水位下降条件下土坡破坏的离心模型试验研究

水位下降引起土坡破坏的规律机理对于发展稳定性分析方法具有重要意义。研制了离心模型试验中超重力场水位升降模拟设备,进行水位下降条件下黏性土坡变形破坏的离心模型试验。根据试验位移测量结果,基于变形与破坏过程集成分析的思路探讨了土坡破坏机理。水位下降导致土坡发生由坡顶向坡脚的渐进性的错动破坏。水位下降条件下土坡的变形和破坏过程是耦合的。变形局部化发展是导致滑裂面出现的根本原因。滑裂面出现后滑动体内部仍发生显著的变形,并与滑裂面上的错动变形相耦合。     

降雨条件下含软弱夹层土坡的离心模型试验研究

进行了降雨条件下含软弱夹层黏性土坡的离心模型试验。试验主要研究了降雨条件下坡体的吸力和变形规律,重点分析了软弱夹层对坡体的影响。测量了含软弱夹层黏性土坡的位移和土坡内一点的吸力。试验结果表明由于软弱夹层的遇水软化和高渗透特性,降雨后含软弱夹层黏性土坡在软弱夹层发生滑出。降雨条件下含软弱夹层黏性土坡的变形可以分为均匀变形、错动阶段和滑坡3个阶段。对降雨过程中的吸力变化与坡体应变变化进行了分析,表明可以通过坡体中各点应变的发展反推出降雨入渗时刻和分布。软弱夹层的存在造成了降雨入渗分布的变化,导致了坡体错动带在该处不再连续,并降低了边坡的稳定性。     

基于图像分析的土坡离心模型试验变形场测量

开发了离心场条件下土坡离心模型试验变形场非接触测量技术并进行了实际应用。基于图像相关分析理论,开发了新的土坡离心模型试验过程中土体位移非接触测量系统以观测离心机运行中土坡的位移。针对简单土坡进行了离心模型试验,测量了土坡的位移场变化过程。测量结果规律性好,表明该非接触测量技术能够较好地测定离心模型试验中土体侧面任意点在任意时刻的位移,适用于离心场环境中土坡变形过程的测量。加载导致土坡在某些位置出现变形集中,意味着这些位置发生了应变局部化。应变局部化的发展与土坡破坏有着密切联系。     

离心场中边坡降雨模拟系统的研制与应用

为了利用离心模型试验研究降雨条件下边坡的变形和破坏特性,研制了一套离心场降雨模拟系统。该系统包括3个子系统:供水加压系统、降雨器、模型箱及防风结构。该系统可通过控制施加压力来调节降雨强度,并能克服离心场中科氏力及高风速对降雨的影响。有效性验证试验结果表明,该降雨系统在模型箱长度和宽度方向均能实现比较均匀的降雨。采用该系统进行了黏性土坡降雨的离心模型试验,结果表明降雨及其入渗过程对边坡的变形有显著影响。     

降雨触发不同级配堆积体滑坡模型试验研究

深入研究降雨条件下堆积体坡失稳规律对滑坡预测预报和防灾减灾具有重要的理论意义和工程实用价值。开发研制了降雨滑坡室内模型试验系统,对3种配制的堆积体土样进行了模型试验。研究了降雨条件下堆积体土坡的渗流、变形、破坏和颗粒运移的规律,探讨颗粒级配对堆积体土坡稳定性的影响。结果表明:坡内土体体积含水率、孔隙水压力和吸力随降雨历程响应明确;湿润锋到达后体积含水率和孔隙水压力持续增加而吸力持续减小,达到峰值后稳定;降雨停止后体积含水率和孔隙水压力立即降低而吸力逐渐增大。坡体破坏瞬时土体位移有一个加速过程。颗粒级配(含石量)对土坡破坏模式具有显著的影响;堆积体含石量为13%,19%,41%的土坡破坏模式分别为多级后退式破坏、冲蚀引起的局部浅层滑动破坏和块状滑动破坏;含石量越小,滑裂面越明显;含石量对细颗粒流失也有影响,含石量越大细颗粒流失越显著,坡脚细颗粒含量越大。     

降水条件下抗滑桩-锚杆加固边坡的离心模型试验研究

锚杆抗滑桩是一种加固边坡的有效结构。本文进行了水位下降条件下素土坡与锚杆抗滑桩组合结构加固土坡的离心模型试验，测量了边坡的位移场变化，分析了锚杆抗滑桩的行为以及土体的变形特性。试验结果表明，锚杆抗滑桩加固导致边坡位移显著减小、改变了滑裂面连续性，并使得坡体破坏表现出显著渐进性。水位下降条件下锚杆抗滑桩加固土坡的破坏过程与变形局部化表现出显著的耦合特性。锚杆抗滑桩结构使得边坡变形均匀化，阻挡了桩侧土体滑动，从而延迟了边坡破坏。     

均质无黏性土流土发生机制室内模型试验研究

通过室内砂槽模型试验模拟均质无黏性土垂向流土的发生发展过程,研究无黏性土发生渗透变形和渗透破坏过程中,土体渗透系数、水力梯度、渗透流量等参数的变化规律,分析土体渗透变形过程中优势流的产生、发展的循环过程,并通过对比试验研究了发生流土破坏后的土体经过一段时间自重固结后的抗渗强度。试验结果表明:均质无黏性土在渗流作用下发生渗透变形的过程中,有一个渗透系数不变的阶段。这一阶段土体中还没有形成优势流,土体处于稳定的安全渗流阶段。土体中优势流的空间可变性造就了一个优势流"形成→发展→消失→再形成"的循环过程,这种循环过程伴随着土体中不断的微小渗透变形。土体发生流土破坏后,破坏区域的土体出现了水力筛分现象,水力筛分过程改变了土体结构,降低了土体的抗渗强度。     

抗滑桩加固黏性土坡变形规律的离心模型试验研究

采用土工离心机及专用振动台,进行了静动力加载条件下抗滑桩加固黏性土坡的离心模型试验。测量了试验过程中边坡的位移场和加速度响应的变化过程以及抗滑桩的位移和应变分布。试验结果表明地震过程中土坡的加速度响应自下而上逐渐增大,震后残余变形的水平分量最值相比震前向坡上部移动。静动力加载过程中,抗滑桩内侧土体存在一个面,其内外两侧的土体位移表现出不同的水平位移变化规律,从而可以将抗滑桩加固土坡划分成4个分别具有不同变形特性的区域;同一高程处桩的水平位移大于内侧土体而小于外侧土体;抗滑桩与土发生较复杂的相互作用,并使得土坡的变形趋于均匀。     

土坡渐进破坏的双安全系数讨论

边坡的破坏是一个渐进累积破坏过程,在边坡剪切带的形成过程中,土体的强度参数c,φ以不同衰减速度进行衰减,因此,c，φ应有不同的安全储备.对不同土性的软化特征进行分析,黏性土土坡随着剪切带的形成,将发生损伤软化,黏聚力c衰减远快于φ的衰减;砂性土土坡随着剪切带的形成,发生剪胀软化,φ衰减快于c衰减.根据不同衰减速度,提出了黏性土土坡按SRF2＞SRF1的方式进行双安全系数分析,砂性土土坡按SRF1＞SRF2方式进行双安全系数分析.同时,提出在不同土性的土坡中,c,φ按不同的方式进行配套折减,供工程界参考和讨论,以逐渐形成共识.     

土坡稳定的非线性极限分析

本文在非线性破坏准则下应用上限极限分析法研究土坡稳定问题,将上限分析法和极限平衡法相结合得到一个最小的上限解。分析中还引入地震系数,用以研究地震条件下的土坡稳定.求解时采用较为简便的逆解法,分析结果以坡度系数的形式表示土坡临界高度。本文分析了强度参数和地震系数对土坡稳定的影响,分析结果与文献中报导的数量不多的离心模型试验结果相比,较为接近。     

Numerical Analyses and Monitoring Performance of Residual Soil Slopes

Changes in the pore-water pressure of unsaturated soil slopes due to rainwater infiltration comprise a crucial factor which affects the shear strength of soils and may trigger slope failures. Two residual soil slopes in two main geological formations in Singapore, the Bukit Timah Granite and the sedimentary Jurong Formation, were fully instrumented. Real-time monitoring systems were developed to examine the pore-water pressure, the rainfall and the groundwater level of the slopes for over a year. The characteristics of the pore-water pressure distributions in both slopes during rainfall were highlighted and compared. The monitoring results indicate that the residual soil slope of the Bukit Timah Granite has a thicker unsaturated zone due to a deeper groundwater table than the residual soil slope of the sedimentary Jurong Formation. A higher permeability of the residual soil of the Bukit Timah Granite results in more rapid changes in negative pore-water pressure due to rainwater infiltration than the residual soil of the sedimentary Jurong Formation. Therefore, the residual soil slope of the Bukit Timah Granite differs from the residual soil slope of the sedimentary Jurong Formation in the changes in shear strength and the variations in the factor of safety during rainfall. The differing characteristics of the pore-water pressure responses during rainfall for these two residual soil slopes are analyzed in the present study based on the results of field measurements and numerical analyses.     

考虑蒸发影响的非饱和土坡渗流分析

运用分形模型理论预测了粘土、粉土与砂土的土-水特征曲线与导水系数曲线。讨论了大气降雨-蒸发作用对非饱和渗流场的变化规律。在大气蒸发作用下,粘土边坡表层土体的负孔压逐渐增大。随着降雨入渗,粘土边坡坡脚处的土体首先达到饱和状态,并出现正孔隙水压。在降雨过程中,粉土边坡与砂土边坡的坡脚处,难以形成正孔隙水压。粘土边坡的实际降雨入渗量较小,且与土体的初始含水量、降雨类型、土体的导水系数等因素有关。非饱和土的实际蒸发量不等于其饱和状态时的土体蒸发能力。当土体达到饱和状态时,两值相等。实际蒸发量与潜在蒸发量的比值是土体表层基质吸力的函数。     

GIS-based three-dimensional slope stability analysis considering rainfall infiltration

Rainfall-induced landslides are a major cause of slope failure in mountainous areas. As rainfall begins to infiltrate a slope the wetting front advances into the soil and reduces its shear strength. Slope failures occur when the reduced shear strength becomes less than the resisting shear strength needed for equilibrium. These areas of instability are usually located near the ground surface where pore-water pressure changes rapidly during infiltration. The wetting front depth in a slope plays an important role in slope stability. In this study a well-known infiltration model, the Green and Ampt model, is integrated into three GIS-based three-dimensional limit equilibrium methods to assess the impact of rainfall on slope stability. This infiltration model can predict the depth of the wetting front during steady and unsteady rainfall. The applied three-dimensional methods are modified according to different positions of the wetting front to reflect the influence of rainfall on slope stability. This approach is capable of calculating safety factors corresponding to individual rainfall events and is also capable of predicting the corresponding failure time. The accuracy of the presented study has been verified by simulating the failure process of a real landslide triggered by a rainstorm.     

现今斜坡工程安全设计理论的根本缺陷与灾难后果

滑坡及其灾难在世界各地、经现代岩土工程设计施工的斜坡中不断地发生。论文提出、分析和论证了造成工程斜坡滑坡的一个本质原因。它就是现代斜坡工程安全设计理论存在根本缺陷。这个缺陷表现在3个方面。第一,土体抗剪强度参数（有效黏聚力和有效内摩擦角）在斜坡安全设计中假定为常数,不随土体孔隙和含水率的增大而减低到零,孔隙水对土体剪切强度的影响仅体现在孔隙水压强对有效应力的影响。第二,经典岩土力学理论（特别是有效应力原理和排水固结理论）仅能预测外部加载产生土体压剪、孔隙率减小、土体强度增大的岩土稳定工况过程。它们不适用于外部卸载造成土体拉张、孔隙率增大、土体强度减少的岩土破垮工况过程。第三,斜坡安全系数是土体抗剪强度与施加剪切应力的比值。由于土体强度本值（品质）很低,加固工程增加这个比值安全系数达到设计最小值时所能够提供的强度本质（品质）增加量也就不高。斜坡工程岩土体的强度和品质没有得到能够防治岩土体拉张变形和滑垮的根本改善和增强。从而,工程人员必须精心全力地确保低品质斜坡工程岩土不破垮和滑塌。可是,又由于工程斜坡众多和它们的降雨、场地和环境变化较大,上述3个方面现代斜坡工程安全设计理论的根本缺陷可以导致：达到安全设计标准的工程斜坡,在施工和营运过程中,能够发生滑垮、产生灾难后果。本论文特别认为,经典岩土力学理论是仅适用于完全压剪的,应称为压剪岩土力学理论。提出了应该建立既适用压剪又适用拉剪的、新的土力学理论和防抗岩土灾害设计方法。     

Performance of Horizontal Drains in Residual Soil Slopes

In tropical and subtropical regions, shallow landslides often occur in residual soil slopes. Short-duration, high-intensity rainfall will increase the pore-water pressure. As a result, the shear strength of the soil in the slopes decreases and the stability of the slopes is affected. In this study, horizontal drains were installed in a residual soil slope in Singapore in order to improve the stability of the slope. The slope was instrumented with tensiometers and piezometers to investigate the effectiveness of the horizontal drains as a slope stabilization method against rainfall-induced slope failures. The variations in water table elevation and matric suction in the slope due to rainfall events were monitored. In addition, numerical analyses of the seepage into the slope brought about by the rainfall were carried out, and the results showed a reasonably good agreement with the data obtained from field measurements. The field measurement results indicated that horizontal drains were indeed effective for lowering the water table and for increasing the stability of the investigated slope. Therefore, horizontal drains are considered to be a useful and economical method for improving the stability of residual soil slopes against rainfall.     

Response of Unsaturated Sandy Soils Under Constant Shear Stress Drained Condition

In order to understand the mechanism and conditions leading to failure of sandy slopes due to the infiltration of rainwater, constant shear stress drained triaxial tests were conducted on three sets of soil samples-normal sand, gravelly sand and silty sand-taken from natural slopes where large-scale landslides have occurred in the past. Water was infiltrated from the bottom of an initially unsaturated soil specimen under constant shear stress drained condition until failure occurred. Such a loading pattern simulated the stress path followed by a soil element on a potential failure plane on a slope subjected to rainwater infiltration. The effects of various parameters reflecting the initial condition, such as relative density, principal stress ratio, degree of saturation and infiltration rate, on the development of deformation during the infiltration process were investigated. The test results confirmed that the development of pore water pressure within the soil is the main reason for the failure of slopes during heavy rainfall. The results obtained can serve as guidelines in developing warning systems against impending rainfall-induced slope failures.     

Stability monitoring of rainfall-induced deep landslides through pore pressure profile measurements

It has long been recognized that field hydrological and geomechanical properties/conditions are the key elements controlling the stability of a slope under the influence of rainfall. Warning systems based on rainfall or ground displacement measurements are popular methods currently being used to minimize the hazards of landslides. When field hydrological monitoring is used, it usually involves a limited number of sensors for either positive or negative pore-water pressure measurements. The available numerical schemes that couple pore-water pressure with a geomechanical analysis are the most suitable for shallow slope failures. Due to the variable and transient nature of the hydrological conditions in earth slopes, field measurements that reflect the pore-water pressure profile on a real-time basis would be highly desirable. Thus, the authors have developed a piezometer system that is based on optical fiber Bragg grating (FBG) pressure sensors. With this system, an array of nine sensors was installed in a single, 60-m-deep borehole to monitor the pore-water pressure profile in a highway slope in Southern Taiwan. This paper describes the details of the FBG sensor array installation in the field and the data obtained throughout three typhoons from 2008 to 2010. The results demonstrate that the field readings can be readily incorporated into the existing mechanics-based analytical framework and can predict the potential of an upcoming slope failure.     

不同降雨强度下红黏土边坡干湿循环试验研究

干湿循环过程中红黏土边坡力学参数发生了变化,红黏土边坡破坏特征和机理与一般土质边坡不同。以贵州红黏土为研究对象,采用浴霸–人工降雨模拟干湿循环,在室内制备了较大尺寸边坡模型,同时在边坡内部不同位置埋设含水率、孔隙水压力和温度传感器,分析了干湿循环下红黏土边坡力学参数演变规律和破坏机理。研究结果表明,随着深度增加,边坡土体含水率受降雨强度影响逐渐减弱,表层含水率受降雨强度影响明显。干燥期含水率呈现先增加后减小的现象。同一降雨强度下,坡脚含水率最大,其次为坡面、坡肩,最后为坡顶。表层孔隙水压力在降雨、渗透期上升,干燥期降低。降雨强度越大,温度变化幅度越大。随深度增加,边坡温度变化幅度逐渐减小。坡脚温度变化幅度较其他部位大。边坡破坏特征由溅蚀→面蚀→片蚀→裂缝→冲沟,未见明显的滑动面。     

华南典型巨厚层红层软岩边坡降雨失稳的模型试验研究

 针对华南巨厚层红层软岩边坡在强降雨条件下极易致灾的问题,采用相似理论,通过制备可表征软岩遇水软化特性的相似材料,构建巨厚层红层软岩边坡相似模型,研究其在中小雨(雨强Id＜25 mm)、大雨(25 mm≤Id＜ 50 mm)、暴雨(50 mm≤Id＜100 mm)等降雨模式下的灾变过程和规律。结果表明：(1) 该类型边坡的变形破坏受降雨模式的影响较大,大雨和暴雨等强降雨条件下边坡岩体逐渐崩解软化,在坡脚处首先达到饱和,产生初始裂缝,在重力及渗透力作用下,裂缝进一步扩展贯通,产生局部破坏,这样,坡脚之上的部分失去支撑,导致整个坡体产生牵引式滑坡。(2) 降雨入渗主要分为无压渗流、有压渗流与饱和渗流3个阶段,边坡表面裂缝主要出现在无压渗流阶段并在有压渗流阶段逐渐扩展贯通、在饱和渗流阶段发生破坏;降雨过程中超孔隙水压力的累积和消散改变了边坡有效应力场的分布,从而引起其位移。(3) 临滑阶段,有效应力和孔隙水压力比位移、位移变化速率等参数对边坡的破坏响应更敏感,因此提出基于应力监测的边坡灾变过程安全预警新思路。     

岩质边坡断续裂隙阶梯状滑移模式及稳定性计算

阶梯状滑移破坏是一类典型岩质边坡破坏失稳模式。在总结断续裂隙阶梯状滑移的岩质边坡地质结构特征的基础上,利用离散元二维颗粒流程序（PFC^2D）模拟研究了边坡阶梯状滑移破裂模式及其演化过程。边坡岩桥可归纳为剪切贯通破坏、张拉贯通破坏及张–剪混合贯通破坏3类。通过岩石细观颗粒黏结力场、岩桥段应力及破裂贯通演化分析,揭示了重力作用下阶梯状滑移是从下而上岩桥逐个渐进性破裂贯通演化的过程,坡体后缘张裂纹发展贯通是下部坡体的牵拉作用造成;以缓倾角阶梯状平行裂隙边坡（岩桥倾角90°,裂隙倾角30°）为例,阶梯状滑移过程大致可分为坡体弹性稳定变形、下部岩桥贯通破坏、中上部岩桥贯通–后缘张裂、整体沿贯通面滑移共个阶段,其中第3个阶段坡体微断裂数急剧增加,为滑裂带扩展至贯通的临界失稳状态。基于滑移模式及其演化过程的认识,建立了岩桥剪切贯通、张拉贯通和张–剪混合贯通三类阶梯状滑移边坡稳定性计算理论模型,推导了考虑岩桥强度和贯通率的边坡安全系数极限平衡计算公式。