Expansive soil as a kind of special soil, its shear strength value is different from the common cohesive soil. In practice, it is proved that in the design of expansive soil slope, not only the soil block strength, but also the crack surface strength must be considered. It is impacted by the crack surface scale and occurrence, in particular, to the strong expansive soil which grows extremely crack surface. In order to simulate more realistic shear failure of strong expansive soil under the control of the crack surface, the in-situ direct shear experiment of strong expansive soil for South-to-North Water Transfer Project in Nanyang section is made; through matching the data of strong expansive soil, and shear strength influencing factors are analyzed. The results show that all of the crack surface development degree, the slope angle and the crack surface fluctuation degree have great influences on the strong expansive soil shear strength.
