Soaked soil sent wall tumbling

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The cause of the collapse of a retaining wall above State Highway 1/Severn St has been determined after Waitaki District Council staff carried out a full inspection of the Oamaru stone and concrete structure.
Several metres of a top tier of the three-tiered wall near the intersection of Severn St and Douglas Tce failed about 4pm on Saturday, sending stone blocks tumbling on to the busy highway.
Waitaki Mayor Gary Kircher said the inspection identified the cause of the collapse as being weather-related and not a structural defect.
“Essentially, what they [council officers] are putting the cause down to is the new soil and material … was very, very wet and the rain has been enough to thoroughly soak that soil and it has created a lot of weight behind that wall.
He said it was thought the drainage on the bank might have been blocked.
“The water’s gone through there [the soil] and not enough has gone through to the drain and has pushed the wall forward,” Mr Kircher said.
He said the movement of material weighing about a tonne resulted in the wall’s failure.
In March, the Waitaki District Council spent $45,000 improving the wall’s stability, removing leaning sections, re-establishing drainage and building a new stone wall.
Part of the new section of wall collapsed, along with an older section.
Council staff are now investigating how the collapsed section of the wall should be rebuilt and what materials should be used.
When the wall was originally constructed by the Oamaru Beautifying Society about 80 years ago, big blocks of Oamaru stone were used.
The lower level was rebuilt about seven years ago using concrete with an Oamaru stone veneer, the same materials used in the most recent works.
Mr Kircher said the wall was not at risk of further collapse.
He rejected speculation on social media the wall had collapsed due to poor workmanship when improvements were made in March, and was “disappointed” with some of the comments circulated.
“Overall, the workmanship was good. The drainage was put in, so it certainly wasn’t the workmanship. It’s a combination of factors and an unforeseen event has certainly been an issue there.”The work was carried out by The Stone Man and Steve McLeod Contracting.