About Project
The project involves around 14 km of tunnels, 7 stations and the removal of around 3 million cubic meters of rock. The tunnels and stations will be excavated by drill & blast and reinforced with rockbolts and shotcrete. A part of the tunnels and the Koivusaari station will be located under the sea. The metro line travels mostly under urban areas with high rise buildings and other critical structures.
Project Name
Länsimetro (the westward extension of the Helsinki – Espoo metro line)
Location
Helsinki & Espoo, Finland
Construction Period
2010 – 2017
Contractor
Länsimetro Oy
Designer
Rockplan Ltd
Another tunnel engineering challenge, which is quite common both in soil and different rock types, is the impact of an underground cavern on its surroundings. Vibrations from blasting, fall of the groundwater level and other excavation influenced processes can cause displacements to the structures near the cavern. Due to tectonics the in situ horizontal stresses near the surface in hard rock in Finland commonly vary between 5-15 MPa. In tunnelling projects this usually means rise of the overburden and shear in joints. Uneven rise and settlement alike, can damage foundations. The forces causing the displacements and deformations are high and so usually uncounterable with reasonable reinforcement measures. For that reason additional effort is put on the design of the best shape and placement of the excavation. That is exactly the case in Länsimetro project.
Länsimetro is a new metro line, that will transport over 100,000 passengers per day from Helsinki centre to Espoo. The project involves around 14 km of tunnels, 7 stations and the removal of around 3 million cubic metres of rock. The tunnels and stations will be excavated by drill & blast and reinforced with rockbolts and shotcrete.
A part of the tunnels and the Koivusaari station will be located under the sea. The metro line travels mostly under urban areas with high rise buildings and other critical structures. For example at Keilaniemi there will be four tower buildings 100 m tall, near or above the metro line and station. The foundation pressure of the buildings will be between 2 and 4 MPa each. In situations like this it is vital to forehand simulate the interaction between the tunnels and the surrounding structures so that critical parts of the construction can be identified and the designs can then be optimized accordingly. It has to be confirmed that the additional load on the surface will not damage the tunnels and the tunnels on the other hand will not cause unacceptable displacements on the foundations of the structures above. Working with this kind of cases with such a variable shapes and load distributions 3D modelling is required to reach the required precision.
