The A2 motorway, the so-called Gotthard route, is one of the most important north-south transport arteries in Europe and one of Switzerland’s busiest motorways: Thousands of car and lorry drivers use the route on a daily basis, which runs from Basle via Lucerne, then through the Gotthard to Lugano and continues on the Italian side in the form of the A9 in the direction of Milan. Along the route it passes through the Melide-Grancia Tunnel in Ticino. New safety regulations called for the tunnel that was built back in 1968 to be renovated. This represents a challenge for the 2 roughly 1,730 m long, twin-lane bores, particularly regarding the construction materials used at the time. It is scheduled to be completed in 2014. The client is the Swiss Federal Roads Office FEDRO (ASTRA). Produced by trenchless means some 45 years ago, no sealing level was planned and executed for the Melide-Grancia Tunnel. So far any underground water accumulated behind the in situ concrete lining and was then run off. There is an intermediate ceiling in the upper section, in which 3 ducts cater for supplying and removing air.
Renovation work will dispose of the intermediate ceiling and lining thus enlarging the useful cross-section. These measures make a seal necessary in sections of the tunnel, which are endangered by water entering through cracks, joints or other faulty patches.
On account of the high traffic frequencies work is only possible at night or outside the holiday season or public holidays. One bore is closed from late evening till early morning and traffic conducted through the other on a bi-directional basis. The construction site can be set up as from 9.15 pm. All the machines are installed and the night shift begins. At 4.00 am the tunnel has to be cleared and all moveable parts removed for safety reasons. As from 5.00 am traffic is able to flow through both bores in a normal manner.
The work undertaken by SikaLavori SA was awarded by the JV “Consorzio Risanamento Galleria Melide-Grancia” headed by Messrs. Edilstrada SA, Lugano. The JV comprises Edilstrada SA, Lugano, Ferrari Ennio SA, Lodrino and LGV Impress costruzioni SA, Bellinzona.
Apart from the company responsible for the sealing operations, SikaBau AG, Cadenazzo branch (SikaLavori SA) and the material supplier MC Bauchemie, Desoi GmbH is also involved in ensuring the necessary measures are applied. Desoi for example, supplied a total of 5 injection units with the Flow Control recording system for acrylate gel and injection packers for multiple use. Flow Control, a 2-component injection system with rinsing pump as well as integrated measurement and recording unit, is a well tested system conforming to valid standards. Desoi is responsible for instructing staff on the spot and technical support.
Curtain grouting with acrylate gel is the most suitable method for application. The cavity of the water-bearing contact zone between the concrete and rock is filled up and sealed by means of this injection technique. Figs. 1 to 4 provided an impression of how the injecting process was executed. The job was undertaken in the following working steps with 2-component injection units (DESOI FLOW-Control with PN1412-3K) and an acrylate gel (MC-Injekt GL-95):
Sealing all joints,
Sealing water-bearing cracks,
Sealing faulty patches in the concrete,
Developing the intermediate sealing,
Concrete cosmetics and
Concrete protection with light coating.
The special requirements and application times call for special service: “Thanks to Desoi’s active support a reliable and competent contact partner was available at all times”, was how Paolo Gattulli, the responsible branch manager of Messrs. SikaLavori SA put it. According to Bernd Kress of Desoi GmbH quality control, for which many aspects had to be taken into account, represents a decisive criterion for the success of the sealing operations. While injecting, important parameters must be permanently measured and recorded. In addition it is of particular importance that the injection pressure corresponds with the planning specifications and conforms to the application. The required mix ratio must always be adhered to as well.
As the parameters are collated in real time each packer can be checked with respect to material consumption, grouting pressure and injecting time. The injection processes carried out can thus be assessed in tabular and graphic form at any time.