One-Dimensional Settlement Theory And Its Influence Factors Of Subgrade Of Unsaturated And Soft Soil

Unsaturated soil consist of solid fluid and air and there is mutual effect between fluid and air.This makes the settlement mechanism too complex to put the theory into engineering practice.Settlement mechanism of unsaturated soil are obviously different from saturated soil.If chosed consolidation theory of saturated soil to design roadbed rather than unsaturated soil's,there will be obvious error.In order to solve this problem,this article studied the existing research results of unsaturated soil consolidation theory and put forward a comparatively complete subgrade settlement theory of unsaturated soft soil under long-term load.In this paper,the main content and research results are as follows:(1)Divided deformation of unsaturated soft soil into two parts and came up with an consolidation-creep model for unsaturated soft soil considering the effects of suction.Combined the unsaturated soil's constitutive model with the control equation of pore water and pore gas and the effective stress principle.Then deduced equations to solve consolidation and creep settlement of unsaturated soil.(2)Chosed a typical project of highway soft soil subgrade as a calculation case.Used respectively the theory method and numerical simulation software to calculate this case.The calculated settlement values ware compared with the observed values.It was found that the final settlement values gotted by the theoretical method could be a good match to the observed values and simulations within the error range.This verified the feasibility of the theory of consolidation-creep settlement in this paper.(3)Using the proposed unsaturated soft soil theory,this article discussed the influence of the soft soil roadbed's boundary conditions and initial pore water pressure distributions on the consolidation speed and the pore pressure development by controlling variable method.Boundaries with better permeability are advantageous to complete the dissipation of pore pressure and accelerate the process of consolidation.When the distribution of initial pore water pressure is uneven within the scope of soil layer,the negative pore water pressure may occur in the process of consolidation.