Research On The Evaluation Of Engineering Characteristic Of The Loose Sediment In The North Of Yangtze River Estuary

The engineering characteristic of soil is the comprehensive representative of the soil parameters essentially. According to the principle of soil classification, to some extent, the evaluation of soil engineering characteristics is namely the study of the soil physical indices,the mechanical indices and the relationship between them. In view of the above understanding, the engineering characteristics of the loose sediment in the north of Yangtze River Estuary are analyzed in this paper.The loose sediment in the north of Yangtze River Estuary is a quite thick loose layer consisting of marine-continental deposit with multi-deposit cycle rhythmites for being influenced by development evolution of Yangtze River,cold-warm periodic variation of paleoclimate,transgression,regression and other factors. For the complexity of geological processes and depositional environment, the conventional physical indices prominently disagree with the conventional mechanical indices representing clayey soil in the north of Yangtze River Estuary So the engineering property of soil such as permeability,mechanical strength and compressibility can't be inferred from its physical indices as usual. The discordance is that the physical indices are softer and the mechanical indices are harder than the usual.Firstly, aiming at the engineering phenomenon, based on reviewing the situation of soil classification,the principal component analysis principle in multi-statistic theory is applied to research the capability that the routine physical indices of soft clay (mainly loam and sandy loam) in the north of Yangtze River Estuary (along the TongQi highway line) reflect soil characteristic. The conclusion is that the pore characteristic indices and grain size composition index can reflect the characteristic of sandy loam mostly. On the other hand, the characteristic index of plasticity can reflect the characteristic of loam mainly. The ability to reflect the basic information of sandy loam by the characteristic index of plasticity is reduced prominently, and it is not all reasonable that the routine method to adopting relative water content (IL) to divide consistency of sandy loam and that sandy loam is subject to clay category in Specifications for Design of Ground Base and Foundation of Highway Bridges and Culverts (JTJ024-85), so it deserves discussion. The results are useful for the modification of criterion in future.Secondly, the grey correlation analysis principle is applied to analyze the relationship between the physical state indices and the mechanics indices of clayey soil in the north of Yangtze River Estuary, which quantifies the correlation among the indices. Essentially more rational,simple and effective standard is established based on Fioravante pore function (Fe) or void ratio (e). The better correspondence is reached between the physical state indices and the mechanical indices by the new standard, compared with the conventional division principle of relative water content (IL). The grey correlation analysis results of loam and sandy loam indicate that the grey correlation between water content ratio and the mechanical indices are the relatively best, so it is not only lead the better correspondence between the index of water content ratio and the mechanical indices but also avoid the influence of error testing plastic limit (Wp) in the conventional division index of relative water content (IL) that establish the new division system of physical state with water content ratio (Ic) as the dominate index. The new evaluation system of physical state offers the foundation for engineering characteristics evaluation of soft clay in the north of Yangtze River Estuary (along the TongQi highway line), and it is useful and valuable for engineering characteristic's cognition of the analogical engineering field for the futureFinally, the physical and mechanical properties of sediment in the north of Yangtze River Estuary (along the TongQi highway line) are researched, a conclusion is drawn that soft clayey soil in the north of Yangtze River Estuary have much higher strength compared with the general soft soil foundation. The conclusion is not only important guidance value for engineering but also offered the foundation for selecting methods of foundation treatment.