Experimental Study On Physical And Mechanical Characteristics Of Marine Soft Soil Under The Change Of Occurrence Environment

The paper takes marine soft soil in reclamation area of Qinzhou Port in Guangxi Province as the research object with the aim of studying its physical and mechanical characteristics under the change of occurrence environment. The researcher adopted a method of combining mechanism simulation technology with indoor soil test, then designed and made the soaking-loading linkage experiment platform. Using overlying load of level four and five kinds of soaking liquid, changing factors of occurrence environment have been memorized by the research object of marine soft soil successfully. After three months of monitoring axial displacement of marine soft soil when preparing the soil sample, the researcher analyzed the soil sample containing environmental elements through main ion components analysis, penetration test, direct shear test, consolidation compression test and etc. Following are the main researching findings:First, through monitoring axial displacement of marine soft soil during the process of preparing the soil sample and indoor consolidation test of soil sample containing environmental elements, the researcher found that soaking liquid environment had influenced on consolidation characteristics of marine soft soil, and Ca2+soaking liquid of high concentrations could most inhibit axial compression deformation of marine soft soil.At the same time, accumulated deformation and consolidation of marine soft soil were influenced comprehensively by two environmental factors, namely overlying load and soaking liquid, but which environmental factor playing a leading role in the process of the consolidation and deformation depended on its own level and degree.Second, through main ion components analysis and indoor penetration test, researcher found rules as follows:there was a correlation among void ratio, coefficient of permeability and main chemical element content of marine soft soil under different environmental factors. During the process of preparing the soil sample, the increase of overlying load would make marine soft soil compacted and partly change its structure, and it could decrease the void ratio and leaching coefficient, which could affect its ion diffusion with the outside soaking liquid and also impact the permeability of marine soft soil. When the marine soft soil got the initial loading of first level, it could have enormous influence on the ion diffusion with the outside under soaking liquid of high concentrations, and it could also make the permeability coefficient decrease in the greatest degree. Under the same environmental conditions, Mg2+was more likely to exchange the ion through more and smaller void of marine soft soil, which showed at a macro level that permeability of marine soft soil, which was in soaking liquid environment with the2.5%mass concentration of Mg2+, was the worst. However, as to soaking liquid, if some strengthening ion concentrations did not reach saturation state, then the change of environmental conditions had no significant effect on ion diffusion between the rest ion in soaking liquid and the related ion in marine soft soil. Except elements with particular strengthening concentrations, the final ion diffusion between marine soft soil and the soaking fluid in different environmental conditions also tended to be the same.Third, through direct shear test and consolidation compression test of marine soft soil memorizing environmental changing elements, the researcher concluded the changing rules of mechanical properties as follows:overlying load of marine soft soil played a decisive role of the value c of soil cohesive force changing, and its influence on the value c was greater than the influence of the chemical constituents in the soaking liquid. And soaking liquid environment affected significantly value φ of internal friction angle of marine soft soil, and what kind of environment factors playing a leading role of affecting value φ of internal friction angle of marine soft soil depended on the degree of environment change. Meanwhile, through comparison under various environment, the researcher found that Ca2+had the most obvious effect on strengthening shear index of marine soft soil such as the value c of soil cohesive force, value φ of internal friction angle effect of the most obvious.In addition, the previous research results show marine soft soil has a stronger memory of the stress history with different environmental factors. And researching findings in this paper can predict that occurrence environment factors such as overlying load and soaking liquid have remarkable effect on the preconsolidation pressure and the formation of structural strength, which can be explained specifically as follows:preconsolidation pressure value of reshaping marine soft soil soaking in the sea water environment, getting in the soaking-loading linkage molding process, can reflect truthfully the stress history of soil modulus, and it is very close to the load value in the process of making marine soft soil module. And as to marine soft soil in the soaking liquid with2.5%mass concentration of Ca2+, calcium cementation was enhanced as the Ca2+increased significantly in marine soft soil, therefore structure strength of the marine soft soil was strengthened, which was reflected by the preconsolidation pressure value under the above environmental conditions was higher than its true stress history.