Boart Longyear on taking underground drilling techniques outside the cavern

Whether it's challenges with an underground coring project, or a surface drilling application where underground coring rigs need to be used, it's the underground drilling crews who need to figure out the logistics and get the job done safely and efficiently says Boart Longyear.

First, you have to start with assembling the team which could be made up of drillers, driller assistants, welders, mechanics, supervisors, and other support personnel. Then scheduling the equipment that will be required on site. But just showing up with a good crew, the right rigs, fuels, and supplies doesn't mean the project will go as planned. Drilling crews have to consider if the work is local or in a remote location, how to travel, will the weather be favorable, does altitude present a problem, will the team have to spend extended time away from family and civilisation, and the list goes on.

Many drilling projects do run smoothly as crews approach with a can-do attitude, great work ethic, diverse skills, vast experience, technical knowledge, and a commitment to safety and each customer's success. The work is strenuous, involves extensive training, and requires their full attention for safety's sake. So how does one tackle more complex challenges that may not have been expected at the drill site. IM received some insights from the Underground Coring Crew at Boart Longyear to see how they have addressed some recent challenges.

First, it is common for drill crews to start a project in a mine that is dry, only to find that not far below the surface, a high volume of water is waiting to blow all of the tooling out of the hole and start filling the cavern. Encountering water in mines can result in a number of dangerous scenarios including becoming a complicated mess, flooding the work area, loss of equipment, risk of injury, and even threating life.

In one such drilling project, a Boart Longyear drilling team had begun their underground coring activities, when they unexpectedly drilled into a cavity of water. Time is of the essence in these situations and a lot of communication is required to keep people safe and to handle the problem before it becomes even more difficult to manage.

In order to shut off the water coming into the mine, the team successfully installed a cement collar casing using a pressure-grouting method, a blow-out preventer (BOP) and rock pack. The BOP is used to seal, control, and monitor water which will prevent future blow outs and any possible uncontrolled release of high-pressure water. This solution allowed the crew to manage the water, keeping the mine clear and dry so the exploration drilling project could be completed.

In another situation, when a US mine was facing a flooding problem that was hindering underground exploration coring activities, they called on the Boart Longyear drilling services team for assistance. This particular mine had two shafts located at different levels, one above the other. Pumps had already been installed in the deeper shaft to pump water to the surface; however, it was the upper shaft that had been flooded and where no pumps had been installed.

Instead of attempting to install additional pumps in the flooded upper shaft to remove the water, Boart Longyear analysed the situation to come up with a better solution. The drill team mobilised their underground coring rigs, taking them down to the lower dry shaft. With the rigs’ ability to setup quickly and drill wide angles, the team drilled a fan-shaped series of up-holes to the flooded shaft area above. Using this technique and taking advantage of gravity to drain the water from the upper shaft, the team was able to move the water into the lower area where the pumps were installed and could move the water efficiently and safely to the surface.

This smart yet simple solution enabled the mine to reopen the upper shaft and start again on mining operations, which included the commencement of their diamond coring exploration project by the Boart Longyear drilling team.

They may be called underground rigs, but that shouldn't limit the variety of applications these mobile and versatile underground rigs can be used for. When a delay was experienced in an underground diamond coring exploration project, a Boart Longyear drilling team started looking into creative ways they could instead utilise the idle underground rigs on the surface.

The underground rigs were quickly put to work on the same mine site, but above ground drilling flat-angled holes. The mine site had a limited surface disturbance permit, which meant that to reach the geological formations outside the area of their disturbance permit, low-angled and flat holes needed to be drilled. Because of their truck-mounted tall masts, surface drill rigs often can't reach these types of formations, whereas the underground rigs could.

Boart Longyear underground drill rigs can drill at low angles from -40 degrees down to flat, following ore veins without disturbing the surface. This means underground rigs have the ability to drill underneath the area where the mining client isn't allowed to disturb the surface and is therefore outside of the issued disturbance permit.

"Using a surface coring rig set up flat, you’re going to be 12 ft (3.66 m) off the ground because the mast is way up on the truck carrier," said John Sanchez, Operations Manager for Boart Longyear's Drilling Services. "With the underground coring rigs, we were able to construct a work platform enabling the team to work right up close and get angles of -40 to -12 degrees with boreholes going 2,600 ft to 2,700 ft (792.48 m to 822.96 m) deep, which the surface rigs couldn't have accomplished."

According to Sanchez, the customer was so satisfied, that the underground coring rigs have been drilling these low, flat-angled boreholes ever since.

Additional examples of Boart Longyear drilling teams utilising underground rigs on the surface includes using horizontal drilling methods for dewatering purposes. The flexibility of the underground rig allows for the drilling of flat to close-to-horizontal boreholes used to create self-draining dewatering boreholes in high walls. Angles used for this purpose are typically between ten degrees up to ten degrees down.

Another benefit compared to other rigs used for dewatering, is that chuck-drive underground coring rigs drill slower, straighter, and deeper and collect core for further analysis. When a customer uses large rotary rigs for dewatering, they get instead chip samples and use lower rotation per minute (rpm) but with higher torque, whereas a coring rig operates at higher rpms and less torque.

When horizontal drilling with underground rigs, pressure grouting techniques are used to add a cement collar casing that will keep the hole from collapsing. A BOP valve can also be added to enable the mining client to shut the water off in the rock formation when it is required. To add more stability, Boart Longyear's drilling service teams will also insert a slotted polyvinyl chloride (PVC) pipe which will keep the hole from collapsing. If you go through a broken zone, when water starts flowing, the hole can bridge off after a couple of months. The PVC keeps the hole open and the water running.

Drilling high walls with underground coring rigs accomplishes two goals with one borehole – dewatering and obtaining core samples. These core samples can be used by geologists to look for fractures, faults, and oxidation. This allows them to identify water-bearing zones within the formation. Although these zones can also be identified in chip samples using rotary drilling rigs, it is more difficult to see them using this method, whereas a core sample will always provide a better physical view of the rock formation.

Boart Longyear is also in a unique position offering both engineered solutions in the forms of reliable equipment and tooling, as well as the experience of well-trained underground coring drilling services teams. As outlined in the previous project examples, the drilling teams bring technical expertise to safely and efficiently drill dewatering galleries, geotechnical borings, tunnel investigations, grouting services, and utility borings.

The company is well-known in the industry for manufacturing LM™ and MDR™ underground drilling rigs that are sold throughout the world. Boart Longyear told IM: "The LM series of rigs feature easily interchangeable components, allowing for space constraints without sacrificing depth requirements. These modular coring rigs offer easier access in tight underground spaces, and mobility for easier moves from hole to hole or shaft to shaft. Boart Longyear's patented tooling offers safer and more efficient up-holes at any angle."