The blasting has started. Nine years of well planned logistics to demolish the old and rebuild a completely new hub bridging Stockholm’s south city district Södermalm with medieval Old Town – while allowing an uninterrupted flow of 480,000 daily passersby – can begin in earnest. The wind is cold and biting this February morning. At nine o’clock, a warning signal has just put the commuter flow of bikes and pedestrians to a halt. A muffled boom from underneath the blasting mats followed by a small vibration gives a hint of what’s going on.
Even so, very few of the people in the crowd are likely to give much thought to the precise calculations that just made it possible to blast away 50kg of explosives in such a densely populated area. About 4000 people live within a radius of 500m from the construction site. Eight hundred people work in the same area, and every day about 480,000 pass through the busy hub in this old sluice area, called Slussen, even if most of them go by bus or on the subway.
“The most challenging aspect of this job is actually the location,” said Anders Hoffman, project manager at Skanska AB, one of the major construction contractors in this huge project that involves more than 25 different contracts. “The flow of transport must never be interrupted by the construction work, and that requires thorough planning. Right here we have to remove at least 10,000m3 of rock. In another location this could have been done in one big blast. Here it will take a year.”
{{image2-a:r-w:300}}The Stockholm City vision is to replace the old and rundown traffic hub that was built in the 1930s with a new hub adjusted to accommodate the present traffic flow, making more way for cyclists as well as for public transport. The area will at the same time be transformed into a venue where new quays give access to the water to better utilise this meeting point between the Baltic Sea and the lake Mälaren. The scheduled completion date is in 2025.
History Abounds
History is everywhere in this area. At the moment the site looks like nothing but a big hole in the ground. The curious passersby could probably spot what’s left of the yellow floor tiles from the supermarket in the old underground shopping mall, and other traces of human activity were unearthed in another corner of the excavated area, namely several staircases dating from houses built in the 15th century. On land and in the water archaeological teams do their excavations to document as much as possible before it is all covered up again by a new dock area as well as new housing, shopping malls, roads and bridges. The latest discoveries were made in the water. Under a layer of modern remains, like shopping trolleys and rusty bicycles, various traces of business have been uncovered.
In the 1600s and 1700s this waterfront area was a bustling trading area with mills, grinderies and slaughterhouses. The location has made Slussen an important hub and focus point for various interests and discussions for centuries. Long before traffic jams were invented this was a major transport route connecting the inland with the Baltic Sea. People have settled and traded in the area since the Middle Ages. In the 17th century, 40 per cent of all iron ore worldwide was shipped through this narrow passage.
At that time elevation of the land made it gradually more difficult for ships to pass. This made the regent Queen Kristina build the very first sluice in 1642. In the early 1700s that lock proved too small and was replaced in 1751. With steamships came the need for a third and even bigger lock in 1850. By now Slussen was not only a passageway for ships and boats. More and more people were using the lock to cross between the Old Town and the growing south city district of Södermalm. An increasing flow of carts and carriages in combination with the growing rail traffic made the movable bridge an obstacle.
{{image3-a:r-w:300}}Several plans were made for a new and more modern passage. All of them were rejected, though. The arrival of the automobile in the 1920s finally got things moving.
The constant bridge openings caused long queues, making the citizens of Stockholm cry out for a new solution that could put a stop to this “Slussen misery”.
“Slussen has been rebuilt every century according to the needs of the time,” Eva Rosman, communications manager for the Slussen Project at Stockholm City, said. “When building the fourth lock in 1931 there were new problems to solve, and I imagine that there were just as lively protests at that time as now. And most likely there were as many that embraced the proposed new and modernistic style as there were people objecting.”
Sensitivity, Experience
Blasting in this sensitive environment requires experience as well as the right equipment, and Skanska subcontracted the small but highly specialised drilling and blasting company Magnus Schakt AB to do the job. “Price and experience in combination with the use of new machines that meet the environmental requirements, that’s why we awarded them the contract,” Hoffman said. “From day one they have been involved in the planning and have shared their expertise in blasting, which is a great advantage for us.”
Mikael Kauppi, the owner and operator of Magnus Schakt, is getting used to people watching his every move. The fencing surrounding the pit hole is itself surrounded by peep holes but this adds no extra pressure for the seasoned blaster. He expertly manoeuvres his Dino DC400Ri top hammer drill rig with hydraulic rollover around the work area.
{{image4-a:r-w:300}}Kauppi recognised that the challenging drill and blast environment required special equipment. “This Dino DC400Ri was the first of its kind in Sweden when I got it a couple of years ago,” Kauppi said. “It’s very flexible, agile and dependable. It drills well, fast and with great precision. It’s perfect for a place like this.”
Before blasting started in January 2017, buildings in the area were surveyed and accelerometers placed on the most sensitive houses, many of which date from the 17th century. The blasting started on street level, and initially the Dino DC400Ri was working just outside a fast food restaurant. Ideally, all windows would have been boarded up as precaution but that was not an option. The DC400Ri has a low noise level and is equipped with the patented Sandvik DustMizer system. The DustMizer binds dust by spraying a mix of water and a natural agent into the rock drill, flushing air into the lower end of the dust collector. In the process the dust is transformed into a harmless damp and grainy soil. As the work has moved further away from house facades and deeper down into the ground, the size of the blasts has become bigger.
The biggest so far has involved 22 drill holes and 61kg of explosives releasing about 100m3 of rock. At the time of writing, there is about five more weeks of blasting to reach the first target of 13m into the ground. To get the logistics right, a new temporary bridge for bikes and pedestrians was required before the drilling and blasting could begin in the neighbouring mountain that will house part of the entrance to a new bus terminal.
“Every load of two to three kilos of explosives will go off 15 milliseconds apart,” Kauppi said. “The result will be a round of
50 to 70 kilos in one blast. That’s the maximum we can use to make sure there are no vibrations damaging the buildings around us.”
Second Generation Customer
{{image5-a:r-w:300}}Sandvik Equipment has for years been a natural part of Kauppi’s specialised business. The good co-operation started when Mikael’s father Magnus Kauppi was running things.
“Since dad bought his first Sandvik drill rig in 1981 it has only been orange machines,” Kauppi said. That means that Stefan Persson, Sandvik Mining and Rock Technology’s sales engineer for surface drill rigs, has been working with two generations of Kauppis, both of whom have appreciated the advantages of using the same supplier.
Kauppi and Persson speak regularly, at least once a week. “Magnus Schakt is a great customer,” Persson said. “They are often looking for new and special solutions, like the Commando DC122R drill rig with standard diesel engine and powered with electricity to work in sensitive blasting missions for the Stockholm City Line project.”
The Dino DC400Ri working its way through the rock at Slussen is one of Magnus Schakt’s latest additions and the second of this model for Kauppi. “I like to stay at the forefront and to try the latest equipment,” Kauppi said. “Besides the rollover option on this one, I particularly like the new dust foam function – the flap feeder DustMizer. That means we do not have to deal with dusty bags and messy vacuum cleaning systems. I also appreciate that the machine is easy to dismount and transport. Unlike this project, many of our assignments are short and transportation has to be fast and easy.”
Article courtesy of Solid Ground (Sandvik Mining & Technology). Photos by Samir Soudah and Rasmus Forsgren.