为了确保爆区附近已建成的各种水工建筑物的安全以及降低爆破难度和工作量，围堰爆破拆除通常采用分期分区的方式进行。针对赞比亚卡里巴北岸水电站扩机工程进水口围堰分期拆除工程，采用三维有限差分方法结合强度折减法和拟静力法，分别对进水口围堰在削薄后造孔损伤前、削薄过程中受爆破荷载作用、造孔损伤后3种情形下的稳定性进行了综合分析，以确保围堰边坡在分期拆除过程中的整体稳定性，并论证分期拆除方案的可行性。数值计算结果表明：围堰背水面边坡削薄处理过程对围堰和背水面边坡的影响是局部的，对围堰背水面边坡的整体稳定性没有产生较大的影响，表明分期拆除方案是安全、合理的。

Blasting demolition of cofferdam is usually carried out by stages and areas to ensure the safety of hydraulic structures near the blasting zone and to reduce the difficulty of blasting and the workload. To secure the global stability of cofferdam slope during phased demolition, and to prove the feasibility of the phased demolition scheme, we analyzed the stabilities of intake cofferdam in three cases: after being thinned and before borehole drilling damage, during thinning process under blasting loads, and after borehole drilling damage. The phased demolition project for the intake cofferdam of extension project of north bank of Kariba hydropower station in Zambia is taken as a case study. Three-dimensional finite-difference method in association with strength reduction method and pseudo-static method were adopted. The results of numerical simulation showed that the safety factor of cofferdam slope was 1.43 after being thinned and before borehole drilling damage, 1.39 during thinning process under blasting loads, and 1.32 after borehole drilling damage, all met the requirements of standard. These results reveal that the effects of thinning process on the cofferdam and the cofferdam slope on land side are only local, with no serious impact, indicating that the phased demolition scheme is safe and rational.