Boundary effect has a significant influence on the permeability coefficient measurement of coarse grained soil in laboratory seepage tests. Based on the composition characteristics of the pore V

b

between soil particles and the seepage equipment wall

a parameter called boundary pore ratio of the soil sample e

b

was defined according to the ratio of the volume of boundary pore Vb to the particle volume Vs which concerns the constitution of boundary pore. Furthermore

based on the uniform circle packing principle

the boundary particle accumulation patterns were established

and a plane geometric calculation model of boundary pore ratio considering the wall treatment layer thickness was proposed. The expression of e

b

was finally derived through space and particle gradation correction.Based on the principle of the equality of e

b

and sample pore ratio e

a criterion called ‘equivalent pore ratio method’ for confirming the optimal thickness of the wall treatment layer hopt was presented. At last

the relationship between the seepage equipment diameter D and the boundary effect was discussed. The researches indicate that the redundant pore caused by the boundary effect would raise the seepage velocity near the seepage boundary. There are three typical plane accumulation patterns of the boundary particles

including two particles pattern

three particles with acute packing angle pattern and three particles with obtuse packing angle pattern

of which the corresponding e

b

increases accordingly. Furthermore

hopt is comprehensively determined by sample gradation

compression degree

particle density

boundary particle accumulation pattern and D. The estimate value of hopt agrees well with the test result. The influence of the boundary effect on the seepage test result becomes less significant as D exceeds eight times of the maximum particle size of soil sample.