The inlet pipe into the storm tank required capping due to the change of use of the tank. The isolating valve was not functional so a decision was made to seal the pipe with a stainless steel plate.
A previous attempt to seal the plate to the wall using a butyl gasket had proved unsuccessful due to deviations in the concrete wall. All of these challenges were compounded by flows through the pipe only being able to be diverted for 2 hours.
Working with the client and the engineering contractor we helped to develop a sealing solution that could be rapidly installed.
A new stainless steel plate was manufactured that was larger to allow better fixing. We proposed locations for holes to be drilled and threaded sockets installed to allow the injection of water stopping resins into the interstitial space between the plate and the concrete.
To give all resin materials the best chance of adhering to the stainless steel plate, the rear side was first prepared by method of abrasive blasting to raise a mechanical profile.
With the plate outside of the tank and prior to the flows being isolated, concentric rings of hydrophobic swellable sealants were applied to the wall mounting face of the plate. The purpose of these was to provide contained interstitial spaces into which hydrophobic polyurethane injection resins could be injected.
By having multiple spaces different resins with different physical properties could be employed and also creating multiple layers where failure would be required for water to egress. The swellable nature of these sealants in contact with water would also mean that if the injection resins were to fail, these would provide a secondary sealing arrangement.
Once the plate had been prepared and the flows isolated the plate was lifted into the tank using a crane.
The engineering contractor drilled and installed the mechanical fixings to allow the plate to be fixed to the wall. A pipe bung was installed within the pipe itself, however previously this had not sealed the pipe entirely so could not be relied upon.
Once the plate was fixed to the wall the central pre formed injection ports that fell within the pipe diameter itself were injected using Normet Tampur 125 applied using cartridges to allow a controlled fill and to avoid over pressuring the void.
Tampur 125 is a rigid polyurethane foam that forms a rapid seal, hence its use in the primary void.
The surrounding interstitial spaces were then injected using Normet Tampur 130 – a semi flexible water stopping polyurethane resin.
This was injected using an injection pump, forcing the resin out of the threaded fixings on the plates perimeter.
The bottom of the plate could not be fixed as intended due to the protrusion from the tank floor. Our quick thinking team formed a fill piece using a rapid setting cementitious mortar in the gulley section in front of the plate, so that the risk of deformation in this area was removed.
In a little over 2 hours we evacuated the tank and the flows were returned. The works were found to be fully effective with no water egress from the plate witnessed.
