Case Studies
London Heathrow Airport Tunnels
Scope of work Structural Waterproofing
Client London Heathrow Airport
Airport Infrastructure Contractors London
DWG was requested to find a solution to water leakage and structural failure on the main road tunnels used to link T5 under Charlie and Delta taxiways. The structure is approx. Fourteen years old and is showing signs of structural failure and water ingress. The design engineers instructed us to stop the leaks but not to change the dynamics of the structure in any way.
This meant that any repair would need to be elastic with the good tensile capability to ensure the original design was not compromised. This eradicated Epoxy resins as an option as this structural repair process would interfere with the existing dynamic issues present. A survey was produced some time ago by the design engineers, and we were asked to provide a budget.
We found that the defects logged were only measured based on what could be seen, and we were asked to find a solution to provide accuracy on costing as this work was potentially a warranty claim against the original construction work.
Our Process
This would involve some investigation work, acid cleaning to remove the Calcite deposits and also neutralize the PH levels required to stop the decay.
A trial area was agreed and work commenced against the survey document and a selection of cracks were addressed to be repaired to determine the severity of the defect and whether this would effectively eliminate water ingress into the structure or move the problem elsewhere.
We discussed and offered the solution of putting in a new waterproof membrane to protect the structure against the sub-soil, but this was discounted as too much intrusive work by the design team.
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Airport Drilling Solutions
Work commenced with drilling into each visible crack, all of which measured more than the survey indicated, by an angle drill intended to intersect the crack at the mid-point through the wall thickness. This drill pattern was repeated approx every 200mm.
Once the drilling is completed, injection packers are inserted and secured. The crack length is also filled using hard, black cement to contain the resin when injected. Each crack is then injected using water to allow every crack to be identified, which has not been visible to the naked eye during the survey. Water flows from crack extensions is marked, and areas are drilled to ensure an effective process when waterproofing is activated.
The area is now prepared for waterproofing and injecting using Acrylinject Elastic Polymer resin. Each area is injected for refusion after preparing the mixture to a pre-set curing time. The curing time dictates the flow rate of injection and the length of time it will seep into the structure without falling through and out into a voided area which will ultimately fail.
