Cable Bolting Rig

Overview

A cable bolting rig installs long flexible tendons of steel strand into rock to provide deep ground support where short rigid rock bolts are not enough. In underground mines the immediate roof can be held with resin or mechanical bolts a few meters long, but large open stopes, intersections, and weak ground need anchors that reach far beyond the loosened zone into competent rock. Cable bolts, typically 15.2 mm to 28 mm steel strand grouted into a drilled hole, do exactly that, tying the near-surface rock back to stable ground several meters away. The rig is a single self-contained machine that drills the hole, mixes and pumps the cement grout, pushes the cable strand up the hole, and sets the surface anchor, all from a protected operator station.

The machine combines the functions that would otherwise need a drill jumbo, a grout plant, and manual cable installation. It is built around a Carrier Chassis that trams the rig through the drives, a Positioning Boom that aims the drilling and cabling head at the roof or rib, and a Grout System that produces the cement column the cable is bonded into. Because cable bolting is slow and repetitive work performed under unsupported or partly supported ground, the rig is designed so the operator stays under a protective canopy for the entire cycle.

Carrier and tramming

The Carrier Chassis is a center-articulated four-wheel-drive diesel chassis. Articulation through the Articulation Joint lets the long machine negotiate the tight curves of mine drives, while the Drive Axle units use planetary final drives and enclosed wet-disc brakes that tolerate the dust, water, and grit underground. Power comes from a Flameproof Diesel Engine fitted with an intake Intake Flame Trap and an Exhaust Scrubber so the exhaust is cooled and cleaned before it enters the mine air. A Powershift Transmission with a torque converter gives smooth low-speed control for spotting the machine accurately under each row of holes. When drilling, the Stabilizer Leg legs are lowered to take the bounce out of the chassis so the feed stays steady.

Boom and feed

The Positioning Boom positions the drilling and cabling head. It slews, lifts, telescopes, and rolls over so the same head can drill a vertical roof hole, then tilt to feed cable, then reposition to a rib hole without the operator leaving the seat. The Drill Feed and Head is a chain-driven beam carrying a Rotation Head that turns the drill string. Flushing water enters the rotating string through the Water Swivel, clearing cuttings and suppressing dust. Holes are advanced with threaded Drill Rod sections coupled in series and a tungsten carbide Drill Bit at the toe. Hole length is the limiting design variable: a single-pass beam can drill to its own length, while telescoping and rod-extension arrangements reach 12 to 15 m.

Cable handling and anchoring

Once the hole is drilled, the Cable Handling System system takes over. Strand is paid out from a braked Cable Coil Dispenser, pulled through a Cable Straightener to remove the coil set, and driven up the hole by a friction Cable Pusher. When the cable reaches depth the Cable Shear shears it to length. At the collar a Bearing Plate spreads the load against the rock and a Barrel and Wedge grips the strand once the grout has cured and the cable is tensioned. Bulbed or birdcaged strand patterns may be used to improve the grip of the grout column along the cable.

Grout system

Bond between cable and rock comes from cement grout, and the Grout System is what distinguishes a true cable bolter from a plain drill. A Colloidal Mixer of the high-shear colloidal type produces a dense, stable grout at a controlled water-to-cement ratio, usually between 0.35 and 0.45. The grout is held in an Agitator Hopper hopper that keeps it moving so it does not settle, then a Grout Pump of the progressive cavity type meters it through a Grout Hose and Lance and lance to the bottom of the hole. Grouting from the toe upward, either before the cable goes in or through a breather tube, ensures the hole fills without trapped air voids that would leave the cable unbonded.

Hydraulics and controls

Almost every function on the rig is hydraulic. The Hydraulic Power Pack pack carries variable displacement piston pumps, a baffled reservoir, an oil cooler, and a Valve Bank of proportional valves that meter flow to the boom, feed, pushers, and pumps. The Electrical System system provides low-voltage power, work lighting, and a Machine Controller that coordinates engine speed, hydraulic demand, and the drilling sequence. The Operator Station sits under a falling-object protective Protective Canopy with a Control Console and a Operator Display so the whole cycle is run from one seat.

Maintenance and variants

Wear concentrates in the grout path: the PC Pump Stator and PC Pump Rotor of the pump abrade against cement and are treated as routine replacement items, and the Grout Hose and Lance is flushed at the end of every shift to stop it setting solid. Drill consumables, the Drill Bit and rod threads, wear with rock hardness. Variants exist for very low seams, where the machine is built long and flat, and for large open stopes, where extended booms and longer cable capacity matter more than a compact profile. Some rigs add automated rod handling and a strand magazine to cut the manual work in a cycle that is otherwise one of the slower tasks in the mining sequence.