Nelson City Council Press Release.
Preparing the Trafalgar Centre to withstand earthquakes has seen Council contractors Gibbons Construction, and project managers Opus, using innovative solutions in ground stabilisation and building construction.
Deep Soil Mixing used to prevent ground movement
Work to ensure that the ground between the Trafalgar Centre and Saltwater Creek does not move sideways in an earthquake has seen contractors using a Deep Soil Mixer (DSM) to create a network of ground-strengthening piles.
The machine, which could be seen towering over the Centre for several weeks in January, works by mixing cement, lime and water with the existing soil, through a hollow drill, in columns up to eight metres deep. 113 columns with a diameter of 80cm were drilled in to the ground, in a honeycomb pattern, over an area 50 metres long and six metres wide.
The columns created a stabilised barrier that will minimise sideways movement of the ground. The work took 10 days, using a machine brought up from Christchurch for the job.
Making sure the environment around Saltwater Creek was not affected by the work was a high priority. Testing by an independent environmental engineer before, during and after the drilling found no measurable effects on the stream. The machine caused no noticeable ground vibration and noise levels were lower than expected.
Heavy lifting with 100-ton crane
The problem of lifting heavy beams in to place was solved using a 100-ton capacity crane, which residents may have seen located outside of the Centre. The crane is being used to lift strengthening steel beams in to place inside the Centre. Roof panels were removed to allow the crane hoist to access the interior of the Centre.
Steel plates were fitted to the base and sides of the existing timber arches and the crane hoist then lifted the large steel beams in to position in between the existing timber arches. The crane was also used to hold the steel in the right location while bolting it on to the timber arches.
This is a safe and efficient way to handle heavy building components. This additional structural steel will form the roof bracing, giving the building extra strength in the event of an earthquake.
The crane had to be set up outside the Centre as the interior timber floor is not designed to withstand the weight of heavy machinery. At 300 – 500 kg each and up to 10m long, the beams are too heavy to lift manually or using a scissor lift.
Work will now continue to strengthen and brace the Centre, develop the new northern building and landscape Rutherford Park for events planned later in the year.
Consulting Engineer for Nelson City Council, Richard Kirby, says that the challenges of strengthening the Trafalgar Centre have been well met by the experts involved. “The engineers, architects, project managers and contractors have been working together to devise cost-effective solutions, using the latest construction technology, both in the ground and within the structure. This has delivered significant advantages as the project has progressed. We look forward to the work being completed later in the year.”
The project involved the design and build of 3 retaining walls to remediate slips, and increase the road width, Hiway Geotechnical’s design involved installation of micro piles, construction of a reinforced concrete footing.