Two-dimensional Numerical Experiment Based On The Permeability Of Soil-rock Mixture Microstructure And Its Size Effect

Soil-rock mixture are not only widely existed in the three gorges reservoir area,southwest China and southeast China,but also used as engineering materials for various constructions.Many geotechnical engineering problems in engineering construction are based on seepage analysis.Because the seepage analysis of soil-rock mixture is mostly based on the equivalent continuous medium theory,the permeability coefficient and its size effect of soil-rock mixture become an important basic problem in soil-rock mixture seepage analysis.At present,there are mainly two methods to study the permeability of soil-rock mixture: geotechnical test and numerical test.Among them,the geotechnical test cost is high,and limited by the sample size,it is difficult to carry out a large number of permeability tests of arbitrary size,and the size effect of permeability coefficient cannot be effectively studied.The numerical test simulates the seepage process based on the mesoscopic structure of the sample,and then calculates the permeability coefficient of the sample,but does not study the influence of the random distribution of the block stone in the sample on the permeability coefficient and its size effect.Therefore,the main research content of this paper is divided into two aspects.Firstly,the numerical test system of the equivalent permeability coefficient of the soil-rock mixture sample is constructed;secondly,for the samples with various rock content and different lvd(the ratio of the side length of the sample to the maximum particle size of the block stone),the equivalent permeability coefficient is tested,and the statistical characteristics of the equivalent permeability coefficient of the samples with different rock content and the variation of REV with the rock content.The results of the study are as follows:(1)Based on saturated seepage theory and numerical manifold method,the MATLAB program for simulating saturated seepage process of soil-rock mixture was developed,ignoring the permeability of rock block.An example shows that the numerical simulation program and the finite element seepage simulation program can be used to simulate the seepage process of soil-rock mixture.In addition,the numerical manifold program is more simple to solve the complex seepage field with many rock blocks,and the difficulty of grid generation is greatly reduced compared with the finite element method.(2)On the basis of the program for generating the microscopic structure of soil-rock mixture,a numerical test system for the permeability of soil-rock mixture was constructed and a MATLAB program was developed.An example shows that the system can effectively determine the equivalent permeability coefficient of soil-rock mixture.(3)The numerical test system in(2)was used to simulate the seepage field of the samples with different rock-bearing ratios and different LVD mixtures,and the equivalent permeability coefficient of the samples was calculated.The statistical analysis shows that the permeability coefficient conforms to the gaussian function distribution when the rock-bearing ratio and LVD are constant.The larger the size of the soil-rock mixture,the more concentrated the permeability coefficient distribution.(4)The equivalent permeability coefficient of samples of different sizes was used to study the size effect of soil-rock mixture.It was shown that: When the rock content does not exceed 0.4,REV is about 10-20 times of the maximum particle size of the sample,and when the stone content exceeds 0.4,REV is about 20-30 times of the maximum particle size of the sample.Meanwhile the REV of the permeability coefficient increases with the increase of the rock content,which is approximately exponential.