Sandvik's Tamrock Axera face-drilling jumbo, purpose-ordered for a government tunnelling project, is initially put through its paces on a 25-m-long tunnel for a seismic chamber.
Gulf Rock Engineering Group, a Sharjah-based drilling and blasting specialist contractor, took delivery of the region's first Sandvik face-drilling jumbo rig, a Tamrock Axera T08-290. Although purpose-ordered for a government tunnelling project in the UAE, early delivery allowed the company to put the jumbo rig through its paces on a 25-m-long tunnel for a seismic chamber, said Jonathan Cottam, General Manager, Gulf Rock.
The seismic chamber, located in the Hajjar mountains and 15 km from the coastline, will be connected to other seismic monitoring centres, including one at the American University in Sharjah. This will allow triangulation of the region's earthquakes. Neighbouring Iran is located on a highly active fault zone and the UAE has experienced recent tremors following these earthquakes. In a joint venture between the University of Sharjah and the University of California in San Diego, the Sharjah Global Seismic Network stations will be jointly run to form part of a global network. The seismographic station will be able to identify the origin, depth and strength of earthquakes in the region to provide a meaningful academic database which can provide valuable information. For example, it will help draw up future building specifications in the United Arab Emirates.
With Halcrow International Partnership as consultant engineer for the Government of Sharjah, Gulf Rock started excavations on the tunnel at Wadi Hilu, about 90 km north-east of the city of Sharjah, in a three-month contract. The tunnel features a 3.9 m wide x 3.9 m high arch profile. Cottam said they experienced very poor Grade 3 and 4 gabbro at the portal but is optimistic this will improve to at least Grade 2. Gulf Rock is drilling 1.2-m deep holes with Sandvik's drill jumbo but hopes to increase this to 2 m once the rock improves, continuing with a 55-hole pattern. Over the first 5 m of tunnel, adjacent to the portal face, the contractor has installed lattice girders at 1-m longitudinal spacing and steel-fibre reinforced shotcrete sprayed to a thickness of 250 mm. The shotcrete is built up over 3-4 layers, each mixed with steel fibres with a 40 kg per cu m mix to enhance tensile strength.
Following the section of lattice girders, a combination of systematic dowelling and shotcrete provide the structural lining of the tunnel. A primary layer of sprayed shotcrete at 60-70 mm thickness is applied before drilling and installation of double-corrosion protected rock dowels. The 2-m long rock dowels are inserted into the roof radially on 1-m centres and thereafter at 1 m longitudinally.
"As we penetrate deeper into the tunnel, a persistent sub-horizontal fault on the face is rising to intersect with the tunnel roof profile. This intersection may also require the installation of lattice girders," said Cottam.
Once fully excavated, an internal wall will isolate the final 5 m to form the seismic chamber. The monitoring equipment will be mounted onto a concrete plinth bolted onto the rock floor to ensure good coupling and transmission of vibrations. The chamber will also be temperature-controlled with less than 1 per cent variation and, since an AC power supply cannot be used, a DC supply will be provided.
Sandvik Tamrock Axera
Sandvik's twin-boom Tamrock Axera tunnelling jumbo boasts fast hydraulics and an advanced drilling control system. The T08-290 has been designed for a face coverage area of 12 sq m to a maximum of 111 sq m, offering accurate hole placement, optimal profiling and minimal overbreak. Its features include built-in diagnostics to minimise maintenance time and an optional basket boom for bolting and utility works. The jumbo operator platform has excellent visibility and ergonomics.
Gulf Rock
One of UAE's leading drill and blast quarry specialists, the Gulf Rock Engineering Group is keen to diversify into civil engineering projects. It recently acted as a blasting sub-contractor to Six Construct for the 1.3-km Wadi Muddiq to Gillay tunnel on the Sharjah-Kalba highway.
© Construction World 2007
