Abstract:

This paper cites the calculation equation of soil porosity corrected by means of the hydrous states of montmorillonite interlayer water，then the mathematic expression is set up to calculate the amount of secondary land subsidence resulted from montmorillonite interlayer dehydration.The model is applied to Xianlin area which is a new city of Nanjing and belongs to the sedimentary basin with channels and vales. The calculation results show that the amount of secondary land subsidence resulted from part interlayer water release of montmorillonite is 6.85 cm. It is estimated that,34 to 46 cm total amounts of land subsidence would have happened in the area before,It is also indicated that，if the remainder interlayer water in montmorillonite interlayer is wholly released，there would be 96.47 cm of land subsidence in the area, Although it would be impossible to come to pass in the real geological environment，this would give us a caution to the prevention of land subsidence hazard. The research on montmorillonite dehydration and its effect on land subsidence would also show us a revelation to the prediction of land subsidence trend.

Key words: montmorillonite, hydrous state of interlayer water, sedimentary basin, land subsidence trend, Nanjing