Extension of the cantonal and uni­ver­sity lib­rary of Fribourg
Extension of the cantonal and uni­ver­sity lib­rary of Fribourg

Extension of the cantonal and uni­ver­sity lib­rary of Fribourg

“Jardins cultivés”* is the name of the ex­tension and building alteration project of the Cantonal and University Library (KUB) of Fribourg. This pro­ject will create a modern and attractive library for the uni­versity and resi­dents of Fribourg. As a cons­ortium partner, Antiglio SA is managing the highly complex trans­formation pro­cess in the middle of Fribourg’s historic district. They are supported by the special civil engineering professionals of Marti AG Bern.

The first buildings of the Fribourg Cantonal Library were built some 120 years ago. Various additions and con­versions followed over the years. How­ever, the infra­structure is now in poor condition, making it necessary to com­pletely re­novate the KUB. Only the listed neo-Baroque façades of the original library will remain.
Before the new buildings can emerge, the old structures need to be de­molished: Antiglio and Marti Bern’s special civil engin­eering team have been working hand in hand on this since the beginning of 2021. They first used micro­piles to bolster the ground under the adja­cent Rue Saint Michel, which required the street to be fully closed for two months. This work alone re­pres­ented a challenge for our teams, as the maps detailing the location of the old gas pipe­lines were not very accurate, which made some adjust­ments necessary. Further pre­paratory work in­volved the in­stallation of a supporting metal con­struction across the street and a brace to protect the outer façades.

The old library building is gutted

The builders then began to hollow out the old library building in stages. A new pre-stressed ceiling slab was ins­talled under the existing roof to support the weight of the entire roof truss. The floor slabs were de­molished from top to bottom, and long­itudinal and trans­verse steel beams were used to secure the façade. Upon ex­posure of the building’s original found­ation, the special civil engineers used further micro­piles to re­inforce the ground. The teams then re­moved the old found­ation in order to install a new one three levels below it.

A highly complex construction site like this doesn't come along three times in your life!
Raphaël Castro,
Projectleader, Antiglio SA

The new excavation

The excavation for the new ex­tension has now been imple­mented where the 1970s annex once stood – directly adja­cent to the old library building. Our specialists first de­molished the first three floors of building, to be equal in height to the top edge of the adja­cent property. It was necessary to build the dia­phragm wall for securing the adja­cent slope out from this ceiling. To en­sure that our workers could safely use the heavy cable ex­cavators and other equip­ment, 350 massive logs were used to support the lower four levels from below. The crew was then able to de­molish the re­maining building and dig out the 18-meter-deep ex­cavation, which was secured with steel girders and a total of three layers of strut pipes. We then imme­diately continued with the southern portion of the plot of land, which was un­deve­loped at the time. Because the con­ditions of the space did not allow any other options, the site was ex­cavated from above from an elaborate solid work plat­form. Struts and anchor points were also used to secure this ex­cavation in several different ways.

Scarce space

The construction site is located in the heart of Fribourg’s bustling historic district, but not only the cramped spaces posed a major logistical challenge. Schoolchildren, students, residents, and tourists are con­stantly on the go every day on the two directly adjacent streets. In the southern section, the ex­cavation directly borders a Catholic library with 6,000 historical books. Safety is there­fore the top priority, and our con­struction crews are in constant contact with the authorities and residents.

*Contest butikofer de oliveira architectes + Synaxis SA

the stakeholders include