边坡稳定分析的一些进展

本文介绍近年在用极限平衡法与有限单元法 ,分析边坡稳定性方面的一些进展 ,在基于极限平衡的解析法上 ,我们导出了多阶斜坡的稳定安全系数与滑裂面角度的计算公式。这对岩质边坡的设计有很高的实用意义。导出了目前采用的各种条分法的统一计算公式。对于非严格条分法 ,用一个平衡方程并假设条间力的作用方向 ,即能求得安全系数 ;对严格条分法 ,用二个平衡方程 ,并假设条间力的作用方向或条间力的作用点位置 ,就能求出安全系数。统一式是一简单的迭代式 ,因而计算简便 ,并有很高精度。提出了两种用有限元法求边坡稳定安全系数的方法 :一种基于极限平衡法 ,对土质边坡采用圆弧搜索法 ,对岩质边坡采用在滑移面上布置节理单元的方法。另一种采用有限元强度折减法 ,便于采用大型软件 ,是一种很有前途的求边坡稳定安全系数的新方法。     

不同支护模式下黄土高边坡开挖变形离心模型试验研究

 为研究不同支护模式下黄土高边坡的开挖变形特征和支护结构性状,以观音堂隧道进口明洞段黄土高边坡为实例,采用土工离心机,开展黄土高边坡在无支护、全断面土钉支护、上部土钉下部预加固桩复合支护模式下的离心模型试验,试验结果表明：(1) 桩–钉复合支护体系能够显著提高黄土高边坡的稳定性,坡体上部土钉的布设有效地调动了边坡更大范围内土体变形的调整,使得边坡土体的潜在滑移面向坡体内侧转移,将潜在滑移面的剪出口位置限制在预加固桩桩顶以下,而下部预加固桩的布设则有效地承担上部滑体的推力作用,保证坡体在开挖过程中的稳定性。(2) 全断面土钉支护在一定程度上起到了加固边坡土体的作用,但由于土钉支护范围有限,当潜在滑移面深度超出土钉加固范围后,边坡土体发生更大范围内的失稳现象,加剧坡体的破坏。(3) 对于黄土高边坡的加固,桩钉复合支护要优于全断面土钉支护。     

三维边坡稳定问题的基本方程与分析方法

基于空间一点应力分析,进行了空间曲面上一点的应力分析,得出了曲面上一点的法向应力、剪应力与应力分量、曲面一阶偏导数的关系。建立了曲面至边坡表面土柱上力的微分平衡方程、力的平衡方程、力矩平衡方程。和库仑屈服条件一起,构成了边坡稳定问题普遍适用的基本方程。采用与二维问题的简化Bishop法类似假定,得出了一种三维边坡稳定性分析的计算方法。算例表明,本文方法计算结果是合理的,具有广泛的应用意义。     

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。     

工程荷载下岩质边坡破坏机理及稳定分析

边坡破坏形式及剩余下滑力的计算是边坡加固设计的重要组成部分,结合西堠门大桥北塔位老虎山南侧天然边坡在左塔柱工程荷载作用下的破坏形式及稳定性分析,从岩体参数选取、工程荷载计算、不平衡推力法的运用及破裂面的规律分析等方面进行了探讨,对工程荷载下岩质边坡稳定分析及工程设计具有较好的借鉴作用。     

Simplified method for analyzing soil slope deformation under cyclic loading

Reasonable assessment of slope deformation under cyclic loading is of great significance for securing the safety of slopes. The observations of centrifuge model tests are analyzed on the slope deformation behavior under cyclic loading conditions. The potential slip surface is the key for slope failure and follows two rules: (i) the relative horizontal displacement along the potential slip surface is invariable at an elevation, and (ii) the soil along the slip surface exhibits the same degradation pattern. These rules are effective regardless of the location of the potential slip surface throughout the entire deformation process of a homogeneous slope, ranging from the initial deformation stage to the failure process and to the post-failure stage. A new, simplified method is proposed by deriving the displacement compatibility equation and unified degradation equation according to the fundamental rules. The method has few parameters that can be determined through traditional element tests. The predictions from the proposed method agree with the centrifuge test results with vertical loading and shaking table loading. This result confirms that the proposed method is effective in predicting the full deformation process of slopes under different cyclic loading conditions.     

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.     

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。     

基于透明土技术土岩边坡滑移机理的模型试验研究

随着工程技术的飞速发展,土岩边坡滑移机理的研究具有重要的意义和工程应用价值。通过透明土模型试验研究坡顶荷载作用下土岩界面接触滑移机理和规律,实现了土岩边坡内部滑移变形的可视化。考虑了岩体Barton节理粗糙度系数、坡体角度和坡体高度等因素对土岩边坡稳定性的影响。利用粒子图像测速(PIV)和激光散斑技术,获得了土岩边坡在坡顶荷载作用下内部变形的特征。试验分析表明,土岩边坡的滑动可分为3个阶段:初始阶段、匀速阶段和加速阶段;在土岩边坡滑移过程中减小岩体Barton节理粗糙度系数、增大坡体高度、增大坡趾角度将引起边坡土体内部较大的位移,进而引发土岩边坡的失稳。采用双排抗滑桩的边坡防护措施后,有效地延缓边坡土体内部位移的发展,提高土岩边坡的稳定性。文中研究成果为揭示土岩边坡滑移机理及其工程防护的有效性提供了重要的理论依据,通过跟踪透明土颗粒的运动轨迹实现土体内部变形可视化的土岩边坡滑移提供了试验依据。     

土钉加固黏性土坡动力离心模型试验研究

 很多滑坡是由地震引发的,为了防止或减轻地震造成的边坡灾害,目前在边坡的加固治理方面已经发展并形成一些较好的方法,而土钉是边坡抗震加固的一种简便有效的方法。采用动力离心模型试验方法,再现地震条件下土钉加固黏性土坡和素土坡的响应;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。基于试验结果,通过对比素土坡和土钉加固土坡的动力响应,探讨土钉加固土坡的变形规律和加固机制。试验结果表明,地震过程中土坡产生不可恢复的累积变形,其大小与输入的地震加速度峰值有关。通过比较土钉加固土坡和素土坡的位移分布,研究土钉加固土坡的机制。引入土单元应变进行分析,结果表明,土钉加固措施能显著地改变边坡的位移场分布,限制土坡的剪切变形,避免滑裂面的产生,从而提高了边坡的稳定性。     

模拟库水位变化的抗滑桩加固边坡离心模型试验研究

 抗滑桩是边坡深层抗滑最为有效的措施之一,以三峡库区边坡抗滑桩加固工程为背景,利用离心模型试验手段,模拟库区蓄水和水位循环变化条件下失稳边坡的抗滑桩加固机制。详细介绍相应的离心模型试验方法,通过对一系列自然边坡和不同桩间距条件下的模型试验,获得库水位变化影响下的边坡变形、破坏模式和抗滑桩受力,探讨滑坡推力的分布以及不同桩间距条件下的抗滑桩–边坡相互作用机制。测试结果表明,受抗滑桩加固的边坡在水位升降作用下仍发生一定程度的变形并产生裂缝,随着抗滑桩的直接支挡和桩后土体由于不均匀位移产生土拱效应后,边坡变形逐渐得到较好的控制。在本试验条件下,随着桩间距的增大,边坡变形总体上表现为增大趋势,但抗滑桩的受力呈现出先增大后减小的抛物线型变化形态,在某一最适桩间距情况下抗滑桩的抗滑性能得到了最充分的发挥,而滑坡推力表现出复合三角形分布特征。该研究结果为桩土相互作用和库区边坡抗滑桩加固机制分析提供了直接的试验依据,对丰富抗滑桩设计理论和库区边坡的防灾减灾研究具有较为重要的意义。     

Centrifuge model tests on the behavior of strip footing on geotextile-reinforced slopes

This paper examines the stability of geotextile-reinforced slopes when subjected to a vertical load applied to a strip footing positioned close to the slope crest. Vertical spacing between geotextile reinforcement was varied while maintaining a constant slope angle, load position, soil density and geotextile type. Small-scale physical tests were conducted using a large beam centrifuge to simulate field prototype conditions. After the model was accelerated to 40g, a load was applied to the strip footing until slope failure occurred. Digital image analysis was performed, using photographs taken in-flight, to obtain slope displacements and strain distribution along the reinforcement layers at different loading pressures during the test and at failure. Stability analysis was also conducted and compared with centrifuge model test results. The vertical spacing between reinforcement layers has a significant impact on the stability of a reinforced slope when subjected to a vertical load. Less vertical distance between reinforcement layers allows the slope to tolerate much greater loads than layers spaced further apart. Distributions of peak strains in reinforcement layers due to the strip footing placed on the surface of the reinforced slope were found to extend up to mid-height of the slope and thereafter they were found to be negligible. Stability analysis of the centrifuge models was found to be consistent with the observed performance of geotextile-reinforced slopes subjected to loading applied to a strip footing near the crest.     

Surficial stability analysis of soil slope under seepage based on a novel failure mode

Normally, the edge effects of surficial landslides are not considered in the infinite slope method for surficial stability analysis of soil slopes. In this study, the limit stress state and discrimination equation of an infinite slope under saturated seepage flow were analyzed based on the Mohr-Coulomb strength criterion. Therefore, a novel failure mode involving three sliding zones (upper tension zone, middle shear sliding zone, and lower compression zone) was proposed. Accordingly, based on the limit equilibrium analysis, a semi-analytical framework considering the edge effect for the surficial stability of a soil slope under downslope seepage was established. Subsequently, the new failure mode was verified via a numerical finite element analysis based on the reduced strength theory with ABAQUS and some simplified methods using SLIDE software. The results obtained by the new failure mode agree well with those obtained by the numerical analysis and traditional simplified methods, and can be efficiently used to assess the surficial stability of soil slopes under rainwater seepage. Finally, an evaluation of the infinite slope method was performed using the semi-analytical method proposed in this study. The results show that the infinite slope tends to be conservative because the edge effect is neglected, particularly when the ratio of surficial slope length to depth is relatively small.     

雨水入渗与膨胀性土边坡稳定性试验研究

采用离心模型试验方法,完成了2组不同坡度的膨胀性土开挖边坡土工离心模型试验,比较了边坡坡度大小对其稳定性的影响,并尝试通过控制注水浸泡时间来模拟短期和长期的雨水入渗,从而再现了降雨条件下膨胀性土开挖边坡的破坏特征和破坏机制。结果分析表明膨胀性开挖边坡表层土体因雨水入渗膨胀软化,强度降低,严重削弱了边坡稳定性;鉴于膨胀性土路堑在雨水入渗后发生浅层滑动破坏,因此,单纯放缓边坡坡度并不是防治这种破坏的最有效措施,重要的是做好隔水防水等处治工作。     

Force equilibrium-based finite displacement analyses for reinforced slopes: Formulation and verification

Formulation and verification for a force equilibrium-based finite displacement method (FFDM) using test results of reinforced model slopes subjected to increasing pseudo-static seismic forces are reported. The FFDM requires, in addition to force equilibrium for a sliced potential failure mass, a hyperbolic shear stress–displacement constitutive law for the backfill soils, a hyperbolic pull-out force–displacement constitutive law for the reinforcement, and a displacement compatibility requirement for adjacent soil slices. As a result, the mobilized reinforcement force is an analytical output, rather than an empiricism-based input as required in conventional limit equilibrium analyses. Analytical results from the FFDM also indicated that a brittle failure is associated with the lightly reinforced failure surface; a ductile failure is associated with the heavily reinforced failure surface, regardless of the extensibility of reinforcement investigated in the present study. Good agreements between the measured and the computed slope displacements and reinforcement forces in response to increases in pseudo-static seismic forces suggest that the FFDM can be used as an analytical tool for evaluating displacements of reinforced slopes subjected to pseudo-static seismic loads.     

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。     

生态边坡客土稳定性研究

讨论生态边坡工程中，喷播到边坡坡面的人工混合物，即客土的力学稳定性问题。通过室内模拟实验得出客土的破坏模式是一条平行于原坡面的直线滑动面。基于直线滑动面破坏模型，对客土进行稳定性分析，推导出有地震、渗流作用下客土稳定厚度的通式。通过讨论通式中的参数，给出客士的稳定设计图表。利用室内模拟实验结果，验证了客土稳定设计图表的有效性。利用客土稳定设计图表，根据给定的设计稳定安全系数可以设计客土的稳定厚度或者推测竣工的生态边坡客土的稳定安全系数。     

Centrifuge model test and numerical interpretation of seismic responses of a partially submerged deposit slope

Partially submerged deposit slopes are o ften encountered in practical engineering applications.Howeve r,studies on evaluating their stability under seismic loading are still rare.In order to understand the seismic behavior of partially submerged deposit slopes,centrifuge shaking table model tests(50 g) were employed.The responses of horizontal accelerations,accumulated excess pore pressures,deformation mode,and failure mode of the partially submerged deposit slope model were analyzed.In dynamic centrifuge model tests,EQ5 shaking event was applied numerically.The results indicated that in the saturated zone of the deposit slope,liquefaction did not occur,and the measured horizontal accelerations near the water table were amplified as a layer-magnification effect.It was also shown that the liquefaction-resistance of the deposit slope increased under multiple sequential ground motions,and the deformation depth of the deposit slope induced by earthquake increased gradually with increasing dynamic Ioad amplitude.Except for the excessive crest settlement generated by strong shaking,an additional vertical permanent displacement was initiated at the slope crest due to the dissipation of excess pore pressure under seismic loading.The result of particle image velocimetry(PIV) analysis showed that an obvious internal arc-slip was generated around the water table of the partially submerged deposit slope under seismic loading.     

红层堆积体高边坡坡体结构及变形规律

 红层堆积体高边坡是红层地区一种特殊的边坡型式。广元到巴中高速公路沿线分布有广泛的红层堆积体高边坡,从红层堆积体的改造过程入手,根据地质条件复查,依据坡顶形态,将沿线的红层堆积体分成：M型、双M型和单侧型;按照土体类型和结构堆积型式分为：层状堆积体、块石土堆积体、黏土层下卧块石土堆积体和块石土黏土中夹杂大孤石4种类型。根据现场调查资料并辅以MIDAS/GTS有限元分析软件,详细分析4种类型的开挖变形破坏特征。所有堆积体均存在坡体浅表层局部滑塌,其中层状堆积体中主要以顺层整体牵引式滑动为主,而在块石土和以黏土构成的堆积体中则主要出现圆弧状滑动面和沿基岩方向的平面滑动。含有孤石的坡体变形和破坏型式,受内部孤石的大小和位置不同而变化明显。堆积体边坡的具体变形特征除与堆积体结构特征有很大关系以外,还要受到其下卧基岩面的形状、倾角等因素影响。地质复查和数值模拟的结果显示,红层堆积体高边坡变形特征和破坏型式也与红层软岩地区同样具有多样化的特点。对进一步分析红层堆积体高边坡病害模式和灾害机制提供基础,也为红层堆积体地区设计开挖支护方法的研究提供依据。     

一种改进的三维边坡稳定性分析方法

在现有的边坡稳定性三维极限平衡法分析的基础上,提出了一种改进方法,该方法考虑了条间作用力和底滑面剪切力方向对边坡稳定性的影响,在假定条柱分界面也处于极限平衡状态的条件下,通过每一条柱三个方向的静力平衡条件,推导出边坡稳定系数的计算公式。通过模型计算反映出边坡按二维和三维问题分析时的边界条件,并进一步证实了潘家铮先生提出的极大和极小原理。