Orientation about the project
Stortingsgaten 6 is a new office complex on 7 floors and a car park on 3 floors below
listing. The 975m plot is bounded by Stortingsgata, Rosenkrantzgata and Prestegata
as well as the neighboring building in Stortingsgata 4. Originally there were two buildings on the site;
Flaggfabrikken and Nordstjernegården. The flag factory dates from 1895 and is listed.
Extensive renovation work was initiated to preserve the facade. The building was
reimbursed with steel core piles for mountains. In connection with these works was built
inflicted settlement damage on the facade with the consequence that the facade facing the backyard was
demolished.
Basic conditions
No basic investigations had been carried out on the property itself, other than a summary of it
existing information about the ground conditions around Stgt. 6. After Nordstjernegården
had been demolished, it was only possible to carry out ground investigations. What was originally thought
mountain level elevation -05 and -1.0 turned out to be the top of a powerfully permeable moraine layer.
The depth to the rock was between elevation -4 and -15. The groundwater was at level 2.
Problem statement
In consideration of nearby buildings, it was necessary to have a tight design
the construction pit. On the basis of trial framing, brace-anchored piling to rock was chosen as
primary safety construction of the construction pit. However, it proved difficult to hit
piled down to the mountain, and only a few pile needles reached down.
Solution
When it was revealed that Stgt. 4 did not stand on mountains, jet piles were chosen both as load carriers
construction solution for Stgt. 4 and as a seal in the moraines overfjell. For sealing sheet piling
it chose jet piles as the sealing method. The piles were installed 60cm down into the rock and up 1.0m above
sheet piling.
Pore pressure and settlement measurements
Four pore pressure measurements were installed prior to excavation below the groundwater level. After
each time it was excavated, measured pore pressure converted to rise height showed a level corresponding to
medium excavation level. This also confirmed that there was a lot of inflow into the construction pit
insignificant. Stortingsgata 4 was followed up with continuous settlement measurements. No
sentences were recorded, neither during the jet pile works nor later during excavation of
the construction pit. However, the flag factory in Prestegata put up to 43mm in connection
with reimbursement with steel core piles.
Conclusion
Despite trial fitting of piles to rock, problems can arise. Alternative solutions must
considered in the design phase. Jet piles can be used in combination with sealing and
structural elements.
OBAS
