Construction work is well under way on the Diftah-Shis tunnel and highway project in the UAE, thanks to equipment from Sandvik, Komatsu and Hitachi, which continues to set the pace for work through a virtually impenetrable mountain range featuring one of the region’s hardest rocks.

The equipment from Sandvik includes a Tamrock twin boom drill jumbo and a newly-delivered CHA 560 surface drill as well as two other Sandvik drills and hammers and Sandvik rock drilling tools.
The project for the government of Sharjah involves the construction of an 11.5-km dual carriageway including 1.2 km twin tunnels. Starting at Dafta, near Masafi some 29 km northwest of Fujairah, at approximately 370 m above sea level, the new dual lane road will rise to 600 m above the sea level at the west portal over 6.15 km to twin 1.27 km long tunnels and onto the village of Shis.
Although just 11.5 km long, the proposed Diftah-Shis road and tunnel project – partially located in both Ras Al Khaimah and Sharjah – passes through a virtually inaccessible mountain range featuring one of the region’s hardest rock and steeply-sided V-shaped valleys often less than 1 m wide at the base. The project has already experienced 4-m-deep ‘flash floods’.
Road works on Phase 1 started in December 2004 in a 42-month contract awarded to Iranian contractor General Mechanic Company (GMC) under the supervision of Halcrow International.  Since starting earthmoving operations, the contractor has received four design variations changing road alignments and more than doubling the earthworks with an increase of 1.2 million cu m.

Design variations
General Mechanic has also been awarded a new 3.5 km extension from the exit of the tunnel to the Shis interchange requiring more than 1.3 million cu m cuttings, of which approximately 60 per cent will be used for infill.
Phase 2 is currently under design and will continue from Shis to Khorfakkan covering a further 19 km and feature 5-km-long twin tunnels.

Faster route
The new 29-km-long route will, on completion, provide a faster route for goods and materials being transported from the busy port facility of Khor Fakkan to Dubai and Sharjah.  The existing road network from the port through Fujairah is very busy and slow moving.
It will also improve transportation for villagers of Shis and surrounding remote villages passing through a mountain range which, until now, had proved to be virtually impenetrable.
Rock throughout the range is predominantly serpentinised peridotite, part of the gabbro family of rocks.
The mountain formation features numerous high peaks in close proximity, dropping into steep but often shallow gorges unlike a conventional mountain range with peaks spaced widely apart. 
“The constant undulations on Phase One have caused major problems.  The exact desired location could not be provided even through the use of GPS techniques.  Often it was necessary to prepare a 500 m long access route to reach a peak above it and begin excavating down to the desired point,” says a spokesman for GMC.
Once again, the contractor is relying on similar techniques using the Rammer breakers.
The access roads are prepared by a Komatsu dozer and ripper where space permits.  Often it is necessary to widen the path with a Hitachi 35-tonne excavator fitted with one of two purpose-ordered Sandvik G88 breakers. 
Once the pass is sufficiently wide, the dozer is re-engaged to clear the access.  The breakers continue to provide essential service breaking through rock outcrops to permit access for the dozer on steep gradients often at 45 degrees and more.
Excavations are now under way to gain access to the east portal from Shis.  This is proving just as difficult, according to the spokesman.

Slope dressing
To ensure the slope stability once the access roads and the route of the highway have been prepared, GMC is preparing a series of benches, using the Rammer breakers to remove overhangs and ensure a smooth surface finish.
Initially the dozer continues to remove any loose material.  Three Tamrock hydraulic surface drills, including the latest CHA560 operated by subcontractor Gulf Rock Engineering Company are then used to drill on the 1:1.5 slope.
“The CHA 560 is a hydraulic surface crawler drill designed for drilling 51 to 89 mm diameter holes up to 25 m in depth, using R32, T38 and T45 extension drill steels.  It is fitted with a HL510 hydraulic rock drill, 5.5 cu m/min air compressor and powered by Caterpillar 3056E diesel engine,” explains a spokesman for Sandvik.
The top bench is generally in two steps to provide a height of between 12 m to 30 m with the rigs drilling at an inverse 76-degree angle.  Thereafter, two to four 12 m-high benches are prepared. Blasting has been taking place on a weekly basis with a minimum of 150 holes drilled. 
The Sandvik hydraulic drills feature Sandvik T38 extension drilling tools including 64 to 76 mm diameter button bits.

Twin tunnels
Tunneling has recently got under way with GMC relying on a Sandvik twin boom drill jumbo.
A pilot tunnel covering 34 sq m was initially cut at both eastern portals according to the project technical manager, Yaghoub Alipour Vaezi, as a precaution for the uncertainty of the rock condition at the open face. 
“At both ends of the tunnel, class 6 type rock had been predicted which was generally very fragmented,” he says.
“As an additional precaution over the first 6 m, the roof was ‘shored’ with 12 support frames and infilled with shotcrete to a depth of approximately 50 cm.  Additionally, the roof was also rock bolted using jumbo’s cradle 1.5 spacing,”  he continues.“The cutting was then enlarged with the top heading excavation measuring 13 m by 6.5 m, which will continue for the first 400 m.  GMC then plans to begin drill and blast on the 45 sq m lower bench, with a reduced floor width of 12.6 m.
“We hope to maintain a 210 m advance on the top bench, thereby meeting the consultant’s specification to eliminate any possible vibrations between both tunnels.”
At the eastern portals, both tunnels are 12 m apart while by the western portal, the distance will have increased to 42 m.
A 2.5 m/day advance is planned for the top bench using a single daily blast depending on the rock conditions; with six different categories of rock condition predicted. Here, Yaghoub is optimistic that generally Class 3 will be experienced ensuring the 2.5 m advance.
Generally GMC is drilling 70 to 80 holes at the face with a variety of spacings and diameters.  For example, 30 to 40 cm along the contour line using 45 mm diameter drill bits and 57 mm diameter bits in the face holes.  Holes are drilled to a depth of 3 m in Class 3 rock reducing to, for example, 1.5 m in Class 5.
“It is taking approximately 5 minutes to drill each 3 m hole in the hard grade, Class 3 rock,” confirms a drilling operator.
He continues: “It is necessary to use different type of carbide grades depending on the class of the rock condition being experienced.”
“Generally we are achieving three face drillings with each Sandvik drill bit and 1,500 drill m with the 4 m Sandvik drifter rods – which we feel is excellent.”
Throughout the drilling, the rock conditions also determine the tunnel excavation radius, for example, in Class 2 7.045 m is specified.  For Class 3, it is 7.07, increasing to 7.295 for Class 5/6; determining the thickness of shotcrete stabilisation.
Despite the hardness of the rock, it is expected to be fragmented and rock bolting with types 1, 2 and 3 support is specified along the full length of both 1.27 m tunnels, he says.
Initially, GMC is concentrating on tunnelling from the west portal but as accessibility is improved from Shis, the contractor is intending the open the east portals and tunnel for the final 300 m – with breakthrough planned for late 2008.

Wadis
The new highway in Phase one is predominantly routed through wadis (dry river beds) and this too is not without its problems.
According to site manager Arash Foroozan Yazdani, the contractor needs to be alert throughout the rainy season even when there is no sign of rain.  “A 4 m deep torrent of water from rainfall a couple of valleys away has destroyed a number of newly-prepared access roads, even though the sun was shining above the site,” he explains.
The constant threat of flooding therefore means that the contractor must park all equipment at higher levels overnight and when not in operation.
The contract specifies that all wadis must be retained, where possible, which means placing culverts up to 140 m long whenever it is necessary to reroute.  It is also sometimes necessary to reroute the wadi with a permanent diversion, explains the GMC spokesman.

Highway construction
By completion of the original Phase one highway, it is estimated that more than 1.5 million cu m of in-fill will be laid.  With the additional design variations, this will virtually double to 3 million cu m with 60 per cent used for infill.
By September this year, according to Yazdani up to 90 per cent of Phase one in the western part of the project had been completed to within 70 cm of additional infill to the sub-grade level.  Backfilling between 29 and 35 m has not been uncommon along the route of the new highway, he says.
According to the contractor, while the work on the project was similar to building a dam – only  “a dam would be easier”.