| With the continuous development and construction of China's railways,the extension space is more and more extensive,so that different regions will encounter different levels of problems.There are a large number of silty fine sand strata in the north of China.The biggest characteristic of the soil layer is the loose,single grain structure of sand particles in a relatively thin arrangement,and the stability is relatively unstable,which shows that the compression deformation is large and the shear failure resistance is low.Therefore,in the current relevant norms and foundation treatment textbooks,most of the(saturated)silty fine sand is used for soft soil foundation treatment.For this kind of foundation,the design mainly adopts gravel pile,CFG pile,screw pile and other measures to deal with.It has a large amount of engineering and high investment.It needs to be deeply studied for the treatment,how to deal with and how to deal with the foundation of silty fine sand.In view of the engineering characteristics of silty fine sand on the passenger dedicated line,the following problems are faced in the treatment of the soil layer foundation:(1)whether the settlement mechanism and development process of the silty sand foundation can meet the requirements of the foundation design under the overburden loading of the backfilling soil layer and the use load,which determines the subsequent foundation reinforcement treatment scheme;(2)the choice of treatment plan should take into account factors such as economy,reliability,rationality and persistence.Aiming at the shortage of the settlement characteristics of the silty fine sand foundation from the PDL,comprehensive,systematic and in-depth reseaches about the development of the silt and silty fine sand foundation would have been conducted based on the Tongliao to Beijing Shenyang high-speed railway subgrade engineering Xinmin station.The main contents are taken as follows:(1)Study on the physical and mechanical properties of silty fine sand.In this chapter,the basic physical and mechanical performance test,routine consolidation test,content of fine particle test and the effects of blending test,etc.were conducted in the laboratory.Through the tests proposed above,researches on the physical and mechanical characteristics and the consolidation deformation of the silty fine sand were performed.Meanwhile,the effects on the consolidation deformation mechanism with different content of fine particle have been studied.(2)Study on The analytic technique of the settlement mechanism of the silty fine sand foundationTaking the silty fine sand from the Tongliao to Beijing Shenyang high-speed railway subgrade engineering as the research object,with the help of the state variables of the transfer matrix method and integral transform method,the mechanism and development of the settlement were analyzed in detail,by applying the effects of the different load,boundary condition,and different fine particle content into one-dimensional and three-dimensional consolidation theory.(4)Study on the consolidation deformation characteristcis of the layered silty fine sand foundation by using the monitoring experimental technology on the typical silty fine sand field.Site monitoring test of typical silty fine sand field were taken out by using the single point settlement and multipoint settlement,pore water pressure and horizontal displacement monitoring components.And the occurrence and development characteristics of the silty sand foundation settlement,layered settlement,pore water pressure and horizontal displacement were obtained at the typical sites.In addition,the site monitoring test results have acquired a good agreement with the finite element analysis results.At the same time,the prediction model of the modified exponential function of the silty fine sand foundation settlement time relation curve was established. |
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