二期围堰泄流槽体型及开挖施工技术

Study on the shape and excavation methods of trench on the second phase cofferdam

某水电站二期围堰受客观条件限制难以全部拆除至设计高程,故在明渠截流前,先在二期围堰上开挖泄流槽导流。截流模型试验结果表明,为增大泄流槽的分流比,降低截流落差,应尽可能降低泄流槽底高程;若向下深挖施工困难,可以扩宽泄流槽。施工过程中,通过分区开挖围堰、一次性爆破防渗墙至设计高程、在防渗墙下游超挖水力冲刷堆碴坑等措施,尽可能深挖泄流槽。

Due to that the demolition altitude is hard to reach under practical limitations,a diversion trench was excavated on the second-stage cofferdam to divert water before the open diversion channel closure of a hydropower station.The hydraulic closure model test results indicated that the shape of diversion trench affects the difficulty of the closure,and reducing the bottom elevation of the diversion trench is essential to reduce the closure drop and increase the diversion ratio of trench.If deep excavation is hard to conduct,an alternative is to increase the bottom width of diversion trench.During the construction,several measures were adopted to dig the diversion trench as deeply as possible,including excavation in different parts,blasting diaphragm wall to the design altitude at one time,and excavating a hydraulic scour pit behind the diaphragm wall.