Planned precision

STOCKHOLM, SWEDEN. Drilling and blasting in the cramped confines of central Stockholm requires a steady hand, perfect planning and agile equipment that can do its job accurately.

The blasting has started. Nine years of well-planned logistics to demolish the old and rebuild a completely new hub bridging the 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 morning in February. 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 50 kilograms of explosives in such a densely populated area. About 4,000 people live within a radius of 500 metres 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.

Challenge accepted
“The most challenging aspect of this job is actually the location,” says 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 10,000 cubic metres of rock. In another location, this could have been done in one big blast. Here it will take a year.”

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 utilize this meeting point between the Baltic Sea and the lake Mälaren. The scheduled completion date is in 2025.

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.

Sandvik solution

Dino DC400Ri with hydraulic rollover proved a good choice for the Slussen project – easy to transport, compact and flexible. The drill rig is well suited for a construction site with limited space. It is possible to drill both vertical and horizontal holes. Dino DC400Ri has a low noise level, which is important at a site beside a residential area. It is equally important to minimize dust. The drill rig is equipped with the Sandvik DustMizer system, a dust collector with flap feeder and water tank.

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.

History abounds
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 percent 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. 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,” says Eva Rosman, communications manager for the Slussen Project at Stockholm City. “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.”

<p>Excavation at Slussen unearthed an ancient stairway and relics from a bygone era.</p>

Excavation at Slussen unearthed an ancient stairway and relics from a bygone era.

<p>Mikael Kauppi, owner of Magnus Schakt, depends on the flexibility of his Dino DC400Ri.</p>

Mikael Kauppi, owner of Magnus Schakt, depends on the flexibility of his Dino DC400Ri.

<p>Passersby are mesmerized by the ongoing redevelopment work beneath their feet.</p>

Passersby are mesmerized by the ongoing redevelopment work beneath their feet.

Blasting in this sensitive environment requires experience as well as the right equipment, and Skanska subcontracted the small but highly specialized 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 says. “From day one they have been involved in the planning and have shared their expertise in blasting, which is a great advantage for us.”

Agile and precise
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.
Kauppi recognized 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 says. “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 Dino 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.

In another location this could have been done in one big blast. Here it will take a year.

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 61 kilograms of explosives releasing about 100 cubic metres of rock. There will be about five more weeks of blasting to reach the first target of 13 metres 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 says. “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.”

Long-term partnership
Sandvik equipment has for years been a natural part of Kauppi’s specialized business. The good cooperation 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 says.

That means that Sandvik Mining and Rock Technology sales engineer for surface drill rigs, Stefan Persson, 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 says.

Tech specs Dino DC400Ri

Recommended hole diameter: 51–76 mm/2–3 in
Drill rod/tube diameter: 32, 35, 39 mm
Hydraulic rock drill: Sandvik RD414, 14 kW (19 hp)
Engine: Volvo TAD570VE, 105 kW (141 hp) (Tier3)/Volvo TAD570VE, 105 kW (141 hp) (Tier4F)
Flushing air capacity: 3.5 m3/min, up to 8 bar
Transport length: 6.6 m/21.7 ft
Transport width: 2.35 m/7.7 ft
Transport height: 2.8 m/9.2 ft
Weight: about 10,000 kg/22,000 lbs

“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 says. “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.