Koster was recently invited to investigate signs of water seepage on a section of track located close to the London Underground’s Farringdon station.
Koster carried out a trial on a section of track (the Metropolitan Line). The brief was to provide an elastic, permanent repair solution which would accommodate the stresses associated with tunnel waterproofing whilst being sympathetic to the ageing construction and causing no detrimental effect to the structure nor the trains passing through.
The construction of the tunnel is multiple layers of brickwork with an assumed tar or bitumen waterproofing layer externally. There was evidence of water seeping from the brickwork, stalactites, heavy salt and soot crust formations throughout the tunnel and a previous installation of injection packers which lined the crown.
Prior to conducting a product trial, a close examination of the tunnel was undertaken. One area which was showing significant signs of water seepage (water ingress via the brickwork) was at the tunnel’s crown.
The areas of active leakage were evident (through old injection packer holes and badly pointed brickwork). These areas of active leakage were initially sealed using Koster Waterstop and KD2 Blitz to immediately prevent the passage of pressurised water.
Once the area was free from running water, the second job was to measure and mark out the borehole positions for Koster Superpackers – small injection lances which have been specially designed to give a superior grip whilst delivering a constant flow of grouting resin. Koster specified the Injection ports to be placed at 400mm centres in a grid pattern, with a single packer positioned in the centre.
The boreholes were drilled to a pre-determined depth which would facilitate the packers. Koster Superpackers were then inserted and the area was ready for the Gel injection. The material used was an acrylic-based resin, Koster G4 Gel, which has a similar initial viscosity to water.
The Koster G4 Injection Gel fills the same minute tracks and veins that water follows when infiltrating the structure. When injected into pore structures, the Injection Gel G4 cures to form an elastic, permanent gel which is then able to move and flex within the brickwork.
The G4 Injection pump was set up and operated from a rolling platform below the scaffold tower, allowing for ease of access to each packer during the injection stage. Following the injection phase, the Koster Superpackers were removed and the boreholes filled using Koster KB Fix 5 fast-set mortar.
Consequently, the water seepage has now stopped and the brickwork lining is now fully protected from future water ingress without compromising the tunnel lining.
Delta Membrane Systems,
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