Stability analysis of unsaturated soil slope during rainfall infiltration using coupled liquid-gas-solid three-phase model

Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase,and solid skeleton in an unsaturated soil slope. In this study, a loosely coupled liquid-gas-solid three-phase model, linking two numerical codes,TOUGH2/EOS3, which is used for water-air two-phase flow analysis, and FLAC^(3D), which is used for mechanical analysis, was established. The model was validated through a documented water drainage experiment over a sandy column and a comparison of the results with measured data and simulated results from other researchers. The proposed model was used to investigate the features of water-air two-phase flow and stress fields in an unsaturated soil slope during rainfall infiltration. The slope stability analysis was then performed based on the simulated water-air two-phase seepage and stress fields on a given slip surface. The results show that the safety factor for the given slip surface decreases first, then increases, and later decreases until the rainfall stops. Subsequently, a sudden rise occurs. After that, the safety factor decreases continually and reaches its lowest value, and then increases slowly to a steady value. The lowest value does not occur when the rainfall stops, indicating a delayed effect of the safety factor. The variations of the safety factor for the given slip surface are therefore caused by a combination of pore-air pressure, matric suction, normal stress, and net normal stress.

Stability analysis of an unsaturated soil slope considering rainfall infiltration based on the Green-Ampt model

Based on the principle of saturated infiltration and the Green-Ampt model,an unsaturated infiltration model for a soil slope surface was established for either constant moisture content,or depth-varying moisture content and the slope.Infiltration parameters in the partially saturated slope were revealed under sustained rainfall.Through analysis of the variation of initial moisture content in the slope,the ponding time,infiltration depth,and infiltration rate were deduced for an unsaturated soil slope subject to rainfall infiltration.There is no ponded water on the surface of the slope under sustained low-intensity rainfall.The results show that the infiltration parameters of an unsaturated slope are influenced by the initial moisture content and the wetting front saturation,the soil cohesion and rainfall intensity under sustained rainfall.More short-term slope failures can occur with the decrease of cohesion of the soil of the slope.The ponding time and infiltration depth differ considering constant or different initial moisture content respectively in the soil slope.Then,best-fit curves of the infiltration rate,ponding time,and infiltration depth to the wetting front saturation were obtained with constant or different initial moisture contents.And the slope failure time is roughly uniform when subject to a rainfall intensity I>5 mm/h.

Experimental study on instability mechanism and critical intensity of rainfall of high-steep rock slopes under unsaturated conditions

Two critical factors,namely intense precipitation and intricate excavation,can trigger rock mass disasters in mining operations.In this study,an indoor rainfall system was developed to precisely regulate the flow and intensity of precipitation.A large-scale model experiment was conducted on a self-designed physical simulation experiment platform to investigate the failure and instability of high-steep rock slopes under unsaturated conditions.The real-time reproduction of the progressive failure process in high-steep rock slopes enabled the determination of the critical rainfall intensity and revealed the mechanism underlying slope instability.Experiment results indicated that rainfall may be the primary factor contributing to rock mass instability,while continuous pillar mining exacerbates the extent of rock mass failure.The critical failure stage of high-steep rock slopes occurs at a rainfall intensity of 40 mm/h,whereas a rainfall exceeding 50 mm can induce critical instability and precipitation reaching up to 60 mm will result in slope failure.The improved region growing segmentation method(IRGSM)was subsequently employed for image recognition of rock mass deformation in underground mines.Herein an error comparison with the simple linear iterative cluster(SLIC)superpixel method and the original region growing segmentation method(ORGSM)showed that the average identification error in the X and Y directions by the method was reduced significantly(1.82%and 1.80%in IRGSM;4.70%and 6.26%in SLIC;9.45%and 12.40%in ORGSM).Ultimately,the relationship between rainfall intensity and failure probability was analyzed using the Monte Carlo method.Moreover,the stability assessment criteria of rock slope under unsaturated condition were quantitatively and accurately evaluated.

Coupled hydro-mechanical analysis of slope under rainfall using modified elasto-plastic model for unsaturated soils

Two modifications for the basic Barcelona model(BBM) are present. One is the replacement of the net stress by the average skeleton stress in unsaturated soil modeling, and the other is the adoption of an expression for the load-collapse(LC) yield surface that can match flexibly the normal compression lines at different suctions. The predictions of the modified BBM for the controlled-suction triaxial test on the unsaturated compacted clay are presented and compared with the experimental results. A good agreement between the predicted and experimental results demonstrates the reasonability of the modified BBM. On this basis, the coupled processes of groundwater flow and soil deformation in a homogeneous soil slope under a long heavy rainfall are simulated with the proposed elasto-plastic model. The numerical results reveal that the failure of a slope under rainfall infiltration is due to both the reduction of soil suction and the significant rise in groundwater table. The evolution of the displacements is greatly related to the change of suction. The maximum collapse deformation happens near the surface of slope where infiltrated rainwater can quickly reach. The results may provide a helpful reference for hazard assessment and control of rainfall-induced landslides.

Application of isotopic information for estimating parameters in Philip infiltration model

Minimizing parameter uncertainty is crucial in the application of hydrologic models.Isotopic information in various hydrologic components of the water cycle can expand our knowledge of the dynamics of water flow in the system,provide additional information for parameter estimation,and improve parameter identifiability.This study combined the Philip infiltration model with an isotopic mixing model using an isotopic mass balance approach for estimating parameters in the Philip infiltration model.Two approaches to parameter estimation were compared:(a) using isotopic information to determine the soil water transmission and then hydrologic information to estimate the soil sorptivity,and(b) using hydrologic information to determine the soil water transmission and the soil sorptivity.Results of parameter estimation were verified through a rainfall infiltration experiment in a laboratory under rainfall with constant isotopic compositions and uniform initial soil water content conditions.Experimental results showed that approach(a),using isotopic and hydrologic information,estimated the soil water transmission in the Philip infiltration model in a manner that matched measured values well.The results of parameter estimation of approach(a) were better than those of approach(b).It was also found that the analytical precision of hydrogen and oxygen stable isotopes had a significant effect on parameter estimation using isotopic information.

基于改进Mein-Larson降雨入渗模型的黄土边坡稳定性分析

【目的】降雨是诱发浅层边坡滑动的主要因素,为了使降雨入渗过程更加接近实际,【方法】在传统的Mein-Larson降雨入渗模型基础上,考虑土体初始含水率非均匀分布,以含水率分布函数对传统Mein-Larson降雨入渗模型进行了改进并验证了改进模型的有效性。分别将传统Mein-Larson降雨入渗模型和改进的入渗模型与非饱和无限长边坡稳定分析方法结合,建立考虑边坡倾角、土体初始含水率和降雨形式的降雨诱发型边坡稳定性问题计算模型并对边坡安全系数计算,最后将计算结果与有限元数值模拟结果对比分析。【结果】结果表明:含水率分布函数计算值接近试验值,当参数A取0.375时,拟合优度达到0.995。采用改进的入渗模型计算出的各时段湿润锋深度与传统入渗模型接近,但是湿润锋比传统入渗模型早7.7 h到达地下水位线。【结论】基于改进的降雨入渗模型的边坡稳定计算模型计算的边坡安全系数与有限元数值模拟结果接近,相比于基于传统Mein-Larson降雨入渗模型的边坡稳定计算模型计算结果更精确,接近工程实际,可为降雨诱发型边坡稳定分析提供参考。

三维地形条件下雨水入渗与地表径流耦合分析

为定量表述降雨发生后不同时刻下三维边坡土壤水分的分布和变化规律,基于有限体积法建立了雨水入渗与地表径流耦合模型.耦合模型分别采用二维不可压缩Navier-Stokes方程和三维非线性Richards方程作为地表径流和地下水渗流的控制方程,在复杂三维地形条件下具有较强的适用性.对一处实际工程的分析结果表明:在三维地形因素的控制下,降雨引发的地表径流主要汇集于总体上自高向低流动的优势径流途径,并对降雨强度的变化产生延迟响应;在地表径流作用下,地表积水深度在局部空间上呈现出地势低洼处远大于地势较高处的显著不均匀分布,并且这种不均匀性随时间不断加剧;地表积水汇集产生的高水力梯度导致低洼处的雨水入渗更为强烈且持久.研究表明,考虑三维地形因素的雨水入渗与地表径流耦合模型能够为实际工程中边坡稳定性分析提供准确合理的数据支撑.

基于野外观测实验的中国东部湿润区降雨入渗模拟分析——以宁波画龙溪流域为例

本文以中国东部湿润区典型小流域浙江宁波画龙溪为例,将野外原位定点观测与模型模拟分析相结合,建立了HYDRUS-1D土壤水模拟模型,选取2016年9月29日、2016年10月7日典型降雨事件分别对模型进行率定和验证,并对2016―2020年不同降雨强度下不同土地利用类型的场次土壤水分入渗开展了观测与模拟,以揭示中国东部湿润区不同土地利用类型下的降雨-入渗规律。结果表明:(1)从土壤水分变化过程模拟来看,HYDRUS-1D模型模拟土壤水分动态变化特征具有较高的精度,90%模拟结果的纳什效率系数达到0.80以上。(2)在同等降雨强度下,4种土地利用类型土壤下渗量从大到小依次为农田、杨梅林、坡耕地、竹林。下渗率受降雨量及降雨强度影响较大,不同土地利用下土壤下渗量随着降雨强度增强而显著增加。(3)土壤下渗量同时也受到降雨历时与前期降雨情况深刻影响。当降雨强度从小雨逐级增加到大暴雨,各土地利用类型下渗量略微增加,但增加量均小于5%。对于历时短、强度高的极端降雨事件,降雨强度超过了下渗强度,形成超渗产流,将出现降雨量大但下渗量反而小的现象。本研究成果可为中国东部湿润区农业生产、三水转化规律等提供理论参考。

多层非均质边坡降雨入渗分析的改进Green-Ampt模型

边坡降雨入渗分析对于降雨型滑坡加固设计、治理和风险防控至关重要。经典的Green-Ampt模型参数虽然具有明确的物理意义,计算便捷,但是忽略了入渗区客观存在的过渡层,并且不能有效分析考虑土体渗透系数空间变异性的多层非均质边坡降雨入渗问题。为此,提出了一种适用于多层非均质边坡降雨入渗分析的改进Green-Ampt模型,考虑了降雨入渗的椭圆形过渡层,推导了不同降雨历时下边坡含水率分布情况。同时,以无限长边坡模型为例,通过4种常见的边坡工况验证了该模型的有效性,并进行了降雨入渗条件下非均质边坡稳定性分析。结果表明:对于设定的4种工况,提出的改进Green-Ampt模型计算的边坡体积含水量分布、安全系数和滑动面深度与Richards方程数值解吻合,而基于修正Green-Ampt模型计算的边坡体积含水量和滑动面分布存在偏差,边坡安全系数偏小。此外,基于提出的改进Green-Ampt模型能够准确识别最危险滑动面位置。研究成果可为多层非均质边坡降雨入渗分析及降雨型滑坡加固设计及风险防控提供理论参考。

普朗铜矿区土壤水分运移动态监测与数值模拟研究

揭示矿区土壤水分特性对生态环境保护具有重要意义。本文基于2023年普朗铜矿草地未采区、草地裂缝区、林地未采区、林地裂缝区不同深度土壤水分监测数据,构建了4个地块的Hydrus-1d土壤水分运移模型,模拟典型降雨事件下矿区不同地块水分通量演变特征及包气带水分入渗深度。结果表明:土壤水分模拟决定系数R2均大于0.6,平均绝对误差RMSE和均方根误差MAE均小于1,建立的普朗铜矿区土壤水分运移模型具有较高的准确度。埋深20 cm处土壤水分通量最大,随着土层深度的加深,各地块土层土壤水分通量均呈明显下降趋势;埋深0~120 cm范围内草地裂隙区、林地裂隙区的土壤水分通量比草地未采区和林地未采区相应提高了3.52%和5.79%;草地平均水分通量(4.07%)大于林地(2.86%)。相同降雨条件下,草地裂缝区入渗深度最大,林地未采区入渗深度最小;单次降雨量达35 mm才能对深层地下含水层进行补给。

基于Mein-Larson入渗模型的浅层降雨滑坡稳定性研究

降雨入渗模型与边坡稳定性方法有机结合是研究降雨诱发滑坡稳定性的有效方法。在深入分析降雨入渗基本理论的基础上,将Mein-Larson入渗模型与基于饱和土、非饱和土以及近似非饱和土的无限边坡稳定性分析方法有机结合,综合考虑了高强度短历时和低强度长历时两种降雨情形,拓展并改进了基于Green-Ampt入渗模型的饱和土和近似非饱和土无限边坡稳定性模型,并依托典型边坡实例对各评价模型的计算结果和适用性等进行了对比分析。

不同降雨量及雨强条件下兰州南山人工侧柏林土壤水分入渗规律

[目的]降雨是干旱半干旱地区土壤水分的主要来源,将野外观测和模型模拟相结合研究降雨入渗规律,可以更系统地掌握土壤水分亏缺状况。[方法]通过定点观测,应用Hydrus-1d模型对兰州南山人工侧柏林土壤水分动态变化进行模拟,评估模型在干旱区的适用性,分析不同降雨条件下土壤水分响应状况和入渗机制。[结果]Hydrus-1d模型在兰州南山人工侧柏林有较好的适用性,且深层模拟效果更优。降雨量<30 mm时,10 cm处土壤含水量对降雨响应最为强烈,30,50 cm处受降雨影响相对较小且有明显的滞后,70 cm以下没有响应;降雨量>8.2 mm时存在湿润峰。模拟期内,最大入渗深度为70 cm,最大入渗量为23.7 mm,入渗深度随时间增加而入渗量和入渗速率却随时间延长而减小。降雨量与入渗量、入渗深度和入渗速率呈显著正相关(p<0.05)。降雨量<20 mm时,降雨强度对入渗量、入渗深度和入渗速率存在显著影响。[结论]使用Hydrus-1d模型可以较好地模拟兰州南山人工侧柏林土壤水分动态变化并计算入渗量、入渗速率和入渗深度,且分析发现降雨量对该地土壤水入渗过程的影响更显著。

基于SWAT模型的荆州市不同土地利用类型对雨水入渗量和径流系数的影响

以荆州市为研究对象,结合试验观测、模型模拟与理论分析,研究不同尺度、区域和降雨条件下土地利用变化对雨水入渗量和径流系数的影响。结果表明,2010—2022年荆州市土地利用类型经历了明显转变,耕地面积缩减,建设用地扩张,林地与草地面积稳定,水域略增,其他用地略减,这些变化导致雨水入渗量呈上升趋势,而径流系数呈下降趋势。不同土地利用类型对雨水入渗量和径流系数的影响各异,林地和建设用地对雨水入渗量产生正面影响,对径流系数则是负面;耕地对雨水入渗量有负面影响,对径流系数则正面;草地、水域及其他用地的影响较为有限。土地利用变化对雨水入渗量和径流系数的影响随尺度、区域和降雨条件的不同表现出差异性和复杂性。

基于Mein-Larson入渗模型的降雨滑坡失稳破坏概率研究

[目的]评价降雨诱发浅层滑坡的失稳破坏概率,为相关研究提供理论依据。[方法]在引入并扩展了Mein-Larson降雨入渗模型的基础上,将Mein-Larson入渗模型与无限边坡稳定性方法有机结合,建立2种降雨情形(高强度短历时和低强度长历时)下降雨滑坡稳定性的确定性评价模型,然后再将蒙特卡洛数值模拟方法与降雨滑坡的确定性评价模型结合,建立降雨滑坡稳定性的概率评价方法。[结果]提出了1种降雨诱发浅层滑坡失稳的概率评价方法。[结论]概率评价方法可以描述降雨滑坡发生及发展过程中存在的不确定性,可以计算不同降雨情形下,不同降雨时刻降雨诱发边坡的失稳破坏概率。该方法的评价结果更符合边坡实际情况。

降雨入渗-地表径流下延安卸荷黄土边坡侵蚀演化特征

明确卸荷黄土边坡降雨侵蚀规律对地质灾害防治和流域生态治理具有重要意义。以延安卸荷黄土边坡降雨侵蚀灾害为研究背景,利用自行开发的降雨入渗-地表径流黄土边坡试验平台,研究降雨强度、降雨历时对卸荷黄土边坡入渗量、径流量、土壤流失量以及坡体含水率的影响,揭示降雨作用下卸荷黄土边坡侵蚀演化规律。研究结果表明:1)降雨初期坡面雨水以入渗为主,入渗量约为地表径流量的2~8倍;随着降雨历时增加,地表径流量呈增加趋势,雨水入渗量呈减少趋势;短历时强降雨条件下地表径流量小于入渗量,而持续强降雨条件下地表径流量大于入渗量。2)坡面侵蚀产沙量与降雨强度呈正相关关系,持续强降雨条件下的土壤流失量约为短历时强降雨的10.81倍。3)地表土体含水率随降雨次数增加呈现快速增长到缓慢增长再到平稳状态的发展过程,随降雨强度降低呈减小趋势;相同雨强下,持续强降雨下的地表土体含水率较短历时强降雨增长了9.62%;坡面中、底部浅层土体含水率增长速率高于坡面顶部。4)持续强降雨下边坡侵蚀灾变演化过程为雨水入渗→浅表层土体增湿→坡面密集溅蚀坑→地表径流→浅、细、短的侵蚀沟槽→深、宽、长的侵蚀沟槽→坡体浅层滑塌,坡面侵蚀破坏范围表现为由坡脚向坡顶逐渐后退。

降雨条件下湖南省红层地区浅层土坡失稳机理研究

红层是典型的“易滑地层”,在降雨条件下很容易发生浅层土质滑坡,因此研究红层地区浅层土质边坡在降雨条件下的稳定性十分重要。本研究以湖南省红层区浅层土质边坡为例,采用修正Green-Ampt入渗模型,对不同坡度、降雨强度、饱和渗透系数和初始含水率条件下的红层地区浅层土质边坡的稳定性进行研究,分析得到了各因素对边坡稳定性的影响规律。边坡坡度<45°时,安全系数随坡度增大而减小,边坡坡度>60°时,安全系数随坡度增大而增大;湿润锋随降雨强度的变化不明显,安全系数随降雨强度的增加变化不明显;随着饱和渗透系数的增加,湿润锋深度增加,边坡安全系数减小;安全系数随初始含水率的增加而减小。研究结果可为红层地区边坡防护工程提供一定的理论依据和实践指导。

Run off-on-out method and models for soil infiltrability on hill-slope under rainfall conditions

The soil infiltrability of hill-slope is important to such studies andpractices as hydrological process, crop water supply, irrigation practices, and soil erosion. A newmethod for measuring soil infiltrability on hill-slope under rainfall condition with run off-on-outwas advanced. Based on water (mass) balance, the mathematic models for soil infiltrability estimatedfrom the advances of runoff on soil surface and the water running out of the slope were derived.Experiments of 2 cases were conducted. Case Ⅰ was done under a rainfall intensity of 20 mm/h, at aslope gradient of about 0° with a runoff/on length (area) ratio of 1 : 1. Case Ⅱ was under arainfall intensity of 60 mm/h and a slope of 20° with a runoff/on length (area) ratio of 1 : 1.Double ring method was also used to measure the infiltrability for comparison purposes. Theexperiments were done with soil moisture of 10%. Required data were collected from laboratoryexperiments. The infiltrability curves were computed from the experimental data. The resultsindicate that the method can well conceptually represent the transient infiltrability process, withcapability to simulate the very high initial soil infiltrability. The rationalities of the methodand the models were validated. The errors of the method for the two cases were 1.82%/1.39% and4.49%/3.529% (Experimental/Model) respectively, as estimated by comparing the rainfall amount withthe infiltrated volume, to demonstrate the accuracy of the method. The transient and steadyinfiltrability measured with double ring was much lower than those with this new method, due towater supply limit and soil aggregates breaking down at initial infiltration stage. The method canovercome the short backs of the traditional sprinkler method and double ring method for soilinfil-traility. It can be used to measure the infiltrability of sloped surface underrainfall-runoff-erosion conditions, in the related studies.

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入渗模型进行了改进,并通过有限元数值模拟方法对改进模型进行了验证。结果表明:当降雨入渗在小于2.5 m时,改进模型理论解和数值解存在一定的误差,当降雨入渗在2.5~5 m时,改进模型理论解和数值解基本一致;改进的降雨入渗模型计算结果较Mein-Larson入渗模型更接近数值模拟结果,改进的降雨入渗模型更加完善和可靠,可推广应用到工程实际中。

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。