The Channel Tunnel ( Gallic: le tunnel sous la Manche ) , widely recognized as one of the universe ‘s greatest civil technology undertakings, is a 50.5km underwater rail tunnel linking Folkestone, Kent in the UK with Coquelles, Pas-de-Calais in France under the English Channel. Even though it began building in 1988 and was opened in 1994, the thought to hold a cross-channel tunnel was foremost mooted more than 200 old ages ago but did non happen due to political, national security and cost considerations. However, with the enormous addition in traffic growing, better and alternate agencies of communicating, convenience and velocity was necessary and therefore the demand for an alternate conveyance path was clearly apparent. The demand for such tunnel was further compounded with Britain fall ining the European Community and the cross-channel traffic duplicating in the last 20 old ages ( taking to the undertaking ) , reflecting improved trading between the Britain and remainder of Europe. The Channel Tunnel would besides be able to supply an alternate competitory nexus between the transit systems of the UK and France, supplying both velocity and dependability to freight bringings. With the strong indorsement from the authoritiess of both crowned heads, the determination to construct the Channel Tunnel was therefore made. In April 1985, the British and Gallic authoritiess issued a formal invitation to possible tenderers for the fixed Channel nexus and finally the contract was awarded to the pool Channel Tunnel Group Limited- France Manche S.A. ( CTG/FM ) ( subsequently renamed Eurotunnel ) .
Figure 1: Undertaking Organization
The Channel Tunnel, with the authoritiess ‘ purpose that it be in private funded and at that place would non be any authorities aid or project, was a build-own-operate-transfer ( B-O-O-T ) undertaking with a grant. The undertaking organisation is shown in Figure 1. In this contract agreement, Eurotunnel would be the proprietor semen operator, which was being funded by the Bankss and stockholders. The authoritiess of UK and France were represented by the Inter-Governmental Commission ( IGC ) , to which the Safety Authority and the Maitre d’Oeuvre ( an independent proficient hearer ) would describe to. The IGC would so do concluding technology and safety determinations. TML ( basically split from CTG/FM so as to divide the functions of owner/operator and contractor ) consisted chiefly of five British contractors ( Translink Joint Venture ) and five Gallic contractors ( G.I.E Transmanche Construction ) and would transport out the building works for the Channel Tunnel in a design and construct contract. Upon completion of the undertaking, the British and Gallic authoritiess would present Eurotunnel a 55 ( which was later revised to 65 ) twelvemonth runing grant to refund the Bankss and stockholders. The Contract was officially signed on 13 August 1986 and the fixed rail was to be to the full commissioned in 1993. The services offered by the Channel Tunnel include the Eurotunnel Shuttle ( a bird service for vehicles ) , Eurostar rider trains and cargo bringing trains.
TML ‘s contract was to plan, construct, and trial and committee the fixed rail tunnel. The Channel Tunnel ( Figure 2 ) was designed to hold three concrete-lined dullards about 50km long, with 37.9km undersea and the remainder under land at either terminals of the English ( Cheriton near Folkstone ) and Gallic ( Pas-de-Calais small town of Frethun ) terminuss ( Figure 3 ) . Two of the running tunnels were designed to hold an internal diameter of 7.6m while the 3rd was a 4.8m service tunnel running halfway between the two and connected to them via 3.3m diameter cross transitions at 375m intervals. 2m diameter Piston alleviation canals linking the chief tunnels at 250m spacing were built to forestall the accretion of differential air force per unit areas and aerodynamic opposition. To ease operations and care, four crossing over caverns were built between the two terminuss to let trains to traverse between the running tunnels. Two crossing overs were laid near to the terminuss while the other two were under the ocean floor, efficaciously spliting the tunnel into three about equal lengths. Figure 4 below shows the chief stages of the undertaking.
Two separate rail tunnels were chosen alternatively of a individual big twin-track rail tunnel because this could minimise building hazard while at the same clip enhance operations, care and safety. The diameters were finalized after design analysis, development and optimisation surveies, taking into consideration the operation and support, velocity and cost of building. The service tunnel provided entree between the running tunnels during normal and exigency state of affairss and was equipped with a guided conveyance system. It was besides where the H2O and pumping brinies run and functioned as a fresh air supply canal to the tunnels in normal on the job status. In add-on, the service tunnel would work as a lead tunnel during building which allowed the workers and applied scientists to measure and determine the chartless land conditions before progressing the chief tunnels.
Establishing on the bing geotechnical probes, past burrowing expeditions and two extra geotechnical and geophysical studies carried out by TML on the English Channel along the proposed tunnel line, it was ascertained that there was a distinguishable sub-unit of the Lower Chalk bed known as the Chalk Marl running continuously between the two terminuss. Chalk Marl, made up of jumping sets of marly chalk and limestone, was found to be the best tunneling medium as it was basically impermeable ( due to its high clay content ) and provided good short term stableness under digging, therefore minimising the figure of supports required ( Figure 5 ) . It was designed to be bored in the bottom 15m of the Chalk Marl bed to minimise the immersion of H2O from the breaks and articulations, but above the Gault clay which is susceptible to swelling when moisture, enforcing high emphasiss on the tunnel liner. The chalk marl strata dipped gently at less than 5o with smaller supplantings of less than 2m due to blaming towards the UK side ; whereas the strata dipped badly towards the Gallic side ( up to 20o ) with much larger supplantings of up to 15m ( Gueterbock, 1992 ) . Chalk at the Gallic side was besides harder, more brickle and fractured. This therefore led to the usage of different burrowing methods on the English and French sides.
The seaward and landward dullards for all three tunnels on the UK side began at Shakespeare Cliff. Construction traffic would come in the tunnel via a new inclined entree ( Adit A2 ) at the Lower Shakespeare site, while worker entree was built via a shaft driven to the tunnel degree from the Upper Shakespeare site ( Gueterbock, 1992 ) . Due to the fast building clip required and the comparatively dry chalk marl at the UK side, it was assessed that the New Austrian Tunneling Method ( NATM ) was most suited for the UK tunnels. One characteristic of the NATM was the interlinking of design, building method, sequence and works and the success of this method depended on the uninterrupted integrating of these elements by the tunneling applied scientists. Six TBMs were used to drive the UK tunnels crossing a entire distance of 84km. The TBMs were operated on an open-face manner with a forepart unearthing subdivision and a rear gripper unit which acted as a impermanent ground tackle point when the cutting caput drove frontward at 1.5m increases ( Anderson & A ; Roskrow, 1994 ) . Excavation of the tunnel and hard-on of the tunnel liners were carried out at the same time. Depending on land conditions, the thickness of the liners ranged between 380mm and 500mm. Expanded concrete liner was used for the UK tunnels where the unbarred liner was expanded against the excavated land. Pads on the dorsum of the liner allowed the formation of an ring to be filled with grout to forestall H2O immersion ( Byrd, 1996 ) . Each 1.5m run alonging ring was made up of eight precast concrete sections with a cardinal section. Cast Fe liner sections were merely used in hapless land conditions.
Over at the other side, the tunnel thrusts started at the shaft in Sangatte in France. Due to the extremely fissured land ensuing in really wet conditions on the Gallic side, a different type of TBM known as the Earth Pressure Balance Machine was used. The TBMs were designed to run both in unfastened and closed manners. Close manner is characterized by the sealing off of the machine from the spoil around it and the cutting caput, therefore maintaining force per unit area on the soil in forepart as it excavated and leting the machine to work in the prohibitionist as the force per unit area in the machine was higher than the outside. The agreement of seals on the TBM allowed it to defy up to 10 atmospheric force per unit areas. When the TBMs reached drier and more favorable evidences, they could so exchange to open manner. While precast subdivisions were besides used on the Gallic side, the stuffs used were different owing to the different dirt conditions: neoprene and grout sealed bolted liners made of cast-iron and high strength concrete ( Anderson & A ; Roskrow, 1994 ) . The Gallic tunnels were made of six 1.4 to 1.6m broad sections plus a cardinal section. A sum of 5 TBMs were employed on the Gallic side, and the dullards from the UK and France were to eventually run into in the center of the English Channel in the tunnel breakthrough stage.
The Channel Tunnel undertaking was immense by any criterion, with a figure of cardinal factors that could potentially impact the parties involved: bi-nationality, private support ( thereby efficaciously reassigning most of the fiscal hazards to the contractors ) , agenda and cost. To remain attractive to investors and Bankss likewise, the undertaking had to run into the undermentioned precedences: lower limit hazard of cost overproduction, lower limit operating cost and upper limit traffic gross. It was recognized, from the beginning, that the chief challenge of the undertaking was to decide the logistical support associated with big graduated table tunneling and the fast-track nature of this undertaking. The direction, finance and proficient challenges related to this undertaking would be explored in the subsequent paragraphs.
