| Affected by climate and other factors,the natural soil near the surface is generally in an unsaturated state.The engineering problems of unsaturated soil are usually closely related to its water holding and mechanical properties.Existing studies show that the type of soil,void ratio(or dry density),stress state,initial water content,micro pore structure,temperature and suction will affect the water holding and mechanical properties of unsaturated soil.At present,the research on water holding and mechanical properties of unsaturated soil mostly stays at the macro level,and the influence of soil pore structure on water holding and mechanical properties of unsaturated soil is less from the micro level.However,the micro pore structure of soil will have a very important impact on the macro engineering properties of soil.It is urgent to study the impact of micro pore structure on the water holding and mechanical properties of unsaturated soil.According to the pore size distribution density curve,the micro pore structure of soil can be divided into single peak distribution,double peak distribution and even multi peak distribution.Taking the red clay in Liuzhou,Guangxi as the research object,this study carried out soil water characteristic curve measurement within the full suction range,isotropic compression test and triaxial shear test to control the suction,and carried out mercury injection test and scanning electron microscope test for soil samples with different structures in different stages of drying process,isotropic compression process and triaxial shear process,Reveal the evolution law of pore structure of soil samples with different pore structure under water force coupling.The main research results are as follows:(1)The compaction sampling technology was optimized.Through mercury injection test,the micro pore structure of soil samples and different types of samples in different areas are measured,and the effects of soil types and sample types on the micro pore structure of soil samples are studied.On this basis,the compaction sampling technology is optimized.(2)For Liuzhou red clay with double pore and single pore structure,the soil water characteristic curve test in the full suction range and the evolution law of micro pore structure in the drying process were carried out respectively.Based on the axial translation technique,filter paper method and saturated salt solution vapor balance method,the soil water characteristic curve test of Liuzhou red clay samples with dual pore and single pore structure with initial void ratio of 1.15 and 0.99 respectively was carried out,and the effects of micro pore structure and initial void ratio on the water holding capacity of Liuzhou red clay were revealed;Through mercury injection test and scanning electron microscope test of soil samples with different suction values,the evolution law of micro pore structure of Liuzhou red clay with double pore and single pore structure during drying is revealed.(3)For Liuzhou red clay with double pore and single pore structure,isotropic compression tests controlling suction were carried out,and the evolution law of micro pore structure during compression was studied by mercury injection test and scanning electron microscope test.The isotropic compression tests with controlled suction(100,200,2730,3290 and 14240 k Pa)were carried out for the double hole and single hole Liuzhou red clay samples with initial void ratio of 1.15 and 0.99 respectively.The effects of initial void ratio and pore structure on the deformation characteristics of Liuzhou red clay soil and the hydraulic characteristics of soil samples during compression were revealed;Mercury injection test and scanning electron microscope test were carried out for soil samples before and after compression,and the evolution law of micro pore structure of double pore and single pore soil samples during isotropic compression was revealed.(4)For Liuzhou red clay with double pore and single pore structure,triaxial shear tests controlling suction were carried out,and the evolution law of micro pore structure during shear was studied by mercury injection test and scanning electron microscope test.Triaxial shear tests with controlled suction(100,200,2730,3290,14240 k Pa)were carried out on double hole and single hole Liuzhou red clay samples with initial void ratio of 1.15 and 0.99 respectively.The effects of initial void ratio and pore structure on the shear strength characteristics of Liuzhou red clay and the hydraulic characteristics of soil samples during shear were revealed;Mercury injection test and scanning electron microscope test were carried out for soil samples before and after shear,and the evolution law of micro pore structure of double pore and single pore soil samples during triaxial shear was revealed. |
