Light at the end of the tunnel

The front of the twin tunnels. This difficult project ?is like building a dam, only a dam would be easier? according to the site manager.

Sharjah’s Diftah – Shis highway, a route that will link the port of Khor Fakkan on the East Coast of Sharjah Emirate to Diftah in the central region, blasted its way into the local record books in October as the project team achieved their first of two tunnel breakthroughs – and in turn created the UAE’s longest rock tunnel.

Passing through some of the highest and steepest ranges in the region, the project forms a strategic road link – enabling goods shipped to the port of Khor Fakkan to be distributed throughout the UAE, while skirting around the rocky out Omani border.

Although just 11.5km long, the project is said to be one of the most difficult in the Middle East due to the geography of the build – both political and physical.

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The government of Sharjah awarded the first phase of the project to Iranian contractor General Mechanic Co, under the supervision of Halcrow International, while a third company, Gulf Rock acts as a subcontractor.

SUPERVISION
Halcrow, as consultant to the Sharjah public works, is responsible for the design and supervision of the road tunnel – involving the construction of approximately 9km of dual two-lane carriageway mountain road; 1.3km twin bore tunnel and a 1km link road.

Besides the tunnels, the project has encountered a number of engineering problems, not least that of building out of a number of wadis – which at one point flash flooded, destroying a number of access roads.

“It has been very difficult – but there is now real progress being made” agreed site manager Asash Foroozan Yazdani on our last visit.

The tunnel has been drilled using equipment such as a new Tamrock CHA560 surface drills, and a Sandvik DT820 twin-boom ‘jumbo’.

After this, the tunnel is blasted through the rock using explosives, and using the New Austrian Tunnelling Method (NATM), which involves stabilisation of the tunnel with rock bolts and spray concrete (shotcrete), before being lined with a waterproof membrane and permanent concrete inner shell.

BLASTING
After each blast, where several hundred tones of rock come down, a specialist with gas testing equipment checks the area.

After these checks and an analysis of the geological conditions are carried out, it is time to send in a Cat 996E wheel loader to remove the rubble, it is then loaded on to one of two waiting Volvo A25E articulated dump trucks (ADTs). It’s also worth noting that no spark-ignition vehicle is allowed near the tunnel – all must be diesel or electric.

Some geological problems have been thrown up – mostly due to a low rock quality density, which slowed the planned blasting speed a little.

In addition, the explosives could only be used when a policeman was present limiting the amount of time for blasting each day, and the storage facilities had to be upgraded.

These and other factors have meant that the total cost of the project is now roughly double that of the original cost estimate.

The second tunnel breakthrough is scheduled for early November.

Where is it?
As we tried to explain last August, Khor Fakkan is actually an exclave of Sharjah, while Diftah itself is in Fujeirah. However, an exclave of Oman prevents the road going to it’s destination directly.

To make matters worse, Sharjah has an exclave in the Oman enclave… Confused?

We certainly were, but the long and short of it is that the road is being paid for by the Sharjah government, but can’t be built through the most direct route, due to the Oman border.