Abstract: Identification and determination of main failure modes are important in dam safety analysis. In traditional analysis, serviceability limit states (e.g., overstressing) are considered together with ultimate limit states. Overstressing may be the cause and initiating factor leading to global failure and must be analyzed. However, overstressing in itself is, generally, not a global limit failure mode. In this paper, this bearing capacity failure mode is included in the limit overturning failure mode. With gravity dam as an example, the limit state function for overturning is derived with the help of moment balance relationship; and methods of determining and estimating the parameters in the function are also discussed. On this basis, a general system failure model for gravity dams in consideration of main ultimate limit states is proposed. An in-service gravity dam is investigated, and the results show that, for gravity dams on intact weak rock foundation, the limit state for overturning caused by overstressing must be taken into account due to inadequate rock crushing resistance.

Key words: concrete dam, global stability, limit overturning, system failure model, limit state function