水位骤降对边坡稳定性影响的模型试验研究

 自然界中存在着大量的临水边坡,比如河岸、海堤、土石坝、水库库岸以及湖岸等,边坡外水位的骤降极易诱发此类临水边坡的滑坡。通过大型模型试验研究水位骤降引致临水边坡滑坡的原因及失稳模式。模型边坡的尺寸为15 m×5 m×6 m(长×宽×高),边坡部分的高度为4 m。在试验中,通过水位控制系统实现坡外水位的骤降,利用数码摄像、高精度传感器、侧面示踪点等仪器设备详细记录水位骤降过程中边坡内的孔隙水压力、土水总压力,滑动面形态及坡面裂缝的形成和发展过程,揭示水位骤降引致边坡失稳的原因及失稳模式。试验结果表明,坡外水位骤降时,坡内水位的下降速度显著滞后于坡外,产生指向坡外的渗流,是滑坡产生的重要原因;松散填土边坡的失稳模式为有多重滑面的牵引破坏模式。该研究结果有助于深入认识水位骤降引致滑坡的机制,可为治理此类滑坡提供科学依据。     

水位变化诱发粉土边坡失稳离心模型试验

粉土具有明显的非饱和土力学特性,坡内外水位变化诱发粉土边坡失稳是常见工程灾害之一。分别针对坡内和坡外水位变化诱发的粉土边坡失稳情况,开展了相应的离心模型试验研究,结合非饱和土力学相关理论分析和数值模拟,揭示了粉土边坡在两种情况下的变形及失稳模式和发生机制。结果表明：当坡内水位超过1/3坡高后,在坡内渗流作用下,粉土边坡呈现逐级侵蚀剥落、从坡脚向坡顶、由浅层向深层的多级滑坡失稳;坡外水位上升将导致松散粉土边坡发生显著湿陷变形,而坡外水位骤降将造成粉土边坡的多重浅层牵引式滑坡。粉土边坡的失稳模式和发展与粉土的非饱和土力学特性密切相关。最后根据模型试验结果提出了相应的粉土边坡渗流失稳工程控制措施。     

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.     

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。     

水位下降过程中气相对土坡稳定性的影响

基于饱和-非饱和水-气二相流模型,对土坡在水位下降过程中的孔隙水压力、孔隙气压力、毛细压力及水相饱和度的变化过程进行模拟;基于模拟得到的不同时刻的渗流状态,采用Bishop简化方法推导出考虑孔隙气压力及坡外水压力的土坡安全系数计算公式,分析了水位下降过程中不同渗透性土坡安全系数的变化规律,及基质吸力和气相的存在对边坡稳定性的影响。结果表明:水位下降过程中土坡的安全系数逐渐减小,水位下降后土坡的安全系数略有增大;考虑气相影响后土坡的安全系数降低,考虑基质吸力影响后土坡的安全系数增大;岸坡土体的渗透率越大,水位下降过程中安全系数较大,而水位下降后安全系数较小。     

水位骤降对边坡稳定性影响的模型试验及数值模拟研究

自然或人工边坡的稳定性研究是当前岩土工程研究领域的热点问题之一。随着三峡等大型水利设施的兴建和投入使用,水位骤降对边坡稳定性影响也引起人们的广泛关注。通过室内模型试验研究水位骤降引发临水边坡滑坡的原因及失稳模式是经济、便捷的常用方法。本试验模型箱的尺寸为2.5m×1.5m×1.5m(长×宽×高),边坡高度为1.05m。边坡体内埋设了10只土压力盒和7只渗压计,用于测量水位骤降过程中土压力和孔隙水压力的变化情况,记录边坡失稳破坏过程中土体内部的变化过程。同时,利用geo-slope软件模拟边坡失稳破坏的整个过程,并且利用数值模拟的结果与试验结果进行对比分析,解释边坡破坏的机理。试验结果表明:水位骤降对边坡稳定性产生很大影响,水位下降速度越快,边坡沉降也就越大,最后形成明显的位移集中区域;边坡的安全系数分别随着水位高程的减小、水位下降时间的增加出现增加最后趋于稳定;在此土质、坡形条件下的边坡破坏的形态与数值模拟所得8min时滑动面的形态相吻合,据此也用试验验证了数值模拟的可靠性。     

三峡库区赵树岭滑坡稳定性物理模拟试验研究

采用3个小比例尺二维物理模型试验,对三峡库区赵树岭滑坡在库区蓄水、水位波动、地面荷载和可能的地震荷载作用下的整体稳定性及其可能的变形、破坏机理进行了研究。采用百分表、网格线和数码相机,对模型的变形和位移进行监测和记录。采用高容重和低容重模型材料,分别模拟地下水位以上和地下水位以下滑坡岩体;根据渗透理论和相似理论,解算水位骤降时模型条件下的动水压力合力矢量,采用施加集中力的方法模拟动水压力;地表建筑荷载采用重晶石–石膏块体模拟;地震荷载采用使模型倾斜的方法模拟。试验结果表明:未来三峡水库运营期间,不论库水位处于175m或145m,还是从175m骤降至145m,建有7层建筑物的该滑坡均整体稳定;而当地震震级大于某级时,该滑坡发生整体失稳,并且库水位从175m骤降至145m时,稳定性最差,其次是145m情况下,175m库水位时稳定性最好;如果发生整体滑坡事件,其滑坡机理为牵引式。     

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。     

库水位升降条件下边坡失稳离心模型试验研究

 三峡库区频发的滑坡地质灾害已愈来愈引起学者的高度重视,其受水位反复升降的影响是库区边坡不同于其他陆地自然边坡的一个显著特点。以离心模型试验为手段,基于三峡库区典型滑坡的工程地质特征,建立相应的土质边坡离心模型。在试验过程中实现对库水位循环升降的控制,模拟库区边坡在水位升降作用下的失稳过程。通过数码摄像、数字图像处理和传感元件测试,获得该试验条件下的土坡在水位升降过程中典型位置的孔隙水压力变化、全断面位移矢量演化(水平位移和沉降)、滑面形态及裂缝形成发展过程,并详细分析边坡在这种外部水环境影响下的变形演化、失稳和破坏模式。试验结果表明,若仅考虑水位升降作用的影响,该试验条件下的库区土质边坡的变形呈现典型的渐进牵引破坏模式,并具备较强的水土软化影响特征;裂缝在变形演化过程中出现交替张开和闭合现象,该失稳模式下的滑面呈折线形态,并在变形破坏过程中次生多级滑面。研究结果为库区滑坡地质灾害机制的深入认识、以及滑坡预防和控制提供了重要依据。     

大位移滑坡形态的物质点法模拟

滑坡是一典型的动力大变形过程,对这种变形很大的问题如欲模拟其变形后的形态,应用传统有限元法会遇到较大困难。应用物质点法这一较新的数值方法对一高边坡发生滑坡的全过程进行了动态模拟分析,同时结合这一分析对大位移滑坡过程进行了讨论。首先将黏性阻尼与运动阻尼相结合,应用动态松弛技术生成边坡初始应力场,初始应力场与有限元计算结果相符。接着将土体黏聚力降为0,诱导稳定边坡滑坡。滑坡模拟过程表明,滑动面的位置和曲率在滑动过程中均不断变化,滑动模式由转动滑动向平动滑动转变,最终形成的稳定边坡坡角小于土体内摩擦角。     

Centrifuge model tests on pile-reinforced slopes subjected to drawdown

Piles are generally an effective way to reduce the risk of slope failure. However, previous approaches for slope stability analysis did not consider the effect of the piles coupled with the decrease of the water level (drawdown). In this study, a series of centrifuge model tests was performed to understand the deformation and failure characteristics of slopes reinforced with various pile layouts. In the centrifuge model tests, the pile-reinforced slopes exhibited two typical failure modes under drawdown conditions: across-pile failure and through-pile failure. In the through-pile slope failure, a discontinuous slip surface was observed, implying that the assumption of the slip surface in previous stability analysis methods was unreasonable. The test results showed that drawdown led to instability of the piles in cohesive soil, as the saturated cohesive soil failed to provide sufficient constraint for piles. The slope exhibited progressive failure, from top to bottom, during drawdown. The deformation of the piles was reduced by increasing the embedment depth and row number of piles. In addition, the deformation of soils outside the piles was influenced by the piles and showed a similar distribution shape as the piles, and the similarity degree weakened as the distance from the piles increased. This study also found that the failure mechanism of unreinforced and pile-reinforced slopes induced by drawdown could be described by coupling between the deformation localization and local failure, and it revealed that pile-reinforced slopes could reduce slope deformation localization during drawdown.     

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。     

土体含水率对边坡动力破坏模式及动力响应影响的振动台试验研究

正确认识地震作用下边坡的破坏模式及动力响应特征可以为边坡抗震设计提供理论指导。为了探讨边坡土体含水率的变化对边坡破坏模式及动力响应的影响,针对该问题展了室内振动台模型试验,分析了不同含水率边坡失稳破坏的物理过程,以及在地震荷载作用下边坡动力响应规律。试验结果表明土体含水率对边坡破坏模式有较大影响,含水率6.8%和10%的砂土边坡分别表现为震裂–溃滑型和震裂–溃散型滑坡破坏形式,含水率18.1%和24.6%的黏土边坡分别表现为震裂–溃散性和震裂–蠕滑型滑坡破坏形式;在参数考虑的范围内含水率较大的边坡比含水率较小的边坡更稳定;在水平动力载荷作用下,边坡表面的土体位移变化规律能够反应出边坡失稳破坏特征;对于该文讨论的砂土和黏土边坡而言,含水率大的边坡加速度放大效应弱于含水率小的边坡;从土体阻尼角度解释了含水率变化对边坡失稳影响的机理。     

Centrifuge modeling of the geotextile reinforced slope subject to drawdown

Geotextile is an effective reinforcement approach of slopes that experiences various loads such as drawdown. The geotextile reinforcement mechanism is essential to effectively evaluate the safety of geotextile-reinforced slopes under drawdown conditions. A series of drawdown centrifuge model tests were performed to investigate the deformation and failure behaviors of slopes reinforced with different geotextile layouts. The deformation and failure of unreinforced and reinforced slopes were compared and the geotextile reinforcement was indicated to significantly increase the safety limit and the ductility, reduce the displacement, and change the failure feature of slopes under drawdown conditions. The slopes exhibited remarkable progressive failure, downward from the slope top, under drawdown conditions. The progressive failure was induced by coupling of deformation localization and local failure based on full-field measurements of displacement of slopes subjected to drawdown. The geotextile reinforced the slope by decreasing and uniformizing the slope deformation by the soil-geotextile interaction. Through geotextile displacement analysis, the geotextile-reinforced slope was divided into the anchoring zone and the restricting zone by a boundary that was independent of the decrease of water level. The geotextile restrained the soil in the anchoring zone and the soil restrained the geotextile in the restricting zone. The reinforcement effect was distinct only when the geotextile was long enough to cross the slip surface of the unreinforced slope under drawdown conditions.     

库水位下降对滑坡体稳定性的影响

以三峡水利工程为背景,针对长江三峡库区水位的周期性调节对库岸边坡稳定性可能产生的种种不利影响,计算了在库水位下降期间,滑坡体稳定性受库水位下降速度影响的变化情况。结合库水位下降期间不同渗透系数滑坡体的实际渗流场,对滑坡体稳定性进行了数值计算分析,得到了库区降水速度和渗透系数与边坡稳定性之间的变化规律,对库区边坡稳定性的研究有一定的参考作用。     

微型抗滑桩双排单桩与组合桩抗滑特性研究

 通过3组大型模型试验,研究微型抗滑桩双排单桩与组合桩在加固边坡时的抗滑特性。边坡位移监测结果表明,微型抗滑桩能提供较大的抗滑力,降低变形速率,对边坡有较好的加固效果;组合桩加固效果更佳,较单桩抗滑力提高6.8%。桩体破坏有3种形式：桩体弯曲、桩土脱空、桩体断裂;双排单桩裂纹倾角较大,为65.7°,呈弯–拉破坏;组合桩裂纹倾角为33.9°,呈拉–剪破坏;后桩裂纹宽度较前桩大。双排单桩桩体自由段土压力沿桩身呈“S”型分布;后桩承受土压力大于前桩,前后桩最大土压力之比为0.53∶1～0.50∶1;桩前滑面层位存在桩土脱空区,土压力最大值在滑移面上10%桩长附近;桩体嵌固段土压力在下滑力较小时呈倒三角形分布;当土压力较大时呈矩形分布。组合桩由于连梁作用,前桩桩顶产生较大的正弯矩,桩身最大负弯矩出现在滑面附近,前后桩最大负弯矩之比为0.67∶1～0.80∶1。     

强降雨下无黏性土坡破坏的影响因素试验研究

利用自行研制的室内水槽模型试验系统,对日本#6,#7和#8硅砂试样开展了固定降雨强度(90 mm/h)下诱发无黏性土坡破坏的模型试验;描述了强降雨条件下无黏性土坡的破坏过程,探讨了坡体厚度、前缘卸荷、土样颗粒尺寸及细颗粒含量对破坏过程的影响规律,分析了土坡破坏过程中的孔隙水压力响应特征。结果表明:①在持续强降雨作用下,无黏性土坡的破坏过程可分为3个阶段,即入渗、初始破坏与主要破坏阶段。②主要破坏阶段拉裂缝自坡脚向坡体中部、坡肩及坡顶渐次出现,且破坏模式受土颗粒尺寸和细颗粒含量的控制,控制机制为土体剪胀效应的强弱。③坡体厚度越小,其破坏过程的持续时间越短,但滑动距离和速率也将越小;前缘卸荷可加速土坡的破坏,并使其具有更长的滑动距离和更大的滑动速率。④当饱和土坡加速变形时,滑动面处会产生超静孔隙水压力,进而诱发突然滑动。与此同时,滑动面处的孔隙水压力由于坡体厚度减小和剪胀效应的发生而急剧降低。     

考虑黏聚力及放坡角度的土钉墙侧土压力计算

基于极限平衡理论及平面滑裂面假定,在考虑土黏聚力及放坡角度的基础上,推导了平面滑裂面剪切破坏角的数学表达式。结果表明:平面滑裂面剪切破坏角与土的黏聚力、计算深度无关,与放坡角度和土的内摩擦角均成线性关系。在剪切破坏角计算的基础上,建立了一个符合实际的土钉墙侧向土压力计算公式。实例计算结果表明:建立的土钉墙侧向土压力计算公式适用于不同放坡角度的土钉墙,不但适用于无黏性土,同样适用于黏性土。     

软土桩基上拓宽路堤的变形破坏离心模型试验

采用离心模型试验手段,以广州高速公路改扩建工程为背景建立模型,设计相应尺寸的模型试验方案,模拟软土桩基上的新路堤拓宽过程,研究软土桩基的变形破坏规律与机理。结果表明:旧路堤主要发生竖向位移,新路堤发生沉降和一定量水平位移; 新路堤坡肩区域出现向坡脚滑动趋势,导致新路堤施工过程中路堤和软基产生滑动破坏; 新路堤中的滑裂面首先出现,从新路堤坡肩到短桩顶端自上而下逐渐形成; 在新路堤滑裂面形成过程中,软基中的滑裂面从旧路堤下的地基表面至新路堤坡脚下地基部分自内向外逐渐形成,2条滑裂面几乎同时达到贯通状态; 管桩发生一定程度的倾斜,在滑裂面出现之前的某一时刻倾斜角度迅速增加; 在局部滑裂面附近位移出现较快增长,变形较为集中; 变形局部化导致了局部发生破坏,而局部破坏促进了变形局部化的进一步发展,二者的耦合发展最终导致土体发生破坏。