Study On Permeability And Deformation Characteristics Of Self-weight Collapsible Loess During Water Immersion

In order to meet the economic development,the Lanzhou area has carried out a series of“Shaving the mountains and Building the city”project,which involves the rebuilding loess filling.Many scholars have carried out in-depth research on the infiltration and deformation characteristics of remolded loess,which proves that remolded loess still has self-weight collapsibility.Based on the existing research,this paper further discusses the problem of the permeability and deformation characteristics of self-weight collapsible remolded loess.In this paper,the self-weight collapsible remolded loess in Lanzhou was taken as the research object.The water holding curve of loess soil samples was tested.The indoor one-dimensional soil column water infiltration experiment was carried out,and the unsaturated infiltration coefficient was obtained by using the improved infiltration front method,comparing the accuracy of the numerical simulation method.The model test of indoor test pit immersion under unloaded self-heavy stress was carried out,and the water field distribution during the test immersion process was obtained and a numerical model was established to simulate.The model test of water immersion in the indoor test pit under the overlying self-heavy stress was carried out,and the law of collapsible deformation of the soil sample during the immersion process was observed.To study the influence of the collapsible deformation on the permeability coefficient,the saturation of the soil sample was tested after pressure consolidation.The main conclusions are as follows:（1）.According to the one-dimensional soil water infiltration experiment,the unsaturated permeability coefficient function obtained by the improved infiltration front method is more accurate than the indirect permeability coefficient function obtained by the indirect method,and has more experimental basis than the application of Hydrus inversion.,provides a reference for the selection of numerical simulation parameters.（2）.The Green-Ampt correction model and Wang Wenyan model and the numerical method based on Richard equation are compared to simulate the water migration process.The accuracy of the unsaturated remodeling loess soil column water migration process is corrected.The Green-Ampt correction model predicts slowly.At the infiltration front rate,the Wang Wenyan model predicts a faster infiltration front rate,and the method based on solving the one-dimensional Richard equation is closer to the measured value than the other methods.It provides a reference for the selection of simulation methods.（3）.The numerical simulation results obtained in this paper can predict the infiltration front in the indoor test pit water immersion test without overlying self-heavy stress,and explains the unsaturated permeability coefficient function obtained by applying one-dimensional soil column and the reliability of numerical method for solving Richard equation.（4）.The difference between the infiltration of one-dimensional soil water and the water infiltration of two-dimensional test pit is analyzed.It is found that with the increase of the diameter of the test pit,the migration law of the infiltration front tends to one-dimensional infiltration under the center line of the test pit.And the infiltration depth of the infiltration front is more consistent with one-dimensional infiltration.（5）.The vertical and horizontal collapsible deformation laws of the soil layer in the process of water immersion under the test of self-heavy stress are obtained.It is found that the vertical deformation is larger than the horizontal collapse deformation,and the deformation of the depression at different depths is obtained.Combined with the change of lateral pressure,the stress redistribution reveals the lateral deformation mechanism during the collapse process.The moisture content of the area near the center line of the test pit increases first,resulting in a corresponding increase in the lateral soil pressure of the K₀coefficient in this area,and the moisture content in the far area below the center line of the test pit does not change,resulting in the K₀ coefficient of the area.The lateral stress is smaller than the area near the centerline of the test pit.Due to the stress difference,the stress redistribution occurs in the soil,and the soil in the nearer region will be laterally deformed by extrusion.