For Councils and Road Authorities, “out of sight and out of mind” is an increasingly unsatisfactory position to take when considering the condition of under-road stormwater culverts.
Deterioration in culverts can lead ultimately to road collapse, sometimes with tragic consequences. Sinking of the road surface above a culvert is often an indication that urgent action is required beyond merely filling the subsidence in the carriageway.
Repetitive loading can cause cracking and joint separation in concrete pipes, while corrosion and abrasion can leave corrugated metal culverts in a dangerous condition.
But roads and highways can’t always be closed while they are dug up and replaced.
The situation is the same for sewer and stormwater pipelines in built up city areas. Under every city and town in the world clay, concrete, steel and cast-iron pipelines, many over 50 years old, that are leaking, cracking and corroding. But digging up these pipelines in built up areas and installing new ones would be prohibitively expensive and unreasonably disruptive to the community.
Authorities realise that ignoring the situation is not an acceptable option, so the Trenchless Technology industry has come into being, developing methods to restore the structural condition and flow capacities of deteriorated underground pipelines using techniques that minimise the need for excavation.
Trenchless Technology is an area where the New Zealand and Australian industry is well up with the world leaders, both in terms of developing innovative construction techniques and carrying out demanding rehabilitation projects.
Some of these techniques can be applied to road culverts. Liners can be installed that restore the structural condition of culverts without needing road excavation or causing disruption.
Design of these liners typically assumes that the existing deteriorated culvert has no remaining strength and so all loads are taken by the liner.
This Paper details three lining systems available in New Zealand for deteriorated sewers that have also been used to structurally line stormwater drains and culverts with diameters from 150mm to 3,000mm. It includes examples of projects where these technologies were used, the design issues addressed, and the challenges overcome.