The Research On The Properties Of 1D-consolidation Of Soft Clay Foundation With Upper Hard Crust In Dongting Lake Area

The soft clay is widely distributed in Chinese coastal areas and inland lakes, where there is usually a natural hard crust to a few meters above it. The physical and mechanical properties of the hard crust are very different from the underlying soft clay. Because of the hard crust's higher strength and lower compression, if it is rationally used, there will be great savings in project cost. However, even if the carrying capacity of the hard crust can meet the requirement, its use is also very little in the current projects. The reason is that there was very little research on the properties of consolidation and deformation on the soft clay foundation with crust. Therefor, with geological exploration data of Yue-Chang expressway, laboratory tests and theoretical analysis, the three aspects such as the engineering properties of hard crust and soft clay in Dongting Lake area, the vertical additional stress spreading on soft clay foundation with dry crust and its theory of 1-D consolidation were studied as follows:(1) With geological exploration data of Yue-Chang expressway, the distribution of the soft clay with dry crust is studied, the statistical characteristics of physical and mechanical parameters of the soft clay and hard crust are analyzed systematically and the relationship between these parameters are obtained by using linear regression analysis. By one-dimensional consolidation test and permeability test, the deformation of the hard crust and soft clay is studied completely, and the empirical formulas of e-lgp and e-lgkv are got. A new method using nonlinear least squares method to get the coefficient of consolidation was gained and its correctness is verified by numerical examples.(2)The problems of two-layer foundation's additional stress under triangular and uniform strip load are numerical simulated by finite element method and the approximation functions between calculation parameters and the layer additional stress distribution coefficient are got by binary regression. Based on "equivalent depth" concept, a more practical formula about the calculation of additional stress on the soft clay with hard crust is derived, and then the calculation of the additional stress under trapezoid load is studied.(3)Based on 1-D Terzaghi consolidation theory, the double ground consolidation model considering the factors of elastic material, arbitrary change in the external load, the arbitrary distribution of initial pore pressure and additional stress is established, and the analytical solution is derived by variable separation method. The effect of distribution of initial pore pressure and additional stress on the consolidation of the soft clay foundation with hard crust is studied by the procedure programmed by author according to Matlab7.0.(4)The double ground consolidation model considering the factors of over consolidation, nonlinear material, variable load, weight distribution and the additional stress distribution is established and the model is solved by semi-analytical method. The impact of the consolidation parameters of hard crust, external loads and additional stress on the consolidation and settlement curves is studied by the procedure of nonlinear consolidation under instantaneous load programmed by author according to Matlab7.0.