Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manholes under surcharged conditions. However, in most of these proposed formulas, all variables of structural elements for the pipes and the manholes have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manholes is needed. In this paper, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes, connected angles among those pipes and drop gaps between inflow pipes and outflow pipe on the energy loss at three-way circular drop manholes were investigated. Based on the experimental results, a new formula that considers all structural elements and the ratios of flow rates between inflow pipes was proposed for the energy loss coefficients at the manholes. In the proposed formula, calculated energy loss coefficients reproduce measured values more exactly than existing formulas do.
2016 Japan Society of Civil Engineers