Investigation of Manhole Cover Displacement during Rapid Filling of Stormwater Systems

Abstract

Stormwater systems are subject to operational issues while undergoing rapid filling during intense rain events. In various instances, air–water interactions take place, and it is possible that the air located in the headspace of manholes will be pressurized. Air pressurization can be created by rapid changes in water free surface within vertical shafts in conditions in which the manhole headspace is insufficiently ventilated. Existing research has indicated that rapid changes in the free surface can be triggered by inertial oscillations/surging and by the release of entrapped air pockets through water-filled shafts. Air pressurization or direct water impact can lead to the displacement of manhole covers, with obvious impacts to the safety of pedestrian and vehicular traffic. However, investigation of this topic has been limited, mostly focusing on conditions in which water level changes result from the sudden filling of vertical shafts. This work presents a numerical investigation using OpenFOAM describing pressures on manhole covers under varying ventilation conditions in shafts undergoing inertial oscillations or sudden release of air pockets. Among tested conditions, pressures associated with the sudden release of air pockets had greater potential to create pressures that lead to manhole cover displacement. It is expected that results from this work can help mitigate such hazardous conditions associated with the rapid filling of stormwater systems.