【作者】 成玉祥；

【导师】 杜东菊； 张骏；

【作者基本信息】 长安大学 ， 地质工程， 2008， 博士

【摘要】 天津滨海新区是继珠江三角洲、长江三角洲之后，又一个重要的经济开发区。随着我国投资战略的变化，天津滨海新区将成为我国又一经济增长点。由于天津滨海新区具有吹填造陆的优越条件，围海造陆成为天津滨海新区获得土地资源的主要途径之一。通过围海造陆所产生的土地资源，距离港口近，更容易产生巨大的经济效益。随着天津滨海新区城市规模的快速发展，通过吹填造陆而获取的土地资源的面积也在不断扩大。而天津滨海新区围海造陆的吹填物料为海底淤泥。所形成的吹填土排水固结时间漫长、灵敏度高、强度低、沉降量大等，必须进行处理。真空预压法是一种是十分适合于处理吹填软土的技术，但是该方法存在处理周期长，必须在泥浆表面形成硬壳后才可以施工等缺点，而且目前人们对其基本机理仍不清楚。本文以天津滨海新区结构性吹填土为例，对天津滨海新区吹填土结构强度形成机理和真空预压处理吹填土的关键技术进行了详细的研究。研究成果从理论上基本明确了吹填土结构强度的形成机理，并对天津滨海新区结构性吹填土的处理上具有重要的实际应用价值。(1)论文通过吹填土的物理性质和化学成分测试、力学性质试验以及原位试验，分析研究表明天津滨海新区吹填土粘粒含量达到45．5～50．1%，具有压缩性强、强度低，渗透性差等特点。(2)为了分析评价土的结构性，论文参照前人研究成果，提出了结构势指数作为土结构性参数。其定义为土结构破坏前后强度差与结构破坏之前强度之比。并提出了土结构性分级标准，为土结构性的分级提供了依据。(3)为了研究天津滨海新区吹填土结构性特征，论文根据灵敏度试验、压缩固结试验、剪切试验和原位十字板剪切试验结果，对不同试验条件下结构性参数进行计算，得出结构势指数为0．77～0．86，证明天津滨海新区吹填土具有强结构性。(4)为了研究吹填泥浆的泌水机理和沉积规律，论文进行了沉降柱模拟试验和微观结构试验，分析结果表明：沉降柱顶部主要为粒径小于0．005mm的粘粒及团粒，呈絮状结构，颗粒之间的接触不是十分明显，大孔隙也不甚发育。沉降柱中部除了粘粒以外，明显地可以看见有粒径大于0．005mm的粉粒存在，粘粒多附着于粉粒之上，孔隙和裂隙都较为发育。而沉降柱底部以粉粒为主，大孔隙极其发育。由此可以得出，粒径较大的粉粒沉降速率较快，粒径较小的粘粒沉降速率较慢。颗粒沉积规律符合Stocke定律，即下沉速率与颗粒直径的平方成正比。微结构参数分析表明：随着沉积深度增大，颗粒和孔隙的等效直径、周长、面积都呈增大的趋势，颗粒和孔隙数量、形态比、圆度呈减小的趋势，沉降柱中部土样的颗粒定向性较差，而沉降柱中部和底部土样的定向性较好。(5)论文通过对未处理土样和真空预压处理土样进行了电镜扫描和微结构参数分析，对真空预压处理前后吹填土微结构变化规律进行了研究。分析结果表明：在未进行真空预压处理之前，吹填土自然沉积状态下非常疏松，孔隙发育。原始沉积的絮凝结构较为明显，而粘粒之间多以团粒的形式存在，粘粒与粘粒之间的接触带很模糊。经过真空预压处理后，吹填土的结构较为紧密，孔隙不发育。粘粒主要以单粒堆砌的形式存在，所以粘粒之间的接触带较为清楚，而且颗粒之间的接触关系多以面面接触为主。微结构参数分析发现与真空预压处理前相比，处理后土样颗粒和孔隙等效直径、面积、周长、形态比和圆度明显减小、颗粒和孔隙数量明显增大，而随深度增加，同样也有此规律。(6)为了研究真空预压过程中影响结构强度增长的因素，论文分析了等效荷载、有效应力增量、孔隙比和含水量与结构强度之间的关系，得出随着等效荷载和有效应力增量的增大，吹填土的结构强度呈增高的趋势。含水量和孔隙比越大，吹填土的结构强度越低。主要原因是在等效荷载的作用下，土体中产生了有效应力增量。在有效应力的作用下，土体得到了逐步固结，含水量降低，孔隙比减小。土体中强结合水的含量越来越少，颗粒或团粒之间的连接越来越紧密，在其接触点上，逐渐产生了胶结作用，从而使结构强度得以提高。(7)论文对吹填土结构强度形成机理进行了详细的分析研究，结果认为吹填土结构强度的形成分为吹填泥浆泌水和吹填土固结排水两个过程。其中吹填泥浆的泌水过程分为以细颗粒絮凝下沉为主的阶段和以泥浆自重固结为主的阶段。吹填土固结排水过程分为早期空气排出、真空渗流场作用下的渗透固结和真空条件下的水分气化排出三个阶段。其中早期空气排出阶段进展速度快，地表沉降速度也快，但吹填土结构强度的提高有限。真空渗流场作用下的渗透固结阶段进展速度和地表沉降速度都较快，在强大的真空压力下形成的真空渗流场作用下，土体得到了固结，所以结构强度得到了提高。真空条件下的水分气化排出阶段进展速度缓慢，主要取决于环境温度和真空度。由于水分被气化排出，土体中的水分逐渐减少，所以，土体的结构强度很大程度上得以提高。但是，由于这一阶段受气化过程控制，其进展速度较慢，该阶段所用时间在整个真空预压过程中所占比重较大，这也是吹填土真空预压法处理周期漫长的主要原因，也导致了处理成本较高。(8)为了实现新近吹填土的真空预压法快速处理，论文提出了表层硬壳替代层、插板技术和水平排水系统三个关键技术的改进思路。采用人工方法形成表层硬壳，对现有的插板机通过降低高度、减小重量和改进动力装置进行改进，并对水平排水系统进行改进，以土工材料代替砂层，同时使水平排水系统可以承担表层硬壳替代层的部分功能。(9)论文为了验证改进真空预压法在新近吹填土处理中的可行性，论文对表层硬壳代替层和水平排水系统进行了试验改进和优化，结果得出以无纺针刺土工布联合土工格栅作为表层硬壳替代层是完全可行的，塑料排水板的插设深度不超过10m。以无纺针刺土工布与高强度海绵组合作为水平排水系统是最优方案。真空预压法可以用于处理新近吹填土。改进真空预压法与现有方法相比，在早期施工阶段可以节约成本40%，同时可以缩短施工时间6个月以上。更多还原

【Abstract】 Tianjin Binhai New Area is another important economic development area following Pearl River Delta and Yangtz River Delta. With the change of investment strategy, it will be a new point of economic growth in China. Because the basic condition is sufficient, Reclamation has been the main method for Tianjin Binhai New Area to obtain land resource. The land resource obtained by reclamation may produce great economic efficiency more easily since it is close to harbor where the economy develops quickly.With the fast development of the Tianjin Binhai New Area city scale, the area of land resources obtained through filling sea increases continuously. Because fill material in Tianjin Binhai New Area is seabed silt,the hydraulic fill has a longer drained consolidation time,higher sensitivity, lower strength and larger settlement,which must be treated before engineering beginning. Vacuum preloading is a kind of appropriate hydraulic fill soft clay treatment method. But the method has such shortcoming as long treat period,and it must form crust on the surface of mud before beginning. At the same time,the research on the basic mechanism and the treatment process are still not clear.Taking the constructive hydraulic fill in Tianjin Binhai New Area as an example,The Structutal Strength Formation Mechanism of Dredger Fill in Tianjin Binhai Area and Key Technique of Vacuum Preload Method are studied in detail. The research result makes the theory of Structutal Strength Formation Mechanism of Dredger Fill clearly,and has important practical value to the construtive hydraulic fill treatment in Tianjin Binhai New Area.(1) The physical property test,chemical composition test,mechanical property test and original test of hydraulic fill in Tianjin Binhai New Area has been done,the research result shows that the clay pellet content of the hydraulic fill in Tianjin Binhai New Area reachs 45.5～50.1%,the hydraulic fill in Tianjin Binhai New Area has strong compressibility.low strength and poor permeability.(2) For evaluating of soil structural feature, referring to study results existed.soil structure potential index defined by the ratio of soil strength difference between before structure failing and after structure failing to strength before structure failing is proposed as the parameter to evaluating soil structural feature.At the same time, the classification standard of soil structure is put forward,it provides basis for soil structure classification.(3) For reseaching structural character of hydraulic fills in Tianjin Binhai New Area,according to sensitivity test, compression consolidation,shear and in situ cross sheer test result, structure parameters of different test condition are calculate,the result show the range of structure potential index of hydraulic fills in Tianjin Binhai New Area is 0.77~0.86,so hydraulic fills in Tianjin Binhai New Area is strong structure constitution.(4) For studing the water separate mechanism and deposition regulation of hydraulic mud,the settlement simulation test and micro-structure test are done.Micro-structure analysis result shows that the flocculent form clay pellet distribute at the top of settlement columniation,grain diameter is less than 0.005mm,the contact of of the grain isn’t very obvious,the big void is seldom,In addition to clay particle,silt particle which diameter is bigger than 0.005mm is existed at the middle of settlement columniation,clay particle is adhere to silt particle,the void and cranny is extensive. the silt particle distribute at the bottom of settlement columniation, the void and cranny is very extensive.So it can be find that the silt particle sedimentation rate is quicker than clay particle. Grain sedimentation is accord with Stocke law,rate is proportion with the square of grain diameter namely.It can be gotten from microstructure parameter analysis that with the sedimentation depth Increasing,the quivalent diameter,perimeter and area of void and grain become larger of void,the number,shape ratio and roundness of void and grain become less, the orientation of the middle of settlement columniation is worse than the orientation of the top and bottom of settlement columniation.(5) For researching microstrcture change regulation of hydraulic fill treated by vacuum preloading and untreated,electronic scanning microscope is used to obtain the microscopic scanning picture of both original hydraulic fill and treated with vacauum preload,at the same time,the microstructure parameter is analyzied.the result shows that before treatment with vacauum preload, the hydraulic fill is very loose under the natural condition,void is is extensive.Flocculent structure is obvious, clay particle is existed in pellet,the contact of clay particles is blurry.After vacauum preload treatment,the structure of hydraulic fill becomes compact,void becomes fewer, clay particle stack each other, the contact of clay particles is very clear,the contact between grains is surface to surface.It can be found from microstructure parameter analysis that after treatment with vacauum preload, the quivalent diameter, area, perimeter,shape ratio and roundnes of void and grain become less,the numberof void and grain become larger,with the depth increasing,the same law exists.(6) The relationship between equivalent load ,effective stress increment, water contain, pore ratio and Structure strength is studied for researching the influence factor of structure strength during vacuum preloading,the result shows that effective stress increment and equivalent load are larger, Structure strength of hydraulic fill stronger, the water contain or pore ratio are larger, structure strength of hydraulic fill is lower.it is because that the effective stress increment is come into being under the equivalent loading.Under the effective stress, the soil structure is formed , and the connect between pellets is more and more close, gradually cementation and coupling come into being on the contact joint or interface, so stronger structure strength is formed.(7) The structural strength increase mechanism of hydraulic fill is researched. It is believed that the formation of structure strength of hydraulic can be divided into two part: hydraulic fill mud removing water and hydraulic fill concretion drainage, hydraulic fill mud removing water process includes pellets flocculate subsidence and fill mud deadweights concretion. The hydraulic fill concretion drainage process includes forepart air discharge, penetrate concretion in vacuum seepage field and water gasification discharge under the vacuum condition. The forepart air discharge stage develops very quickly, and the surface sedimentation rate is quick too, but the increase of structure strength of hydraulic fill is limited. The penetrate concretion rate in vacuum seepage and field the surface sedimentation rate is rapid. Under the vacuum seepage field coming from strong vacuum pressure, soil consolidates and the structure strength increases. The water gasification discharge under the vacuum condition develops very slow, the rate is controlled by environment temperature and vacuurm degree. The water is gasified and gets away, the water contain of hydraulic fill drops off, so ...the structure strength increases significantly. But this process is controlled by gasification process and develops slowly. The proportion of the time spending on the water gasification discharge process to the whole time that vacuum preload needed is great, so the hydraulic fill treatment period by vacuum preload is very long, and the same time, it’s cost is very high.(8) For quickly treating freshly hydraulic fill by vacuum preloading, the improving thinking of three key technique including surface crust substitute layer, drainage shutter insert technique and level drainage system is provided. Surface crust is artificially built,mending drainage shutter insert machine existed through Lower height, minishing weigh,improving dynamical equipment and mending level drainage system through replacing sand layer by other material.thus, level drainage system can be used as surface crust substitute layer.(9) For validating the feasibility of vacuum preloding in treating freshly hydraulic fill, surface crust substitute layer and level drainage system is mended and optimized.The result shows that no-weave sting cloth combining with engineering gridding is fully feasible to substitute surface crust, the drainage shutter insert depth can’t exceed 10 meters, and combination no-weave sting cloth with high strength sponge is the best level drainage system. So vacuum preloading can be used to treat with freshly hydraulic fill. Comparing with vacuum preloding now used ,mended vacuum preloding can save about 40% early constrction cost of ,and shorten constrction time 6 month.更多还原