Helicoidal-Ramp Type Drop Shaft to Deal with High Head Drop Works in Manholes

A helicoidal-ramp type-drop shaft (DRS), which efficiently absorbs energy and to let water fall gently, usually installed at high head drop connection manholes on sewage systems. Nowadays, as the increase of depth and flow discharge, methods to inflow into DRS is diversified, and air entraining countermeasures have been taken. So, we examined and verified the inflow method and air entraining countermeasures by hydraulic model testing. The inflow part of DRS is basically a cylindrical pipe connection. But actually water tank connection method is also used widely, which may cause backwater impacts to the upstream, damaging facilities,vibration and noise. As an alternative inflow shape, guide wall connection method was examined. Additionally, entrained-air may cause decreased pipe efficiency, sewege gushing, and damage of manhole. Then we verified the function of supposed air exhaust system and confirmed the necessary length of the air intake pipes, and the effectiveness of supposed drainage pipes.