With a daily volume of around 40 000 vehicles the Wallring Tunnel, built between 1963 and 1966, is none of the most important inner-city traffic arteries in Hamburg. The tunnel consists of two tubes, each with two carriageways. The central section houses supply facilities, a service gallery and an escape route. The Wallring Tunnel was designed as a frame structure which is open at the bottom due to the fact that it stands above the groundwater level and therefore requires no bottom closure. It was built using the cut-and-cover method and runs under Hamburg city centre between the Alster and Elbe rivers, is 550 m long and crosses the intersections at Georgsplatz, Spitalerstrasse, Mönckebergstrasse and Steinstrasse. It passes close to a deep bunker at Steintorwall next to the main railway station and passes over three subway tunnels.
2013 the city state’s budget finally allocated 30 million euros to its rehabilitation. Thus, in 2014, the LSBG (“State Agency for Roads, Bridges and Waterways of the Free and Hanseatic City of Hamburg”) was able to kick off the construction project.
The road construction activities began in 2014, with the safety and fire protection work in the two tunnel tubes being initiated in 2016. Over the next two years, almost the entire electrical system was replaced, a loudspeaker system installed, video surveillance, fire alarm cables and CO2 measurement equipment modernised, and escape routes, emergency recesses and emergency call stations updated.
As the tunnel floor is separated at one point from the underlying section of subway line 3 by a 22 cm thick reinforced concrete slab, it was not possible to provide a continuous drainage conduit. Instead, a pumping station shaft with parallel, i.e. redundant, pumps had to be built in each tunnel tube as part of the refurbishment package in order to ensure – at any time – that accumulating water can be pumped away via the subway tunnel system. 12 000 m² of road surface were newly asphalted, and a barrier system was installed in order to close the tunnel to traffic if this were ever deemed necessary. The construction work required had to be carried out while keeping the tunnel tubes operational. This meant working a total of 700 nights over the length of the project.
Hazardous interior Cladding
However, the planning engineers had an even bigger headache relating to the safety of the original concrete reinforcement within the tunnel tubes. In order to improve the lighting conditions inside the tunnel, the walls had been covered with frost- and acid-resistant white split-face tiles, creating a cladding of between 3 and 4 cm in thickness on a 1.5 cm layer of mortar. This cladding system was far below the standards specified in modern fire protection regulations. In the event of a severe fire in either of the two tunnel tubes, a temperature of more than 500 °C would have occurred at the reinforcement, jeopardising its structural integrity.
The fire protection specifications for tunnel construction stipulate that, in the event of a fire, load-bearing reinforcement must not heat up to more than 300 °C. This must be ensured by providing a concrete cover of sufficient thickness. Needless to say, in the case of tunnels in cities with adjacent transport structures, the requirements set are particularly exacting.
In keeping with the relevant German technical code ZTV-ING, Part 5, and risk analyses based on longer fire durations recently included therein, such tunnels and their reinforcement must be designed so that effective fire resistance is guaranteed for a period of 60 minutes at 1200 °C followed by a 110-minute cooling phase. The construction materials used for such applications must correspond to building material class A (non-combustible) according to DIN 4102 and must not release any substances that could be injurious to either personnel or the structure itself.
Nafufill KM 250
MC’s experts in Product Management and Sales advised the client LSBG and its planning engineers WvS Zivilingenieure Hamburg to choose an effective, tried and tested concrete replacement in order to achieve reliable structural fire protection in the Wallring Tunnel. The sprayable polymer-modified cement mortar (SPCC concrete replacement) specified for the job needed to verifiably comply with the ZTV-ING tunnel fire curve extended to 60 minutes. The experts recommended the fire-resistant, fibre-reinforced PCC/SPCC concrete replacement Nafufill KM 250 from MC. This fibre-reinforced concrete replacement is also characterised by its very good flexural and compressive strength behaviour (R 4 mortar to EN 1504 Part 3) and high carbonation resistance. It is also resistant to de-icing salts and chloride penetration.
A Mammoth Task
Execution of the work was entrusted to the French company Eurovia, a world leader in road and transport infrastructure construction. Schachtbau Nordhausen Bau GmbH was commissioned with the SPCC work and began installing the Nafufill KM 250 replacement onto the prepared surfaces in November 2016. A layer thickness of approximately 4.5 cm was to be applied by wet spraying. This technique ensures low-dust and low-rebound processing compared to dry-sprayable SPCC mortars. The target area amounted to 21 000 m². The huge volumes involved also meant MC’s logistics would feel the heat: their task was to ensure that a constant flow of Nafufill KM 250 was always available, even though deliveries during the construction phase were limited to the night time. Due to the size of the project and the short construction period, this sometimes meant six 21-tonne truckloads per week. However, the challenge was met in full: During the entire construction phase, there was always enough Nafufill KM 250 available on site for the ongoing spray-coating work. The total quantity ultimately supplied was 2100 tonnes delivered in 101 truckloads. Eventually, the whole rehabilitation project was completed on schedule and on budget.