Studies On The Nonlinear Large Strain Consolidation Theory For Layered Structured And Rheological Soft Soils

Natural soft soils are widely distributed in coastal areas and areas along rivers,which have layered,structural,high compressible and rheological properties.However,it brings challenges due to ground settlement with the large-scale infrastructure construction in these areas as the rapid economic development in China.Therefore,it seems quite necessary to build more suitable models considering engineering properties of soft soils,and to have a deeply systematic study on the theory of consolidation for reasonably predicting the development of ground settlement.Some shortages currently available in the theory of consolidation,and the layered,structural,and rheological properties as well as geometry,material,compression,and seepage nonlinear variation during the consolidation process can not be fully considered.Thus,it is of great theoretical and practical significance to study the nonlinear small and large strain consolidation theory for layered structured and rheological soft soils.This paper started from studying the consolidation theory of layered soft soils,using analytical and semi-analytical methods gradually to investigate the nonlinear small and large strain consolidation theory for single-and multi-layered soft soils,and the nonlinear small and large strain rheology theory for layered soils.The consolidation behaviors of structured soft soils and the influences of soil properties on consolidation were analyzed in details.The main achievements are summarized as follows:(1)Analytical expressions were derived for one-dimensional nonlinear consolidation for layered soft soils under constant and time-dependent loading,and one dimensional consolidation for layered soft soil induced by time-dependent pumping from phreatic or confined aquifer,by employing separation of variables,matrix recursion method,Duhamel integration approach.The consolidation behaviors influenced by soil properties were analyzed,regarding compressibility,permeability,thickness and loading with two kinds of field drainage conditions.(2)Based on previous experimental studies,the nonlinear compression model,permeability model and calculation model for yield stress were established.Then,the consolidation process of single-layered structured soils was analyzed in details with two kinds of field drainage conditions.The solutions were obtained using semi-analytical method,and validated by comparing with existing solutions.And on this basis,the nonlinear consolidation of multi-layered structured soils study was carried out,and the influence of structural property and other factors,such as loading,the nonlinear variation of soil parameters were investigated.(3)The nonlinear large strain consolidation model was established considering sedimentation,structural property,layered property,geometric and material nonlinearity.By means of semi-analytical method,the solutions of nonlinear large strain consolidation of single-and multi-layered structured soils were obtained and validated.Then the results were compared with the solutions of small strain consolidation of structured soils and large strain consolidation neglecting structural property.The result turns out that the degree of consolidation calculated by small strain theory is greater than the calculated value of the large strain theory for structured soils,and the settlement of the former is smaller than that of latter.The settlement calculated by large strain consolidation theory neglecting structural property is significantly greater than structured soils.(4)Based on Yin&Graham VEP model,the parallel equivalent time line model for structured and rheological soft soils was established,and the one dimensional rheological consolidation of layered soils was studied.Then,according to the variation of secondary consolidation coefficient with the stress level,the non-parallel equivalent the time line model was established,and was applied in non-linear consolidation problem.Next,the non-parallel equivalent time line model for structured and rheological soft soils was established,and semi-analytical method was used to solve the rheological consolidation problem of layered structured soils.Finally,the influence of rheology on consolidation behavior was discussed.(5)The layered,structural,and rheological properties and sedimentation of soft soils,as well as geometry,material,compression,and seepage nonlinear variation during the consolidation process were fully taken into consideration in consolidation theory under time dependent loading.Based on the parallel and non-parallel equivalent time line model for structured and rheological soft soils,respectively,the nonlinear large strain consolidation for layered structured and rheological soft soils was studied.The influence factors of consolidation behavior were discussed;meanwhile,the comparisons with other theories were analyzed.