Swell dilatability is the main geological problem in Xiangjing and Hanshi highway project. By X-ray diffraction and grain analyses, higher contents of ascanite and illite were found in the former highway, but the content of quartz, feldspar and chlorite are found low. The swell dilatability in the two highway sites were the same, low or middle level, but the difference in the content of clay minerals resulted in the higher swell dilatability in Xiangjing highway site. Moreover, the sedimentation quantity in 50 kPa was larger than its dilatability.