Visit us on Facebook

Wastewater Main Upgrade Central Christchurch


New Horizontal Civil Infrastructure: Waste Water Main and Laterals Upgrade in the Central City, Christchurch.

Client: Fletcher Construction Limited

Principal Stakeholder: Christchurch City Council 

Duration: 25 November 2013—26 February 2014 

Consultant: SCIRT — The Stronger Christchurch Infrastructure Rebuild Team

Project Overview
Inside trench shoring shield a 6m sewage pipe lengths are fast and accurately laid.

Replacing earthquake damaged wastewater infrastructure in the Central City, Christchurch, North East of the Avon River, along Barbadoes Street between Cambridge Terrace and Bealey Avenue. Most of the wastewater network in the Central City was more than 100 years old, most was constructed from earthenware pipe. These structures were badly damaged due to rapid ground acceleration and liquifaction in the quakes. Installed new wastewater mains and replaced wastewater laterals from the mains up to property boundaries. Work started at Cambridge Terrace and progressed north towards Bealey Avenue.

Work commenced by the Barbadoes Street Bridge at Cambridge Terrace, due to narrow lane widths the road was reduced to one lane only in the first week. To reduce the duration of this lane restriction, night works took place for the first week. Following this work Barbadoes Street was reinstated to two lanes as work progressed north. Further lane restrictions were put in place when necessary.

The work site was first set up; underground services were located, fences put up, machinery and supplies were arranged on site. We worked close to the Barbadoes Street Cemetery and other properties with notable trees located nearby. To avoid damaging trees we worked with a Council approved arborist.

Beca Consultants provided the sewer main design while Fletcher's provided independent testing of the work's accuracy and compliance while the work was in progress.

Waste water pipe specifications;Barbadoes St to Bealey Street site map

  • 300mm x 6m PVC-U gravity sewer pipe, rubber ring joint 
  • Installed gradient/pipe fall of 0.18 degrees 
  • Number of precast, reinforced concrete manholes; 10
  • Number of laterals; 18
  • Length of lay; 600m 

Waste Water Upgrade Methodology   

Combination open cut trench and shored trench Short swing radius Volvo ECR235 and ECR145 are well suited to confined jobsites.

Our crew excavated the trench with our short swing radius, 24-ton Volvo ECR 235CL excavator which works in one lane of traffic so is well suited to the confined jobsite and results in minimal traffic disruption. The trench face was cut back to a safe slope using two digger buckets, first wide, then narrow. Custom hydraulic quick-fit enables fast changing of attachments on-the-fly from safety of the cab. All our excavators are custom fit with front-end dozer blades, this increases machine versatility in job applications such as backfilling trenches and site clean up.

Excavation tasks include; 

  • truck spoil loading, 
  • digger break-up of asphalt spoil as "recycled backfill", 
  • trench shoring shield lifting and insertion, forward repositioning in trench. 

Optimal Truck movement logistics14-ton Scania P420 tipper truck removes excavation spoil.

Three 6 x 4 tipper truck drivers co-ordinate with excavation and backfill digger operators via RT to optimise progressive spoil removal egress with backfill gravel delivery. Delivery trucks frequently serve dual duty for spoil removal during their rotation.

Pipe lay preparation

The trench backfill crew sustains a fast and accurate, co-ordinated effort of crew and machines. The trench man or drainlayer and team set the fast pace of the pipe lay by sustaining intensive manual labour and maintaining precise verification to laser guide every 6m length of pipe laid. 

The drainlayer lays the pre-cut, 6m permeable geotextile envelope, pinning it to the walls of the trench. The 15-ton Volvo ECR 145 CL, and 5.9-ton ECR 58 digger operators coordinate to lay fine bedding gravel fill, drainlayer shovels and tamps this fill manually as required to conform to pipe-fall. Digger lifts and inserts the vibrating plate compactor, the drainlayer compacts the pipe cover gravel. 

Note, when the trench is shielded at depths greater than 1.5m the digger operator's visibility is limited by the shield walls so a "spotter" assists the digger operator with accurate and safe distribution of backfill in the trench.  

Pipe Lay 6m lengthe of sewer pipe laid, aligned and joined inside trench shoring shield, Barbadoes Street, Christchurch.

The digger transfers and inserts 6m pipe lengths in sling from stack to trench with hands-on spotter assist. Drainlayer checks front alignment of placed pipe to laser guide then carries out pipe fitting preparation and fitting sub tasks;

  • prep rubber o-ring seal,
  • prep pipe interior/exterior clean of debris,
  • manual fitting of pipe joint (with assist),
  • release fitted 6m length from sling.

Coordinating with drainlayer, digger operator begins backfill process with fine pipe cover gravel layer which is manually shovelled and tamped then vibrating plate compacted by the drainlayer to secure pipe position. Compactor is slung in and out, pipe fall is checked and micro-adjusted at leading edge by drainlayer.

Waste Water Upgrade Methodology Backfill, Compacting and Road Recovery

Overlapping the above tasks; 

  • the lead digger operator repositions the trench shield forward 6m for the next iteration of pipe lay and fit
  • the two backfill digger operators and two compacting and cleanup crew layer and compact coarse and fine aggregate to fill the trench.
  • the intermediate coarse layer is shovelled manually as required then compacted with vibrating plate followed by Bomag walk-behind vibrating roller
  • the top fine layer fills the trench and is compacted as above then finished with Sakai tandem vibrating roller
  • a combination of manual and power broom, shovel and Iseki front-mounted road sweeper coordinate to recover road surface.

Parallel Task Workflow 

The co-ordinated performance of combinations of the above activities results in the job progressing fast, with a high level of precision and strict adherence to job specification. 

Prefabricated Manhole Placement

Excavation tasks and backfill are same as for trench except the trench is cut wider to accommodate manhole base section and a custom manhole trench shoring shield is placed.

Permeable geotextile envelope is placed then bedding layer is laid, precisely levelled and compacted to laser guide. Placement position is targeted by trenchman.

Meanwhile above ground; the base section inlet & outlet pipe holes are drawn and the inlet is knocked out and prepared for joining to sewer line. The manhole base section is lifted, precision placed and levelled. Concrete corbels are constructed to the inlet and outlet joints via hand-mix small batch concrete insitu.

The Laser is repositioned to outlet of new manhole and set to gradient specification. Upon completion of the line, each manhole base is manually coved with a smooth radius of grout up to the inlet and outlet pipes.

Manhole base to surface sectioning and covering

Each riser section is sealed, lifted, and placed—sectioning the manhole up to the surface, finally the manhole is capped with cover. 

Fast trench backfill layering and compaction.

Line Gradient, Trench In-Place Density and Water Content Testing

Depending on contract specifications, proof testing is carried out independently or by TruLine every 100m of line laid. The line gradient is checked and in-place density and water content checks of trench-aggregate layers by nuclear method are carried out. 

Worksafe Site Safety and Traffic Management The sewage line gradient is tested every 100m.

Traffic Safety management was carried out by STI in consultation with Truline's crew. The worksite risk hotspot is crew managed in the immediate vicinity of the leading excavator and pipe laying front. When digger operator's visibility is limited by trench shield walls, spotters provide cover safety as required. All digger transfers of equipment and supplies is also hands-on spotted by one or two people depending on assessed risks in confined site. Tipper truck reverse ingress and egress is also spotted.

Progressing 10m behind the pipe front the trench and road is recovered to a state cleaner than before excavation. The combined dig-and-backfill, shoring method reduces risky exposed trench area to the absolute minimum, this method optimises the site to a safety standard second-to-none internationally.

Plant Fuel, Consumables and Breakdown Contingencies

Each day fuel supply tankers contain sufficient for continuous day of operation for all plant on site. Stock of all ordinary plant consumables are stored on site. In the event of extraordinary plant breakdown, such as excavator hydraulics, on-site repair is carried out by approved third-party support provider.

Spill Kits for petroleum products are kept handy on site where refuelling takes place or where there is a possibility of a hydraulic fluid rupture.  Safety Data Sheets (SDS) are kept handy on site where appropriate. 

Wastewater Main Upgrade Central Christchurch Slideshow

>> Click to view the Wastewater Main Upgrade Central Christchurch Slideshow >>

Slideshow controls: [1] Double-click to "pause" any slide, [2] Double click to "play"/continue the show. [3] Jump to any slide in the show by clicking on the relevant thumbnail. [4] To escape at any time click "x" top right.

Contact us

TruLine Civil is determined to incrementally improve the service we deliver our clients, and the quality and range of civil engineering services that we offer to owners and stakeholders who expect excellence.

Excellence in Infrastructure.

TruLine Civil.

Interested in our services? You can contact us +64 (21) 228-5090 and ask for Geoff Powell or e-mail me at 

Christchurch Address 

Greywacke Road extension,
New Zealand 

Credits: Photos and case study documentation by Shaun G. Waugh


Click thumbnail for larger image

Wastewater Main Upgrade Central Christchurch

Our Difference

  • Award Winning
  • ISO 9001 Certification
  • NZTA Prequalified
  • ACC Tertiary Level
  • Family Company

Learn more ...