Drill+split first for Norway’s Oslo-Ski Follo Line 07 Oct 2015

The main tunnel works for Norway’s largest transportation project, the Oslo-Ski Follo High Speed Rail Line Project, are officially initiated by the country’s Minister of Transport Ketil Sovik-Olsen.

Norwegian Minister of Transport Ketil Sovik-Olsen (left) and Elca Romano of drill+blast works contractor Condotte
Photo credit: NTB Håkon Mosvold Larsen

As part of the main US$156 million drill+blast works – one of five EPC contracts covering construction of the 22km-long Follo Line Railway between Oslo Central Station and the new transport hub at Ski – Italian construction company Società per Condotte d´Acqua SpA (Condotte) will execute the drill+split excavation method. This will be the first time such a method has been utilised in Norway.

The construction area is located in Ekeberg Hill, close to Oslo Central Station. A cavern is to be built to combine the inbound Østfold Line and the new double track Follo Line, which will cross existing tunnels and infrastructure including a crossing of Ekeberg Oil Depot. Due to the sensitive urban location, some of the works will be conducted using the drill+split method, without the need for traditional blasting.

Drill+split is selected for the Follo Line due to the proximity of sensitive surrounding infrastructure and existing tunnels. Project Director Erik Smith, for the owner the Norwegian Rail Administration (Jernbaneverket), said Condotte has extensive experience that is directly relevant for this challenging aspect of the Follo Line Project.

Briefly, the method involves drilling a large number of holes in the tunnel face following a precise geometric pattern. Splitting of the rock is achieved by a hydraulic cylinder that forces a wedge into the drill hole, breaking the rock into smaller pieces in the process. The method implies very low vibration and enables a high measure of control of the drilling operation.

Drill+split to be used for sensitive excavations under Ekeberg Hill

The contract with Condotte for the EPC drill+blast works was signed in February this year. The planning, engineering and design process commenced immediately after the signing of the contract, along with various other preparatory activities. Condotte established its construction site in May, and in August the first tunnelling activities were initiated. Following an early construction phase using drill+split, drill+blast will be the main excavation method.

The official initiation ceremony, attended by Norwegian Minister of Transport Ketil Sovik-Olsen, took place at the Follo Line Project’s construction site at Sydhavna in Oslo, where the construction of a new tunnel for the inbound Østfold line now has begun.

The EPC drill+blast contract is scheduled for completion by early 2018. The US$1.2 billion contract to excavate 20km of twin running rail tunnels using 4 x 9.1m diameter TBMs is held by Acciona/Ghella. Obrascón Huarte Lain (OHL) holds the US$310 million contract to remodel Ski Station and construct the 3.5km of overland alignment along the 22km-long route.