【作者】 岑仰润；

【导师】 龚晓南；

【作者基本信息】 浙江大学 ， 岩土工程， 2003， 博士

【摘要】 我国广大地区分布着工程性状较差的软粘土，对软粘土地基处理一般采用排水固结法。作为排水固结法的一种，真空预压加固软土地基近年得到了广泛地应用，取得了很好的工程和经济效益。目前有关真空预压加固地基的理论研究落后于工程实践，制约了该工法的进一步发展和工程应用，有必要对此进行系统的研究。 首先对不同土样进行了一系列室内真空固结和加载固结的对比试验，通过对试验结果的比较分析，明确了抽真空引起土样固结的原因，即抽真空作用会在四个方面对试样产生影响：毛细管势的改变、封闭气泡的排出、汽化现象及大气压的作用，而其中大气压的作用是最主要的。抽真空作用下试样的固结状态与情况与试样中负压分布、大气压的作用情况和变形约束条件等因素有关。在固结状态相同的情况下，真空固结和加载固结显示的固结性状基本一致。 在此基础上，通过堆载预压与真空预压的对比阐述了真空预压加固地基机理，分析了影响真空预压加固地基最终加固效果的各个因素：场地地质条件、抽真空作用强度、地下水赋存情况及竖向排水体的设置等。提出了一些与真空预压加固地基设计相关的概念和处理方法，如定义真空预压加固区场地形状系数，提出按加固土体体积来确定射流泵数量、根据工程需要动态设计开泵量、增加停泵标准中对开泵量的规定等设计思想等，论证了真空预压加固地基时地下水位下降的理论极限深度为10m，而实际极限深度约为6m。提出由现场实测资料反分析竖向排水体中的负压分布的方法，通过对若干工程实例的反分析，认为真空预压下负压分布沿竖向排水体的分布基本均布，其值约在膜下真空度的50％左右。 在室内试验及现场试验基础上，证明真空预压加固地基过程中，负压区土体仍是饱和的，不能用非饱和土理论来计算负压区的固结性状，并辨析了负压与吸力的概念。在与加载固结比较的基础上进行了真空固结过程的应力、应变分析，对真空预压加固地基的曼德尔效应做了初步评价。在以往研究成果的基础上，系统给出了有关真空预压若干固结解答。 总结了真空预压加固地基渗流计算和固结计算的基本方程，介绍了采用有限元方法进行真空预压加固地基固结计算的基本过程。着重论述了真空预压加固地基数值分析中对土体本构方程的选择、砂井地基等效转换、分析荷载步的确定、竖向排水体的界定、地下水下降的处理、密封帷幕的处理、附近补充水源的处理等问题。 在分层总和法思想基础上，提出了真空预压加固地基固结沉降计算方法。分析了真空预压加固地基总沉降的组成，对各部分沉降计算做了分析，并建议按联合堆载量大小来总结真空预压加固地基沉降修正系数。特别分析了真空预压加固地基工后沉降产生的机理及组成，提出了相应的计算思路。讨论了真空预压加固地基时地基土随固结强度增长的计算方法，建议按联合堆载量大小来总结真空预压加固地基强度修正系数。在圆弧稳定分析基础上，初步建立了真空预压加固地基的稳定分析分区模型，将地基分为竖向排水体区和非竖向排水体区，在竖排区内考虑地基土随真空固结的强度增长，而在非竖排区不考虑地基土的强度增长。并简单论述了地下水位下降、联合堆载、土工材料等因素对稳定分析的影响。更多还原

【Abstract】 Soft clay is distributed in the vast area of China with poor engineering property. In recent years, vacuum preloading is extensively used to treat soft clay ground, whereas the development of the theoretic study in vacuum preloading cannot follow the progresses in engineering, which has limited the progress and application in engineering practice. Therefore, it is necessary to systematically study the mechanics of vacuum preloading. In this paper, some aspects of vacuum preloading were studied as follows.Vacuum consolidation test and load consolidation test were performed and compared for different kind of soil samples. After analyzing the results of tests, the four major mechanisms of vacuum consolidation were defined as: variation of capillary potential, drainage of sealed bubbles, vaporization and action of atmosphere pressure, in which, the action of atmosphere pressure is the most important factor. The distribution of negative pore-water pressure, the action of atmosphere pressure and the restraint of deformation determined the consolidation status of vacuum consolidation. In the same consolidation status, similar properties of consolidation were observed for either vacuum consolidation or load consolidation.The mechanics of vacuum preloading was discussed by contrast of vacuum preloading and heaped preloading. The factors affecting the result of vacuum preloading for ground consolidation were as follows: the geological conditions of site, the intensity of vacuum pumping, the condition of underground water and installation of vertical drainage line. Through analysis of these factors, some conceptions and design principles were proposed for vacuum preloading. A site topographic coefficient was defined. The design principles were suggested. The total pump numbers installed should be determined according to soil volume to be treated. How many pumps were turned on should be based on the dynamic design according to project target. And how many pumps should be in operation in standard shut off procedure. It was approved that although the theoretical boundary of decline of groundwater level is 10m, the actual boundary is only about 6m. A method to back analysis the distribution pattern of negative pore-water pressure along vertical drainage line was proposed. Some practical vacuum preloading projects were analyzed. The results showed that distribution patterns of negative pore-water pressure along the vertical drainage line were uniform and the magnitude was about half of the vacuum degree under the membrane.Based on the results from both laboratory test and field application of vacuum preloading it can be concluded that soil is water-saturated in the processes of vacuum consolidation or vacuum preloading. Thus, the consolidation properties in negative-pressure area cannot becalculated by using the theory based on non-saturation soil. Negative pore-water pressure and suction were specified. Stress and strain variations during vacuum consolidation were analyzed and the effect of Mandel in vacuum preloading was evaluated. Some solutions for vacuum preloading consolidation were derived on the basis of previous research findings.Fundamental equations of seepage and consolidation analysis of vacuum preloading were generalized. Basic process of vacuum preloading analysis using FEA method was introduced. Some key subjects of numeric analysis were discussed such as: selecting principles of constitutive equations of soft clay, the equivalent theory of vertical drains ground, the definition of load step, the determination of vertical drains as well as the treatment methods of the decline of groundwater level, sealing wall and nearby water source.On the basis of layered method, a method to calculate the consolidation settlement of vacuum preloading was deduced. The elements affecting total settlement during vacuum preloading consolidation were discussed. The principle that defined the coefficient of total settlement correction by the magnitude of combined loadings was suggested. The mechanism and compone更多还原