New Zealand Geotechnical Society (NZGS) Symposium 2021
The City Rail Link project connects the existing Britomart rail terminus in Auckland’s CBD with the Mt Eden Station on the North Auckland Line. The c.3km-long route traverses a wide range of geology and ground conditions. Most of the tunnelling will be within Waitemata Group rocks (East Coast Bays Formation, ECBF) that underlie much of the wider Auckland region, while shallower structures at the north and south of the project will also encounter younger sediments (Tauranga Group); volcanic materials (Auckland Volcanic Field, AVF); made ground (including reclamation). . Show more…Desk studies and early site investigations established a broad model of ground and groundwater conditions, while later investigations focused on specific design requirements, material characterisation and/or ground risks (and opportunities). Targets included a 10m-thick mega-bed (in ECBF) at Karangahape Rd Station; anomalous ECBF weathering profiles; complex AVF materials and geometry at the south end of the project; a pre-Holocene paleo-channel under Britomart; post-volcanic spring/pond deposits in the valley between two volcanoes in the south; and undocumented structures in the built environment. Various works packages were procured using a variety of contract styles. However, procurement documentation has generally included a geotechnical baseline report (GBR), supported by ground data in geotechnical data reports. An observational approach was specified for parts of the works, particularly where opportunities for ground investigation during the design phase were limited. Innovation during procurement includes the use of 3D ground models in two of the contracts. A static 3D model was included (for information) for the Mt Eden enabling works area, to illustrate the complex relationships between proposed structures and varied ground units. In a world-first, for Seequent’s Leapfrog/Central the main works tender included a cloud-based 3D geology model and geotechnical database for each tenderer, readily allowing development of their own geology model and facilitating alignment on geotechnical risk during the Alliance GBR process. Show less…
