有限元强度折减法在滑坡治理稳定性评价中的应用

陕西省岚皋县某滑坡地质条件较差,工程对边坡稳定性要求较高,传统的极限平衡法在确定边坡安全系数时需要假设滑动面形状,不能得出准确的计算结果,采用有限元强度折减法,分别分析了该滑坡原始坡面、开挖后坡面(未支护)及支护后的边坡稳定系数.验证了采取抗滑桩治理后边坡的稳定系数有很大的提高,说明在该滑坡治理中采用抗滑桩是可行的.     

兰永一级公路顺层滑坡抗剪强度参数确定及应用

兰永一级公路工程修建过程中在路堑边坡开挖时形成了顺层边坡,以K23+520处的大型顺层滑坡最为典型。由于岩土体抗剪强度参数在边坡稳定性分析和加固设计中不可或缺,为了更好地实现其余类似边坡的加固设计和稳定性分析,以K23+520处的滑坡为研究对象,提出含有软弱夹层的顺层滑坡结构面上抗剪强度参数的确定方法:对已知一个滑动面位置的滑移–拉裂破坏模式下的顺层滑坡,通过结合顺层滑坡失稳条件(临界高度、局部稳定系数)及变形破坏特征对满足刚体滑移模型下的多组强度参数进行逐步修正,得到了满足工程应用要求的强度参数取值,并将结果用于类似边坡的加固设计和稳定分析。方法不仅适合兰永一级公路K23+520处顺层滑坡结构面上抗剪强度参数的确定,还适用于类似滑坡工程强度参数的确定,具有一定的工程实用价值。     

不平衡推力法的弹塑性有限元改进

结合杭金衢高速公路K111碎石土滑坡工程实例,研究如何使极限平衡法与有限元法有机结合应用于边坡稳定性计算和分析中,以及碎石土边坡稳定性系数与滑动面抗剪强度发挥程度的关系。研究结果表明,可以采用弹塑性有限元边坡稳定性极限分析法,得到边坡接近破坏状态时滑坡体的塑性变形破坏区,然后据此确定边坡的滑动面;通过野外工程地质勘探揭示,该法确定的潜在滑动面与实际滑动面基本相符;可根据极限状态下塑性应变值的大小确定滑面带上不同抗剪强度取值段,采用全面考虑滑面上岩土体抗剪强度不同发挥程度的不平衡推力法计算碎石土边坡的稳定性系数;采用该方法进行碎石土边坡稳定性分析能更加真实地反映边坡所处的实际状态。     

福建某滑坡的岩土工程勘察和治理

一项科学的滑坡岩土工程勘察及治理计划流程如下:利用现场勘察、监测、土样室内重复剪试验、资料分析等方法,细致深入的了解滑坡区自然地理条件、工程地质条件、地震及地震效应、地层及工程地质层、水文地质情况,评价滑坡稳定性,并测算滑动面土层综合抗剪强度参数,分析滑坡的原因,并进行科学的预测,据此制定治理策略。下文以福建某滑坡为例,简要概述岩土工程勘察与治理计划流程。     

岩质边坡单折线滑动面稳定性影响因素分析

针对岩质边坡单折线形滑动面这一特定滑动模式,主要从内因方面对边坡的影响因素进行分析,先采用多因素正交试验对影响单折线滑移型岩质边坡稳定的因素进行敏感性分析,得出下滑面黏聚力、坡高、坡角和下滑面摩擦角的敏感度高于其他因素,继而对工程中较关注的滑动面上物理力学参数对边坡安全稳定性进行分析,得出在黏聚力变化和一定时,对稳定系数的影响.     

公路边坡稳定模拟分析及治理措施

基于极限平衡理论,分析了边坡的物质成分、结构构造、雨水渗透下岩土渗透性、抗剪强度以及裂隙等对边坡稳定性的影响,并应用G-SLOPE／W软件对建筑边坡进行了稳定性计算。研究结果表明：该边坡在构造上具有倾向与坡面一致的特点,同时,上部全、强风化的二云石英片岩裂隙十分发育,在雨水的作用下,岩土的抗剪强度降低,导致顺层滑坡;该建筑边坡的稳定性较低。通过对边坡采用琐应力锚杆支护法和梁格结构的治理措施,既能保持边坡安全,又能达到加固和绿化的目的。     

基于滑动面搜索新方法对地震作用下边坡稳定性拟静力分析

 采用一种适于任意曲线滑动面的新方法,对地震作用下边坡的稳定性进行拟静力分析。首先,通过算例对比分析验证新方法的可行性。然后,分别在地震竖直和水平加速度系数kv,kH变化时对边坡稳定性进行研究,在kH,kH与kv共同作用下对分层土坡的局部和整体稳定性进行探索,在土层参数变化时对边坡地震稳定性的影响进行分析,从而可得：(1) kH存在一个特殊值使kv的变化对边坡的稳定性影响很小;(2) 当kH和kv的增大引起临界滑动面范围增大时,会导致边坡由局部稳定性变为整体稳定性,当kH和kv的增大引起滑动面下滑点上移时,会导致边坡由整体稳定性变为局部稳定性;(3) 黏聚力 c的变化对滑动面范围影响较大,其对安全系数的影响与地震强度有关;(4) 不同土层参数时,kH对边坡稳定性的影响较kv大。     

高边坡滑坡的分析与防治

高速公路高边坡,常因施工改变了场地岩土工程条件,导致开挖边坡常发生滑坡现象,需采用加固补强措施。文章结合某高速公路工程项目高边坡滑移,所进行的施工勘察、加固治理过程。根据勘察资料和施工监理,对该边坡产生滑坡的岩土工程条件和稳定性进行了分析,提出了防治措施。     

广西膨胀岩土滑坡治理工程实录

我国工程建设大规模的开展和极端气候影响导致膨胀岩土滑坡问题越来越多,而现有相关规范尚不能满足膨胀岩土滑坡治理工程的要求。收集广西44个膨胀岩土滑坡治理工程资料,先对3个典型的滑坡治理工程进行剖析并分析成败原因,指出滑动面和抗剪强度的合理确定是膨胀岩土滑坡治理成败的关键;然后统计分析广西膨胀岩土抗剪强度指标、地基水平抗力系数和岩层与砂浆的黏结强度;最后提出常规方法治理膨胀岩土滑坡应注重的技术要点：必须设置截排水系统且应满足相关膨胀土规范要求;削方减载在永久治理工程中应慎用;挡土墙设计应满足相关膨胀土规范要求且高度不宜超过3m;抗滑桩锚固段需超过大气影响深度,成孔时应减少水对桩周岩土的软化;锚杆(索)支护应慎用,锚固段应超过大气影响深度,成孔必须干作业。     

岩土参数反算在工程应用中的分析

由于岩土体的复杂性和室内外试验的不确定性,在选定物理力学参数时存在许多实际困难,综合考虑各种因素的影响,基于传递系数法来反算边坡稳定性强度参数,选取合理的计算参数对边坡稳定性进行分析。数值分析结果表明,岩土体强度参数内摩擦角φ和黏聚力c对边坡稳定性影响较大,且内摩擦角φ较黏聚力c对边坡稳定性更为敏感。反算分析方法对完善岩体工程问题的设计理论起到重大的指导作用。     

青海高原龙穆尔沟红层滑坡变形机制的地质分析与模型试验研究

 以西久公路(S101线)龙穆尔沟DH6#红层滑坡为典型代表,采用地质分析与室内模型试验相结合的方法,对河谷下切和雨水浸润作用下青海高原红层滑坡的变形破坏过程进行研究。在地质力学模型试验中,以坡体开挖来模拟河谷下切卸荷作用,采用均匀毛细浸润技术模拟雨水入渗改变岩土强度的现象。以位移量作为重要指标,先分析河谷下切和雨水浸润对坡体变形的单独影响,再将二者综合分析,并分析二者的作用权重。结果表明,河谷下切和雨水浸润作用在红层滑坡的变形过程中均扮演重要角色,认为坡体变形的根本原因是以红层特殊岩土性质为基础的2次强度衰减过程：河谷下切引起的坡体卸荷松弛(第一次强度衰减)以及临空面的出现是滑坡发生的基础;长期的雨水浸润作用造成岩体强度软化(第二次强度衰减)是滑坡发展的直接原因。把以龙穆尔沟DH6#滑坡为典型代表的高原红层滑坡的变形机制归纳为：原始地貌→河谷下切→坡体卸荷松弛→岩土强度衰减→水的作用→岩土强度进一步衰减→坡体整体滑移。     

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。     

基于模态参量变化的边坡动态稳定分析新方法

边坡稳定问题一直是岩土工程领域研究的重要课题,但对于基于模态参量变化的动态稳定分析研究不多。因此,研究将坡体重点区域的黏聚力作为动态参量,实现边坡体动态稳定分析评价。基于GIS三维滑坡分析模块,结合实时固有振动频率对黏聚力参量进行调整,实现坡体更加客观的强度折减。固有振动频率与滑坡黏聚力关系的构建,可以有效解决数值分析中参数选取和调节的困难。通过试验和实际边坡的应用,基于模态参量变化的动态数值分析,避开了极限平衡法主观缺点,模拟结果更加符合客观实际。同时,分析结果更加客观、合理,在充分考虑边坡的空间特性的同时,也能客观评价强度折减情况,为边坡稳定性分析提供一个客观有效的新方法。     

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。     

边(滑)坡工程设计中安全系数的讨论

不同的安全系数定义会引起计算得到的边（滑）坡安全系数与作用在抗滑桩上推力设计值的不同，造成边（滑）坡设计的混乱，因而有必要对边（滑）坡安全系数作出统一的定义。探讨几种不同安全系数定义形式，不同的安全系数定义对安全系数的数值与滑坡推力设计值都是不同的，指出按照传统的计算方法与目前国际上采用的边（滑）坡安全系数的定义，采用强度储备安全系数是较合理的，也符合边（滑）坡破坏的实际情况，因此建议一般情况下采用强度储备安全系数作为边（滑）坡的安全系数，在特殊情况下，采用超载储备安全系数更能符合设计情况。下滑力超载安全系数不符合工程实际，因为随着荷载的增大，抗滑力也会增大，实际上不会出现这种情况，不宜采用。     

强降雨作用下的浅层滑坡稳定性分析

根据实测和室内物理力学试验结果以及工程实践，研究强降雨作用下浅层滑坡稳定性系数与滑面带抗剪强度指标及滑体饱水面积比三者的关系，建立其数理统计相关式。依据建立的数理统计相关式，对采用不分离接触弹塑性有限元强度折减算法分析强降雨作用下浅层滑坡稳定性的难处进行初步探讨。结果表明：首先，可以利用建立的数理统计相关式，选择不同滑体饱水面积比求出强降雨时滑面带的等效抗剪强度指标，作为不分离接触弹塑性有限元强度折减算法中滑面带上接触单元的抗剪强度指标；然后，采用该算法分析强降雨作用下的浅层滑坡稳定性，通过建立的数理统计相关式计算滑坡的稳定性系数，为该类型浅层滑坡稳定性分析和较准确地预报提供更加可靠和充分的依据。研究结果揭示了强降雨对浅层滑坡变形解体和破坏的作用机理，表明强降雨是诱发浅层滑坡的最关键因素。     

Research on the improvement of rainfall infiltration behavior of expansive soil slope by the protection of polymer waterproof coating

The repetitive expansion and contraction cracks, as well as the strength attenuation induced by the precipitation-evaporation cycles, are important factors influencing the instability of expansive soil slopes. In this study, a polymer waterproof coating was proposed to protect the expansive soil slope against slope instability caused by precipitation penetration. The bonding performance of expansive soil blocks (with different soil densities) and polymer waterproof coatings (with different coating thicknesses) were analyzed by performing a laboratory pull-out test. The impacts of different protection methods and protection layer coverage on rainwater infiltration behavior were studied using three groups of slope model tests and numerical simulation approaches. The results showed that the bond strength between the expansive soil test block and the coating increased with the increase in soil compaction density, and the test block strength was an important factor affecting the bond performance. The influence of density of test block on bond strength was greater than that of coating thickness. The calculation formula of bond strength was obtained by fitting the test results. Compared to the unprotected slope, the fluctuation of soil moisture content and rainwater infiltration rate in the slope protected by polymer coating was found to be the least. Protective layer of polymer coating proved to have the most significant role in blocking rainwater infiltration, followed by polymer coating + three-dimensional vegetation net protective layer. When the coverage rate of the protective layer exceeds more than 90%, the effect of blocking rainwater infiltration was remarkable. Simultaneously, the variation range of slope water content, rainwater infiltration depth, and infiltration rate decreased significantly. This research result provides a new solution for expansive soil slope protection and rainwater infiltration control.     

Influence of intrusive granite dyke on rainfall-induced soil slope failure

Intrusive granite dykes and their weathered layers can have great effects on seepage into slopes and on their stability. However, few studies of this topic have been reported. Using the Zhonglincun landslide as an example, we investigate the impact of a dyke and its weathered layer on the formation mechanism of a rainfall-induced residual soil slope failure. The sliding mass of Zhonglincun landslide is mainly composed of residual soils of both tuff and an intrusive granite dyke. We used laboratory soil column tests to obtain rainfall infiltration characteristics of the two residual soils. The SEEP/W mode of Geo-studio software was then used to replicate the above soil column tests to back-analyze unsaturated hydraulic parameters of the two soils, which were later used to simulate seepage fields and stress-strain fields of the slope under Typhoon Tailim. The results indicate that the movement of rainwater in the residual soil of the granite dyke is much faster than that of the residual soil of the tuff. Rainwater infiltrates rapidly into the granite soil, and then flows laterally into the tuff residual soil, raising the groundwater table in the slope, especially near the contact between the two residual soils. This leads to a rapid increase in pore-water pressure and initiates the serious deformation of the landslide. The granite dyke and its residual soil have played a key role in the formation of Zhonglincun landslide.

     

Performance of an instrumented slope covered with shrubs and deep-rooted grass

Green technology, an integrated design approach that combines vegetation and engineering design methods, can be applied to improve slope stability. Orange Jasmine is a small tropical evergreen shrub which has deep root systems and is considered to be a drought-tolerant plant that adapts well to a wide range of climatic and soil conditions. It can also grow in infertile soils, limestone soils or loam. Vetiver grass has been widely cultivated in many tropical and subtropical regions of the world for soil and water conservation, land rehabilitation, and embankment stabilization. Vetiver grass has deep roots (2–4 m) and adapts well under extreme conditions of temperature, soil, moisture, soil acidity, and alkalinity. The role of Orange Jasmine and Vetiver grass in minimizing rainwater infiltration, for improving the stability of slopes, was investigated on a soil slope in Singapore with its tropical climate. Two slope sections, covered with Orange Jasmine and Vetiver grass, were instrumented with tensiometers, installed at different depths within the slope, and a rainfall gauge. The instruments were connected to a real-time monitoring system to study the pore-water pressure, the rainfall, and the groundwater level in the slope throughout a one-year period. The pore-water pressure characteristics within the slope sections covered with Orange Jasmine and Vetiver grass are analyzed and presented in this paper. The analyses indicate that both Orange Jasmine and Vetiver grass played a significant role in reducing rainwater infiltration into the slope, minimizing the loss of matric suction, and hence, the shear strength of the soil during rainfall and, as a result, maintained the stability of the slope. Vetiver grass and Orange Jasmine appeared to be similar in effectiveness in terms of reducing the rainwater infiltration into the slope.     

考虑降雨入渗条件下边坡稳定性的研究进展

在导致滑坡失稳的众多因素中,降雨是影响边坡失稳的主要诱发因素,边坡土体自身的复杂性决定了降雨入渗对边坡的影响是非常复杂的,通过总结国内外对降雨引起边坡失稳现象的研究进展与现状,结果表明:主要研究是从基质吸力、土体的应力状态、土体的变形、降雨强度、降雨持时、土体的渗透性和土体中的裂隙等方面分析了降雨入渗对边坡稳定性的影响,随着降雨的入渗,降雨强度对边坡稳定影响显著,降雨间隔时间和方式对边坡稳定性也有较大影响,目前国内外在这一方面缺乏系统全面的研究。最后总结了进一步研究方向与目标。