Wellington, New Zealand's city council sought a solution to repair the 1,350 mm of South Karori storm water corrugated culvert. During the past 50 years of its service, the culvert’s invert had fully degraded over its entire length of 220 meters from erosion and corrosion, with holes up to 500-mm deep throughout the culvert.
The culvert was installed simultaneously with the surrounding subdivision, so it followed the natural stream bed, featured four bends, vertical and horizontal deviations of up to 32 degrees, and was backfilled with up to 10 meters of cover. The proximity of the residential properties meant a trench- less, nondisruptive solution was required with at least a 50-year design life and an application that is less than 100-mm thick. The area also was popular for hiking and mountain biking, so public access had to be maintained during construction.
A regional consulting firm was hired to find a suitable product to meet the budget and timeframe specifications of the council. After reviewing sub- missions, Concrete Treatments NZ Limited (CTNZ) was awarded the project by proposing GeoSpray geo- polymer mortar as the structural solution.
CTNZ provided a solution in the form of a structural liner, which was formed using the GeoSpray system supplied by Clock Spring Co. & NRI. The repair area was cleared of any debris and the culvert bedding was reinstated. Then the invert was repaired using pumped concrete so the GeoSpray mortar could be applied. The project required various thicknesses along the length of the culvert, ranging from 42.5 to 50 mm.
As part of the overall project process, Regional Council for its Environmental Management Plan gave CTNZ approval, and CTNZ communicated with the neighborhood residents regarding the project. A temporary access track needed to be built to safely access the culvert. All aquatic species were captured and taken 100 meters upstream from the work site. Once the regulatory preparation was done, the liner design was finalized and reviewed prior to installation.
After the GeoSpray mortar was applied, Flexible Iris baffles were installed to accommodate migrating fish, and riprap was placed on either side of the culvert for protection. The temporary access track was rein- stated back to the environment through planting of local tree species, and the mountain bike track was lengthened and enhanced. The project was completed on time and within approved budgets, without any time extensions for inclement weather experienced during the contract.