Pressure plate tests and double-ring infiltration tests are carried out for typical undisturbed strong and medium expansive soil and rock of the middle-route of South-to-North Water Transfer Project. According to the soil water characteristic curve and test results

the water-holding characteristics and its influence factors of different expansive soils and rocks are comparativly studied; and the variation of water volume change coefficients are calculated and analyzed. On that basis

the change characteristics of permeability coefficient and its nonlinear relationship with matric suction are discussed; and the infiltration characteristics and rules of expansive soils and rocks are summarized. The results show that

water-holding characteristics are influenced by the physical properties

mineral composition and structure characteristics of expansive soils and rocks. The sample with stronger expansion potential

higher fine grain content and smaller pore structure has lower dehydrated rate. Permeability coefficient and water volume change coefficient decrease with the decrease of the moisture content; and these parameters are influenced by dry density and expansion potential

which also have power function relationship with matric suction. The research results can provide calculation parameters and theoretical basis for the engineering construction.