Future-proofing the Toowoomba Bypass project

The Toowoomba Second Range Crossing (also known as Toowoomba Bypass) is a 41km long dual carriageway bypass and partial ring road that was completed in 2019. During construction it was discovered that reinforced concrete pipe culverts, located in the valley beneath the fill under the road alignment, had lost structural integrity. The culverts needed repairing to ensure the overland flow hydraulic capacity complied with design requirements. The seven culverts, measuring between 1350mm and 2200mm in diameter, with lengths ranging between 80 and 160m, each contained at least one damaged barrel, and several were compromised in up to five separate locations.

Mainmark used a multi-faceted approach to relining the reinforced concrete pipe (RCP) culverts, which involved inserting site fabricated corrugated metal pipes (CMPs) inside the damaged RCP culverts and then filling the annulus between the CMP and the original RCP culverts with a proprietary lightweight cementitious grout (Terefil). The grout was pumped from a single injection point, quickly and easily flowing to fill the annulus. The solution restored structural integrity to the compromised culverts, with minimal impact to hydraulic flow capacity. Mainmark's solution ensure the project's construction timelines, whilst complying with specific DTMR project requirements and providing a 100-year warranty.

Mainmark's engineering work to remediate the compromised concrete culverts with custom CMPs and the unique, environmentally inert Terefil grout solution allowed the 41km, $1.6 billion Toowoomba Bypass to reach stringent industry compliance standards set by the Queensland Department of Transport and Main Roads (QDTMR). The bypass has since been able to reduce travel time across the Toowoomba Range by up to 40 minutes for heavy commercial vehicles, improving freight connections to major ports and markets while relieving pressure on local roads by redirecting trucks away from Toowoomba's CBD, which enhances liveability in the Toowoomba and Lockyer Valley areas.

Mainmark's engineered solution contributed significantly to the Toowoomba Bypass' ability to reach design compliance and achieve project completion within the allotted timeframe. By combining custom manufactured corrugated metal pipes, which were designed and developed by Roundel Civil Projects Pty Ltd, with the unique Terefil grout solution, Mainmark was able to maintain the system's hydraulic capacity and provide long-term strength and stability to the existing concrete culverts, without performing major excavation or compromising the existing structure. The joining and sealing systems used to connect each section of CMP (ranging between 6 and 12m long) was specifically developed by Mainmark to withstand the grout pumping pressures during grout placement. Mainmark also utilised a specially developed landing skid, reel and winching system to install the CMP sections in a safe and economic manner. Mainmark's Terefil grout, which rheological parameters were specifically custom designed by Mainmark to allow long pumping distances without segregation, far surpasses that of ordinary grout material, contains a uniformly distributed matrix of air bubbles generated by mixing cement slurry with stable, pre-formed synthetic proprietary foam. The mixture results in a lightweight cellular concrete fill which can be pumped greater distances through a grouting pipe than typical grout void fillers.