
and the proposed risk analysis model integrates with the advanced first-order and second-moment (AFOSM) method to calculate the overtopping probability of levee system. The proposed model is used to evaluate the effects of the
freeboard and flood-diversion channel on the flood-control ability of the levees in the Keelung River, which were designed
based on the 3-day, 200-year design rainfall event. The numerical experiments indicate that the hydrologic uncertainty factors
have more effect on the estimated maximum water level than hydraulic and geomorphologic uncertainty factors. In addition,
the freeboard and the flood-diversion channel can effectively reduce the overtopping probability so as to significantly enhance
the flood-control capacity of the levee system in the Keelung River. Eventually, the proposed risk analysis successfully quantifies
the overtopping risk of the levee system under a scenario, the increase in the average 200-year rainfall amount due to climate
change, and the results could be useful when planning to upgrade the existing levee system. 相似文献
10.
Shih-Nan Chen Lawrence P. Sanford Evamaria W. Koch Fengyan Shi Elizabeth W. North 《Estuaries and Coasts》2007,30(2):296-310
The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified
Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment
transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function
of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction
of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation
qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased
as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital
velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in
higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted
lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion
rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification.
Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates
alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed. 相似文献
11.
Detection of water infiltration and deformation of unsaturated soils by elastic wave velocity 总被引：1，自引：1，他引：0
Intense rainfall is the most important landslide trigger. In many mountainous environments of the world, heavy rainfall has caused many landslides and slope failures in a matter of seconds without warning. Therefore, an early warning system can be an effective measure to reduce the damage caused by landslides and slope failures by facilitating the timely evacuation of people from landslide-prone areas. In this study, we propose an idea to correlate soil moisture changes and deformations in slope surface by means of elastic wave propagation in soil. Constant shear stress drained triaxial tests where water was infiltrated from the bottom of specimen until failure, and slope model tests under artificial rainfall were performed to investigate the response of elastic wave velocities during pre-failure phases of rainwater infiltration and deformation. Analysis of the results has established that the elastic wave velocity continuously decreases in response of moisture content and deformation, and there was a distinct surge in the decrease rate of wave velocity when failure was initiated. Possible mechanisms were interpreted based on the test results. It is proposed that a warning be issued at switch of wave velocity decrease rate. This approach can thus serve as the basis of an early warning system for landslides and slope failure considering both moisture content and deformation. 相似文献
12.
黄河三角洲沉积物抗侵蚀性动态变化差异研究 总被引：1，自引：0，他引：1
为研究波浪循环荷载作用过程中,细粒土沉积物抗侵蚀性特征的演化及其发生机制,在现代黄河三角洲北部及东北部选择两个典型研究区（遭受严峻侵蚀的车子沟渔村试验区及基本处于侵淤平衡的黄河海港试验区）进行了一系列波浪荷载模拟试验、侵蚀水槽试验及沉积物物理力学性质测试。试验结果发现：原车子沟渔村试验区沉积物抗侵蚀性在无波浪荷载作用或较短的波浪荷载作用条件下,普遍高于黄河海港研究区,但由于其更显著的液化特性,该区沉积物抗侵蚀性更容易被波浪荷载作用降低,这是造成车子沟渔村研究区遭受严峻潮滩侵蚀的重要原因。另外,结合试验结果,对两个研究区沉积年代及沉积物粒度成分特征的分析可知,波浪荷载作用导致海床下部细粒物质向上输运这一次生改造作用加速了海床沉积物的“粗化”进程,从而推进海岸带地区细粒沉积物抗侵蚀性特征的演化 相似文献
13.
14.
在弯道水槽中展开系列试验,研究水力冲刷过程中均质土岸坡冲刷崩塌输移与河床冲淤过程及其影响因素。该过程及变化特征可描述为:水下坡面侵蚀及坡脚淘刷导致岸坡失稳崩塌;暂时堆积在凹岸坡脚处的崩塌体加剧附近水流紊动程度利于其输运与分解;分解后较粗的颗粒随弯道螺旋流以推移质形式被输移至下游凸岸落淤,较细的颗粒大部分都随水流以悬移质形式被携带至下游出口;水流结构随岸坡及河床变形而调整;如此循环往复。试验成果进一步表明:冲刷状态下,试验材料黏性越小、近岸流速越大、作用时间越长,岸坡冲刷崩塌量及河床冲刷量都越大;同条件下岸坡冲刷崩塌总量大于河床冲刷总量,且河床相对冲刷率随岸坡冲刷崩塌量的增大而减小,数值范围为0.40~0.92。 相似文献
15.
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
16.
Jie Yin Zhan-e Yin Xiao-meng Hu Shi-yuan Xu Jun Wang Zhi-hua Li Hai-dong Zhong Fu-bin Gan 《Environmental Earth Sciences》2011,63(2):407-414
Shanghai is physically and socio-economically vulnerable to accelerated sea level rise because of its low elevation, flat
topography, highly developed economy and highly-dense population. In this paper, two scenarios of sea level rise and storm
surge flooding along the Shanghai coast are presented by forecasting 24 (year 2030) and 44 (year 2050) years into the future
and are applied to a digital elevation model to illustrate the extent to which coastal areas are susceptible to levee breach
and overtopping using previously developed inflow calculating and flood routing models. Further, the socio-economic impacts
are examined by combining the inundation areas with land use and land cover change simulated using GeoCA-Urban software package.
This analysis shows that levee breach inundation mainly occurs in the coastal zones and minimally intrudes inland with the
conservative protection of dike systems designed. However, storm surge flooding at the possible maximum tide level could cause
nearly total inundation of the landscape, and put approximately 24 million people in Shanghai under direct risk resulting
from consequences of flooding (e.g. contamination of potable water supplies, failure of septic systems, etc.). 相似文献
17.
粘性土体具有较强的抗冲能力,其抗冲性强弱决定了河岸的侵蚀速率。为了估算河岸的侵蚀速率,确定粘性土体的起动条件、侵蚀系数及两者之间的数量关系非常重要,为此开展了荆江段河岸粘性土体起动条件与冲刷特性的水槽试验研究。根据试验结果获得了粘性土体的起动流速与土体液限/自然含水率之间关系以及起动切应力与干密度、起动切应力与液性指数之间的定量表达式,综合反映了粘性土起动条件与其物理性质指标之间的关系;结合冲刷特性试验结果,还获得了土体侵蚀系数随起动切应力的变化规律,并与已有其他试验结果进行了比较。结果表明:荆江河岸粘性土侵蚀系数均比相同条件下其他公式计算值偏大,这与该试验土体中粘粒含量相对较低、土体结构受到扰动等因素有关;根据试验结果,拟合得到了荆江河岸粘性土侵蚀系数与起动切应力之间定量关系式,其相关系数R2=0.90,故该关系式能为荆江段崩岸过程的计算提供参考依据。 相似文献
18.
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
19.
文章对近年来基于生物固土技术的防风固沙研究进行了回顾和分析。常用于防风固沙的生物过程包括基于微生物或酶诱导碳酸钙沉积（MICP或EICP）的矿化固土技术,加入黄原胶等生物高聚物作为辅助剂,可获得更好的固土效果。土壤风蚀过程中,除了风力本身,风携带的跃移颗粒对土的撞击,也是侵蚀破坏的重要因素,这在生物固化土风蚀试验中体现明显。生物固化防风固沙的处理过程简单易行,以尿素和钙盐作为处理材料,用细菌或脲酶作为催化诱导媒介,对土体进行单遍喷洒处理即可获得很好的抗风效果。室内抗风试验中,将风蚀速率与临界起动风速两个指标结合是较为合理的评估方法。在室内和现场条件下,表面贯入强度测试可用来快速测定处理效果和抗风性能。目前的现场试验研究表明,生物固化土中植物可以生长,但是极端条件下生长受限。为了将该方法推向实用,需要从多重侵蚀因子作用下的抗风力侵蚀能力、生态恢复能力和现场施工技术等方面进一步研究探索。 相似文献
20.
On the effect of moisture bonding forces in air-dry soils on threshold friction velocity of wind erosion 总被引：5，自引：0，他引：5
SUJITH RAVI TED M. ZOBECK† THOMAS M. OVER‡ GREGORY S. OKIN PAOLO D'ODORICO 《Sedimentology》2006,53(3):597-609
Wind erosion is a dominant geomorphological process in arid and semi-arid regions with major impacts on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. The understanding and modelling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions. In arid regions during the dry season, the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity. By a series of wind tunnel tests and theoretical analyses, this dependence of threshold velocity on near surface air humidity is shown for three soils of different textures: sand, sandy loam, and clay loam. The results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40% and 65%, while above and below this range the threshold shear velocity increases with air humidity. A theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the humidity of the overlying atmosphere. The conditions under which soil-atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions. 相似文献