The effect of clay dehydration on land subsidence in the Yun-Lin coastal area, Taiwan

The smectite dehydration theory developed by Ransom and Helgeson was applie d for simulation of land subsidence in the Yun-Lin coastal area, Taiwan. Th e volumetric reduction of smectite clay at equilibrium state was computed b y assuming that the dehydration of interlayer water in smectite clay can be described with a regular solid solution reaction. By using the in situ str atigraphic data collected from the subsidence monitoring wells in the simul ated area, the amounts of land subsidence caused by smectite dehydration in three scenarios with pressure variation were calculated. The results indic ate that significant amounts of land subsidence can be attributed to smecti te dehydration. This finding reveals that smectite dehydration is of import ance for assessment and prediction of land subsidence. Additionally, the re sults also indicate the overburden weight has a larger effect on clay dehyd ration than the effective stress change resulting from over-pumping, althou gh both of them induce relatively minor variations on land subsidence.