Study of Unloading Relaxation for Excavation Based on Unbalanced Force and Its Application in Baihetan Arch Dam

Unloading relaxation of rock masses in an excavated interface is unfavorable to the performance of the dam foundation system. To evaluate its effects better, a new evaluation method for unloading relaxation is presented in which the unbalanced force beyond the yield surface is proposed as the quantitative criterion of unloading relaxation. It is used for the Baihetan arch dam to analyze the unloading relaxation characteristics and its effects on the displacement, stress, fracture and global stability of the dam. The results show that the unbalanced force is mainly located on the surface of the slope where faults are exposed, which agrees well with the observations. Unloading relaxation has a limited impact on the displacement, stress, fracture and global stability of the dam and LS331 should be paid more attention. The optimization of dam shape is also discussed, the result of which is that it is better to have a smooth dam shape and the slope of the scarp should be lowered.