Inspecting the surface of a giant wastewater tunnel

Cities worldwide are adapting their infrastructure to cope and plan for the water needs of people and the environment. New Zealand’s largest wastewater project is underway to ensure the supply of the most vital resource over the next hundred years while improving the environmental outcomes and building the resilience of the current waste pipelines.

The Watercare Central Interceptor Tunnel for this project has reached an exciting stage. The teams’ giant new Tunnel Boring Machine [TBM], built in Germany, Hiwa-i-te-Rangi, reached 1,100m of excavation.

The main contractor, Ghella Abergeldie Joint Venture (GAJV), will take six years to build the Central Interceptor, with most construction work underground. The 190m long TBM will bore through the earth’s substrate and lay segments of the tunnel as it goes.

With a planned length of 14.7km, the new underground tunnel is on its way to being the country’s largest wastewater tunnel. Visible above-ground construction will be contained to the 16 sites where vertical shafts will be built and connections made to local sewer networks and overflow points.

The first shafts at Māngere and May Rd shaft A are already well under construction. The Māngere shaft is 40m deep with a diaphragm wall extending from -50 to -54m underground, creating the deepest diaphragm wall in New Zealand history. While May Rd shaft A has a smaller diameter, some 67m deep, the lower 40m is shotcrete-lined to stabilise the walls.

Photo: Band scan point cloud data from May Rd vertical shaft captured by the Leica Nova MS60 displayed in Leica Infinity office software]

Comparing Surfaces of Scanned Structures

The Ghella Abergeldie Survey Team working on this project are equipped with the latest Leica Geosystems technology, including the new Leica Nova MS60 MultiStation, a powerful robotic total station with 3D laser scanning capability. One of the most powerful features of the new MS60 is the Inspect Surfaces App, which is proving popular with surveyors worldwide as a valuable tool to compare the surfaces of scanned features.

The survey team positioned the Leica MS60 at the bottom of the vertical shaft using the Resection setup option in Leica Captivate field software to inspect the construction. Then they used the Inspect Surfaces App to compare the scan with the shaft design using a “heat map”, which shows inconsistencies between the design and the real structures.

This enabled GAJV surveyors to communicate directly with the construction team on-site and in real-time to immediately identify surface inconsistencies.

“The Inspect Surfaces App was just what we were looking for. The ability to directly compare reality with design in the field is of huge benefit. The Leica MS60 is our “go-to” instrument, and we are looking forward to using it on different stages of the tunnelling project.”

Les Whalley – Mine Surveyor, Central Interceptor Project

 

The Ghella Abergeldie Survey Team has also taken delivery of several Digital Levels with invar staffs, Leica Geosystems robotic total stations, and controllers with the advantage that data is captured in Captivate on both. Leica Infinity office software enables the team to combine and process data sets for QA checks to be completed.

As this project progresses, Bryan Claridge and the team from Global Survey New Zealand will provide ongoing technical support and assistance to this highly complex and crucial project.

A Long-Term Strategic Infrastructure Project

There is no doubt that the Central Interceptor Project is a crucially important project for Auckland and one of the country’s largest-ever undertaken. It is designed explicitly by Watercare to deliver better and more effective wastewater management within the Auckland region and provide future growth.

Historically older stormwater pipes have been overwhelmed in heavy rain and overflowed into the city’s natural waterways. Over six years, the Central Interceptor tunnel will be built to help make Auckland’s waterways cleaner.

The Central Interceptor tunnel will run underground from Grey Lynn to the Māngere Wastewater Treatment Plant. It will have several linked sewers and shafts along the route for collecting and transferring wastewater into the tunnel. Once complete, it will be the longest wastewater tunnel in New Zealand history.

Ghella Abergeldie has more than 150 years experience with tunnelling and wastewater projects of this size across the globe.