Surface solutions

Surface rock excavation jobs are not necessarily associated with major infrastructure schemes like roads and railways. Indeed, some of the most difficult work comes in urban settings, where contractors are not only challenged by the rock conditions, but also by the need to be considerate, by keeping dust, noise vibration and general disruption to a minimum.

A typical example of this is came with the extension of a shopping centre in Sollentuna, about 20 km north of Stockholm, Sweden where owner/operator Roland Sjögren used the combination of a Commando 120 rig and Sandvik Alpha 250 rock tools to excavate the foundation pit.

“The new Sandvik Alpha 250 rock-tool system works incredibly well,” he said. “At one work site I drilled with it for several days in very poor rock, in which the drill-string &rattled' in protest, yet the tool system held out admirably. Sandvik Alpha 250 is a good thread, and it is very easy to uncouple when you need to change the bit.”

A key requirement at the Sollentuna shopping centre is of course to keep disruption to a minimum. It is a challenge Mr Sjögren relishes. “I am quite happy to work near houses and other buildings, where the demands on me as a rock blaster are much higher,” he declared. “Cautious blasting assignments are my speciality.”

From the radio remote-control box around his waist, Mr Sjögren deftly lowers the Commando's boom, raises the jacks and drives the rig remotely to the next drilling spot. He walks safely ahead of the machine, which follows him like an obedient dog. The lightweight, versatile, four-wheel drive, highly maneuverable Commando 120 is perfect for this kind of job.

The crucial part of a drill rig is of course the rock drill, Hex 1. It has been developed specially for the Commando 120. It has a greater percussion frequency and impact power than its predecessor as well as a higher rotation torque. The rig is also equipped with a larger compressor to ensure efficient flushing, even with higher drilling rates and larger drilling bits.

The four-wheel drive makes the Commando 120 even more agile than before. The machine is equipped with a powerful 37 kW engine, and a 24 Volt electrical system ensures improved cold starting.

But the rig itself is only part of the story. Durable and efficient rock tools are critical to good penetration rates and minimising downtime, and this is where the Sandvik Alpha 250 system comes in. It features a unique, high-strength interface between the rod and the bit that was initially developed for underground applications. The surface version, which uses Hex 25 shank rods, followed shortly afterwards, partly ast the request of Sandvik drilling tools salesman Tommy Johansson.

“Trials went exceptionally well, so much so that customers who had previously complained of problems with conventional rope-threaded equipment suddenly fell silent. It has become the first choice of tool system for single-pass drilling with the Commando 120 and other light rigs in the Uppland area of Sweden,” he said.

In contrast to drill rods with a conventional rope thread, behind which is a bottleneck that often limits the service life of the rod, Sandvik Alpha 250 has a straight, very rigid connection between the rod and the drill bit. The rigidity has been achieved by shortening the thread and creating a close fit between the back of the bit skirt and the base of the Hex 25 rod section. With the bottleneck eliminated, the risk of bending and breakage when collaring holes on uneven rock surfaces is greatly reduced and the tool system drills much straighter holes.

Indeed, this the greater quality of holes means that drilling professionals like Mr Sjögren think they will be able to use smaller bits and hole diameters. Mr Sjögren normally uses 38 to 45 mm bits for urban drilling jobs. “But,” he said, “I am going to try drilling 35 mm holes with Sandvik Alpha 250. It makes no sense to continue drilling 38 mm when I mostly charge the holes with 25 and 28 mm cartridges.”

Selection Criteria

Concerns like safety, efficiency and solid back-up from suppliers, are key to the success of drilling operations anywhere in the world. For example, J.B. Jones Drilling, one of the biggest and drill & blast contractors in Atlanta area of the US uses these criteria to select equipment. Most of the company's work now involves site preparation for house building, including road cuts and outfall work, preparing trenches for sewer and water lines. That means its drills must work in a variety of rock and soil conditions, everything from granite to mud - or “swamp” as founder Joe Jones calls it.

The company uses Tamrock Ranger 700-2s, Ranger 800-2s, CHA 1000s and CHA 1100s. It also runs a Rammer breaker. “Safety has always been our number one concern for our employees,” said Mr Jones, “And Sandvik Mining and Construction has always been very good about providing the training that can help our operators run these drills in a safe and efficient manner.”

Company manager, and Mr Jones' daughter, Caroline Jones added, “I feel that the Tamrock drills, due to their versatility, give us the opportunity to be more flexible with whatever conditions we find, from mud to rock. And when ground conditions are bad, we can still get the Tamrock drills to the work sites.”

Tamrock Ranger drills are crawler-based, self-contained, hydraulic top-hammer rigs used in construction, quarrying and surface mining operations. An optimal hammer and power pack for each of the series' four models (including the Ranger 500-2 and the Ranger 600-2) ensures that every hole size between 51 mm and 127 mm can be drilled efficiently, even in extreme or fractured rock.

The Tamrock Rangers' efficient design mounts the power pack at the rear, counterbalancing the boom and feed assemblies; this reduces overall weight and makes them exceptionally stable. The rigs' revolving superstructure swings in a 120° arc (180° is optional), offering a large coverage area - 17,6 m² (with 26,4 m² optional). This also allows the operator to face towards the drilling spot at all times.

Using the best products available on the market obviously help the likes of Caroline Jones and Roland Sjögren sharpen their competitive edge. But what is perhaps more important is the relationship they have with their suppliers - companies like Sandvik that listen to their requirements, and deliver whole systems of rigs, tools and back-up that make a big difference to overall productivity and safety. •