Like many major metropolitan areas across the globe, Turkey’s largest city, Istanbul, faces challenges related to transportation, as well as water and wastewater infrastructure. To help address these challenges, Istanbul officials have turned to Lovsuns Tunneling Canada Ltd. to provide solutions.
Istanbul is the only city in the world connecting two continents: Asia and Europe. With its approximately 14 million residents, it is also one of the largest cities worldwide. Traffic jams are a daily routine, and for that reason a massive extension of the metro system is under construction. At the same time, the government is investing large sums to improve the water and wastewater management. In both fields, tunneling offers the best solutions for a modern mega city like Istanbul.
Underground Transportation in Istanbul
In 2017, 24 TBMs will be ordered for the extension of the metro tunnel system. For the Metro M7 extension, Lovsuns delivered a 6.12-m EPB TBM, previously used for the Toronto-York Spadina Line Extension. The TBM was refurbished in Lovsun’s Toronto facility and skinned up to 6.5 m. The TBM started the 4-km drive in late 2016 in the densely populated Kabatas area on the European side of Istanbul to bore two sections.
The Istanbul Metro system is around 150 km long with nearly 90 stations (more than 65 underground). It is complemented by a line of premetro (Hafif Metro), a suburban train, a tram system, an urban network of buses and a funicular. Four Metro lines on the European and two on the Asian side of Istanbul are used by more than 1 million commuters with rising numbers. The Metro started in 1989 its service to redeploy the commuter traffic from the streets to urban underground transportation.
Metro currently has five lines under development, either in the planning or construction phases:
- M3: Kirazli – Bakirköy-IDO (planned to open in 2019)
- M4: from Tavsantepe (formerly known as Kaynarca) to Istanbul-Sabiha Gökçen International Airport (7.4 km; construction finish is planned for 2018)
- M7: Mecidiyeköy – Mahmutbey; construction began in February 2014 and was later extended from Mecidiyeköy via Fulya, Yildiz (previously known as Darphane) and Besiktas to Kabatas, totaling around 24.5 km with 19 stations (due to open in 2018)
- M8: Cross-city Line on the Asian side from Bostanci to Dudullu (14.3 km, start of operation is planned for 2019)
- M9: Tangential Line through western suburbs from Ikitelli Sanayi to Ataköy (13 km, planned to be finished in 2019)
Section for Metro M7 from Fulya to Kabatas
The Istanbul Metro currently is undergoing a massive extension with more than 70 stations and over 330 km of route under construction. The most will be constructed on completely new lines and some will be added to the existing routes. The Metro M7 is the largest project, started in 2014 to be executed in two stages and is planned to start service in 2018. The new route includes 19 stations from Mahmutbey in the Northwest to Kabatas in the Southeast, an important ferry hub for commuters between Asia and Europe.
“We are challenged here extremely by the very narrow urban environment,” explains Tunnel Manager Yigit Gencay from Alsim/Alarko. Preparations for the 81-m wide and 105-m long job site started in January 2016 by securing the surrounding mountainous residential zone with earth piling.
Originally, the Metro line was scheduled to end in Mecidiyeköy, but then plans changed and the Metro was extended to Kabatas with four more stations. The original plan was to build only a launch shaft and a parking house in Fulya, but then changed to a Metro station due to the high population in this district. The civil works were given to two different contractors and Alarko won the contract for the extension line, the construction of the station and all electromechanical works.
Two shafts are situated at the Fulya job site. From one shaft the tunnel heads by NATM to Mecidiyeköy. The second one is the launch shaft for the TBM to drive to Kabatas with return in a second tube back to Fulya. The shaft is 33 m deep with 12 m diameter. The 4.5-km tunnel will go from Fulya via Yildiz (Darphane) and the very popular Besiktas area to the final station Kabatas directly at the ferry port. Underground the two shafts at the Fulya job site will be connected to the Metro station platform, which will be underground 240 m long and on surface 80 m.
Using the launch shafts for the TBM and the NATM tunnel, the underground station was built. Then, from the wall of the station, a 15-m long pilot tunnel toward Kabatas was drilled and a thrust frame was built for the TBM. After that, the 110-m long TBM with back-up was assembled in the station to start drilling in the pilot tunnel for using as soon as possible the EPB mode. At Yildiz and Besiktas, the stations will be build first and then the TBM will drive through the stations.
In the Fulya area, sand and mudstone are expected with some groundwater. Toward Besiktas, alluvium and clay zones may be encountered, along with seawater near Kabatas due to the close proximity of the Bosphorus.
“Our EPB TBM from Lovsuns provided the perfect counter-balance between ground conditions and ground water with the cutting shield,” Gencay said. The TBM is designed to operate under 4 bar pressure. The tunnel alignment is planned to be 33 m deep in Fulya, 80 m in Yildiz, 20 m in Besiktas and finally 40 m in Kabatas. The tunnel slope from Fulya to Kabatas goes 4.5 % downhill.
Near Besiktas and Kabatas, a water pressure of 2.5 bar with quickly changing ground conditions are expected. For the client and the contractor, it was very important that the TBM be able to cope with a range of different ground conditions. For that reason, the TBM is capable of using polymer pumping equipment and also pressurized bentonite in the cutting chamber with additives, foam and air. If there is a loss of pressure caused by critical ground conditions, two pressurized and one electronical bentonite tank can be used to stabilize the ground.
To fill the gap between the ground and the outside of the lining, crews will use a two-component grouting system:
- a grout mixture made of cement, bentonite, water, filler (eg, fly ash), retarder or stabilizer (24-hour reaction time) and
- a sodium silicate (accelerator for grouting), which speeds the stabilizing of the grout mixture as quick as possible
To prevent settlements due to the difficult ground conditions and to protect the historical and other residential buildings, drilling and installing the segments must be done more or less simultaneously. With the grout mixture, which needs 10 to 15 seconds of gel time to become stable, it is much easier. The grouting pressure will be 0.2 bar more than the ground pressure. To inject the grout there are 8 grout lines in total, but only 4 lines will be used at the same time. To make sure that the working area is safe, at the outer ring are three brushes installed containing grease.
The TBM is also designed to perform probe drills. On the one hand, it is possible to know more about the ground in front of the shield. On the other hand, if the ground is collapsing or is very fractured, it is easier to arrange an umbrella shield with the 12 angular boreholes.
The contractor also tried to stay on the safe side by ordering a TBM built with durable steel quality to allow longer stops due to repair works in the cutting chamber, and a double articulated shield to help with TBM accuracy.
The logistical problems for a job site in this overcrowded, highly populated City are huge. Everything needs to be delivered on time or directly transported to an outside storage area. The logistic center on the Fulya job site is very small. The muck will be transported in the tunnel with rolling stock and muck cars to the shaft, taken with a crane from shaft ground to surface and dumped in a 20.5-m long, 35-m wide and 4-m high large pool and also continuously cleared. Every day around 60 dump trucks with 40-ton loading capacity leave the job site for the dumping station around 25 km away.
The segments – 15 to 20 rings every day – reach the job site from the segmental production plant which is 25 km far also just in time due to the very small storage capacity.
Progress of construction
In mid-September 2016 assembly of the TBM started and in mid-October 2016 the first ring was built. The total construction time for the tunnel with the Lovsuns EPB TBM only in direction from Fulya to Kabatas is planned for 12 to 13 months. After start of railworks, electromechanical and signaling works, the interior construction of the station will be executed. The distance between both tubes is around 32 m and becomes closer as closer the tunnels reach the station. The second tube from Kabatas to Fulya starts around 6 months later due to archeological examinations in the Kabatas and Besiktas areas.
The TBM is a rebuilt mixed face EPB machine with a cut diameter of 6.57 m. Lovsuns built new a cutterhead, forward, stationary and trailing shields, as well as the main drive system. The rest of the machine has been refurbished. The maximum pressure is 4 bar. The machine is designed for an advance rate of 6 m/hr. The TBM including back-up is 91 m long with 11 m of TBM and 80 m of back-up. In addition, the TBM with back-up has a weight of 563 tons. The cutterhead face and rim is made of high resistant chromium carbide to prevent higher abrasion. The hydraulic main drive contents motors delivers a total power of 1,200 kW to the cutterhead. Maximum torque of the cutting head is 6,199 kNm at a speed of 1.8 rpm. The operator station is specially equipped with programmable logic controller (PLC) with an integrated logging system that records information about the performance of cutterhead, screw conveyor, main drive, grout injection and much more.
The TBM has an automatic tunnel guidance system and the LNSS ground conditioning system with a foam injection rate of 193 m3/h. The grout injection system delivers two different components (component A with 24 m3/h and component B with 2.4 m3/h) with 16 bar maximum pressure. The ventilation system shows a capacity of 450 m3/min.
The second project is a bypass tunnel for a wastewater line in Istanbul’s Zeytinburnu district. It is part of the Turkish government’s plan to increase the number of treatment plants from around 650 in 2015 to more than 2,150 in 2023.
The 3.91-m diameter EPB TBM from Lovsuns finished the first 2-km long bypass in Zeytinburnu. The Turkish construction company Eferay Yapi Ticaret A.S. together with Lovsuns celebrated the first breakthrough in September 2016. The TBM started in a 21-m deep launch shaft and broke through into the 12-m deep target shaft after around 9 months boring. Normally the boring time should be much shorter, but problems with the muck transportation due to winter weather hindered process.
“Drilling of the first tunnel started after one month of assembly in mid-December 2015,’” said Project Manager Muammer Cinar. “The overall project includes 10 km of tunnels, divided in the first 2-km long and a second 8-km long section.”
The geology found in the area included sandstone, siltstone, clay and soil with the potential for groundwater inflow. During the last 150 m drive, the TBM headed under a highly populated area. Here grouting to stabilize the ground helped to prevent higher water ingresses and simultaneously secured the stability of the buildings on the surface. Due to these measurements, the advance of the tunnel was very good. Thanks to the crew and the machine the best shift showed an advance of 15.6 m, the best daily advance was 31.2 m and in the best week 153 m of the tunnel was driven. The best monthly result occurred in April 2016 with 512 m. The regular overburden was between 8 and 40 m, but the last 150 m before reaching the target shaft, the tunnel passed only 6 m under the foundations of the nearby housing areas.
After the first breakthrough in Zeytinburnu, the TBM was disassembled and transported to the second launch shaft in Ayazaga, also situated on the European Side of Istanbul. The second drive will be 7.29 km. Here the ground will be limestone and sandstone. The drive will be divided in two sections with an intermediate shaft after 4 km. All shafts have a diameter of 9 m. Originally it was planned to use more shafts, but due to the small diameter of the TBM this is not necessary. The start of the drive is early 2017. The inner lining will be constructed with concrete lining (5+1 segments), which are built in a segment factory 20 to 25 km away and delivered to the job site just in time.
For the muck transport, rolling stock were used in the tunnels. The muck will be transported by trucks to an old mining area in the northern part of Istanbul. This is the only place to deliver the muck for the whole European Side of Istanbul and especially in winter it is very difficult for transportation.
The EPB TBM is designed as a mixed face soft ground and rock single shield. The shield diameter is 3.91 m with a cut diameter of 3.94 m. The maximum pressure is 3 bar. The machine is designed for a minimum curvature radius of 400 m and an advance rate of 6 m/h. The whole TBM is 89 m long with a TBM length of 8 m and a back-up length of 80 m, altogether weighing approximately 650 tons.
The shield is equipped with 20 single, 2 twin and 1 quad replaceable disc cutters for the rock cutting mode and 28 ripper teeth, 40 scraper tools and 2 oil pressurized wear indicator ripper teeth for soft ground configuration. The hydraulic main drive contents motors which delivers a total power of 524 kW to the cutterhead. Maximum torque of the cutting head is 1,883 kNm with a speed of 2.66 —rpm. The operator station is specially equipped with a PLC that controls all machine functions and records the data. Integrated in the PLC is a logging system recording information about the performance of cutterhead, screw conveyor, main drive, grout injection and more.
Lovsuns has transitioned from Lovat to Caterpillar and now is a subsidiary of the Chinese company Liaoning Censcience Industry Co. Ltd. (LNSS) when Caterpillar tunneling assets were sold in October 2014.
“Only one month after that deal, in November 2014, we continued the success story of our company with the order of the 3.9-m diameter EPB TBM to bore two wastewater tunnels in Istanbul. We designed and engineered the tailormade TBM in Toronto and completely produced it in the facility in Liaoyang, China – successfully united the best practice, knowledge and technology of both companies for the highest advantage of our customer,” said Hongyu Xue, General Manager of Lovsuns Tunneling Canada Ltd.
Dipl.-Ing. Roland Herr is an international freelancing journalist and author, with particular emphasis on Europe and Southeast Asia. He can be reached at firstname.lastname@example.org.