Abstract：Jiangya Hydraulic Project is situated in the basin of the Loushui River in Hunan Province，China. After the reservoir is impounded，significant lifting deformation of the dam along with its surrounding valley is observed. The theory of the formation mechanism and the future forecasting are discussed. The 131 m high dam of Jiangya Hydraulic Project is located on the northwest limb of regional syncline(Jiangya syncline)，there exist a series of aquifers and impermeable layers. A hot water artesian aquifer is found right under the dam foundation. The reservoir impounding began in Aug. of 1998，and to Feb. 2001，the biggest lifting of both banks of the valley was measured 21.8 mm，generally 15–10 mm；the lifting of the grouting gallery in the dam was measured 34.5 mm with a mean value of 31 mm. Based on both the site investigation and data analysis，the hypothesis of dilatancy mechanical model，that the lifting deformation is caused by the pressure change resulting from moving interstitial water in rock mass is proposed. In order to verify the model，a rock mechanical simulation test has been carried out using the MTS stiff testing machine. The test result strongly supports the model. According to the results combined with in-situ geological analysis，the“syncline flexural slip”mechanism is believed to be responsible for the lifting of Jiangya dam and its surrounding banks. The authors also forecast that this lifting and subsiding phenomenon will reduce progressively，and eventually diminish. The latest data have confirmed the forecast made five years ago.
