Abstract: In the expansive soil region of the middle route of south-to-north water transfer project, cement modified soil with certain content and thickness is required to replace expansive soil in order to protect the canal slope. In the process of soil exchanging and filling, problems are often encountered, including suspension of exchanging-filling operation, weathering and cracking of slope soil, scour damage of filled layer and mal-draining of groundwater. If the above problems are mishandled, the quality of soil exchanging and filling will be affected, and may even cause the slope deformation failure. In this paper, these problems are analysed in depth, and corresponding engineering treatment measures are put forward, and crucial points of the construction process are also given. It is of guiding significance for the engineering construction of expansive soil.

Key words: expansive soil, cement modified soil, operation plane, weathering and cracking, middle route of south-to-north water transfer project