Abstract: Typical soft soils from Lian-Yan Expressway (Lianyungang section) and Hu-Su-Zhe Expressway (Suzhou section) were selected to study the geotechnical properties through general indexes and specific sections indexes considering depositional environment， respectively. The effects of depositional environment， clay fraction， clay minerals， and pH values on geotechnical properties of soft soils in LY and HSZ were discussed. The research results are as follows: Lianyungang marine clay gradually deposits with the sea level change in alkaline condition. Its material sources derives from marine sediments. Clay fraction is dominant and the principal clay mineral of the soils is illite-smectite mixed-layer mineral. Differing from the Lianyungang marine clay， Suzhou lacustrine soft soil gradually deposits in neutral condition and weak alkaline condition. Its material sources derives from Maoshan and Tianmushan. Silt fraction is dominant and the principal clay mineral of the soils is illite. Water content is lower while the unconfined compressive strength and sensitivity are higher than that of Lianyungang marine clay.

Key words: soft soils, depositional environment, material sources； clay mineral； geotechnical properties