Johnson St Bridge

Scope of Work

Our team installed 1830mm diameter casings with 25mm wall thickness, up to 33m long, through 18m of overburden into 340mPa granite rock. A 7m deep rock socket was completed below the casing tip. Due to the undulating bedrock profile, with grade differences of 2.2m across the casing diameter, pipe piles were fabricated on-site with cutting teeth and passed to a 160-ton crane on the work platform. The pier piles’ cut-off elevation was 3m below low water, necessitating a specially designed reinforcing cage suspension bracket to support splicing and concrete pouring. All concrete used was 45 mPa, tremie poured.

To excavate overburden, we employed a Leffer LKG1-180 Spherical grab, directly disposing of material into trucks. For seating the steel casing into bedrock and completing the 7m deep sockets, we utilized a Wirth PBA 612 Pile Top drill with a reverse-flood drilling system, recycling water through containment tanks.

Challenges & Solutions

The project’s primary challenge was maintaining installation accuracy, critical due to the pier substructure’s method. We achieved precision with all piles installed within 35mm of design position and 0.5 degrees of vertical. The rest pier, intermediate pier, and east abutment were supported by 1220mm diameter piles drilled through overburden, seated into bedrock, and completed with 3-5m rock sockets, reinforced and tremie concreted as specified.

Utilizing a Nissha RT150 rotator and Down-hole Hammer reverse-circulation drilling system, we managed tailings through a closed loop, ensuring clean and efficient operations. Each pile was flushed with fresh water and inspected via video to meet strict quality standards.

Overall Impact

This project exemplified CDI’s ability to deliver high-quality, precise construction in challenging conditions. Our innovative methods and dedication to excellence ensured the successful completion of the Bascule pier, reinforcing our reputation as a leading specialty foundation contractor.