Access tunnel for metro extension in Stockholm saves 200 tonnes CO2e

The contract was mainly soil excavation, rock excavation, rock reinforcement and sealing by grouting for tunnels as well as earthwork and water /sewerage work:

• Execution of one tunnel in rock.

• Rock tunnel was used as a working tunnel for 4713 Main tunnel contractor and as a service tunnel after the project was completed.

• Open cut is about 120m long.

• Rock tunnel about 235 m long.

• Cross tunnel of about 30 m long is also included.

Fence and gates were also set up around the work area.

There was an environmental permit which regulated all the critical activities that interacted with the surrounding environment during the construction phase.

The contractor put together a project specific sustainability management plan that gave the strategies and plans for all aspects of sustainability. The plan consisted of an introduction, purpose and application, information about the project, management of sustainability aspects, risks and opportunities and report and follow up.

Each aspect was described, had a goal, listed measures to reach the goal and how to follow up and report them and who was responsible for each part.

The aspects evaluated were:

• Groundwater impact

• Noise

• Vibration

• Discharge to water

• Chemical products

• Built in products

• Resources and climate impact

• Waste management

• Socially sustainable product chains

• Air pollution

• Dust and clean work site

• Nature, historic environment and remains

The contractor was also certified according to ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018

People and communities

During construction stage there were several ways for the community to leave comments, such as through costumer service, mailbox, open houses (some postponed due to covid), information stands at municipality days/markets.

Every year the team conducted an attitude survey and sent out newsletters to update the community. Before each blast text messages had been sent out and information video for kids has been produced and shared. There was also a separate project website, a Facebook page and LinkedIn.

Through the legal process there was also an environmental permit that regulated how aspects that can affect nearby residents must be managed and controlled, such as noise and vibration and water management.

Land use and landscape

The construction site and the tunnel started at a previous industrial site. All openings can withstand 100-year rain with a climate factor of 1.2 without damaging the facility.

Delay reservoir had to be 12 m3 to withstand a 100-year rain. The reservoir is now 30 m3 and thus, with margin, large enough to cope with surface water runoff.

Environmental permit regulates how contaminated soil is to be handled, which is strictly followed in the project.

The water environment

A water budget was drawn up, calculating how much water was used in different processes. A control program was put in place according to environmental permit and drainage water was checked and measured continuously.

Rainwater water was reused for blasting/dust management and a water treatment plant was also put in place.

Transport

Suppliers of concrete, gravel, wood and asphalt were chosen based on their distance from the project location. Steel was sourced from Swedish suppliers.

Unloading took place at night to reduce the environmental impact, especially with regard to traffic congestion on the local streets.

Train and boat transports were not possible to the project due to the location of the project. Therefore, the project made the best of the situation and tried to use the trucks as resource efficiently as possible. For example, both explosives and grouting cement were delivered on delivery rounds where the supplier collects several deliveries within the same area and coordinates these.

Physical resource use and management

A workshop was held to evaluate efficiency and resource use and impact. The identified measures were listed in a resource plan where they were followed up.

The climate impact was reduced by about 200 tonnes of CO2 equivalent, compared to design, even with more tunnel excavation than originally planned. Much of this was from the changed recipe for grout.

There was a separate mass management plan put together. Products were environmentally (and health) evaluated through Swedish system ”BVB” where they were also logged with information about the products, such as recycled content and waste management for the products.

Energy came from 100% wind power through green contracts and 100% HVO (Hydrogenated vegetable oil).

Suppliers were assessed regarding social sustainability (how large amount will be used, whether the material contains risk material and whether the material comes from a risk country).

A locally placed crushing plant has been put in place (agreement between client and municipality). This has been used for excavated masses and to buy back bulk fill. No waste was sent to landfill.

The client’s drivers were primarily to use BREEAM Infrastructure as a tool to constantly improve the environmental and sustainability work and to increase its sustainability standard between each contract.

A receipt on doing the right things measured on an international level, concrete way of showing environmental work. Motivation is branding and communication and the client's bonus.

A particularly innovative element was the manual ventilation in tunnel so it could be changed after needs to reduce energy use.