Abstract: The rheological properties of the soft rock mass have a significant impact on the longterm stability of a deep buried tunnel. This paper presents the triaxial creep test results on argillaceous siltstone samples from Pakistan NeelumJhelum hydropower project. An index rheological relationship was developed based on the test results. The parameters of the relationship were back analyzed from the construction monitoring results on the rock mass during the water diversion tunnel excavation. The calibrated parameters were used in the longterm stability analysis of the tunnel structure. The results indicate that, after 10 years of tunnel operation, the vertical deflection at the crest of the tunnel is 20.3 mm and the horizontal deformation is 18.1 mm. The stress in the lining structure is predominantly compressive with a maximum compressive stress is 63.4 MPa, which located at the crest and middle portions of the tunnel. From these analyses, lining strengthening measure should be taken.

Key words: Rheological Properties, Soft Rock, Deformation Estimation, Longterm Stability