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Rock crumbles at the Central Library worksite


Liisa Joensuu/Tmi Magic Words

Even though the Central Library will be a modern library for the digital age, it is born through very traditional methods. In December 2015, there is rock blasting, removal of rock waste and digging soil going on in the pit outlined by supporting walls. Even for unique architecture, the soil must be prepared by the usual methods.

Digging and blasting could only begin after the district heating and cable technology crossing the worksite had first been moved onto new routes. More than 50 park trees also had to be removed from the area, so that the city could move them and plant them elsewhere. In addition, starting the work requires traffic arrangements and new signage; the signs for bicycle and pedestrian traffic start already from Linnunlaulu.

There are many glass buildings around the Central Library worksite, so the areas where blasting is done are carefully protected. This is done using blasting mats, which can be seen in a pile on the left side of the image. The blasting mats are made out of old lorry tyres bound to each other with steel cables.

The Chief Planner of the Central Library project, Pirjo Lipasti from the Helsinki City Library, is familiar with the project’s years of history. Now that there is finally activity at the plot, it is a pleasure to have a meeting with the site manager Kyösti Kontio and the site engineer Risto Sell from the earthmoving company E.M. Pekkinen Oy. The plan drawing that shows the rectangular shape of the building’s foundation was being studied at the site office. E.M. Pekkinen Oy acts as the main contractor during the work on the foundation and the concrete construction in the library basement, i.e. until the autumn next year.

“There are 20,000 cubic metres of soil to be excavated in total, and we had already excavated 17,000 cubic metres at the start of December, so the digging is nearing the end. The contaminated soil was delivered to the appropriate locations, but a large amount could be reused. The clean soil has been used in areas such as Jätkäsaari to provide a foundation for park construction, in Vuosaari to fill in old dock basins and in Petikko to build a golf course,” says Kyösti Kontio.

A historical period of construction is ongoing in the Helsinki city centre. The Parliament Building is being renovated at the same time as the construction of the Central Library is starting. The tarpaulin with an image of the Parliament Building gives almost a castle-like impression. You could hardly find a more valuable neighbourhood or location for construction in Helsinki.

One of the first actions at the Central Library plot was to construct a fence around the worksite.
“We made one of the finest fences of all time while we were at it,” Kyösti Kontio opines.
 The services of the Central Library are presented in words and images on the pale blue plywood base. The fence is nearly half a kilometre long, which means that it has plenty of space for a general discussion of the Helsinki City Library and the Finland 100 jubilee year; the library is one of the projects of the year.

“The Central Library is a meeting place of many different kinds of thoughts and ideas, which is why a part of the fence is reserved for announcements by citizens and organisations,” notes Pirjo Lipasti.

The fence has holes, through which you can take a peek at the phases of construction. The southernmost holes are at the Sanomatalo building’s side of the fence.

Inside the plywood fence, the pit is lined with a total of 1,800 square metres of sheet pile wall. The steel supporting wall has been anchored into the ground by using 80 evenly spaced anchors. The purpose of the sheet pile wall is to keep the soil outside the pit in place and prevent the nearby streets from starting to slant towards the pit.

The pit is 40 metres wide and 160 metres long – much longer than a football field but about one half narrower.

The beavers have taken over the worksite

In December 2015, there were 20–30 people working at the worksite depending on the requirements of different phases. Nearly one half of the people at the site are from E.M. Pekkinen, and the rest are subcontractors. Recently, a brand new sticker has appeared on the helmets of Pekkinen’s earthmoving experts: a beaver reading a book.

The sticker is an inside joke that improves the team spirit. When Salla Savolainen, a children’s book illustrator and the wife of the site manager Kyösti Kontio, presented the idea and a sticker showed up on Kyösti’s helmet, everyone wanted one just like it. The beaver is reading a construction guide. The back cover says: Part one, foundations and basement. The beaver can also be found on the official logo of E.M. Pekkinen, but here it has found a more playful form. Among other things, Salla Savolainen is known for illustrating the ‘Heinähattu ja Vilttitossu’ children’s books by Sinikka and Tiina Nopola.

The “beavers” were tasked with blasting 10,000 cubic metres of rock in total. They prepared for the task by conducting extensive inspections of the nearby properties. All in all, roughly 400 computers sensitive to vibration were protected in the neighbourhood.

“There are 11 vibration meters in the surrounding area monitoring the passage of the blast waves. The meters have been placed in locations such as Kiasma and the Music Centre. The vibrations caused by the blasts have been so small that the meters have barely registered them. We carry out the last blasts before 6 p.m., so that we won’t disturb the evening concerts at the Music Centre. The meter at the Music Centre has not so much as peeped once,” Risto Sell says.

The blasting will continue until the next year, probably until the turn of March, if everything stays on schedule. In the sensitive environment, the vibrations caused by the blasts have been purposefully maintained at only one third of the legally permitted level of vibrations due to blast waves.

The earthmoving work will continue until March, when the concrete construction phase will begin according to the schedule. The foundation stone of the Central Library will be laid in May, after which the construction of the basement floor can begin.

The formwork, concreting and construction phase are done completely by hand. Prefabricated units are not used in the foundation and basement work, which means that when there are no seams between elements, the building can be made more securely leak-tight.

The Central Library will open in December 2018.

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