STOCKHOLM BYPASS | PROJECT
Above: Horizontal drill core through the regional fault zone showing several meters of continuous core loss (pieces of wood)
CAPITAL TRAFFIC CHALLENGE Stockholm, at present, has major road traffic problems. The current motorway, and Stockholm’s main traffic artery, is called Essingeleden. It became operational in 1967, shortly after Sweden switched to driving on the right-hand side of the road. It includes a 210m-long tunnel, the Fredhallstunneln, which lays claim to be one of the busiest in Europe. Essingeleden itself is the busiest road in Sweden.
It was designed for an estimated 80,000 vehicles a day and currently takes around twice that rate. It is, therefore, heavily congested, subject to delays, severe wear and tear, and there is frequent need for lane closures for maintenance. It is also subject to a congestion charge, money from which is helping to pay for the Stockholm Bypass - the cost of which is projected to be SKr 51.0 billion–Skr53.5 billion (US$5.1 billion–US$5.4 billion).
DEVELOPING A SOLUTION As well as being huge, Stockholm Bypass has been a long time coming. It has been in planning, in various forms, since 1966. Permission to build was granted in 2009 and the project has been under construction since 2014, though there was a pause of several months thereafter following elections and a change of government before works restarted, in 2015. Stille joined the project in 2017. “That was in what you might call the middle of the process,” he says.
Each tunnel is about 17m wide – “actually 16.4m with
some over-blasting,” he says. “You always take a little more rock when you drill and blast.”
GEOLOGY AND TUNNELLING “It is a drill and blast project rather than excavated by TBM; the Scandinavian geology rather dictates that,” says Stille. Geologically, the area has hard crystalline rocks,
gneiss and granites - “fairly old - about 2 billion years,” he says. “So as an old rock it has gone through a lot of different tectonic sequences. A lot of things have happened to it. But the matrix is hard and of good quality, generally speaking.” Such rock is hard to tunnel through; the payback is
that, once tunnelled, the tunnel has strength. For most of the route of the Stockholm Bypass the rock walls are self-supporting, he says. “It doesn’t really need support in a global perspective,”
he adds. “But we may have wedges of rock that could move, or we may have blocks that could fall out, and those we support with rockbolts.” He continues: “Of course, there could be smaller
blocks as well, and something could happen to those over time, so we do support the surface with shotcrete. But that is only to carry fairly small loads. Generally speaking, the shotcrete is only about 50-75 millimetres thick. It is only to protect against the smaller rocks falling.”
Table 1: Mechanical properties for the rock mass in the regional fault zone utilised in the numerical calculations
Parameter
Cohesion [MPa] Friction angle [°]
Young’s modulus [GPa] Tensile strength [MPa] Poisson’s ratio [-]
Transition part 1.0 46
0.01 0.25
Centre part 0.6 35
Dilation angle [°] 00 3.0
0.7 0
0.25
April 2025 | 15
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