Rock to Road

Equipment Pits & Quarries
Rock drilling solution delivers safety and productivity

Rock drilling solution deliber safety and productivity


July 28, 2008
By Andy Bateman


Topics

With fewer new roads being built, today’s roadbuilders are often involved in projects to upgrade and widen existing highways for additional passing lanes, clear zones and improved lines of sight. Where road widening involves rock removal, the challenge is deciding how best to make relatively narrow cuts in rock that is frequently steep sided, uneven and inaccessible. This roadbuilder’s solution is an excavator mounted custom drill that is delivering good productivity, good reach and safer one-man operation.

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With fewer new roads being built, today’s roadbuilders are often involved in projects to upgrade and widen existing highways for additional passing lanes, clear zones and improved lines of sight. Where road widening involves rock removal, the challenge is deciding how best to make relatively narrow cuts in rock that is frequently steep sided, uneven and inaccessible. This roadbuilder’s solution is an excavator mounted custom drill that is delivering good productivity, good reach and safer one-man operation.


Drilling and blasting supervisor Bob Bambrick explains that Cruickshank Construction Ltd. was successful bidder on Ministry of Transportation of Ontario (MTO) contract 2007-4020 to widen, regrade and repave an 11.3 km section of Highway 41 north of Kaladar. Here, part of Highway 41 runs immediately alongside Upper Mazinaw Lake, with the original pavement cut out of native granite. New work included drilling and blasting rock outcrops on the two lane highway’s west side to create sufficient additional width for 3 m wide shoulders on both sides and improve sightlines for southbound traffic.


Cruickshank’s custom solution teams a Furukawa HD712 drifter with a TEI Rock Drills rotary head and drifter rail, all mounted on a Caterpillar 235C excavator. A separate 300 cfm compressor provides the air for the drill’s dust collection and clean out system. According to Bambrick, this set up combines the productivity of a crawler drill with a safer set up that does not require a second man on the face during drilling.


If the top of a rock face is inaccessible, a contractor drilling steep and narrow rock cuts along a road has only really two choices – use a drill working up on the face itself or drill from the road surface below. Bambrick explains: "If a machine such as a crawler drill is used, access tracks have to be cut into the rock face. On this contract, the rock cuts ranged in width from 0.5 to 3.0 m so it would not be cost effective to spend time making tracks for these narrow cuts. Alternatively, drill access can be provided by berms, built at right angles to the face and out into the roadway. This method would have also been impractical here as berms would occupy the southbound lane and so require daily reconstruction."


Contract conditions state that work inside temporary lane closures cannot begin until 30 minutes after sunrise and the road has to fully reopened to traffic at least 30 minutes before sunset. It is significantly more cost effective to have the holes drilled by a machine working from the road surface.

"This approach eliminates the issue of face access but does require a much larger machine to provide the necessary reach. Drilling from the road is not new, but our previous air operated models required a second person on the face and were less productive in any case. With the new set up, the drill is operated by remote control from the excavator cab. No personnel are close to the drill while the hole is being drilled, thereby eliminating the risk of entanglement with moving parts as well as noise and dust. At the same time, the excavator is operating from a firm and level road surface."


On this contract, 76 mm diameter pre-shear holes were drilled at 0.76 m centres, followed by production holes, typically 3.66 m deep, at 1.53 m centres in single or double rows depending on local conditions. The unit also proved useful where blasting mats had to be hung from steep rock faces. In these situations, 0.6 m deep holes were drilled at 1.53 m centres, with a 0.9 m long steel rod inserted into each hole to provide a firm wall anchor for blasting mats weighing up to 2750 kg.


Turning to equipment capacity, Bambrick reports typical production rates of 275 m per day although that figure can vary widely with operating conditions. On flat ground the rig can drill at a height of just less than 6 m from the excavator pad to the bit and its horizontal reach is 7.3 m. For the operator, being seated some 2.5 m above the road level provides an improved line of sight as well as additional protection from loose rock. At over 42 tonnes, the 235C has both the weight and durability to provide a stable platform for the drill.


Bambrick credits Furukawa dealer Eastrock Inc. for combining the unit’s elements into a practical working tool. Eastrock did a considerable amount of initial work to fit together the mast, head and drifter, add hydraulic lines, a dust collector and follow up with site support. After a successful first season, the unit has been in Eastrock’s Ottawa shop for the addition of a custom designed and fabricated single rod adder. Bambrick explains: "The rod adder carries a 3.7 m rod. Allowing 0.6 m for the stabiliser, the drill’s 6.1 m long first rod provides 5.5 m net drilling depth, so the 3.7 m provided by the additional rod will enable us to drill a 9.2 m hole in a single pass."

Bambrick adds that the HD 712 drifter was selected based on good performance by a Furukawa HCR 1200 production blast hole drill, also fitted with a HD712 drifter, that is typically on production blast hole duty at Cruickshank’s Kemptville quarry.


For transportation the unit currently needs two floats as the 9.2 m long mast has to be removed. To simplify and reduce the cost of future moves, Bambrick is looking into the possibility of towing the mast on a smaller at a smaller dedicated trailer, probably towed behind a 5-tonnes capacity truck. n