There are many advantages to small-scale construction machinery, even when the projects are 'mega', like easy access to sites even with tough ground conditions. These compact machines have high mobility, and are easily repositioned; it doesn't take very long for them, to put it shortly, to be up and running. That is to say, there are savings in time and money. A report from the remote regions of Laos on the use of Putzmeister spray concrete pumps in the $ 830-million Nam Ngum II hydroelectric project brings ample evidence that small is beautiful and profitable.
In Laos, in Southeast Asia, hydroelectric power plays an important role in the economy. As important as domestic use is the export of hydropower to neighbouring Thailand, bringing in the foreign exchange needed to fund infrastructure projects. In fact, power from the Nam Ngum I project is being sold to Thailand since 1971.
Work on the current major construction site of Nam Ngum II, to be completed by the year 2011, is progressing. The project includes a 169-metre-high arch dam, a 615-MW hydroelectric power station with an output of 615 MW and two 1-km-long headrace tunnels, each with a diameter of 12 metre. Nam Ngum II is
being built under a contract awarded to a Thai construction firm, with Bangkok-based Ch. Karnchang as principle contractors.
The project is being built on the Nam Ngum River, a tributary of the Mekong, and upstream of Nam Ngum I; the area of the water basin of 86 sq km. Before the valley is flooded, loose rock on the relatively steep mountainsides must be prevented from causing a possible landslide. These areas are anchored using spray concrete. For this, Ch. Karnchang employs two small, hydraulically-controlled Putzmeister P 715 TD piston pumps, which regulate the synchronised addition of the hardening accelerator by means of separate metering devices. The P 715 TD model is essentially equivalent to the earlier BSA 702 D PM fine concrete pumps and achieves a pump output of up to 18 cu m per hour.
Easy Cleaning
The P 715 TD concrete pumps have a piston stroke of over 700 mm, a delivery cylinder diameter of 100 mm and are driven by a 30 KW diesel engine, with the option of an electric motor. They can be used not only to spray concrete, but also to deliver concrete through piping and hoses. In this application, the maximum grain size in the concrete should not exceed 16 mm.
Putzmeister's design gives the pump an exemplary solution for cleaning the actual core and hopper. It is done through the side-mounted flaps on the upper section of the hopper, the design provides for access to all areas of the machine that have come into contact with concrete by the time pumping is over.
Ch. Karnchang operates a small fleet of PM machines: in addition to the two P 715 TD fine concrete pumps, the firm also works with three S 5 mortar pumps, a large BSA 2110 HP-D high-pressure concrete pump and a MXR 32 stationary boom.
Seismic debut for underground drill jumbo in Sharjah
Gulf Rock Engineering Group, a Sharjah-based drilling and blasting specialist contractor, has taken 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 has 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.The Axera T08 is very simple to operate and drills a 'true straight line', says rig operator Tam Bahadur, with 15 years underground drilling experience in India, Nepal and the UAE. "It is very accurate," he said. "Because of the poor quality rock it can take up to 5 min to drill 1 m but this will speed up as the rock improves." He is certain that the project will enhance Gulf Rock's experience in underground works.
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. "More tunnels will be specified in the future with fewer large-scale road cuts, calling for our underground drilling and blasting experience. Tunnelling has a smaller environmental impact and in general poses fewer long-term geotechnical problems rather than extensive open cuts," said Cottam.
"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".
© Construction World 2007
