Groundfix

CATEGORY 1: Projects with a value of less than $1 million

Grouting under pressure

Projects don’t come much bigger than the $1.4 billion Waterview Connection Project currently under construction by the Well-Connected Alliance (WCA), and a lot of the work is being achieved by small sub-contractors. Groundfix was invited by the WCA to tender for drilling and pressure grouting treatment works pre-excavation of a number of the Waterview Connection tunnel cross passages. This WCA sub-contract started June 29, 2015 and was completed September 16, 2015. The value was $295,000. During the first tunnel drive, high ground water flows were experienced near to the tunnel midpoint. It was identified that unless this groundwater CATEGORY flow was very substantially reduced, project 1 CONSTRUCTION EXCELLENCE AWARDS 2016 WINNER CATEGORY 1 minimum specification conditions would not be met and works within the cross passages during excavation and lining processes would be extremely difficult. The treatment works within the tunnel boring machine driven tunnel required drilling through the in-situ tunnel lining, from within one of the tunnels, to within 300mm of the adjacent tunnel lining. Pressure grouting was applied to seal out water bearing joints/fissures/fault zones.

These works were undertaken in the deepest section of the tunnel relative to ground surface where the water pressure and flow was at its highest.

Pressure grouting through carefully sequenced patterns of drill holes with specially designed and controlled grout mixes using specialist grouting additives was used to successfully seal out water, reducing water flow through full face excavations to only a trickle.

The treatment works was completed ahead of time, with double the number of cross passages treated than originally envisaged, and within the original budget.

Project works proved a substantial challenge with numerous risks, notably drilling through tunnel linings to within close proximity of the second tunnel, pressure grouting over pressurising the tunnel linings, blocking of the supply line to the tunnel boring machine requiring constant access through the tunnel, and the requirement of full interlock guarding of the drill mast rotating parts in accordance with health and safety regulations at the time.

All these activities relied very heavily on the expertise of the Groundfix team. l