The influence of moisture content

compacting energy and swelling potential grade on California bearing ratio(CBR) of expansive soils is experimentally studied. It is found that the moisture content of maximum CBR is always higher than the optimum moisture content. The difference increases as the compacting energy or swelling potential grade increase. The unsaturated soils theory is applied to explain these characteristics. The regularity is due to the different gas-water phases of expansive soils with different saturation degrees. When the saturation degree is less than the boundary saturation ratio

the CBR value increase assumes the exponential relationship along with the increment of saturation degree. But when the saturation degree is more than the boundary value

the strength property is similar with saturated soil and the CBR value is controlled by the dry density.