Active design is an expression that has been used fore some years now. This paper will present a case study from an excavation of two cavern constructions (80m long × 16m wide × 12m high) and access tunnels in a Bryozoan limestone in southern Sweden. By using various geophysical survey methods like for instance resistivity soundings, in combination with core drilling and geophysical well logs a geological model of the proposed construction site could be created. In this process not only the geological composition was studied but also the physical properties of the limestone was investigated. The geological model gave indication of how the final design of the caverns should be carried out to overcome problems with fault zones and ground water intrusion. During the excavation of the limestone from the cavern rooms, geological surveys were carried out to assist in the event of a redesign of the cavern constructions. The active calibration of the geological model made it possible to change and reduce the reinforcement of the rock mass. Measurements of the overburden were also taken during the excavation to monitor the setting/compaction of the limestone cover. After the cavern constructions were completed but before the final lining of the rooms, the limestone exposed at cavern walls and roof were surveyed i.e. the induration and fracturing was determined. This was done in an attempt to calibrate and validate the geological model. By active design and calibration of the geological model during the complete excavation, it has been possible to optimize both the location as well as the final cavern design. For the purpose of this article it has also been possible to reveal the actual geological explanations supporting the basic geological model.
Some of the Tele communication facilities in Sweden are designed as underground constructions.