Compared to the overall construction costs of a tunnelling project, the process of waterproofing a tunnel involves almost negligible expense. But this is not to under-rate the importance of incorporating a durable and reliable waterproofing system. Waterproofing is a necessity, not only to protect the tunnel interior from water ingress but also to protect the surrounding environment from water egress caused by activities associated with the construction and operation of the tunnel.
Various methods are available to the tunnel engineer in the bid to achieve a watertight environment in a tunnel. These range from the localised sealing of the longitudinal and radial joints of a segmentally lined tunnel, using caulking or joint sealing, to the installation of a full waterproof membrane along the entire length of the tunnel. Such a membrane is placed between the temporary and primary, or primary and secondary linings.
A waterproofing system relying entirely on caulking and seals will rarely provide a 100% water free tunnel interior. If design specifications demand a zero level of water ingress, the alternative method of membrane placement, whereby water is directed down the plastic membrane to a drainage channel, is usually preferred. In T&T International, Oct ’98, Aloys Schlütter, then of Niederberg-Chemie, describes how, at the beginning of the 1970s,waterproofing using the then new method of single-layer plastic membranes was implemented in transalpine traffic tunnels.
GSE Lining Technology produces GSE TunnelLiner, a multi-layered, co-extruded polyethethylene membrane consisting of three separate polyethylene films, which are combined during the manufacturing process. They form a homogeneous, monolithic geomembrane, with complete impermeablility qualities claimed. The outer two layers are produced from white polyethylene with a black inner film that assists visual inspection of the membrane for fault identification. GSE TunnelLiner is also produced in translucent polyethylene, allowing weld integrity visual inspection to take place. GSE Lining Technology provides a full range of accessories that combine to form a complete tunnel lining system.
Hilti of Liechtenstein manufactures a waterproof system combining a geotextile fleece and a watertight membrane. The fleece is attached to the shotcrete lining of the tunnel wall by means of plastic washers, allowing it to serve as a dewatering layer for the membrane. The watertight membrane is then attached to the plastic washer by means of hot air welding. The plastic washers are set by Hilti tools.
A different approach to waterproofing has led the design team at Shobonds to prefer to control water flow from tunnel walls rather than contain it. Contained water can result in a build-up of pressure, says the company, which leads to water finding a least line of resistance, possibly resulting in perennial repairs having to be carried out. Shobonds SI Boards forms a mechanical lining to the tunnel interior and allows water seeping from the concrete to drain down into a drainage system at road level.
SI Boards are installed and secured to the lining concrete by anchors and TECS-BOLTs and to each other by the designed male and female board ends. Initially, in preparation using TECS-BOLTs, metal fittings are secured (for installing the boards to the lining concrete) to the female sections of the boards. The first board to be installed to the tunnel lining is to the apex of the crown. This board must have two female ends. Subsequent boards with male and female ends are then placed until the profile is lined. Once installed, the joints and ends should be treated with polyethylene foam and both bottom ends of the Board-installed area in the longitudinal direction of the tunnel should be finished by applying a scaler.
Cavity membrane systems
Since the introduction of BS 8102 in 1990 – ‘Protection of structures against water from the ground’ – the use of cavity membrane systems in the UK has increased rapidly. The system involves a studded membrane structure that is designed to equalise damp pressure and divert, control and drain water via a continuous void created by the membrane. The membrane is used with aggressive groundwater to divert water to the station culvert.
Delta Membrane Systems has developed a cavity membrane called the Delta PT for negative side water management. The Delta PT membrane is fixed back to the substrate with specially designed sealed fixing plugs at 250mm horizontal and vertical centres. A mesh is welded to the internal face of the membrane to support a plaster finish.
Two coats of high impact plaster to a combined thickness of 15mm are then applied to the membrane. The plaster is based on anhydrous calcium sulphate. The total thickness is made up to 23mm, reduced on some applications where it is critical to the kinetic envelope. The system does not serve merely to dam, divert or hide the problem; in addition, long-term control of the problem and protection of internal finishes is achieved. Delta PT is guaranteed against deterioration for 30 years.
Seals and gaskets
German company CarboTech has for many decades been developing and manufacturing advanced technology for sealing water and gas leakage, cavity filing, crack repairing and consolidating for the tunnelling, civil engineering and mining fields. The relatively newly developed CarboCryl injection agent, a two-component methacrylate system, is used for sealing building surfaces and hardening fine-particle sand and clay soils as it has a very low viscosity. CarboCryl is applied using the CT-GX 5-11 injection pump. The machine is pneumatically operated and can be run from an electrical mini-compressor with a rating of not less than 3kW.
Another new system from CarboTech is the flexible two-component polyurethane resin, CarboCrackseal, which is used for elastic sealing of fissures and cavities in concrete, masonry and bricks. The resin has a high adhesive strength on dry and humid surfaces and can seal fissures thinner than 0.1mm.
Waterproofing and concrete repair material specialist Ronacrete offers a comprehensive range of materials for use in tunnel waterproofing. These include Ronafix, a single-part modified styrene butadiene liquid additive for cement mortars and renders. Ronafix is claimed to enhance the physical and chemical properties of renders, providing waterproofing and frost and mild chemical resistance while promoting adhesion to construction surfaces. Ronacrete Monoplug is a setting repair mortar used for stopping the flow of water seeping through concrete. Ronacrete Unidri is a surface applied waterproofing slurry that seals render and concrete. It penetrates the concrete’s surface and grows crystals which block the matrix pores whenever moisture is present. Ronabond PU Stop is a liquid polyurethane resin for filling and sealing cracks which are subject to the presence of moving or still water during the crack filling and sealing operation. The resin foams on contact with water and fills the crack and seal against the passage of water.
The Rascor Group covers the whole field of preventative and remedial waterproofing for all areas of civil engineering and building construction. The company offers a range of services, including studies for analysis of preventative and remedial waterproofing, design of waterproofing schemes for new-build and refurbishment schemes, preparation and assessment of tender documents, performance of waterproofing works and acceptance of defects correction/handover at end of defects liability period.
Rascor has developed RASCOflex grouts for waterproofing penetrations. RASCOflex is an acrylic grout with a viscosity comparable to water, allowing the finest cracks to be grouted. It is solvent free, with a pH of approximately 9-10 and is fire resistant and non-flammable. Controlled swelling with 10-15% increase in volume occurs upon contact with water, causing negligible pressure build-up. A waterproof barrier is achieved through the swelling action, it has a high compatibility with metal and plastics and is frost resistant.
CV Buchan and Dunlop Precision Rubber have combined their specialist resources to develop and market a new generation of hydrophilic compound. Bucseal is a hydrophilic rubber seal for tunnel and shaft segments that expands to a minimum of five times its original volume when immersed in water. It comes in strip form complete with adhesive for fixing in purpose made grooves around the segment. The adhesive is applied to smooth and clean surfaces in one coat and allowed to become tacky. The strip, when correctly positioned, is firmly pressed on to the adhesive using a small hand roller to develop the bond fully. Strips can be joined together using a fast setting adhesive or by a cut butt joint. Providing a double layer seal between the joints is achieved by applying the strip around all four sides of each segment. There is a delay of several hours between contact with water and swelling but Bucseal should not be allowed to become wet before installation and must be stored in a dry place.
Phoenix specialises in sealing profiles for single shell lining and has recently developed the anchored seal. Since 1968, the company has developed compression profile seals for TBM driven tunnels, fitted with prefabricated steel or concrete segments. Phoenix has developed more than 40 different profile shapes and established eight different cross sections, allowing supply to all kinds of tunnels, from supply and disposal tunnels to large railway and road tunnels.
The Phoenix anchored tunnel seals are anchored directly into the concrete segment, offering a variety of advantages: there is a shortened process in the segment factory due to time savings for correction of imperfections and cleaning of the groove. Costs are reduced because of the negation of glue and glueing equipment as well as time for mounting the gaskets, while environmental pollution is minimised because there are no glue or solvents present. A high adhesion is realised between the gasket and concrete and the design maximised the distance water has to travel through the concrete to circumvent the seal.
Charcon Tunnels is the sole distributor in the UK of Hydrotite, a compound of polychoroprene (neoprene) and hydrophilic resin which is manufactured in Japan by CI Kasei Co. Hydrotite is compressed in a joint and expands to fill the joint gap and exert pressure between the joint faces to resist the passage of water. Hydrotite expands to seven times its volume when in contact with water. New developments at Charcon include a patented method of co-extruding Hydrotite with rubber which has been used to develop a hybrid hydrophilic/EPDM gasket. Advantages over the single gasket include the fact that the initial precompression seal has the ability to seal leaks that result from joint displacement. A thinner lining and a simpler detailing are possible as the twin seal is combined in a single feature.
Gumba Last has developed a range of elastomeric waterstops for waterproofing joints in in-situ concrete structures that remain waterproof despite alternating joint width and water pressure on account of their elastic response. This negates the possibility of plastic flow that can cause other types of waterstop to detach themselves from the concrete, allowing seepage of water around the flanges.
Elastomeric waterstops possess sufficient natural stiffness not to be displaced during casting and compacting of the concrete and are capable of withstanding temperatures of up to 180°C. Joints in the elastomeric waterstops are vulcanised, featuring the same strength as an unjointed waterstop, which means that the complete sealing system/network is unaffected by weak points. Gumba’s range of waterproofing products also includes waterstop systems for structures in high hydrostatic pressure areas; capping joint waterstops; compression seals; thermoplastic waterstops made of PVC-P, centrally placed or externally placed for expansion or construction joints; and JEKTO grouting tubes for construction or casting joints for the combination with waterstops.
DeNeef offers specialised groundwater control services with a broad line in chemical grouts, epoxies and waterstops. Products include Hydro-Active Cut, a hydrophobic, water activated, 100% solid, polyurethane expanding rigid foam for permanent water cut-off in non-moving cracks and joints. Hydro-Active Flex LV has the same specifications but is designed for use in moving cracks and joints.
HA Sealfoam is a hydrophilic, water activated, polyurethane injection resin designed to control water at seal moving, non-structural cracks in concrete. Also available is the 100% guaranteed water stop – the Injecto Water Stop System. A reinforced tube in the form of a conduit brings expanded polyurethane grouts into construction joints; cold joints; pipe penetrations; keyways; block outs; and tie-in slabs. The Trioject Water Stop System is designed for the same use, except that it has an injectable hose with three injection channels. DeNeef has a range of caulk-applied water swelling sealants called the Swellseal range. This includes Swellseal Gungrade, Swellseal 2010, Swellseal No. 8 and Swellseal Joint.
Tricosal specialises in waterproof design systems associated with construction and expansion joints and offers a wide range of products. The company also carries out sub-contracting work, offering a range of services for construction and renovation projects. For sealing new structures, Tricosal provides: Fuko, the re-injectable hose; Duroseal, the hydrophllic gasket; Duroseal, the hydrophilic paste; and Tricomer, the PVC waterstop. To extend the service life of existing structures there are: acrylate resins; PU-resins and foams; cement grouts; and cement coatings. The re-injectable Foko system allows easy inspection as each joint can be tested against water ingress. All kinds of resins can be employed. The products have been used on many large tunnelling projects, including the Boston Central Artery Tunnel Project and the Melbourne City Link.
