That was the WSP team's aim when providing detailed engineering design and permitting support for the Nevada Gold Mines (NGM) Cortez Hills underground (CHUG) mine above 3800 expansion, in Nevada, USA.
WSP was responsible for the design of an ore handling system which included feeder breakers, a rock breaker, ore slide, ore bins and apron feeders, as well as a lined surface stockpile and water retention pond. Our team also designed a materials receiving area on surface, borehole systems to distribute materials such as fuels, lubricants and chemical additives below surface, and underground infrastructure including a cemented rockfill plant, a shotcrete plant, a fuel and lube bay, maintenance shop and a wash bay.
With safety at the forefront, the WSP team reviewed the design and equipment for potential hazards that could be eliminated, rather than controlled, through innovative design.
Innovative ways to keep workers safe
Our team incorporated two design elements that are expected to play a significant role in improving safety and turnaround times on maintenance, while also reducing costs, at the CHUG mine. Both pertain to the ore handling system which includes five ore bins which are 20 feet long, 20 feet wide, and 50 to 70 feet tall, with a ten-foot high vertical portion with a ten-foot high tapered cone that forms part of the ore bin. The chute leads to a feeder that supplies broken ore to an apron feeder, and hence to the conveyor system that takes the ore to surface. This whole system spans two mine levels and conveys ore up one of the declines, approximately 8,000 feet in length and 1,000 feet vertical.
With a focus on improving efficiency and safety, the first design innovation involved mechanical assistance for the spile bar insertion and retrieval process.
Spile bars are steel bars that are driven horizontally through holes in the sides of the ore bin chutes, through the broken rock that is in the bin. Spaced about four inches apart, spile bars form what are in effect horizontal fence posts which create a barrier to support the rock material in the bin while the apron feeder below is being serviced. After servicing is complete, the bars are pulled back through the holes and out of the bin to allow the flow of broken rock to continue.
Historically, it is difficult to drive spile bars through the rock mass in a bin and then pull them out again. In many mines, the bars are forced through the holes in the bin using a sledgehammer, which can be both time-consuming and hazardous.
Our team designed an insertion device using a hydraulic breaker similar to a jackleg. The drill is mounted on a cylinder that pushes the drill forward, which in turn is mounted on a trolley that can pivot. The trolley moves along a semi-circular monorail that allows the drill to access both sides of the bin. The trolley is used to position the hydraulic drill and cylinder in front of each of the holes in the bin in turn, holding the drill steady while it hammers each spile bar through the rock mass inside the bin, one at a time.
After all the bars are inserted, it is then safe for servicing to be carried out on the apron feeder. Clips attached to the end of each bar allow them to be pulled out of the bin using the same insertion device. This process can be conducted by one person and is a great improvement in speed and safety of operation.
The other WSP design looked to improve the reliability and safety of the ore-handling system – specifically, the bin that feeds the apron feeder. The bin’s walls are protected by replaceable metal liners that take the brunt of the impact from rock moving through the system. As “wear items” these liners must be inspected and changed out as needed.
In most mines, replacing these liners must be done from inside the bin at the bottom of a 70-foot rock raise. This has the potential to put employees at risk from “hang-ups” – pieces of rock that can get stuck on the shaft’s rough rock walls and fall unexpectedly.
Because of this danger, our team designed the bin so that the metal liners can be replaced from the exterior, eliminating the need for employees to enter the bin. This innovative design significantly improves worker safety as well as speeds up the maintenance process.
Our team's innovative designs are just one piece of this complex project. The CHUG project brought together WSP staff from six different offices and a wide range of disciplines from mechanical and electrical engineering, to rock mechanics, construction management and geotechnical engineering. This team worked in a collaborative and integrated fashion, giving Barrick confidence in the design and execution, as well as gaining efficiencies through the delivery of the entire scope by a single consulting firm.
Construction of this project was completed in 2020.
This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.