Experimental Research On Hydraulic Characteristic Of Coarse-grained Soils Of High-speed Railway Subgrade

Hydraulic characteristic of coarse-grained soils of high-speed railway subgrade mainly include soil water characteristic curve and penetration function. Among them, the soil water characteristic curve (SWCC) describes the relationship between the matrix suction and water content; Penetration function describes the relationship between the permeability coefficient and the matrix suction. Hydraulic characteristics of coarse-grained soil of high-speed railway subgrade profoundly influence internal moisture migration and long-term accumulative deformation of the subgrade. Therefore, make sure packing hydraulic properties of unsaturated soil in the railway is of great significance to research and engineering practice. This paper revolves around microscopic pore structure of coarse-grained soils and the characteristics of hydraulics problems, has carried out the test theory and method of research, the main contents are as follows:(1) Analysis the influence of micro pore volume, the porosity and the pore distribution under different content of fine particles and water content on compaction degree of coarse granular soil by the CT test. Qualitative analysis the change of micro pore in the process of compaction with scanning electron microscope (SEM). And connecting with the mercury injection pore (MIP) test to obtain the distribution of particle, three peak pore distribution curve is proposed.(2) A test device for determining hydraulic parameters of coarse-grained soil is presented thoroughly in this paper. Measured the soil water characteristic curve of subgrade filling in different degree of compaction and fine particle content, using the van-Genuchten Model fitting formula, to verify the applicability of the apparatus. Also, the relationship bewteen unsaturated hydraulic conductivity and matrix suction of such soil could be obtained by transient profile method, to provide hydraulic parameters for research on the laws of the subgrade moisture migration model.(3) One-dimensional Stress Controllable Volumetric Pressure Plate Extractor (1D-SDSWCC) was launched to research the soil water characteristic curve on wet phase of subgrade filling with the largest fine particles size is2mm. In comparison with the test results of infiltration column to analysis the influence of grain size for soil water characteristic curve.(4) By the MIP test, the pore size distribution of coarse-grained soils under different compaction were measured. On the basis of the principle of capillary, the soil water characteristic curve is derived through pore distribution curve of subgrade filling soil, and compared with the laboratory test results. The pore size distribution is also derived from the experimental test of water characteristic curve to compare with the second chapter, and coarse granular soil microscopic pore distribution are discussed.