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Overcoming problems with hole deviation

5th February 2013


A quartzite quarry in Virginia wanted to increase its production and had also been experiencing problems with hole deviation. It replaced its drilling equipment with a Tamrock Pantera rig equipped with Sandvik’s new Sandvik60 drill steel. Productivity has gone up by more than 50 per cent, they’re able to use the same rig at two other quarries – and their holes are straighter. By Steve Minett.

Salem Stone Corporation was started in 1983 when Leonard D. Hill bought the Sylvatus Quarry, near Hillsville, Virginia. Sylvatus is a quartzite quarry and the company now also owns six other quarries in Virginia and West Virginia. Three of them produce limestone products, one ‘accostone’ (which is a limestone variant) and two are sandstone quarries. Salem Stone employs 150 people, 22 of them at Sylvatus. 75 per cent of the stone produced from Sylvatus is used for road surfacing by the states of Virginia and West Virginia. This consists of fractions ranging in size between 3/57 to 2 inches. Other products include three classes of ‘rip-rap’, ‘erosion stone’, for road verges and stone for walling.

Difficult drilling

Roger Ramey, Superintendent based at the Sylvatus Quarry, explains that, “we do all our own drilling and blasting. The drilling conditions at Sylvatus are really quite difficult. The rock is very hard and abrasive and the geology is seamy with vertical fault lines. Hole deviation is a major risk in these conditions. It can result in ‘blow outs’ during blasting, especially if the deviation occurs towards the bottom of the bench. If hole deviation was really significant, we would have to re-drill holes.”

New drilling equipment

This risk, together with a desire to increase production, motivated a major upgrading of the quarry’s drilling equipment. “Eight months ago we had two rigs operating here using T45 drill steel. We decided to replace these and as part of the selection process for the new equipment, we carried out trials of rigs from three different manufacturers here at the quarry. Our drill rig operator, Berlin Cook, had a big say in the final selection. The one he liked best was a Tamrock Pantera rig. We tried out a Pantera 900 using T51 steel, but this really wasn’t big enough for our requirements. So, we finally settled on a Pantera 1100 using the new Sandvik60 drill steel.”

Increased productivity

One of the major benefits from acquiring the new rig has been a very significant increase in productivity: “I’d say it’s increased more than 50 per cent. Firstly, we now using one rig at Sylvatus, where previously we had two rigs. This has been an obvious saving in terms of machine maintenance and having only one driller. Secondly, we’re now also using the Pantera at two other quarries. Previously, the drilling at these quarries had been sub-contacted. So, again, this has been another obvious saving.”

In terms of service life for the drill steel, Roger reports that, “the life of the T45s varied a lot, but I’d say that the average was 8,000 feet. The Sandvik60s, however, are lasting around 14,000 feet. In addition, we’ve got a very good service from the local Sandvik Tamrock distributor on replacement steel.”

The average drilling rate of the Pantera over a week is 3,000 feet. Though it recently achieved a record week drilling 6,000 feet in one of the company’s limestone quarries. And, with the new rig, each foot drilled is more productive, as Roger explains; “Since switching to the larger drill steel, we’ve also increased the size of hole we use from 3.5 to 4 inches. The larger holes mean that we can spread out the pattern of holes we drill for each round.”

Straighter holes

In addition to raising productivity, the Pantera-Sandvik60 combination has also addressed the other major issue which motivated the company to change its drilling equipment; namely hole deviation. According to Roger Ramey, “the hole deviation problems which we were experiencing with the T45 steel have improved by about a third since we switch to Sandvik60. I believe that the female coupling arrangement in the Sandvik60 steels has contributed a lot to this improvement in hole straightness.

More holes a day

Berlin Cook, the rig operator, reports that, “on the old rigs I was able to drill an average of 10 holes a day, whereas with the Pantera and the Sandvik60 steel, I’m averaging 16 a day.” Another feature of the new equipment which Brian likes a lot is the ease and speed of the automated decoupling system; “I’d say that the decoupling process is 50 per cent  faster on the Pantera compared to the previous rigs.”

Fig. 1. Salem Stone recently acquired a new Tamrock Pantera 1100 drill rig.

Fig. 2. Berlin Cook, the rig operator, reports that, “on the old rigs I was able to drill an average of 10 holes a day, whereas with the Pantera and the Sandvik60 steel, I’m averaging 16 a day.”

Fig. 3. The Sylvatus Quarry, near Hillsville, Virginia.

Fig. 4. According to Roger Ramey, Superintendent based at the Sylvatus Quarry, “the hole deviation problems which we were experiencing with the T45 steel have improved by about a third since we switch to Sandvik60.”
 









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