基于SPH的土质边坡稳定性及失稳后大变形数值模拟

本文采用光滑粒子流体动力学(SPH)法对土质边坡稳定性及其失稳后的大变形进行数值模拟研究。该方法既可以分析边坡的稳定性系数和潜在滑移面,又可以对土质边坡失稳后的大变形过程进行模拟,从而弥补了传统数值模拟分析方法的不足,为土质边坡稳定性及失稳后滑坡大变形分析提供了一种新的方法。首先,采用Fortran语言编写了模拟土质边坡稳定性及失稳后滑坡大变形分析的SPH程序;其次,采用一个经典算例,验证了本文程序和方法在进行边坡稳定性分析时的准确性;最后,为验证该法模拟黏性土质边坡滑坡大变形的准确性,笔者自行设计了一组黏性土体滑坡大变形物理实验并与SPH模拟结果进行了对比。研究成果表明,基于弹塑性本构模型及D-P屈服准则的SPH方法可以较准确的模拟稳定性系数及潜在滑移面,并且可以较准确地模拟失稳后的滑坡大变形发展过程,弥补了目前数值模拟方法的不足,是一种值得推广的新型稳定性及滑坡大变形分析方法。     

某滑坡强度参数反演与稳定性分析

滑坡稳定分析时抗剪强度参数的选取对稳定性判断有决定性作用。本文针对有滑坡征兆的边坡,先利用地质力学分析初步判断边坡的安全系数,然后利用数值模拟获得应力场,再采用混沌粒子群优化算法搜索滑面,发展了基于滑坡征兆的边坡稳定分析方法,通过工程案例探讨了该方法的应用。结果表明:合理的安全系数假设与工况调查是进行稳定性反演的前提;采用极限平衡有限元方法计算边坡安全系数能够逼近地质判断结果、临界滑动面位置也基本一致,但由于采用变形协调方法计算应力场,滑面法向、切向力更加符合实际;采用所提方法分析工程实际时与现场勘察结果可相互对照分析,能令结果更为合理。     

降雨入渗对泥岩-土混填路堤稳定性的影响

降雨入渗是诱发泥岩-土混填路堤边坡失稳的主要因素之一,为了揭示降雨对泥岩-土混填路堤边坡稳定影响的变化规律,选取济邵高速公路一典型路段的泥岩-土混填路堤边坡进行人工降雨模拟试验,对边坡土体中的孔隙水压力、边坡土压力和变形进行监测;探讨雨水入渗对路堤边坡稳定性的影响,推断滑坡的形成机制和预测边坡的稳定发展趋势.原位综合监测和数值分析结果表明:降雨入渗影响下泥岩-土混填路堤边坡的滑动变形区的变形量以坡面最大.裂缝的出现使得雨水更容易进入深层土体,土体吸水崩解、软化,强度急剧下降,使得边坡的稳定性安全系数在降雨后显著降低.     

降雨入渗对泥岩–土混填路堤稳定性的影响

 降雨入渗是诱发泥岩–土混填路堤边坡失稳的主要因素之一,为了揭示降雨对泥岩–土混填路堤边坡稳定影响的变化规律,选取济邵高速公路一典型路段的泥岩–土混填路堤边坡进行人工降雨模拟试验,对边坡土体中的孔隙水压力、边坡土压力和变形进行监测;探讨雨水入渗对路堤边坡稳定性的影响,推断滑坡的形成机制和预测边坡的稳定发展趋势。原位综合监测和数值分析结果表明：降雨入渗影响下泥岩–土混填路堤边坡的滑动变形区的变形量以坡面最大。裂缝的出现使得雨水更容易进入深层土体,土体吸水崩解、软化,强度急剧下降,使得边坡的稳定性安全系数在降雨后显著降低。     

大岩淌滑坡的弹粘塑性自适应有限元分析

应用弹粘塑性自适应有限元方法，对大岩淌滑坡进行了变形与稳定分析。主滑带采用节理元模拟，当滑坡土体出现拉剪屈服区或具有临空面的压剪屈服区时，沿拉剪屈服区的前缘或压剪屈服区的后缘自动加密网格且采用节理元模拟，搜寻新的开裂面，以判断滑坡体是否会产生新的滑动破坏模式。经计算分析，大岩淌边坡的破坏模式是整体破坏，其整体安全系数约为1．143，不存在新的局部滑动破坏模式。     

有限元法在边坡稳定与加固分析中的应用

在边坡的稳定分析中，应用有限元强度折减法，能够得出边坡在达到极限平衡时的危险滑动面，和以往对滑动面形状和位置进行假设的方法相比，强度折减法更加的方便和实用。本文通过有限元强度折减法，分析边坡开挖和锚索对边坡的加固作用，边坡采用分步开挖的方法，运用ANSYS软件输入初始应力的方法模拟边坡在自重应力下的应力应变情况。采用两点集中力的方法来模拟压力型话索框架对土体的加固，运用锚索经验公式反应锚索在土体中的抗剪作用，两种方法相结合，能够比较真实地反应预应力锚索对边坡的压密加固过程和在土体中所起到的刚度作用，能够在实际工程中加以应用。     

益湛线某路堑边坡滑动变形分析

对益湛线K331+320~+600左侧路堑边坡的现场滑动变形破坏特征进行了分析描述,阐述了产生滑动变形的主要原因,利用工程地质分析法和滑坡传递系数法综合评定,表明滑坡现状条件下不稳定,必须对滑坡进行整治,建议采用支挡为主截排地表水和疏排地下水为辅的综合整治措施。针对工程特点,强调在滑坡整治过程中,应加强对边坡岩土体的取样和测试工作,根据岩土体工程地质条件动态设计,做到既经济又安全。     

高填方机场滑坡体变形监测及稳定性分析

对某高填方机场出现裂缝的边坡进行变形监测,分析监测数据,并结合地质勘探和数值模拟结果,表明该处边坡存在滑坡的危险;分析造成滑坡变形的主要原因是回填加载时增加的主动土压力引发老滑坡重新产生新滑动。因此提出该高填方机场边坡稳定处理措施,以削挖重新回填为主。     

边坡土体变形和剪切带形成机制室内试验与数值模拟研究

以砂土边坡为研究对象,建立室内试验模型,并采用图像采集和分析技术获取土体变形过程。同时基于有限差分软件FLAC3D建立滑坡三维模型,分析边坡内部剪切带和变形破坏机制。结合室内模型试验和数值模拟结果,分析了边坡剖面、剪切带(滑动面)处土颗粒位移场分布后发现:当土体完全失稳失去承载能力时剪切带完全贯通,滑移体内土体向下加速滑动;土体破坏失稳以后,边坡出现由坡顶贯通至坡趾上方的滑动面,滑动面上部接近圆弧状,下部水平呈直线型;随着加载的持续,土体受影响的范围增大的同时,位移也越来越大;剪应变云图可以直观地观察到剪切带贯通形成圆弧滑动面的过程,并且随着加载的持续,出现明显剪应变的区域由坡顶向下发展,剪应变主要集中在剪切带区域;边坡受载时边坡内部测点均经历土压力缓慢增大、快速增大、下降后趋于稳定3个阶段,以受荷面中心点向水平、竖直2个方向,土压力逐渐减小。     

库岸古滑坡离心模型试验研究

针对一库岸古滑坡进行了水位骤降条件下 失稳机制 的离心模型试验。 离心模型的制作考虑了原型边坡的大尺寸和非均质特征,离心试验过程中进行了上下游水位的实时控制,试验后进行了边坡土体物理特性和强度特性的对比试验。离心试验结果表明：水库蓄水导致坡脚抗滑阻力降低,坡体前缘出现裂缝并随着水位上升出现坡脚坍滑;水位骤降坡体内产生向外的动水压力,加剧坡脚滑动并形成牵引式滑坡趋势;坡脚被加固后边坡变形情况得到明显改善,滑动被阻止,边坡整体稳定性提高。离心试验前后边坡土体的物理力学试验结果揭示：坡脚滑动会造成坡体土密度和含水率重新分布,并导致近滑动区土体强度特性改变、强度指标下降。 另外,水下土体随浸没时间增长黏聚力会降低直至消失。     

An experimental investigation on slope stability under drawdown conditions using transparent soils

This paper presents an experimental investigation into slope failure during water-level drawdown using transparent soil. The internal characteristics of slope failure are not well-known due to the limitations of the techniques used in the experiments conducted to date. In this study, transparent soil is used to visualize the process of slope failure. We developed a water-level control system to implement simulation of the drawdown of the water level at various speeds and used a charge-coupled device camera to capture images during the entire slope failure process. Particle image velocimetry was used to measure the displacement of the sand particles and identify the sliding zones. The flow paths of the fluid inside the slope were illuminated using an organic dye. The results show that the slope failure process can be divided into two stages: surface and overall sliding. The overall sliding of the slope is caused by the gradual development of partial instability, and the failure mode is a cyclic failure. The slope angle is different above and below the water level during the process of sliding. In our experiments, the slope angle is about 20° above the water level, which is the same as the final stable slope angle, and about 35° below the water level, which is the same as the initial slope angle. This means that the drawdown influences the angle above the water level but has little influence on the angle below the water level. The results of this paper provide a better understanding of the physical behavior and failure mode of soil slopes caused by drawdowns near the coast.     

Stability analysis of bank slope under conditions of reservoir impounding and rapid drawdown

Stability of an ancient landslide in a reservoir area is analyzed by using centrifugal model tests, soil laboratory tests and numerical analysis. Special attention is paid to variation in water level, simulation of large-scale heterogeneous prototype slope, and strength reduction of sliding zone soils after slope sliding. The results of centrifugal model test show that reservoir impounding can reduce sliding resistance at the slope toe, followed by toe collapsing and front cracking of slope. Rapid drawdown can produce hydrodynamic pressure towards reservoir at the front of slope. Deformation is observed in the middle and upper slope, which reduces the slope stability further and forms the pull-typed landslide trend. Reinforcement of slope toe is effective for preventing the progressive failure. The results of laboratory test show that slope toe sliding will lead to the redistribution of soil density and moisture content, which will reduce the shear strength of soil in sliding zone, and the cohesion of immersed soil is reduced gradually and finally vanishes with time. The numerical results show that the strength reduction method used in finite element method (FEM) is very effective in capturing the progressive failure induced by reservoir water level fluctuations, and the evolution of failure surface derived from numerical simulation is very similar to that observed in centrifugal model test.     

Stability analysis of bank slope under conditions of reservoir impounding and rapid drawdown

Stability of an ancient landslide in a reservoir area is analyzed by using centrifugal model tests, soil laboratory tests and numerical analysis. Special attention is paid to variation in water level, simulation of large-scale heterogeneous prototype slope, and strength reduction of sliding zone soils after slope sliding. The results of centrifugal model test show that reservoir impounding can reduce sliding resistance at the slope toe, followed by toe collapsing and front cracking of slope. Rapid drawdown can produce hydrodynamic pressure towards reservoir at the front of slope. Deformation is observed in the middle and upper slope, which reduces the slope stability further and forms the pull-typed landslide trend. Reinforcement of slope toe is effective for preventing the progressive failure. The results of laboratory test show that slope toe sliding will lead to the redistribution of soil density and moisture content, which will reduce the shear strength of soil in sliding zone, and the cohesion of immersed soil is reduced gradually and finally vanishes with time. The numerical results show that the strength reduction method used in finite element method (FEM) is very effective in capturing the progressive failure induced by reservoir water level fluctuations, and the evolution of failure surface derived from numerical simulation is very similar to that observed in centrifugal model test.     

岷县漳县6.6级地震永光村滑坡致灾机制分析

2013年7月22日甘肃省定西市岷县漳县MS6.6级地震,诱发了大量黄土滑坡和崩塌灾害。基于对岷县梅川镇永光村西侧泥流状黄土滑坡的现场勘察、探井取样和高密度面波勘探,得到了该滑坡的地形条件和土层分布特点。通过对滑坡体土样进行室内动三轴液化试验,验证了该滑坡土体在地震作用下发生液化的可能。结合动力有限元法和强度折减法,分析了该滑坡在地震作用下的动力响应特征和动力稳定性的影响因素。结果表明:震前的持续强降雨,导致滑坡体表层黄土含水率升高,抗剪强度降低,在强地震荷载作用下,黄土层之间存在拉应力效应,表层土体发生液化,造成该斜坡失稳瞬间发生,发生长距离滑移。     

三维离散元法解析砂型泥石流细观运动特征研究

基于散体介质理论的三维离散元数值分析方法,引入粘滞阻尼模型考虑系统耗能效应,求解固体作用力和流体连续性方程,充分考虑流固耦合作用,对中、细标准砂泥石流过程进行仿真分析,得到不同砂型泥石流破坏过程及渗流场、颗粒速度场、孔隙率、颗粒接触数等参数变化规律。分析表明,中砂、细砂分别表现出分层渐进式和流滑型的破坏模式,这与已有物理试验现象吻合,验证该模型的适用性,并从渗流场分布规律深刻解释该现象发生机理。泥石流过程中土颗粒速度矢量变化规律从细观上揭示了隐藏在颗粒内部的相互碰撞、摩擦、滑动等复杂运动特点,从宏观上揭示了中砂土坡脚薄弱位置率先突破,主滑动体形成直至完全失稳的分级渐进式破坏过程。进一步分析了土体孔隙率和平均接触数分布云图变化规律,中砂泥石流过程中随颗粒运动,滑动体孔隙率逐渐增大,颗粒接触数逐渐减小,并且这种发展趋势逐渐往坡后方土体蔓延;进一步揭示了中砂泥石流分级渐进破坏过程与颗粒速度场分析规律一致。分析结果表明了该模型方法在模拟泥石流这种大变形、流固耦合问题上的适用性,这对泥石流复杂机理的更深入探索是有益的。     

水位变化引起分层边坡滑坡的实验研究

通过对分层的边坡在水位变化时滑坡的模拟实验，起的滑坡，重点考察了水位涨落速度对坡体稳定的影响，考察了分层坡体的滑坡模式、坡体变形、破坏和渗流引以及坡面从产生张拉裂缝直到形成滑面的整个过程，并对这类滑坡中的现象给出了定性解释。最后用有限元对实验坡体进行了应力和位移的静力场分析，计算结果与实验结果基本一致。     

膨胀土边坡物理模型试验研究

进行了一系列压实膨胀土的大型静力模型试验,对边坡土体吸湿后的含水率、膨胀变形等进行了实时监测。试验成果显示,膨胀土边坡浅层土体吸湿后其含水率场分布不均匀,干湿分界面处土体易由于不均匀膨胀变形而导致局部剪切错动,并随水分在坡体内的迁移,局部滑动面逐渐向边坡纵深扩展,在不同深度、不同部位形成多重剪切滑动面,最终导致边坡整体塌滑。针对静力模型试验进行了考虑膨胀性的非线性有限元计算,比较了边坡自重条件下和吸湿后应力场的变化,可知吸湿引起顺坡向正应力在干湿分界面处变化剧烈,剪应力明显增大,强度折减法得到的模型试验边坡安全系数仅0.92。研究成果表明：影响膨胀土边坡浅层稳定性的最根本原因并非膨胀土的超固结性或裂隙性,而是土的胀缩特性。     

强度折减有限元法模拟边坡牵引式破坏过程

 针对边坡牵引式破坏由下向上逐次滑动的特点,应用强度折减有限元法多轮次计算模拟边坡破坏过程。对模拟计算的方法,采用二分法确定每一轮的强度折减系数;用静力平衡条件将局部破坏区域的土体转化为坡面荷载;用折减系数按轮次逐次变小的控制标准判别是否为牵引式滑坡。以锦江水库左坝头边坡为工程实例,模拟结果与实际情况基本相符,说明此计算方法可行。     

Deformation and failure mechanism of slope in three dimensions

Understanding three-dimensional(3D)slope deformation and failure mechanism and corresponding stability analyses are crucially important issues in geotechnical engineering.In this paper,the mechanisms of progressive failure with thrust-type and pull-type landslides are described in detail.It is considered that the post-failure stress state and the pre-peak stress state may occur at different regions of a landslide body with deformation development,and a critical stress state element(or the soil slice block)exists between the post-failure stress state and the pre-peak stress state regions.In this regard,two sorts of failure modes are suggested for the thrust-type and three sorts for pull-type landslides,based on the characteristics of shear stress and strain(or tensile stress and strain).Accordingly,a new joint constitutive model(JCM)is proposed based on the current stability analytical theories,and it can be used to describe the mechanical behaviors of geo-materials with softening properties.Five methods,i.e.CSRM(comprehensive sliding resistance method),MTM(main thrust method),CDM(comprehensive displacement method),SDM(surplus displacement method),and MPM(main pull method),for slope stability calculation are proposed.The S-shaped curve of monitored displacement vs.time is presented for different points on the sliding surface during progressive failure process of landslide,and the relationship between the displacement of different points on the sliding surface and height of landslide body is regarded as the parabolic curve.The comparisons between the predicted and observed load e displacement and displacement e time relations of the points on the sliding surface are conducted.The classi fi cation of stable/unstable displacement e time curves is proposed.The de fi nition of the main sliding direction of a landslide is also suggested in such a way that the failure body of landslide(simpli fi ed as"collapse body")is only involved in the main sliding direction,and the strike and the dip are the same as the collapse body.The rake angle is taken as the direction of the sum of sliding forces or the sum of displacements in collapse body,in which the main slip direction is dependent on progressive deformation.The reason of non-convergence with fi nite element method(FEM)in calculating the stability of slope is also numerically analyzed,in which a new method considering the slip surface associated with the boundary condition is proposed.It is known that the boundary condition of sliding surface can be described by perfect elasto-plastic model(PEPM)and JCM,and that the stress and strain of a landslide can be described properly with the JCM.     

降雨条件下滇西典型土质滑坡渗流特性分析

降雨是诱发滇西土质滑坡灾害的主要因素,选择滇西红层典型土质滑坡——思铺滑坡做深入的调查,考虑降雨入渗的影响,基于饱和-非饱和渗流理论,利用有限元方法,对强降雨条件下思铺滑坡地下水渗流场动态进行了数值模拟,得到了滑坡地下水压力水头、总水头变化、流速的变化规律,为滑坡的稳定性分析和滑坡预测提供重要的分析数据。