In 2016, one of the service tunnels connecting the project to the existing railroad in the Oslo Port had to go under the access tunnel for the port’s underground oil depot. The access tunnel was equipped with pipes used for transfer of oil coming by ships into the depot as well as to the trains transporting it for processing. Due to the importance of the equipment in the access tunnel there were very strict limitations for vibrations. The limit was 10 mm/s and the construction company planned to continue D&B up to 40 m from the crossing, then they wanted to start using Drill & Split (D&S) method to prevent exceeding the limits. However, at a distance of 55 m the contractor exceeded the vibration limits almost four times (38 mm/s). It was decided to go for Drill & Split, but that meant significant losses of time & money. The D&B advance just before the stop was 1.5 m per day compared to D&S that was only 30 cm per day.

As a supplier of the project with explosives and detonators. Austin Norge offered a solution to this challenge. The blasting pattern was revised for using Emulex cartridge products and E*STAR detonators were introduced with specially prepared timing. Utilizing QED and Blasting Solutions software packages were used to prepare the optimal configuration. A series of full profile blasts were done with very promising results and predictable vibrations.

After the initial tests the D&B continued with daily advances of 1.5 m (one blast per day). Later in the project, the face was split into top and bottom sections to be blasted separately. The full face had 160 holes, utilized the same number of E*STAR detonators and 148.5 kg of Emulex explosives with specific consumption of 1.21 kg/m3. There was continuous presence of Austin technical support on site to provide expertise, needed changes in the charging, or the timing plan, based on the measured vibrations as well as the programming and blasting of E*STAR detonators. Over a period of 5 weeks the project advanced past the 40 m distance line and continued up to 28 m from the tunnel crossing when the D&B was stopped by the contractor.

In 5 weeks Austin managed to get the customer 12 m closer to the tunnel crossing than it was originally intended, saving 40 work days and 20,000 USD on D&S, compared to the original plan.