Study On Simplified Analytic Method For Consolidation Of Unsaturated Soils

Unsaturated soils are widely existed in practical engineering.However,current engineering design and calculation theory basically set saturated soil as the calculation object.In the study of consolidation theory,the unsaturated soil domain has not obtained the same theoretical and practical results as the one-dimensional consolidation theory of Terzaghi saturated soil.Therefore,in the field of consolidation theory of unsaturated soils,further research is needed to obtain simplification and practical theoretical methods to solve practical problems.In this paper,after summarizing the research results of the field of consolidation of unsaturated soils at home and abroad in recent decades,based on Fredlund’s theory of one-dimensional consolidation of unsaturated soils,a simplified analytical calculation method has been proposed.The content of this article can be summarized as follows:1)First,in the one-dimensional compression test of unsaturated soil,the compressive relationship of effective stress principle of saturated soil is introduced to replace the constitutive relation expressed by the state of double stress,and govern equations composed of two bivariable partial differential equations obtained.2)When solving the set of equations,considering the initial excess pore water,the gas pressure is caused by instantaneous loading.In the calculation of the pore pressure change,Hilf theory has been introduced and an improvement been made that is more in line with the actual situation.A simplified approximate calculation method has been obtained.The analytical solution has been obtained by separation variable method and the coupling effect of water and gas has been considered.3)This result is simplified to be a check under saturated soil conditions.The results are in good agreement with the classical solution of one-dimensional consolidation equation for Terzaghi saturated soil.Then,the method of this paper is compared with Fredlund’s solution.The results of the dissipative process of pore water and gas pressure are close to each other.The deviation of the calculated results can meet the engineering accuracy requirements and the rationality of the results of this paper have been shown.On this basis,the changing law of the consolidation process under different working conditions has been further analyzed.Through the above calculation research,the change laws of pore water and gas pressure in different stages of consolidation and the laws of the effect of changes in consolidation depth and permeability coefficients of water and gas on the consolidation have been obtained.4)Based on the one-dimensional analytical solution,the analytical method is extended to the two-dimensional plane consolidation problem with the constitutive relation in the original article.Compared with the numerical solutions in the literature,the accuracy of the analytical method in this paper is verified.The calculation of the effect of the distribution of initial pore pressure on the consolidation has performed using a classic case study in the literature.The research results of this paper have high academic value in perfecting the study and analytical methods of unsaturated soil consolidation theory,and provide a theoretical guidance for the application of engineering simplification.The consolidation rules obtained in the paper also have a certain degree of engineering design reference value.