Reduction in Soil Strength with Increase in Density

Laboratory and field data are presented which show that, for certain given moisture contents, increases in density result in increases in strength as measured by the California Bearing Ratio (CBR) up to a certain density, after which increases in density result in a decrease in CBR. Confirmation of the decrease in strength is presented as field observations of the behavior of a silty clay soil in accelerated traffic tests. The decrease in strength is believed to be the result of the development of pressure in the void phase of the soil structure. As long as the combination of moisture and density is such that no pore pressures develop, increases in strength occur with increase in density. When pore pressures develop, further increases in density produce decreases in strength.