LOCATION Pines WWTP, Burnham School Road, Burnham   •  PRINCIPAL Corde / Selwyn District Council •  PROJECT DATES November 2021 – August 2022 

Construction of a new Clarifier structure at Pines WWTP in Selwyn.

Structure: The structure consisted of a 30m diameter x 7m high concrete tank with a reinforced segmental concrete floor slab, prestressed precast panels/in-situ joints, post tensioned walls and an in-situ launder box and outlet manhole.

Design:  Tank design was provided by Stantec.  CSL worked collaboratively with the main contractor and Stantec to optimize some elements/materials to benefit all parties.  Temporary works designs for launder box construction, precast installation and post tensioning works were provided by CSL.

• Water retention structure.
• All Tank construction activities were self-performed by CSL’s highly experienced Reservoir Crews.
• Strong collaboration with stakeholders.
• In-situ concrete Elements.
• Precast concrete elements.
• Post tensioning.
• Significant heavy lifts/large craneage component.

Construction:  Tank ring beam and floor was constructed in segments using waterstop and sealant joints for crack control. Multiple pours were required using a hit and miss strategy coupled with water curing to minimise shrinkage.

Precast wall panels were cast in CSL’s Christchurch Precast factory, before being delivered to site and installed by the site team.

In-situ stitches were formed and poured in 2 lifts (1 pour) using a highly flowable 13mm aggregate mix to provide a watertight joint. The launder box was formed and cast using cantilever brackets attached to the precast units, again being cast in a hit and miss manner.

Performance:  The tank was completed on time and passed the water test with no leaks or seepage witnessed.

Health and Safety:  A comprehensive Site-specific Safety Plan was created and adhered to for the duration of this project in accordance with company policies and laws.

Environmental:  A comprehensive Environmental Plan was created and adhered to in accordance with local bylaws incorporated as necessary and mitigation measures placed where necessary.