WORK IN PROGRESS. Technical Note. Technical description of key issues of Tunnel solutions. 1. Introduction

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1 WORK IN PROGRESS Technical Note 26 January 2012 Technical description of key issues of Tunnel solutions To: From: Whom it may concern Femern A/S 1. Introduction This technical note describes how each of the two tunnel solutions for a fixed-link crossing the Fehmarnbelt will perform, and the construction methods likely to be used. The two solutions are an immersed and a bored tunnel. The construction technologies used for these are basically different. This difference affects the cross section and alignment of the tunnel, the operation of the fixed-link and the impact on the environmental footprint. The note also compares the two solutions on a technical and factual basis. The design of both solutions is based on the same requirements. These are that the link accommodates a dual-track railway and a four-lane motorway, including full emergency lanes, and that it does so on the basis of the same requirements for safety, quality and life expectancy. In addition both designs (i) make use of proven concepts and proven technology, (ii) provide effectively the same ability to users of the motorway and the railway to reach a safe haven and (iii) provide equivalent access facilities to rescue services. Although both designs are based on the same functional requirements and certain aspects are similar they have different consequences with respect to cost, construction time as well as operation and maintenance. The two solutions are described for the purpose of comparison in chapter 3 and 4 after a brief general description of the immersed and bored tunnel construction methods in chapter 2. The construction methods are described in chapter 5 and 6. Chapter 7 sets out the technical facts of each solution. For further detailed technical information, reference is made to the Consolidated Technical Report, December The Fehmarnbelt Fixed Link is under development. The texts and illustrations represent the state of that development at October The final designs and selection of construction methods will be prepared by the contractors. Consequently the described design and working methods in this note may differ from the actual design and the actual construction methods. However, such differences are not expected to affect the validity of the observations made or the conclusions drawn in this technical note. Both solutions reflect the optimum technical design solution for the particular type of tunnel envisaged. Page 1/36

2 2. General Description of Construction Methods Immersed Tunnel Method (IMT) The immersed tunnel requires that prefabricated units are floated to the site of the tunnel and then immersed in a dredged trench. They are then connected to previously placed elements or the abutments using seals (GINA and Omega) to assure water tightness. This means that the use of immersed tunnel technology is limited to those areas that provide the opportunity to float the prefabricated units. These units (elements) can be of any shape as long as they float. The elements are submerged by taking in water into ballast tanks inside the element which is later replaced by permanent ballast to prevent floating. Normally the elements are located in a dredged trench just below the seabed with sufficient cover to protect the tunnel against impact damage from sinking ships and falling objects (anchors). Each element comprises a number of segments separated by contraction joints with watertight seals. These joints give the tunnel longitudinal flexibility thereby reducing tensile stresses and avoiding cracking. Shear keys at the joints prevent the relative lateral and vertical displacement of the segments. Concrete technology has developed to a stage where watertight concrete elements can be produced without the use of an external membrane. The first concrete immersed tunnels (IMTs) were constructed in the 1930s, and since then have been constructed all over the world. Concrete tunnels without an external membrane have been constructed since 1975, and recently with success in water depths greater than in the Fehmarnbelt. Bored Tunnel Method (TBM) A bored tunnel is constructed by drilling a hole in the soil or rock. Where the soil is known to be unstable the boring process takes place inside a steel shield which protects against collapse. Inside mechanical equipment is used to loosen and remove the soil. At the rear end of the shield a concrete lining is installed forming the permanent tunnel wall. During the boring process the shield is pushed forward by hydraulic jacks operating against the installed tunnel lining. The tunnel cross section has to be circular (or to comprise combinations of circles) to allow the cutter head or heads to rotate. When boring through soil the bored face has to be supported to prevent soil and water from entering the tunnel boring machine (TBM). Earth pressure shields use, via a screw conveyor, the natural soil to build up the support. If needed, the characteristics of the excavated soil can be improved with additives to support the face. Slurry shields support the bored face by means of air pressure on a bentonite slurry which forms a cake to seal off the soil. To counteract for buoyancy and secure a stable boring front the depth of the bored tunnel must be sufficient to leave soil cover over the tunnel to at least the diameter of the tunnel tube. This normally defines the vertical alignment. The concrete lining consists of rings normally 1.5 to 2.0 meters wide. The rings are made up of a number of prefabricated segments. Leakage of water is prevented by rubber gaskets around the perimeter of the segments. These gaskets are kept in compression by the Page 2/36

3 tangential ring force in the tunnel lining and the axial jack forces applied when moving the shield forward. The joints between the segments give the tunnel flexibility. The rings and segments are bolted together to prevent shifting and to assure that the joints remain in compression. The bored tunnel process allows the creation of tunnels deep underground without access from above and, where there is sufficient cover above the tunnel, having only marginal effects on the ground surface. The presence of water which is a prerequisite for an immersed tunnel is merely an added risk for a bored tunnel. The concept of boring a circular tunnel from within a steel cylindrical shield has been used all over the world since the middle of the 20 th century. Modern technology ensures that the TBM can excavate through almost any type of material. But it performs best in homogenous ground. TBMs can limit ground movement and settlements, making them well suited for tunnel construction under cities, where building settlement could prove to be an issue. Some tunnels using the TBM technique have been constructed as large as 15.5 m outer diameter, and other considerably smaller diameter tunnels have been excavated with lengths exceeding 50 km using a number of TBMs. A bored tunnel is created with a tunnel boring machine, which in principle is a mobile factory. Figure 2-1: Tunnel boring machine Page 3/36

4 3. Immersed Tunnel Characteristics Alignment The horizontal alignment for the immersed tunnel solution is shown in longitudinal profile in Figure 3-1. The route passes east of Puttgarden, crosses the Fehmarnbelt starting with a soft curve changing to a straight line and reaches Lolland east of Rødbyhavn. Figure 3-1: Longitudinal profile of the alignment Vertical scale differs from the horizontal scale Shows depth beneath the sea surface The total tunnel length, including the cut-and-cover sections is 18,460 m for the road and 18,345 m for the rail. The vertical height difference is about 50 m with the lowest level of the road alignment at m. The road and rail tubes are part of one single cross-section and therefore the road and rail alignment have the same vertical profile over the tunnel section. Tunnel Cross Section The tunnel accommodates a combined road and railway in one level within a concrete structure, see Figure 3-2. The two road tubes in the standard elements are approximately 11.0 m wide and are located on the west side of the tunnel. Each road tube contains two traffic lanes, one emergency lane, marginal strips and a step barrier and cladding along the walls. A central gallery, approximately 2 m wide, is located between the two road tubes. The gallery is divided into three levels. The lower level contains pipelines from the drainage sumps and water supply pipes for the fire hydrants and fire suppression system. The mid level of the central gallery is located at road level, and provides space for use by maintenance staff and a place of temporary refuge in the event of an evacuation from one road tube to the other. There will be access via fireproof doors for approximately every 100 m. The upper part of the central gallery is used as a service gallery, predominantly for cable routing from the special elements to the installations throughout the tunnel. Page 4/36

5 Two railway tubes, each with a width of approximately 6 m, are located on the eastern side of the tunnel. Each tube has space for one track, fixed to a concrete slab. Emergency walkways are located on both sides of each track. The upper part of the walls and the roof of the interior of the rail and road tubes are provided with material which protects the concrete against the adverse effect of a fire and assures that structural integrity remains intact during and after a fire. Standard and Special Elements There are two types of tunnel elements: standard elements as shown in Figure 3-2 and special elements as shown in Figure 3-3. The 79 standard elements represent the crosssection for the majority of the immersed tunnel. There are ten special elements, located approximately every 1.8 km which serve a number of functions. The approximate crosssectional dimensions of the standard and special elements are as shown in Figure 3-2 and Figure 3-3 respectively. Each standard element is approximately 217 m long. Figure 3-2 Cross-section of standard element with dimensions in metres Figure 3-3: Cross-section of special element with dimensions in metres The special elements provide space within the tunnel for the electrical and mechanical equipment needed for the operation systems of the tunnel. The special elements penetrate deeper into the seabed than the standard elements in order to house a lower level for equipment such as pumps and transformers. The maintenance staff has access to all road Page 5/36

6 and rail tubes regardless of the traffic. In the western road tube is a lay-by for parking of service vehicles outside the emergency lane, from where there is access to the underlying levels via stairs at both ends of the lay-by and via a lift at one end. These access provisions make the special elements wider on the western side compared to the standard tunnel elements. Tunnel Trench The tunnel elements are placed below the original seabed in a dredged trench, as shown in Figure 3-4. A bedding layer of crushed rock, placed in the trench, forms the foundation for the elements. A combination of locking fill and general sand fill is backfilled along the sides of the elements, while a protection layer of large stones is placed across the top of the element. This layer is in general 1.2 m thick. Within the Natura 2000 area, covering a stretch of approximately 4 km, further backfilling with dredged material on top of the protection layer will be made, so that the natural seabed is quickly re-established. Figure 3-4: Cross section of dredged trench with tunnel element and backfilling Page 6/36

7 Reclamation Areas Along both the German and Danish coastlines land claimed from the sea (reclamation areas) will accommodate the seabed material from the dredging of the trench for the immersed tunnel. These areas will be landscaped into green areas. The reclamation area on the Fehmarn side is located east of the breakwaters of the existing harbour. On Lolland there are two reclamation areas, located on either side of the existing harbour. The reclamation areas on Lolland extend approximately 3.7 km east and 3.5 km west of the harbour and reach approximately 500 m into the Fehmarnbelt. The total area is approximately 335 ha, with approximately 145 ha west of the harbour and approximately 190 ha east of the harbour. No reclamation areas extend further into the Fehmarnbelt than the breakwaters of the existing harbour. Portal Areas The Fehmarn tunnel portal building is located behind the existing coastline in a dip in the landscape. The Lolland portal is located in the reclamation area. Both portal structures comprise ramps and a cut-and-cover section. The road and rail ramps differ due to their different gradients and horizontal alignments. As the road and railway descend along the ramps, they are gradually aligned to be parallel and at the same level before entering the cut-and-cover tunnel. The concrete section of the ramps is a U-shaped reinforced concrete structure. Figure 3-5: Portal area on Fehmarn, longitudinal section and plan view Page 7/36

8 Before entering the fully enclosed cut-and-cover tunnel, the road and railway enter the "lightscreen section". The lightscreen section provides a gradual transition from daylight to the artificial tunnel lighting. The cut-and-cover part beyond the lightscreen section is approximately 440 m long. The base slab, side walls, and roof are constructed from reinforced concrete cast in-situ. The main portal building which houses the central control facility is located on top of the cut-and-cover section. The portal building at the Fehmarn side is located next to the cut-and-cover section but underground so that the buildings are not visible in the open landscape. Figure 3-5: Portal area on Lolland, longitudinal section and plan view Technical Installations The tunnel technical systems for the immersed tunnel are, apart from the devices which have to be installed in the tunnel tubes, concentrated in the equipment rooms in the special elements, the cable ducts between the road tubes and the cable troughs in the railway tube. Ventilators for the road tubes are placed in niches in the roof of the elements. The central control room is located in the Lolland portal building. Portal buildings at both sides are provided with water basins for the fire suppression and fire fighting system. Page 8/36

9 4 Permanent Works - Bored Tunnel Alignment The horizontal alignment for the bored tunnel solution follows the same broad corridor as the immersed tunnel alignment. However the bored tunnel comprises two separate road tubes and a railway tube each with a varying separation distance along the alignment with a maximum corridor width of 280 m, see Figure 4-1. Figure 4-1: The bored tunnel configuration The total tunnel length, including the cut-and-cover sections is 19,576 m for the road and 21,230 m for the railway. The vertical height difference is about 72 m with the lowest level of the road alignment at m. The vertical road and rail alignment is shown in Figure 4-2 and Figure 4-3 respectively. The road and rail alignment have different gradients. Figure 4-2: Longitudinal profile of the railway alignment Vertical scale differs from the horizontal scale Page 9/36

10 Shows depth beneath the sea surface Figure 4-3: Longitudinal profile of the road alignment Vertical scale differs from the horizontal scale Shows depth beneath the sea surface Bored Tunnel Structures The bored tunnel structures are formed by a pre-cast, segmented, circular concrete lining and internal structural components which forms the road and rail decks, side gallery, access roads and plant rooms. The railway tunnel has a nominal internal diameter of 15.2 m, while the two road tunnels have an internal diameter of 14.2 m. Concrete Lining Each of the three bored tunnels will require approximately 10,000 concrete rings, each consisting of 11 segments. A total of 330,000 segments will therefore be prefabricated. Each ring consists of ten standard segments and one wedge-shaped element that 'locks' and secures the finished concrete ring in position. Each segment is provided with a sealing rubber gasket along the sides. As the segments are installed, the gaskets are pressed together so that water cannot penetrate into the tunnel through the joints. The gaskets can withstand water pressure of up to 15 bar. Each segment is bolted to the adjacent segment in the ring, and each ring is also bolted to the adjacent ring. The thickness of the linings is 600 mm in sections where the tunnel passes through the hard, glacial clay-till. The Puttgarden area, on the other hand, has more difficult soil conditions which require the thickest concrete lining of 750 mm in all three tunnels. Where exposure to a fire is possible the lining is protected with a layer of fire protection material. This material assures that in the case of fire the structural integrity of the tunnel remains intact. Page 10/36

11 Internal Structures Road Tube The total cross-section of the motorway is approximately 11 m wide, and the road tubes are located west of the railway tunnel. Each road tube contains two traffic lanes, one emergency lane, marginal strips, a step barrier and cladding at the walls. At the top of the circular cross-sections, the necessary jet fans and signage are installed, see Figure 4-4. Figure 4-4: Cross-section of one of the two road tubes The motorway tubes contain an approximately 2 m wide fireproof side gallery with access from the emergency lane. There will be access, via fireproof doors, at approximately 100 m spacing along the tubes. The gallery also provides access to the levels below the road deck (on the lower floor) via stairs or ramps. This lower floor contains the necessary plant rooms, a cable duct, pump rooms and a rescue and service road with access for all vehicles of full normal height and with sufficient width to allow two vehicles to pass each other. Internal Structures Rail Tube The railway tunnel is divided in the middle by a fireproof central gallery and is thus divided into two separate tubes, each with a width of approximately 6 m. The rail tracks are installed directly on the concrete deck (slab track). Emergency walkways are arranged on both sides of each track and jet fans are installed at the top of each tube, see Figure 4-5. The fireproof gallery in the middle provides (i) access from each railway tube (ii) space for plant rooms (iii) space for cables. Below the rail level there is an access road for rescue Page 11/36

12 and service which can be reached from the railway deck via ramps and stairs. Appropriate access roads for rescue vehicles are established in both portal buildings. Figure 4-5: Cross-section of railway tunnel with two separate tubes in one tunnel cross section Reclamation Areas Along both the German and Danish coastlines reclamation areas will accommodate the bored soil and other excavated material, in total 19.2 million m 3 (incl. a bulking factor of 1.3; 14.8 million m 3 in situ) about 50% being produced on either side. The areas will be landscaped with nature of which will depend on the quality of the material delivered from the separation plant. The reclamation on the Fehmarn side is located east of the breakwaters of the existing harbour. On Lolland there are two reclamation areas, located on either side of the existing harbour. The reclamation areas on Lolland extend approximately 3.7 km east and 3.5 km west of the harbour and reach approximately 500 m into the Fehmarnbelt. The total area is approximately 335 ha, with approximately 145 ha west of the harbour and approximately 190 ha east of the harbour. The neither reclamation areas extend further out into the Fehmarnbelt than the breakwaters of the existing harbour. Portal Areas The bored tunnel portal buildings are located inland behind the existing coastline at different locations for the railway and motorway. The two road tunnels start from one launch box. For both rail and road tunnel the access road for rescue and services enter from the side into the portal area where they are fed into the bored tunnel cross section under the road deck. The bored tunnel section ends where the depth of cover over the tunnel is reduced Page 12/36

13 to half the tunnel diameter. An embankment is placed over the tunnel alignment where the cover is less than one tunnel diameter to assure minimum groundcover. The portal buildings on Lolland are placed on top of the cut-and-cover part of the tunnels. On Fehmarn the portal buildings are placed underground so that the buildings are not visible in the open landscape, see Figure 4-6. Figure 4-6: Bird view of the Fehmarn portal area of the bored tunnel solution Technical installations For the railway tunnel the transformers that convert high voltage from main electrical supply, which runs longitudinally through the tunnel, into lower voltage are housed in the plant rooms in the central gallery of the railway tunnel. Cables are located in the duct above the transformer plant rooms. For the road tunnels the transformers are placed below the road deck in the gallery. For both road and railway tunnel drainage sumps are located under the rescue services access road with pump rooms next to the access road tubes. Ventilation is along the length of the road and rail tunnels (longitudinal ventilation) and is provided by jet fans located at the tunnel crowns. The central control room is located in the Lolland portal building. Portal buildings at both sides are provided with water basins for the fire suppression and fire fighting system. 5. Construction and Temporary Works Immersed Tunnel Dredging Temporary work harbours are planned located inside the reclamation areas on the German and Danish side. They will be used as a safe haven for contractor s vessels and to deliver, store and handle materials and equipment. Page 13/36

14 The dredging for the immersed tunnel comprises a total quantity of 22.6 million m 3 (incl. a bulking factor of 1.2; 18.8 million m 3 in situ) of which the majority is from the tunnel trench. The dredging will be mainly mechanical dredging. The dredging method is selected to reduce the extent of sedimentation spill and to ease handling of obstacles, such as boulders in the trench. The dredging material is uncontaminated and will be re-used to create the reclamation areas. These areas are planned to be established by first constructing a containment dike around the reclamation areas in front of the existing coastline. The dredged materials will subsequently be incorporated in the reclamation areas behind the containment dikes. Standard Element Production The standard elements will be produced in a controlled environment in a factory. The factory is located in line with a launching basin consisting of an upper shallow section and a deeper section which gives access to the Fehmarnbelt via a floating gate, see Figure 5-1. Each element is cast in short sections called segments. The full length and width of each segment is cast in formwork at a fixed location, and after a minimum curing period, the segment is pushed free of the casting bed by hydraulic jacks and out into the shallow launching basin thereby creating a space for the next segment to be cast. Once sufficient segments for one element have been made, they are joined by tension cables, ballast tank systems are installed and watertight bulkheads are mounted to create a floating transportable unit. The launching basin, surrounded by dikes and gates, is filled with water until the tunnel elements float. Then the tunnel elements are pulled into the deep section of the launching basin and moored, after which the water level is lowered down to the water level in the Fehmarnbelt. Subsequently the sliding gate and floating gate can be opened and the elements towed out. Eight casting lines will be needed for production of the tunnel elements in order to meet the planned time schedule. Page 14/36

15 Figure 5-1: Production of elements using an industrial production method Logistics of Construction Materials The high production rate means that the materials required for construction are expected to be delivered to the production site by means of both lorries and vessels. Cement, sand, rock and steel reinforcement for concrete production are expected to be delivered by vessels. Tunnel Element Towing The tunnel element will be connected to four tug boats and towed from the production site to a holding area near the tunnel trench in the Fehmarnbelt. Before towing, a system of ballast tanks is installed inside the element. Figure 5-2: Towing a tunnel element Cleaning and Tunnel Foundation of the Tunnel Trench The trench is cleaned of unwanted sediment before placing a foundation layer of crushed rock. The layer will be placed using a barge equipped with a fall-pipe. The crushed rock will be supplied by self-unloading bulk carriers directly from the quarry. The bulk carriers will Page 15/36

16 moor alongside the barge and unload the crushed rock via a conveyor belt. The crushed rock is then placed into the trench via the fall-pipe. Figure 5-3: Placing crushed rock as the foundation for tunnel element Immersion of Tunnel Elements Before immersion, the tunnel element is connected to pontoons that are positioned over the tunnel trench and moored to anchors. The immersion starts by filling the ballast tanks with water until the freeboard of the floating element is reduced to zero. The ballast tanks are then further filled to create the required weight for the element to sink. During the immersion operation, the tunnel element is held in position by the two pontoons using suspension wires, as shown in Figure 5-4. The position of the pontoons is controlled by mooring wires connected to anchors on the seabed. Figure 5-4: Immersion of an element from an immersion pontoon (cross-section through the centre of the element) During the immersion, the tunnel element is gradually lowered into position next to the previously immersed element. The newly immersed element is then pulled into place against the previously immersed element by means of hydraulic cylinders. The resulting space between the steel bulkhead of each element is initially sealed by a fitted rubber membrane (Gina gasket). This seal is finally completely compressed by the water pressure at the op- Page 16/36

17 posite free end of the element. The ballast tanks are then filled further until the minimum weight required to keep the element in place has been achieved. Once the tunnel element is correctly positioned, locking fill is placed around the element again by using a hydraulic fall pipe. Figure 5-5: A tunnel element is towed by tug boats to the Øresund tunnel (Denmark) Backfilling and Covering the Tunnel Once a tunnel element has been installed the trench is backfilled with suitable materials and a protection layer of approximately 1.2 m on top is provided. For the protection layer, rock will be transported from a quarry, possibly using a barge towed by a tug boat, and, depending on the water depth, either placed by pushing rock over the side of the pontoon or by grabs mounted on the vessel itself. Within the Natura 2000 area, covering a stretch of approximately 4 km, the tunnel will be lowered a bit further in order to allow for extra backfilling with natural seabed material on top of the protection layer, so that the natural seabed is quickly re-established. Page 17/36

18 Figure 5-6: Backfilling of the trench and protection of the immersed tunnel Special Element Production The ten special elements are expected to be constructed as steel concrete composite structures in an existing facility such as a shipyard. In the facility a watertight steel body consisting of an inner and outer hull will be constructed. The body forms the outline of the special element and is provided with steel bulkhead at each end as with the standard elements. After launching of the steel body it will be towed to a casting platform near the site where the space between the inner and outer hull is filled with concrete. The concrete has a high liquidity in order to fill completely the compartments between the inner and outer hull. When filled with concrete the element will float with a minimum freeboard as the standard elements do. The further process of transport and immersion is equivalent to the process used for the standard elements. The inner and outer hull are provided with dowels and/or welded steel angles to create a shear connection between the concrete and the steel hull in order to let it act as a composite sandwich structure. Completion Works When the backfilling around an element has been completed and the protective layer has been placed, water is pumped out of the ballast tanks inside the tunnel element while ballast concrete is cast along the full length of the tunnel floor. Then the ballast tanks and the steel bulkheads separating the tunnel elements are removed and finally the joints between the elements are completed and the tunnel interior can be finished. Closure Joint The immersion will take place simultaneously from the German and Danish coastline. At the middle of the Fehmarnbelt the remaining gap between the last two elements will be closed by means of a steel hull connected to the elements by watertight seals. Inside the hull reinforced concrete is cast to connect the two sections. Construction Sites The production site must be included in the EIA assessment, and consequently it has been decided that the production of the tunnel elements will be located in a purpose-built casting factory east of Rødbyhavn. The production site is partly located onshore and partly located offshore but inside the reclamation area, as shown on Figure 5-7. The on- shore area is approximately 200 ha. Page 18/36

19 Figure 5-7: Production plant for tunnel elements on Lolland Page 19/36

20 Next to the construction site for the cut-and-cover section between the portal buildings and the immersed tunnel on Fehmarn a temporary harbour is planned. This includes unloading and storage facilities for the construction works on Fehmarn, as shown in Figure 5-8. The size is approximately 30 ha. Figure 5-8: Temporary work harbour on Fehmarn conceptual design 6. Construction and Temporary Works Bored Tunnel Work Harbours Temporary harbours (work harbours) are located in the reclamation areas on the German and Danish side. They will be used for the delivery, handling and storage of materials and equipment. Limited dredging is required to assure access up to a draft of 8 m. TBM Each tunnel tube is bored with two TBM, each of which starts from excavations (launching boxes) on land from Denmark and Germany, respectively, to meet halfway below the Feh- Page 20/36

21 marnbelt. All six boring machines are expected to be slurry-shield TBMs that operate using a special mixture of slurry containing bentonite. The tunnel boring machine consist of a circular steel shield, a cutterhead at the front, an excavation chamber behind the cutterhead, (provided in case of a mix shield with a submerged wall to separate a pressurized air cushion from the boring front), an air lock to access the chamber, jacks around the internal circumference of the shield to push the shield forward, feeder lines for the bentonite slurry and for the mortar to inject in the tail void, a segment erector in the tail end of the shield, a pipeline to transport the excavated soil/slurry mix, a segments transport line and an operator s cockpit: all as shown in Figure 2-1. Booster stations provide the pressure to pump the slurry and excavated material. A factory for the production of the segments and a separation plant to reclaim the bentonite completes the production chain. The boring machines are equipped with a stone crusher fitted at the base of the machine. This crusher breaks down large stones into smaller pieces that can be transported with the other materials in the slurry through the pipeline to land. The primary method of handling boulders and stones is to crush them while they are still firmly fixed in the soil in front of the cutter head. The boulders are broken down to a suitable size so they can pass through the openings of the cutter head to the stone crusher. A special version of a slurry TBM is a mixshield TBM, which is a tunnel boring machine with a double-chamber system that can precisely control the surface pressure by means of a combination of slurry and compressed air, as shown in Figure 6-1. Figure 6-1: Typical mixshield machine with double chamber Page 21/36

22 Production Process The boring operation takes place by the soil ahead of the machine being loosened by a number of hardened cutter discs and teeth fitted in the rotating cutter head. Circular disks break down stones and boulders. The cutter head rotates, normally at 3 to 5 revolutions per minute while being pressed forward. The bored soil is transported into the excavation chamber via holes in the cutter head, as shown in Figure 6-1. The cutter head is enclosed in a steel shield which protects against collapse and soil ingress until the permanent concrete lining is installed. The cutter head is specially manufactured to match the specific soil conditions and the size and length of the bored tunnel. The bentonite slurry stabilises the bored face (the soil) in front of the cutter head and is mixed with the bored materials so that they can be pumped through a pipeline to separation plants on land where the bored material is separated from the slurry. The slurry is reused. The majority of the bored materials are used to form new land areas off both coasts, although primarily along the south coast of Lolland. At the rear end of the shield, the permanent concrete lining is installed in the form of segments that make up a full ring. The segments are installed from inside the tunnel boring machine by a device that lifts the individual segments and places them in position (by a vacuum erector). Mortar is used as grouting between the concrete ring and the soil to ensure full contact between the tunnel structure and the surrounding soil. The motorway and railway decks and the rooms and galleries in the tunnel are formed of pre-cast elements, where possible. These elements will be transported and installed immediately along with the completion of the individual tunnel sections using rolling gantry cranes working right behind the tunnel boring machines. Maintenance As each tunnel boring is very long and passes through several types of soil, which can cause various problems such as unexpected high wear on the cutter head, regular maintenance of the cutter head and its cutting tools is essential. This means that it is necessary to be able to access the working chamber in front of the cutter head. Access is complicated by the fact that there is a water pressure in front of the cutter head of up to approximately 6 bar. Access to the working chamber can take place via air locks in the front section of the tunnel boring machine. The air locks allow personnel without specialist training to operate under pressures of up to 3.6 bar. At a pressure of more than 3.6 bar, special divers are required to enter the working chamber, which complicates the work considerably. It is estimated that up to 70% of the repairs will take place under pressures of more than 3.6 bar. In addition to the planned maintenance works, it is only considered necessary to have access under high pressure in emergency situations. In a mixshield TBM, it is possible to create access to hollow spokes of the cutter head for some maintenance activities. This can be done under atmospheric conditions reducing the risk of the boring machine and its back-up system being flooded in the event of high water pressure in front. Page 22/36

23 A consequence of boring under water is that contamination of the lubrication system for the working parts of the main bearings or the gearboxes due to the high pressures may happen. Because a main bearing is larger in diameter than the internal diameter of the constructed tunnel a number of complications arise should a replacement of the part prove necessary. Mid-Tunnel Docking of the TBMs To optimise the boring process and limit wear on the boring machines TBMs shall simultaneously bore each tunnel from each coast approximately 10 km boring by each machine. Depending on respective progress they will meet approximately at the mid-point of the respective tunnels. When the TBMs meet their outer shield will create the necessary protection to establish a safe working chamber for the concluding construction works, including insitu casting of the internal concrete lining. The rest of the boring machine will then be dismantled and removed including the associated back-up system. Separation Plant and Storage Area for Bored Materials A total of 19,200,000 m³ (incl. a bulking factor of 1.3; 14.8 m 3 in situ) of bored clay and other excavated materials is expected with approximately 50% on either side Fehmarn and Lolland. It is planned that all material is used to create new land (reclamation areas). However it is difficult to predict the form and volume of the excavated clay going into the separation plant. In the worst case some of the clay will have been dissolved in the slurry, which means that even a large separation plant will have difficulties in separating the clay from the slurry which will reduce the use of the land reclamation. The water from the separation plant is processed in a water treatment plant on site to a point where particulate content is acceptable for direct discharging into the sea, or into a local watercourse. The potential for use of the bored material will depend largely on the water content, and the resulting strength of the material. It is assumed that all material from the separation plants can, to some extent, be used for land reclamation areas with approximately 15% on the German and 85% on the Danish side. About one third of the materials is expected to be fine-grained (less than 0.01 mm). It may be difficult to use this fraction of very fine material, but it is assumed that it also can be handled as part of the reclamation works. The proposed separation method is expected to reduce the water content to an acceptable level. However, the strength of this material will be less than that before excavation. The finest -grained materials will be deposited in small basins to prevent them being washed away over time. Even in the long term it is unlikely that such material will be able to support vehicular and possibly pedestrian traffic. The total area proposed for the land reclamation is approximately 360 ha. It is planned that a large part of the area being established as a network of basins surrounded by dikes that also carry the necessary access roads for dumpers, see Figure 6-3. Page 23/36

24 Power and Water Supply to Site Mixshield-TBMs and associated equipment will have a high consumption of electricity over a total bored length of 60 km. The separation plants will also have a high consumption. In addition to the fresh water required for the production of concrete and for staff welfare facilities, there is also a demand for a large volume of water for the production of slurry. The latter may utilise the brackish water from Fehmarnbelt. Construction Sites The construction sites on both the Danish and German side are planned for production and storage of lining segments and internal pre-cast elements, separation plants with storage and handling areas, slurry production plants, concrete batching plant and construction areas for the portal and ramp structures. A total of 330,000 segments will be produced for the concrete lining within a period of approximately 3.5 years. This will require high-capacity concrete casting facilities with appropriate storage areas for hardening and storage. Prefabricated elements will also be produced for the motorway and railway decks and partition walls. It is proposed that both the segment and element prefabrication sites be located close to the individual tunnel portal buildings. The total area for each separation plant is approximately 3.6 ha, including storage area for temporary storage of the filtered materials. The storage area must typically have space for spoil equivalent to 5 days of production, i.e. approximately 44,000 tonnes or 22,000 m³. The construction site on Fehmarn does not have a readily available supply of fresh water in the quantities required, and it is therefore expected that all fresh water to the site will be delivered by tanker by sea. Figure 6-2: Fehmarn construction site Page 24/36

25 Figure 6-3: Lolland construction site 7. Comparison Below, the TBM option is compared with the immersed tunnel on the following aspects: Technology Cross section Alignment and portal location Structural aspects and seals Permanent on-shore footprint Safety concept Installations and maintenance concept Geological hazards Logistic Temporary on-shore footprint Soil re-use Resource requirements Construction cost estimate Construction programme 7.1 Technology Immersed Tunnel: Proven Concept Immersed tunnels of the proposed segmented concrete tunnel type have been widely used in Western Europe, but only in water depths of up to 25 m. Recently for the Busan Geoje tunnel in South Korea, a similar concept, has been applied successfully in a water depth of 45 m while the Bosphorus immersed tunnel in Istanbul, Turkey, has been successfully installed in almost 60 m of water. Page 25/36

26 In terms of length, the Fehmarn tunnel will be by far the longest immersed tunnel. However, it will be constructed by using known technology for dredging, production of elements and the transport and immersion of the elements. Element production The envisaged production method for the immersed tunnel elements was used successfully on the Øresund and the Busan Geoje Link in South Korea. The envisaged eight production lines for the Fehmarn will each produce the same number of elements (10) as was produced by each production line used for the Øresund tunnel. Trench dredging The excavation method for the trench relies on dredging into the seabed with floating equipment with direct access to the seabed, and further into the tunnel trench. This allows flexibility with respect to changing techniques and equipment where so required. This approach is traditional, well known and widely used and is not affected by the trench length. While the IMT solution would require the longest dredged section for any IMT in the world, the quantity to be dredged is not remarkable in terms of other dredging applications. The excavation method is reliable and a technically feasible method at the dredging depths that will be encountered and with respect to the type of soil to be dredged. Numerous examples are available to support this statement. Transport and immersion of the elements The transport and immersion is based on traditional technology used in many immersed tunnels and other civil engineering projects around the world. Recent examples are the Busan Geoje tunnel in South Korea and the Bosphorus immersed tunnel in Istanbul, Turkey where this technology was used in water depths of up to almost 60 m, under severe marine conditions and in a busy international sea lane. The reliability of the transport and immersion is not affected by the tunnel length. Indeed increased length improves the utilization of the equipment which can be designed for well-defined conditions during the transport and immersion operation. All aspects of the immersed tunnel technology, as applied for the Fehmarnbelt Fixed Link are proven. Bored Tunnel: Concept Proven Ten bored tunnels with diameters in the range of 14.5 up to 15.5 m (seven slurry and three EPB shields) have been successfully constructed in recent years. It has been possible to resolve the problems encountered during construction of these large diameter TBMs and bored tunnels. Accordingly a bored tunnel in the range of 15 to 16 m can be considered proven technology for distances up to 4 km. New upcoming tunnel projects in Seattle and St Petersburg requiring TBMs of 17.5 m and 19.2 m diameters respectively have recently been awarded to TBM contractors; these tunnel drives are of the order of 2.7 km and 1.0 km respectively. The performance of the TBMs of this diameter has yet to be proven. In addition there is no evidence available as to the performance of TBM of over 10 m diameter in the difficult geological conditions which are present in the Fehmarnbelt. Page 26/36

27 The boring machines will need to be designed as a technical compromise to cope with the variety of geological conditions that will be encountered along the alignment. All together approximately 60 km tunnel has to be constructed by six very large diameter TBMs. In comparison, the IMT consists of 18 km tunnel produced by using proven technology. TBM design challenge For the bored tunnel, the investment costs of the TBMs amount to less than ten per cent of the total construction costs, but the performance of each of the six TBMs in the variety of conditions encountered is critical to the the success of the project. TBM functionality has to take into account the specific conditions such as high water pressure, the large diameter tunnel, the length to be bored, the abrasive nature of the soil, the properties of the unique Palaeogene clay, and the presence of boulders. Although each individual condition can be and has been addressed in design on other projects no TBM is known to have been designed to deal with the diameter and length required of the Fehmarnbelt fixed link and the prevailing geological conditions. To design and build such a machine would be to extend the art of tunnel boring well beyond the existing boundaries of technology. Limited number of qualified TBM suppliers The tunnel boring machines are fabricated outside the construction site by a specialist producer. The number of producers who have previously produced tunnel boring machines approaching the size and quality required is limited to the European mainland, Japan and North America. 7.2 Cross Section Immersed Tunnel The immersed tunnel cross section is rectangular and encloses tightly the required traffic envelopes and the required additional space for installations. It comprises two road tubes (two traffic lanes and an emergency lane) of about 11 m wide with a gallery, internal width of 2 m in between and two railway tubes of about 6 m internal width in one single cross section. All tubes are interconnected by cross passages approximately every 100 m and via the special elements. The arrangement makes it possible to make use of the non-incident road tube in case of an accident in the other road tube or railway tubes. An easy approach to the site of an accident is possible as all tubes are at the same level. The width of the footprint of the immersed tunnel including the dredged trench is approximately m depending on the slope stability. No structural elements need to be installed after immersion as the road and rail deck are integrated parts of the tunnel cross section. Page 27/36

28 Bored Tunnel The bored tunnel comprises three separate tunnel tubes; two for the motorway and one for both the rail tracks. All tubes are circular due to the construction method applied. The net internal widths of the road and railway tubes are the same as for the immersed tunnel. There are no interconnections (cross passages) between the tunnel tubes. The bored tunnels provide a mean of escape per approx. 100 m to an adjacent gallery within the tube and secondary access to the refuge area under the road and railway decks. Access routes for rescues services are located at a level below the road and rail deck. Pre-fabricated structural elements need to be installed within the lining to form the road and rail deck, escape gallery and plant rooms. 7.3 Alignment and Portal Location The horizontal alignment for the immersed and bored tunnel solution follows the same broad corridor. However, the width of the immersed tunnel is 42.2 m and the maximum spacing between the rail tube and the eastern road tube is approximately 280 m (80 m between the two road tubes). The vertical alignments differ due to inherent differences in the construction method. Immersed Tunnel The portal buildings on either side are shared by the railway and the road. The road lanes and rail tracks are aligned within a corridor of about 45 m in plan. In the immersed tunnel the road alignment has the same gradient as the rail in the tunnel and the cut-and-cover section. The Lolland portal building is located inside the land reclamation area; the Fehmarn portal building is located on land. The deepest point of the road and rail alignment is at m and m resulting in a height difference of m and m respectively. The lengths of the various parts of the alignment are listed in Table 7-1. For the immersed tunnel the seabed will be restored which includes a protection layer and within the Natura 2000 area, covering a stretch of approximately 4 km, further backfilling with dredged material on top of the protection layer will be made, so that the natural seabed is quickly re-established. Bored Tunnel For the bored tunnel it is technologically not possible to bundle the roads and rail alignment such that the portals for the road and rail tunnels can be shared. The bored tunnels cannot be placed directly beside each other, and require a separation distance to ensure that the excavations do not influence each other, ensuring all tunnels are stable in the ground. A typical separation distance of about 16 m (one diameter) is needed. Page 28/36

29 The road and rail can have different longitudinal gradients and reach the surface at different locations. The required separation between the bored tunnels (three separate tubes) results in a maximum corridor width of the bored tunnels of approximately 280 m in plan. The vertical road and rail alignment are independent and not the same. The bored tunnel has to be excavated from starting shafts (launching boxes) located inland providing space to build up the boring machine including all trailers. The deepest point of the road and rail alignment is at m and m resulting in a height difference of m and m respectively. The lengths of the various parts of the alignment are listed in Table 7-1. For the bored tunnel there is no requirement to openly excavate through the coastline or the seabed. However, the coastline will be affected by the reclamation areas. Bored IMT Rail Road Rail Road Total Project Length 29,900 m 25,350 m 27,100 m 25,350 m Total Length between tops of ramps 23,420 m 20,135 m 19,840 m 18,830 m Length of Tunnel (including Cut & Cover) 21,230 m 19,576 m 18,345 m 18,460 m Table 7-1 Comparison of Lengths The bored rail tunnel is 3,580 m longer, and the bored road tunnel is 1,305 m longer than the immersed tunnel, when measured from top of ramp to top of ramp. 7.4 Structural Aspects and Seals In the axial direction the immersed and bored tunnel behave as a beam on an elastic foundation with a relative low foundation pressure. A high flexibility is created by the joints between the segments for the immersed tunnel and the rings for the bored tunnel. Joints are at intermediate distances of approximately 22 m for the immersed tunnel and 2.0 m for the bored tunnel. External water and soil pressure create mainly compression in the circular bored tunnel rings whilst the immersed tunnel takes the pressure as a combination of bending and compression in the roof, base slab and walls. Immersed tunnel The immersed tunnel has transverse joints only. The cross section is cast in one continuous process avoiding longitudinal joints between the roof/base slab and walls. The water tightness of the seals between the segments relies on the adherence between the steel strip which is vulcanized into the rubber water stop and the concrete. No compression is needed for its functionality, to the contrary functionality remains under tension and opening of the joints. Page 29/36