| Seepage in soil may cause major engineering problems such as leakage of diversion canals,dam break of earth-rock dams,etc.A large number of projects show that internal seepage erosion disasters such as piping and flowing soil mostly occur in graded discontinuous gravel soil.The pore structure model of graded discontinuous gravel soil is constructed by CT scanning technology and three-dimensional reconstruction.The pore structure is characterized and the seepage simulation is carried out to explore the change of permeability when the fine particle content gradually increases to the near-critical fine particle content under the absence of different particle sizes.It can effectively understand the permeability law inside the graded discontinuous gravel soil,expand the application of CT scanning technology in the analysis of geotechnical mesostructure,and also provide a new method for the study of porous media seepage.The main work and research results of this paper are as follows :(1)Nine samples with missing particle sizes of 0.25-0.5mm,0.5-1mm,1-2mm and fine particle content of 30%,32%,34% were configured.The CT images of the samples were obtained by CT scanning technology.The contrast enhancement,median filtering and region selection of the images were performed by Avizo software.Then the three-dimensional reconstruction and REV characterization unit selection were performed to obtain the pore structure model of each sample.(2)According to the statistical model parameters,it is found that the pore connectivity and distribution uniformity of the 0.25-0.5mm particle size missing group are the best.The increase of fine particle content has little effect on the uniformity of pore distribution,but has a great influence on the homogeneity of samples.The difference of particle size loss has a great influence on the uniformity of pore distribution and the number of pores formed.The increase of fine particle content will increase the fractal dimension of the sample and weaken the uniformity.The lack of particle size has no significant effect on the surface fractal dimension.(3)The parameters of the ball-stick model of each sample were statistically analyzed.It was found that the equivalent radius,throat length and coordination number of the pore throat showed a unimodal distribution,and the homogeneity was good.The 0.25-0.5mm particle size missing group compared with the other two particle size missing groups,the distribution of pore throat size characteristics is poor,but the topological structure is better than other samples,and the connectivity is strong.(4)With the increase of fine particle content,the average flow velocity and pressure in each direction of the 0.25-0.5mm particle size loss group increased first and then decreased.The average flow velocity of the 0.5-1mm particle size loss group decreased first and then increased slightly,and the average pressure increased gradually.The average flow velocity of the 1-2mm particle size missing group gradually decreased,and the average pressure decreased first and then increased.(5)With the increase of fine particle content from 30 % to 34 %,the average flow velocity,streamline,permeability and permeability of the three groups of samples with different particle size loss generally decreased in all directions.Due to the discontinuity of gradation,although the content of fine particles is increasing,the pores formed by coarse particles cannot be effectively filled by fine particles.It is speculated that with the increase of average seepage pressure,fine particles may still be washed away under the action of seepage,and the subsurface erosion piping eventually develops into flow soil damage. |
