【作者】 陆杨；

【导师】 徐千军；

【作者基本信息】 清华大学 ， 水利工程， 2005， 硕士

【摘要】 边坡除了受到恒定的重力作用以外,地下水的作用对其稳定性通常也是一个不能忽视的因素。而由于降雨等原因,地下水位往往会在一定范围内往复变化,使得在稳定的地下水位以上的部分岩土体经常处于干湿交替的状态。这对边坡的长期稳定性十分不利。人们常用的极限平衡和极限分析方法只适用于比例加载,应用于交变载荷条件,不仅在理论上缺乏完备的依据,而且可能会高估边坡滑动的安全性。一个突出的例子是膨胀土边坡,用常规极限方法对膨胀土边坡进行设计而失败的例子并不罕见。另一方面,每个地区的降雨等天气过程都具有一定的随机性,因而地下水的运移规律也有一定的不确定性,人们最多只能得到地下水位的变化范围。利用非线性弹塑性有限元方法来研究土坡的渐进性破坏不仅会遇到本构模型上的困难,其载荷条件往往也很难合理地描述。为此,本课题采用塑性力学的安定分析方法对干湿交替条件下边坡的长期安全性进行研究。所完成的工作和取得的研究成果主要包括:1.将强形式机动安定定理引入交变孔压条件下的边坡安定分析。以孔压为变化因素研究边坡的安定性,目前尚未见到其它相关文献。为了避免机动安定定理对时间积分的困难,本文采用强形式的机动安定定理,并开发了相应的程序。这大大简化了安定上限分析的难度和计算量,对在岩土结构中推广安定分析是一个有益的尝试。2.提出边坡稳定极限分析的单元集成法。单元集成法采取单元网格划分模式,应用塑性力学上限定理,从变形协调条件出发,通过构造不同的滑块形式建立机动许可的速度场,根据外力功率和内能耗散率相平衡的原理确定安全系数。通过优化速度场,得到最小的上限安全系数。单元集成法兼具有限单元法与极限平衡条分法的优点,为采用塑性力学上限定理来分析边坡的稳定性提供了一种通用性较强的手段。3.分析比较影响边坡安定的各项因素。通过大量的极限与安定性数值分析,深入、系统地研究了各种水位变化范围、材料参数、边坡角、滑裂面形状、滑动模式对边坡的极限与安定安全系数的影响。给出了一系列极限与安定安全系数曲线,为边坡的安全评定提供了一定的理论和设计依据。4.采用安定分析定量地评价膨胀性软岩边坡的长期稳定性。将安定分析方法应用于交变孔压条件下的膨胀性软岩边坡长期稳定性的评价,所得到的安定安全系数与最不利水位条件下的极限安全系数相比已经产生了颠覆性的变化。这从理论上初步解释了为什么坡度很小的膨胀土边坡不能长久地维持稳定。更多还原

【Abstract】 Besides dead loads such as gravity load, slopes are usually subjected to othervariable loads. Among all of these variable loads, groundwater is an un-neglectablefactor. Since rainfall and other reasons, groundwater level may fluctuate within aprescribed range. This makes upper part of the slope body, which is above the basicwater level, subjected to the cyclic underground water variation. In the long-term,slopes operating at large-scale underground water fluctuation will eventually fail. Soit poses a disadvantage to slopes. Commonly accepted limit-equilibrium and limitanalysis methods can only be applied to linear static loading conditions. When theyare used in alternating load conditions, these methods not only lack of stricttheoretical basis, but also may overestimate slopes’ stability. Typical example is theexpansive soft rock slope. Expansive soft rock slopes designed safely by limittheorem but eventually failed events are not rare in practical engineering. On theother hand, weather conditions such as rainfall in one region is a random event,accordingly, ground water locomotion also represent some randomicity. So peoplecan only obtain the range of the ground water level. Non-linear time-steppingmethod was developed to analyze the incremental deterioration of slopes. Althoughtheoretically it seems feasible, in practical analysis some difficulties may beencountered not only on how to describe constitutive model but also on loadconditions uncertainty. In this thesis, shakedown theorem in the Theory of Plasticitywas adopted to analyze the long-term stability for slopes subjected to alternatewetting and drying conditions. Research work includes:1. An upper bound shakedown analysis based on strong version of Koiter’stheorem is employed to analyze slope stability which subjected to alternate porewater pressure. Presently, there was no other related literature focusing on takingpore water pressure as the variable load to study the slope’s shakedown character. Inthis study, in order to overcome the difficulties from time integrals, strong version ofKoiter’s theorem was employed and a computer program was developed. Thisnumerically simple method greatly reduces the difficulties shakedown analysisbrought. It is also a promising attempt in geothechnical engineering.2. Element Integration Method (EIM) was proposed to analyze slope stability.From the compatibility conditions, adopting element meshing mode and employingupper bound theorem in the Theory of Plasticity, EIM constructed a kinematicallyadmissible velocity fields through a multi-wedge failure mechanism in the form of asmall number of discrete blocks with inclined surface and linear or curved bases.Based on the energy-work balance equation, the factor of safety can be calculated.The problem of finding optimum upper-bound safety factor can be set up as anonlinear programming problem by optimizing the slicing mode of each associatedvelocity field. EIM combines the advantages of Finite Element Method and theMethod of Slices. It provides a relatively powerful and general tool for employingupper bound limit theorem in slope stability analysis.3. Analyzing and comparing every factors influence on slope shakedown.Through a lot of numerical examples, results obtained from shakedown analysis ofslopes with different geometric features, ground-water patterns, strength parameters,sliding modes are compared with those obtained from the limit-equilibrium and limitanalysis method. A series of limit and shakedown safety factor curves were given inthe thesis. These figures provide some theoretical and designing basis for slopestability evaluation.4. Adopting shakedown theorem to quantificationally evaluate the long-termstability of expansive soft rock slopes. Employing shakedown theorem, long-termstability analysis of expansive soft rock slopes, which subjected to alternate porewater pressure, was performed. Results obtained using the present method are totallydifferent from those obtained using other commonly used methods. Theoretically,this gives an answer to the problem why expansive soft rock slopes with small slopeangles can not maintain their long-term stability.更多还原