Improving steel casing installation in underground mines

In underground mining, steel casing or steel pipe is used to line holes that have been bored or drilled for rising mains water, utility lines and paste fill, protecting the contents from damage and loss into open voids or broken ground.

Installing steel casing using conventional welded methods can be time consuming and costly for underground mining projects. Depending on the requirements, it can take days to install and necessitates additional labour and equipment hire, such as boilermakers, chairing frames, cranes or integrated tool carriers.

Following a rigorous development process, Australian mining contractor Pybar Mining Services is offering an improved service.

Pybar chief operating officer Brendan Rouse said the company’s specialist drilling division received a tender for in-the-hole (ITH) drilling and installation of steel casing for paste fill application.

“The team identified an opportunity to streamline the drilling and installation process by using one drill to conduct the drilling, reaming and casing operations while also improving safety, efficiency and reducing delays associated with carnage, suspended loads and hot work in an underground environment,” Rouse explained.

In collaboration with steel casing manufacturers and engineers, a threaded casing installation system, which is far more productive that traditional welded methods, was designed.

The ability to lift, rotate and lower the casing mitigates some of the risk associated with the casing hanging up or becoming stuck part way down the bore hole – common issues often encountered when installing steel casing.

Completely eliminating hot work and the associated management controls from the underground environment, the threaded casing system features specially designed joints comprising of external couplings with machined tool joints, specialised installation tooling and casing hanger.

The casing has been engineered to exact specifications and ensures a consistent pressure rating is maintained throughout the length of the installation. The method results in flush internal joints, greatly increasing the life expectancy over the butt-welded casing method by reducing wear points for erosion of the casing.

For life of mine applications, ceramic coating is also available to further increase the casing life. In addition to paste fill, casing can be manufactured to suit a variety of applications, including service holes and rising mains applications.

The Cubex Aries ITH drill, a recent addition to PYBAR’s drilling division, was designated as the ideal drill for installing the system.

While raise bore rigs have previously been used to install steel casing, the highly flexible Aries ITH offers a far greater range of angles where casing can be installed over raise bore or conventional welded methods. Costs can be further reduced with longer lengths of casing and, compared to the raise bore installation, there is no requirements for cement pads.

Productivity gains at Gwalia

The Aries ITH has recently been used to complete a drill, ream and casing installation project at St Barbara’s Gwalia gold mine in the Goldfields region of Western Australia.

A pilot hole was diamond drilled due to the shallow design angle of the hole. The Aries was then used to ream the hole to 254mm in diameter and install the six-inch schedule 80 steel casing in the 82m hole, 24 degrees below horizontal.

The casing was installed in a single shift without incident. It is estimated that using welded methods, the installation would have taken up to five days.

“The results at Gwalia clearly demonstrate the efficiencies achievable by applying this method. In addition to increased productivity, we strongly believe this method greatly improves the safety and quality of the casing installation for our clients whilst greatly reducing the associated labour costs over conventional steel casing installation methods,” Rouse said.

Mounted on a mobile articulated carrier, the Aries can drill on a 360-degree rotation plane making it one of only a few tyre-mounted drills with this capability that is available for contract services in the Australian market. Service, production and slot holes can all be drilled with the one machine.