【作者】 张敬；

【导师】 闫澍旺；

【作者基本信息】 天津大学 ， 岩土工程， 2007， 博士

【摘要】 将真空预压技术拓展于水下软基的处理即水下真空预压一直未能实现,其主要原因是水下真空预压加固机理尚不甚清楚以及水下施工工艺存在诸多难题。而随着沿海滩涂的开发和港口建设向深水发展,水下真空预压加固软土地基技术在水下开挖工程、高桩码头的岸坡处理工程和防波堤工程等领域有着广阔的应用前景和适用性。为发展和推广水下真空预压预压,本文采用模型试验、理论分析和数值模拟等研究手段,对水下真空预压技术的真空产生机制,加固机理、和施工工艺和监测手段等进行了系统的研究。通过理论计算和试验研究对抽真空设备和真空产生机制进行了研究,研究表明抽水系统中射流泵部分可作适当改进,改进后的抽真空设备可产生75-95kPa的真空度,可以应用于水下真空预压。当阀门关闭时随着设备入水深度的增加,水头损失增大,因此所获得的真空度呈降低的趋势,随着入水深度的增加抽真空设备内的流量明显增大,其变化趋势与实验获得的观测数据基本相符。室内模型试验表明,在水深10m下,通过室内水下真空预压和真空联合堆载预压的对比模型试验(水深逐级增加至10m),证实了膜上水压可以作为预压荷载,水下真空预压的预压荷载等于预压前的孔隙水压力和预压后(完全固结)的孔隙水压力之差,当膜下砂垫层中的孔隙水压力小于0时,膜上水可全部作为预压荷载起作用,这时水下真空预压的预压荷载等于膜上水压和膜下真空度之和。在水下真空预压过程中,加固区边界外的水产生向边界内渗流不会引起土体破坏。提出了水下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水下真空预压加固地基固结计算的基本过程;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、位移和孔压边界条件处理、密封膜的处理等问题;对水下真空预压加固过程进行了数值模拟。针对水下施工的特点,对水下真空预压中的关键性技术滤管铺设、膜的铺设和射流泵的安装等进行了系统的研究,并对水下真空预压的关键施工工序—水下铺膜技术进行了研究,提出了水下铺膜车的设计构想。技术经济分析证明,水下真空预压具有较好的适用性和良好的经济效益。对水下真空预压监测技术和手段进行了研究,提出用液体压差沉降仪来测量地表沉降和分层沉降的方法,即通过不同测点处孔隙水压力的差值来观测地表沉降和分层沉降。更多还原

【Abstract】 Soft soil is distributed in the vast area of the world with poor property. Vacuum preloading is popular soft soil improvement technology in civil, port, communication, and hydraulic engineering. Usually, Vacuum preloading is limited in land because of the complexity of underwater engineering and the uncertainty of mechanism in underwater vacuum preloading. With the development the construction and technology, the research and application of underwater vacuum preloading can be possible and necessary. The study was directed toward the research and development of the mechanism of underwater vacuum preloading technique, the equipment for vacuum pumping and the technological process for implementation of underwater vacuum preloading.During the feasibility study, the existing land-based vacuum pumping equipment was tested in the water and rationally analyzed by way of combining theoretical research with model testing. It was known from the laboratory tests that, the land-based vacuum equipment was capable of producing a vacuum of 95 to 75 kPa and they could be used in underwater vacuum preloading.The working mechanism of the water on top of the sealing membrane was studied through laboratory model tests and theoretical analyses. The pre-loads produced by the underwater vacuum preloading equal the sum of the water pressure on the sealing membrane and the vacuum beneath the sealing membrane. In the laboratory tests, when the water head was 10 m, the whole water pressure (100 kPa) could be converted into pre-loads. During the implementation of underwater vacuum preloading, the infiltrated flow of water from outside the boundary of soil being consolidated wouldn’t result in the failure of the soil mass. During the laboratory tests, the change of jetting parameters with the water depth in different circumstances during vacuum pumping was also studied to achieve a series of regular patterns. And the laboratory model tests of underwater vacuum preloading have verified the working mechanism of underwater vacuum preloading and the conversion of water pressure into pre-loads.Basic theory and governing equations of underwater vacuum preloading were firstly introduced. Basic process of underwater vacuum preloading analysis using finite element method was introduced. Then using finite element method, a numerical study on the process of underwater vacuum preloading was conducted. Some key subjects of numeric analysis were discussed such as: selecting principles of constitutive equations of soft soil, the treatment methods for boundary condition of displacement and pore water pressure, the simulation of sealing membrane.Base on the feature of underwater construction, some key technology of underwater vacuum preloading were studied such as: the laying of sealing membrane and filer tube, the installing of vacuum pump. The study was focus on one of the key procedures, the underwater sealing membrane laying technology and a concept of underwater membrane-laying vehicle was presented in this study. It is suggest by monitoring technology of underwater vacuum preloading construction study that the settlement of ground surface can be measured by liquid differential pressure settlement metre. This method obtains the settlement from the differential value of pore water pressure at each measuring point. The cost-effectiveness analysis revealed that underwater vacuum preloading has fairly good applicability and economical efficiency.更多还原