Three major European general contractors – Skanska, Costain, and STRABAG – formed a joint venture, SCS JV, to optimize the construction of the London tunnels of HS2, a national high-speed railway linking London, Birmingham and the north of the country. SCS JV is constructing 13 miles of twin-bore tunnels on the HS2 route, terminating at Euston station in central London.
The Copthall Green Tunnel is an 880m long structure that sits between the Northolt Tunnel and the Colne Valley Viaduct on the northwest edge of London. It is a “cut and cover” tunnel. The “cut and cover” concept involves digging a trench, constructing a tunnel, and then returning the surface to its original state using earth that is excavated during the digging of the trench.
The tunnel is being constructed using reinforced concrete – tied steel bars with concrete poured around them to form a strong box structure – allowing the trains to pass through and enabling green landscaping above. To create the roof of the box tunnel, a 40m long temporary deck is positioned between the box walls all supported by a moving gantry frame called a “roof traveler.”
The East Portal section of the Copthall tunnel is a crucial location for stockpiling the tunnel boring machine risings, which will be further used to backfill the tunnel wings and roofs. Considering the fact that stockpile locations are limited, it is crucial to maintain a continuous sequence between concrete and backfilling works.
In its earlier use of the ALICE platform, SCS JV focused on issues to be solved during the preconstruction phase of its work. But with the Copthall Tunnel, SCS JV instead employed ALICE during the execution phase of the project. The question at hand for SCS JV was: what were the optimal excavation and backfill rates for the tunnel – rates that would allow the team to avoid stockpiling earth by running a continuous cycle?
With ALICE, the SCS JV team was able to simulate and evaluate four different potential scenarios to determine the optimal production rates by testing various excavation rates and shifts, and continuously updating the database as work is progressed. The platform’s “what if” analysis capabilities gave SCS the ability to explore and refine options – and ultimately to zero in on the best answer.
The SCS JV team uses ALICE to update construction progress by using the platform’s 3D model and then quickly running simulations based on the latest data. After choosing the optimal one, the team informs the contractual ‘Clause-32’ programme using ALICE data and generates a weekly lookahead plan for the site.
"Using ALICE during the execution phase of our work on the Copthall Tunnel has enabled us to identify opportunities to work even more efficiently during the course of the build."Senior Project Manager, SCS JV
With the ALICE platform, SCS identified the ideal production rate, which was then adopted by the build team. What’s more, through its exploration of alternative options, SCS JV was able to generate more than three months of float for the project schedule.
“Using ALICE during the execution phase of our work on the Copthall Tunnel has enabled us to identify opportunities to work even more efficiently during the course of the build,” said Raymond Moloney, Senior Project Manager at SCS JV. “It also has helped us to reduce schedule risk by increasing float. This work represents a second big win for us with ALICE, and we are keen to use this construction optioneering solution on other projects as we continue our work on the HS2 network.”
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