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Auckland, New Zealand, prevents flooding with pipe rehabilitation
As is the case in many other municipalities around the world, the city of Auckland, New Zealand, has utilized galvanized corrugated iron culverts as part of its drainage network. Typical installations are designed to enable roads and rails to cost-effectively traverse creeks, streams and small rivers. The original purpose for the installation of the Kashmir Road culvert is not entirely clear, but it may have been to improve residential development opportunities or to address stream-bank erosion that could threaten an existing residential dwelling. Whatever the reason for its installation, nearby residential dwellings were under threat due to the looming collapse of the 1.8-m (70-in.) diameter culvert as a result of eroded ground support and missing culvert invert for the majority of its 30-m (98-ft) length. The local council was concerned that failure of the pipe could destabilize adjacent land and cause flooding of neighboring properties.
Open-cut replacement—14 days: Removal of old pipe and replacement with new pipe. This option would require sheet piling to support the nearby residential dwellings and, whilst technically feasible, was discounted due to environmental concerns, cost and disruption to local residents.
Cured-in-place pipe—7 days: Installation of resin-impregnated liner inside old pipe. This option offers minimized risk to local residential dwellings. It can be installed with minimal disruption to local residents. However, there are some concerns of its impact on stream fauna.
GeoSpray—7 days: Reinstatement of lost culvert invert using premix concrete to reduce some culvert collapse risk. The installation of centrifugally cast geopolymer mortar inside old pipe provides fully structural rehabilitation and presents minimal risk to local residential dwellings. It can be installed with minimal disruption to local residents. It is environmentally friendly due to the product being inert once cured.
The council chose GeoSpray geopolymer mortar due to the lower installation cost, limited disruption to local residents and environmental credential and performance. The city did not choose open-cut due to cost, difficulties with machinery access due to site constraints, disruption and noise.
Day 1: Conducted complete consultation with local residents regarding project. Removed private property fencing and installed temporary access stairs to gain stream access.
Day 2: Set up temporary bypass, including upstream dam and three-stage downstream sediment traps to protect the stream. Removed woody debris and river stones. Cleaned the culvert using high-pressure water blasting equipment.
Day 3: Installed concrete fill to reinstate culvert invert.
Day 4: Set up a dedicated GeoSpray truck and ancillary equipment and applied first coat of GeoSpray mortar to 30 m (98 ft) of culvert and allowed it to set.
Day 5: Applied second coat of GeoSpray mortar to 30 m (98 ft) of culvert and allowed it to set.
Day 6: Applied final coat of GeoSpray mortar to culvert.
Day 7: Cleaned up site, reinstated private-property fencing, removed temporary access stairs, reinstated private properties and disestablished from site.
The project delivered a quality structural rehabilitation outcome to budget under challenging access constraints and weather conditions.