Tunnel Business Magazine

APR 2018

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TUNNELINGONLINE.COM F E A T U R E S T O RY 3 6 TBM: TUNNEL BUSINESS MAGAZINE // APRIL 2018 possible. Internal tests have confirme brane samples which were 1 year old were washed and fresh concrete was placed on top. Bond results confirmed the above investigation resulting in bond v a Because of the dry sprayed method of the membrane appli- cation, stop-and-go of the membrane application was possible without jeopardizing the final quality of the tunnel lining. COMPATIBILIT Y WITH OTHER WATERPROOFING SYSTEMS The original design of the stations and tunnels required sprayed waterproofing all round (fully tanked). Since the curing process of the sprayed membrane is caused by water evaporation from the membrane, the surface and eventual wa- ter ingress has to be managed upfront. During the excavation process, the surface needs to be relatively dry since a water- proofing membrane cannot be sprayed on running or dripping water. At the Whitechapel and Liverpool Street station there was a significant water ingress and it was decided to adapt the waterproofing design. The solution was a hybrid waterproofing system – a combi- nation between the spray-applied waterproofing system and a PVC sheet membrane. The spray-applied membrane was applied in the crown and the sheet membrane in the invert. This hybrid system was able to handle the water ingress but an adaption on the lining thickness was needed. A special design for the interface between the spray-applied membrane and the PVC sheet membrane was developed together with the sub- contractor for the sheet membrane which complied with the required 120-year design life. This meant also that the overall thickness and the reinforce- ment of the lining had to be increased because a PVC sheet membrane doesn't allow a composite action as with a double- bonded spray-applied membrane. Injection hoses were in- stalled in case a contact grouting was needed after placing the cast in-situ invert. INFLUENCE OF REGULATING LAYER In order to optimize the application of the spray-applied mem- brane, it is advised to use a regulating layer in order to smoothen the surface of the sprayed concrete by a fine mortar. In the project a 40 mm layer was specified. The aim of the regulating layer is: Improve the irregularity of the surface Reduce the consumption of the membrane Easier quality control Although mortar was specified, different contractors didn't use the same type of mortar. Different solutions were adopted from ready mix to dry sprayed bagged mortars. The applica- tion of the regulating layer required special attention. Using the correct spraying technique, a smooth surface could be achieved. In some cases the regulating layer did not result in the required surface improv o created some additional problems which were only visible after the applica- tion of the membrane. These problems were caused by the ventilation and/or the porosity of the regulating layer. During construction, water can find its way through the primary concrete, entering the tunnel. The regulating layer has to have a similar or higher durability and properties as the sprayed concrete used during the excava- tion. If that is not the case, water can migrate over a bigger area showing a bigger damp area. These areas can vary from a few sq in. to several sq ft. In case of a more porous regulating layer, different experiences were made. The tunnel ventilation was causing some problems in localiz- ing water ingress. With a high air speed and low humidity some- times damp spots were not noticeable since the water evaporat- ed quickly into the dry air showing a dry regulating layer. When the application of the membrane started, the membrane sealed off the regulating layer and water was trapped inside the regu- lating layer which sometimes created a water blister behind the membrane. Although this did not create a major problem, still these areas had to be repaired using a simple injection tech- nique. Packers were installed and some acrylic resin injected into the regulating layer/crack in order to seal it off. It was ad- vised to inspect the tunnel lining for damp spots by lowering the ventilation speed so they would be easier to locate. Porosity of the regulating layer was also an issue to be ad- dressed. With a low performance and porous mortar the water could migrate inside the regulating layer, making it more diffi- cult to locate the correct entry point of the water from the pri- mary lining into the regulating layer. The standard procedure is to install an injection packer without the injection nipple so it could act as a release point for the water. Then the waterproof- ing membrane would be applied. The packers act like a temporary drainage for the water and afterward for injection with an acrylic resin. In reality it was seen that after application of the membrane, the water was not released through the packer but was traveling farther in- side the regulating layer and appeared in a different location. It proved again that water travels the path of least resistance and the regulating mortar has to be of a high quality in order to avoid these problems.After discussion with the contractor it was decided to inspect the concrete before the regulating layer was installed so the exact location of the water ingress could be determined. A long packer was installed, acting as a temporary drainage. The regulating mortar was applied and after hardening of the mortar, the area with the damp spot was sealed off by a fast-reacting membr oc TSL865). By using this fast-setting product the water was forced to leave the system through the packers. This mem- brane is based on the same polymer technology but doesn't have the same properties such as flexibility and crack bridg- ing. The fast-setting membrane always needs to be over- sprayed with the waterproofing membrane. BASF's Clement added: "Spray-applied membranes have a proven track record and experiences are gained with every jobsite globally. The membrane is part of a system: concrete properties, quality of the regulating layer and water treatment are all factors that contribute to the success of the system. If de- signed correctly the system can allow a reduction of the lining thickness but the full system has to be considered. This means the correct design of the primary and permanent sprayed con- crete, the use of a high-performance regulating layer, the dou- ble-bonded waterproofing membrane and the sprayed or cast concrete inner lining. Any compromise in this respect can lead to problems and delay during the construction process." This article is an adaptation of the paper "Experiences with Spray- Applied Waterproofing Membranes," written by Frank Clement of BASF Construction Chemicals and Karl Gunnar Holter, Department of Geology and Mineral Resources Engineering, NTNU (Norwegian University of Science and Technology).

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