| Tianjin has a long history of reclamation project. Since Tanggu port was built in1939, different scales of reclaimed land was proceeded successively along the coast and Haihe River in Tianjin region. In recent years, with the large-scale construction and development of Tianjin Binhai New Area, reclamation project become the main way to obtain new land resources, thus formed a large amount of construction of soft soil foundation. However, with a large number of reclamation engineering implemented, produced a series of practical engineering problems such as the soft soil base surface uneven settlement, a long time to produce large amount of post-construction settlement and so on. A large number of scientific research and engineering experiences show that the rheological properties of soft soil is one of the main reasons for these problems. In the process of the reclaimed land building formed a lot of soft soil foundation, the impact of the rheological properties shows particularly significant. The characteristics of soft soil foundation, not only affect the construction of various buildings on the structure stability and safety of long-term use,but also for the sea land building engineering formed by the soft soil base itself can produce ground settlement crack, the loss of fill elevation, caused secondary geological disaster and a series of serious engineering problem, resulting in huge economic losses. Therefore, studies the sea land building form the characteristics of the rheological consolidation of soil in soft soil foundation, seeking the relationship between stress-strain and time of soft soils to analysis of the nature of its produce the rheological mechanism of soil has become the current research and the actual engineering problems needed to resolve.To solve the problem which occurred in the reclamation project because of the rheological properties of the soft soil foundation theoretically or practically, studyingthe consolidation and rheological properties of soft soil as well as the law in nature is an important topic. Based on the national natural science fund project(No.41172236),the national natural science foundation for young( 41402243) and the doctoral program fund projects by ministry of education(20120061110054), using the soft soil foundation of Tianjin coastal region as the research object, the following researches have been done.According to the engineering geological situation of the sampling site, the basic physical properties, soluble salt content, pH value, cation exchange and grain size analysis of the soft soil in Tianjin coastal region have been tested, to determine the basic characteristics, which provides research foundation for the next step soft soil consolidation test.Considering the secondary consolidation deformation, we established one-dimensional rheological consolidation differential equation based on Terzaghi consolidation theory. And we simplified the calculation process and parameters of one-dimensional rheological consolidation differential equation based on Secondary consolidation coefficient and Singh-Mitchell empirical creep model. The improved one-dimensional rheological consolidation differential equation can fully reflect the relationship between strain and stress and time in the process of rheological consolidation of soft soil, and this can provide theoretical basis for macro mechanical test and microstructure analysis.In order to solve the one-dimensional rheological consolidation differential equation considering the secondary consolidation deformation, we took Tianjin coastal soft soil as the research object and carried out the secondary consolidation tests using the high pressure consolidation apparatus, then the development of creep deformation of soil under different stress conditions is obtained, after that we analyzed the secondary consolidation characteristics of littoral soft clay. By analyzing the data, we got the variation of central fishing area soft soil consolidation coefficient,and analyzed factors affecting the coefficient of consolidation such as physicalproperties soil, test load factors, compression index and so on. Then we proposed a method for relationship between strain rate and volume change to differentiate the primary and secondary consolidation, and this method has been proved suitable for all kinds of load.To provide the basis for micro mechanics model, micro scale experiment, X-ray diffraction analysis for clay materials, as well as observation of clay micro structure characteristics before and after consolidation and creep with scanning electron microscope and mercury injection test, determining the pore distribution and its change were done. Hydration water characteristics of soft soil in Tianjin coastal region was tested, determining the adsorption quantity of hydration water. And the evaluation for characteristics of micro connection between soil particles was done.On the basis of secondary consolidation experiments and microstructure studies,and using a new soft soil rheological one-dimensional consolidation model,we can propose physical models that can describe the microstructure of soil deformation characteristics under load. Through the mechanical analysis of these models, we have derived the relationship between macroscopic and microscopic mechanical parameters.Soil pore distribution, microstructure deformation characteristics, stress-strain relationship, thickness of bound water film are involved in models, and by use of finite difference method for the new soft soil to solve rheological one-dimensional consolidation model. Taking a comprehensive consideration of other factors about stress history and external loads, compressibility, rheological properties, permeability and relative thickness of the foundation soil body, and comparing the model calculations with experimental values, the error is small, so the model is reasonable. |
