The geological investigations during construction of Neixiang-Zhenping section of Nanjing-Xi’an railway revealed that Nanyang expansive soils origins not only from Quaternary alluvial

diluvial clays but also Neozoic lacustrine clays. Expansive clays with different origins differ in terms of space distribution and engineering characteristics. X-ray diffraction tests indicated main expansile clay mineral of Nanyang Expansive soils is mixed-layer illite/montmorillonite. Change of water content will result in significant difference in swelling force and dilatancy for the compacted soil sample because of the variation in material composition and physicochemical properties. To compacted samples prepared by same expansive soil material

the smaller the prepared moisture content the higher the expansive force. Even if the moisture content only reduced 1 %-2 %

the corresponding expansive force would upper to 200 %. The direct shear strength is affected by calcareous cement degree and nodes content. As high or very high expansive clays

if nodes content were less than 15 %

the reduced value of direct shear strength after dried and saturated cycle would be 40 %- 60 %; Whereas direct shear strength would reduced no more than 40 % if nodes content were 25 %-30 %. The geological properties

engineering characteristics

expansibility of compacted samples and direct shear test date of swelling soils are analysed

suitability for embankment is discussed

and suitability grades is presented in this paper. Applications of the subgrade-construction techniques developed based on the research work have achieved good effect.