Coupling Study On Macro And Mesoscopic Seepage And Deformation Of Moraine Soil Dam Materials In The Alpine Region Of Southwest

With the gradual expansion of hydropower construction in the alpine and high-altitude areas of southwest China,the icy soil material commonly found in this area has attracted people’s attention and has been tried to be applied in hydropower engineering construction.However,the construction of earth-rock dams using icy soil requires understanding of its engineering characteristics.The glacial soil studied in this paper was taken from the Gushui area of Shangri-La.Through various laboratory tests and numerical simulations of particle flow,the basic physical properties,mesoscopic changes under macroscopic stress,coupling effects of seepage deformation of glacial soil dam materials under hydraulic pressure,and the development of hydraulic fracturing mesoscale cracks are studied.The principal contents can be seen from the following.1.Determine the particle gradation,moisture ratio and proportion of the undisturbed moraine soil by laboratory tests;determine the optimal moisture content and maximum dry density by indoor compaction tests;determine the cohesion of 95% compacted ice soils by laboratory tests physical and mechanical properties such as force,internal friction angle and permeability coefficient.2.Based on the PFC2 D platform,carry out biaxial simulation test of icy soil particle flow to calibrate mesoscopic parameters.By carrying out the numerical simulation of large-scale direct shear and consolidation experiments of icy soil,the microscopic changes of icy soil under macroscopic stress are studied.3.Carry out numerical simulation of fluid-solid coupling particle flow in glacial soil,study the coupling effect of seepage and deformation of glacial soil dam material under the action of water pressure,and determine the setting of seepage parameters.4.Determine the fracture toughness of the 95% compacted ice soil,establish a fluid-solid coupling model for hydraulic splitting of the ice soil core,determine the crack initiation stress and failure form under different stress conditions,and analyze its mesoscale cracks The main reasons for the development and corresponding improvement measures are proposed.The results of the paper show that:1.In its natural state,the moisture ratio of ice-accumulated soil is 3.16%,its proportion is 2.67,and the particle gradation is not uniform;its optimum moisture content is 7.9%,and its maximum dry density is 2.17g/cm3;95% compaction degree of ice-accumulation The cohesion of the soil is 189.02 k Pa,the internal friction angle is 39.82°,and the permeability coefficient k20 is 3.36×10-7m/s.2.The mesoscopic parameters calibrated by the particle flow biaxial numerical simulation test have sufficient reliability in the simulation of the shear and seepage particle flow of the frozen soil,and can analyze the macroscopic force of the frozen soil from a mesoscopic perspective.The meso-deformation under the action shows the coupling effect of seepage and deformation of the glacial soil dam material under the action of water pressure.3.Fracture toughness of 95% compacted ice soil.Hydraulic splitting of ice soil core is the joint action of tension failure and shear failure between internal particles,and tension failure is the dominant factor.Contemporary,the results proposed that by adding clay into the natural icy soil to increase the cohesion of the glacial soil,the probability of hydraulic splitting of the glacial soil core can be reduced.The primary innovation of this paper is as follow:For the first time,the PFC2 D software was used to carry out the numerical model of the laboratory test,fluid-solid coupling and hydraulic splitting of the icy soil,and the microscopic changes,seepage deformation coupling effects and the development of meso-scale cracks under the macroscopic force of the glacial soil were explored.