One-Dimensional Consolidation Of Saturated Clays Under Time-dependent Loads Based On Non-Darcy Flow

There sometimes exits notable difference between the solution of one-dimensional consolidation of saturated clay layers based on Terzaghi's theory and the field settlement observations, which can be in a certain extent ascribed to the terzaghi's assumptions that the flow of pore water in these soil layers may not obey Darcy's law, the external vertical load is constant in time, and etc. Therefore, By using modified odemeter, the laboratory tests of permeability and consolidation are carried out, and one-dimensional consolidation characteristic under time-dependent loadings based on non-Darcy flow is investigated in detail. The main work and research results are as follow:The results of permeability test for a kind of clay in Henan show that the flow in this soil doesn't obey Darcy's law and it can be described by the two-section flow model of Hansbo's, and the results of consolidation test under the low-frequency cyclic loading for this soil show that the consolidation theory based on Darcy flow is not always suitable for all cases. Therefore, the Hansbo's formula for the non-Darcy flow was introduced to modify Terzaghi's one-dimensional consolidation equation considering that the compressibility of soil in the over-consolidated state is usually less than that in the normally consolidated state. The cases under the cyclic loading with low-frequency are taken into account by using the presented eqution. The numerical analysis is performed by using the finite difference method, and the computer program is 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 of pore water obeys Darcy's law is compared with the analytical solution based on Terzaghi's one-dimensional consolidation theory. The comparison between theoretical and the experimental results for the aboved consolidation tests proves the the validity of the presented theory based on Non-Darcy flow. Then the effects of non-Darcy flow parameters, the period of loading and the compressibility of soil in the over-consolidated state on the consolidation process are investigated. The results indicated that,under the cyclic square loading, both degrees of consolidation in terms of settlement and pore water pressure are shown as vibratory increase with time, and the amplitude of degree of consolidation in terms of pore water pressure is greater than that in terms of settlement. In addition, it is found that the settling velocity of foundation is delayed by the non-Darcy flow, and it decrease as the period of loading shortened or the compressibility of soil increased in the over-consolidated state.In order to investigate the influence of construction load in the conditon of non-Darcy flow, Terzaghi's one-dimensional consolidation equation of saturated clay is extended to the case under the monotone increasing loads, and numerical analysis is performed by using the finite volume method. The numerical results indicate that non-Darcy flow delays the dissipation of pore water pressure in saturated clay layers, thereby the rate of settlement of these soil layers is less than the solution based on Darcy flow. In addition, the influence of loading rate on the consolidation behaviors is remarkable in the construction period and in the initial stage after its completion of construction. Therefore, the influence of the construction speed can be ignored in computation of the final settlement quantity.