ZHANG Guoxin, NIU Xinqiang, LUO Xiangyu, YAN Tianyou

Abstract: In the raising of gravity dam by thickening back slope, there are problems of load sharing and interface bonding between new and old dam blocks. When the force is transmitted by partial interface, the traditional material mechanics method and integral rigid body limit equilibrium method are no longer suitable for stress and stability calculation. This paper introduces the finite element method for the simulation of gravity dam heightening, and puts forward the finite element equivalent method for stress and stability calculation of new and old dam blocks. Taking Danjiangkou dam 7# section as an example, the multi-condition calculation of different interface states is carried out, which is compared with the elastic-plastic finite element strength reduction method. The results show that: 1) the finite element equivalent internal force method can consider the complex conditions such as separation of interface, material difference be? tween new and old dam blocks, and foundation heterogeneity, and it can eliminate the stress concentration at dam heel and contact point of new and old concrete by the finite element equivalent internal force method. It has the advantages of finite element method and material mechanics method. Its equivalent internal force can be calculated by stress integration and direct reaction force method, the accuracy of equivalent internal force obtained by direct reaction force method is higher, 2) When the finite element equivalent method is used to calculate the dam foundation stress and the safety factor of overall and local stability of new and old dam blocks, the control standard for stress and stability shall meet the requirements of current specifications, 3) When the force is transmitted from the partial interface between new and old concrete, the unfavorable condition of stress is the opening of the lower part of the slope section, while for dam block stability the unfavorable condition is the opening of the upper part and the bonding of the lower part of the interface, 4) When the bonding area of the middle and lower parts of the slope section of Danjiangkou 7# dam section is more than 20% of the total, the stress and stability meet the specification requirements. This conclusion is consistent with the theory of "Limited Combination of Interface",  5) The elastic-plastic finite element method is an effective one to analyze the heightening of gravity dam. When the same calculation model and yield criterion as the material mechanics and rigid body limit equilibrium method are adopted, the same results can be obtained and the same control standard can be adopted. However, when different models and yield criteria are adopted, the control standard needs to be studied separately.

Keywords: gravity dam heightening, thickening back slope, finite element simulation, bond interface of new and old concrete