The N1 Porto tunnel project is a 650m segment of large-scale civil engineering plan to improve traffic flow between Porto's downtown district, the Santo Antonio hospital district and the highway access. The tunnel is being excavated into a massive "Granito do Porto" granite structure, 4 - 20m below a highly urbanized environment of Porto, Portugal.
The project was originally started in 2000 and was stopped due to the inability to mechanically excavate the granite rock. The city of Porto engineers then turned to traditional drilling and blasting techniques.
The use of traditional electric or non electric detonators did not easily comply with the specified environmental and safety requirements concerning blast and vibration control, resulting in the process taking far too much time. The introduction of digital blasting was proposed to overcome these concerns.
The tunnelling operations started again on January 2004 with 50Kg and 1.0m (3.3 ft) blasts 4.5m (15ft) below Porto building foundations. The use of the DAVEYTRONIC® digital blasting system improved the tunnel advance rate, +190% in sound granite.
An overall reduction of 60 operating days in the duration of the excavation of the upper section of the project was reached, while maintaining all specified environmental standards.
This timesaving will permit the contractor to complete the tunnel construction in the City of Porto specified period of one year.
