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1.
Soil moisture is a key process in the hydrological cycle. During ecological restoration of the Loess Plateau, soil moisture status has undergone important changes, and infiltration of soil moisture during precipitation events is a key link affecting water distribution. Our study aims to quantify the effects of vegetation cover, rainfall intensity and slope length on total infiltration and the spatial variation of water flow. Infiltration data from the upper, middle and lower slopes of a bare slope, a natural grassland and an artificial shrub grassland were obtained using a simulated rainfall experiment. The angle of the study slope was 15° and rainfall intensity was set at 60, 90, 120, 150, and 180 mm/hr. The effect these factors have on soil moisture infiltration was quantified using main effect analysis. Our results indicate that the average infiltration depth (ID) of a bare slope, a grassland slope and an artificial shrub grassland slope was 46.7–73.3, 60–80, and 60–93.3 cm, respectively, and average soil moisture storage increment was 3.5–5.7, 5.0–9.4, and 5.7–10.2 mm under different rainfall intensities, respectively. Heavy rainfall intensity and vegetation cover reduced the difference of soil infiltration in the 0–40 cm soil layer, and rainfall intensity increased surface infiltration differences on the bare slope, the grassland slope and the artificial shrub grassland slope. Infiltration was dominated by rainfall intensity, accounting for 63.03–88.92%. As rainfall continued, the contribution of rainfall intensity to infiltration gradually decreased, and the contribution of vegetation cover and slope length to infiltration increased. The interactive contribution was: rainfall intensity * vegetation cover > vegetation cover * slope length > rainfall * slope length. In the grass and shrub grass slopes, lateral flow was found at a depth of 23–37 cm when the slope length was 5–10 m, this being related to the difference in soil infiltration capacity between different soil layers formed by the spatial cross-connection of roots.  相似文献   

2.
To clarify the changes in slope stability of loess slopes under the coupling action of rainfall and vehicle loads. Experiments with different water contents under different environmental conditions were carried out indoors, and the relationship function between water content and shear strength parameters was obtained; Secondly, based on Geostudio, an equivalent layered calculation model of water content-strength parameters of loess slope was established, the variation law of soil sample matrix suction with volumetric water content was measured by volumetric pressure plate tester. Finally, by using a combination of finite element analysis of saturated/unsaturated seepage and limit equilibrium analysis of slope stability, the SLOPE/W module in the modeling software GeoStudio is used to calculate and analyze the effects of vehicle loads, rainfall intensity, rainfall duration, and other working conditions on the stability of loess slopes, respectively. The results show that when the lane is in the middle of the slope, the vehicle load parameters have little effect on the uphill stability, but have a greater impact on the downhill; With the increase in rainfall, the change curves of the slope safety coefficient gradually overlap when the vehicle loads are four-axis,five-axis, and six-axis. This shows that when studying the change of slope safety factor under the dual influence of vehicle loads and rainfall, rainfall is the main cause of slope stability; The change rate of slope safety factor increases gradually with the increase of rainfall, and the change trends of the upper, lower and overall parts of the slope are similar.  相似文献   

3.
以甘肃省西和县西山Ⅲ号滑坡为例分析了地震与降雨耦合作用对滑坡稳定性的影响。采用GEOSTUDIO软件对其进行了天然及地震降雨耦合作用两种条件下的数值模拟。通过计算结果对比可知,西山Ⅲ号滑坡在天然状态下处于稳定状态;地震降雨耦合作用对西山Ⅲ号滑坡的稳定会起到很强的削弱作用,滑坡将处于失稳状态。在此处采用的计算条件下,相同降雨量下地震与不同降雨强度的耦合作用显示,降雨强度越小雨水入渗相对越多,地震作用下超孔隙水压力影响区域越大,滑坡越不稳定。  相似文献   

4.
持续降雨是边坡发生失稳破坏的主要诱因之一,基于饱和—非饱和渗流理论,对梅州市大埔县某边坡的渗流场进行模拟,研究在不同降雨工况下该边坡土体体积含水率的时空变化规律。研究结果表明:相同条件下,降雨强度越大(降雨历时越长),边坡表层土体体积含水率变化越大;降雨强度60 mm/d历时1 d的暴雨对边坡表层土体体积含水率的增幅作用存在着一定的滞后性,其余工况未表现出滞后现象;降雨强度为120mm/d和300 mm/d的两种工况各研究点任意时段体积含水率较为接近;当降雨强度达到60 mm/d以上时,边坡内部体积含水率空间变化主要受降雨历时影响,降雨历时越长,降雨入渗深度和体积含水率变化越大。  相似文献   

5.
Natural loess slopes are characterized by a strong geological structure, which is an important factor in maintaining slope stability. The magnitude and duration of the earthquake may disturb the soil structure at different levels degrees, locally changing the arrangement between soil particles. The process of rainfall humidification weakens the cementation between soil particles, and the disturbance and humidification change the structural state of the soil, which in turn causes sliding of the slope along with the decay of soil mechanical properties. As slope instability is often the result of a series of post-earthquake ripple effects, it is of great scientific significance to study the mechanism of slope instability due to the structural decay of earthquake-damaged loess exacerbated by rainfall. In this paper, the impact of structural decay of loess on slope stability is simulated by GEOSTUDIO software under three conditions: pre-earthquake rainfall, post-earthquake rainfall and earthquake, taking the landslide in Buzi Village, Min County, Gansu Province as an example. The comparative analysis of the calculation results shows that the structural properties of the slope without earthquake disturbance are influenced by infiltration amount. When it is fully saturated, the structural properties are similar to those of saturated soil, and the safety factor is reduced by 12.9%. In addition, the earthquake intensity and duration have different degrees of structural damage to the soil. When the structure is fully damaged, it is similar to that of remodelled soil, and the safety factor is reduced by 45.84%. Notably, the process of the earthquake and the following humidification generates the most serious damage to the loess structure, with a reduction in the safety factor of up to 56.15%. The quantitative analysis above obviously illustrates that the post-earthquake rainfall causes the most severe damage to structural loess slopes, and the resulting landslide hazard should not be underestimated.  相似文献   

6.
During the 2003 Sanriku‐Minami earthquake, Japan, a flowslide was triggered on a slope of about 13.5º. The displaced landslide mass developed into a flowslide and deposited on a horizontal rice paddy after traveling approximately 130 m. To study the trigger and movement mechanisms of this landslide, field investigation and laboratory ring‐shear tests were performed. Field investigation revealed that the landslide originated from a fill slope, where a gully was buried for cultivation some decades ago, and shallow ground water was present. Undrained monotonic and cyclic ring‐shear tests on a sample (pyroclastic deposits) taken from the source area revealed that the soil is highly liquefiable, and its steady‐state shear strength can be little affected by overconsolidation. Using the seismic records of the earthquake, probable seismic loadings on the sliding surface were synthesized and applied to the samples in ring‐shear tests, which were performed under undrained or partially drained conditions. The undrained and partially drained tests revealed that shear failure can be triggered by the introduction of seismic loading and formation of excess pore‐water pressure. The generation of excess pore‐water pressure along with increase of shear displacement and the inhibited dissipation of excess pore‐water pressure due to the thickness of the saturated soil layer above the sliding surface probably enabled the continued post‐failure landsliding. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

7.
连续降雨条件下某震后高边坡稳定性分析   总被引：2，自引：0，他引：2       下载免费PDF全文
基于饱和-非饱和渗流理论,综合考虑降雨入渗引起土体重量增加、渗透力增大以及抗剪强度降低等因素的影响,建立降雨条件下震后高边坡有限元模型,运用自编计算程序USLOPE-FEM进行稳定性分析。研究结果表明:未降雨之前,坡体塑性应变主要集中分布于松散堆积体下部与基岩分界面,边坡已经接近临界平衡状态;降雨量20mm/h时连续入渗使边坡上部土层含水量增加,负压区消失且出现饱和区;随着降雨时间延长,坡体表层暂态饱和区逐渐向内部推移,土体的重量和渗透力显著增大、抗剪强度明显降低,坡体中剪应力整体增大,塑性应变区向坡顶扩展而逐渐贯通;连续降雨6h后,临空面表层出现局部滑塌,连续降雨36h后整个堆积层将沿基岩滑塌逐步堵江。研究成果可为强降雨条件下边坡安全性评价提供参考,也为该边坡的失稳预警与滑坡防治积累资料。  相似文献   

8.
Knowledge of the mechanisms of rain‐induced shallow landslides can improve the prediction of their occurrence and mitigate subsequent sediment disasters. Here, we examine an artificial slope's subsurface hydrology and propose a new slope stability analysis that includes seepage force and the down‐slope transfer of excess shear forces. We measured pore water pressure and volumetric water content immediately prior to a shallow landslide on an artificial sandy slope of 32°: The direction of the subsurface flow shifted from downward to parallel to the slope in the deepest part of the landslide mass, and this shift coincided with the start of soil displacement. A slope stability analysis that was restricted to individual segments of the landslide mass could not explain the initiation of the landslide; however, inclusion of the transfer of excess shear forces from up‐slope to down‐slope segments improved drastically the predictability. The improved stability analysis revealed that an unstable zone expanded down‐slope with an increase in soil water content, showing that the down‐slope soil initially supported the unstable up‐slope soil; destabilization of this down‐slope soil was the eventual trigger of total slope collapse. Initially, the effect of apparent soil cohesion was the most important factor promoting slope stability, but seepage force became the most important factor promoting slope instability closer to the landslide occurrence. These findings indicate that seepage forces, controlled by changes in direction and magnitude of saturated and unsaturated subsurface flows, may be the main cause of shallow landslides in sandy slopes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
Recent publications from field and simulation studies indicate that runoff per unit area decreases as the length of the slope being observed is increased. This scale effect has been observed and documented for slopes with a uniform infiltration capacity as well as for slopes along which infiltration capacity is variable. This paper presents the design and testing of a laboratory flume for the study of the processes that lead to this scale effect, particularly for the case of slopes covered with crops. The features of the flume include reliable experimental control of soil water content prior to rainfall, high intensity rainfall without erosion, uniform crop growth along the slope, and the option of varying the infiltration rate independently of rainfall and soil characteristics. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

10.
滑坡是一种破坏性非常强的地质灾害,其中地震与降雨均为诱导滑坡发生的关键因素。从降雨期间发生地震的角度考虑,基于Green-Ampt降雨入渗模型对Newmark模型进行改进,推导两因素耦合作用下的边坡安全系数FS。以云南省鲁甸县某一区域为例,分别开展无降雨、降雨无积水与降雨积水三种情况下的地震滑坡危险性预测及坡度与入渗深度因子对位移影响分析。通过比较上述三种情况,得到研究区域内的Newmark累积位移分布及危险性区划。结果表明：与未降雨情况相比,后两种情况下地震滑坡高危险程度区域面积占比计算区域随着降雨时间的增加从1%分别提高至9%、12%,滑坡低危险程度区域面积从51%分别降低至35%、33%;坡度值与入渗深度值越大,滑坡位移越大,危险性越高。Newmark改进模型充分考虑了降雨对地震滑坡产生的促进作用,能更好地反映出研究区每个场点相对的滑坡危险性,对滑坡危险性预测具有一定指导意义。  相似文献   

11.
Rainfall thresholds for shallow landslide initiation were determined for hillslopes with two types of bedrock, permeable sandstone and impermeable mudstone, in the Boso Peninsula, Japan. The pressure‐head response to rainfall was monitored above a slip scarp due to earlier landslides. Multiple regression analysis estimated the rainfall thresholds for landsliding from the relation between the magnitude of the rainfall event and slope instability caused by the increased pressure heads. The thresholds were expressed as critical combinations of rainfall intensity and duration, incorporating the geotechnical properties of the hillslope materials and also the slope hydrological processes. The permeable sandstone hillslope has a greater critical rainfall and hence a longer recurrence interval than the impermeable mudstone hillslope. This implies a lower potential for landsliding in sandstone hillslopes, corresponding to lower landslide activity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

12.
1920年海原8.5级大地震诱发的石碑黄土塬滑坡,因其规模大、坡度小、滑距远的特点成为业界关注焦点,目前对该滑坡的物理力学过程仍无统一认识。基于此,文章通过理论分析和数值计算方法研究该滑坡初始状态、地震动力响应和流滑发展过程。为分析震前斜坡初始状态,建立考虑斜坡表面拉裂缝中侧向水压力作用的力学计算模型。结果表明,拉裂缝中侧向水压力削弱了斜坡整体稳定状态;为研究地震时斜坡动力响应过程,建立数值计算模型,获得地震时斜坡饱和土层的孔隙水压力比和斜坡位移的变化特性;为解释远程滑坡,将液化后土层等效为流体,借鉴泥流滑距估算理论,求算石碑塬滑坡的滑距,计算结果与前人现场考察结果吻合。  相似文献   

13.
The pore water pressure head that builds in the soil during storms is a critical factor for the prediction of potential slope instability. We report findings from a 3‐year study of pressure head in 83 piezometers distributed within a 13‐ha forested catchment on the northern coast of California. The study's primary objective was to observe the seasonal and storm‐based dynamics of pressure head at a catchment scale in relation to observed rainfall characteristics and in situ topography to better understand landscape patterns of pressure head. An additional goal was to determine the influence of the interaction between rainfall and forest canopy in altering delivery of water and pressure head during the large storms necessary to induce landsliding. We found that pressure head was highly variable in space and time at the catchment scale. Pore pressures peaked close to maximum rainfall intensity during the largest storms measured. The difference between rainfall and throughfall delivered through the canopy was negligible during the critical landslide‐producing peak rainfall periods. Pore pressure was spatially variable within the catchment and did not strongly correlate with surficial topographic features. Only 23% of the piezometers located in a variety of slope positions were found to be highly responsive to rainfall. Topographic index statistically explained peak pressure head at responsive locations during common storms, but not during the larger storms with potential to produce landslides. Drainage efficiency throughout the catchment increased significantly in storms exceeding 2 to 7 months peak pressure head return period indicated by slowing or cessation of the rate of increase of pressure head with increasing storm magnitude. This asymptotic piezometric pattern persisted through the largest storm measured during the study. Faster soil drainage suppressed pressure head response in larger storms with important process implications for pore pressure development and landslide hazard modelling. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
Badland areas are usually regarded as impermeable zones which generate high runoff and are very vulnerable to sheetwash and rainsplash. To test those considerations sprinkling experiments using two rainfall simulators were carried out on slopes of varying aspect in the northern Negev (Israel). For one unit 1·5 m2 plots were used with rainfall of natural characteristics at 36 mm/hr intensity and 43–48 minute duration, runoff being recorded and water/sediment samples taken every 5 minutes. The second unit was used on 30–50 m2 plots but rainfall energy production was below that of natural rainfall. Results show that due to the high stability and strong flocculation of clay-rich aggregates rainsplash is ineffective in surface sealing so that infiltration capacities remain high despite intense, prolonged rainfall. Aspect differences are reflected in variation of surface properties despite homogenous bed-rock, which cause marked differences in hydrological response. North-facing slopes respond more quickly, more frequently and produce more runoff than south-facing slopes. Non-uniform runoff generation is also seen within plots of one aspect reflecting subtle variations in surface properties. Comparison of rainfall intensity and duration used during the experiments with those prevailing under natural conditions shows that under present day conditions surface flow in the Zin valley badlands must be extremely infrequent and denudation rates very low.  相似文献   

15.
Abstract

Sheet sediment transport was modelled by artificial neural networks (ANNs). A three-layer feed-forward artificial neural network structure was constructed and a back-propagation algorithm was used for the training of ANNs. Event-based, runoff-driven experimental sediment data were used for the training and testing of the ANNs. In training, data on slope and rainfall intensity were fed into the network as inputs and data on sediment discharge were used as target outputs. The performance of the ANNs was tested against that of the most commonly used physically-based models, whose transport capacity was based on one of the dominant variables—flow velocity (V), shear stress (SS), stream power (SP), and unit stream power (USP). The comparison results revealed that the ANNs performed as well as the physically-based models for simulating nonsteady-state sediment loads from different slopes. The performances of the ANNs and the physically-based models were also quantitatively investigated to estimate mean sediment discharges from experimental runs. The investigation results indicated that better estimations were obtained for V over mild and steep slopes, under low rainfall intensity; for USP over mild and steep slopes, under high rainfall intensity; for SP and SS over very steep slopes, under high rainfall intensity; and for ANNs over steep and very steep slopes, under very high rainfall intensities.  相似文献   

16.
In this work, a transient rainfall infiltration and grid‐based regional slope‐stability model (TRIGRS) was implemented in a case study of Yan'an City, Northwest China. In this area, widespread shallow landslides were triggered by the 12 July 2013 exceptional rainstorm event. A high‐resolution DEM, soil parameters from in‐situ and laboratory measurements, water table depths, the maximum depth of precipitation infiltration and rain‐gauge‐corrected precipitation of the event, were used as inputs in the TRIGRS model. Shallow landslides triggered on the same day were used to evaluate the modeling results. The summarized results are as follows: (i) The characteristics and distribution of thirty‐five shallow landslides triggered by the 12 July 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth, area and volume less than 3 m, 200 m2 and 1000 m3, respectively, (ii) Four intermediate factor of safety (FS) maps were generated using the TRIGRS model to represent the scenarios 6, 12, 18 and 24 hours after the storm event. The area with FS < 1 increased with the rainfall duration. The percentage of the area with FS < 1 was 0.2%, 3.3%, 3.8% and 5.1% for the four stages, respectively. Twenty‐four hours after the rainstorm, TRIGRS predicted that 1255 grid cells failed, which is consistent with the field data. (iii) TRIGRS generated more satisfactory results at a given precipitation threshold than SINMAP, which is ideal for landslide hazard zoning for land‐use planning at the regional scale. Comparison results showed that TRIGRS is more useful for landslide prediction for a certain precipitation threshold, also in the regional scale. (iv) Analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

17.
Hortonian runoff was measured in the laboratory from uniform slopes of lengths of 1·5, 3·0, and 6·0 m for steady, high‐intensity rainstorms with durations of 1·0 to 7·5 min. A clear reduction in runoff per unit slope length was found as slope lengths were increased. This effect becomes more pronounced with decreasing storm duration. The runoff data were used to validate a simple process‐based model that combines the Philip‐two‐term infiltration equation with the kinematic wave overland flow principle. The predicted and experimental results agreed well. Laboratory findings were extrapolated with the aid of the model to slopes and rainfall durations similar to those found under West African conditions. The calculated reduction of runoff per unit length is similar to reported observations. Thus, this process‐based model can largely explain the phenomenon of runoff reduction with increasing slope length. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

18.
A common factor in landslide activation (or reactivation) is subsurface moisture and associated pore pressure variations linked to rainfall. Monitoring of these subsurface hydrogeological processes is necessary to improve our understanding of water‐induced landslide activation. Geophysical approaches, electrical methods in particular, are increasingly being applied to landslide monitoring because they provide non‐invasive spatial information in heterogeneous subsurface environments that can be difficult to characterise using surface observations or intrusive sampling alone. Electrical techniques are sensitive to changing subsurface moisture conditions, and have proven to be a useful tool for investigating the hydrogeology of natural and engineered slopes. The objectives of this investigation were to further develop electrical resistance monitoring for slope stability assessment, and to validate the approach at an intermittently‐active UK landslide system to advance the understanding of complex landslide activation mechanisms. A long‐term transfer resistance dataset was collected from a grid of electrodes to allow spatial monitoring of the landslide. These data were interpreted using a synthesis of rainfall, temperature, GPS and piezometric records. The resistance data were corrected for seasonal temperature variations and electrode movements were monitored, as these processes were shown to mask moisture related changes. Results reveal that resistance monitoring is sensitive to soil moisture accumulation, including changes in piezometric levels, and can be used to study the principal activation mechanism of slow‐moving shallow earthflows. Spatial monitoring using resistance maps was shown to be particularly valuable as it revealed the evolution of subsurface moisture distribution, in the lead up to landslide activation. Key benefits of this approach are that it provides a simple, rapid and non‐invasive means of spatially monitoring subsurface moisture dynamics linked to landslide activation at high‐temporal resolution. Crucially, it provides a means of monitoring subsurface hydraulic changes in the build‐up to slope failure, thereby contributing to early warning of landslide events. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

19.
Flow and deformation failure of sandy slopes   总被引：2，自引：0，他引：2  
The effects of earthquake induced pore pressure on seismic and post seismic stability conditions of cohesionless slopes are investigated with reference to the infinite slope scheme. In cohesionless slopes the shear strength reduction caused by pore pressure build-up may lead the slope to a deformation failure or to a flow failure if liquefaction conditions are approached. Two critical values of the seismic induced pore pressure ratio are introduced to evaluate the effect of shear strength reduction on the slope failure mechanism. The results are given in the form of stability charts and a procedure for the evaluation of the seismic stability condition is described. The procedure gives useful information about the failure mechanism that slopes may exhibit and the displacement analysis which should be carried out.  相似文献   

20.
It is critical to understand and quantify the temporal and spatial variability in hillslope hydrological data in order to advance hillslope hydrological studies, evaluate distributed parameter hydrological models, analyse variability in hydrological response of slopes and design efficient field data sampling networks. The spatial and temporal variability of field‐measured pore‐water pressures in three residual soil slopes in Singapore was investigated using geostatistical methods. Parameters of the semivariograms, namely the range, sill and nugget effect, revealed interesting insights into the spatial structure of the temporal situation of pore‐water pressures in the slopes. While informative, mean estimates have been shown to be inadequate for modelling purposes, indicator semivariograms together with mean prediction by kriging provide a better form of model input. Results also indicate that significant temporal and spatial variability in pore‐water pressures exists in the slope profile and thereby induces variability in hydrological response of the slope. Spatial and temporal variability in pore‐water pressure decreases with increasing soil depth. The variability decreases during wet conditions as the slope approaches near saturation and the variability increases with high matric suction development following rainfall periods. Variability in pore‐water pressures is greatest at shallow depths and near the slope crest and is strongly influenced by the combined action of microclimate, vegetation and soil properties. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

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