When the rock work for the new Building 29 at the University Hospital in Umeå was carried out, precision and caution were in focus when the 60 metre long, 10 metre deep and 14 metre wide shaft for the culvert system was blasted out.
- We had to work with extreme precision and sensitivity, given that we were so close to the hospital's radiation unit with, among other things, vibration-sensitive equipment, says Lasse Melin, at Norrbottens Bergteknik.
Building 29 is a new property for a pharmacy, forensic medicine, IVF clinic and administration. Norrbottens Bergteknik was responsible for drilling, rock excavation and steel sheet piling for the foundation and the connection to the hospital's culvert system.
Sophisticated blasting
To make the blasting as gentle as possible, sensitive blasting was used with many holes and tight spacing, about four holes per square metre.
- This is a method that we use in contexts where the conditions are particularly sensitive. The blasting is very controlled and gives good results, says Lasse.
Steel sheet piling protects against collapse
Precision was also required for the rock reinforcement work. 12-metre long and 127 mm wide steel pipes were drilled down with a c/c distance of about one metre and welded together to stabilise the ground and protect the shaft from collapse and subsidence. This was particularly important for the surrounding hospital properties that stood a few metres from the edge.
The steel sheet piling was reinforced with surrounding steel hammer bands. These were anchored with 12 metre long bolts to a diameter of 76 mm and tightened with 110 tonnes. The drill holes were grouted with concrete before the bolts were tightened with a hydraulic torque wrench.
- The work went well and the co-operation with our client Umeå Entreprenad and Region Västerbotten went smoothly. All visitors and employees also showed an understanding of our work, says Lasse.
