Delivering a multi-billion-dollar, multi-record-breaking infrastructure project under immense public scrutiny is no easy feat – but it’s part of the challenge for James Holbrook, Director of Operations and Integration at Sydney Motorway Corporation (SMC).
James is part of the SMC management team which is leading the delivery of WestConnex – Australia’s most significant investment in road infrastructure; forming the central spine of Sydney’s future motorway network with connections to the future Western Harbour Tunnel, Sydney Gateway and F6 Extension.
At around 30 kilometres in length, the WestConnex project comprises the widening and extension of the New M4; duplication of the New M5; and connection of the two motorways to provide a long overdue underground link to create a seamless free-flowing western bypass of Sydney’s central business district for motorists.
Ahead of the Australian Tunnelling Conference, James told us that integrating WestConnex’s constituent projects (the New M4, New M5, and M4-M5 Link) and contending with extensive tunneling operations has created some significant challenges throughout.
“WestConnex has created some unique engineering challenges, the most significant being how we integrate three separately delivered tunnels with different D&C contractors while maintaining existing and proposed road operations. This is crucial as we need to ensure that when the M4-M5 link opens to motorists in late 2022, all stages of the WestConnex project work as one.
“Prior to getting to that point we’ve had to overcome a number of significant tunnelling and engineering challenges with both the M4 East and the New M5, in order to meet the final technical performance outcome for the projects.
“Twin nine kilometre tunnels are a major feature of the New M5 project which will run parallel to the existing M5 East to provide a non-stop underground journey between St Peters and Kingsgrove, doubling the motorway corridor from two to four lanes in each direction.
“With the New M5, not only are we excavating some of the largest sections of road tunnels ever seen in Australia (20m wide with junction caverns with 30m spans), but that is combined with the highly complex systems of shafts and tunnels required for the motorway ventilation operations.
“However, this engineering challenge is further exacerbated by the presence of known (and previously unknown) geotechnical conditions associated with the crossing of palaeochannels (deep soil sediments) and the nearby Cooks River.
“Geotechnical site investigations undertaken by the D&C contractor identified ground conditions that were significantly more challenging than originally anticipated. This included bedding features and fault zones that would create significant water inflow into the proposed tunnels.
“These challenges are relatively unique for Sydney, which is generally known for its good tunnelling conditions, when compared globally. And naturally, every time you unexpectedly hit a problem area, the cost and duration of the project is impacted.
“To address these challenges and meet the construction programme requirements, the D&C contractor has employed a number of design solutions and construction methodologies to mitigate the geotechnical issues.
A new challenge has been the adoption of Building Information Modelling (BIM) on a project of such complexity and magnitude.
“BIM or Digital Engineering has never been undertaken on any transport infrastructure projects in Australia before, including our own M4 East and New M5,” said James.
“Based on some of the integration challenges we face with the delivery of the M4-M5 Link and combined with the need to consider the nature of the technical information required to operate a road tunnel of such complexity for the next 40 years, we believed it called for a new approach.
“We’ve had to look at digital output and its future use in a much more meaningful and pragmatic way.”
James Holbrook will talk in further depth about the unique challenges of WestConnex and share insights into how these have been overcome at the Australian Tunnelling Conference – to be held 15-16 October 2018 in Sydney.