Simplified algorithm (SPA) and simulation algorithm (SUA) is two basic method for preloading water-filled spiral case structure. In this paper, A weak simulation algorithm (WSA) based on the contact slippage is used to simulate this problem for NUOZHADU hydropower project. The methodology proposed is effectively to construct stress field of spiral case surrounding concrete. It overcomes the limitation of simplified algorithm in which the contact relationship of spiral case and concrete was

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... ed. However, that relationship is a key factor to make both interaction and transfer force characteristics more complicated. The focus of the paper is on the stress field of the concrete. The comparisons with simulation on the simplified algorithm are taken, and the results show that the method on WSA proposed in this paper is able to well captured the mechanics characters than SPA method; Due to friction the result is increased and conservative. The maximum stress of surrounding concrete mainly occurred at the top of spiral case at each sections where the influence of contact is the strongest. So, it indicates that the contact is indispensable for this problem.