【作者】 苑晓青；

【导师】 王清； 夏玉斌；

【作者基本信息】 吉林大学 ， 地质工程， 2012， 博士

【摘要】 近年来，世界上土地资源日趋紧张，各国学者都致力于寻找新的手段开发土地。利用从海域中吹填上来的淤泥进行围海造陆，既可以清理海港、码头，还可以疏浚航道，保护环境，同时可以降低运输物源砂料的工程造价，提高地基处理效率，满足工程需要，是一种变废为利、一举两得的好方法。但从海底疏浚出来的淤泥具有含水率和粘粒含量极高、孔隙比极大等特殊的工程地质性质，使得吹填土必须经过一定的处理后才能使用。工程上常采用真空预压法对其进行加固，但采用这种方法的前提是要求土体具有一定的强度，即土体表面形成硬壳，这需要2~3年的时间，极其浪费时间；而在对吹填土进行真空加压的过程中，土体由于受到强大的真空吸力作用，粘粒会随着水一同向竖向排水体处迁移，使得排水体周围包裹着一层厚厚的泥膜，严重制约土体的固结过程，影响工程效率。另外，利用处理后的吹填土作为建筑物地基使用过程中，土体的工后沉降量值很大，而且沉降达到稳定所需要的时间很长，往往可达到几年甚至几十年，由此引发的工程破坏及失稳事故更应引起我们足够的重视，所以有必要对吹填土的次固结变形特性及影响因素进行深入研究。本论文结合国家自然科学基金项目“分级真空预压固结法在高塑性吹填土中物理模拟与颗粒运移规律的研究”(NO.41172236)和国家自然科学基金项目“海积软土地基加固过程中有机质的作用和影响”(No.40372122)的资助，针对高粘性吹填土的特殊工程地质性质，提出两种改良的真空预压法：直排式真空预压法和分级式真空预压法，分别进行了室内模拟试验的研究，并对比分析了两种方法加固吹填土的加固效果；同时，针对吹填土的工后沉降量值较大，可能给工程带来严重安全隐患的问题，对天津、大连两地吹填土的固结及次固结特性进行分析，并对次固结系数的影响因素进行了探讨；应用非线性小波阈值法对两种真空预压法的实测沉降数据进行小波降噪处理，剔除沉降中的偶然误差，提取真实的沉降数据；最后，建立了BP神经网络模型对土体最终沉降量进行了预测，评价两种真空预压法的最终固结效果，并对模型进行了验证，达到可以预测土体沉降量的目的，为吹填土地基处理工程分析设计提供科学的理论基础。本论文共分八章，第一章为绪论，介绍了选题依据和研究意义，总结了真空预压法、软土次固结特性、小波分析理论以及吹填土沉降预测等方面的国内外研究现状，并给出了论文的主要内容及技术路线和论文的创新点。第二章对比研究了天津、大连两地吹填土的基本性质，总结了吹填土的普遍特征，指出高粘性高有机质含量吹填土的特点。第三章介绍了两种新型真空预压法：直排式真空预压法和分级式真空预压法的室内模拟试验装置和试验方法。第四章对两种新型真空预压法的加固效果进行了对比分析，包括试验的监测数据、土体力学性质、物理性质和化学性质及微观孔隙特征，从宏观和微观相结合的角度反映高粘性吹填土的固结规律，评价两种真空预压法的加固效果。第五章详细分析了天津、大连两地吹填土的固结及次固结特性，并对次固结系数的影响因素进行了深入探讨。第六章利用非线性小波阈值法对两种真空预压法的实测沉降数据进行了降噪分析，剔除偶然因素引起的误差，使得沉降数据更接近真实值。第七章建立了三层BP神经网络模型对降噪后的沉降数据进行了沉降量的预测，并对模型进行了验证。第八章为结论和展望，总结了本文所得到的结论并对下一步研究工作提出建议。更多还原

【Abstract】 The Dredger fill means a kind of man-made deposits which is pumped by dredgerand mud pump from the offshore or channel to the specified position. Coastal citiesusually take dredger fill as the raw material for land building project. However, the specialsoil needs to be processed to use as it has many characteristics of high moisture content,high porosity ratio, high compressibility, high clay content, low strength, low permeabilityand so on. The premise of using vacuum preloading method in engineering is the bearingcapacity of dredger fill, that means the surface of dredger fill would become hard shellcommonly in2or3years. And under the powerful vacuum suction effect, particles willmove with the water to drain pipes, the large plastic pipes are surrounded with large fineclay of dredger fill and then are formed mud membrane, which seriously influence thedrainage consolidation of dredger fill and cause lower consolidation efficiency. So, it isnecessary to looking for a suitable vacuum preloading consolidation method for high highclay content dredger fill. And when take the dredger fill with high clay content and highorganic matter content as building foundation in the process of use, the post-constructionsettlement is often very large, and the time of settlement reaches to stabilization is verylong, often needs to reach for years, or even decades, very adverse to engineering. So it isvery meaningful to conduct the thorough in view of the secondary consolidationdeformation characteristics of dredgrer fill and influence factors to the forecast for thedevelopment of the settlement of dredger fill.According to the above problems, this paper first made through research on the basicproperties of dredger fill from Tianjin and Dalian, discussed the engineering geologicalproperties of high clay content dredger fill. Then used the straight-line vacuum preloadingmethod to reinforce Dalian dredger fill with laboratory simulation test, making sure that pipes type and distance were main purpose in straight-line vacuum preloading process. Inthe process of the laboratory simulation test, monitoring the variations of vacuum degree,settlement and pore water pressure, after the test, tested and analysised the mechanicsproperties, physical and chemical properties, microstructural features, Comparing thereinforcement effect of the six model boxes on different types and distance of drain pipes.The results shown that straight-line vacuum preloading can greatly reduced the vacuumpressure relay frictional cost, improve the strength of the soil and shorten the constructionperiod.The above straight-line vacuum preloading experiment can shorten the period ofconsolidation, but the experiment analysis found that the phenomenon of drainageplugging was still serious. Thus, the paper used the step vacuum preloading method toreinforce Tianjin dredger fill with laboratory simulation test in order to improveconsolidation efficiency of high clay dredger fill. The main concept of this method is to setup proved staged and stepped vacuum degree instead of one-time80kPa vacuum loadwith the consolidation of dredger fill, that is soil water separation stage, self-weightdeposit stage, vacuum preloading20kPa-40kPa-80kPa stage, making the water out of thesoil body gradually, achieving the goal of reducing the clay grain migration and unevensettlement. In the test process, monitoring the settlement, displacement and pore waterpressure. after the test, and after each stage, testing and analysised the mechanicsproperties, physical and chemical properties, microstructural features, comparing thereinforcement effect of dredger fill in different stage.The soil consolidation deformation includes not only the primary consolidationdeformation, but also the secondary consolidation deformation. The primary consolidationdeformation is a deformation process that gradually eliminating the water in the pore ofsoil and the excess pore water pressure dissipating gradually, the effective stress increasinggradually, until the excess pore water pressure is completely dissipated; the secondaryconsolidation deformation is after the excess pore water pressure is completely dissipated,under the condition of effective stress is invariable, the soil particle surface hydrated filmintegrating and soil particle structure adjusting caused as time growth and slow theincrease of soil skeleton creep deformation. For the dredger fill after vacuum preloading,the post-construction settlement is very large, cannot be ignored. Thus, this paper testedand analysised the primary consolidation deformation and secondary consolidation characteristics of Tianjin and Dalian dredger fill, it is proved the primary consolidationcoefficient and secondary consolidation coefficient were not with a constant, but with theconsolidation pressure changes, compared the primary consolidation and secondaryconsolidation properties; Also discusses the influence of the state of soil consolidation,pre-load, add lotus and add lotus time to the secondary consolidation coefficientThe settlement curves of the straight-line vacuum preloading and the step vacuumpreloading were not smooth linear, there were many discontinuous points indwell them,existed some certain errors, that made the settlement curves deviating from the real value.The sources on errors were affected by external environment factors and human readingerrors and the instrument measuring precision, and the degree of influence wasunknowable, That influence made the settlement curves deviating from the real value andaffected on the final settlement prediction, to accurately predict the soil settlement was adifficult problem. According to this problem, the nonlinear wavelet threshold denosingmethod was used to disposal the monitoring settlement curves of Tianjin and Daliandredger fill, extracted stable data to better predict the final settlement.At last, according to the problem that commonly theory calculate methods onlyconsidered the primary consolidation settlement, and ignoring the secondary consolidationsettlement, the prediction results had a certain gap with actual settlement, made thecalculation results difficulty to meet the design requirements. So the BP neural networkmodel was put forward to predict the settlement of dredger fill. And training the settlementdata of the straight-line vacuum preloading and the step vacuum preloading after denoised,fully learning the regularity of samples, predicting the final settlement and analysis theprediction results.This paper was baesd on laboratory simulation test, proposed two vacuum preloadingmethods: the straight-line vacuum preloading and the step vacuum preloading, usedphysical, chemical and microscopic test means, comparatively analysised the materialmigration rules, the strength properties and microstructure characteristic of the twomethods in the process of consolidation; and analysised the primary consolidation andsecondary consolidation characteristics, discussed influencing factors of the secondaryconsolidation coefficient; at last, using the nonlinear wavelet threshold denosing methodto disposal the monitoring settlement curves, eliminated the influence of the accidentalerrors to the settlement curves, and then set up the BP neural network to predict the final settlement, analysised the reinforcement effect of the two methods, provided a theory basisfor speeding up the consolidation efficiency of dredger fill, and finally served forengineering.更多还原