Kapiti News
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Your local news from Paekakariki to Otaki
Wednesday, May 28, 2014
Piles of work Unsung hero
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KAP220514SPLcasing
GROUND BREAKING: The casing being used to build an earthquake-proof underground structure for the expressway’s Waikanae River bridge. The scale of the casing is evident as site superintendent Kevin Hammond takes a break inside the massive steel tube, which protrudes three metres above the ground surface. PHOTOGRAPHER: MARK COOTE
Quake-proof bridge a complex project CLOE WILLETTS Construction of the expressway’s Waikanae River bridge started last week, in an extremely intricate underground piling process that will create a foundation for the bridge that is resistant to earthquakes. As one of New Zealand’s biggest ever piling projects, 35 bored piles will be built in Kapiti, with the role of holding the bridge’s full weight. Project foundations manager Matt Zame said after looking closely at the devastating Christchurch quakes, the Transport Agency wanted to create a foundation for the bridge that “will survive almost everything”.
“When we have a big earthquake, some of the very saturated sand and silt material liquefies and starts bubbling up, allowing the embankments to move, which is last thing you want. “By improving the big wedge of ground underneath the bridge, it means it’ll pretty much stay where it is.” He said there is great complexity in the building of bored piles, which will cost the agency about $18 million in work alone. Part of the step-by-step process is the injection of bentonite — a type of clay — into the piling holes to hold them open. “As the bentonite starts to migrate into the sand, it
builds a membrane and blocks up all the pores, creating an impermeable barrier.” The river bridge site is currently home to a plant containing 600 cubic metres of bentonite fluid, secured in big shipping containers. Mr Zame said construction of just one bored pile includes the pouring of 270 cubic metres of concrete, which is around 60 truckloads, which is injected into the centre of the pile. “Following the pouring of the concrete, the bentonite comes to the surface, which we pump back to the plant for storage, where it is cleaned and reused for the next pile. “Since we keep
recirculating it, as well as doing test piles, we are saving a lot of money.” The project’s innovative casing method, used for pouring the concrete, is also saving the agency “roughly over half a million dollars”. Unlike similar projects, which see steel casings left inserted underground, expressway contractors are using one removable casing for the entire development. “No one can see all the effort that goes into building these piles, only work done from the ground up. “We’ve never built anything this big here in New Zealand, so there’s a lot of trialling, but we’re very happy with the results so far.”
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