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

The traditional Terzaghi's one-dimensional consolidation theory has great limitation on estimating saturated clay's settlement. The experience shows that there sometimes exits the notable difference between the solution of consolidation degree derived from Terzaghi's theory and the measured value, which can be in a certain extent ascribed to the fact that the flow of pore water in saturated clay may not obey Darcy's law. So the odemeter is modifiled in this paper. And one-dimensional consolidation theory based on Non-Darcy is studied systemically through theoretical analysis and many test of permeability and consolidation. The main work and research results are as follows:1) The traditional oedometer is improved based on the predcessor's foundation on account of its shortage on the permeability tests. By using the modified osmotic oedometer, the consolidation and permeability tests can be successively carried out, which can be used to study the permeability characterics of the soil specimen under different loads. By controlling the drainage condition through the triple volves, not only the double drainge tests can be conducted, but also the single drainge tests can be done and the pore water pressure at the bottom of the soil specimen can be measured. Moreover, the new apparatus has some merits such as simple conformation and good watertight behavior. Its application to some tests gives reasonable results in comparson with the traditional consolidation tests and permeability tests. In addition, a phenomenon is found that the pore pressure from the bottom of specimen inclines to delay by using the single drainage tests.2) Based on the consolidation and permeability tests of saturated clays in Henan, the permeability of clays under different consolidation pressures are systematically investigated by using the modified osmotic oedometer. Experiments prove that the flow in this soil doesn't obey Darcy's flow and it can be described by the two-section model of Hansbo's. Experiment results show that permeability and void ration of clay are nonlinear relationship, the permeability of clays decreases nonlinearly with consolidation pressure increasing. Then the relations of the void ratio and the flow parameters are analyzed. The results indicated that permeability coefficient k and void ration e are in semi-logarithmic relation and parameter i0?m and void ration e are in linear relation. Meanwhile, experiment results of consolidation show that the applicability of Terzaghi's one-dimensional consolidation theory has definite limitation. If the seepage flow of clay doesn't obey Darcy's law, the theory isn't likely to apply and needs modify.3) In order to improve the precision of consolidation computation, Terzaghi's one-dimensional consolidation theory is modified based on the non-Darcy flow described by the power function for the lower velocity of flow and the linear function for higher velocity of flow, and the numerical analysis is performed by using the finite volume method.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-dimension consolidation theory. Comparisions are made between theoretical curves and the measured curves from the tests. It is concluded from the contrast that the actual process of consolidation is simulated more rationally by the consolidation theory of Non-Darcy flow. Then the effects of the parameters of non-Darcy flow on the consolidation process are investigated. The numerical results indicate that the non-Darcy flow delays the dissipation of pore water pressure in saturated clay layers, thereby the consolidation velocity of settlement of these soil layers is smaller than the solution based on Terzaghi's theory. Besides the coefficient of consolidation Cv, a new parameter I1 composed of the threshold hydraulic gradient i1, the thickness of soil layer H and the vertical uniform load p0 is introduced to characterise the consolidation of these soil layers.4) The consolidation tests under the cyclic loading with low-frequency were carried out, which can be used to study the effects of the period of loading and load intensity on the foundation. 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 were taken into account by using the modified Terzaghi's one-dimensional consolidation equation and the numerical solution was performed using the finite volume method. Comparisons is made between theoretical curves and the results of consolidation tests of the cyclic loading with low-frequency. It shows that the theoretical curves based on Non-Darcy flow are in more accordant with tests. Then the effects of the parameters of non-Darcy flow, the rate of loading, the period of loading and the compressibility of soil in the over-consolidated state on the consolidation process were investigated. The results indicated that, under the cyclic square loading, both degrees of consolidation in terms of settlement and pore water pressure were shown as vibratory increase with time, and the amplitude of degree of consolidation in terms of pore water pressure was greater than that in terms of settlement. In addition, it was found that the settling velocity of foundation was delayed by the non-Darcy flow, and decreased as the period of loading shortened or the compressibility of soil increased in the over-consolidated state.5) Terzaghi's one-dimensional consolidation theory was generalized to take account of the case under the monotone increasing loadings in order to study the effects of the construction loads on the consolidation of clays. Numerical analysis was performed by using the finite volume method. The effects of the parameters of non-Darcy flow and the rate of loading on the consolidation process were investigated. The numerical results indicated that the the Hansbo's flow delays the dissipation of pore water pressure in saturated clay layers; thereby the rate of consolidation of the layers decreases as the parameter of the Hansbo's flow increases. The influence of the loading rate on the consolidation behaviors is remarkable mainly in the construction period and in the initial stage after its completion of construction.