Abstract: There exists an expansion of expansive soils with large thickness and high moisture content along water diversion project from Yangtze River to Huaihe River. In this study, the modified expansive soil is used as a cover to protect the canal slope. The large-scale project results in a large quantity of construction surplus materials which are difficult to be disposed. Thus to reuse the surplus materials has an important effect on the progress and the cost of the project. This study shows that the optimum moisture content of the surplus materials is higher than that of the native modified soil, which is easier to be compacted and is more advantageous for in-site compaction control. There is little difference between direct shear strength characteristics of the surplus materials and the native modified soil. The shear failure exhibits characteristics of over-consolidated soils. The strength of the surplus materials has no obvious change with the curing time. The degree of expansion of the surplus materials with cement of 5% is far less than that of the weak expansive soil and exhibits logarithmic decay with time. The coefficient of permeability of the surplus materials with cement of 5% is in the order of 10^-5, which is larger than that of the native modified soil. The control index of permeability coefficient of the replacement layer should be comprehensively analyzed and determined according to the thickness of the replacement layer and climatic conditions. The volume of the surplus materials produced by slope cutting is related to the slope length and slope ratio, accounting for more than 20%.