Mikkelä vehicle tunnel excavation

​HSY’s Board of Directors approved on 14 November 2014 Skanska Infra Oy as the contractor for Espoo’s Mikkelä vehicle tunnel and open excavation with its tender price excluding value added tax at 5,450,000 euros.

A total of approx. 70,000 m3 of rock needs to be excavated. The open excavation will focus on the extension of HSY’s Mikkelänkallio depot. The vehicle tunnel of approx. 900 m is to be excavated in the southern edge of the open excavation bends under Ring III in two branches. They will enable the efficient continuation of the excavation of the actual caves in the Blominmäki bedrock later on.

​Contrac​t schedule

The contract lasted until September 2015.

Pre​​paratory work

  • Tree felling and clearing begins in week 49.
  • Site fencing, weeks 50–51.
  • Establishment of the site base, weeks 51–01.

​Excavation a​nd finishing work

  • Open excavation to the tunnel’s mouth, weeks 51–8.
  • Vehicle tunnel excavation from the mouth approx. 300 m, weeks 9–24.
  • Courtyard open excavation, weeks 9–24.
  • Courtyard pipeline trench excavation and finishing work, weeks 25–30.
  • Vehicle tunnel branch excavation 300 m onwards from the pile, weeks 25–36.
  • Contract completion, week 38.

​Work ​shifts

  • Open excavation phase and vehicle tunnel in the 1-drift phase, Mon–Sat 6 am–10 pm.
  • Vehicle tunnel in the 2-drift phase, uninterrupted three-shift work.


The noise caused by the drilling work may cause disturbances to the surroundings. Blasts will cause vibrations.

The shock wave created by blasts may cause windows to ring. The shock waves will be dampened with rubber and log mats. Blast smoke from the tunnel will exit at the mouth of the vehicle tunnel. A sound signal will be emitted before the blasts. Kalliotekniikka Oy will take care of property inspections and damping of equipment sensitive to vibrations. Before starting the excavation, a bulletin will be distributed to the nearby properties within the area of impact of the excavation.


In the open excavation phase, traffic will be stopped before blasts on Mikkelänkallio and Kulkurinmäki roads. Also in the beginning of the contract, there may be a need to use the Mikkelänkallio road as a waiting area for lorries. Traffic signs will be used to warn about the site and site traffic. The site traffic will be mostly lorry traffic. Road cleaning will be carried out as needed.

A maximum of approx. 20 loads of rock waste per hour will be transported away from the site avoiding rush hours. During the day, a total of approx. 50 rock waste loads are driven and at maximum approx. 100 loads. Other traffic caused by the site is minor.

​Site inspector: Reino Väisänen, Ramboll Finland Oy
Client’s representative: Jari Heikkilä, Ramboll Finland Oy​