Bath Street Watercourse

In September 2020, WSP were engaged to deliver the Options Assessment and Site Investigation Phases of the project. This was expanded to include Preliminary and Detailed Design, as well as construction support. More recently, WSP was engaged to carry out roading upgrade design for this project.

WSP services included:

• Three Waters
• Structural and Buildings
• Geotechnical
• Contaminated Land
• Planning and Community Engagement
• Survey, Architecture
• Vibration Monitoring
• Fire engineering

The project required deep excavations, in soft reclamation fill (some of which is contaminated), in a narrow corridor, adjacent to multi-storey, unreinforced brick heritage buildings that are susceptible to the effects of settlement and vibration. The project was perceived by the client to be one of their highest risk current endeavours.

The primary structural risks associated with installation of the new watercourse were damage from construction vibration and settlement due to excavation and de-watering. The risk of damage to buildings was mitigated by vibration monitoring.

WSP recommended a vibration monitoring and management methodology, developed in collaboration with DCC and the Contractor, along with condition assessments before and after to monitor cracking/defects. Keeping vibration within acceptable limits was also critical to protecting the public from falling masonry in a busy CBD area. Fitting all the pipes and 3m deep manholes at the low point in Bath Street was extremely challenging, due to it being a very constricted area for services. To overcome this challenge, WSP created a detailed 3D model and worked with multiple disciplines to agree a design and construction solution.

To mitigate the risk of further pipe collapse, WSP, in collaboration with the Contractor, designed a solution to reline (with a blank end) the old watercourse pipe, preventing further flow down the pipe via the collapsed section. Stormwater was then pumped to an alternative stormwater catchment.

Collaboration

WSP worked in an ECI type arrangement with Downer, with no formal contractual linkages. A number of mechanisms supported close collaboration between DCC, WSP and Downer, including weekly project meetings (to discuss programme and project risks), Design & Project Risk Workshops, Safety by Design Workshops and Construction Review Workshops.

This close collaboration, along with a holistic approach to risk management, supported the de-risking of what was a highly complex construction project affecting multiple businesses in the CBD. We carefully managed the project scope and were awarded subsequent design stages of the project.

There was a significant change, eight weeks from delivery when we stopped work on Option 1 and commenced Option 2 (due to unforeseen landowner delays). This was a massive change for the team, however despite this, we delivered to a tight programme and under budget (approx. 3% of the agreed WSP fee was not charged to the client - in the region of $65K).

Due to WSP’s rigorous management of project risk, the client was protected from unforeseen project costs (e.g. building damage/construction delays).

There were high levels of client satisfaction with this project, which was extremely high risk for the client and carefully managed around costs and potential delays

Risk Management

Shortly after the commencement of the project in September 2020, WSP convened a Project Risk Review Workshop with DCC, Downer, and Fluent Solutions Ltd, who were involved in an early project phase. Following the workshop, WSP drafted and disseminated a Project Risk Register to DCC and Downer. WSP maintained and updated the Project Risk Register as the project progressed, and new risks were identified. WSP convened several Project Risk Workshops with DCC and Downer to review and update the risk register, mitigations, and actions.

A key risk management approach was the production of a suite of Building Risk Maps. This enabled DCC to plan property negotiations, and Downer to plan their methods of working adjacent to at-risk buildings. This component of the risk management was particularly well received by DCC.

A comprehensive Actions and Decision Register was utilised, which identified where these had an influence on the final design of the permanent works, and supported the management of liability between parties.

Engagement Undertaken

WSP led the stakeholder engagement on behalf of DCC up to the construction phase, liaising with all building and business owners in the vicinity, and the development of the various consents for the project.

We were instrumental in delivering an outstanding result in terms of stakeholder communications, with zero adverse comments to Council. We collaborated closely with the DCC Communications Advisor and was fully embedded in project meetings and risk workshops. This meant we developed a strong understanding of project risks, and the engineering and construction challenges, and communicated this in a way that impacted parties could understand. Our involvement was instrumental in gaining stakeholder and community understanding and buy-in to the project.

Health & Safety (H&S) / Safety by Design (SbD)

Two SbD workshops were held, which WSP, DCC and Downer attended. The first focused on the Three Waters; watercourse pipe and civil permanent works design, and the second on the structural design of the modification to 326 Moray Place. The workshops identified the highest risks to health and safety, which were analysed by the Design Team, with a focus on reducing or eliminating these risks through design.

We worked with Downer to undertake ground investigation works and vibration trials, to mitigate the risk of damage to buildings and falling masonry (a key risk, given the number of heritage buildings impacted). We also developed a suite of Project Site Safety Plans, and Safe Work Method Statements for specific site activities. This robust approach led to the achievement of zero recordable safety incidents.

Working with Downer in an ECI environment required a WSP Safety Plan that was both integrated and aligned with the wider Constructor Safety Plan, with H&S protocols around overlapping duties well understood.

WSP contracted to local company, NZ Heritage Properties to complete Archaeological Assessments. Benefits to DCC included an upgraded network which has been future-proofed for at least the next century; upgraded streetscapes are being delivered; removed the risk of more sink holes forming.

Some archaeological discoveries were made during the works, too. These included a 19th century Doctor Conquest Health Bitters bottle and a pair of shoes.

This project provided extensive upskilling of local and regional young engineering talent.