Christchurch's flat and liquefaction-prone ground prompted an investigation into new methods of pipe installation.
Christchurch ground conditions are very difficult to work in. The city was built on flat land with high water table levels on ground that was once predominantly swamp.
The poor and permeable ground with high water table levels makes the digging of trenches and the installation of underground pipework a difficult and costly operation. These difficulties and subsequent expenses were exacerbated in the post-earthquake scenario by the scale of the rebuild project and the large amount of resources needed to complete the task. In pre-earthquake "business-as-usual" situations, the amount of work carried out was comparatively small and there were local contractors familiar with the conditions. Post-earthquake there was an influx of new drainage contractors who, although experienced in areas outside Christchurch, were not familiar with the complexities of these local conditions.
The consequences of this were many, but three significant ones were:
- Low quality installations
- Slow installations
- Costly installations
It was not good enough to demand better quality from the industry; the methods specified needed to be examined to determine if they were necessary to achieve the required result, and if not, alternatives needed to be considered to allow innovative and/or cost saving approaches to be adopted.
The purpose of this assessment was to look at some of the current specification requirements associated with the pipe installation and to look for alternatives that could improve on the points bulleted above.
The recommendations included changes to the Council's Construction Standard Specification (CSS), greater flexibility when choosing pipe and embedment materials, and making standards more flexible to suit different sites.
Many of the recommendations of this report were adopted by the Christchurch City Council.