In many cases ground treatment before excavation will be more economic than water problem rectification by grouting or other methods.
Economical cementitious grouts, perhaps with additives, may well be adequate for grouting where there is little water movement and for larger cracks and cavities. If grouting is carried out before excavation the chances of water movement, and thus washout of the grout before curing, are lower due to minimal pressure differentials. If a full grouting programme of the surrounding ground has been carried out to seal the excavation, water ingress may no longer be a problem. Nevertheless grouting of the rear of the lining is valid for both structural and water-control properties, especially where there is an annular gap such as behind a pre-cast lining.
Although more expensive, grouting with synthetic materials, otherwise known as chemical grouts, should be more effective in higher grout water pressures and water flows, as well as being more able to penetrate finer fissures and the pores of fine sands, for example. The Orica-group Minova CarboTech range of ground-injection grouts are based on polyurethane and organo-mineral resins, and acrylates as well as microcements, all of which are designed for use in high groundwater pressures, depending on other conditions.
Even with the best laid plans for designing in waterproofing, the circumstances of construction may make corrective waterproofing necessary. For example in construction of the recent cut-and-cover tunnel for Hamburg’s new airport terminals, the excavation was supposed to be protected by diaphragm walls. However, one section of wall leaked, carrying soil into the excavation and breaking a high-pressure water pipe in the process, damaging an access bridge. Contractor Brückner Grundbau stabilised the ground and sealed the water leaks by drilling Minova Wiborex bolts from the surface into the affected area and injecting through them with Minova CarboPur WT and CarboPur WFA fast reacting resin grouts. During removal of the debris, the area was again injected with CarboPur WFA through injection lances. Normal construction could then proceed under dry conditions.
Tecinvest of Wommelgem, Belgium, produces a range of grout products under the Spetec trade name for waterproofing, crack injection, cavity filling and sewer repair as well as rock anchors and soil stabilisation. These include mono- and multicomponent resins including low viscosity (110cPs) forms for better penetration. These exhibit another feature of ‘chemical’ grouts, that of flexibility that allows the grout in situ to accommodate possible ground movements after curing. According to Tecinvest the Spetec PU 52 LowVisco 2-component, solvent-free grout can be used to create a waterproof membrane by injection, with a typical reactivity time of 20 minutes.
Concrete solutions
Structural concrete used in tunnel linings is generally of low water absorbency (not more than 2% according to the BTS Specification for tunnelling) but various approved mix ingredients and additives can be used to improve concrete’s inherent impermeability. However concrete and its aggregates are subject to shrinkage cracking. Even though sample testing can assess the extent of shrinkage, this still has to be taken into consideration when assessing possible permeability. Loading may also cause further cracking and increased permeability.
The Sika ViscoCrete range of concrete additives are designed to impart specific properties to concrete for both casting and spraying, including the improving of impermeability by reducing the possible water/cement ratio. Means of reducing concrete permeability, and also improve related properties, include reducing the water/cement ratio, but where pozzolanic materials are available at reasonable costs they can be used as a substitute ingredient. Microsilica can be used in cast concrete to reduce permeability, but also in sprayed concrete to improve bonding and reduce slump. In fresh-sprayed concrete, microsilica can reduce permeability to prevent aggressive agents from penetrating and attack the concrete and reinforcement, improving sulphate and chloride resistance.
A proprietary manufactured form of pozzolanic material from Norway is Elkem Microsilica. Elkem Materials is the world’s leading microsilica supplier. The design life of tunnel concrete in these applications is at least 100 years with minimal maintenance.
Membranes
Plastics membranes are one of the most widely used means of comprehensive tunnel waterproofing. Although forming an impermeable barrier careful, skilled installation is necessary to ensure that the membrane is adequately supported to withstand expected water pressures, ensure that no sharp rock or other objects penetrate the membrane causing leakage paths, and to ensure securely sealed joints between adjacent sheets. Penetration problems can be alleviate by good surface preparation, application of a sprayed concrete smoothing layer, or the installation of an outside fleece layer that can also offer drainage paths.
The Sika group has a wide range of composite and non-layer membranes depending on the performance required. At the simpler end of the scale Sikaplan-14.6 III-Tunnel is an unreinforced, plasticised PVC membrane for cut-and-cover tunnels. It is resistant to common aggressive elements in groundwater and soil, including soft water. It can be welded with hot air ‘torches’ and can be used on damp or wet substrates. The top (signal) layer is coloured yellow and the bottom layer dark grey.
A waterproofing geocomposite membrane manufactured by Flag of Bergamo was used in the rehabilitation of La Contessa Tunnel, Perugia, Italy for the ANAS national road administration. The tunnel had suffered from high water circulation on the permeable arenaceous ground. The membrane was installed in unlined sections together with internal cladding. Water control measures also included the laying of 50mm-diameter drainage pipes. In a 94m-long cut-and-cover section waterproof mortar was supplied by Kimia of Ponte Felcino
Sprayed on
The choice of sprayed concrete for primary lining, and sometimes, permanent lining, can present particular problems in water conditions. Whilst bonding can be improved by careful mix design for low slump and high bonding, water flows that are not under high pressure can be combated by grouting or channelling to a drain. Drain passages can be formed by specialised dimpled linings, nonwoven textile fleeces or channel covers such as the Sika Aliva system placed over cracks and other water inlets. In these ways a dry surface is preserved to facilitate easier sprayed concrete application. The drainage channels may be incorporated into the lining, but are more often made redundant by an injection grouting programme, or the installation of a full-profile membrane.
Another approach to channelling in the permanent lining is to form channels in planned joints. Phoenix supplies 100mm-wide drainage joint seals for this purpose to keep water within the channel.
One of the most significant developments in tunnel waterproofing in recent years has been the introduction of reliable synthetic spray-on membrane systems as an alternative to installing sheet membrane (T&TI Sep. 2007 p35-37). Sprayed membranes can be used easily on irregular profiles and in locations, such as junctions and services chambers where lining with sheet membranes would be laborious. Existing services could be covered up during application, whereas they would have to be removed for sheet membrane installation or the membrane installed around them. Sprayed membranes are also more tolerant of rough rock surfaces. For more regular profiles sprayed membrane application can be carried out using the new robotic spray units as used for sprayed concrete.
In a recent application of UGC’s Masterseal 340F sprayable membrane it was combined with sheet membrane in the Collombey road tunnel in Switzerland. The lower part of a drill-and-blast section of this tunnel lies below groundwater level where the engineer preferred to use Masterseal rather than the PVC membrane used in the upper part of the profile since the lining below groundwater level would be subject to full water pressure. This lining was applied using a UGC Meyco Roadrunner mechanised spray system. The sheet membrane represents a drainage system with pipe collectors installed in both sides of the tunnels. In a cut-and-cover section a bitumen membrane was used for waterproofing. The contractor was a Murer and Züblin JV with the Scandinavian Rock Group as specialist sub-contractor.
Special conditions included a relatively low ambient temperature of 3-6oC necessitating application of the Masterseal 340F in two or three thin layers to ensure proper curing. These were applied on a ‘smoothing’ layer of 4mm-thick sprayed concrete. Where local seepage areas of bare rock were present Masterseal DR1 drainage fleece was applied to present a dry surface for spraying. Use of sprayed membrane ensures that there is no migration along the membrane/substrate interface, lessening the risk of seepage, although any eventual damage is easy to repair says BASF UGC.
SikaProof SB is a 2-component, bitumen-based, spray applied waterproofing membrane for seamless waterproof of below-surface structures such as cut-and-cover tunnels and basements. A catalyst reacts with a polymer-modified bitumen emulsion in mid-air, causing it to break down cure. The material is non-toxic, odourless and approved for use with potable water.
Gaskets and seals
Whilst offering remedial grout systems as with many other suppliers, Rascor emphasises various preventative waterproofing systems for vulnerable sites in the tunnel structure such as construction joints, and movement and expansion joints. Preventative waterproofing now accounts for over 80% of the Company’s turnover. Systems also include injectable seals for joints and services glands through walls, plus dummy joints for crack control. Developed for basement waterproofing but also applicable to cut-and-cover tunnelling and similar methods, Rascor’s integral White Tank system is designed to replace use of bitumen for waterproofing concrete structures that Rascor claims is largely obsolete. This system utilises the concrete structural elements themselves as the basis of the waterproof barrier. Additional joint seals and waterproofing grouts may be needed if concrete quality is not sufficient.
Where any form of jointed lining is used, whether pre-cast or cast in situ, it is vital to seal these joints to prevent leakage, and maybe also to cushion the effects of subsequent movements after construction. Specialist manufacturers produce many standard designs of gasket seals, and if required, custom-designed profiles. Leading suppliers include Phoenix of Germany (part of ContiTech AG, the Continental Group) and Dätwyler of Switzerland. Designs vary according to factors such as expected pressure, the design and size of the joint, the means of installation and the nature of any water contamination.
Phoenix now has access to a broader range of elastomer expertise in the Continental Group from other industrial sectors to combine with its long expertise in profiles and gaskets for segmentally lined tunnels, cut-and-cover excavations and pipe jacking. Compression sealing gaskets are available for both concrete and steel cast lining segments in a range of over 50 standard sections. Recent transport tunnel projects supplied include the Netherlands Groene Hart Tunnel; the Hallandsastunnel, Sweden; and the Metro Dubai Red Line.
Within a list of recent Phoenix innovations there are an anchored seal installed during concrete segment production, and one, called the ‘Evolution Seal’ that combine a hydrophilic swelling strip within a compression seal, provided even more and early security against water passage. The anchored seal was developed in conjunction with the contractor Hochtief and TBM manufacturer Herrenknecht. Using this process gasket installation is not only a factory process but also becomes more efficient without costly gluing and reducing environmental impact.
Dätwyler recently entered into a new partnership with Vertex of Mogadore, Ohio for the manufacture of cast segment seal frames and corners. In the US the group holds patents for gasket technologies in prefabricated concrete construction and synthetic and concrete pipes. The first project to be delivered with gaskets was the Brightwater Treatment System East in Seattle for the 5.08m-diameter, 4.2km-long tunnel. The 2,800 segment rings require 17,000 sealing ‘frames’ with 68,000 vulcanised corners. Others scheduled for supply of seal corners include the North Dorchester Bay CSO Storage Tunnel and the Allegheny River Tunnel in Pittsburg.
Watertightness must also be a consideration for sewers and vertical structures. In the first water ingress may load pumping systems excessively whilst creating possible long-term structural security and environmental problems. In vertical structures, especially those that cross the water table, water pressures may not be high but the possibilities of 2-way flow can present possible structural problems by removal of soft and small-grain ground that surrounds the structure. A recent introduction in this field has been the new CSD Plus 3 manhole seal from Theodor Cordes, a manufacturer that is also a distributor for Phoenix. These prelubricated seals have an integrated vertical force element that locks the gap between manhole ring. The seal is easily installed on the spigot and the vertical force transfer element ensures accurate location without reworking the gap, and also reduces pollutant attack on the main seal. No mortar is required. The seal itself is made from styrene-butadiene-rubber (SBR), which is proven in surface water and sewerage applications. An integrated self-sliding ‘leap’ protects the main seal against damage and limits horizontal shear stress on the joint.
Sika has also introduced a manhole compression sealing strip made of 16mm-diameter, preformed butyl rubber. It can also be used with pipes, gutter drain joints and lightweight precast panels. The seal is permanently flexible and non-shrinking.
Joint sealing using low-pressure injection guns is facilitated by having a secure, uniform, base to the rear of the joint to save on material and assist full treatment of the joint itself. The new Sika PEF backing rod can perform this function. It is weather resistant, easily compressible and does not absorb water itself. A wide size range is available in lengths of 20 or 50m. Once in place the gun-applied sealant is applied. This may be elastomeric or a self-expanding polyurethane foam. Neither will adhere to the backing rod, ensuring unrestricted movement of the sealant.
BASF UGC’s Roadrunner mechanised spraying equipment can be used for Masterseal waterproofing membrane application as well as shotcreting. BASF UGC’s Roadrunner mechanised spraying equipment Switzerland’s Collombey tunnel, showing waterproofing membrane covering the crown and UGC’s Masterseal sprayed on below groundwater level Switzerland’s Collombey tunnel Segment gasket seal test equipment in the Phoenix laboratories Segment gasket seal test equipment A collection of profile injection moulds from Daetwyler Rubber Profile injection moulds from Daetwyler Rubber Daetwyler Rubber CoexSwell segment gaskets with integral swelling compound used on pre-cast concrete waiting installation on the Marmaray Tunnel’s bored section Daetwyler Rubber CoexSwell segment gaskets Installing Phoenix drainage joint seals in the Dichtungen Tunnel Installing Phoenix drainage joint seals
