Our assignment
BanaVäg i Väst is one of Sweden’s largest infrastructure projects and comprises 16 sub-phases. The phase between Bohus and Nödinge is divided into three construction contracts in which Skanska Sweden is working on the single largest BanaVäg i Väst phase, namely, the general contract E33.
We work in a heavily trafficked and accident-prone area. Creating a safe working environment has thus been a key component of our planning work. Well-planned traffic detours enable us to create separate surfaces between the worksite and existing traffic.
During the course of the project, traffic will be redirected in a number of phases to enable the entire expansion. When working in the proximity of operational railways, railway guards are constantly on duty to ensure that the work can be conducted safely.
Skanska’s subproject commenced in August 2009 and is scheduled for completion in December 2012. At its peak, 150-200 people are working on the project.
The construction process
The stretch on which we are working is located in the Göta Älv Valley, which has low-lying sections alongside the river with thick clay layers that are limited to the east by very hilly areas of exposed bedrock. The bedrock slopes to the west and in some areas very steeply.
In some sections of the project area, the clay is more than 60-meters thick. The clay is also very loose in large sections of the area and there are also elements of quick clay. Minor shortcomings in the excavation and filling work can have major consequences, the worst of which are landslides. Accordingly, we have a number of fulltime geo-engineers working on the project.
Strict restrictions govern the conduct of our work. For all excavations and filling material larger than two meters, geo-engineers must participate in the pre-task planning and approve the work plan and procedures.
Foundation-reinforcement crucial
A large portion of the work involves foundation-reinforcement work, including pile driving, lime-cement pillars, temporary reinforcements using sheet piling and light filling material.
When pile driving, we have driven concrete or steel piles down to the bedrock to form a foundation without the risk of subsidence. In this project, pile driving has primarily been used at the Jordfall Bridge site.
Lime-cement pillars are the strongest and most cost-effective way of avoiding subsidence. A machine that is slightly more than 20-meters tall uses a rotating “whisk” to drill into the ground and inject a composite of lime and cement into the drilling hole. The lime cement subsequently absorbs moisture, allowing the cement and lime to harden into a pillar in the ground.
When temporary sheet-piling reinforcements were used, we vibrated steel planks into the ground, which create a “wall” allowing us to excavate downward vertically on one side without being forced to use shallow embankments, which take space. How deep we drove the sheet piling planks depended on how deep we needed to excavate.
Subsidence future proofed
The foundation bed was filled with light filling material, lightweight-expanded aggregate or polystyrene foam, which has a significantly lower density than traditional rock crush material. As the weight is reduced; so too is the risk of future subsidence.
This type of project entails stringent restrictions on movements in the existing surroundings. When working in proximity of the rail track (which we essentially always are) and the Jordfall Bridge, we conduct daily control measurements of any movement in these structures.
Road construction
In the construction of the local road east of the E45, parts of the bedrock were blasted away, thus creating a shelf on which the road can rest. We always work in close proximity to the existing traffic, which makes the work complicated. The bedrock that we blasted is also very high and sloping. The slope made access difficult for the drilling rigs and other machines. The height requires us to blast the bedrock in several height phases.
Extensive fissuring in the rock required sawing out certain sections to enable the careful removal of rock. The final rock face has been strengthened with bolts and braces for safety reasons.
The entire power grid was rebuilt. Many excavations are very deep and to create a safe traffic scenario, we deployed excavation-free methods for a number of power lines. This requires us to either drill or force the power lines underground, which means that we only have to excavate the starting and end points.
Every day, the Bohus-Nödinge stretch accommodates 26,000 vehicles, about 9 percent of which comprise heavy-duty vehicles. Accordingly, the expansion is being conducted in phases to allow traffic to flow as usual.
Railway construction
At the same time as we are expanding the railway track, existing rail traffic must operate as usual, meaning that 60 trains pass our working area every day.
For the new track to be connected, rail traffic was completely shut down for five consecutive weeks during the summer, both in 2010 and 2011, at which time we demolished the former railway, reinforced the foundation and subsequently built up a new track. During these intense weeks, work was conducted round-the-clock, seven days a week. Replacement buses were used and freight transportation was transferred to trucks.
Jordfall Bridge
The Jordfall Bridge accommodates about 22,000 vehicles per day, about 9 percent of which comprise heavy-duty vehicles. We have thus built the bridge in phases to allow traffic to flow as usual.
The expansion has been conducted under a well-planned process, whereby we began by building parts of the new bridge, which were subsequently connected to the existing bridge. We then demolished the old sections to be removed and finally join the last sections to create a complete traffic junction. In total, the construction encompasses six major phases.
When we are finished, we will have a grade-separated crossing (traffic junction) instead of the previous traffic-light controlled junction.
The project in figures
• 325,000 cubic meters of excavated earth
• 70,000 cubic meters of excavated rock
• 400,000 tons of crushed materials
• 26 000 cubic meters of light filling materials (lightweight-expanded aggregate and polystyrene foam)
• 45,000 tons of surfacing
• 21,500 meters of power lines
• 9,000 meter power lines and cables
• 1,000 meters of bridge/trough/wall for the new traffic junction in Bohus
• 900 meters of concrete walling with noise barrier along the E45
• 540,000 meters of lime-cement pillars
• 8,000 meters of concrete piles
• 6,500 meters of steel piles
• 14,500 cubic meters of concrete
• 1,650 tons of reinforcement bar
