With an economy growing at eight times the rate of many European nations and a young population expanding by 1.6 per cent per year, Turkey is a country in the process of massive civil infrastructure expansions. From road to rail, hydropower to wastewater, the nation is experiencing a rapid uptick in tunnelling projects.
Straddling the European and Asiatic landmasses, Turkey can be thought of as a geological patchwork, marked by older rocks mixed with younger igneous and volcanic rock types. More than 80 per cent of the country’s land surface is rough and mountainous, making both agriculture and travel a challenge.
The numerous variables combine to make Turkey not only a hotbed for difficult tunnels, but also an emerging market for hybrid TBMs. "Turkey is seated on an active tectonic belt, and is especially complex," says Melih Algan, general manager for Turkish consultancy Geoma. "In this type of geology typical problems are heterogeneity of ground and uncertainties due to limited site investigation possibilities.
"Practically, this requires flexible TBM systems to cope with differing ground conditions. TBMs with additional capabilities such as probing and grouting, over-excavation, bentonite injection systems, and controlled excavation (such as that possible with an EPBM) are preferable for owners and contractors."
Levent Ozdemir, mechanical tunnelling and mining consultant and retired Professor of Mining Engineering at the Colorado School of Mines, adds: "There is challenging geology and it is a high tectonic area in Turkey. Contractors are looking for a machine that can go through any type of ground, just like everyone else. More EPBMs are running there now than in the past, and some slurry machines, and these conditions include variable ground."
While the current TBM market in Turkey is booming, that wasn’t always the case. As early as the 1990s, there was only one instance of TBM tunnelling in a local industry more comfortable with NATM and drill and blast methods. Multiple factors, from government initiatives to fast-paced project schedules, have made tunnelling in Turkey what it is today.
The rise of TBM tunnelling
Turkey’s first instance of TBM tunnelling was from 1987 to 1989, using a 5m diameter Robbins double shield TBM for the 2.4km long Dalyan-Moda wastewater tunnel in Istanbul.
Following that project, financial constraints and an unstable economy kept the tunnelling market small, while local contractors were more familiar with conventional tunnelling methods. A lack of available project funding led to several government initiatives to subsidise tunnel projects from an annual budget, which differed from year to year and increased the duration of tunnelling projects.
The trend continued in the 1990s, though several programs began that increased contractor familiarity with TBMs, according to Ozdemir: "I got involved in Turkish tunnelling in the early 1990’s, when I went to meet Professor Bilgin at Istanbul University. We planned and started giving short courses on mechanized tunnelling technology, in order to introduce Turkish contractors to the idea of TBM tunnelling.
"In the mid-90’s we were awarded a research contract from NATO to establish a rock cutting lab, similar to the facilities at the Colorado School of Mines in the US. Equipment included a linear cutting machine, a small boring machine, and test equipment for rock strength and abrasivity measurement. The university started doing a lot of work with tunnel contractors and engineers."
In the early 2000’s, work began on metro projects using EPBs in Ankara and Istanbul, and TBMs were specified in several hard rock hydroelectric tunnels. "From 2002 onward was a big turning point for the tunnelling industry," said Yunus Alpagut, owner of ATES Muhendislik Insaat San, which has been involved in the industry for more than 25 years. "A new government was elected that was eager to start large infrastructure projects. The financial capabilities of Turkish banks increased greatly following major reforms, and Turkey’s credibility increased [with] European banks, thus opening up credit for the projects.
"Project handover lengths were shortened by the government at the same time that the build-operate-transfer model increased in popularity, demanding fast project completions. TBMs emerged as a solution for rapid tunnelling." From that point on, more and more TBMs were specified for challenging projects, including the first successful underpass of the Bosphorus dividing the Asian and European sides of Istanbul, completed in 2009 for a water tunnel project.
Sustainable hydropower
Most recently, the Turkish government put into place a nation-wide initiative for sustainable hydropower, particularly in the eastern part of the country. "Turkey does not have enough coal and oil reserves to sustain its annual growth rate, so the future [aim] will be to generate most electricity through hydropower projects," says Alpagut. "In the northern and southern regions of Turkey it is mountainous and there are many small rivers to be tapped as energy sources, but these are often in difficult and harsh environments."
Overcoming Challenges at Kargi
One such project will result in one of Turkey’s largest hydroelectric stations, located in a remote area of Corum Province about three hours from Ankara. The Kargi Kizilirmak Hydroelectric Project will source water from the Kizilirmak River to generate clean electricity. Up to 470GWh will be generated annually — enough to power about 150,000 homes. The project, owned by Norwegian company Statkraft, is scheduled to go online by the end of 2013.
A power station and 11.8km long headrace tunnel through volcanic rock are being constructed by contractor Gulermak. A 10m diameter Robbins double shield TBM is currently more than 350m into the tunnel after experiencing incredibly challenging ground conditions. Mixed weak ophiolite with high clay content and water inflows are keeping progress measured. The geology is expected to continue for the first 3km of tunnel, which will be segment-lined. After excavating this formation geology is expected to change to more competent basalt and andesite for the remaining 8.8km. Ground support will change correspondingly, to ring beams, rock bolts, wire mesh, and a final lining of steel fiber shotcrete. "The types of ground support made the design of the TBM and back-up unique — there are many features that require adequate space, from shotcreting to rock drilling to segment lining," says Jeff Gioitta, project manager for TBM supplier Robbins.
More than 150 people are employed at the site. "We have had some very impressive efforts by the Gulermak and Robbins teams," says Glen Maynard, Robbins field service site manager. "After the TBM had bored 175m with a temporary conveyor system, tunnelling was interrupted to install the permanent tunnel conveyor system. Gulermak completed this installation in six days; on day seven the continuous conveyor system was operational, and normal boring operation was resumed." Maynard explains that early signs on the project were promising with regards to TBM advance, with shifts topping 15m, and 20m daily advances becoming a regular occurrence.
Hydropower surge in Adana Province
Yet another example of the massive hydropower initiative can be seen in Adana Province, located in southern Turkey near the Syrian border. That region is home to the Yamanli I and II Hydroelectric Projects, as well as numerous other projects to harness power from the local rivers. Robbins project manager, Martino Scialpi, speaks of the remote jobsite that will host a 4.3m diameter double shield TBM: "It’s about 200km from the city of Adana, and only about 120km of that is paved road. It is located in a valley surrounded by high mountains, where there are numerous civil works projects underway — Yamanli II is the third hydroelectric project in this same valley." Because of the high elevation, crews are also racing to launch the machine before the end of September, as winter temperatures are known to drop to a chilly minus 20oC.
The hard rock machine for Yamanli II is set to excavate a 9.3km long headrace tunnel through limestone, with some karstic cavities and at least one fault zone expected. Crews for the contractor NTF Construction will conduct probing and pre-grouting in several target zones that are expected to contain more difficult ground. The completed headrace tunnel will source water from the Goksu River, with an annual generating capacity of 78MW — enough to power up to 78,000 homes.
High-speed rail and highway
Difficult access to jobsites in mountainous regions, including the remote Kargi and Yamanli sites, is a common problem. The dilemma is symptomatic throughout the country, spurring growth in the highway and railway sectors. New metro lines are being built in Istanbul, with a population of about 14 million, while long highway and rail tunnels are being planned to bisect the country. "Travel in the east-west direction of Turkey is easy, but to travel in the north-south direction there are high mountain ranges and long tunnels are needed. Mountain passes are also needed, and these are under study," says Alpagut.
Dual mode TBM
A new machine design is being tailored for these often large diameter road and rail tunnels in variable ground. The dual mode TBM, for tunnels ranging from 12 to 15m in diameter, is customised for the highly variable conditions seen in many of the country’s more mountainous areas, which can range from sandstone and mudstone to quartzite and schist. The hybrid TBM will feature a design optimised to switch seamlessly between pressurised and non-pressurised EPB mode, as well as hard rock mode. A retractable muck ring will allow the TBM belt conveyor to stay within the machine, so that in-tunnel conversions between a belt and a screw conveyor are not needed.
Soft ground and short sections of rock will be excavated using a specially designed screw conveyor, which can operate efficiently in both the pressurised and non-pressurised environments. The oversized screw can be rotated faster to handle short sections of hard rock while minimising any loss in efficiency. If a long section of hard rock is encountered, the belt conveyor will move forward and lock into place to allow non-pressurised rock boring through the section.
Projected growth
For the near term, projected growth in Turkey looks robust and there is general consensus that TBM and tunnel demand will continue to increase. "Istanbul is becoming the financial capital of the Middle East and Near Asia. Turkey is one of the most stable countries in the region, and many international companies are moving there. Turkish contractors are also doing more business in Middle Eastern countries such as Kuwait, Iraq, Saudi Arabia, UAE, Qatar, and Libya," says Ozdemir.
With continued growth-focused initiatives, more challenging tunnel projects are being planned and are under study. One such project will involve twin 15km highway tunnels in the high mountains along the Black Sea from Rize to Erzurum, which Ozdemir notes will be very challenging. Others include a highway tunnel under the Bosphorus at water pressures up to 10 bars, which will need to be designed for stability in a seismic zone.
The speed with which Turkey has adopted TBMs and embraced underground structures makes it one of the most exciting emerging markets today. "The growth there is unbelievable. I go back there about three times a year and there are so many new TBM projects coming up," said Ozdemir. "When I first was involved in the Istanbul metro construction, I was astonished to see that those tunnels were being built by NATM — a very difficult prospect in the city. Today, most metro tunnels are being built with TBMs."
