Environmental factors are taken into account when building the West Metro
The Metro is a good environmental choice
The Metro is an environmentally-friendly mode of transport, which does not lower urban air quality. The introduction of the West Metro will substantially reduce greenhouse gas emissions and improve the air quality, at least in the neighbourhood of the Länsiväylä motorway in Espoo and Western Helsinki.
Calculated in passenger kilometres, it is estimated that the metro will reduce the number of car trips between Matinkylä and Kivenlahti by 20,000 km on weekdays, which is equivalent to 200-300 cars being taken off the streets. Based on an estimate for 2035, traffic-related carbon dioxide emissions are expected to drop by 1,000-2,000 tonnes per year.
The high transport capacity and durability of the Metro fleet will also add to metro’s ecological sustainability. One metro train can transport the same number of passengers as 700 passenger cars. Automation of the metro will further reduce energy consumption, as energy use becomes more efficient and passenger numbers increase.
Groundwater level under observation
During the construction process, the impacts of the metro on the immediate surroundings are being monitored. A key issue is the groundwater level, which is measured using standpipes in the impact area of the excavation work. Particular attention is being paid to potential ground settlement. For monitoring purposes, settlement pins have been attached to buildings, which enables the measurement of potential changes and prevention of damage, if necessary.
Structural damage is being prevented by ensuring that the pressure level of pressurised groundwater does not drop too low. The groundwater pressure can also be increased or maintained by recharging the pressurised groundwater table. Continuous ground settlement monitoring is being performed in the areas with a high risk of ground settlement.
On the Hannusjärvi Lake, the groundwater level is being intensively monitored during construction. The bedrock around the metro tunnel is being sealed in compliance with the highest watertightness requirements, and the drainage water from the metro tunnel is being led outside the Hannusjärvi Lake’s catchment area.
In addition to the groundwater level and ground settlement, surface water quality, the amount of seepage into the rock chamber and the quality of drainage water are also being monitored. If necessary, seepage into the tunnel is being prevented by means such as injection sealing of the rock. During excavation, water removed from work sites through access tunnels passes through a separation process for sand and oil, before being drained into the sewage system.
When in operation, the metro tunnel will have no effect on the flow or quality of surface waters. No environmentally hazardous substances will be transported or stored in the metro tunnels.
Vibration and noise levels are being monitored
Prior to and after excavation, inspections are performed on all properties within 150 metres of the excavation site, in order to examine the condition of buildings. The first inspection is performed to establish the condition of the buildings before construction work begins, and the second, post-construction inspection checks on whether any damage has been caused by vibrations.
Before excavation work begins, sensitive equipment is protected against vibration; during the work, a vibration meter is used to measure the level of vibration to which buildings and sensitive equipment are exposed near the excavation site. These measurements are monitored in real time using a separate vibration monitoring system.
In residential areas, blasting can mainly occur between 7 am and 10 pm. During excavation, it is also permitted on Saturdays from 9 am to 6 pm. Work phases that cause a great deal of noise should be performed between 7 am and 6 pm and restrictions have been set for any work phases performed at later times. Working hours and the related restriction have been set by the Espoo Environment Centre.
When completed, the metro will cause very little vibration
Once the metro has begun operating, the vibration it causes will remain minimal, and will have no impact on the durability of superstructures. The metro rails provide a very smooth passage for the trains, since they are joined by welding and are placed on a tarmac bed. ‘In the case of the current Helsinki metro, no major vibrations have been detected in either the damped or undamped sections of the tunnel.
The West Metro will not cause any noise likely to disturb people living or working in the buildings above the metro line. The ‘structure-borne noise’, based on the vibration transmitted to the building framework, will remain very low. Plans for preventing structure-borne noise have been made using 3D computer modelling, for example. This has enabled anticipation of which buildings and areas are the most susceptible to structure-borne noise, and the rail materials for these areas have been selected accordingly. Noise insulation has been installed along the entire length of the West Metro tunnel, excluding the sections that pass under the sea or the Länsiväylä motorway, where it is not needed.
Measurements were performed to monitor how well noise and vibration targets were met; measuring devices can be installed in locations such as the cellars of residential buildings. According to the measurements made, the structure-borne noise level has remained below the target value of 30 decibels. Even on quiet premises, sounds made by the metro cannot be discerned above the background noise.
No important cultural sites on the metro line
The metro line has been mapped to identify any sites with valuable landscapes or of high cultural historical value. No such sites have been found in the immediate vicinity of the metro line. The nationally valuable Kauklahti railway station is located around two kilometres north of the line, and the summer cottage settlement along the old Helsinki steamship routes is located in Suvisaaristo, south of Soukanniemi. These areas are located far from the metro line’s small-area superstructures, and the bedrock construction has no effect on them.
In addition, no ancient monuments protected under the Antiquities Act, historically significant roads or known sections of the First World War fortress zone have been identified in the immediate vicinity of the metro route.
A metro running deep underground is environmentally safe
Because the West Metro line runs deep along the entire length of an underground tunnel, the line has no immediate environmental impacts. The construction work has no impacts on areas that form part of the Natura 2000 network, nature reserves or areas belonging to nature conservation programmes.
Birdlife around the Finnoo wastewater treatment plant basin has been taken into account in the construction work, with the contractors avoiding very noisy overground construction work during the nesting season. Nor does the construction work endanger areas inhabited by flying squirrels, or the breeding or habitats of the moor frog.
The flying squirrel habitats in Finnoo were mapped and studied before the construction work began. The metro shafts in the area have been located so as to cause flying squirrel habitats as little disturbance as possible. The environmental permit defines which main passage routes, or tree-top connections, used by flying squirrels must be preserved. All tree felling in the flying squirrel area has been performed before the nesting season, before 1 April.
The flying squirrels have been taken into account by various means during construction. For example, a so-called tree protection fence has been built on both sides of the work site access road leading to the Suomenlahdentie metro shaft. This protects the trees used by flying squirrels and guarantees their continued access to the area. At the Meritie access, the temporary transfer of the main water pipe to make room for the metro shaft was implemented using an overground solution, eliminating the need for excavation on the side of the flying squirrels’ forest.