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Desert storm

Engineers in the Middle East are blasting through mountains to bring major road access to remote villages. Bernadette Redfern went there.

It is silent amid the Hajjar mountains in Sharjah, one of the United Arab Emirates.

The sun is so strong that the blue sky has gone grey with the haze and the heat distorts the mountain peaks, making them look as if they are gently vibrating.

Of course the igneous gabbro peaks, which rise to a maximum of 3,000m above sea level, are perfectly still, that is until blasting contractor Gulf Rock Engineering detonates the charges placed in the rock face and an explosion rocks the peace of the afternoon.

The existing road between Shawkah and Munaiy is being widened as part of a major road project undertaken by the government of Sharjah. Along with six other contracts, all designed and supervised by Halcrow, the road scheme will provide 110km of new road stretching from the city centre of the emirate near the University, out to Kalba on the east coast (see map).

Its function is both to link remote mountain villages and to provide better tourist access to the east coast. The Shawkah to Munaiy section is 19km of this route and is right in the centre of the mountain range.

'Construction of the highway began at both ends of the route and completion of the middle section will provide the final connection for a completely free flow highway from Sharjah to Kalba, ' says Halcrow director for highways in the Middle East and Asia, Abdul Matin Khan.

To blast away huge sections of rock and realign the rock face, work has to start at the top of the mountain, 'You have to start at the top. You only get one shot at it and the first thing you think is how are we going to get up there?' says Halcrow resident engineer Jett Smith.

Smith has spent the past six years working on road projects in the Hajjar mountains. Contractors have to zigzag up the rock face in bulldozers, tracking right to left steadily, slowly climbing to the peak.

'The surveyors go out first and measure the 19.6m offset (from the centre line of the road). We then try to follow them up, ' says Smith.

Before any excavation or blasting can start the team must decide on the new alignment of the rock face. 'Then you have to look at the exposed face and see if the rock is hard or soft, ' he says.

'Typically the softer weathered rock is on the top and we would start with a shallow slope of one in one, ' he says.

As the hard rock is reached the slope steepens and each change in gradient is separated with a flat bench area. From the road level the new rock face typically begins with a 6m high section at a one in four slope and then benches before stretching up a further 12m at one in two.

To insert explosives into the rock face, contractors had to drill holes in to the mountain at approximately 0.8m centres. 'In an ordinary blast, the choice of opening direction and therefore drill hole orientation would be towards the existing road, ie perpendicular to the bench, ' says specialist blasting contractor Gulf Rock's project manager, Jonathan Cottam.

'However due to the existing hazards, the rock had to be drilled and blasted with the opening parallel to the bench almost as a trench configuration to help prevent rock falling onto the road, ' he says.

The existing hazards include overhead power cables, steel pylons, fibre optic cables and the existing single carriageway road.

This road has to stay open throughout construction apart from short temporary closures for individual blasts.

To minimise disruption Gulf Rock decided to use non-electric initiation systems. Unlike electrical systems these chemical detonators can set off the explosives with a millisecond delay.

'This reduces the instantaneous co-operating charge and hence peak particle velocity, effectively splitting the explosion into lots of tiny blasts, ' says Cottam.

Therefore the explosion is more controlled and less flyrock is produced; the unexpected projection of blast debris beyond the designated danger zone.

As an extra precaution a heavy geotextile material was draped over the explosion face to further contain the blast.

After blasting, the additional carriageway will be constructed in the same materials as the existing road, with typically a 40mm asphalt wearing course, a 40mm base course and a 120mm gravel sub base. The entire project is due for completion in June 2005.

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