Ground engineering and asset preservation specialist, Mainmark, has used proprietary technology to address ground subsidence risk and fill a concrete culvert at Brisbane Airport in just three weeks.

Mainmark was contracted by Brisbane Airport Corporation, via a main works contractor, to complete permanent abandonment works of a 280m concrete enveloper culvert beneath an operational runway.

The project forms part of a broader program of works at the airport, which to date has included a temporary dredge pipeline installed beneath an operational runway to enable the placement of sand surcharge for the New Parallel Runway (NPR).

Following the removal of the temporary dredge pipeline that was installed in the concrete enveloper culvert, a site inspection revealed some structural damage to the existing enveloper, which Mainmark was contracted to repair.

The repair project was completed in two stages and adhered to the site’s safety standards. In keeping with the airport’s operational requirements, the project was completed over three two- day shutdown periods.

First, the pipe was sealed using Mainmark’s structural resin injection technology to protect the pipe against further water ingress. This advanced method is a proven solution for strengthening and re-supporting sunken structures. It is based on the expansive power of multi-component mixtures made from structural geopolymer resins and hardeners.

The second stage of the project required Mainmark to completely fill the pipe. Given the critical nature of runway operations, the specifications for a strong, yet light, fill material were rigorous.

The project required a lightweight and flowable solution with no shrinkage. It needed to achieve a minimum of 300 kPa compressive strength in 24 hours and a minimum value of 1 MPa at 28 days with a drycast density no greater than 1,400kg/m3. A stable filling with high sulphate resistance was specified, and a fast solution was needed to minimise downtime.

image02Mainmark developed a proprietary grout design mix using Terefil™, an air-entrained, lightweight cementitious mass void fill material, to meet the specifications. The mix was trial batched, cured and independently tested prior to the works to ensure pumpability and compliance with the project’s specifications.

Working around busy site conditions, Mainmark batched the grout locally. It was augmented and pumped on site using a purpose-built pump and truck-mounted injection equipment. As access to the runway pavement was not permitted during the works, Mainmark fabricated and installed six three-inch high-pressure grouting conduits within the pipe, totalling 1400 metres. These conduits allowed grouting to be undertaken from a single access point at one end of the pipe.

The filling operation was monitored in real time by 16 sacrificial cameras installed within the crown of the pipe, which ensured the pipe was completely filled and there were no air pockets in the crown of the pipe.

As a highly flowable and easily placed material, Terefil™ was ideal for this project. It does not require pre-loading or compaction for settlement mitigation, will flow into spaces to fill voids, and exhibits shrinkage of less than 0.1 per cent.

Compared to typical foam fills, the proprietary technology used in Terefil™ has increased stability, greater lift thickness, and can be pumped greater distances. Extensive compressibility testing has validated the ability of Terefil™ to resist cell collapse from pressure.

The project was successfully completed on time and within budget. The injected grout delivered a minimum strength of 1000 kPa and Mainmark provided a warranty of 50 years on work and material, with an estimated design life in excess of 100 years.

This partner content is brought to you by Mainmark. For more information, visit

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