降雨作用下碎石土滑坡稳定性演化过程分析

不同的降雨强度和历时导致滑坡体内渗流场的动态演变,同时也影响着滑坡稳定性的变化,但目前对降雨作用下的滑坡稳定性变化规律的研究并不多。本文选取铜仁地区石灰溪滑坡进行案例研究,基于饱和—非饱和渗流理论和极限平衡理论,采用SLOPE/W模块研究在不同降雨强度及不同降雨历时组合工况作用下石灰溪滑坡在降雨中及降雨后1~7天的稳定性演化特征及规律。研究表明在不同降雨强度条件下,滑坡稳定性在第一天降雨过后急剧恶化,稳定性系数迅速减小,随着降雨强度的增大滑坡稳定性恶化明显,当降雨强度为100 mm/d时滑坡稳定性已经基本接近于整体滑动的状态;滑坡在降雨过程中稳定性系数迅速减小,随着降雨历时的增大滑坡稳定性恶化明显,当降雨历时为2天、3天时滑坡已经整体失稳。     

连续降雨条件下某震后高边坡稳定性分析

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。     

含水率对花岗岩边坡风化层界面剪切特性的影响

为了研究含水率变化对成层状风化花岗岩边坡稳定性的影响,进行了一系列单调直剪试验.设置四种含水率(13％、17％、21％和25％)和三种干密度(ρd1、ρd2、ρd3),分析不同干密度下含水率对花岗岩残积土-全风化花岗岩界面剪切特性的影响.试验结果表明:在低含水率、高干密度和低竖向应力下,界面剪应力易发生剪切软化,反之,更易发生剪切硬化;含水率越高,最大剪胀量越小,且干密度越大,最大剪胀量受含水率变化的影响越小;含水率升高会大幅降低界面抗剪强度,且干密度越大、竖向应力越小,界面抗剪强度随含水率的变化率越大.     

太湖平原高度城镇化下降雨特征时空变化研究

随着人类活动和气候变化影响的加剧,降雨特征变化引发的洪水问题日益突出,探讨其时空演变特征对保障高度城镇化地区洪涝安全有较大理论和实际意义.本研究以高度城镇化的太湖平原地区为例,选取降雨强度、降雨历时、降雨集中程度和降雨峰值程度为降雨类型特征指标,以高分辨率短历时加权集合降水资料MSWEP(multi-source weighted-ensemble precipitation)为基础探讨了快速城市化发展下(1979—2016年)不同降雨历时—强度—类型的时空演变规律及其演变机制.研究结果表明：(1)研究区的降雨频次呈现出强度小、历时短、雨量集中于中期和高峰型降雨发生的频次高的特征;同时历时较短、集中于前期和后期的降雨频次趋于增加,而历时较长、集中于中期且中峰型降雨的频次趋于减少.(2)城镇化对降雨雨型的影响分析发现,高城镇化水平地区较低城镇化水平地区的降雨量更大,其中降雨强度大于25 mm/d的大雨和暴雨事件更易发生;并且更倾向于发生前期型和高峰型的极端分布降雨.随着城镇化发展研究区更易于遭受因降雨量过于集中而导致的雨涝灾害.     

改进Mein-Larson模型的花岗岩残积土边坡降雨入渗研究

在我国发生的众多滑坡灾害中,最为突出的一个致灾因素是降雨。针对降雨诱发滑坡的研究一般是将边坡失稳的机制作为着手点,研究湿润锋向下发展的运移规律。针对Mein-Larson降雨入渗模型在模拟水分入渗过程中未充分考虑初始含水率分布的非线性这一不足,引入考虑初始含水率分布的非线性即指数分布进行土体含水率分布、土体累计入渗雨量的修正,并进行改进Mein-Larson降雨入渗模型的研究,通过试验验证了改进之后的降雨入渗模型的正确性与合理性。     

Mein-Larson入渗模型的改进研究

降雨入渗模型对于降雨型滑坡稳定性的评价是相当重要的,目前常用的降雨入渗模型是Mein-Larson入渗模型,但该模型假定了土体初始含水率沿深度方向为一定值,而实际上土体初始含水率沿深度方向为非线性分布的.考虑到实际的土体初始含水率分布情况,提出了描述土体初始含水率的分布的反比例函数,对Mein-Larson入渗模型进行...     

我国典型沙漠(地)流动风沙土的深层渗漏量及动态变化

土壤水分是干旱生态系统的重要制约因素,一直是干旱区研究和生态建设的热点和难点问题,对降雨的深层土壤渗漏水量仍缺少定量观测研究.本文采用作者自主研发的YWB-01型土壤深层水分渗漏计量仪对毛乌素沙地等4大沙漠(地)的流动沙地测试记录了降雨入渗到150 cm以下深层土壤的渗漏水量,连续2年的资料表明:(1)降雨的深层渗漏水量自东向西由半干旱区向干旱区递减,其中:乌审旗流动沙地渗漏水总量高达508.4 mm,占同期降雨量58.4%,磴口的渗漏水量为23.8 mm,占降雨量13.9%,而阿拉善左旗和右旗未测试到渗漏水量,但≥25 mm的强降水对干旱和半干旱区流沙地深层土壤水分的渗漏补给具有重要作用;(2)渗漏水量的季节变化与降水的变化趋于一致,但有一定滞后,在降雨量较大地区,二者变化的相似性更强;(3)单次较强降雨在降雨开始的40~55 h后出现一个渗漏水量峰值,渗漏速率增加较快但其减少相对缓慢,持续渗漏过程长达150 h左右,降雨量越大,渗漏水量峰值就越高,渗漏水量所占降雨量的比例也越高;受降雨强度、雨量和历时的共同作用,就低强度、长历时和单次降雨量大的降雨事件更有利于降雨对沙地深层土壤的渗漏补给;(4)受土壤冻融作用的影响,在快速消融期3月份出现一个小的渗漏补给峰值.研究结果对我国干旱和半干旱区沙地水资源的准确评估和合理利用及生态建设具有现实指导意义.     

降雨径流过程驱动因子的室内模拟实验研究

降雨径流过程的驱动作用可以归结为两个方面: 第一是降雨过程的影响, 第二是下垫面变化的影响. 通过179场室内降雨径流模拟实验发现, 无论是降雨历时还是降雨强度都会影响汇流的滞时, 这与传统的假设有明显的矛盾. 尤其是在降雨历时小于全面汇流时间和较小的降雨强度下这种非线性关系的影响十分明显. 由此可以推定, 单位线用于南方湿润地区的降雨径流过程模拟更为合理, 而在北方的干旱、半干旱地区, 由于降雨强度变化快, 降雨历时短, 所以使用时要特别注意降水条件. 这也说明了过去的水文模型在北方地区的产汇流效果不好的原因. 降水历时较小时, 流域的汇流特性有较为剧烈的变化, 因为此时流域未达到全流域汇流, 这反映了实际北方降雨径流情况, 因此单位线使用时必须进行适当的非线性校正. 当降雨历时大于流域的全面汇流时间以后整个流域达到蓄泄平衡, 适用于南方长时间降雨径流关系和产汇流的基础理论研究. 在充分降雨条件下, 洪峰流量、降雨强度呈线性关系, 而与下垫面无关, 降雨强度与峰现时间成负线性关系. 流域的调蓄量与降雨强度和洪峰流量呈线性关系, 受下垫面影响和作物截留作用十分明显, 而与作物截留的位置关系不大.     

降雨和地震耦合作用对滑坡稳定性的影响——以甘肃西和Ⅲ号滑坡为例

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。     

地震后降雨作用下堆积体滑坡模型试验研究

为研究震后降雨作用下堆积体滑坡的灾变机理、裂缝发展规律、滑坡启动时间等问题,以甘肃省舟曲县江顶崖滑坡为对象,采用振动台及人工降雨模型试验,开展4组相同地震烈度不同降雨强度的震后降雨试验。研究结果表明：(1)地震作用使坡体发生剪切破坏,震后降雨工况坡体呈现土体流失的浸蚀破坏,在坡脚处产生明显的剪出口,震后降雨作用诱发堆积体滑坡发生局部失稳。(2)地震作用使坡体中部产生剪切裂缝与错台,后缘处产生“圆弧状”张拉裂缝,在后期降雨中,裂缝变形随降雨强度增大而加剧,并在降雨中期发生突变变形。(3)地震烈度相同的情况下,滑坡启动时间与降雨强度呈指数函数关系,土体沉降变形与降雨强度呈对数函数关系。研究成果可为堆积体滑坡在震后降雨作用下的预警及防治提供参考。     

Coupling action of rainfall and vehicle loads impact on the stability of loess slopes based on the iso-water content layer

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.     

Impact of the Rainfall Intensity and Seepage on Slope Stability in Loess Plateau

In recent years, with the increase of traffic construction in mountainous areas in China, road slope traffic accidents have become more and more common. In addition, natural disasters such as landslides, collapses and subgrade settlements caused by rainfall, driving load, seasonal variation and groundwater distribution are frequent. In particular, rainfall is one of the most common factors leading to slope instability (landslide). Therefore, this paper proposes the seep module based on the application software Geo-studio, and analyzes the slope soil parameters and slope stability under five types of rainfall conditions:light rain (10 mm/d), moderate rain (25 mm/d), heavy rain (50 mm/d), rainstorm(100 mm/d), and torrential rain (250 mm/d). The critical safety factor under rainfall intensity is fitted with nonlinear curve by sine function. The results show that the fitting curve of rainfall intensity and safety factor on the upper slope is excellent. The residual points are evenly distributed in the belt area of±0.1, and the data basically conform to the nonlinear sine model, indicating that the curve plays an essential role in slope health diagnosis.     

Field studies on the influence of rainfall intensity,vegetation cover and slope length on soil moisture infiltration on typical watersheds of the Loess Plateau,China

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.     

Assessing dominant factors affecting soil erosion using a portable rainfall simulator

Investigating the causes of soil erosion is difficult in natural conditions owing to the presence of other factors. Without simplifying the experimental conditions, studying soil behavior with its numerous parameters while considering factors such as vegetation cover, topography, and rainfall is difficult and in most conditions impossible. The application of simulation approaches is therefore necessary to simplify the prototype. In this research, the effects of physical soil factors such as texture and antecedent soil moisture, along with land slope and vegetation cover were evaluated in the Taleghan watershed, Iran, using a rainfall simulator and soil erosion plots. For this purpose, a 89 × 120 cm rainfall simulator producing 24.5 and 32 mm/h rainfall intensities of 30 min duration, as a common condition of the study area, was used at 144 locations over soil erosion plots with dimensions of 95 × 125 cm. Plots had slope classes of 12-20 and 20-30 %, different soil textures, different antecedent soil moistures, and medium to poor vegetation cover conditions. It was found that for 24.5 and 32 mm/h rainfall intensities, the sediment yield had high correlations of-0.771 and -0.796 with vegetation cover and slight correlations of 0.045 and 0.029 with land slope respectively. Regression equations for predicting the sediment yield were also developed for different conditions.     

The mechanism of slope instability due to rainfall-induced structural decay of earthquake-damaged loess

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.     

The significance of rainstorm variations to shallow translational hillslope failure

Landsliding in eastern Scotland results from high-magnitude rainstorms generated under either cyclonic or anticyclonic conditions, particularly during the summer. Data from Aviemore indicated that cyclonic storms produce higher rainfall totals than anticyclonic storms, as well as being of longer duration and lower intensity. The distribution of rain during individual storms also varies with the synoptic conditions under which the storms are produced. These different rainfall characteristics produce different geomorphic responses, which can be investigated in detail using physical based modelling. In this paper, a physically based coupled hydrology–stability model is used to assess the significance of these rainfall characteristics to soil moisture response and slope instability for mature podsols. The results provide evidence that rainstorms of different synoptic origin produce varying hydrological response, involving both the extent and the timing of moisture content change. This affects the depth and timing of slope failure, with anticyclonic storms promoting a large, rapid response in the factor of safety at shallow depths within the soil. Cyclonic storms produce a more gradual response, with the region of probable failure being deeper. Futhermore, each of these storm types is associated with different rainfall distributions, and this is also shown to have a significant effect on the timing and depth of slope instability.     

Influence of soil moisture hysteresis on the functioning of capillary barriers

Previous experimental studies of capillary barriers have identified highly hysteretic soil moisture retention characteristics in the materials used. In this study, numerical modelling is used to analyse the role of soil moisture hysteresis in capillary barrier functioning. Comparisons between published experimental results and model simulations indicate that soil moisture hysteresis was a necessary inclusion in the modelling approach to adequately reproduce pore water pressure distributions and the timing of breakthrough occurrences. Under hypothetical intermittent infiltration and evaporation conditions, the predicted volumetric water content in the moisture retention layer was significantly different for hysteretic and non‐hysteretic models. The hysteresis effect was found to be dependent on the nature of infiltration–evaporation cycling, although the predicted volume of flow through the hysteretic barrier was lower than that of the non‐hysteretic case, regardless of the nature of the cyclic upper boundary conditions. For practical engineering designs, where the water leakage through the barrier is the primary concern, the inclusion of soil moisture hysteresis in numerical modelling is needed. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation

The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance ofvetiver grass mulch (VGM) in soil and water conservation.The study involved field ...     

The role of overland flow and subsurface flow on the spatial distribution of soil moisture in the topsoil

Many investigations show relationships between topographical factors and the spatial distribution of soil moisture in catchments. However, few quantitative analyses have been carried out to elucidate the role of different hydrological processes in the spatial distribution of topsoil moisture in catchments. A spatially distributed rainfall—runoff model was used to investigate contributions of subsurface matric flow, macropore flow and surface runoff to the spatial distribution of soil moisture in a cultivated catchment. The model results show that lateral subsurface flow in the soil matrix or in macropores has a minor effect on the spatial distribution of soil moisture. Only when a perched groundwater table is maintained long enough, which is only possible if the subsurface is completely impermeable, may a spatial distribution in moisture content occur along the slope. Surface runoff, producing accumulations of soil moisture in flat flow paths of agricultural origin (field boundaries), was demonstrated to cause significant spatial variations in soil moisture within a short period after rainfall (<2 days). When significant amounts of surface runoff are produced, wetter moisture conditions will be generated at locations with larger upstream contributing areas. Copyright © 2001 John Wiley & Sons, Ltd.     

Internal soil moisture and piezometric responses to rainfall-induced shallow slope failures

Better knowledge regarding internal soil moisture and piezometric responses in the process of rainfall-induced shallow slope failures is the key to an effective prediction of the landslide and/or debris flow initiation. To this end, internal soil moisture and piezometric response of 0.7-m-deep, 1.5-m-wide, 1.7-m-high, and 3.94-m-long semi-infinite sandy slopes rested on a bi-linear impermeable bedrock were explored using a chute test facility with artificial rainfall applications. The internal response time defined by the inflection point of the soil moisture and piezometric response curves obtained along the soil–bedrock interface were closely related to some critical failure states, such as the slope toe failure and extensive slope failures. It was also found that the response times obtained at the point of abrupt bedrock slope decrease can be used as indicators for the initiation of rainfall-induced shallow slope failures. An investigation of spatial distributions of soil water content, ω (or degrees of saturation, S_r), in the slope at critical failure states shows that the 0.2 m – below – surface zone remains unsaturated with S_r 40–60%, regardless of their distances from the toe and the rainfall intensity. Non-uniform distributions of ω (or S_r) along the soil–bedrock interface at critical failure states were always associated with near-saturation states (S_r 80–100%) around the point of bedrock slope change or around the transient ‘toe’ upstream of the slumped mass induced by the retrogressive failure of the slope. These observations suggest the important role of the interflow along the soil–bedrock interface and the high soil water content (or high porewater pressure) around the point of bedrock slope deflection in the rainfall-induced failure of sandy slopes consisting of shallow impermeable bedrocks. The present study proposes an ‘internal response time’ criterion to substantiate the prediction of rainfall-induced shallow slope failures. It is believed that the ‘internal response time’ reflects the overall characteristics of a slope under rainfall infiltration and can be as useful as the conventional meteorology-based threshold times. The ‘internal response time’ theory can be generalized via numerical modeling of slope hydrology, slope geology and slope stability in the future.