Author(s): Tian Jingjie; Chen Yunliang; Wu Chao; Wang Bo
Linked Author(s): Wang Bo
Keywords: Hydraulics; Overtopped cofferdam; Sub-cofferdam break; Numerical simulation; Transient characteristics
Abstract: Overtopped cofferdam is often applied to the diversion of Mountain River because of the economy and rationality. It can reduce the size of diversion structure. To not raise the water head between overtopped cofferdam and the foundation pit, the height of overtopped cofferdam should be controlled. To extend the time of constructing in the flood season, setting up the sub-cofferdam on the overtopped cofferdam is often adopted in the construction of hydro project. The sub-cofferdam on overtopped cofferdam would break before flood overflows and the flow characteristics are vital to the safety of cofferdam. The flow velocity on overtopped cofferdam is very quick after the sub-cofferdam breaks, so it is difficult to test the transient hydraulic parameters by the physical model. To research the initial overflow of overtopped cofferdam, a new method was introduced in this paper. The transient flow on overtopped cofferdam after sub-cofferdam break was numerically simulated by the turbulent model. The transient characteristics for different heights of sub-cofferdam were compared, such as flood propagation, discharge process, maximal velocity. The different water filling levels in the foundation pit were also analyzed, including flow state, flow field etc. Then the all-around data of transient flow after sub-cofferdam break could be obtained. The results of computing indicated that the higher the sub-cofferdam was, the larger the maximal discharge was and the quicker the maximal velocity was after the sub-cofferdam break. Therefore, flow scouring damage of the cofferdam slope protection would be very serious when the sub-cofferdam was higher. The flow on the downstream slope would be quicker and the water head between the foundation pit and the energy dissipation flatform would be greater without the water-cushion in the cofferdam foot. So the cofferdam foot would be damaged much possibly. The research showed that sub-cofferdam should not be too high. In the meantime, it was necessary that the foundation pit was filled with water near the energy dissipation flatform before overflow. All the conclusions suggested that further research into the initial overflow of overtopped cofferdam would be worthwhile.
Year: 2013