Theory Of One Dimension Non-linear Consolidation Of Cohesive Soil Based On Non-linear Seepage

The model of consolidation about complete and saturated soil which includes model of stress-strain and model of pore water seepage, involves two aspects of continuum mechanics: continuum mechanics of porous media and continuum mechanics of seepage flow. Over the years scholars have focused on the research of constitutive model of soil non-linear stress-strain, and have neglected of the effect of non-linear seepage pattern of pore water to consolidation. Based on theory of non-linear seepage of pore water, the one-dimensional non-linear consolidation characteristics in the effect of non-linear seepage and the law of non-linear seepage consolidation of cohesive soil have been discussed and explored.One-dimensional seepage consolidation is the most basic issue of soil mechanics, So far it has been still the important tool of calculation about foundation settlement and the scope of land subsidence. Although there are many disadvantages, it reveals the essence of consolidation of soil seepage through which the basic law of soil consolidation is easily understood, and it is still good consistent with the actual situation by simple amendment. For issues of more simple one-dimensional consolidation (such as instantaneous load-on and linear or elastic model), analytic method is the most accurate method of calculation. Because the relationship of stress-strain is often manifested as nonlinear, Then the accuracy of analytical solutions is often difficult to meet the actual needs. Furthermore, the analytic method is also very difficult to make accurate characterization for the nonlinearity of seepage in the process of consolidation (such as changes of the permeability coefficient). Numerical method has become the most effective tool and finite difference method has become the most common method to numerical simulation of one-dimensional consolidation of seepage, because it has simple and clear physical meaning and smaller workload of programmers, the finite difference method has been often used for numerical analysis of the one-dimensional consolidation.Predecessors have had a wide range study on theory of non-linear seepage. The mechanism of non-linear seepage has been summarized from pore structure of the porous medium, interaction between flow and solid and properties of flow, and seepage of cohesive soil has also been recognized not to be consistent with the linear Darcy's law. Although there are many mechanisms effecting non-linear seepage, some mechanisms are not accurate for characterization. So it is difficult to establish a model of seepage considering all mechanisms. Through analysis of common characters of non-linear seepage, the calculation model of non-linear seepage containing the parameters of non-linear seepage, such as starting pressure gradient, to be starting pressure gradient, critical pressure gradient and power index, has been raised from the point of hydrodynamic of bound water. It considers effects of porosity ratio and hydraulic gradient:K=K(e)·ψ(I)In which K(e) is the function of porosity ratio e,ψ(I) is characteristics function of non-linear seepage.Terzaghi model is the most basic theory of soil mechanics, but it includes too many assumptions, such as soil is the linear elasticity, coefficient of consolidation remains constant in the process of consolidation, load should be imposed instantaneously and so on. Many of these assumptions are inconsistent with the actual situation, and does not well reflect the non-linear characteristics of consolidation of soil seepage. Therefore the calculation to consolidation and settlement of soil using this method is inaccurate. The amendment for Terzaghi model has been made from the law of non-linear seepage, the model of non-linear elastic stress-strain and the load changes with time and so on in the paper.In this dissertation the assumption that seepage is in conformity to the Darcy's law has been modified using the model of non-linear seepage in Terzaghi theory, and numerical calculation procedure (NDFTERM) has been compiled which achieves one dimension linear numerical simulation of consolidation considering the nonlinear seepage. Simulation results show that the non-linear seepage has more significant impacts to the process of consolidation of cohesive soil presenting as more obvious lag dispersed phenomenon of super-static pore water pressure, which can give more reasonable explanation to some consolidation phenomenon.To the scope of non-linear seepage, numerical experiments have showed that the excess pore pressure intercepted by starting pressure (or planned to activate the pressure gradient) is the major factors to lead to be not full consolidation. When the excess pore pressure intercepted is much smaller than the largest excess pore water pressure in the process of consolidation, its impacts can be ignored.There is a big difference between the assumption of the linear elastic soil and the mechanical characteristics of cohesive soil in Terzaghi consolidation theory, so it does not well reflect the law of nonlinear consolidation of cohesive soil. Based on the study of Davis, Li Bingheand others, a numerical procedure (ODNLC) has been compiled to carry on numerical analysis of one-dimensional non-linear consolidation. The rusult is consistent with analytic solution of Davis and others which proves that there are some differences btween consolidation definited using excess pore pressure and that definited using settlement, the changes of permeability coefficient and lateral limits compressibility coefficient along with the effective stress and porosity satio and the size of load are the non-linear factors affecting soil consolidation, and it also indicates the effects of non-linear consolidation to soil settlement. In the dissertation, the non-linear seepage has been introduced to the model of one-dimensional nonl-inear consolidation, the model of one-dimensional nonl-inear consolidation has been advanced considering the non-linear seepage, a numerical calculation procedure (ODNLCNDF) has been compiled, and the simulation of one-dimensional non-linear consolidation has also been achieved considering nonlinear seepage for the first time.The load acted on the soil is changing with time in many practical situations. Based on the previous work of predecessors, consolidation analysis has been made considering the load changes with time which proves that there is a clear difference between consolidation rules of soil under the changed loads and Terzaghi theory. Instantaneous effect of consolidation of load obtained by calculation which can be looked as linear increase is not so clear, and this is also the main reason that forecast calculation is bigger in the practical issues. The cycle of load has a clear influence on the consolidation of soil for the load similar to the sine wave.For the load which has a significant variation, the effective stress of soil is variatied, so it does not only study the process of soil compression, but also take into account the differences between the process of resilience-compression and compression of soil when the effective stress has the attenuation. The dissertation points out limitations of the theory of one-dimensional non-linear consolidation considering the load changes advanced by Li Binghe, Geng Xueyu and others, the effective stress can be considered as indicators judging compression of soil and the process of rebound-compression, and the theoryof one-dimensional non-linear consolidation of changed load should be extended to that of arbitrary changes of load of one-dimensional non-linear consolidation. Through simple modifications, the theory can be extended to the theory of consolidation considering the greatest consolidation stress in advance.A numerical procedure (ODNLCTVL) has been developed to carry through the study on numerical simulation considering one-dimensional non-linear consolidation of changed load, and it has been found that the rules of the one-dimensional nonlinear consolidation of soil under the changed load have differences with that of instantaneous consolidation which includes linear load and the consolidation of fluctuated load. In addition, considering the influence of compression of soil to its consolidation and settlemen, it is very necessary to consider plastic deformation of soi.A numerical procedure (ODNLCNDFTVL) has also been developed to carry through thestudy on numerical simulation aimed at the model of one-dimensional non-linear consolidation based on non-linear seepage in the action of changed load, and it is found that there is a same great influence of non-linear seepage to one-dimensional nonlinear consolidation in the action of changed load which performs general lags in the process of consolidation and Darcy seepage. In the linear process of loading, the rules of consolidation is consistant with that of Darcy seepage. The hysteresis effect of nonlinear seepage is more significant, but it decreases rapidly in the process of cyclic loading.