Study On Non-Linear Seepage Characteristics And Long-term Deformation Characteristics Of Saturated Clay

The traditional Terzaghi’s one-dimensional consolidation theory is based on Darcy’s law.Practices show that there always exists the significant difference between the solution ofconsolidation degree derived from Terzaghi ’s theory and measured value. This can be largelyattributed to the fact that Terzaghi ’s theory considering the linear seepage neglects of the effectof non-linear seepage pattern of pore water to consolidation, which can not reveal the essenceof seepage consolidation. Based on theory of non-linear seepage of pore water, characteristicsof non-linear seepage and its effect on the one-dimensional non-linear consolidation have beendiscussed through consolidation tests, permeability tests and theoretical analysis. Also, the lawof non-linear seepage consolidation of saturated soil is summarized. By the way of laboratorytest on the saturated clay, the characteristics of primary and secondary consolidation of soil isdiscussed in non-Darcy flow condition. Specifically, the non-linear seepage characteristics ofsaturated clay from different consolidated pressure is studied using Rower consolidationsystem of GDS.Combining the analysis and mercury-injection test, the inner mechanismand influence rule of non-linear seepage of saturated clay in theory.The main work andresearch results are as follows:（1） Consolidation and permeability tests of remolded clay samples are carried out.Experiments show that fluid flowing in saturated clay exhibits nonlinear characteristics. Theflow curve is made up of linear part and non-linear part, and there are minimum startinghydraulic gradient, initial hydraulic gradient and critical hydraulic gradient. The level of initialhydraulic gradient increases with the increase of consolidation pressure; The rule of boundarylayer，s changing under different pore diameters and pressure gradient, which is the majorfactor affecting nonlinear flow, is analyzed.It is proved that boundary layer thicknessdecreases with increasing different diameters and pressure gradient and the mechanism isanalyzed from change of viscosity of bound water and solid-liquid interaction. On the basis ofabove theories, a flow equation considering boundary layer is established. Finally, thenumerical relation of initial hydraulic gradient and boundary layer thickness under differentconsolidated pressure is fitted, showing significant linear relationship.（2）Through the mercury injection test, it is researched that the microscopic pore sizedistribution changes under different consolidation pressure, showing that the process ofconsolidation is essentially the process that the larger pore gradually changes into smallerpore. The larger pore is compressed preferentially, then the smaller one is compressed.Ultimately, large pore accounts for the proportion to be few, and smaller one accounts for theproportion to be more. Moreover, the relationship between microscopic pore size distributionparameters and macroscopic parameters is researched with fractal theory and the calculatingequation, which is expressed by the dual fractal dimensions of porosity and tortuosity. At last, the accuracy of the equation is proved by comparing the calculated value with the experiments.（3） Comparision is made between the theoretical flow curves basing Hansbo’s modeland measured flow curves, showing the validity of the Hansbo’s model in describingnonlinear characteristics of saturated clay. One-dimension nonlinear consolidation functionon the basis of Hansbo’s model is derived with reference to Terzaghi’s one-dimensionalconsolidation. In order to analyze the differences in influence on consolidation degree caused byDarcy’s law and non-linear flow, the contrast results are given between the theoreticalconsolidation degree from Terzaghi’s one-dimensional consolidation and experiment, indicatingthat the low-speed flow of nonlinear flow decreases the consolidation velocity. In addition,the relative proportion for primary consolidation and secondary consolidation of totaldeformation is also analyzed by one-dimensional secondary consolidation tests. The resultthat the relative proportion for secondary consolidation increases with higher consolidationpressure reflects the effect on long-term deformation retardation of pore pressuresdissipation having, caused by non-darcy flow at low velocity.