Beachville Road Seawall Construction

Scope

• Break out and removal of existing wall
• Trimming of the seabed to the design profile
• Placement of reno mattresses to prevent tidal under-scour of the seawall ‘toe’
• Construction of wall core and revetment using multiple layers of geotextile, gravel and rock
• Installation of architecturally designed precast panels along the top of the seawall
• Supply of construction materials, including the specialised rock required for the revetment

Project Description

The area around Beachville Road suffered lateral spreading and liquefaction in the Christchurch earthquakes. Impacted structures included the road’s eastern seawall. Sections of the wall collapsed during initial shaking and failed under the increased weight loading caused by liquefaction and spread.

This high profile project was awarded to Seipp Construction based on our submission of an innovative construction methodology and our ability to provide the specialised plant and expertise required to deliver works in a challenging tidal, marine environment.

Construction works were undertaken along the half-kilometre stretch of Beachville Road which fronts the estuary line. This included significant works below sea level - both for removal of the old wall and construction of the lower components of the new structure.

A specialised methodology was required, implemented by a team with the right expertise and the right equipment. It was essential our approach mitigated risk and gave maximum certainty on delivery - the top of the seawall bounded the new coastal pathway and needed to be completed to enable the pathway to open.

We built the new seawall in sections, with each section constructed inside a dry ‘cell’ created by sheet piling and dewatering. As each section of wall within a cell was completed, it was tied-in to the completed section of wall in the preceding cell. Using this approach, the 500m long seawall was constructed in 23 – 35m sections, with up to four sections under construction at once.

The successful implementation of our ‘alternative’ methodology was based firmly on our ability to procure plant and technology which was highly fit-for-purpose. Where required, we developed innovative systems to streamline the more difficult aspects of construction and make these achievable. However, all aspects of the overall success of construction were characterised by the ability of our individual experts to collaborate, problem-solve and work together as a team.

Our performance on this project was consistently excellent, resulting in accolades and high levels of satisfaction across our entire stakeholder group, including from our client Downer and the asset owner, Christchurch City Council. We received an overall performance rating of ‘Excellent’ from Downer; and comments from CCC’s Infrastructure Rebuild Liaison Manager, Ross Herrett included “The Beachville Seawall is a brilliant piece of engineering, constructed by an outstanding contractor… Quite simply, the finished product is amazing.”

Our delivery of the Beachville Road Seawall, was also recognised in the 2016 Civil Contractors NZ, Contractor of the Year Awards, winning both the $1.5 - $5M category and the award for Best Overall Project.