白鹤滩拱坝谷幅变形预测及不同计算方法变形机制研究

中国已建成的特高拱坝如溪洛渡、锦屏一级等,在初期蓄水过程中均表现出了谷幅收缩的异常现象。而拱坝是高次超静定结构,对坝基变形尤其是不均匀变形非常敏感。从有效应力改变和岩体材料泡水弱化这一谷幅变形机制和边界施加位移这一计算手段出发,利用弹塑性有限元方法,计算并预测白鹤滩拱坝在初期蓄水过程中可能产生的谷幅变形,并分析了谷幅变形对大坝位移和应力的影响。结果表明:两种方法的计算结果相差很大;从有效应力改变和岩体材料弱化角度出发,白鹤滩拱坝两岸山体可能产生的最大谷幅收缩不大于40mm,且该谷幅变形不会很大程度上降低拱坝的整体稳定性,只是使坝体产生了新的应力集中区。而拱坝对施加边界位移具有很强的超载能力,但谷幅收缩对坝体应力的影响极小。对比发现,坝基不均匀变形是影响拱坝应力的关键因素。

Prediction of deformation of valley width of Baihetan arch dam and deformation mechanisms of several methods

The super high arch dams built in China, such as Xiluodu and Jinping, show abnormal phenomenon of reduction of valley width during the initial impounding stage. The arch dam is a high-order statically indeterminate structure, which is very sensitive to deformation of dam foundation, especially non-uniform deformation. Based on the deformation mechanism of valley width and the method for calculating the boundary displacement, the possible deformation of valley width of Baihetan arch dam in the process of initial impounding is calculated and predicted, and its effects on the displacement and stress of the dam are analyzed by using the elastoplastic finite element method. The results show that the two methods are greatly different. From the perspective of change of effective stress and weakening of rock mass materials, the maximum reduction of valley width is no more than 40 mm, and it will not greatly reduce the overall stability of the arch dam, but only causes new stress concentration area on the dam body. However, the arch dam has strong overload capability to the boundary displacement, and the impact of the reduction of the valley width on the stress of the dam is very small. The non-uniform deformation of the foundation is the key factor which affects the dam stress.