The Ring Rail Line is an important rail loop for the Helsinki metropolitan area, that will reduce road traffic and will promote the EU’s climate policy objectives. It is also a 30 minutes rail link to Helsinki-Vantaa International Airport. Construction began in 2009 with three access tunnels.

Twin tunnel under the airport
The Ring Rail Line tunnel will have twin single-track tubes, with connecting tunnels as well as shafts and access tunnels leading to the surface. The tubes will be divided into fire sections and will have connecting corridors between them. Access tunnels will be located at regular Intervals

Technical and safety facilities will be located in stations and connecting tunnels. Pumping stations and collector basins will be built at stations and the lowest points in the tunnel.

Owing to Finland’s cold winters, each mouth of the tunnel will have to be insulated to prevent freezing. Insulation will be installed over a distance of about 2,500 metres.

The tunnel is being excavated by drill-and-blast. Finnish bedrock is very hard and it is not possible to use a tunnel boring machine for this purpose.

Tunnel excavation
Tunnelling in hard Finnish bedrock is a chain of different work stages that is repeated from one blast to the next. The time needed to get ready to blast takes a single shift or an entire day, depending on the nature of the rock. In part of the Ring Rail Line tunnel the rock is highly fractured. This significantly increases the amount of time needed for reinforcing and slows down work. Reinforcing includes shotcreting, bolting and injection. Before this can be done loose rock must be scaled from the ceiling and walls of the tunnel mechanically.

“In Finland a new railway line is usually built through the middle of forests. The Ring Rail Line is an exception, since it runs through residential and business areas practically the whole way,” says Maija Salonen, project manager of the Ring Rail project.

Strict environmental regulations must be observed in excavation work for the Ring Rail Line. The contractor is responsible for controlling environmental noise and vibration.

“In the environmental study maximum permissible vibration levels are set for buildings with different types of foundations, along with noise ceilings. Before work starts inspections are conducted to determine the condition of buildings in areas that may be affected as well as any existing damage. Inspections generally cover 100 metres on either side of the line. If necessary, equipment that is sensitive to vibration is insulated. Air control for Helsinki-Vantaa International Airport is located near the tunnel under the airport and is full of sensitive equipment, which must not be damaged by vibration,” Salonen explains.

Gauges installed in buildings will measure vibration caused by blasting. Sensors will measure swaying, amplitude, frequency ranges and the duration of blasts. Results will reach the site office over the Internet within seconds after each blast. A cap has also been placed on the amount of explosives that can be used at any one time. The limits that have been set by authorities must not be exceeded, but if results show that this has happened, the amount of explosives will be reduced.

After the contract has been completed, final inspections will be conducted to determine whether buildings have suffered any damage. The contractor is liable for the cost of repairs.

The Ring Rail Line’s permit under the Water Act requires that water used in the blasting process or dripping inside the tunnel must be removed from the tunnel. Once solids such as drilling grit have been allowed to settle, water can be pumped to ditches or the sewer or rainwater network after pH neutralisation (originally pH 9) and oil separation. Water pumped from the tunnel must not cause silting or corrosion at outlet points. The condition of pipes and ditches above and below outlet points will be monitored. The permit does not set limits on nitrogen or nitrates.

Groundwater and surface water will also be monitored during different stages of work.

Scope of work
Supervisor Esa Kiiski from construction management consult Ahmainsinoorit says, “Time schedules are tight and rock conditions vary. Rock is crushed. Blasting vibrations, especially adjacent to Finnair headquarters and other challenging environmental issues exist near ground water areas. The nearby Paijanne tunnel brings household water to whole capital area.”

The scope of work consists of:
– Open cut and shafts: 150,000m3,
– Rock excavation, underground: 1.5Mm3 (sections < 60m2), railway tunnels 2 x 8km, two railway stations 250,000m3 volume and 280m long
– Sprayed concrete: 18,000m3 unreinforced + 36,000 m3 steel-fiber reinforced,
– Rock bolting: Hot-dip galvanized rock bolts, 3 – 6m totalling 500km (120,000 pieces) and CT-bolts 28,000 pieces
– Continuous test drilling (MWD)
– Pregrouting if needed. Pregrouting pressure 5MPa, 18 – 28 holes, 24m / hole. Cement is microcement Rheocem 650 or Cementa 20.

Drilling by computer
A computer-based Atlas Copco Advanced Boom Control (ABC Total) is in use for the Ring Rail tunnel project to help with the demanding conditions. Computer placed drill holes lead to a longer advance, an accurate excavated tunnel profile and minimun damage to the surrounding rock. The result is significant savings in the costs of blasting, mucking reinforcement.

Tunnel Manager by Atlas Copco as well, is a support software for planning, administration and evaluation of the drilling operation. It is a Windows-based support program, that runs on a regular stand-alone office PC. In the beginning of drilling work, the Ring Rail project provided drawings and standard information to prepare detailed construction plans, such as tunnel profiles, drill patterns, tunnel alignment tables and charts defining the position and alignment of the laser beam. The plans are prepared on a PC and transferred to the drilling rig on a disk. Actual data collected during drilling can be recorded on a disk transferred back to the office PC and analysed. This way the accurate data is always available.

Rock study
The rock excavated in the Ring Rail Line project has been studied, and possibilities to use crushed rock in railway and road structures have been evaluated. About 1.5M cubic metres of rock is being excavated to build the 8-km twin tunnel. Economically feasible uses have been sought for the rock that will be left over after the project. Crushed rock is either used to build the railway bed and for ballast or is hauled off and screened. The best solution for the project is to use as much crushed rock as possible in substructures or embankments, so that aggregates will not have to be transported to the site from elsewhere.

Excavated rock is crushed and used in substructure layers, provided it meets quality requirements. Rock that is left over is placed in embankments or crushed and used in construction elsewhere.

Any aggregates that are used in substructure layers must meet technical requirements that have been set to ensure a service life of 100 years. In the case of crushed rock the main criterion is degradation. This causes permanent transformations that can result in settling as well as an increase in reversible deformations and water retention capacity, leading to higher frost susceptibility. Strength requirements are set in order to minimise degradation.

Fire safety tested in Switzerland
To test fire safety, Poyry Infra conducted simulations in Switzerland in late 2008 and early 2009 according to the existing solution (VE2A1), which called for the Viinikkala, Aviapolis and Airport stations to be designed and for space to be reserved for a station with two halls in Ruskeasanta, along with a shaft to remove smoke and balance pressure, an access tunnel and connecting tunnels to the station and the twin tubes.

For the fire simulation an aerodynamic simulation was first conducted using a model based on the geometry of the tunnel in stage one of the Ring Rail Line project together with information on train traffic and climate conditions. This defined the aerodynamic starting point and then the fire simulation was carried out using a 3D programme. A train fire was simulated according to the most critical scenario and location and a maximum fire load of 40MW. The test assumed exhaust fans operating at 58m3/s at a pressure of 900Pa.

The location that was chosen for modelling is the deepest part of the tunnel section, which lies between the Viinikkala and Aviapolis stations and is ten metres below sea level. Fires were simulated for two different cases in which a train was running from west to east.

In the first case the fire was in the rear of the train and exhaust fans blew from the direction of Vainikkala towards Aviapolis. Rescue personnel approached from the direction of Vainikkala.

In the second case the fire was in the front of the train and exhaust fans blew from the direction of Aviapolis towards Vainikkala. Rescue personnel approached from the direction of Aviapolis.

The simulation assumed that a train was stopped in the deepest part of the tunnel when fire broke out and that passengers immediately got off on the safe side and proceeded through the connecting tunnel to the other tube or via an exit shaft before stations’ smoke doors closed six minutes after the fire started. The windows on the train broke after five minutes, causing the burning process to accelerate. The exhaust fans turned on one minute after the smoke curtains closed (seven minutes) and reached full strength one minute later (eight minutes). The fire reached full strength in 20 minutes. The total duration of the simulated fire was 30 minutes.

The simulation showed that in both cases the temperature in the tunnel on the side approached by rescue personnel did not exceed 70 degrees C at a height of two metres, although combustion gases at the crown of the tunnel in this location could rise to a temperature between 140 degrees C and 200 degrees C. Further away, temperatures fell to less than 100 degrees C at the crown of the tunnel. Smoke no longer flowed towards the exhaust fans 10-12 minutes after the fire started. Smoke was blown in the other direction at a rate of about 3.5m/s. This exceeds the required rate of 3m/s.

According to the simulation the exhaust fans are strong enough to blow smoke from the railway tunnel in both scenarios, and conditions in the tunnel did not become too dangerous for passengers getting off on the safe side within six minutes or for rescue personnel arriving within about ten minutes to put out the fire.

Effect of cold also simulated
The effect of freezing temperatures on the Ring Rail Line tunnel was also simulated by Poyry Infra in Switzerland. Simulations were based on different station solutions, the geometry of the Ring Rail Line, station plans, and information on local weather conditions and train traffic. The effects of changing baseline information and engineering solutions on the temperature in the tunnel were also studied. The results can be utilised in planning insulation and other measures aimed at controlling heat in the tunnel.

Ways to reduce cold were tested by keeping pressure-balancing shafts closed at the sites reserved for future stations. This reduces the natural air flow resulting from differences in air pressure between the mouth of the tunnel and the pressure-balancing shaft (‘chimney effect’). Keeping shafts closed did not affect the aerodynamic results (air flow speed, pressure) for the Aviapolis and Airport stations significantly, so other ways to reduce cold were studied.

Different measures and structural solutions can be applied to reduce cold in the Ring Rail Tunnel according to what risks are considered acceptable. A risk-free solution, which means insulating structures so as to eliminate problems altogether, even in the coldest winters, would result in very high construction costs. Other options involve saving money during construction and using it later on to improve the effectiveness of temperature monitoring and maintenance measures. The solution that has been adopted for the Ring Rail Line lies somewhere in between. The tunnel and shafts will be insulated in areas where risks are unacceptable, and cold will also be reduced by building heat transfer tunnels between the tubes at both ends of the tunnel. Areas that remain susceptible to cold will be monitored closely and necessary maintenance measures will be carried out promptly.

Microbe population in the tunnel
A microbe population was found during tunnelling under the eastern runway at Helsinki-Vantaa Airport in summer 2010. The population consists of normal soil bacteria whose growth has been stimulated by glycol and other substances that have seeped into the ground from the runway. Glycol is used to de-ICE aircraft.

In February 2011 VTT Technical Research Centre of Finland completed a study concerning the effects of glycol seepage on concrete and steel structures. The study showed that seepage will reduce the service life of tunnel structures.

When glycol breaks down, it forms acidic by-products and carbon dioxide, which have a corrosive effect on the tunnel and its walls as well as structures extending into the bedrock. When bacteria nourished by glycol seep into the tunnel and come in contact with oxygen, this speeds up their growth. The resulting glycol breakdown products form a harmful chemical environment for steel and concrete materials.

Research indicates that in the case of the Ring Rail Line tunnel the chemical environment would cause steel and concrete materials to deteriorate. Deterioration would be rapid, and an acceptable service life (50-100 years) could not be achieved with ordinary solutions.

The Finnish Transport Agency has arranged a planning of alternative solutions and has selected seven planning offices for this purpose.

In operation in 2014
The Ring Rail Line will cost EUR 605M (USD 854M), divided as follows: Finnish Transport Agency EUR 389M (USD 549M), City of Vantaa EUR 186M (USD 263M) and Finavia Corporation EUR 30M (USD 42M). The project will receive EUR 18M (USD 25M) of TEN-T support from the EU. The line will go into operation in 2014.

The twin tunnels are being cut by drill and blast Water in the tunnel will be pumped to ditches or into the sewer network after pH neutralization Drill and blasting work is restricted by noise and vibration limitations