Modular hydraulic propping equipment from Groundforce is proving a highly efficient support solution for a series of major basement excavations in Gothenburg, Sweden.
The Karlastaden (Karla City) development, in the Lindholmen district of the city, will comprise a total of nine high-rise buildings and includes the 245m-tall Karlatornet (Karla tower) residential block which was completed in 2020, and is the tallest building in the whole of Scandinavia.
Having completed its contract on Karlatornet which was the first phase of the project Groundforce is now on site at the second phase (Capella). Adjacent to Karlatornet this residential block will also include specially designed retirement care apartments.
The basement is a large, rectangular excavation measuring 72m long by 60m wide with a cut-out in one corner. Although relatively shallow (between 2m and 3m) the soft clay soil means that the steel sheet-piled retaining walls require support until the basement slab has been cast.
In the majority of basements, Groundforce props are installed across the full width of the excavation but in this instance that was not possible because the sides of the excavation were at different levels.
Instead, the sheet-piled retaining walls were braced across the corners using Groundforce MP150 hydraulic props as ‘knee’ braces.
The MP150 props were installed as raking props, transferring the lateral loads from the waling beam to concrete thrust-blocks cast into the floor of the excavation.
Excavation to full depth progressed from the centre of the basement out to the sides, leaving an earth berm providing initial support for the sheet-piled retaining wall. This permitted Serneke to cast the concrete thrust blocks in predetermined locations and install the MP150 raking props.
The 150-tonne capacity MP150 props each have 1,000mm of hydraulic adjustment and are delivered to site at mid-stroke, giving the client 500mm of adjustment in either direction.
“All the loadings were supplied by the client’s consulting engineer and it was then a simple matter of sizing the equipment” says Groundforce European Sales Manager Sam Oldroyd.
Using a proprietary modular hydraulic propping system allowed Groundforce to minimise the total number of components required. Following the sequence of excavation and installation of the basement slab, Serneke was able to remove the props from one corner of the excavation, once the structure had become self-supporting, and relocate them in the opposite corner.
“Our experience of Groundforce has been very good. They have delivered according to plan from design, to delivery, to installation on site. Groundforce’s equipment has not only given us a flexible and safe way to support our sheet-piled retaining walls but has saved us time” said Christian Olofsson, Project Manager, Serneke Sverige AB
The modular design means our props can be incredibly flexible,” says Sam. “You can quickly modify the length by adding or removing components.” This meant that switching the location of each prop was both quick and easy.
In total, the Phase 2 excavation required only four MP150 knee-braces and four MP150 raking props. “If we can reduce the number of props required, that will drastically cut down on transport and cost,” explains Sam.
Over the past few years, Groundforce has developed a strong reputation amongst Scandinavian contractors who have employed its system on sites in Sweden, Norway and Denmark.
Groundforce supplied its modular system for Phase 1 of the Karla Tower last year and completed its 15-week Phase 2 contract just before Christmas.