Controlling leaks in tidal manholes
In this case study, we explain how we were able to control water ingress in tidal manholes to prevent damage to the structures and stop waste water leaving the manhole network.
Oxford Hydrotechnics were approached by the client, to address historic sea water ingress into a number of foul water manholes, many located within metres of the edge of an estuary.
Movement of additional sea water through the manhole joints and other defects created the risk of surcharging further on in the manhole network, whilst also allowing foul water to exit the manhole, posing a potential threat to the local environment.
H2OX highly skilled engineers identified that the leaks had been caused by age related degradation of the sealant located within the joints, leading to failure and subsequent ingress.
Oxford Hydrotechnics’ solution was to reinstate the waterproofing of the structure by injecting a lightweight, polyurethane foam, into the joints and other leaking defects, in order to close off the avenues through which water could travel.
Drill ports were installed into the structure at engineer specified angles, by a trained confined space team. Injection packers were inserted and the defects were flushed with a dilute acid solution. A highly mobile injection pump was then used to inject H2OX’s P500 resin, through the packers.
The resin travelled through the leaking flow paths within the structure and cured on contact with water at a tailorable rate. As the resin cured, it expanded, pushing it deeper into the structure, before curing to create a closed cell foam, through which water was no longer able to travel.
In each location, between two and six manhole rings were treated.
Balancing measures that would usually be in place to control the flow of water to each manhole were switched off. H2OX also requested that the work be carried out at high tide to ensure that any leaks that became active during
treatment would be visible, allowing them to be treated at the same time.
As resin was injected, it travelled through the leaking flow paths, before emerging at the next active defect. Once cured, the surface resin was easily stripped from the structure by hand.
In each treated manhole, the resin cured within the flow paths and created a permanently flexible seal, effectively controlling the water ingress whilst having the added bonus of preventing the defect from reoccurring.