Engineering Characteristics of Natural Wide Grading Gravelly Soil in Construction of Extra-High Earth-Rockfill Dam

Wide grading gravelly soil is an advantageous anti-seepage material in construction of high earth-rock dam. From the experience of earth-rockfill dam construction at home and abroad, it is more and more common to use wide grading gravelly soils such as moraine soil, weathered rock and gravel soil as anti-seepage material in construction of high earth-rockfill dams. Regarding the engineering characteristics of natural wide grading of soil material for 300m core-wall earth-rockfill dams in this paper, a series of physical and numerical tests were carried out to study its permeability and mechanical properties. By comparing the characteristics of impermeable soil materials of the projects already built and to be built at home and abroad, the preliminary indicators of impermeable soil materials are as follows: 1) Combined with the existing engineering experience and test results, the content of particles with particle size greater than 5mm should be neither over 50% nor lower than 30%. The content of particles with particle size less than 0.075mm should not be less than 15%; the content of clayey particles with particle size less than 0.005mm should not be less than 6%. 2) It is appropriate to control the permeability coefficient of impermeable soil material at less than 1×10-5cm/s.