MANAJLE & PREDEJANE – Preparing for EU membership

At present, this section of Corridor 10 only has two lanes and is often overloaded with trucks heading south to Macedonia and Greece. Accidents are frequent, espe-cially in summer when the road is jammed with European holidaymakers but the tun-nels will ease the congestion and also bring environmental and safety standards into line with EU regulations. The entire project, which is estimated to cost more than ?50 million, is being developed by Euro Alliance, a consortium of two Bulgarian companies with Euro Alliance Tunnels as the main partner and Roads & Bridges Ltd responsible for building the corresponding roads and bridges, for the state-owned company Koridori Srbije.

Longest in Serbia
At 1.8 km, Manajle will be the longest road tunnel in Serbia. It will be a twin tube project (one for each direction of traffic). Ten kilometres to the north is the Predejane tunnel which has the same design and construction team. One of the Predejane tubes will be 870 m long and the other 1 050 m. The operation at both sites is continu-ous and based on two 12-hour shifts with a combined workforce of 170. According to Stojan Petrovski, General Project Manager for both tunnels, most of the engineers are from Bulgaria and about 90% of them are skilled. ?It?s difficult to find skilled work-ers here so we brought our own,? he says. ?They have a lot of experience of working on other similar projects.?
Site preparations began in September 2013 and both projects are due for comple-tion in March 2016.
Petrovski says: ?So far we?ve developed about 40 percent of the tunnels but we have been delayed by the geological conditions which are more complex than we first anticipated,? says Petrovski.
As in Slovakia, the geology features pockets of good, competent rock as well as poor ground. ?It?s not even proper rock; it?s pure clay,? says Petrovski. This variability means that the project requires frequent changes of tunneling technology; drill and blast in competent rock and hydraulic ham-mers and excavators in the poorer sections.
The company uses the New Austrian Tunnelling Method (NATM) that provides optimized tunnel support behind the face.

Unpredictable advance rates
According to the original project study for Manajle and Predejane, the company was expecting to use drill and blast for most of the drive. ?That would have been much faster of course, but because of the geological con-ditions, we?ve been forced to work this way, making progress slower,? says Petrovski. Advance rates depend entirely on the geology. In good ground, it can be about three meters per shift. ?We don?t neces-sarily see this as a huge problem though,? Petrovski says. ?This is the situation and we just have to deal with it.? Helping them deal with it is the equipment employed in each tunnel. Blasthole drilling in the good rock sections at both sites is carried out by Atlas Copco Boomer E2 and Boomer L2 drill rigs. ?We have two units, one of each model at each tunnel. The Boomer E2 rigs are from Atlas Copco Rental and the L2 units are our own machines that we brought over from Bulgaria,? explains Velin Mahov, Construction Manager for both projects. One of the rented rigs is a new unit fea-turing the RCS 5 computerized rig control system for positioning and high precision drilling. When it arrived, Atlas Copco spe-cialists were on hand to train the operators on how to use it with maximum efficiency. When working in the poorer rock Atlas Copco MB 1700 hydraulic break-ers mounted on excavators are used. The company has three of these which were also brought from Bulgaria: ?They?ve served us well in other projects so now we?re using them here,? says Mahov.

Pipe-roo?ng in weak zones
In the weaker zones, pipe roofing is used for crown support. This gives less overbreak and ensures safety for the workers. Here, the Boomer drill rigs come in handy once again to drill the holes and install the pipes in an umbrella pattern. In addition, two Atlas Copco Unigrout grouting units, one for each of the tunnels, are used for grouting the pipes.
In one shift, seven pipes, each 15 m long, are installed. ?This is normal,?? says Mahov. ?We just need two days to finish a whole pipe umbrella.? Once the pipes have been installed, the company uses four Atlas Copco M400T pumps for injection grouting of self-drilling anchors. Ventilation is provided by five different  fans, one of which is a new Atlas Copco Serpent AVH 125 which has a flow rate of 14?42 m3/second and 37?110 kW of nominal power. All of the equipment is covered by a ser-vice agreement which stipulates the pres-ence of an Atlas Copco service technician on site from Mondays to Fridays to monitor the machines, conduct preventive mainte-nance and replace parts. Atlas Copco has to respond to any issues within 24 hours. Besides Serbia, Euro Alliance is active in tunnel construction projects in several countries at the same time including four in Germany, two in Spain and two in Bulgaria.