Friday, October 21, 2011

CHCH EQ repairs: Fitzgerald Ave wall repair progressing well...

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Christchurch EQ: Fitzgerald Ave wall repair progressing well: New northbound lanes to open April 2012

A piling rig is being used to insert the steel casings for the stone columns. Image supplied. The following update was posted on the Stronger Christchurch blog on Friday, October 21st, 2011.
Roads are something no one really notices until things go wrong. Fitzgerald Avenue – one of Christchurch’s ‘four avenues’ – was extensively damaged in February’s earthquake. The northbound lane suffered severe cracking up to two metres deep along the Avon River. Fortunately, the southbound lane only suffered minor damage and has been able to remain open, enabling repairs to occur while keeping traffic flowing.

The Stronger Christchurch Infrastructure Rebuild Team is using an innovative technique to stabilise the ground and adjacent riverside retaining wall that supports the road. Five hundred stone columns, each 600 millimetres in diameter, are being inserted into the ground to a depth of ten metres over a 200 metre length of the road.

The stone columns are constructed by pushing a steel casing into the ground. The casing is then filled with gravel and removed leaving the densified gravel behind. This makes the surrounding ground denser, stronger and improves ground water drainage. In the event of an earthquake the improved ground helps prevent liquefaction and supports structures.

Reconstruction of the riverside retaining wall will commence once the stone columns are completed. The road surface will then be reinstated. Damaged water and wastewater lines will also be repaired and a new footpath constructed. Finally, once the northbound lane has reopened, the southbound lane will be reconstructed.

Progress is tracking well, with 370 of 550 stone columns completed. Around 50 additional columns will need to be added to the original design due to the poor nature of a section of ground and this may result in a slight delay. The Downer team, who is placing the stone column piles remains dedicated to opening this section of Fitzgerald Avenue as quickly as possible. To do this the team has extended their working hours to 10pm each evening. Downer is aiming to open the road where they are currently working (all going well) by April 2012 subject to weather and construction. Once this section of work is completed there may be more work on Fitzgerald Avenue in the future.

Wednesday’s weather (on 19th October, 2011) didn’t help progress. A combination of high rainfall and high tides flooded the whole site as it is much lower than the proposed road level, causing works to be abandoned for the day. Concrete retaining wall panels being produced locally here in Christchurch are well underway and Downer will commence the construction of the retaining wall within 2 weeks.
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