Uncertainty quantification of landslide runout motion considering soil interdependent anisotropy and fabric orientation

Landslides - Natural soils often exhibit an anisotropic fabric pattern as a result of soil deposition, weathering, or filling. This paper aims to investigate the effect of soil interdependent...     

A simplified three-dimensional shallow landslide susceptibility framework considering topography and seismicity

Shallow landslides are a prevalent concern in mountainous or hilly regions that can result in severe societal, economic, and environmental impacts. The challenge is further compounded as the size and location of a potential slide is often unknown. This study presents a generalized approach for the evaluation of regional shallow landslide susceptibility using an existing shallow landslide inventory, remote sensing data, and various geotechnical scenarios. The three-dimensional limit equilibrium model derived in this study uses a raster-based approach that uniquely integrates tree root reinforcement, earth pressure boundary forces, and pseudo-static seismic accelerations. Contributions of this methodology include the back-calculation of soil strength from a landslide inventory, sensitivity analyses regarding landslide size-pixel size relationships, and the determination of shallow landslide susceptibility for a landscape or infrastructure considering various root, water, and seismic conditions using lidar bare-earth DEMs as a topographic input. Using a distribution of inventoried landslide points and random points in non-landslide locales, the proposed methodology demonstrated reasonable correlation between regions of high landslide susceptibility and observed shallow landslides within a 150-km² region of the Oregon Coast Range when the water-height ratio was 0.5. The method may be improved by considering spatial hydrologic conditions and geology more explicitly.     

Reliability analysis of piles in spatially varying soils considering multiple failure modes

In most limit state design codes, the serviceability limit checks for drilled shafts still use deterministic approaches. Moreover, different limit states are usually considered separately. This paper develops a probabilistic framework to assess the serviceability performance with the consideration of soil spatial variability in reliability analysis. Specifically, the performance of a drilled shaft is defined in terms of the vertical settlement, lateral deflection, and angular distortion at the top of the shaft, corresponding to three limit states in the reliability analysis. Failure is defined as the event that the displacements exceed the corresponding tolerable displacements. The spatial variability of soil properties is considered using random field modeling. To illustrate the proposed framework, this study assesses the reliability of each limit state and the system reliability of a numerical example of a drilled shaft. The results show the system reliability should be considered for the serviceability performance. The importance measures of the random variables indicate that the external loads, the performance criteria, the model errors of load transfer curves and soil strength parameter are the most important factors in reliability analysis. Moreover, it is shown that the correlation length and coefficient of variation of soil strength can exert significant impacts on the calculated failure probability.     

考虑循环变温的软土热固结模型

在能源岩土工程发展需求背景下,土体工程特性的温度效应研究受到了国内外学者的广泛关注。针对现有关于循环变温热固结理论研究的不足,提出考虑循环变温条件下土体先期固结压力随温度循环次数变化的关系式,计算多次循环变温后软土的固结压缩量。在此基础上,推导考虑循环变温的太沙基固结修正公式,分析整个循环变温过程中孔压和固结沉降的变化规律。最后通过与单元体测试结果进行对比,验证该计算模型的可靠性。研究结果表明,在循环变温和瞬时荷载的耦合作用下,土体的沉降变形和孔压随温度循环次数的变化而变化,且影响程度与循环次数相关;新型热固结模型为涉及循环变温的岩土工程问题分析提供了一定的理论支撑。     

高速远程滑坡飞行数值分析

许多大型高速远程滑坡在近程活动阶段呈现凌空飞行运动,其飞行过程必须考虑空气动力学效应和地面效应,但是直接求解高速滑体凌空飞行运动的偏微分方程是困难的。因此,以往的研究只给出了定性分析或粗略的计算结果。本文将以头寨沟滑坡为例,使用数值模拟方法研究高速滑体凌空飞行的运动规律。结果表明,高速滑体凌空飞行时空气动力效应更多地表现为对滑体的抬升作用;高速滑体因空气动力效应的影响而产生不断增大的水平推力和竖向抬升力,使得水平加速度不断增大,竖向加速度不断减小,导致滑体的水平速度不断增大,而竖向速度则趋于稳定值,当水平速度远超过竖向速度时,滑体的飞行姿态将接近于平行于地面。因此,与不考虑空气动力学效应的情况相比,高速滑体凌空飞行时间更长,飞行距离更远,更加符合滑坡的实际情况。     

A tentative fault propagation description by three-dimensional finite-element analysis

A 3-dimensional finite-element analysis is used to describe the behavior of a block affected by an incipient fault and subjected to a tectonic thrust which is oblique in relation to the fault.The aim of this study is to describe computed fault evolution, stress modifications induced in the whole block by this evolution and possible effects of these stresses.Some of the results obtained match well enough with observations made on the zone from which the model was derived; some other results are not in agreement with observations and thus emphasize the limitations of this kind of computing.     

Post-failure analysis of landslides in spatially varying soil deposits using stochastic material point method

This paper presents the probabilistic analysis of landslides in spatially variable soil deposits, modeled by a stochastic framework which integrates the random field theory with generalized interpolation material point method(GIMP). Random fields are simulated using Cholesky matrix decomposition(CMD) method and Latin hypercube sampling(LHS) method, which represent material properties discretized into sets of random soil shear strength variables with statistical properties. The approach is applie...     

Predictability of long runout landslide motion: implications from granular flow mechanics

Quality of landslide motion prediction is directly linked to the understanding of the basic flow mechanisms. Although it is known that landslides are granular mass flows and granular flow mechanics is an established area of research, hypotheses on landslide motion are still based on simple geometrical relations and heuristic assumptions. New insights into the development of flow properties of high-speed, high-concentration granular flows are given by results of discrete particle simulations: rapid granular flows are self-organizing dynamic systems that are forced to develop a plastic body rheology. This behaviour must be described by a coefficient of internal friction μ_CM that refers to the center of mass of a flow. Coefficients of rapid granular flows of inelastic and rough particles, which are typical for common rock materials, do not vary significantly around μ _CM ≈0.45 that is definitively smaller than the friction coefficient of soil creep (≈0.6). The motion of the center of mass is superimposed by the spreading of the granular mass that is controlled by the same plastic body rheology. This combined motion is a scale-invariant self-similar process that depends only on the drop height of a landslide and its volume. This allows specification of implications that must be given special attention in the development of future models for landslide prediction.     

Numerical study of the runout behavior of the Kamenziwan landslide in the Three Gorges Reservoir region,China

Landslides - The evaluation of landslide runout behavior plays a vital role in the risk assessment of landslides. In this study, the runout behavior of a landslide that occurred on December 10,...     

Probabilistic failure analysis of infinite slopes under random rainfall processes and spatially variable soil

Rainfall-induced landslides occur during or immediately after rainfall events in which the pore water pressure builds up, leading to shallow slope failure. Thereby, low permeability layers result in high gradients in pore water pressure. The spatial variability of the soil permeability influences the probability such low permeability layers, and hence the probability of slope failure. In this paper, we investigate the influence of the vertical variability of soil permeability on the slope reliability, accounting for the randomness of rainfall processes. We model the saturated hydraulic conductivity of the soil with a one-dimensional random field. The random rainfall events are characterised by their duration and intensity and are modelled through self-similar random processes. The transient infiltration process is represented by Richards equation, which is evaluated numerically. The reliability analysis of the infinite slope is based on the factor of safety concept for evaluating slope stability. To cope with the large number of random variables arising from the discretization of the random field and the rainfall process, we evaluate the slope reliability through Subset Simulation, which is an adaptive Monte Carlo method known to be especially efficient for reliability analysis of such high-dimensional problems. Numerical investigations show higher probability of slope failure with increased spatial variability of the saturated hydraulic conductivity and with more uniform rainfall patterns.     

考虑非饱和土基质吸力的丁家坡滑坡变形机制及稳定性评价

丁家坡滑坡位于云阳县黄石镇中湾村,对拟建的云阳—开州（云开）高速公路安全具有潜在的威胁。为了查明丁家坡滑坡特征,开展了野外工程地质测绘、钻探与试验测试,采用Geo-studio完全耦合计算模式分析了不同降雨工况下滑坡渗流场、应力场、位移场的变化,考察了基质吸力在滑坡稳定性评价中的作用,并计算了不同降雨历时、降雨强度下滑坡的稳定性系数。结果表明：（1）丁家坡滑坡的斜坡地形、松散的岩性、潜在的临空面等因素决定了滑坡的形成与发育,坡体渗透性较好,降雨作用激励滑坡的变形,目前该滑坡处于蠕滑阶段;（2）降雨入渗后,坡体孔隙水压力增加,基质吸力减小,有效应力和抗剪强度降低,在土-岩界面形成剪应力集中,产生应变和位移,滑坡变形破坏;（3）高强度短历时的降雨使坡体浅层迅速饱和,易形成浅层滑,低强度长历时的降雨使坡体浸润较深,易造成深部滑动,其潜在滑动面主要为土-岩界面;（4）在非饱和状态下土体基质吸力对滑坡的稳定性具有重要影响;（5）目前滑坡处于基本稳定状态,一旦发生降雨,滑坡稳定性将降低,降雨历时越久、降雨强度越大,滑坡越易失稳。相对于滑坡Ⅱ区,滑坡Ⅰ区对云开高速公路安全的影响更大,应该重点对滑坡Ⅰ...     

Stability analysis of an ancient landslide considering shear strength reduction behavior of slip zone soil

In this paper, the stability of an ancient landslide during the first impounding of a nearby reservoir is investigated through the analyses of the shear strength reduction behavior of slip zone soil. In view of the experimental observations, an empirical strain-dependent soil model is established and is then incorporated in finite element analyses. The numerical analysis results show that the failing sections progressively develop due to the soil strength declines from peak toward residual, and the shear zone propagates within the front slope. It is demonstrated in the numerical results that the toe weighting measure has a significant effect on restraining the shear displacements of the soils and preventing the progressive failure of the landslide. The field observations further confirmed the stability condition of the reinforced landslide.     

Influence of spatially random soil on lateral thrust and failure surface in earth retaining walls

The present study investigates the influence of spatial variability of soil properties on the lateral thrust and failure surface of a 6?m high frictionless rigid earth retaining wall in active condition. The drained friction angle of the soil is modelled as a log-normal anisotropic random field in two dimensions, using the Cholesky decomposition technique. The effect of horizontal and vertical scale of fluctuation is observed on the lateral thrust. The failure surface in the backfill is found to be more or less similar for different combinations of spatial variability in vertical and horizontal directions. Monte-Carlo simulation technique is used to compute the probability of failure and to obtain the worst-case spatial variability configuration.     

Probabilistic analysis of strip footings resting on a spatially random soil using subset simulation approach

The failure probability of geotechnical structures with spatially varying soil properties is generally computed using Monte Carlo simulation (MCS) methodology. This approach is well known to be very time-consuming when dealing with small failure probabilities. One alternative to MCS is the subset simulation approach. This approach was mainly used in the literature in cases where the uncertain parameters are modelled by random variables. In this article, it is employed in the case where the uncertain parameters are modelled by random fields. This is illustrated through the probabilistic analysis at the serviceability limit state (SLS) of a strip footing resting on a soil with a spatially varying Young's modulus. The probabilistic numerical results have shown that the probability of exceeding a tolerable vertical displacement (P _e) calculated by subset simulation is very close to that computed by MCS methodology but with a significant reduction in the number of realisations. A parametric study to investigate the effect of the soil variability (coefficient of variation and the horizontal and vertical autocorrelation lengths of the Young's modulus) on P _e was presented and discussed. Finally, a reliability-based design of strip footings was presented. It allows one to obtain the probabilistic footing breadth for a given soil variability.     

考虑三维波动的饱和土中管桩群桩的水平振动研究

考虑桩周饱和土和桩芯饱和土的三维波动效应研究了饱和土中管桩群桩的水平振动,得到了管桩群桩的水平动力阻抗。将桩周土和桩芯土视为两相饱和土,并利用多孔介质理论来描述其力学特性。运用数学物理手段求得了桩周饱和土和桩芯饱和土的水平动力阻抗。运用波的传播理论和叠加原理,同时考虑边界条件和三角函数的正交性,求得了管桩群桩中任一根管桩的水平作用力。考虑刚性承台处管桩桩顶位移协调条件和桩顶水平作用力平衡条件,得到了饱和土中管桩群桩的水平动力阻抗。以2×2管桩群桩为例分析和讨论了有关物理参量对饱和土中管桩群桩水平振动特性的影响。研究结果表明:实芯群桩与管桩群桩的水平动力阻抗都存在一定的差异,频率较小时需要考虑桩芯饱和土与桩周饱和土性质的差异对管桩水平动力阻抗的影响,管桩长径比和管桩壁厚对饱和土中管桩群桩水平振动的影响较大,在实际工程设计中需要重点考虑桩身尺寸。     

Critical slip surface and landslide volume of a soil slope under random earthquake ground motions

Finding the critical slip surface and estimating the landslide volume are of primary importance for slope seismic design. However, this may be difficult due to the uncertainty of ground motions. To address this problem, a new method for calculating uncertainties is recommended in this paper, especially for the critical slip surface and landslide volume under random earthquake ground motions. Firstly, a series of intensity–frequency nonstationary random earthquake ground motions were generated based on an improved orthogonal expansion method. A given number of potential slip surfaces were set in a soil slope. Subsequently, the factor of safety (FOS) of each slip surface for all ground motions was calculated and the minimum FOS curves were obtained. It was found that the critical slip surfaces and failure times are uncertain under different earthquakes. The Monte Carlo method was used to verify the accuracy of probability density evolution method (PDEM), and the results of the PDEM and the Monte Carlo method are consistent, meaning that the PEDM has higher computational efficiency. Moreover, the distributions of earthquake-triggered landslide volume and landslide depth were analyzed by considering equivalent extreme events. Both landslide volume and depth exhibit a normal distribution for a homogeneous soil slope. The framework of this study is meaningful for slope seismic design in engineering, for example, the location of critical slip surface can be used for slope reinforcement, and the distribution of sliding volume can be used for disaster assessment.     

空间三维滑坡敏感性分区工具及其应用

对于滑坡敏感性分区目前有三种方法:定性法、统计法和基于岩土定量模型的确定性方法。定性法基于对滑坡敏感性或灾害评估的人为判断;统计法用一个来源于结合了权重因子的预测函数或指标;而确定性法,或者说是物理定量模型法以质量、能量和动量守恒定律为基础。二维确定性模型广泛用于土木工程设计,而无限边坡模型(一维)也用于滑坡灾害分区的确定性模型。文中提出了一个新的基于GIS(地理信息系统)的滑坡敏感性分区系统,这个系统可用于从复杂地形中确认可能的危险三维(3-D)滑坡体。所有与滑坡相关的空间数据(矢量或栅格数据)都被集成到这个系统中。通过把研究区域划分为边坡单元并假定初始滑动面是椭球的下半部分,并使用Monte Carlo随机搜索法,三维滑坡稳定性分析中的三维最危险滑面是三维安全系数最小的地方。使用近似方法假定有效凝聚力、有效摩擦角和三维安全系数服从正态分布,可以计算出滑坡失稳概率。3DSlopeGIS是一个计算机程序,它内嵌了GIS Developer kit(ArcObjects of ESRI)来实现GIS空间分析功能和有效的数据管理。应用此工具可以解决所有的三维边坡空间数据解问题。通过使用空间分析、数据管理和GIS的可视化功能来处理复杂的边坡数据,三维边坡稳定性问题很容易用一个友好的可视化图形界面来解决。将3DSlopeGIS系统应用到3个滑坡敏感性分区的实例中:第一个是一个城市规划项目,第二个是预测以往滑坡灾害对临近区域可能的影响,第三个则是沿着国家主干道的滑坡分区。基于足够次数的Monte Carlo模拟法,可以确认可能的最危险滑坡体。这在以往的传统边坡稳定性分析中是不可能的。     

A FEM-MPM hybrid coupled framework based on local shear strength method for simulating rainfall/runoff-induced landslide runout

Landslides - Limited by the independence and its defects of each general software package, simultaneous analysis of runoff, seepage, and large-deformation analysis is still an inevitable challenge....     

基于多源试验数据空间变异土体参数概率反演及边坡可靠度更新

岩土工程现场勘察试验通常只能获得有限的试验数据,据此难以真实地量化土体参数的空间变异性。提出了考虑土体参数空间变异性的概率反演和边坡可靠度更新方法,基于室内和现场两种不同来源的试验数据概率反演空间变异参数统计特征和更新边坡可靠度水平,并给出了计算流程。此外为合理地描述土体参数先验信息,发展了不排水抗剪强度非平稳随机场模型。最后通过不排水饱和黏土边坡算例验证了提出方法的有效性,并探讨了试验数据和钻孔位置对边坡后验失效概率的影响。结果表明：提出方法实现了空间变异土体参数概率反演与边坡可靠度更新的一体化,基于有限的多源试验数据概率反演得到的土体参数均值与试验数据非常吻合,明显降低了对参数不确定性的估计,更新的边坡可靠度水平显著增加。受土体参数空间自相关性的影响,试验数据对钻孔取样点附近区域土体参数统计特征更新的影响明显大于距离取样点较远区域。