Abstract: In order to study the permeability characteristics of the broadly graded gravelly soil, triaxial seepage tests in the presence of different gravel contents. The test results show that, with the increasing gravel content,the structure types of the broadly graded gravelly soil can be divided into three different kinds,including suspend-dense structure, dense-framework structure and framework-pore structure. When the gravel content increases, the permeability coefficient decreases slowly first, then increases slowly, and increases quickly finally. Dry density has main influence on permeability coefficient, so does the moisture content. The permeability coefficient is obviously different near the optimum moisture content, so we should pay attention to controlling the moisture content in construction.

Key words: broadly graded gravelly soil, triaxial permeability test, dry density, moisture content, permeability coefficient, gravel content