土边坡地震反应及其动力稳定性分析

本文建立了计算土边坡地震反应及评价其动力稳定性的一个数值分析模型，将上边坡在动力作用下的应力状态简化为自重应力状态和附加动力状态的叠加，并对这两个应力状态分别进行研究。本文用时域集中质量显式有限元方法结合多次透射公式，研究了无限域中边坡在动力作用下的位移场和应力场，提出了土边坡动力稳定性的定量评价方法。     

蒙脱石晶体胀缩规律及其与基质吸力关系研究

研究了饱和、非饱和膨胀土中对膨胀土工程力学特性有重要作用的胀缩性矿物──蒙脱石晶体的膨胀、收缩变化规律, 将蒙脱石晶体中晶层之间的各种作用综合归纳为收缩和膨胀两种作用势, 并通过实验研究和分析, 给出了膨胀势和收缩势随层间距变化的表述公式, 以及非饱和膨胀土基质吸力随层间距的变化规律, 为进一步研究膨胀土的胀缩机理和非饱和土的基质吸力势提供了一种新的理论基础和研究途径.     

非饱和黄土微观结构与黄土滑坡

原状黄土属于非饱和黄土,对非饱和黄土的微观结构研究对于研究黄土地区边坡的稳定性具有重要意义。通过研究区黄土的SEM图像的微观结构分析和利用Janbu法对典型黄土滑坡进行边坡稳定性的计算分析,认为该地区黄土的内部微观结构以架空结构和镶嵌结构为主,在大颗粒上附着的胶结物较少;随着深度的增加,土体上覆压力增大,土体具有明显的挤压变形现象;黄土体在天然状态下处于极限稳定状态,随着含水量增加,边坡稳定性下降,达到饱和状态时,处于不稳定状态;随着黄土地区经济的快速发展,人类水事活动和工程性经济活动广泛开展,人为因素逐渐成为诱发滑坡发生的主导因素。     

等吸力三轴剪切试验中非饱和黄土强度变形及水量变化特性

通过饱和原状黄土常规三轴试验和非饱和原状黄土等吸力三轴试验研究吸力和净围压对非饱和黄土强度变形的影响,并用HUANG等、胡冉等和方祥位等提出的土水特征曲线模型分析剪切过程中排水规律。研究结果表明：等吸力下原状土样固结剪切体积变形随净围压增大而增大;等净围压下原状土样固结剪切体积变形量随吸力的增大基本呈减小趋势。p-q平面内饱和土CSL线逐渐超过低吸力下非饱和土CSL线,原因在于随着p值增大,相对于非饱和土,饱和土孔隙比越来越小,较小孔隙比对抗剪强度的贡献逐渐大于非饱和土吸力对抗剪强度的贡献。应用固结稳定的数据拟合出HUANG等和胡冉等提出的模型参数,并预测剪切过程中的排水量,发现剪切速率对排水量有影响,这两种模型适用于剪切速率慢,排水充分的情况,而方祥位等提出的模型对不同剪切速率会拟合出不同的参数。     

地震作用下非饱和土主动土压力极限分析半解析法

地震是诱发边坡失稳的主要因素之一,重力式挡土墙作为一种广泛采用的岩土支挡结构,有必要对其地震稳定性问题进行深入的研究.为有效评估地震作用下非饱和填土的主动土压力,基于极限分析上限原理和拟动力法,提出一种半解析水平片分法,计算具有非线性分布特征的非饱和土重力和地震惯性力所做外功率,并构建功能平衡方程,得到非饱和填土主动土压力显示半解析解.通过与解析解对比,验证该方法的合理性,并通过算例分析,揭示吸力效应的强化机制和非饱和填土主动土压力的地震响应规律.结果表明:忽略吸力效应会高估填土的主动土压力,吸力的强化作用不仅取决于填土类型,还与地震动特性密切相关;水平和竖向地震动对土压力有较大影响, 土压力系数峰值随土剪切模量的增加略有增加并向负方向移动,随地震周期的增加略有增加并向正方向移动;填土倾角较大时,坡顶附加荷载的影响更加显著;对于倾角大于100°的填土,墙G土界面摩擦角较大时,土压力相对较高.     

饱和黄土场地原位试验及液化势评价

目前,主要依靠室内动力试验对黄土液化势进行评价。由于黄土特殊的结构性,室内试验对其饱和的过程较为复杂,且与实际场地饱和黄土差异明显,导致室内黄土液化试验结果并不能代表现场饱和黄土的抗液化强度。本文选取兰州市西固区寺儿沟村某饱和黄土场地进行钻孔测试,现场实施了标准贯入试验、静力触探试验以及剪切波速测试。应用Robertson的土类指数分类图对该场地不同含水率黄土的土类进行了界定,确定了饱和黄土属于类砂土,有液化势。应用NCEER推荐方法,计算了3组原位试验数据的饱和黄土循环抗力比（CRR）,通过与1976年唐山地震和1999年集集地震液化土CRR对比,得出了饱和黄土抗液化强度很低的结论。     

地下采煤情况下地表黄土边坡稳定性分析

针对近年来我国西北黄土地区地下采煤诱发地表变形,从而导致地表黄土边坡失稳及滑坡问题,使用显式有限元、动力学大变形计算方法以及土动力学基本理论进行分析研究,并提出一种适用于地下动态扰动对地表边坡稳定性影响的分析方法。通过计算分析得知,地下采煤对地表边坡稳定性的影响是一个动态的过程,所提方法具有较高的计算效率,且能够分析边坡的渐进破坏过程。     

考虑非饱和特性的黄土湿陷性与微观结构分析

利用扫描电子显微镜测试技术对3个场地16个土样的微观结构进行观测,并使用图像处理软件对微观图像进行处理、对土样孔隙的几何特征参数和分维数进行了提取,土样孔隙分布分维数为1.816~1.936。利用分形几何学原理建立非饱和土的孔隙分布函数,对天然湿度下黄土中水分分布进行分析,运用回归分析的方法对孔隙的分维数、非饱和孔隙孔隙率和湿陷性的关系进行了分析。结果表明：孔隙分维数越大,孔隙结构越复杂;天然湿度下处于非饱和状态的黄土孔隙孔径均大于40μm,黄土的湿陷系数随着孔隙分维数、非饱和孔隙孔隙率的增大而增大,非饱和孔隙是造成黄土湿陷的主要原因。     

黄土湿载结构性模型在黄土边坡动力稳定性分析的应用

土的结构性是土颗粒空间排列和粒间粘结综合作用所表现出来的力学效应。在地震荷载作用过程中,天然土边坡的结构性参数主要体现应力和变形的共同作用,反映地震荷载作用过程中应力和变形的协调关系及结构性土的结构损伤过程(即抗剪强度参数的变化规律)。首先通过分析认为用结构性参数来定量判断地震荷载作用过程中黄土边坡的稳定性更具合理性,其物理意义更明确;其次通过分析黄土地区某一天然边坡在Ⅸ度地震烈度作用下的黄土边坡动力稳定性,验证结构性参数作为边坡稳定性分析判据的可行性,且这一方法能定量地确定边坡滑动面的位置及所对应的安全结构性参数。     

大气作用下膨胀土地基的水分迁移与胀缩变形分析

运用土体渗流和蒸发理论,建立了大气-非饱和土相互作用模型;以现场观测的气象数据作为边界条件,进行了地基土中水分迁移的数值模拟,得到了大气作用下地基土体含水量的动态分布规律。计算结果表明,地基土中含水量变化幅度随深度增加而递减,3.5 m深度以下土体的体积含水量基本不变,从而确定了南宁地区膨胀土地基的大气影响层深度为3.5 m。在此基础上,结合已有膨胀土胀缩性指标的干湿循环效应研究成果,提出了一种同时考虑干湿循环效应和1.0 m深处含水量变化的膨胀土地基胀缩变形计算方法,通过算例将该法与传统方法进行比较,结果显示该法更加符合工程实际。     

A low‐dimensional physically based model of hydrologic control of shallow landsliding on complex hillslopes

Hillslopes have complex three‐dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and soil depth. To investigate the stability of complex hillslopes (with different slope curvatures and plan shapes), we combine the hillslope‐storage Boussinesq (HSB) model with the infinite slope stability method. The HSB model is based on the continuity and Darcy equations expressed in terms of storage along the hillslope. Solutions of the HSB equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. The presented model is composed of three parts: a topography model conceptualizing three‐dimensional soil mantled landscapes, a dynamic hydrology model for shallow subsurface flow and water table depth (HSB model) and an infinite slope stability method based on the Mohr–Coulomb failure law. The resulting hillslope‐storage Boussinesq stability model (HSB‐SM) is able to simulate rain‐induced shallow landsliding on hillslopes with non‐constant bedrock slope and non‐parallel plan shape. We apply the model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). In the presented model, the unsaturated storage has been calculated based on the unit head gradient assumption. To relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case, we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method. The results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability. Therefore, it can be concluded that the presented dynamic slope stability model (HSB‐SM) can be used safely for slope stability analysis on complex hillslopes. Our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others, whilst divergent convex hillslopes remain stable (even after intense rainfall). In addition, the relation between subsurface flow and hillslope stability has been investigated. Our analyses show that the minimum safety factor (FS) occurs when the rate of subsurface flow is a maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Copyright © 2008 John Wiley & Sons, Ltd.     

Poro-mechanical coupling influences on potential for rainfall-induced shallow landslides in unsaturated soils

Rainfall-induced landslides are a common occurrence in terrain with steep topography and soils that have degradable strength. Rainfall infiltration into a partially saturated slope of infinite extent can lead to either a decrease or complete elimination of soil suction, compromising the slopes' stability. In this research the rainfall infiltration coupled with deformation of a partially saturated soil slope during rainfall infiltration is analyzed. The limit equilibrium conditions and the shear strength relationship of a partially saturated soil are employed to develop an analytical solution for calculating the stability of an infinite partially saturated slope due to rainfall infiltration. The analytical solutions are able to consider the influence of the coupled effects on the stability of the slope. The factors that affect the safety of a partially saturated slope of infinite extent are discussed. The results indicate that the poro-mechanical coupling of water infiltration and deformation has an important effect on the stability of the infinite unsaturated slope.     

加筋土边坡临界滑动场

在分析加筋土边坡稳定性时,将加筋材料的作用视为施加于滑面上的等效力,建立了满足力平衡的加筋土边坡安全系数的计算格式;将边坡临界滑动场数值模拟方法进行推广,提出了基于力平衡的加筋土边坡临界滑动场计算方法,可以得到形状任意的临界滑动面及边坡最小安全系数。通过算例,比较加筋前后临界滑动面和安全系数的变化,并探讨了加筋水平间距、强度、长度对加筋土边坡稳定性的影响。     

The influence of water retention curve hysteresis on the stability of unsaturated soil slopes

Hysteresis is a common feature exhibited in hydraulic properties of an unsaturated soil. The movement of wetting front and the hysteresis effect are important factors which impact the shear strength of the unsaturated soil and the mechanics of shallow landslides. These failures are mainly triggered by the deepening of the wetting front accompanied by a decrease in matric suction induced by infiltration. This research establishes a method for determining a stability analysis of unsaturated infinite soil slopes, integrating the influence of infiltration and the water retention curve hysteresis. Furthermore, the present stability analysis method including the infiltration model and the advanced Mohr–Coulomb failure criterion calculates the variations of the safety factor (FS) in accordance with different slope angle, depth and hydrological processes. The experimentally measured data on the effect of hysteresis are also carried out for comparison. Numerical analyses, employing both wetting and drying hydraulic behaviour of unsaturated soil, are performed to study the difference in soil‐water content as observed in the experiments. The simulating approximations also fully responded to the experimental data of sand box. The results suggest that the hysteresis behaviour affect the distribution of soil‐water content within the slope indeed. The hysteresis made the FS values a remarkable recovery during the period of non‐rainfall in a rainfall event. The appropriate hydraulic properties of soil (i.e. wetting or drying) should be used in accordance with the processes that unsaturated soil actually experience. This method will enable us to acquire more accurate matric suction head and the unsaturated soil‐shear strength as it changes with the hysteretic flow, in order to calculate into the stability analysis of shallow landslides. An advanced understanding of the process mechanism afforded by this method is critical to realizing a reliable and appropriate design for slope stabilization. It also offers some immediate reference information to the disaster reduction department of the government. Copyright © 2011 John Wiley & Sons, Ltd.     

基于拟动力法的抗滑桩加固边坡地震稳定性分析

地震力作用下土质边坡动态稳定性研究对实际边坡工程有着重要的意义。采用拟动力法结合简化毕肖普法研究坡顶抗滑桩加固土质边坡在地震力作用下的动态稳定性。尽管拟静力法是目前处理地震力最为广泛的方法之一,但其局限性在于无法考虑地震力随时间变化且忽略了地震波在土体中的传播。而拟动力法采用正弦波模拟地震波在土中传播,并考虑地震波从坡脚传递到坡顶的相位差以及阻尼力对边坡稳定性的影响,通过边坡安全系数的变化揭示土质边坡在地震力作用下的稳定性变化规律。将得到的结果与拟静力法进行对比,突出了拟动力法的优势。最后,考虑水平地震加速度系数、加速度幅值放大系数以及土体内摩擦角对边坡稳定性的影响,以期对实际工程提供理论借鉴。     

How hydrological factors initiate instability in a model sandy slope

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.     

Lateral water flux in the unsaturated zone: A mechanism for the formation of spatial soil heterogeneity in a headwater catchment

Measurements of soil water potential and water table fluctuations suggest that morphologically distinct soils in a headwater catchment at the Hubbard Brook Experimental Forest in New Hampshire formed as a result of variations in saturated and unsaturated hydrologic fluxes in the mineral soil. Previous work showed that each group of these soils had distinct water table fluctuations in response to precipitation; however, observed variations in soil morphology also occurred above the maximum height of observed saturation. Variations in unsaturated fluxes have been hypothesized to explain differences in soil horizon thickness and presence/absence of specific horizons but have not been explicitly investigated. We examined tensiometer and shallow groundwater well records to identify differences in unsaturated water fluxes among podzols that show distinct morphological and chemical differences. The lack of vertical hydraulic gradients at the study sites suggests that lateral unsaturated flow occurs in several of the soil units. We propose that the variations in soil horizon thickness and presence/absence observed at the site are due in part to slope‐parallel water flux in the unsaturated portion of the solum. In addition, unsaturated flow may be involved in the translocation of spodic material that primes those areas to contribute water with distinct chemistry to the stream network and represents a potential source/sink of organometallic compounds in the landscape.     

Effect of air mobility in a soil pipe on water flow through a model hillslope after pipe clogging

Soil pipes (continuous macropores expanding laterally in the soil subsurface) are a key factor controlling hillslope water cycles and sediment transport. Soil pipes usually enhance slope stability under rainfall events through their high water drainage ability, and pipe clogging by sediments is regarded as a risk for slope failure. In this study, we conducted a bench-scale pipe clogging experiment to clarify the effect of air mobility in soil pipes on water flow and water pressure build-up in the slope at the clogged point. Before pipe clogging, the soil pipe drained rainwater effectively and lowered the groundwater table. After the pipe clogging event, the mobility of air in the soil pipe before the clogging determined the water flow in the slope. When the air in the soil pipe connected to the atmosphere and moved freely, the water level in the soil pipe increased at the pipe clogging, and water pressure build-up was limited near the pipe outlet. On the other hand, when air in the soil pipe was entrapped by the clogging, water pressure suddenly increased, and the groundwater table of the whole slope rose correspondingly. This study clearly demonstrated the importance of pipe morphology with respect to air connectivity between the pipe and atmosphere to elucidate the water flow and slope stability during the pipe clogging event. © 2019 John Wiley & Sons, Ltd.     

Geophysics For Slope Stability

A pre-requisite in slope stability analyses is that the internal structure and the mechanical properties of the soil or rock mass of the slope, are known or can be estimated with a reasonable degree of certainty. Geophysical methods to determine the internal structure of a soil or rock mass may be used for this purpose. Various geophysical methods and their merits for slope stability analyses are discussed. Seismic methods are often the most suitable because the measurements depend on the mechanical properties that are also important in the mechanical calculation of slope stability analyses. Other geophysical methods, such as electromagnetic, electric resistivity, self-potential, and gravity methods, may be useful to determine the internal structure, but require a correlation of found boundaries with mechanical properties.