4/2/2012

Project innovations are piling in


The Perth City Link Rail Alliance is putting in place a number of innovations to improve safety, reduce error and save time.

Though they may sound like household items, qui (pronounced key) cutters, d-wall vacuums and single handling in the cage lifting process are all onsite improvements to simplify the way the project is delivered.

Qui cutter
Typically, pile heads are removed from the concrete using manually operated jack hammers that create dust, vibration, noise and ‘flyrock’ safety issues.

Foundation Project Engineer Maggie Suchorska said qui cutters were identified as a safe and fast way of removing the pile heads, with minimal noise and vibration.

“The Qui cutter method involves casting an expandable foam into the concrete, which reacts with the water in concrete and expands to create a continuous crack when the concrete sets,” she said.

“When the crack appears, the pile head can be lifted from the rest of the pile using an excavator or crane, removing many of the safety issues originally linked with this work.”

D-wall vacuums
Diaphragm walls, a.k.a d-walls, are water-blocking reinforced concrete walls used to build the Fremantle Tunnel foundations.

Built from the bottom-up, concrete is poured into trenches that contain bentonite, a water absorbing mineral that fills the trench and prevents the walls from collapsing before the concrete is poured.

The concrete can become contaminated when it mixes with bentonite, making it unusable for permanent works.

Usually, this contaminated concrete is broken down using jack picks and replaced. Identifying an opportunity to reduce noise and improve the safety on this process, vacuum trucks are used to ‘suck-up’ the top layer of Bentonite and contaminated concrete, before the concrete hardens.

Prefabricated steel reinforcement cage lifting and hanging process
The steel reinforcement cages for the D-wall panels are fabricated offsite, then transport to site and lifted in the excavated trench.

To achieve the length of the D-wall panel, the first reinforcement cage is lowered into the trench and held in position to enable the second reinforcement cage to be spliced to the first. Once this is completed the whole panel is lowered to the final position. Concrete is then placed using the tremie method.

Previously the lifting chains around the reinforcement cages were removed ‘blind’.

After consulting with the onsite team a single handling method that would reduce the amount of time taken to adjust the cage to the correct hanging height was identified.

Through the simple process improvement, safety has increased dramatically as no works in the Bentonite is required, and the interaction between lifting chains and hanging chains is eliminated.