Studies On The Non-linear Rheologic Consolidation Behavior Of Layered Soft Clayey Soils

Based on the iterative methods and general analytical solution available for the problem of one-dimensional linear elastic consolidation of layered soils, a semi-analytical method is established herein for complex one-dimensional consolidation problems. By adopting linear rheological model of three units and non-linear rheological model of time lines, the semi-analytical method is respectively applied to solve the problem of one-dimensional consolidation of layered soft clayey soils with linear or non-linear rheological characteristics.A corresponding computer program named AODNRCLS is developed for the first time for solving non-linear rheological consolidation problem, in which important characteristics of soft clay such as its non-linear rheological and layered properties, the variation of permeability, the self-weight and time-dependent loading can be taken into account. The reliability of the program is verified through being compared with other known analytical solutions and numerical methods. Once the non-linear rheological characteristics of soils ignored, AODNRCLS turns to be the available computer program NAODCLS that was for solving small-strain non-linear consolidation problem. If the nonlinear property of soils is ignored further, AODNRCLS will return to ODCALS that was developed based on the one-dimensional linear elastic consolidation theory of layered soils.Both linear and non-linear rheological consolidation behavior of soft clayey soils are then analyzed in detail by using AODNRCLS. A variety of consolidation curves are prepared and the influence of various factors on the dissipation of pore pressure and the development of settlement and degree of consolidation are discussed.It has been shown that in one-dimensional consolidation problem considering rheological characteristics of soil, there exists two consolidation degrees defined in different terms, i.e. Up which is in terms of effective stress and Us which is in terms ofsettlement. While Up shows the rate of the dissipation of excess pore pressure (or the increase of effective stress), Us indicates the rate of the development of the surface settlement of the system. And there exists significant difference in numerical value between Up and Us, especially for layered soils. Generally, the main factors affecting non-linear rheological consolidation behavior are: the ratio of compression index and permeability index (i.e. cc/ck or); the ratio of coefficient of secondary consolidation and compression index (i.e. ca/cc or ); the non-dimensional parameter cc /(I + e0); reference time tref ; self-weight of soil (or the ratio qu/z0) and the rate of loading (Tvc or tc).The study also shows that rheology of soil not only increases settlement, but also observably decreases the rate of the dissipation of excess pore pressure. On the other hand, the dissipation of excess pore pressure also affects the development of rheological deformation of soil. This coupling action between the rheology of soil and the dissipation of excess pore pressure demonstrates that it is not reasonable to factitiously divide the process of consolidation into two independent ones, i.e. primary consolidation and secondary consolidation.It is the work presented herein that for the first time in the study of consolidation theory takes consideration of important properties of soft clayey soils such as non-linear characteristic, layered behavior and rheology in the same time, and provides efficient tools to give solution to one-dimensional non-linear rheological consolidation of layered soils. This develops consolidation theory and makes it more perfect.