By Peter Samuel
Work proceeds on the southern section of the Stockholm ring road. The toll roadway of 4.5km length has 3.5km underground and 1.0km of surface work plus a bridge. It involves twin tubes, 3-lanes in each direction. The underground 3.5km section is mostly driven tunnel in hard granite and involves two three-level director connector interchanges underground that involve separate tubes and bridging, and extra tunneled approaches where there is some cut and cover work. A total of nearly 20km of tunnel is involved counting all the air shafts, drains and separate ramps as ell as the mainline. The design is for 70km/hr posted speed with 3.5m wide (11.5') travel lanes, a rightside breakdown lane of 2m (7') and leftside 1m (3.3'). Overhead there is 5.8m (19') pavement to ceiling with 1.0m for signage and ventilation jetfans giving 4.8m clearance (15.5') for traffic. 1.6m cub meters of rock is being removed. American made Atlas Copco rigs are drilling the rock which is loaded with site sensitized emulsion explosives and wheel loaders are removing spoil. Construction is under buildings so the explosive strength has to be precisely controlled. Heavy grouting of the route is required to prevent the tunnel acting as a drain which could lower the water table in the area.
The section under construction is part of an originally planned 14km of new urban motorway that was in a ring of about 4km radius from the historic center. 6km of existing surface and elevated motorway formed the western part of the ring, and north and south sections being partially built form spurs off this. Amid enviro/neighborhood protests, litigation and cost increases, an eastern section has been abandoned at least for now. The original plan involved a full ring of 20 centerline km, 21 full or partial interchanges, most underground and 28 toll points. The rationale was to intercept all radials into the center and direct traffic around and under surface streets or into parking structures. Ventilation structures were a major source of controversy and the present work is a major compromise on the original plan. It is a C-shape plan. (see TRnl#13 March 97 p4)
Another major part of plans to improve the center of Stockholm is underground carparks, 14 of which have been designed. Housing 2500 vehicles they will cost $70m or $28k/parking place. Five are being built as rock caverns in self-supporting rock while nine, in poorer conditions, are conventional concrete structures. A city-owned company will own them and pay for them with parking fees.