Experimental Study On Physical And Mechanical Properties Of Glacial Deposit For Clay Material From Freezing Area In Southwest

As water conservancy and hydropower projects in China are gradually advancing to high-altitude and cold areas,glacial soil,as a widely distributed material in the local area,can be used in earth-rock dam projects.However,for construction in areas where glacial soils are distributed,it is necessary to understand the characteristics of glacial soils.The glacial soil studied in this article was taken from Gushui in Shangri-La.Through various indoor tests,SEM scanning electron microscopy,XRD,XRF tests and CT tests,the basic physical properties,permeability and strength characteristics of the soil are studied.The main contents of the test are as follows.1.A geotechnical experiment was carried out to test the basic physical and mechanical properties.The basic physical and mechanical properties of the glacial soil in Gu Shui,such as moisture content,specific gravity,boundary moisture content,particle gradation,and maximum dry density,were obtained.2.Carry out a series of XRF,XRD,SEM and other microscopic tests on the glacial soil in Gu Shui to find out its element and mineral composition.Observe its microstructure intuitively.Use CT technology to observe and count the overall pore structure of the soil,and use AVIZO and other software to reconstruct the pore model in three dimensions.to obtain the pore structure and fractal parameters of the soil.3.The relation curve or model between these indexes and the condition of sample preparation is established to seek its internal law.Obtain the pore structure and fractal parameters of the soil ofmicroscopic tests.The research results of the thesis show that:1.The natural moisture content of the glacial soil material is 3.16%,the specific gravity is 2.67,the density is 1.513g/cm3,the liquid limit is 20.78%,the 10mm liquid limit is 18.81%,the plastic limit is 13.90%,and the plasticity index is 6.99,the liquidity index is-1.56.The optimal moisture content of glacial soil is 7.7%,the maximum dry density is 2.17g/cm3,and the particle gradation is relatively uneven.2.The permeability coefficient of natural ice-covered soil is k20=4.19 X 10-3.When the dry density increases by 0.05g/cm3,the permeability coefficient will decrease by an order of magnitude.When the glacial soil sample is in a loose state as the load increases,the compression coefficient will gradually increase and then decrease,and the compression modulus will first decrease and then increase.The cohesive force c value of the glacial soil sample with a particle size of less than 2mm is the largest when the water content is 12%.The value of c decreases as the moisture content shifts to both sides of 12%,while the value of the internal friction angle of glacial soil decreases with the increase of moisture content.In the direct shear test of medium-grained soil,the cohesive force of the 79%dense glacial soil sample is c=59.96kPa,=25.02°;the cohesive force of the 95%dense glacial soil sample is c=189.02 kPa,=39.82°.After the glacial soil is compacted,the strength is significantly improved,and the overall strengthening effect of coarse particles on the properties of the soil is obvious.3.The overall porosity of the CT scan sample is 7.58%,and the majority of them have an equivalent diameter of 50-100 μm.The pores with an equivalent pore diameter greater than 2000um occupy a higher volume,and most of the pores have better overall connectivity.Based on the maximum sphere method,the maximum coordination number is 33,and the average coordination number is 2.The throat and pores are well coordinated,and the connectivity is strong.Through the SEM test,the porosity of the glacial soil will be significantly reduced after compaction,which is about 25%of the natural state.The main innovations of this paper are as follows:1.Physical and mechanical properties tests of glacial accretion are carried out systematically,especially direct shear test of glacial accretion with medium coarse-soil properties based on special equipment developed by Nanjing Soil Instrument Company.2.CT test of glacial accretion with medium coarse-soil properties is carried out and the internal texture of glacial accretion is tested...