Support design, Wynyard Walk Pedestrian Tunnel, Sydney, Australia

A world-class walkway, the pedestrian tunnel allows people to walk from Wynyard Station to Barangaroo in approximately six minutes, avoiding steep inclines and road crossings. The project increased capacity of Wynyard Station to meet current and future demands, including catering for the Barangaroo development which accommodates 23,000 office workers and attracts up to 33,000 visitors per day.

PSM was engaged to design the temporary tunnel support and permanent structural lining of the pedestrian tunnel, as well as provide for drainage and waterproofing. Detailed site investigations were undertaken to assess the stability of the footings of the overlying 21-storey building.

Construction phase services included geological mapping of exposed conditions, assessment of construction works and instrumentation results, and review of support requirements.

This shallow tunnel is very close to live traffic and buried services, with the tunnel crown excavated through old fill at the Western portal. Existing infrastructure included footings from a 21-storey building founded just above the tunnel.

Engineering and technical opportunities included:

• Compromised spanning ability of the rock above the intersection known as the kink due to the presence of a deep sewer trench requiring development of a novel support system
•  Redesigning a more compact tunnel lining during construction to fit beneath unexpectedly deep services
• Tight horizontal and vertical displacement limits, in particular for the footings of the overlying building.

Following rigorous assessment and modelling, PSM’s tailored approach included:

• Assessment of the stability of the footings of the overlying 21 storey building
• Provision of construction phase services including geological mapping of exposed conditions, assessment of construction works and instrumentation results, and review of support requirements
•  Use of an innovative structural engineering approach whereby temporary support at the ‘Kink’ intersection behaviour changed from 2D to 3D before breakout which involved arching in two directions and intricate design and construction
• Development of a rational load sharing approach to acknowledge the structural contribution of the primary support to the permanent structure
• Redesign of the 25 m long primary-as-permanent section which required development of structural and waterproofing details to achieve the functions of both the temporary and permanent support in a much more compact form.

• Concrete Institute of Australia 2017 Award for Excellence in Concrete in the Infrastructure category.

PSM successfully interacted with numerous stakeholders and provided practical solutions to a range of extremely complex design issues and constraints, including unforeseen geometric constraints. PSM’s innovative design solutions satisfied all project requirements and were successfully implemented by the contractor.

Services: #Award Winning #infrastructure #Tunnelling