Following extremely severe earthquake damage to nearby pipes in 2010 and 2011, two new gravity sewer pipes in central Christchurch were urgently needed to create alternative gravity sewer service for the surrounding residential area.
To install these particularly challenging deep connecting sewers, Stronger Christchurch Infrastructure Rebuild Team (SCIRT) partner Downer Construction approached Iplex Pipelines, with PVC piping preferred due to the material’s durability and compatibility with other PVC sewers currently in service.
Installation from within
Measuring 450 mm in diameter, the 24 m pipes would be located some 4 m beneath Tonbridge Lane and Carlton Mill Road – near one of the highest volume traffic sites in Christchurch City. Site conditions included an extremely flat 0.14 per cent alignment grade for the sewer pipes, a high water table, working space constraints, public disruption, soft ground and the need for significant pipe depth.
These circumstances combined to ensure pipe replacement via either conventional open-cut techniques or horizontal directional drilling was impractical. Instead, a laser guided boring method was chosen in tandem with a segmented-pipe installation, which allowed jointing to be completed at depth within the drive pit.
A preferred choice
For the pipeline, Iplex opted for a 450 mm diameter Laserbore rebate-in-wall flush-jointed pipe using PVC-M Series 1 PN 12 Rhino pressure pipe. This solution became Downer’s preferred choice and the pipes were manufactured in 1 m effective lengths to fit over the equipment outer casings and augers.
The joints were assembled by standard PVC solvent cement jointing techniques within the drive pit, allowing minimal 20 minute cure times on each pipe joint before applying drive forces. In association with manufacturing partner Strata Precision Plastics, Iplex engineers developed the Laserbore flush joint. Trial assembly and physical joint testing was completed at the Iplex IANZ-accredited laboratory in Palmerston North prior to production.
All hands on site
During the installation, Iplex technicians were on-site and provided technical support to both SCIRT and Downer. Prior to installation, hands-on training for the pipe handling, jointing and preparation of solvent cement joints was also completed with onsite specialists.
Following the first drive, the accuracy of the final invert alignment was within 2 mm of the desired target.