Abstract: The safety factor of arch dam, which is an important standard of dam safety evaluation, shows a great disparity between design value and actual value. In order to rationally identify the ral safety condition of arch dam, a large number of high arch dam projects are discussed. An estimation formula of the actual possible safety factor of arch dam is derived by correcting the actual strength of concrete and the maximum possible stress of dam structure by using multi-arch beam method. Results demonstrates that the actual safety factor could be guaranteed to be larger than 1.0, which indicates a rational safety margin. The design safety factor could achieve the real security requirements.

Key words: safety factor, actual stress, multiaxial strength of concrete, arch dam