THE GROWTH of the Turkish tunnelling industry is "like a bullet from a gun" according to its tunnelling society chairman Nuh Bilgin, "you cannot stop it". In Istanbul alone, as Tunnels and Tunnelling goes to press, seven TBMs are in operation on two metro projects in Istanbul and five TBMs are working through utility projects. A further 14 TBMs are being procured for the Bostanci-Dudullu, Besiktas -Mecidiyeköy, Bakirköy Ido-Kirazli and Ikitelli-Ataköy sections of the metro. Elsewhere, the Ovit and Zigana road tunnels are progressing well and a great number of hydropower and rail projects are underway.
"The Turkish tunnelling industry really is growing very fast, Turkey needs to be sharing and acquiring experience in every field of tunnelling: planning, management, engineering, rock mass characterisation and also at an academic level," says Bilgin. The Turkish Tunnelling Society (TTS) was established in August 2012 in response to a growing demand from the industry. It now boasts 800 individual and 47 corporate members. The group has since organised two expos, four short courses and two international symposiums. In November this year it is hosting the second ‘TBM Digs’. The society also began celebrating an annual Tunnelling Day on 3 December last year. It has a lot to celebrate. According to Bilgin, in three years the industry will be fulfilling some EUR 35bn (USD 40bn) worth of work. This will be across all sectors: metro tunnels, utility tunnels, road tunnels, rail tunnels, hydropower and mining. The TTS takes a close interest in mining in the country and 30 of its members are miners.
"We believe that mining and tunnelling have very common activities, like excavation, ventilation, tunnel support, muck removal, and safet," says Bilgin.
GrowinG pains
The rapid expansion of the industry brings challenges. In two years around 30 TBMs will be working on tunnelling projects that have not yet broken ground. The TTS is nervous over the requirement for experienced crew, in particular TBM operators, TBM engineers and, especially, mechanical engineers. To solve this problem, the TTS has ordered a TBM simulator to ramp up the training of skilled operators and engineers. The society will run courses and issue certificates in a few different disciplines.
Tunnelling in Turkey Scope
A key creator of demand – besides the now-familiar growth in population and trend towards urbanisation – is government policy. A trend for Build-Operate-Transfer makes largescale projects feasible, but there has also been an upturn in investment at a local level.
Istanbul is the jewel of Turkish tunnelling. With a more than 15 million, and rapidly rising, population, infrastructure is having to grow fast.
Before 2004 there were only 45km of metro line. Between 2005 and 2013, some 141km has been constructed, with a further 400km to open by 2019.
According to the TTS more than 800 tunnels are planned for hydropower projects. Some 85km of road tunnels are to be built in the next few years, and for rail around 78km is expected. A star project for the TTS is the Eurasia Tunnel, completed recently. "Martin Herrenknecht says that the Eurasia project, with its double deck tunnel driven under 11 bars of pressure beneath the Bosphorus Strait, is the most challenging project so far this century," says Bilgin. "The project was realised by Yapi Mertkezi, Korea’s SK, and E&C. It won an ITA Award last year. The TTS is very proud of this achievement."
Other road tunnels are necessitated due to Turkey’s mountainous terrain. As can be seen in Table 2, the national target for road tunnel construction up to 2023 is 330,056m. A general outlook of recent road and highway tunnels projects constructed and under construction is given in Table 1, which covers tunnels with a length of more than 1.5km
Technical requirements
Tunnelling in Turkey faces some interesting geological challenges. The local geology is particularly complex, with major faults in the countries north and east, which also results in minor faulting in these regions. Projects in these locally notorious areas have encountered squeezing ground making TBM tunnelling difficult, excessive water ingress, TBM face collapses (e.g. the Kargi hydropower project, the Dogancay energy tunnel, the Gerede water tunnel and the Nur Dagi rail tunnel).
Mixed ground conditions with ophiolites, graphitic schists and melanges with boulders are other fundamental difficulties have led to squeezing and blocking of the TBMs, or in some extreme cases have caused complete failure of the segmental lining and evacuation of the tunnel. Notably the Kosekoy high speed rail project needed to be evacuated and the Uluabat hydropower project experienced extreme squeezing problems.
"Dykes in the continental crust are generally found in swarms," adds Bilgin. "Two TBMs were abandoned in Gerede project due to these difficult conditions. The presence of dykes, sills and small intrusions cutting the Palaeozoic sedimentary rocks in the Istanbul region are known all to well to practicing tunnel engineers. These andesitic rocks, which are generally considered to be of Cretaceous age, make fractures in the country’s rock and cause several problems during TBM excavation such as blocking the cutterhead and excessive disc cutter consumption.
"Typical examples of this are the Goztepe-Kadikoy metro tunnels, and the Melen water tunnel. The Beykoz utility tunnel is one of the most difficult tunneling projects in Istanbul. The presence of clay minerals existing within the geologic formations is also one of the main reasons clogging the cutterhead of TBM, as was experienced on the Suruc water project."
The general directorate of state hydraulic works (DSI) is the primary state agency for Turkish water resources. It is responsible for planning, management, execution and operation of projects in this sector. Tables 4 and 5 give a summary of major irrigation and water supply tunnels respectively
