One-dimensional Nonlinear Consolidation Theory Of Saturated Clay Based On Non-Darcy Flow

There sometimes exists large difference between the computation results from Terzaghi's one-dimensional consolidation theory of saturated clay layers and the field observed settlements, which can be in a certain extent ascribed to that the non-Darcy characteristic of flow and the nonlinear deformation of soil are not taken into account in this theory. Therefore, the variable head permeability tests for the clay of a place in Henan had been carried out. The results show that the flow of pore water in this soil with the smaller void ratio doesn't obey Darcy's law, and can be described by Hansbo's formula. Then, the nonlinear of soil deformation, the Hansbo's formula for the non-Darcy flow, the soil depth and the gravity stress factors were introduced to modify Terzaghi's one-dimensional consolidation equation. and the numerical analysis is performed using the finite difference method, and the computer programs were developed with the computer language of Fortran 90. In order to verify its validity, the numerical solution by the present method for the case that the flow water obeys Darcy's law was compared with the analytical solution based on the non-linear consolidation theory proposed by Davis and Raymond (1965). Then the effects of the parameters of non-Darcy flow, the soil depth and the gravity stress were investigated. From the numerical results, some conclusions can be arrived as follows:(1) Whether non-Darcy's characteristic of flow is taken into account or not, the pore pressure dissipation rate and settlement rate considering the self weight stress of soil are greater than these that not considering the latter. Whether the self-weight stress of soil is taken into account or not, the non-Darcy flow delays the dissipation of pore water pressure in saturated clay layers and the foundation settlements, and the pore pressure dissipation rate and the settlement rate will decrease with the increasing of the non-Darcy flow parameters m and I1, or the ratio c of the compression index and the permeability index, that is, they will be overestimated if the non-Darcy's characteristic of flow is taken no account of.(2) For the cases that self-weight stress of soil is constant in depth, if the value of c is smaller, the pore pressure dissipation rate and ground settlement rate will increase with the increasing of the surface load, and the pore pressure dissipation rate is slower than the theoretical value of Terzaghi's theory while the settlement rate is faster than the theoretical value of Terzaghi's theory in the early stage of consolidation, but the conclusions maybe the reverse in the later time of consolidation; If the value of c is greater, the pore pressure dissipation rate and the settlement rate are slower than the theoretical values of Terzaghi's theory, and the rate of settlement will increase with the increasing of the surface load, while the pore pressure dissipation rate is a relationship with the surface load, that is, the rate of pore pressure dissipation will decrease with the increasing of the surface load in the early stage of consolidation while it will increase the surface load in the later stage.(3) For the cases that self-weight stress of soil changes with depth, if the value of c is smaller, the greater the buried depth of soil, the faster the rate of pore pressure dissipation, however, with the increasing of the value of c, the influence of the buried depth of soil on the pore pressure dissipation will decrease, and it gradually comes in sight that the rate of the pore pressure dissipation will increase with the increasing of the buried depth of soil in the early stage of consolidation, while it will decrease with the increasing of the buried depth of soil in the later stage of consolidation. However the characteristic of the foundation settlement rate is different to that of the pore pressure dissipation rate, that is, if the value of c is smaller, except the case of zero depth, the rate of foundation settlement will increase with the increasing of buried depth of soil, however, if the value of c is greater, the rate of foundation settlement will decrease with the increasing of buried depth of soil, and the influence of the buried depth of soil on the settlement rate will increase with the value of c.