Gamuda-WCT turns to Sandvik for Qatar road-building solution

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The western section of the road runs from Al Shamaniyah to Nasarit on the outskirts of Dukhan, located 80km west of Doha. The new highway forms part of a proposed major road system providing access to the long-awaited causeway to Bahrain, the Salwan Road to Saudi Arabia and the new North Road.

Sandvik Tamrock drill rigs and rock tools are improving productivity on a 40km-long road project in Qatar, as the contractor works on tough terrain.

A Gamuda-WCT joint venture is building the US $206 million (QR750 million) western section of the Dukhan Highway, which is being built on a bedrock of fragmented coral limestone with pockets of hard limestone.

Built 18 years ago, the two-lane highway is being upgraded to a dual four-lane highway to provide improved access for the development of Dukhan Industrial city.

Originally, the contractor opted to use hydraulic hammers to ‘chisel' the limestone, relying on a fleet of more than 100 hammers fitted to 20-30-tonne excavators. But in some areas it was found that the hammers made little impact on the pockets of hard limestone, causing the contractor to fall behind schedule.

The decision was then taken to buy a fleet of six hydraulic drill rigs including three Sandvik Tamrock rigs - a Ranger 700 Rock Pilot, a Ranger 700 and a CHA 700. All six rigs have been fitted with Sandvik rock tools including T51 drill rods, shank adapters and 102mm ballistic button Retrac drill bits.

A key advantage of the Ranger rigs is that the rock drill and articulated boom are mounted on a revolving ‘turntable' superstructure, offering a drilling coverage of up to 26.4m². Therefore, more holes can be drilled from a single set-up, which ensures increased production and allows the operator to face towards the drilling spot at all times.

All three machines are hydraulic, self-propelled surface rigs, all equipped with a rod-handling system. They are self-contained units, providing fast progress with high power, and offer precision drilling and versatility.

The Ranger 700 Rock Pilot features a Caterpillar diesel engine and gearbox powerpack, which divides the power for hydraulic pumps and flushing air compressors. The powerpack is mounted crosswise at the rear of the rig to ensure a counterweight on the opposite side of the boom and feed, regardless of the drilling direction.

Another advantage is its high suction-capacity dust collection system, which makes it perfect for working in an urban environment. The machine complies with the local health and safety and environmental regulations and also with the labour regulations, with its roll-over-protected, wide-visibility operator's cabin.

On a 300mm x 300mm drill pattern, up to 200 holes are drilled on each shift to a depth of 3m. The hammers then loosen the limestone using the 102mm diameter drilled holes.

Using this technique means that 75% of the rigs engine power is being used for drilling power compared with typically 50%. The rigs are therefore providing virtual non-stop drilling power - often just swinging the boom for each hole.

As a direct result the contractor is achieving approximately 6,000m per drill bit without regrinding.

Hard pockets of limestone are being cut into in order to build underpasses on the route.

In these areas, the rig operator has still been able to drill each 3m-deep hole in less than three minutes using the Sandvik drilling tools.

Approximately five million m³ of limestone will be excavated along the two 40km sections with three million m3 being used as infill. Additionally, 500,000m³ will be used for sub-grade and approximately 1.2 million m³ for the sub-base.

By mid-January, three lanes over 10km had been asphalted, approximately 25km sub-grade had been laid and with a completion date of August, 65km still remain to be drilled and ‘chiselled'.

According to the project manager, John Reynolds, he is confident of making up the delays in excavation caused by the harder rock conditions than forecast with the delivery of the three Sandvik Tamrock rigs and drilling tools.

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