【作者】 丁金华；

【导师】 陈仁朋； 包承纲；

【作者基本信息】 浙江大学 ， 岩土工程， 2014， 博士

【摘要】 膨胀土作为世界范围内广泛分布的特殊土,对相关地区的工程建设造成了极大破坏和影响,一直是岩土工程领域研究的难题之一。浅层失稳破坏是发生在铁路、公路、水利等工程中最普遍最频繁的膨胀土边坡破坏现象,但目前对浅层失稳破坏机理缺乏足够的认识,传统的极限平衡稳定性分析方法不能如实反映和解释膨胀土边坡此类破坏的真实性状,也制约了工程建设中如何采取合理有效的处理措施以解决由于其特殊性质带来的工程问题。因此,深入研究膨胀土边坡的浅层失稳破坏机理,并在此基础上探讨相应的工程措施是保障工程设计安全和经济性的关键。本文结合南水北调中线工程的膨胀土边坡稳定问题,针对膨胀土最本质的工程特性——膨胀性开展深入研究,通过大型静力物理模型试验,研究压实膨胀土边坡在没有裂隙、超固结性、干湿循环等因素的影响下,由于水分入渗引起的边坡膨胀变形和滑动的发生发展破坏全过程。在“湿度应力场”理论基础上,提出一种非饱和渗流场-膨胀变形场-应力场的多场耦合数值分析方法,结合模型试验和数值分析成果,阐述了膨胀土边坡浅层失稳的破坏机理。在此基础上,从加筋土的筋—土作用机理出发,研究土工格栅对膨胀土膨胀变形的约束效果,及其对边坡浅层稳定的改善作用,为确定合理的膨胀土工程处理措施提供理论依据。通过本文的研究,得到的主要结论如下：(1)针对膨胀土边坡极为普遍的浅层失稳破坏形式,采用大型物理模型试验(6m×2m×2.8m),并结合湿度场-膨胀变形场-应力场的耦合数值模拟分析,揭示出膨胀土边坡浅层失稳的本质在于膨胀土的膨胀性。由膨胀变形控制的膨胀土边坡浅层渐进性失稳破坏机理可阐述如下：膨胀土边坡在受到外部水力边界作用时,首先导致边坡内含水量场发生时空不均匀分布,继而引起土体的不均匀膨胀变形,应力应变场发生重分布,在非饱和-饱和浸润交界区域形成剪应力集中区,产生局部剪切破坏,并逐渐向边坡深部扩展,最终形成多重剪切面,边坡发生渐进性失稳破坏。(2)针对膨胀土边坡稳定性分析,在“湿度应力场”理论基础上,提出一种结合非饱和-饱和渗流场、膨胀变形场、应力场多场耦合作用的有限元数值分析方法,通过对模型试验的仿真模拟,证明这种多场耦合分析模型和方法可以真实反映膨胀土边坡的浅层渐进性失稳过程,为深入理解边坡浅层稳定性的破坏机理提供了有用的分析手段。(3)基于温度膨胀和湿度膨胀的相似性,采用热—固耦合有限元数值分析方法,根据室内膨胀土无荷及有荷膨胀试验成果,反演得到不同含水率、干密度和荷载作用下的膨胀系数变化规律。结果表明：膨胀系数受含水率、干密度、荷载等因素的综合影响,在低荷载条件下含水率和膨胀系数近似符合线性关系。因此,在多场耦合数值计算中采用低荷载条件下对应的含水率—膨胀系数(饱和度—膨胀系数)关系来反映边坡不同部位湿度变化引起的膨胀系数的变化规律。(4)采用大尺寸膨胀模型试验,系统研究了铺设土工格栅后膨胀土的吸湿膨胀变形发展规律,获得了不同格栅参数(强度、类型、铺设层数和方式等)对膨胀变形的影响规律,对土工格栅抑制膨胀变形的可行性进行了评价。(5)通过大型物理模型试验,对土工格栅处理膨胀土边坡浅层稳定的效果进行了研究,为膨胀土工程处理措施提供了基本的试验依据。更多还原

【Abstract】 Expansive soil distributes widely throughout the world as a special soil, and it triggers many serious damages of geotechnical structures. The progressive failure of expansive soil slope at shallow depth occurs frequently in railway, highway, hydraulic engineering, etc. But the current methods of stability analysis and the failure mechanism of expansive soil slope have some serious defects and can not to reflect properly the particularity of expansive soil slope failure.Based on the stability problems of expansive soil slope of the South-to-North Water Transfer Project, this paper focused on the very essence property of expansive soil, swelling behavior, and carried out a series of large static physical model tests of the compacted expansive soil slope. The test results revealed the whole sliding process of expansive soil slope without fissure, overconsolidation, and wetting-drying circle, etc. Combining the multi-field coupling numerical analysis with unsaturation-saturation moisture field, swelling deformation field and stress field, the expansion failure mechanism for the shallow instability of expansive soil slope is proposed.Furthermore, this paper studied the geogrid-confined effects on swelling deformation of expansive soil by a series of expansion model tests and mastered the swelling deformation rules with different geogrids type, strength, numbers of laying layer and fixed ways of geogrid front end. The physical model test of geogrid-reinforcement slope of expansive soil showed that geogrids can reduce the swelling deformation and improve the whole stability of expansive soil slope. The feasibility of geogrid dealing with the expansive slope stability is proved. The research results provide a theoretical basis and experimental data for disposition methords of expansive soil engineering slope.The main conclusions are as follows:(1) For the expansive soil slope, a series of large static physical model tests(6mx2mx2.8m) of the compacted expansive soil slope and the multi-field coupling numerical analysis indicate that, the fundamental factor influencing the slope shallow instability is the swelling behavior, not the fissure or strength reduction by overconsolidation. The failure mechanism of the shallow progressive instability of expansive soil slope can be elaborated:the moisture filed of expansive soil slope becomes nonuniform in space-time after absorbing water from rainfall, and it generates the nonuniform deformation within the certain shallow layer of the slope, the stress-strain filed redistribution is obvious. The local shearing failure occures firstly at the shallow wetting-drying surface because of the shear stress concentration, then expands deeper into the slope, finally, the multiple shearing surfaces lead to the whole progressive sliding of the expansive soil slope.(2) For the stability analysis of the expansive soil slope, a multiple-filed numerical analysis method coupling unsaturation-saturation, expansion deformation, and stress filed is proposed. Furthermore, the analogue simulation of the physical model tests proves that this method can reappear and reflect truly the progressive sliding failure.(3) By referencing the tempreture expansion therory, the moisture swelling coefficient of expansive soil is back analyzed according to the indoor expansion tests with or without vertical loading.(4) The swelling deformation rules of expansive soil with geogrid-confinement are related to different geogrids type, strength, numbers of laying layer and fixed ways of geogrid front end, etc. The expansion model tests prove that geogrids can reduce the lateral swelling deformation significantly.(5) The large physical model tests show that the stability with geogrid-reinforced expansive soil slope is improved and the swelling deformation decreases to a certain extent.更多还原