Pump Station and Pressure Main No.128

The paper discusses the design and construction aspects of the wastewater Pump Station 128 and the associated Pressure Main 128 being constructed by the Stronger Christchurch Infrastructure Rebuild Team (SCIRT) in the New Brighton area of Christchurch. The existing wastewater pump station was damaged beyond repair by the February 2011 earthquake and the decision was taken to build a new pump station and pressure main at an alternative location to avoid the Red-Zoned area around the existing pump station. The new pump station has a capacity of 625L/s and the new DN 800 PE 100 pressure main is 3km long, routed under the Avon River and is being installed using directional drilling. This makes Pressure Main 128 the biggest directionally-drilled pressure main in Christchurch and the project presents unique challenges. The existing pump station has Archimedes screw pumps whereas the new pump station uses submersible pumps and operates in duty/assist/standby arrangement. The pump station site and pressure main route suffers from poor ground conditions so several innovative design techniques have been used to improve ground conditions and avoid effects of differential settlement.

The paper discusses both the design and construction stages of the projects including pros and cons of directional drilling technology for the pressure main, pipe welding, pipe testing, inlet design of the pump station, wet well hydraulics, proper pump selection to minimise wear and tear, odour treatment and ground improvement strategy to mitigate seismic-related damage and construction issues.

This paper provides valuable lessons to the industry on how to improve the design and construction of these important large wastewater structures.