North East Link Project, Melbourne, Australia Lower Plenty Road Interchange Diaphragm Wall Works-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes diaphragm-wall construction for the Lower Plenty Interchange on Melbourne’s North East Link Project, delivered by the Trevi Australia/Wagstaff Piling joint venture. The work involved 471 panels, up to 43 metres deep, with a 2.5-year installation programme.<br /><br />Construction faced contrasting ground conditions. The eastern side contained strong, hard siltstone that was slow to excavate, while weaker western rock was easier to cut. High groundwater and heavily fractured, folded rock created significant trench-stability risks. Several panels collapsed, sometimes after excavation and replacement of dense working bentonite with lighter casting slurry. Other contributing factors included large panels, long open periods, fluid-level fluctuations and inadequate fluid management.<br /><br />Bentonite became unusually dense as fine siltstone particles accumulated; standard desanding equipment could not remove the finest particles. Following collapses, the team reassessed stability and changed its methods: reducing panel widths in shear-zone areas, sequencing work to limit open time, and keeping casting bentonite heavier to provide greater lateral support. Collapsed panels were treated with grouting and lean-mix concrete, although repairs and re-excavation caused further difficulties, including slurry contamination.<br /><br />The presentation also highlights the importance of groundwater monitoring, careful slurry testing and management, and avoiding rushed compliance with specifications. An untested polymer used to meet a viscosity requirement caused bentonite to deflocculate overnight, contributing to a collapse. Other topics included congested reinforcement cages, glass-fibre cages for TBM soft eyes, and cross-hole sonic testing, which showed possible concrete-flow or signal issues around tube couplers and reinforcement.<br /><br />Overall, the project demonstrates how geological variability, construction sequencing and support-fluid control interact, and why field conditions must inform both design assumptions and construction procedures.

Keywords

diaphragm wall

Lower Plenty Interchange

North East Link Project

Trevi Australia

Wagstaff Piling

bentonite slurry

groundwater monitoring

panel collapse

hard siltstone

construction sequencing