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GEOLOGY The geological and geotechnical conditions along the alignment of the first 18 km of the Athens Metro lines had been extensively investigated, analysed and evaluated. The results of this survey were used as a basis in order to develop the geotechnical parameters required for the safe design of tunnels, stations and other underground structures. The geological substratum of the city of Athens consists of a series of geological formations known as the system of the Athenian Schist, mainly at the depth range of the Metro works. �Athenian Schist� is a term used to describe a sequence of originally sedimentary, flyschlike rocks of possible Upper Cretaceous age, which have subsequently suffered metamorphosis. The system includes clayey and calcareous sandstones, greywacke, siltstones, limestones and shales. Igneous activity has locally introduced peridotitic and diabasic bodies causing lithologic deformation and significant deformation of the pre-existing members. It is possible that during the geological era of Eocene the Athenian Schist formations suffered intense folding and thrusting. Additional factors, which affect rock mass quality, are the widespread weathering and the alteration of the deposits. As a consequence, the rock mass is highly heterogeneous and anisotropic not only in the macroscopic-geotectonic scale of Attica Basin, but mainly in the mesoscopic scale of the tunnel works. This inherent heterogeneity of the Athenian Schist rock masses gives rise to uncertainty while correlating adjacent boreholes, something that renders the design of reliable geological sections particularly difficult. The quaternary formations deposited over the Athenian Schist consist of river deposits (argillaceous and sandy materials, as well as conglomerate usually of a small thickness). In addition, large areas are covered by diluvial deposits among the hills consisting of clay silt and sand in alternations with breccia loosely cemented. Finally, a surface layer with recent deposits or artificial backfillings of various thickness (16m) exists in the majority of the areas along the alignment of the Project. These deposits were formed during the historical years. The Athenian Schist consists, in general, of rocks with a small permeability, with the exception of rocks with a large secondary porosity (open discontinuities, karsts in calcareous rocks, heavily fractured material of massive rocks). Thus, in general, no large quantities of underground water, which would make more difficult the execution of excavation works were encountered, despite the fact that based on the readings of the piezometers the levels were only a few metres below surface.
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The Metro has been designed in such a way as to address the impact of the most adverse conditions of seismic activity recorded to date, according to the Greek Design Standards. Prior to the construction of the Project, geotechnical investigations were carried out in order to obtain the appropriate information required for the design of such a Project. The program included more than 350 boreholes which supplemented the 200 boreholes executed along the line alignment during previous surveys, i.e. one borehole, on average, at approximately every 30m along the entire length of the alignment. Each borehole was performed at a depth of approximately 20-30m below surface. The execution of geotechnical surveys continued even during the construction phase and 1100 additional boreholes have been executed in order to serve the needs of the Base Project. The most important geotechnical activities carried out by ATTIKO METRO are as follows: •
• • •
•
Survey of the geological and geotechnical conditions with 1100 boreholes, most of which were executed with continuous soil and rock core sampling, while some of them were used for the execution of on site tests for the optimum investigation of the conditions prevailing at the levels where the Project is constructed, as well as for the installation of special geotechnical monitoring instruments. Geophysical surveys, using various techniques, such as the ground radar penetrating the soil tracking down buried data, such as underground river channels, P.U.O. networks and possible major archaeological finds. Measurement of the underground water table along the tunnel alignment in order to estimate the general direction of the water flow, as well as any annual variations of water level for the optimum planning of the Project. Development of the main parameters of soil and rock strength, to be used for the design of the Project structures. These parameters are based on results of laboratory tests of soil and rock samples, as well as on other data collected from in situ tests. An extended geotechnical monitoring program before, during and after the execution of excavation works is executed for the safety of the overlaying and/or adjacent buildings and structures, as well as for the verification of the assumptions regarding the Project planning.
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CONSTRUCTION METHODS The entire ATHENS METRO project is underground. In this way, its objective, i.e. the rapid transfer of citizens in the wider area of the capital is achieved. For the construction of the underground Metro stations and tunnels, up-to-date methods, which ensured safe, workmanlike and rapid completion of the project, were applied. The project construction methods were used either separately or combined one to another, as deemed applicable, always in relation with the geological conditions and the in situ conditions of the surrounding area.
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•
Excavation with the use of Tunnel Boring Machine (TBM). This method was applied for the boring of tunnels; in particular TBM1 (named IASSONAS) was used in Line 2 section from LARISSA Station to AGHIOS IOANNIS Station, while TBM2 (named PERSEFONI) was used in Line 3 section from KATEHAKI Station to SYNTAGMA Station.
•
Excavation with the use of the Open Face Shield (OFS). This method was used for tunnel boring and specifically for the construction of DAFNI – AGHIOS DIMITRIOS tunnel section of the Base Project, 765m. long, as well as for ANTHOUPOLI – PERISTERI Line 2 section, 910m. long.
•
Excavation with the use of Earth Pressure Balance machine. This method was applied for tunnel boring and namely for the construction of the tunnel section from DOUKISSIS PLAKENTIAS to XANTHOU Shaft, 3,374m total long, of Line 3 extension to Doukissis Plakentias, while ths machine is now “working” for the construction of the extension of Line 2 to Elliniko.
•
Use of the New Austrian Tunnelling Method (NATM). It was used for tunnel boring, at soils with poor mechanical characteristics, as well as for the excavation of some stations of the Project, namely PANEPISTIMIO, AKROPOLI, AMBELOKIPI, MONASTIRAKI, OMONIA, as well as for the excavation of the deepest section of SYNTAGMA Station. Moreover, the method was used at large parts of the network extensions to Doukissis Plakentias, to Aghios Dimitrios, to Aghios Antonios, to Egaleo, etc.
•
Use of the Cut and Cover method. This method was mainly used for the excavation of the stations of the Project, as well as in a few cases, for the excavation of tunnels at locations where problems were encountered due to poor mechanical characteristics of the soil. Many sections of the Athens Metro network were constructed using this method, such as the Stations: SEPOLIA, ATTIKI, LARISSA, METAXOURGHIO, SYNGROU-FIX, N. KOSMOS, AGHIOS IOANNIS, DAFNI of Line 2, as well as ETHNIKI AMYNA, KATEHAKI, PANORMOU, MEGARO MOUSSIKIS, EVANGELISMOS, SYNTAGMA (Line 2 Station which is located at a smaller depth). This method was also used for ATTIKI-LARISSA and KATEHAKI-
ETHNIKI AMYNA tunnel sections. The said method was also used for several sections of the extensions, such as AGHIOS DIMITRIOS & AGHIOS ANTONIOS along Line 2, HALANDRI & DOUKISSIS PLAKENTIAS Stations along Line 3, as well as a section of DAFNI – AGHIOS DIMITRIOS tunnel. •
Use of the Cover and Cut method. This method constitutes a variation of the cut & cover method and was used only at SYNTAGMA Station of Line 2, due to the particularity of the area.
Tunnel & Station Construction using the Underground Conventional Boring Method (ΝΑΤΜ) Ι. General The underground tunnel boring method using conventional means (known as NATM method or New Austrian Tunneling Method) is the second (in terms of preference) construction method applied internationally for the construction of tunnels using the underground boring method. The Tunnel Boring Machine (ΤΒΜ) is the method, which is preferably used for the construction of tunnels. In urban areas where Metropolitan Railways (Metro) are constructed, it is important not to disturb the functions of the city even if this implies increase in the financial cost of the projects. Using the underground construction methods for stations and tunnels, the occupation of areas at the surface (squares, streets, private plots, etc), the relocations of PUO pipes (water, power, telephone supply, etc) traffic diversions and archaeological excavations are avoided. As to the Athens Metro, the NATM method was widely used both for the construction of tunnel sections and some of the Stations at the center of Athens. In particular, it was used for the construction of PANEPISTIMIO, AKROPOLI, AMBELOKIPI, MONASTIRAKI, OMONIA and SYNTAGMA Stations. Moreover, the said method was applied at large sections of the network extensions to Doukissis Plakentias, Aghios Dimitrios, Aghios Antonios and Egaleo. ΙΙ. Construction Methodology The basic principle of this method is to maintain the strength of the environment at the surface surrounding the tunnel and fully utilize it. Controllable soil deformation with the use of flexible retaining – contrary to previous views concerning “heavy” retaining-has positive
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effect and has as a result the safe development of the soil strength. The methodology of the project design/construction is the following: • •
• •
•
•
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Geotechnical/geological investigations and tests are executed (on site and laboratory) for the identification of soil characteristics in the area where the tunnel has been planned to be bored. The design (calculations and drawings) of the excavation and the temporary retaining of the tunnel is under way based on the geotechnical characteristics of the soil, which resulted during the previous phase. Moreover, the design of the permanent (final) lining of the tunnel is prepared. The excavation is executed using conventional mechanical means (road header, conventional excavator, etc) and sometimes the excavation front is directly retained at several phases, depending of the quality of the soil. Upon completion of the excavation, which is gradually performed depending on the characteristics of the rocks and the project, there follows a system of temporary retaining consisting of shotcrete lining (gunite), rockbolts, steel frames etc. In case of soil with poor characteristics, prior to the excavation, forepoling beams are installed in the entire area over the tunnel vault in the form of an umbrella providing protection to the excavation front. Frequently, excavation is performed in two phases, the upper semi-section (vault) and the lower semi-section (invert). Depending on the subsoil and the geometry of the tunnel the excavation can be performed in more than one phases. The time of installation of the initial retaining, as well as the completion of the full ring of the lining are important for the monitoring of deformations. The system of direct support, along with the soil surrounding the tunnel constitute the bearing structure of the tunnel at this phase. Ground water can be often encountered at the Athenian subsoil; in this case, systematic pumping is performed during the construction. Throughout the construction, the behavior of the subsoil and the temporary retaining are monitored on a systematic basis, i.e. the settlements at the soil surface and the adjacent buildings any convergence within the tunnel, the increase/decrease of ground water level, etc are measured. Safety of the buildings located adjacent to or over the alignment of the tunnel is a particularly crucial issue and it is addressed via continuous monitoring by means of the appropriate instruments and on site visits by ATTIKO METRO engineers. The results of the measurements are compared with the assumptions and the results of the design and, if needed, the necessary modifications to the support system and the time sequence of works are made. In addition, these data are used for the identification and/or the checking of the assumptions of the design of the permanent lining of the tunnel, which will subsequently follow. The final (permanent) lining of the tunnel is constructed when the system of the initial support has reached conditions of balance. The permanent lining provides increased safety as to the project lifetime creates a unified interior surface and improves its water tightness. The permanent tunnel lining is made of in situ cast reinforced concrete. Special segment metal forms, usually self-supporting
ones, are used, thus significantly reducing the time and the cost of the project. There are hydraulic levers, which can adjust the desirable thickness of the lining. The overall length of such moulds is in the order of 10-12m. depending on the section. Firstly, the lower part of the tunnel (invert) is constructed and special water stops are placed at the construction joints for waterproofing. At a later stage the vault is concreted with the use of self-supporting segment metal forms. Upon completion of injection, it takes some hours to remove the metal forms. In view of achieving adequate concrete strength rather shortly, its mix is enriched with chemical admixtures. Given that there is a small void between the crown of the concrete and the soil at the tunnel top, there follows cement grout injection for filling the voids. ΙΙΙ. Water tightness In the Technical Specifications of the Project, the required degrees of water tightness for the various parts of the Metro structures are specified. In the Base Project, the stations were specified to be fully watertight, while at the tunnels the existence of restricted areas of humidity at the points of the construction joints was acceptable. The basis for the sufficient waterproofing of the underground projects is always the design and workmanlike construction. Special attention should be paid to the concrete mix, the compaction and maintenance after the laying procedure as well as the adequate coverage of the reinforcement. As to the Metro tunnels, it was not required to place a waterproofing membrane, while the limited water penetration was acceptable. At the new Metro extensions, the specifications were even stricter and it is required to place a waterproofing system even at the tunnels of the Project. At the Metro stations, any penetration and surface damp patches are not acceptable since these locations house passengers or personnel rooms, machinery and electrical installations areas, architectural finishes etc. In order to ensure the above, water tightness systems are used with materials and work of appropriate quality. Waterproofing membranes are usually made of PVC or polyethylene and are placed between the temporary and the final lining of the tunnel, protected with geotextile. The parts of the membranes are welded in an appropriate manner, while at the locations of the construction joints (concreting interruption or joint displacement) water stops are placed. All materials are subject to tests placed on site the project and adhere to German specifications DS 853 and DIN 16726. ΙV. Resistance to time It is indicatively stated that the Metro structures lifetime is estimated at 100 years. The resistance of the permanent lining of tunnels and stations relates to the concrete class (strength), its mix (water/cement ratio, type of cement, admixtures), cracks formation and thickness of reinforcement coverage.
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As to environmental conditions, special consideration is given. The existence of drastic elements (chloride, sulphur elements) in the ground water is controlled and it is taken into consideration in the design of the concrete mix and the sizing of the bearing elements. The condition “damp outside/dry inside” leads to penetration and accumulation in the interior of the structure of such harmful elements, putting the reinforcement at risk of corrosion. In these cases, the protection measures introduced consist in low penetrability of concrete, limitation of cracks and water tightness. It is pointed out that the materials to be used in the Metro (reinforcement bars, concrete, water tightness, anchors, etc) should comply with the Specifications and the most updated international standards. The Contractor ought, prior to their delivery at the worksites, to submit for review all the relevant certificates, the compliance tests, the relevant mix designs, the quality control system, etc.
Construction of Tunnels & Stations using the CUT & COVER method Ι. General Despite the fact that the underground tunnel boring methods, either using the TBM or conventional mechanical means (NATM), are preferably used in central areas of the city, as we move away from the said areas we turn to the cut & cover method for the construction of both tunnels and Metro stations. This method is also used in case there is available area even if we are in the city centre. This happens because the cut & cover method is cost effective and more simple, safe and easy to control in its implementation. The disadvantages of the method as regards its implementation are as follows: a) all PUO pipes located in the area where excavation works are to be executed should be removed, b) an archaeological investigation should precede in order to identify any antiquities – which is very important for Athens, and c) all required traffic diversions should be effected. These interventions are time consuming, increase the cost, while at the same time the archaeological investigations involve great uncertainty as to the duration and their final cost. Although the method is simply called “open cut”, in fact it is a “cut & cover” method, since the structures upon their completion are backfilled and they finally become underground, as the case is when construction is made using the underground boring method is used.
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ΙΙ. Construction methodology The methodology of the cut & cover is simple in terms of conception. At first, the trench is excavated and its slopes are appropriately retained – as to the Metro works, the slopes are always vertical. Then, the permanent bearing structure of the station or the tunnel “is built”, starting from the foundation upwards, i.e. as this is the case for an ordinary structure. Finally, the structure is backfilled up to the surface of the soil and the area is reinstated. In particular, the phases are as follows: •
A geotechnical/geological investigation and tests (on site and laboratory ones) are executed in view of identifying the soil characteristics in the area where our structure is to be constructed.
•
A design is prepared (calculations and drawings) related to the excavation and the temporary retaining, based on the geotechnical characteristics of the soil which resulted from the previous stage. Moreover, the design of the permanent bearing structure is carried out.
•
Prior to the commencement of the main works, the required archaeological excavations are carried out, all the PUO pipes (related to water supply, power supply, telephone connection etc.) and the eventual traffic diversions are executed.
•
The temporary retaining of the excavation usually consists of circular concreting piles, whose diameter is in the order of 0, 80 – 1, 00 m., spaced at 1,50,-2,50m along the perimeter of the anticipated excavation prior to its commencement. The pile row is connected at its pile cap by means of a strong concreting beam. The excavation is carried out using conventional mechanical means (excavators, hammers etc.) up to a fixed depth, e.g. 3,5m and then anchors are placed at holes, which are drilled at the soil through piles. These anchors are long enough (in the order of 15-25m) and they are prestressed using the force provided for by the design. Then a wire mesh is applied along the perimeter of the trench and a shotcrete is placed. Subsequently, the excavation continues up to the next level and another series of anchors is placed and prestressed. This cycle continues up to the final level of the excavation, where the structure will be founded. If there is ground water at the surface of the trench, then the said water is discharged through systematic holes/piping at a depth of 3-4m. on the retaining structure/excavation and they are pumped using the appropriate drainage system.
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•
The water proofing system of the structure, as the case is for the entire new Metro network, is placed at the invert and the peripheral surfaces at the perimeter of the trench and it consists of geotextile, waterproofing membrane and water stops.
•
The construction of the bearing structure is carried out in phases starting from the foundation, and then follow the walls, the roof slab in case of a tunnel. As to the stations, the construction of intermediate flat slabs and walls. The construction commences with the installation of the steel reinforcement of the foundation slab (or general lean concrete slab), as provided for by the design. Subsequently, class C25/30 concrete is injected, in phases along the entire length of the construction with the provision of appropriate joints. The construction of the remaining elements of the permanent structure is made in a similar way.
With regard to the retaining works, it is clarified that the retaining of the excavations at the Athens Metro was executed exclusively with the use of drilling piles made of reinforced concrete (shaft piles) and prestressed anchors. At the first sections, the “Berlin method” was used; based on this method steel piles are placed up to a depth retained squarely with the use of steel struts, while at layers of the subsoil which are at a greater depth, a lighter retaining is used with reinforced shotcrete and passive ground bolts. This methodology was used at Larissa Station and at a large section of Attiki – Larissa tunnel section.
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Construction of the Stations using the COVER & CUT Method The Cover & Cut method (or “ top-down� method) is a variation of the cut & cover method. The phases of this construction methods are as follows: 1. the vertical retaining panels (piles, diaphragm walls, etc.) along the perimeter of the excavation to follow are constructed from the surface, 2. an excavation is initially carried out up to the level of the roof slab of the structure. Depending on the excavation depth, a light retaining of the slopes may be needed, 3. the roof slab on the excavation bottom is concreted. The slab is connected with the perimeter retaining and it is supported on it, 4. backfilling works are carried out over the slab and the surface of the soil is reinstated, 5. the excavation works for the station or the tunnel commence underneath the roof slab by means of the ramp which has been left at a certain point. The excavation is executed in phases, while the required retaining elements (e.g. anchors, struts) are installed gradually. 6. upon completion of the excavation of the entire trench, works related to the construction of permanent bearing structure elements commence. These elements usually consist in the raft (foundation slab) and the lateral walls, while in case of a station it is also the construction of intermediate floor slabs. In case diaphragm walls are used as a lateral retaining means, other permanent walls are not constructed, since the same diaphragm wall act as a final perimeter structure.
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The advantages of this method consist in the reduced time of extended worksite occupations and the rate of reinstatement and release of the area for use (vehicular circulation, squares etc) for use and finally the mitigation of disturbance as to the functions of the city. Its disadvantages are the increased cost and the more complicated construction procedure. As to the Athens Metro, this method was used only for SYNTAGMA Station (of Line 2) due to the particularity of the area. The design provided for the construction of steel piles along the perimeter of the station and the concreting of the roof slab in Amalias Avenue in two phases, in terms of the road pavement width and then the construction of the station in phases as described above. During the construction of the bearing structure of the station, the external walls were constructed from down to top. In their interior, the steel piles were integrated, thus being part of the permanent walls of the Station. It is pointed out that the cover and cut method by means of diaphragm walls is foreseen to be the construction method for the Thessaloniki Metro Stations.
Hard Rock Shield, Tunnel Boring Machine (ΤΒΜ) The TBM Hard rock shield was designed by Mitsubishi Japan Company and constructed by NEYRPIC FRAMATOME MECHANIQUE (NFM) FRANCE. The length of the TBM, including back-up Gantries and California switch is 150m long. The overall weight is 1650 tones. The TBM works comprise of 850.000 m3 excavated material & 350.000 m3 of Concrete. The TBM works with a four-shift system, 35 men per shift surface and underground activities for seven days per week. The TBM crew was 21 men. The TBM 1 named “IASON” and the TBM 2 “PERSEFONI”. The TBM can be separated into two sections:
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•
The TBM Cutter head (Shield).
•
The Back - up Gantries. The first excavation by the TBM1 started on 25 April 1994 from Larissa station. The first Breakthrough at Deligianni Station was on 13, May 1995.
The rates of the TBM have been 4.5 to 17 m / working day or about 3 to 12 rings/working day. Individual daily rates, not considering stoppages for breakdown, etc. ranged from 19.5 to 24 m / working day or about 13 to 16 rings / working day. A typical cycle for 1,5m advance of TBM requires 25 min. for excavation, 30 min. for ring erection and 5 min. for cleaning and preparation. The TBM cutter head, the revolving part, excavates (9516mm diameter) the hard and soft ground Tunnel with a variable rotational speed of the cutter head from 0 to 4 rpm and rated torque 1140 to 1368 tons - m. The length of the Cutter Head is 1500 mm long. The cutter head has 63 pieces hard disks, 17� inch diameter placed at individual radius & 200 pieces drag bits. The disc cutters and drag bits could be replaced from the rear side of the cutter head. The two over cutters mounted at the periphery of the cutter head created an over cut of 60mm and allowing a better steering of the shield and reducing the TBM friction forces. The cutter head rotate in both directions, clockwise and anti clockwise by 16 hydraulic motors (180kw) reducing gears with maximum output speed 57,6 rpm and maximum working pressure 350 bars. The propulsion of the TBM is electric hydraulic. The front shield has an outside diameter 9456 mm and the rear shield an outside diameter 9440 mm. The overall length of front and rear shield is 7515 mm long. The shield weights 880 tones. The skin of the rear shield is 92 mm thick. The front and rear shields are articulated one to the other. The two parts of the shields are connected by 16 articulation jacks 360 mm diameter, 260 bar which make it possible to orient one body in relation to the other in all spatial directions. The total stroke of the articulation cylinders is 500 mm and allow for retraction of the front shield plus cutter head up to 300 mm thus creating access to the face. Minimum tunnel curve radius of the profile is 300m & compensation curve radius is 250m. The amount of the excavated material for a complete stroke of 1,5m advance was approximately 192m3. The excavated material passes into the cutter head chamber through openings (32 % of the cuter head face is open to the ground) of the cutter head periphery. Then picked up by the cutter head blades and lifted up the top part, it falls into the hopper. The cutter head hopper empties the excavated muck onto a conveyor belt (primary conveyor) located at the level of the tunnel axis. The length of the primary conveyor is 18,25 m and 1,2 m width. From the primary conveyor, the muck is dropped onto the secondary belt conveyor 28,80 m length and then to the third conveyor belt 38,00 m length located on the structures of the back-up gantries.
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The third conveyor then pours into a shuttle conveyor 30 m length that moves parallel to the tunnel axis for filling the mucking cars without moving them. At TBM operation all the excavated material is collected to the muck skips by the belt conveyors. The conveyor belts are designed for a capacity of 950 t/h or 750 m3/h. If water appears in the ground, the primary conveyor belt is retracted and a safety gate isolates the cutter head chamber from the interior area of the shield. An emergency pump 140 kW is installed in front of the hopper to evacuate the water from the cutter chamber via tube extension device. The flow rate is 82 lt./s and 60 m of water pressure. The max inflow of ground water encountered during excavation was 120 lt. / min. The TBM moves forward by pushing against the last prefabricated segmental tunnel concrete ring with the 28 hydraulic thrust jacks (320 mm diameter) and with 5600 tones (260 bar each Jack) force. The resultant force on the ground face was up to 3000 tones or 42 tones/m2. The maximum extended stroke of the pushing jacks is 2300 mm allowing sufficient space for ring erection, within the rear shield. The front shield of the TBM is fitted with 6 radial jacks (front grippers) with conical shape (250mm diameter, 350 bar) and extended stroke up to 150 mm. The front grippers are preventing the TBM from rolling during excavation on hard rock ground conditions. The conical shape is preventing damage of the grippers steel during excavation. The rear shield has 4 grippers (160mm diameter, 350 bar) with an extended stroke of 150mm. The rear grippers keep the rear shield in position when the front shield is retracted with the
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articulation jack for changing the cutter discs and for ground inspection. A neoprene tail seal 270mm long, mounted on the edge of the rear shield, provides leak tightness between the ground and shield during TBM advance and grouting the annulus void between the ring and the excavated tunnel. For inspection of the neoprene the tail seal, the extension of the front grippers and retraction of the rear shield is required. The TBM control room placed at back up 1st gantry is about 25m backwards from the excavated face. The operator controls the front and rear shield to keep them on line and level. The acceptable tolerance of the segmental tunnel lining from the Design Tunnel Axis (DTA) is 80mm. The TBM front and rear shield position is accurately defined by the guidance system, which records its attitude in terms of lead, look-up or overhang and roll. The TBM is guided by a system of laser sighting (CAP/ZED). The ZED system uses laser indicates the Horizontal and Vertical position of a tunnel-boring machine and transmits this to cap system. The laser beam is set up and aligned by conventional Theodolite techniques. The laser beam provides a clearly identifiable line and a recognizable spot continuously projected on the rear shield target face by using survey station in the crown of the tunnel. The Cap system read those values and the pilot, in manual or automatic mode, tries to maintain those values by activating the pressures and the flow rate of the pushing jacks, the speed of rotation and the Cutter Head torque. In case of important deviation noted by the ZED system a compensation curve is defined which consists to progressively bring the Tunnel boring machine on the theoretical path by several cycles of boring strokes.
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Earth Pressure Balance, Tunnel Boring Machine (ΕΡΒ) The EPB is designed to excavate in heterogeneous ground conditions, avoiding the formation of over breaks and surface settlements, during shield advance through the considered zones and particular under buildings. The EPB for Stavros extension line 3 designed and constructed by Herrenknecht A.G., Germany. Assembly of the EPB and back up gantries took place at Doukisis Plakendias station. The concrete raft of the station equipped with a sliding path, consists of two steel plates, each to support the shield of the EPB. The steel plates placed in concrete parallel to the centre line of the station raft tunnel. The propulsion of the EPB is electric-hydraulic and moves forward by pushing against the last prefabricated segmental tunnel concrete ring with the 28th shove rams. The Earth Pressure Balance (TBM) Shield is capable to operate in “open mode” (nonpressurized screw conveyor) and closed mode (pressurised screw conveyor). The EPB is divided in two main parts • The shield • The back up system The TBM and Back Up System is divided into sections for transport and site assembly. The Shield components are designed to facilitate transportation, assembly and dismantling operations, including removal in-tunnel and abandonment of the body (skin) for ground support. All non – replaceable parts have a minimum design life of 10,000 operating hours. The working pressure is 3 bars and the outside diameter of the shield is 9440mm. The complete EPB length including the back up system is 90m. The TBM shield, designed to withstand all loads and forces occurring from the ground overburden, Earth and loads and forces arising from operating the TBM, both in normal mode and in modes required correcting misalignment of a radius of 250m. Deformations caused by any of these loads are limited to allow the undisturbed operation of the TBM. Seven numbers of inclined penetrations in shield sleeves fitted with shut off valves spaced around the periphery for angular ground investigation and treatment. The TBM shield consists of the front, the centre and the back shield. The front shield incorporates the following items: Cutter Head : The EPB cutter head structure and main bearing with its support system is rated to absorb the maximum forces envisaged in operation.
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The cutter head is a substantial structure, to provide the necessary mechanical support to the tunnel face. It incorporates the necessary abrasion protection features to enable the shield to complete the excavation of the tunnel through the various geological conditions. The cutter head incorporate the following: • A combination of interchangeable cutter picks (drag bits) and roller cutter discs with replaceable wears protection. • Manually extended (10–20-30 mm) over cutters • All cutting tools are designed capable to be replaced from the rear face of the cutter head To maintain the ground face control with the EPB machine, the excavation is started by rotating the cutter head and adjusting the floor door openings to a pre-selected width. As the machine thrust cylinders extend, the ground at the front of the EPB and inside the cutting head is pressurized. The earth pressure cells within the cutting head measure this pressure. Once the pressure exceeds limit preset, the hydraulically controlled Pressure Relieving Gates are forced open allowing material to pass thought these gates and onto the primary conveyor. Man lock : An air lock conforming to CEN prEN12110 includes a 2-compartment, 4 man main compartment with 3 bar working pressure. Shield articulation cylinders : The front shield connected with articulation jacks operated with 250 bars, which makes possible to orient the back shield in relation to the front shield in all spatial direction. Main bearing : The main bearing is designed to transmit the cutter head torque and thrust forces. It has a rating of 10,000 hours L10 life and to take in account that the EPB is drive curves with a minimum radius of 250m. The outer and inner main bearing sealing systems is capable of protecting the bearing for 10,000 hours. A bulkhead designed to act as a pressure vessel end, to withstand the hydrostatic soil pressure of 3 bars, plus any adequate safety margin. Conditioning agents : When the soil can be conditioned to achieve the necessary plastic fluidity it is possible to balance and control the excavation volume against the advance of the shield.
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The conditioning agents are added through the bulkhead to the excavated ground so that conditioning can begin immediately and ensure that all material in the cutter head chamber has been transformed into the correct consistency. The Conditioning agents, including plain water, bentonite based mud’s, chemical polymers and the foaming agents, have been introduced for three principal reasons: 1. To lubricate the flow of material through the cutter head compartment and the screw conveyor 2. To improve the permeability of the material in very wet ground condition to prevent the passage of water out through the discharge gate of the screw conveyor. 3. To improve the consistency of the material for easier handling of the muck from the discharge gate to final disposal. The foam conditioning material is a compressible air bubble, encapsulated in a detergentlike (92-94%) fluid, which added to the excavated material and keep the particles of the soil apart by reducing the internal friction and permeability of the soil. The centre & back shield shield incorporates the following items: Shove, Pushing rams : The Pushing jacks are spaced around the back shield grouped to one shoe, permit articulation and square contact with the segmental tunnel lining. With reference to the sectioning of the segment lining – 7 standards segments & 1 key segment the number of jacks necessary are 28, coupled two by two. The 28 thrust rams have to work 5 to 7 groups separately. The hydraulic system of the jacks is designed to provide two working modes extraction and retraction speeds: • Advance of the machine (low speed and high pressure) during recycle sequence • Segment tunnel lining erection (high speed and low pressure). The nominal working pressure in the hydraulic system is limited with 350 bars. Tail skin : Provision for constant continuous pressure grouting the annulus of the tunnel lining with cementation grout through ports in the tail skin. The grouting behind the segments will be executed simultaneously during boring operation. A tail seal with grouting system with a 2-row of bolted wire brush seals rated to withstand a hydrostatic pressure of 3 bars and to preventing leakage of ground water or grout. The lifetime of the bolted wire brushes is for 1 Km tunnel.
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One-row spring steel plates (270 degrees) is provided and installed to the upper side of rear shield periphery from the position time 700 clock up to 4oo clock and another row between the front and back shield articulation area. Screw conveyor : The screw conveyor is installed through the sealed Bulkhead into the cutter head chamber and removes the excavated material during the EPB advance. When the cutter head rotates, the propulsion system is engaged, and the screw conveyor starts. The speed of rotation of the screw conveyor anger determines the rate of excavation while maintaining control of the excavated face. The excavated material, which removed via an Archimedean screw conveyor, from the cutter head-mixing chamber at high pressure, discharged at the other end of the screw at atmospheric pressure, onto the first belt conveyor. This is done by controlling the rate of discharge via the discharge throttle at the upper end of the screw conveyor. Belt conveyor system : The belt conveyor system removes 650m3/h of excavated spoil from the screw conveyor in closed or open mode working condition. The excavated material are transported through the segmental tunnel lining by belt conveyor system Segment Erector : The segmental tunnel ring is erected after the EPB advance by 1,5m with in the tail of the rear shield. The erector is used for the placement of the pre-cast reinforced concrete segments equipped with a single pick up head of semi-rotary type. In case of total loose of power supply (Breakdown) the vacuum system is capable to maintained (faultless seals) the segmental holding force for 30 min. The erector provided with a clockwise and anti clockwise rotational movement of +/- 200 degrees spaced equally above the invert of the tunnel. The erector has a pendant and remote control, to provide clear visibility of all erector movements. The six degrees of freedom are describes here below, which the erector designed, activated by hydraulic jacks with telescope arms and operated separately or simultaneously. • Rotation around longitudinal axis of the TBM (in both direction clock and antic lock wise). • Extension
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• • • •
Longitudinal movement. Adjustment around longitudinal axis. Adjustment around radial axis (pitching). Rotation movement around radial axis
The erector system is designed for the installation of one ring within a period of 30 min. There are two types of conical reinforced concrete rings Left and Right which allow the Tunnel lining rings to turn towards left or right, up wards and down wards. Each type of ring (weight 40.6 tones) consists of 8 PCs segments, 5 regular segments, 2counter segments and one key segment. The erection of the segments starts at the bottom and alternately, left / right, the ring is built up to the key segment using the segment erector arm. The key segment is inserted in parallel with the Tunnel axis at the end of the ring in place. The conical shape of the left and right rings are designed to have the key segment position between the upper side 9 to 3 o’ clock. The elastomeric compression rubber gasket glued to the mating faces of each segment, is being compressed between segments and rings of the Tunnel Lining and guarantees the water tightness of the Tunnel. The segments are bolted together with a high strength steel bolts Φ25mm, 500mm long with plastic sockets placed under the bolt washer (80*27*8mm) on each side of the joints. A concrete segment invert is placed after the ring erection to complete the Tunnel Lining. Above the invert segments track rails are placed, type 38 kg/m for sliding the TBM back up Gantries and the rolling stock. The invert segment left as permanent invert is grouted in placed by the two grouting pumps located at back up of the TBM. Grouting system : The grouting activities, behind the segments are executed simultaneously during boring operation. The grout is filling the annular void by three positive displacement single piston pumps “ Schwing KSP, 12-2D”. The grout flows easily, while being pumped with pump pressure of 2 bars. The grouting equipment powered by an electro-hydraulic power pack. The grout is mixed at the site surface batch plant, transported into the TBM by the main track trains, in mortar agitator tanks and is stored on the frame behind the grouting pumps at the back up of TBM.
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Control room : An air-conditioned control cabin is positioned at the gantry one of the back up system, at a distance of 22m from the excavated face. The control cabin contains all remote controls and indications for the safe operation of the EPB and its environment. The operation control cabin has space for a minimum of 4 persons. The control monitor and record the operational parameters of the TBM and its systems. A closed circuit television installed in the control room observe the followings: • The tunnel lining build area • The transfer of soil from screw to the crusher and to the primary belt conveyor • TBM end of back-up system. The control room is equipped with computerized guidance system. The guidance system SLS-T, relating to the services of the EPB has been developed by VMT GmbH. The SLS-T provides all the important information, which is necessary to drive the EPB along the designed tunnel axis. The Maximum deviation of the actual tunnel axis from the design tunnel axis in horizontal and vertical axes is +/- 40mm. In case of important deviation noted by the Guidance system a compensation curve is defined which progressively bring the EPB machine on the theoretical cycles of boring strokes. The back-up system has the following features and capabilities: • Fully decked, closed bottom where required with a single-track system and, segment off loading. • The back up system trailer will run on wheel on track rail • Cranes for the unloading and transfer of the tunnel lining segments from the delivery wagons to the segment supply magazine. • Rail lifting and transfer facility, for installing the construction rail track and segment tunnel invert in the invert of the bridge area. • The length of the bridge between the TBM shield and the first gantry is sufficient to place rails of 9 metres long and 4 pcs of tunnel invert segments. • Soil conditioning systems and equipment. • The Foam processing plant which consist of the following • Continuous grouting system. The filling of the annular gap behind the concrete ring • Tail sealer grease pumping system.
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• • •
Provision for the extension of all surface connection services (Ventilation, Communication systems, De-watering pipes, Mains power supply, Compressed air Cooling water, Generator) Welfare and toilet facilities to include; toilets, washing, mess room. The ventilation system for the TBM, which consist of one-turbo ventilator. The passage volume is 816m3/min and the cross section of the ventilation tube 1* Φ800 mm.
All EPB electrical equipment and installations comply with the European standards and designed to operate under the following environmental conditions: • Ambient temperature 40 degrees • Dust content heavily dust laden atmosphere • Humidity up to 85% relative humidity The machines are equipped with a flexible trailing cable (3*95mm) contained on a powered reeling drum capable of extending up to 250m behind the rear of the EPB backup system and the total installed power was , App. 3,580 [kW
Open Face Shield Tunnel Boring Machine (OFS) The Open face Shield (OFS) tunnel-boring machine is used to provide initial ground support when tunnelling is in soft ground, typically clays & Silts. It is fitted with fore pole Blades that, under unstable ground conditions can be advanced into the uncut ground, in front of the OFS to support the arch and the face. HERRENKEHT GmbH designed the Athens Metro OFS named “DAFNI”, for excavation of rock with maximum unconfined compressive strength (UCS) of 120 Mpa. The OFS is operating under atmospheric pressure and does not require a closed system for pressure balance at the tunnel face. The arch of the ground is supported by the skin of the Shield, ensuring the excavation of soil, the segmental tunnel lining ring erection under safe conditions and the better control of ground settlement. The OFS consisted of 2 main sections: 1. 2.
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Front Shield: including the Fore pole blades over 180° arc, in the top section, road header, two excavating shovels, two telescopic drilling machines, face rams, twin control cabins and a screw conveyor. Rear Shield and tail skin: including segment erector, grout injection points, tail seal brushes and de - watering equipment.
The OFS can be dismantled in place, and the machine parts can be removed in pieces through the constructed tunnel. The drive of the OFS main equipment is electric hydraulic with the following Characteristics: Over all length of the OFS
12,68 m
Total Installed Power
4000 KW
Main Power Supply
20 kV (3 * 95 mm2)
The OFS front section is equipped with a telescopic Road header boom, with 83 picks (arranged in a spiral) and two telescopic loading shovels. The Road header and the excavator shovels are controlled during the excavation, through two control identical cabins. The Road header operator can select individually the extension of the seven fore poling plates, starting from the tunnel crown for face protection. The over cutting profile is computer controlled and the excavation cycle time for a rock ground condition (UCS 70 Mpa), is about two hours. Safety interlocks exist to prevent Road header operation from the drilling machines operation and the fore pole plates during OFS advance. The excavated over cutting profile (cutting edge of over cut up to 50 mm) by the road header boom is determined in relation to the present position of the Shield, the outer diameter of the segments and the requirements imposed by the alignment of the Design tunnel Axis (DTA). Each tunnel shove excavation is 1.5m long, for placing a segmental tunnel ring and is performed by two half shoves 750mm long. The Road header, telescopic boom has an axial movement of cutting profile 1100mm, in front of the hood. The road header can reach the lower part profile by retracting the screw conveyor and using the seven fore pole plate’s extension to support the face and the crown. The rotation of the Road header is in one direction (clock wise). Water or foam spray and de-dusting system are used to reduce dust during the excavation mode. The Fore pole blades consists of seven fore poling plates (stroke of 1100 mm up to 1700 mm) and the seven extending breasting plates, arranged in the upper part of the OFS front section cutting edge.
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The fore poling plates No.3, 4 & 5 (Crown) can be extended up to 1.7m, the No. 2 & 6 up to 1.4m and the No. 1 & 7 up to 1.1m. The maximum operating pressure for both extension and retraction movement is 250 bar. The fore pole advance force range from 5 up to 127 tonnes and retraction force from 7 up to 64 tonnes. During the OFS excavation time, the fore pole plates operation thrust force is 50 bars (25tones). By extending forward the seven fore pole plates, after the excavation, the OFS provides a sufficient stability in the tunnel crown and support almost of the non-cohesive ground. In soft ground conditions the fore poles used to trim the profile of the ground. Each fore pole plate carries a breasting plate (operating pressure of 250 bar or 100 tonnes) with four (4) holes 120mm diameter to allow ground anchoring when plates are fully open and to provide active mechanical support to the corresponding tunnel face. Ripper teeth are placed on the lower part of the front shield skin. To prevent the possibility of rolling phenomenon the front shield is adjusted by all thrust jacks cylinders, hydraulically create forces, which lead to correction of the shield, position during tunneling. The lower half of the shield is fitted with two face rams (Elephant feet, 2300mm stroke, holding pressure 300bar). The excavated material is guided to the screw conveyor hopper by the telescopic excavator shovels (extension up to 2000mm). The excavator shoves are mounted on each side of the Road header. The screw conveyor fixed to the front and rear shield, discharge the excavated material to the crusher through the primary conveyor belt. The screw conveyor can be retracted and extended and makes possible liberation of the screw if any excavated material squeezes it. The screw conveyor consists of conveyor helix-telescopic station and planetary gearing. The crusher is installed between the primary and secondary belt conveyor. The maximum product size after crushing with twin roll sizes is not exceeds the 200 x 200mm. The amount of the excavated material for a shove of 1.5 meter is approx. 192m3 with a squeezing factor of 1,8. The excavated material passes, through the screw conveyor to the primary conveyor belt (7m long, 1m wide), located at the level of the tunnel axis and then to the crusher machine.
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The second belt is conveyor 29m long, 1.2m wide and the third conveyor belt is 38 m long, 1.2m wide and is located on the structures of the back-up gantries and continues the removal of the excavated materials. The third conveyor dumps the material to the shuttle conveyor (30 m long, 1.2 m wide), which moves parallel to the tunnel axis and fills the empty main wagon skips without moving them. The conveyor belts are designed for a capacity of 950 t/h (750 m3/h). The train side tipping spoil cars (Munhlhauser , 6 cars , 30 m3 capacity each ) are parked between the OFS Back-up gantries , dispose the material through the dumping wall , installed at the site area. Three gripper pads are fitted to the rear shield body for stabilising the OFS Shield, during segment erection in hard rock conditions. The gripper pads can be extended up to 150mm with operating pressure 300 bars. The 28 hydraulic thrust rams are positioned in a way (arranged in 14 x 2 pieces) that they can support the prefabricated concrete tunnel segments used during erection. A total thrust of 5,600 tons (Power 2 x 160kw) is available from the thrust rams, to advance the Shield by pushing against the pre-fabricated segmental tunnel ring. Two rows of wire brush tail seals are fitted to the rear shield supplied by grease, excluding the ground water and the primary grout from re-entering at the Rear Shield. The Tail Shield skin thickness is 70 mm. The greasing system is controlled automatically by means of pressure sensors. Two emergency pumps 35KW (400volt) are installed at the segment erection area to evacuate the water. The TBM control room placed at back up 1st gantry is about 25m backwards from the excavated face. The operator controls the front and rear shield to keep them on line and level. The acceptable tolerance of the segmental tunnel lining from the Design Tunnel Axis (DTA) is 80mm.
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FIRST GENERATION OF TRAINS GENERAL INFORMATION Number of Trains
28 (Lines 2 and 3)
Train Composition
6 Cars
Doorways per car
4 per side
Train Capacity
224 Seats 806 Standees (5 Passengers/m2) 1030 Passengers / Train
Customer Amenities
Forced Air Ventilation Automated Station Announcements
TECHNICAL FEATURES
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Train Configuration
Two 3-car units coupled back-to-back Driving Trailer- Motor Car- Motor Car
Train Length
106m
Car Width
2800mm
Car Height
3600mm
Interior Headroom
2180mm
Train Weight
178 tons empty 245 tons fully loaded
Gauge
1435mm
Operating Voltage
750 VDC
Traction Motors
4-153kw DC motors per motor car
Traction Controls
DC Chopper / microprocessor controls
Braking
Regenerative-Dynamic / pneumatic
Average Acceleration
1.00m / s2
Average Deceleration
1.08m / s2 (Normal) 1.20m / s2 (Emergency)
Maximum Speed
80km/h
Car body Construction
Stainless Steel
COMMERCIAL INFORMATION Contractor
OLYMPIC METRO Consortium
Major Rolling Stock Suppliers
SIEMENS ABB- DAIMLER-BENZ GEC/Alsthom
Primary Manufacturing Locations
Nurnberg, Germany La Rochelle, France
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SECOND GENERATION OF TRAINS GENERAL INFORMATION Number of Trains
21 (7 DC/AC Trains and 14 DC Trains)
Train Configuration
6 Cars
Doorways per Car
4 fitted type sliding doors per side
DC Train Capacity
196 Seats 866 Standees (5 Passengers /m2) 1062 Passengers /Train
DC/AC Train Capacity
158 Seats 868 Standing (5 Passengers/m2) 1026 Passengers/Train
Passenger Amenities
Air Conditioning Units in Trains Destination signs inside the trains with provision for alternating messages Areas designated for the exclusive use by Persons with Special Needs Wide gangways allowing for balanced distribution of the riders' load within the vehicles Door open pushbuttons which are operated by the passengers in off-peak hours Strict noise limits
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Train Configuration
Two three (3)-car units coupled back to back Driving / Motor Car - Trailer Car - Motor Car
Train Length
106m
Car Width
2800mm
Car Height
3690mm
Interior Headroom
2100mm to 2200mm
DC/AC Train Weight
202 tons empty 275 tons (5 Passengers/m2)
DC Train Weight
182 tons empty
255 tons (5 Passengers/m2) Gauge
1435mm
DC/AC Train Operating Voltage
750VDC/25kVAC
DC Train Operating Voltage
750VDC
Traction Motors
4 Χ 170kW AC per driving motor
DC/AC Train Traction Controls
Converter AC-DC, VVVF Inverter (IGBT technology)
DC Train Traction Controls
VVVF Inverter (IGBTtechnology)
Braking
Regenerative/Dynamic/Pneumatic
Average Acceleration
1,00m/s2
Average Deceleration
1,1m/s2 (in normal conditions) 1,20m/s2 (in emergency conditions)
Maximum DC/AC Train Speed
120km/h
Maximum DC Speed
80km/h
Carbody Material
Stainless Steel
Other Information
Comprehensive Fault Indication and Identification System Simulated revenue service tests Reliability proof program
COMMERCIAL INFORMATION Contractor
HANWHA-Rotem Consortium
Major Rolling Stock Suppliers
MITSUBISHI VAPOR KNORR-BREMSE
Main Manufacturing Countries
S. Korea, Japan
Delivery
2004
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