Mainmark fills Nelson culvert no longer in use

The box culvert had a two tier design, with a 0.6m elevation change at the midway point of the culvert roof. One section of the culvert measured approximately 9.5 lineal metres across with a height of 2.4 m, and the other about 8.3 metres across with a height of 1.8 m. 

The product used to fill the culvert had to be flowable, but also heavier than water to prevent any material floating rather than filling the space. The Downer team was having difficulty in providing a clear method that would meet the QA requirements for their client. The team also had limited access into the culvert, which meant filling it completely was more of a challenge.

Carl McCoy says, “We chose Mainmark as they have engineering expertise in that area and were also able to supply the right materials for the job.”

“Our original proposed method wouldn’t have worked for the client’s specification, so Mainmark was brought in to develop a methodology that would work.”

The Mainmark team consulted on the design of the culvert fill and decided to use Terefil, a technology used to create lightweight cellular concrete. For this project’s needs, the bespoke mix consisted of sand, cement, and Terefil polymer. This was engineered to meet the required density and strength of the project — 1,100 – 1,200 kg/m3 target density and a target strength of 1.5 – 2.5MPa.

Terefil was particularly suitable as it can be designed for specific applications and its flowable nature was able to overcome the unique two tier design of the culvert . 

Belal Haidari, the Site Engineer from Downer, says a few factors made Terefil ideal for the job. “The methodology of being able to pour it into the culvert, and being able to fill those little gaps at the top. The material being really flowable and reaching the required strength over a very short period of time was also something we considered.”

“It worked well with the spacing and the amount of room that we had.”

Up to 82m3 of the bespoke Terefil was supplied after consulting on the plans provided by Downer, and the work was finished in a total of 3 working days.

At the conclusion of each stage of the fill, verification was met with Terefil being observed coming out of the installed breathers. This, in conjunction with the theoretical volume being reached, marked the completion of the works.

Mainmark was able to meet the project requirements and deliver a specified, premium product in a timely manner. The team’s input on design and ability to deliver a bespoke solution was the ideal outcome for Downer and their client.

As the site engineer, Haidari comments that “It was a good crew on site, really switched on and onto it when doing the checks and making recommendations. That made a big difference.”

7- and 28- day compression test results of the Terefil material showed that the desired strength specifications were met. Mainmark was able to perfect a methodology for large culvert abandonment projects, including overcoming difficult access issues.