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The Channel Expressway: Twin-bored road tunnels under the English Channel
The Channel Expressway: Twin-Bored Road Tunnels under the English Channel R. Comolli, F. Cuaz, V. Ferro and B. Pigorini
AbstraetmThe proposal for a fixed link between France and England by means of a submarine tunnel under the English Channel has been examined in its various aspects of layout, tunnelling, ventilation, safety and operation criteria. The choice of the underground solution has been suggested by the low depth (40--60 m) of the Channel sea bottom between Calais and Dover, and by the presence, at an accessible depth, of a quite continuous geologic stratum of chalk marl with a low ponneabili~ and fair compressive strength. The submarine road tunnel is 48 km long and is constituted of two tunnels with an external diameter of12.10 m. The excavation of the two main tunnels will be done with prototypical tunnel boring machines allotted to the various sections,for an average excavation rate of 25 m per day over a five-year period. The lining is made of precast concretesegments laid by two erectorsfrom the machine itself. The suggested longitudinal ventilation system has short supplementary ventilation tunnels for airfiltration, external and adjacent to the main two tunnels and of the same diameter. The ventilation is influenced and facilitated by the input offresh airfrom two vertical shafts connected with islands on the open sea. Safety equipment is foreseen for communication and information inside the tunnel as well as to guide transit in the dangerous zones. A new lighting system has been proposed.
General Design Criteria i
t may be of interest, before entering into the illustration of the construction methods and ventilation criteria, to discuss the logical process that led to the definition of the basic features of this project. The Promoter and the Consultant were both convinced that the preferable solution for the important Channel fixed link was a submarine crossing that would be suitable for both trains and motor vehicles. Thus, any decision was dependent mainly upon the nature of the ground, its tunnelling characteristics and the desired capacity and efficiency of the structure. The following considerations were assumed as fundamental design criteria: (1) The lower chalk mart is very suitable for boring by full-face Tunnel Boring Machines (TBMs). (2) The maximum allowed diameter for such TBMs was defined as approx. 12 m.
This paper is drawn from the SPEA engineering study for the English Channel fixed link proposal by Sealink/British Ferries Ltd. Present address for Mr Comolli and Mr Pigorini: SPEA S.p.A. Via Cornaggia, 10 Milan, Italy. Present address for Mr Cuaz: Societa per il Traforo del Monte Bianco, 11013 Courmayeur, Aosta, Italy. Present address for Mr Ferro: Politecnieo di Torino, Corso Duca degli Abruzzi 24, 20129 Turin, Italy.
l'aide d'un tunnel sous-marin sous la Manche a ite'examin/e pour dill~rents aspects de la planification, des techniques tunnelikres, de la ventilation, de la s/curit/ et des critkres defonetionnement. Le choix d'unc solution souterrainc a it/suggiri ~ lafois par la faible profondenr de la Manche entre Calais et Douvre (40--60 ra) et par la pr/sence fi une profondeur accessible d'un strata g/ologique assez continu de craie de Marle que posskde une faible perralabilit/ et une r/sistance ~ la compression raoyenne. Le tunnel fourier sous-marin a uno longuenr de 48 km et est constitul de deux tunnels ayant chacun un diamktre de 12.10 m. L 'excavation des deux tunnels principaux sera effectu/e avec des tunnoliers prototypes allou~s aux diff/rentes sections et le tuux d'excavation sera en moyenne de 25 m porjour sur une p/riode de 5 ans. Le rev~tementest constitu/de segments pr/fabriqu/s en b/ton qui seront posls par des ajusteurs-monteurs ;1 partir de la machine elle-mhne. Le systkrae de ventilation longitudinale sugglrl comprend des courts tunnels suppl/mentaires de ventilation pour la filtration de Fair. Ces tunnels de mg~nediam2tre seront situls fi l'ext/rieur et adjacents aux deux tunnels principaux. La ventilation sera inflnencle etfacilit~e par l'arrivle d'airfrais provenant de deux puits verticaux connectis fi des ~les en pleino met. Des iquipements de slcuritl pour les communications et les informations h l'intlrienr du tunnel et le guidage du traffic darts les zones dangereuses sont privas. Un nouveau systg,me d'iclairage a aussi itl propos/.
(3) Inside a 11.30-m-net-diameter tunnel, a highway with two lanes plus an emergency lane can be executed, in compliance with the prescription of the official Terms of Reference. (4) Two twin tunnels of this kind, connected by skewed crossovers of the same size every 500 m would provide the configuration with the maximum level of flexibility and safety. (5) The major difficulty to be overcome, at this point, was the ventilation of the road tunnels; air treatment of the railway tunnel was considered to be a much easier problem to solve. (6) After a very thorough analysis, comparison and discussion of the two alternatives--transversal or longitudinal ventilation of the road tunnels--the longitudinal option was selected. Even though the ventilation of the 18-kin-long central submarine section represented a world record, it was considered .essential in this case to eliminate an emergency air intake shaft from the sea in the center of the Channel. This is why such an innovative design, based upon the advanced experience with the Japanese Kan-Etsu Tunnel, was developed. With regard to the location of the rail tunnel with respect to the twin road tunnels, the following two alternatives were considered: (1) Case I, involving two large-diameter road tunnels between
T~,*llmg and U~l~r&ro~ SpaceTec/moto,~j,Vol. 1, No. 3/4, pp. 261-269, 1986. Printed in Great Britain.
R~um6---La proposition d'un lien permanent entre la France et l'Angleterre fi
0866-7798186 $3.00+.00 ~) 1986 Pergamon Journals Ltd.
which is a smaller rail tunnel; and (2) Case I[, involving a twin road tunnel with rail tunnels alongside it. The Case II solution finally was chosen because of the following main advantages that it offered: (1) The adjacent road tunnels represent the optimum, in terms of flexibility and safety, because of the possibility of diversion/inversion of traffic flows from one tube to the other; (2) Each of the road tunnels could be considered as a spare-structure to the other, while the rail tunnel represents an additional safetyway, in case of emergency; (3) The time of intervention and of evacuation in case of grave accidents or fire is shorter than in Case I. (4) The efficiency/cost ratio of the mechanical and electrical installations in the road tunnel (ventilation, lighting, telecommunications, controls, etc.) was optimized in Case II. This paper concerns the project study of the road tunnel link (Figs 1 and 2).
Geological and Geotechnical Conditions The first geological investigation for the fixed link of the English Channel dates back to the nineteenth century. As a result of renewed interest in the project in 1958--59, 1964-65 and 1971-72, an
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Figure 2. Typical cross-section of the tunnel. extensive site investigation comprising nearly 100 marine boreholes, geotechnical tests and seismic surveying at sea, was carried out (Channel Tunnel Study Group 1966, Grance and Muir Wood 1970, Destombes and Shephard-Thorn 1971, Gould et..al, 1975). The Channel was once a dry chalk valley flooded by the melting of ice from the polar ice caps, with coastal erosion contributing to its development. Tectonically, the Dover Straits transects the northern limb of the major east-west Tertiary Weald-Boulonnais anticline, in which Jurassic and Cretaceous rocks are gently deformed over a structurally complex base of Paleozoic rocks. Within the area of the project, Cretaceous rocks from the Gauh (Albian) to Upper Chalk (Senonian) are present. The succession of rocks actually considered during the study is summarized in Table 1. The geological profile in Fig. 3 shows, in simplified form, the succession of strata in which the Channel Expressway Tunnel lies: Upper and Middle Chalk--white chalk and white marly chalk, composed over 90% of CaCOs, badly fissured and water bearing, is found on the tunnel alignment on the French land section portal. Lower Chalk--chalk marl, composed
40-80% of CaCO3, with low permeability, relatively free of fissures, is encountered over the whole undersea section. Gault Cla.y-----a stiff, overconsolidated clay, with a CaCO3 content varying from 40 to 15%, with very low permeability and low swelling characteristics, is encountered by the lower part of the tunnel cross-section, along a very short undersea section and at the English portal. The Lower Chalk and the Gault Clay strata thin out from the English to the French side, from 80 to 65 m, and from 40 to 11 m, respectively. The thinning of the Gauh Clay is highly significant because it overlies the permeable Lower Greensands. Median value geotechnical test results are summarized in Table 2. The most important ground factors in the tunnelling of the Channel Expressway are (1) permeability and (2) compressive strength.
Permeability Permeability in chalk is secondary, as the intact chalk has a k of 10-7 or less. The matrix permeability of the chalk marl is nil for practical purposes, due to its high clay content. The effective bulk permeability in-situ is entirely due to
262 TUNNELLINGAND UNDERGROUND SPACE TECHNOLOGY
fissures, fractures and faults. Faulting, involving major displacement, is virtually absent from the study area. Minor faults and fissures were detected geophysically with throws of 1-3 m, some of which can be associated with the anticlinical structure. Only one fault, with a sizeable throw of 12 m, would cross the alignment in the French undersea section (see the geological profile in Fig. 3). Permeability test on the overall permeability of the chalk marl showed that it does not, in general, exceed the order of 5X 10 -5 cm/s; and only exceptionally exceeds the order of 5 X l0 -4 cm/s. The occurrence of such water-bearing fissures is a major, but not insuperable, tunnelling hazard, because of a small proportion of fissures being open to give selective fissures flow. Water in the fissures must exert considerable hydrostatic pressure on the extrados of the lining, which is completely impermeable. As is described below, ground treatment may be performed eventually to allow tunnelling to proceed safely. It is planned to inject the ground with cement grout where the water inflow is greater than can be reasonably handled by pumping; with the grouting of the space between lining and ground, at least some of the hydrostatic pressure can be carried by the surrounding ground.
Compressive Strength Chalk marl is a low-strength rock, with compressive strength varying from 250 to 450 kg/cm 2, regardless of the moisture content (approx. 15%); for the 40% clay-sized material, the strength varies from 300 to 100 kg/cm 2, with an average of 50 kg/cm ~. The theoretical stand-up times of a tunnel are dependent, among other conditions and rock characteristics, on joint spacing and tunnel diameter. Chalk marl has joint spacing between 0.4 and 1.10 m. Stand-up time for the 12-m-diameter structure of the Channel Expressway Tunnel might be on the order of three to five days. These results illustrate the favorable characteristics of the chalk marl for ease of mechanical boring and, in particular, for adequate strength to resist the stresses in the rock mass and low permeability. Geology has greatly affected the route of the chosen bored twin Channel Expressway Tunnel. Tunnelling
The philosophy that has led to the proposed arrangement and sizes of the tunnels is fully discussed elsewhere in this paper. The choice of circular profiles and the decision on the tunnel diameters have been made in the light of the most up-to-date knowledge of current tunnelling technology. In reaching these decisions, consideration has been given to a number of factors including the tunnel
Volume I, Number 3/4, 1986
Table 1. Generalized stratigraphy of cretaceous rock in the Channel Tunnel study area. (Modified after Destombes and Shephard-Thorn 1971.) Approximate thickness on the English side
General lithological description
Approximate thickness on the French side
Upper chalk (100 m)
White chalk with flint nodules
Upper chalk (70 m)
Lower chalk (65 m)
White marly chalk : some flints in the upper part, hard nodular Melbourne rock (12 m) at the base.
Lower chalk (80 m)
a. Plenues Marl : very thin greenish marl (2 m)
switchgear, grouting equipment, and rails for the trains of spoil skips. The spoil is removed from the cutting face by baffles built into the cutter head, travels on conveyor belts through the machine, and is carried away in rail-mounted skips.
Probing Ahead and Grouting
Gault (40 m)
Middle Chalk (75 m)
b. White Bed or White Chalk : homogeneous very pale yellowish grey marly chalk (18-20 m). c. Grey Chalk : rhythmic alterations of pale to medium grey more or less marly chalk (22-26 m) d. Chalk Marl: dark grey chalky marl (22-27 m) e. Chloritic Marl : sandy marl with glauconite (1-5 m)
Lower chalk (65 m)
Clay : blue gray calcerous clay
Gault (11 m)
lengths, the versatility and reliability of tunnel boring machines, and the capacity of the industry to supply such machines. Consideration has also been given to the stress distribution within the rock and possible deformations of the cavity before it is lined. The circular profile has advantages from the point of view of statics and because it facilitates the use of a precast concrete lining.
average, following the experience with a 260-m length of the British end of the 4.50-m service tunnel for the Channel Tunnel, driven in 1975. The long lengths of the tunnel within the chalk marl provide a favorable situation for the economic use of a full-face tunnel boring machine (TBM). Cutter power consumption will probably be quite low. The use of TBMs is also attractive in that it will provide a reasonably healthy work environment for personnel working at the tunnel face. It is envisaged that TBMs will be used for all tunnel lengths except for the short section on French land, the crosspassages between the two tunnels, and the curved sections for the filtering stations. The principal components of the TBM are: the full-face cutting head equipped with picks or disks; the shield; the reaction ring; the spoil removal system; and the lining erector. Behind the machine a mobile platform mounted on rails will carry the main transformer and
Excavation The ease of excavation of chalk marl by tunnel boring machines was clearly shown by the trials with the Beaumont machine in 1880-1882 for the Abbotscliff tunnel. On that project a drivage rate of 30 m per day was achieved; the tunnel was left unlined and is, from what can be seen of the few hundred meters now exposed, still standing (Gould et al. 1975). Morgan et al. (1977) indicate that the tunnelling machine has been shown to be capable of excavating in chalk marl and lining at a rate of about 3 m/h on • 2oo I" 8.250 km + .8 ,150 .-, ~.~.,,.__ "~-I00 . : ~ ~ . DOVER ~
Lining The type of lining conventionally used with TBMs is a precast reinforced concrete lining consisting of segments built into a ring. In this tunnel, where the TBM will leave a relatively smooth hole through the chalk, the lining is fixed by a wedge segment that expands the lining against the bore. The normal tunnelling procedure is to advance the excavation by the width of one ring of segments at a time and
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It is expected that the permeability of the ground will be governed more by open fissures in the rock than by the general permeability of the chalk; however, it is not possible to calculate accurately the precise quantity of water inflow without the practical experience of excavating within the stratum. The random nature of the fissure pattern will necessitate careful advance exploration of the ground by probing ahead of excavation. Potential problems with water inflow can then be anticipated and controlled by suitable ground treatment prior to excavation. By these methods, the inflow of water into the tunnel can be restricted to manageable amounts. Tunnelling had to stop during probing, thereby reducing the theoretical rate of tunnel advancement. The space restriction within the TBM increases the difficulties of the probing, and specialised equipment will be required to supply information on the lithological variations and discontinuities while tunnelling is in progress. This equipment consists of drill ring and an electronic system capable of logging drilling parameters and processing the data in real time. Probe drilling was normally carried out at 50-m intervals on the 260-m length of the British end of the service tunnel for the Channel Tunnel, in 1975 (Morgan et al. 1977).
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Volume 1, Number 3/4, 1986
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 263
Table 2. General characteristics of lower chalk and Gault.
Geological layer Grey chalk
Chalk marl
Glauconitic
Calcimetry (Ca 003 content %)
Compressive strength (kg/cm2)
Dry density (g/cm2)
above 80%
40-120
1.82-2.13
17.0-8.8
below 80%
68-156
1.99-2.25
13.0-6.7
above 60%
40-139
1.98-2.26
13.0-6.1
below 60%
34-93
1.8~2.08
19.0-10.0
below 60%
17-103
1.97-2.34
14.0-5.5
0.01-0.8
below 40%
11-79
1.71-2.01
21.0-11.0
0.01-0.8
Water content
(%)
Permubility (cm/s x 10 -4)
0.1-14
0.0~5
marl
Upper gault
immediately erect the new ring, fitting the segments to each other and the previously fitted segments to each other and to the previously completed ring. The lining is made watertight by caulking the joints between segments. The lining will be installed no more than 25-30 m from the heading, immediately behind the propulsion equipment. This will also serve to maintain the integrity of the ground, far from the limit of the stand-up time and from the hazards arising from loosened rocks. Precast concrete segments have a high compressive strength but a relatively low tensile strength. When used in circular rings, most of the ground loading is carried in direct compression and the tensile stresses in the ring are usually minimal because the flexibility at the cross-joint allows the ring to deform to a slightly elliptical shape. The uniformity of the rock along the tunnel route allows the use of a constant lining thicktaess throughout the tunnel. The segments will be reinforced with a b o u t 90-100 kg of reinforced concrete per cubic metre of concrete. Segments cast with a higher-strength concrete ani:l more reinforcement'may be required in some sections of the tunnel. Circular precast.concrete segmental rings provide an immediate permanent lining of great strength provided that, after erection, they are brought into intimate contact with the surface cut by the boring ma'chine.'This is achieved by filling the annulus between the lining and the ground with cement grout. The grouting normally should be carried out as soon as practicable after the erection of the lining to ensure a ~niform distribution of load in the liningand to minimise ground movements. The grouting also assists in reducing the ingress of water into the tunnel. The grouting operation will be c a r r i e d out in the area between t~he switchgear
platform and the point where spoil is loaded into the skips.
Construction of Cross-passages and Filtering Stations Full-face tunnel boring machines a r e not suitable for the construction of the cross-passages between the tunnels o r the curved passages which accommodate the filtering stations. It is anticipated that boom-heading machines will provide the most economical means of forming these sections of the tunnel. These machines use a directional boom with a c y l i n d r i c a l b pineapple---or ripper-shaped cutter head which rotates on a longitudinal or transverse axis. Although in general the boom-type header yields lower rates of production that the full-face TBM, it is fully controllable and is more versatile for cutting irregular shapes and different tunnel sizes. It can be mounted on a gantry or truck to meet the specific requirements. Unlike the full-face TBM method, this excavation method will not produce a perfect cylindrical excavation. The difficuhies of erection within an irregular profile normally preclude the use of a precast concrete segment lining. Instead, ~n in-situ concrete lining will be used in these areas with a total thickness of 400-600 mm. The outer ring of lining villi consist of I00-200 mm of shotcrete s'.upported by ribs and mesh; the inner ring will be poured concrete.
Construction of Tunnels under French Land Side Approximately 1.5 k m - o f the twin tunnels will be constructed under land on the French side of the Channel. The choice of tunnelling method for this section is influenced by the more difficult ground conditions and the shortness. of the continuouslengths required. At the portals, the combination of con-
264 TUNNELLINGAND UNDERGROUND SPACE TECHNOLOGY
straints posed by the geological conditions, the local morphology and environmental factors will necessitate some pretreatment of the ground above the arch tunnel before excavation. It is anticipated that the initial 200 m of the entrance to each tunnel will be constructed using the "umbrella arch" method. Excavation and lining will be carried out by the conventional methods described above for the filtering stations.
Driving Performance Geological conditions suggest that the full-face TBM would be successful with a lining which would supply ground support within 24 h. The boring and lining operations must be precisely coordinated if one operation is not to interfere with the other. It is not possible to maintain a continuous cutting operation as there are inevitable delays between shoves and, particularly in a long tunnel, it is difficult to avoid delays caused by the spoil removal and precast segment supply operations. The r a t e of advancement of the tunnel is, therefore, normally constrained by the rate of handling and transporting the spoil and precast segments, and is somewhat less than the maximum cutting rate. Having considered all these factors, a monthly progress rate of 600-700 m/month for the first tunnel of the pair is a conservative figure to use in developing a construction program. The development of the construction program for a large project such as this depends on an economic balance between two extremes: (1) A very short construction period necessitating a large construction plant. In this case, the major plant items a r e the tunnel boring machines, which a r e highly specialised; the majority of their
Volume 1, Number 3/4, 1986
cost would have to be written off to the project. (2) A long construction period, which normally leads to a lower total capital cost of the works but also leads to higher debt servicing costs, as no revenue will be generated until the completion of the tunnels. In this project, consideration of these alternative programs shows that the most favorable balance between these extremes is achieved by a construction period on the order of five years. In formulating a construction program, the following criteria have been adopted: (1) Work at the tunnel face will proceed continuously (8 h per shift, three shifts per day) for an average of 27 days per month. It is envisaged that cutting operations will be continued through two 8-h shifts per day, and that the third 8-h shift will be used for forward probe drilling, ground treatment and machinery maintenance. (2) Construction of the tunnels will proceed simultaneously from both sides of the channel, with an average TBM progress of approx. 25 m per working day. Driving performance in the longest undersea sections will be approx. (3) The cross-passages and filtering station passages will be formed from the completed sections without interfering with the main tunnel progress. The subdivision into work sections will permit an additional TBM to be employed in the English land section and will allow the tunnels in the French land
U.K.
section to be constructed by conventional means. A significant item in the construction program is the time required to design, manufacture, and set up the five TBMs and ancillary equipment. The total time required for this activity is estimated at two years; the programme allows a 12-month period between award of contract and commissioning of the first TBM. "
Ventilation System The ventilation system of a motorway tunnel bored in the rock underlying the Channel represents a complex problem, as a function of the many constraints and boundary conditions which make difficult an optimal technical-economical solution to the problem of supplying adequate ventilation. The most severe constraint affecting the choice of ventilation system is the undersea section, which has a length of about 38 kin. In this section there may be very few ventilation shafts, making it difficult to ventilate the tunnel effectively and without excessive costs. The design of the ventilation system for the Channel road tunnel complies with the recommendations of the PIARC Tunnels Technical Committee reports. Smoke dilution presents a major challenge to the designer, as it requires 3 to 7 times the air quantities required for other pollutants. A transverse ventilation system was first examined, but this type of solution would be expensive because it requires
Cross over every 5 0 0 m
the construction of central island, a ventilation duct (approx. 27 kin), and transversal links between the ventilation duct and the main tunnel tubes for the distribution of the air; in addition great power is required for ventilation with this type of system. Therefore, a longitudinal system of ventilation (Figs 4 and 5) has been proposed as feasible. In this system, the fresh air flow rates adopted make it possible to remain within the permitted limits of CO concentration, while the air opacified by the smoke is periodically filtered along each of the two main tunnel tubes. Filtration of dirty air (DA) is effected with electrostatic smoke precipitators, arranged between sections in parallel (by-pass sections) in each main tunnel tube. The dirty air in the tube is largely sucked from the by-pass section, filtered from smoke, and restored with good visibility of the tunnel air, within the limits of transparency allowed by the PIARC recommendations. The solution involving the filtration of the smoky air in motorway tunnels is not, as everyone knows, a new solution. It has, in fact, been applied in Japan in some tunnels, although none are as long as the Channel Expressway Tunnel (CET) (Baba and Okano 1982, Baba et al. 1979, 1982, 1985, Ohashi et al. 1983). It must be added that the feasibility of this ventilation system is also considered from the point of view of the technical time necessary for completion of the CET. It is possible that, by that date, the implementation of the EEC regulations relating to the reduction of CO pollution
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Volume 1, Number 3/4, 1986
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 265
LEGEND @
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Figure 5. Air filtering station. (European Economic Community 1970, 1985) will have reduced the current value of q°co=0.7 CO/h Veh to values even lower than those indicated by Pischinger et al (1985) and taken into account in some of our calculations (q°co=0.4). In addition, it may be assumed that there will be areduction in the emission of exhaust smoke from diesel engines (Pischinger et al. 1985b). This will make the filtration operation (calculated on the basis of the current value, q°T= 16 m2/ht, indicated by the PIARC) easier. Finally it should be noted that although, on the one hand, the longitudinal ventilation system is being applied to a very long tunnel, there are, on the other hand, particularly favourable conditions in this case as a result of regular and fluid traffic in the tunnel. What we have, in fact, are two oneway tubes, each with two traffic lanes and an emergency lane. The customs police and toll barriers at the entrances, as well as the governing of the speed and the lane behavior of light and heavy vehicles, will tend to create a filtered and controlled traffic flow unlike the case of tunnels with free access on motorways. In addition, by taking action on the bars that provide access to the road downstram of the toll houses, it will be possible to control the flow of traffic entering the tunnel by computer with a suitable program, on the basis of the traffic flow in the tunnel.
General Design Criteriafor Ventilation The
37.8'-km
undersea
section is
divided into three sections by the provision of two islands, located outside the main shipping lanes, containing ventilation shafts and the necessary equipment. The tunnel section lengths are given in Fig. 3. Figure 2 details the tunnel crosssectional arrangement from which a 68.54-m 2 free cross-sectional area above the road deck has been calculated. The air flow velocity restriction recommended by PIARC thus gives an available longitudinal air flow volume value that has been used in the assessment of 650-700 m3/s. On the premise that the use of electrostatic precipitators effectively negates the necessity for air flow rates for smoke dilution the maximum permissible longitudinal air flow quantity of 650 m / s will control CO and NO emissions from 3000 vehicles per h, doWn to a speed of 20 km/h for the tunnel sections near France and near the English cast; and down to a speed of 62 km/h for the central section. By reducing the traffic volume, emissions at lower speeds can be controlled in the central section; however, given the predicted future reduction in exhaust emissions, the design traffic volume can be accommodated down to a speed of 22 km/h. The general fluid dynamics equation under continuous operating conditions for a single tube, expressed in terms of pressure with respect to a reference pressure, is as follows:
A PR + APt + APm + AP~ + APH+ PB~ APF++AP~+Hv+H8 P~
266 TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
(l)
in which the various terms have the following meaning: APR=Variation in pressure due to frictional resistances along the tunnel, including the intake and exhaust shafts. APe=Variation in kinetic pressure due to variations in the speed of the air along the tunnel sections. APt=Draught of the shafts. APm=Piston effect due to the vehicles moving in the direction of the air (speed of air). APw=Action of the wind on the tunnel portals, on the intake or on the outlet sections of the shafts. APH=Variation in barometric pressure between the portals on the intake or outlet sections of the shafts. APBa=Pressure drop in the air cooling coils. Apyl=Pressure drop in the filtration stations. AP~=Pressure drop in the sound attenuators. Hv=Fan total pressure. HB=Booster fan total pressure. Equation (1) is valid for the case in which all of the aforementioned fluid dynamic resistances are in series. In evaluating the total fan pressure, the portion accounting for the Saccardo effect is included, and corresponds to the pressure required to introduce air into the tunnel section. The Saccardo effect induces a thrust on the air in the tunnel and is effective over certain calculated lengths. Booster fans are provided between precipitator stations to maintain
Volume 1, Number 3/4, 1986
the air flow along the tunnel. Booster fans are also provided in the sections of tunnel in which the air flows are normally induced by the Saccardo effect from the main supply fans and the precipitator station fans. Figure 6 shows a ventilation circuit for one tube section, from supply fan inlet to exhaust fan outlet, divided into segments each allotted segment number. Equation (1) may be written and solved for various segments of the section under consideration. Values are established for the allowable smoke concentrations and for the filtration efficiency of electrostatic precipitators along the tunnel. By applying the mass balance equations to Segment 4-5 of the tube, including the filtering station (see Fig. 6), it is possible to deduce values for the tube sections between the stations along the tunnel. Figure 5 represents a solution for one filtering station. The air in the tunnel is heated and its temperature raised due to heat released from: (1) the flow of cars and trucks; (2) the ventilation equipment (3) the electrical equipment in the tunnel; and (4) the lighting and signalling equipment. For the design traffic flow M=2000 Veh/h, the greatest heat is contributed by cars and trucks.
Though the solution provided by the thermal balance equation is written for an infinitesimal segment of the tube, it is possible to obtain the air temperature trend along the tube. In Fig. 7, line (a) represents the temperature distribution in one section of the tube. Since the air temperature in the tunnel would reach high values which could not be tolerated, it is necessary to provide a cooling plant to reduce the air temperature. This cooling process is performed by a chilled water system utilizing a refrigeration plant. The chilled water feeds coils provided at the intake points of the supply air fans and at selected filtering stations along the tube (see Fig. 7). Line (b) in Fig. 7 illustrates the air temperature trends due to this cooling process and identifies the position of the cooling stations necessary to obtain an air temperature of less than approx. 30°C. Safety and Operation Criteria Safety in road tunnels can be defined as the ability of the tunnel operator to inform the users properly of driving conditions in the tunnel; to obtain information quickly about any anomalous event occuring in the tunnel; and to .9o ~4 o.
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Volume I, Number 3/4, 1986
transmit information and instructions to meet the new, changed conditions of traffic, while at the same time adopting the appropriate measures to remove the causes of the trouble. The type and quantity of the equipment to be installed for this purpose are mainly related to the tunnel length and the traffic volume expected therein. It is evident that the longer a tunnel is and the heavier traffic conditions are, the higher are the risks of accident, fire traffic stoppages and slowdowns. Tunnels in Japan are classified into five classes according to their length and traffic volume. The longest and more trafficked tunnels belong to class AA: these need to be suitably equipped to provide the best protection to the users and service personnel, as well as to the tunnel structures and installations. The Channel Tunnel would belong to class AA. Each of the two tubes will be provided with two control rooms----one for each portal--manned around the clock. Safety equipment and signals--which are a constituent part of the safety facilities--would be placed along the tunnel, spaced at intervals equal to multiples or submuhiples of 500 m, this being the distance between the crosspassages connecting the two tubes of the road tunnel. Consequently, green arrows and red crosses above each land would be installed every 250 m--i.e, at every crosspassage and halfway between the crosspassages. The green arrows switched on advise that the lane is open, while the red crosses indicate that the lane is closed. Flashing amber arrows instruct the drivers to shift to the lane open to traffic. Whenever a lane is not usable because of road works or other obstructions, the prescribed signals for works are indispensable. Signs that must be repeated, e.g. speed limit, no parking or waiting will be installed every 2000 m. Telephones, essential for safey, would be installed in emergency recesses 2 m high, 2 m wide and 1 m deep, clearly marked and well-illuminated; and would be provided with dust-tight glass doors to keep them clean in the usually dusty and dirty road tunnel environment. Opening the door of a telephone recess switches on a flashing yellow light over it. One recess will be located near each cross-passage; another two will be placed between one cross-passage and the next; hence, a recess will be located every 167 m, i.e. at a distance equal to one-third of 500 m. The operator at the control room will be able to see on a display panel the location of the telephone where the call is coming from. It is also convenient to install alarm buttons, fire extinguishers, hydrants and power sockets into emergency recesses. Additional alarm buttons also could be installed halfway between recesses. In this case also, the operator in the control
TUNNELLING AND UNDERGROUNDSPACE TECHNOLOGY 267
room can pinpoint the location the alarm comes from. Another facility essential to safety is closed-circuit television. The TV camera would be installed at 250-m intervals, i.e. at every cross-passage and midway between cross-passages. This distance can allow a good general view of the traffic. Reduced spacing would require an excessive number of cameras. In each control room, a single monitor would show the pictures taken by 12 TV cameras, thus reducing to 16 the number of monitors, not counting those connected to the cameras located outside the tunnel• This CCTV system would be linked to other safety facilities (alarm buttons, telephones, fire extinguishers and detectors, traffic detectors). In the case of an alarm given by any of these facilities, the monitor--usually the one connected with an external camera-would automatically show the area involved. A radio installation would also be provided so that drivers in the tunnel can listen to two radio stations, one transmitting in English and the other in French. The installation would also be used for service communications (operation, fire brigade, ambulances, etc.). Signs at the tunnel entrance would give drivers information about the frequencies that can be tuned in inside the tunnel. The operator at the control room can introduce messages for the drivers on these same wave lengths, giving necessary information, advice and instructions. Listening to the radio can make less tedious the time spent driving in a tunnel. This becomes a very important factor when the tunnel is so long. For the same reason, two different types of lighting systems are to be provided which would alternate every 6 km (approx. 5 rain drive). One system consists of 36W fluorescent lamps arranged along two continuous rows; the other, of 250W high-pressure sodiumvapour lamps, placed 10 m apart, arranged alternately in two rows i.e. at 20-m intervals on every single row. The roadway and walls would be finished with light colours and the wall color would change every 6 kin. A 100-m-long transition zone separating each and a km-long tunnel section would be lit by means of 400W high-pressure sodiumvapour lamps arranged in three rows, thus creating intensely bright "sunlight windows (400 cd/m 2, as opposed to 14 and 15 cd/m 2 in the 6-kin-long tunnel sections). Thus, drivers would have--both physically and psychologically--the vivid impression of driving through a series of different tunnels. Two (2) fire extinguishers, of the power type and with a unit capacity of 6 kg, would be placed into the emergency recesses. Hydrants, connected to the water mains under pressure, would have a pressure at the outlets of 6-7 atm. and a flow of 1200 l/min. Fire detectors installed in separate single units would
send to the control room an alarm of any temperature rise exceeding a certain value. Nevertheless, this type of tunnel must have its own fire-fighting organization, with staff and equipment permanently available on the spot. At the beginning, a fire is almost always small: therefore, prompt action is essential• The presence at each portal of trained firefighters and special equipment can prevent, in most cases, the development of a dangerous fire. Naturally, in particularly serious contingencies, action by local fire brigades from both countries would be necessary• The operational staff for the Channel Tunnel would consist of 36 people at each tunnel portal for traffic control and assistance in case of accident or fire. Thus, every portal would be covered by a team of seven people during each of the three work shifts. Every hour the tunnel would be inspected alternatively by two patrols of two people each, who would drive a fast vehicle---a motorcycle or Land Rover-and carry temporary signs, as well as fire-fighting and rescue equipment. Therefore, during each eight-hour shift, four people would be in charge of surveillance for each portal. Another three people would be available at the portals, along with other specially equipped vehicles ready to intervene in case of emergency, e.g. fire or accident. The adoption of strict traffic regulations would limit the transit of hazardous material through the tunnel, allowing only those goods for which the level of risk is reasonably acceptable. A speed limit of 100 km/h was proposed for cars; and a speed limit of 80 km/h for trucks and for coaches with more than nine paying seats• The speed limit proposed for commercial vehicles carrying hazardous materials would be 60 km/h. A long tunnel such as this one inevitably implies the provision of two separate managing centers, at the English and the French portal, respectively. Each center would have its own operational department (equipment and installations, safety facilities) and administrative offices (accounting, purchase and warehouse, toll, EDP center). • The formation of operational teams including personnel from both countries is never--as our experience has proven-an advisable solution. This is due not only to the difficulties arising from having to move throughout such a long tunnel, but also to the actual differences in language, attitudes and work practices. Therefore, a fair distribution of functions among the personnel from both countries, assigning them duties and responsibilities in a well-balanced form, must be provided. In this and other areas the rule of reciprocality must be carefully respected. The staffworking at both portals must be numerically equal and their distribution, based on their specific duties, should be
268 TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
similar. Insofar as the operational services are concerned, the duties would be divided on the basis of common instructions, among the personnel assigned to each portal, who should look after the maintenance and safety of the tunnel mid-section adjacent to their respective portal. The operational procedures concerning the technical services and safety facilities, as well as those regarding trafic regulations, should, of course, be the same. Each control room will provide for the surveillance of the entire tunnel. Traffic controllers, who would be required to speak both languages, should maintain mutual contact and act in agreement. In addition, the administrative staff would follow common instructions despite the different accounting and fiscal procedures in force in the two countries. []
Acknowledgements Warmest thanks to Sea Containers Ltd for having allowed this presentation at the Seikan Colloquium, and personal thanks to company President Mr J. B. Sherwood and Vice-President Mr D. K. Bray for their contributions to the project.
References Baba, T. and Okano, K. 1982. Ventilation system of the Tsuruga Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield,
ed.) pp. 367-382, 403-420. Baba, T., Ohashi, H. and Nakamishi, F. 1979. A new longitudinal ventilation system using a electrostatic precipitator for long vehicular traffic tunnel. Third International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, 1SAVVT, Sheffield, 1979 (BHRA, Cranfield,
ed.), pp. 201-226. Baba, T., Ohashi, H. and Uesaki, K. 1982. Aerodynamic specialities in connection with the Tsuruga Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield, ed.).
pp. 403-420. Baba, T., Ohashi, H., Nakamichi, F•, Inami, E. and Akita, I. 1985. Recent trends in ventilation systems of long vehicle tunnels in Japan. Fij2h International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, Lille, 1985 (BHRA Cranfield, ed.), pp. 371-388. Channel Tunnel Study Group. 1966. Channel Tunnel: Site Investigations in the Strait of Dover 1964-1965, Vols. I-IV.
Destombes, J. P. and Shephard-Thorn, E. R. 1971. Geological results of the Channel Tunnel site investigations. 1964-1965 Report 71/ 11, pp. 1-11. Institute of Geol. Sciences, HMSO. European Economic Community, 1970. Directive 70/220/EEC, Journal L76. European Economic Community, 1985. Directive Proposal 85/C, 245/01. Gould. H. B., Jackson, G. O. and Tough, S. G. 1975. The design of the Channel Tunnel. Struct. Eng. 53: 45-62. Grance, A. and Muir Wood, A. H. 1970. The site investigations of the Channel Tunnel. Proc. Inst. Civ. Engrs 45: 103-123.
Volume 1, Number 3/4, 1986
Morgan, M., Barratt, D. A. and Tilley, D. H. 1977. The tunnelling system for the British section of the Channel Tunnel, Phase II Works. TRRL Laboratory Report 734, pp. 1-56.
Ohashi, H., Mizuno, A., Nakahori, I. and
Volume l, N u m b e r 3/4, 1986
Ueki, M. 1983. A new ventilation method for the Kan-Etsu Road Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield, ed.), pp. 31-47. Pischinger, R. and Schweiger, H. 1985a.
Determining exhaust emission of motor vehicles in tunnels. Fifth International Syrap. on the Aerodynamics and Ventilation of Vehicle Tunnels, Lille, 1985. (BHRA, Cranfield, ed.), p. 405. Pischinger, R. and Schwieger, H. 1985h. lbid, p. 395.
TUNNELLING AND UNDERGROUNDS,PACE T~'-CHNOLOGY 269
AbstraetmThe proposal for a fixed link between France and England by means of a submarine tunnel under the English Channel has been examined in its various aspects of layout, tunnelling, ventilation, safety and operation criteria. The choice of the underground solution has been suggested by the low depth (40--60 m) of the Channel sea bottom between Calais and Dover, and by the presence, at an accessible depth, of a quite continuous geologic stratum of chalk marl with a low ponneabili~ and fair compressive strength. The submarine road tunnel is 48 km long and is constituted of two tunnels with an external diameter of12.10 m. The excavation of the two main tunnels will be done with prototypical tunnel boring machines allotted to the various sections,for an average excavation rate of 25 m per day over a five-year period. The lining is made of precast concretesegments laid by two erectorsfrom the machine itself. The suggested longitudinal ventilation system has short supplementary ventilation tunnels for airfiltration, external and adjacent to the main two tunnels and of the same diameter. The ventilation is influenced and facilitated by the input offresh airfrom two vertical shafts connected with islands on the open sea. Safety equipment is foreseen for communication and information inside the tunnel as well as to guide transit in the dangerous zones. A new lighting system has been proposed.
General Design Criteria i
t may be of interest, before entering into the illustration of the construction methods and ventilation criteria, to discuss the logical process that led to the definition of the basic features of this project. The Promoter and the Consultant were both convinced that the preferable solution for the important Channel fixed link was a submarine crossing that would be suitable for both trains and motor vehicles. Thus, any decision was dependent mainly upon the nature of the ground, its tunnelling characteristics and the desired capacity and efficiency of the structure. The following considerations were assumed as fundamental design criteria: (1) The lower chalk mart is very suitable for boring by full-face Tunnel Boring Machines (TBMs). (2) The maximum allowed diameter for such TBMs was defined as approx. 12 m.
This paper is drawn from the SPEA engineering study for the English Channel fixed link proposal by Sealink/British Ferries Ltd. Present address for Mr Comolli and Mr Pigorini: SPEA S.p.A. Via Cornaggia, 10 Milan, Italy. Present address for Mr Cuaz: Societa per il Traforo del Monte Bianco, 11013 Courmayeur, Aosta, Italy. Present address for Mr Ferro: Politecnieo di Torino, Corso Duca degli Abruzzi 24, 20129 Turin, Italy.
l'aide d'un tunnel sous-marin sous la Manche a ite'examin/e pour dill~rents aspects de la planification, des techniques tunnelikres, de la ventilation, de la s/curit/ et des critkres defonetionnement. Le choix d'unc solution souterrainc a it/suggiri ~ lafois par la faible profondenr de la Manche entre Calais et Douvre (40--60 ra) et par la pr/sence fi une profondeur accessible d'un strata g/ologique assez continu de craie de Marle que posskde une faible perralabilit/ et une r/sistance ~ la compression raoyenne. Le tunnel fourier sous-marin a uno longuenr de 48 km et est constitul de deux tunnels ayant chacun un diamktre de 12.10 m. L 'excavation des deux tunnels principaux sera effectu/e avec des tunnoliers prototypes allou~s aux diff/rentes sections et le tuux d'excavation sera en moyenne de 25 m porjour sur une p/riode de 5 ans. Le rev~tementest constitu/de segments pr/fabriqu/s en b/ton qui seront posls par des ajusteurs-monteurs ;1 partir de la machine elle-mhne. Le systkrae de ventilation longitudinale sugglrl comprend des courts tunnels suppl/mentaires de ventilation pour la filtration de Fair. Ces tunnels de mg~nediam2tre seront situls fi l'ext/rieur et adjacents aux deux tunnels principaux. La ventilation sera inflnencle etfacilit~e par l'arrivle d'airfrais provenant de deux puits verticaux connectis fi des ~les en pleino met. Des iquipements de slcuritl pour les communications et les informations h l'intlrienr du tunnel et le guidage du traffic darts les zones dangereuses sont privas. Un nouveau systg,me d'iclairage a aussi itl propos/.
(3) Inside a 11.30-m-net-diameter tunnel, a highway with two lanes plus an emergency lane can be executed, in compliance with the prescription of the official Terms of Reference. (4) Two twin tunnels of this kind, connected by skewed crossovers of the same size every 500 m would provide the configuration with the maximum level of flexibility and safety. (5) The major difficulty to be overcome, at this point, was the ventilation of the road tunnels; air treatment of the railway tunnel was considered to be a much easier problem to solve. (6) After a very thorough analysis, comparison and discussion of the two alternatives--transversal or longitudinal ventilation of the road tunnels--the longitudinal option was selected. Even though the ventilation of the 18-kin-long central submarine section represented a world record, it was considered .essential in this case to eliminate an emergency air intake shaft from the sea in the center of the Channel. This is why such an innovative design, based upon the advanced experience with the Japanese Kan-Etsu Tunnel, was developed. With regard to the location of the rail tunnel with respect to the twin road tunnels, the following two alternatives were considered: (1) Case I, involving two large-diameter road tunnels between
T~,*llmg and U~l~r&ro~ SpaceTec/moto,~j,Vol. 1, No. 3/4, pp. 261-269, 1986. Printed in Great Britain.
R~um6---La proposition d'un lien permanent entre la France et l'Angleterre fi
0866-7798186 $3.00+.00 ~) 1986 Pergamon Journals Ltd.
which is a smaller rail tunnel; and (2) Case I[, involving a twin road tunnel with rail tunnels alongside it. The Case II solution finally was chosen because of the following main advantages that it offered: (1) The adjacent road tunnels represent the optimum, in terms of flexibility and safety, because of the possibility of diversion/inversion of traffic flows from one tube to the other; (2) Each of the road tunnels could be considered as a spare-structure to the other, while the rail tunnel represents an additional safetyway, in case of emergency; (3) The time of intervention and of evacuation in case of grave accidents or fire is shorter than in Case I. (4) The efficiency/cost ratio of the mechanical and electrical installations in the road tunnel (ventilation, lighting, telecommunications, controls, etc.) was optimized in Case II. This paper concerns the project study of the road tunnel link (Figs 1 and 2).
Geological and Geotechnical Conditions The first geological investigation for the fixed link of the English Channel dates back to the nineteenth century. As a result of renewed interest in the project in 1958--59, 1964-65 and 1971-72, an
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Figure 2. Typical cross-section of the tunnel. extensive site investigation comprising nearly 100 marine boreholes, geotechnical tests and seismic surveying at sea, was carried out (Channel Tunnel Study Group 1966, Grance and Muir Wood 1970, Destombes and Shephard-Thorn 1971, Gould et..al, 1975). The Channel was once a dry chalk valley flooded by the melting of ice from the polar ice caps, with coastal erosion contributing to its development. Tectonically, the Dover Straits transects the northern limb of the major east-west Tertiary Weald-Boulonnais anticline, in which Jurassic and Cretaceous rocks are gently deformed over a structurally complex base of Paleozoic rocks. Within the area of the project, Cretaceous rocks from the Gauh (Albian) to Upper Chalk (Senonian) are present. The succession of rocks actually considered during the study is summarized in Table 1. The geological profile in Fig. 3 shows, in simplified form, the succession of strata in which the Channel Expressway Tunnel lies: Upper and Middle Chalk--white chalk and white marly chalk, composed over 90% of CaCOs, badly fissured and water bearing, is found on the tunnel alignment on the French land section portal. Lower Chalk--chalk marl, composed
40-80% of CaCO3, with low permeability, relatively free of fissures, is encountered over the whole undersea section. Gault Cla.y-----a stiff, overconsolidated clay, with a CaCO3 content varying from 40 to 15%, with very low permeability and low swelling characteristics, is encountered by the lower part of the tunnel cross-section, along a very short undersea section and at the English portal. The Lower Chalk and the Gault Clay strata thin out from the English to the French side, from 80 to 65 m, and from 40 to 11 m, respectively. The thinning of the Gauh Clay is highly significant because it overlies the permeable Lower Greensands. Median value geotechnical test results are summarized in Table 2. The most important ground factors in the tunnelling of the Channel Expressway are (1) permeability and (2) compressive strength.
Permeability Permeability in chalk is secondary, as the intact chalk has a k of 10-7 or less. The matrix permeability of the chalk marl is nil for practical purposes, due to its high clay content. The effective bulk permeability in-situ is entirely due to
262 TUNNELLINGAND UNDERGROUND SPACE TECHNOLOGY
fissures, fractures and faults. Faulting, involving major displacement, is virtually absent from the study area. Minor faults and fissures were detected geophysically with throws of 1-3 m, some of which can be associated with the anticlinical structure. Only one fault, with a sizeable throw of 12 m, would cross the alignment in the French undersea section (see the geological profile in Fig. 3). Permeability test on the overall permeability of the chalk marl showed that it does not, in general, exceed the order of 5X 10 -5 cm/s; and only exceptionally exceeds the order of 5 X l0 -4 cm/s. The occurrence of such water-bearing fissures is a major, but not insuperable, tunnelling hazard, because of a small proportion of fissures being open to give selective fissures flow. Water in the fissures must exert considerable hydrostatic pressure on the extrados of the lining, which is completely impermeable. As is described below, ground treatment may be performed eventually to allow tunnelling to proceed safely. It is planned to inject the ground with cement grout where the water inflow is greater than can be reasonably handled by pumping; with the grouting of the space between lining and ground, at least some of the hydrostatic pressure can be carried by the surrounding ground.
Compressive Strength Chalk marl is a low-strength rock, with compressive strength varying from 250 to 450 kg/cm 2, regardless of the moisture content (approx. 15%); for the 40% clay-sized material, the strength varies from 300 to 100 kg/cm 2, with an average of 50 kg/cm ~. The theoretical stand-up times of a tunnel are dependent, among other conditions and rock characteristics, on joint spacing and tunnel diameter. Chalk marl has joint spacing between 0.4 and 1.10 m. Stand-up time for the 12-m-diameter structure of the Channel Expressway Tunnel might be on the order of three to five days. These results illustrate the favorable characteristics of the chalk marl for ease of mechanical boring and, in particular, for adequate strength to resist the stresses in the rock mass and low permeability. Geology has greatly affected the route of the chosen bored twin Channel Expressway Tunnel. Tunnelling
The philosophy that has led to the proposed arrangement and sizes of the tunnels is fully discussed elsewhere in this paper. The choice of circular profiles and the decision on the tunnel diameters have been made in the light of the most up-to-date knowledge of current tunnelling technology. In reaching these decisions, consideration has been given to a number of factors including the tunnel
Volume I, Number 3/4, 1986
Table 1. Generalized stratigraphy of cretaceous rock in the Channel Tunnel study area. (Modified after Destombes and Shephard-Thorn 1971.) Approximate thickness on the English side
General lithological description
Approximate thickness on the French side
Upper chalk (100 m)
White chalk with flint nodules
Upper chalk (70 m)
Lower chalk (65 m)
White marly chalk : some flints in the upper part, hard nodular Melbourne rock (12 m) at the base.
Lower chalk (80 m)
a. Plenues Marl : very thin greenish marl (2 m)
switchgear, grouting equipment, and rails for the trains of spoil skips. The spoil is removed from the cutting face by baffles built into the cutter head, travels on conveyor belts through the machine, and is carried away in rail-mounted skips.
Probing Ahead and Grouting
Gault (40 m)
Middle Chalk (75 m)
b. White Bed or White Chalk : homogeneous very pale yellowish grey marly chalk (18-20 m). c. Grey Chalk : rhythmic alterations of pale to medium grey more or less marly chalk (22-26 m) d. Chalk Marl: dark grey chalky marl (22-27 m) e. Chloritic Marl : sandy marl with glauconite (1-5 m)
Lower chalk (65 m)
Clay : blue gray calcerous clay
Gault (11 m)
lengths, the versatility and reliability of tunnel boring machines, and the capacity of the industry to supply such machines. Consideration has also been given to the stress distribution within the rock and possible deformations of the cavity before it is lined. The circular profile has advantages from the point of view of statics and because it facilitates the use of a precast concrete lining.
average, following the experience with a 260-m length of the British end of the 4.50-m service tunnel for the Channel Tunnel, driven in 1975. The long lengths of the tunnel within the chalk marl provide a favorable situation for the economic use of a full-face tunnel boring machine (TBM). Cutter power consumption will probably be quite low. The use of TBMs is also attractive in that it will provide a reasonably healthy work environment for personnel working at the tunnel face. It is envisaged that TBMs will be used for all tunnel lengths except for the short section on French land, the crosspassages between the two tunnels, and the curved sections for the filtering stations. The principal components of the TBM are: the full-face cutting head equipped with picks or disks; the shield; the reaction ring; the spoil removal system; and the lining erector. Behind the machine a mobile platform mounted on rails will carry the main transformer and
Excavation The ease of excavation of chalk marl by tunnel boring machines was clearly shown by the trials with the Beaumont machine in 1880-1882 for the Abbotscliff tunnel. On that project a drivage rate of 30 m per day was achieved; the tunnel was left unlined and is, from what can be seen of the few hundred meters now exposed, still standing (Gould et al. 1975). Morgan et al. (1977) indicate that the tunnelling machine has been shown to be capable of excavating in chalk marl and lining at a rate of about 3 m/h on • 2oo I" 8.250 km + .8 ,150 .-, ~.~.,,.__ "~-I00 . : ~ ~ . DOVER ~
Lining The type of lining conventionally used with TBMs is a precast reinforced concrete lining consisting of segments built into a ring. In this tunnel, where the TBM will leave a relatively smooth hole through the chalk, the lining is fixed by a wedge segment that expands the lining against the bore. The normal tunnelling procedure is to advance the excavation by the width of one ring of segments at a time and
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It is expected that the permeability of the ground will be governed more by open fissures in the rock than by the general permeability of the chalk; however, it is not possible to calculate accurately the precise quantity of water inflow without the practical experience of excavating within the stratum. The random nature of the fissure pattern will necessitate careful advance exploration of the ground by probing ahead of excavation. Potential problems with water inflow can then be anticipated and controlled by suitable ground treatment prior to excavation. By these methods, the inflow of water into the tunnel can be restricted to manageable amounts. Tunnelling had to stop during probing, thereby reducing the theoretical rate of tunnel advancement. The space restriction within the TBM increases the difficulties of the probing, and specialised equipment will be required to supply information on the lithological variations and discontinuities while tunnelling is in progress. This equipment consists of drill ring and an electronic system capable of logging drilling parameters and processing the data in real time. Probe drilling was normally carried out at 50-m intervals on the 260-m length of the British end of the service tunnel for the Channel Tunnel, in 1975 (Morgan et al. 1977).
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- - 5 0 .-:~
O L__
5°I
S NGATTE
50,
__
Legend
5 .__l
__
~
~
~"" I O ~ ; : " " ~ ~ __
15 __1,
~
MIDDLE CHALK white marly chalk
.... '~"20 ";/'~ ...... __ ~ ~ , . ~
~
,5 __
~
LOWER CHALK I I white and grey chaLk ~
...... Weathered horizon
L__
~
"
.~l
4 0 " , :- - ' ; ; ' ; ' ' " ~ --
LOWER CHALK chalk marl
~
45 ~
.
47.570 --~!km
GAULT blue cLay
~ ~ FauLts
Figure 3. Geologicalprofile of the Channel Expressway.
Volume 1, Number 3/4, 1986
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 263
Table 2. General characteristics of lower chalk and Gault.
Geological layer Grey chalk
Chalk marl
Glauconitic
Calcimetry (Ca 003 content %)
Compressive strength (kg/cm2)
Dry density (g/cm2)
above 80%
40-120
1.82-2.13
17.0-8.8
below 80%
68-156
1.99-2.25
13.0-6.7
above 60%
40-139
1.98-2.26
13.0-6.1
below 60%
34-93
1.8~2.08
19.0-10.0
below 60%
17-103
1.97-2.34
14.0-5.5
0.01-0.8
below 40%
11-79
1.71-2.01
21.0-11.0
0.01-0.8
Water content
(%)
Permubility (cm/s x 10 -4)
0.1-14
0.0~5
marl
Upper gault
immediately erect the new ring, fitting the segments to each other and the previously fitted segments to each other and to the previously completed ring. The lining is made watertight by caulking the joints between segments. The lining will be installed no more than 25-30 m from the heading, immediately behind the propulsion equipment. This will also serve to maintain the integrity of the ground, far from the limit of the stand-up time and from the hazards arising from loosened rocks. Precast concrete segments have a high compressive strength but a relatively low tensile strength. When used in circular rings, most of the ground loading is carried in direct compression and the tensile stresses in the ring are usually minimal because the flexibility at the cross-joint allows the ring to deform to a slightly elliptical shape. The uniformity of the rock along the tunnel route allows the use of a constant lining thicktaess throughout the tunnel. The segments will be reinforced with a b o u t 90-100 kg of reinforced concrete per cubic metre of concrete. Segments cast with a higher-strength concrete ani:l more reinforcement'may be required in some sections of the tunnel. Circular precast.concrete segmental rings provide an immediate permanent lining of great strength provided that, after erection, they are brought into intimate contact with the surface cut by the boring ma'chine.'This is achieved by filling the annulus between the lining and the ground with cement grout. The grouting normally should be carried out as soon as practicable after the erection of the lining to ensure a ~niform distribution of load in the liningand to minimise ground movements. The grouting also assists in reducing the ingress of water into the tunnel. The grouting operation will be c a r r i e d out in the area between t~he switchgear
platform and the point where spoil is loaded into the skips.
Construction of Cross-passages and Filtering Stations Full-face tunnel boring machines a r e not suitable for the construction of the cross-passages between the tunnels o r the curved passages which accommodate the filtering stations. It is anticipated that boom-heading machines will provide the most economical means of forming these sections of the tunnel. These machines use a directional boom with a c y l i n d r i c a l b pineapple---or ripper-shaped cutter head which rotates on a longitudinal or transverse axis. Although in general the boom-type header yields lower rates of production that the full-face TBM, it is fully controllable and is more versatile for cutting irregular shapes and different tunnel sizes. It can be mounted on a gantry or truck to meet the specific requirements. Unlike the full-face TBM method, this excavation method will not produce a perfect cylindrical excavation. The difficuhies of erection within an irregular profile normally preclude the use of a precast concrete segment lining. Instead, ~n in-situ concrete lining will be used in these areas with a total thickness of 400-600 mm. The outer ring of lining villi consist of I00-200 mm of shotcrete s'.upported by ribs and mesh; the inner ring will be poured concrete.
Construction of Tunnels under French Land Side Approximately 1.5 k m - o f the twin tunnels will be constructed under land on the French side of the Channel. The choice of tunnelling method for this section is influenced by the more difficult ground conditions and the shortness. of the continuouslengths required. At the portals, the combination of con-
264 TUNNELLINGAND UNDERGROUND SPACE TECHNOLOGY
straints posed by the geological conditions, the local morphology and environmental factors will necessitate some pretreatment of the ground above the arch tunnel before excavation. It is anticipated that the initial 200 m of the entrance to each tunnel will be constructed using the "umbrella arch" method. Excavation and lining will be carried out by the conventional methods described above for the filtering stations.
Driving Performance Geological conditions suggest that the full-face TBM would be successful with a lining which would supply ground support within 24 h. The boring and lining operations must be precisely coordinated if one operation is not to interfere with the other. It is not possible to maintain a continuous cutting operation as there are inevitable delays between shoves and, particularly in a long tunnel, it is difficult to avoid delays caused by the spoil removal and precast segment supply operations. The r a t e of advancement of the tunnel is, therefore, normally constrained by the rate of handling and transporting the spoil and precast segments, and is somewhat less than the maximum cutting rate. Having considered all these factors, a monthly progress rate of 600-700 m/month for the first tunnel of the pair is a conservative figure to use in developing a construction program. The development of the construction program for a large project such as this depends on an economic balance between two extremes: (1) A very short construction period necessitating a large construction plant. In this case, the major plant items a r e the tunnel boring machines, which a r e highly specialised; the majority of their
Volume 1, Number 3/4, 1986
cost would have to be written off to the project. (2) A long construction period, which normally leads to a lower total capital cost of the works but also leads to higher debt servicing costs, as no revenue will be generated until the completion of the tunnels. In this project, consideration of these alternative programs shows that the most favorable balance between these extremes is achieved by a construction period on the order of five years. In formulating a construction program, the following criteria have been adopted: (1) Work at the tunnel face will proceed continuously (8 h per shift, three shifts per day) for an average of 27 days per month. It is envisaged that cutting operations will be continued through two 8-h shifts per day, and that the third 8-h shift will be used for forward probe drilling, ground treatment and machinery maintenance. (2) Construction of the tunnels will proceed simultaneously from both sides of the channel, with an average TBM progress of approx. 25 m per working day. Driving performance in the longest undersea sections will be approx. (3) The cross-passages and filtering station passages will be formed from the completed sections without interfering with the main tunnel progress. The subdivision into work sections will permit an additional TBM to be employed in the English land section and will allow the tunnels in the French land
U.K.
section to be constructed by conventional means. A significant item in the construction program is the time required to design, manufacture, and set up the five TBMs and ancillary equipment. The total time required for this activity is estimated at two years; the programme allows a 12-month period between award of contract and commissioning of the first TBM. "
Ventilation System The ventilation system of a motorway tunnel bored in the rock underlying the Channel represents a complex problem, as a function of the many constraints and boundary conditions which make difficult an optimal technical-economical solution to the problem of supplying adequate ventilation. The most severe constraint affecting the choice of ventilation system is the undersea section, which has a length of about 38 kin. In this section there may be very few ventilation shafts, making it difficult to ventilate the tunnel effectively and without excessive costs. The design of the ventilation system for the Channel road tunnel complies with the recommendations of the PIARC Tunnels Technical Committee reports. Smoke dilution presents a major challenge to the designer, as it requires 3 to 7 times the air quantities required for other pollutants. A transverse ventilation system was first examined, but this type of solution would be expensive because it requires
Cross over every 5 0 0 m
the construction of central island, a ventilation duct (approx. 27 kin), and transversal links between the ventilation duct and the main tunnel tubes for the distribution of the air; in addition great power is required for ventilation with this type of system. Therefore, a longitudinal system of ventilation (Figs 4 and 5) has been proposed as feasible. In this system, the fresh air flow rates adopted make it possible to remain within the permitted limits of CO concentration, while the air opacified by the smoke is periodically filtered along each of the two main tunnel tubes. Filtration of dirty air (DA) is effected with electrostatic smoke precipitators, arranged between sections in parallel (by-pass sections) in each main tunnel tube. The dirty air in the tube is largely sucked from the by-pass section, filtered from smoke, and restored with good visibility of the tunnel air, within the limits of transparency allowed by the PIARC recommendations. The solution involving the filtration of the smoky air in motorway tunnels is not, as everyone knows, a new solution. It has, in fact, been applied in Japan in some tunnels, although none are as long as the Channel Expressway Tunnel (CET) (Baba and Okano 1982, Baba et al. 1979, 1982, 1985, Ohashi et al. 1983). It must be added that the feasibility of this ventilation system is also considered from the point of view of the technical time necessary for completion of the CET. It is possible that, by that date, the implementation of the EEC regulations relating to the reduction of CO pollution
Return cross over every 3 km
I
u
o I
m
France
Air and traffic fLow
ELectrostatic precipitators
Corner vanes Fans
5o i
AuxiLiary machines VentiLatior shaft
@®'
@
| -
-
®
|
@ ©® V
a
@
'
©
France
Schematic Layout of tunnel (undersea Length) m
o i----
500 I
IO0O I
Type A Cross over B Return cross over C Precipitator bypass
2000 I
Figure 4. Schema of the longitudinal ventilation systemfor the Channel Expressway.
Volume 1, Number 3/4, 1986
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 265
LEGEND @
AXIALFANS(REGENERATEDAIR) ELECTROSTATICPRECIPITATORS
@
ELECTRICMOTORS
@
ELECTRICALSWITCHBOARDS
SECTION A - A
i®(~) COOLINGCOILS
,
®
AIR CONDITIONINGUNITS PLANROOMAMBIENTA,C,
\
(~) DIFFUSER SOUNDATTENUATOR (~) DUMPERS AIR SUPPLYDUCT (~) FLEXIBLEJOINT
[Q@DROPELIMINATOR _
° °
FALSECEILING @ DISTRIBUTIONGRATE FRESHAIR STALEAIR E) ONLYFORCOOLINGFILTERS
Figure 5. Air filtering station. (European Economic Community 1970, 1985) will have reduced the current value of q°co=0.7 CO/h Veh to values even lower than those indicated by Pischinger et al (1985) and taken into account in some of our calculations (q°co=0.4). In addition, it may be assumed that there will be areduction in the emission of exhaust smoke from diesel engines (Pischinger et al. 1985b). This will make the filtration operation (calculated on the basis of the current value, q°T= 16 m2/ht, indicated by the PIARC) easier. Finally it should be noted that although, on the one hand, the longitudinal ventilation system is being applied to a very long tunnel, there are, on the other hand, particularly favourable conditions in this case as a result of regular and fluid traffic in the tunnel. What we have, in fact, are two oneway tubes, each with two traffic lanes and an emergency lane. The customs police and toll barriers at the entrances, as well as the governing of the speed and the lane behavior of light and heavy vehicles, will tend to create a filtered and controlled traffic flow unlike the case of tunnels with free access on motorways. In addition, by taking action on the bars that provide access to the road downstram of the toll houses, it will be possible to control the flow of traffic entering the tunnel by computer with a suitable program, on the basis of the traffic flow in the tunnel.
General Design Criteriafor Ventilation The
37.8'-km
undersea
section is
divided into three sections by the provision of two islands, located outside the main shipping lanes, containing ventilation shafts and the necessary equipment. The tunnel section lengths are given in Fig. 3. Figure 2 details the tunnel crosssectional arrangement from which a 68.54-m 2 free cross-sectional area above the road deck has been calculated. The air flow velocity restriction recommended by PIARC thus gives an available longitudinal air flow volume value that has been used in the assessment of 650-700 m3/s. On the premise that the use of electrostatic precipitators effectively negates the necessity for air flow rates for smoke dilution the maximum permissible longitudinal air flow quantity of 650 m / s will control CO and NO emissions from 3000 vehicles per h, doWn to a speed of 20 km/h for the tunnel sections near France and near the English cast; and down to a speed of 62 km/h for the central section. By reducing the traffic volume, emissions at lower speeds can be controlled in the central section; however, given the predicted future reduction in exhaust emissions, the design traffic volume can be accommodated down to a speed of 22 km/h. The general fluid dynamics equation under continuous operating conditions for a single tube, expressed in terms of pressure with respect to a reference pressure, is as follows:
A PR + APt + APm + AP~ + APH+ PB~ APF++AP~+Hv+H8 P~
266 TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
(l)
in which the various terms have the following meaning: APR=Variation in pressure due to frictional resistances along the tunnel, including the intake and exhaust shafts. APe=Variation in kinetic pressure due to variations in the speed of the air along the tunnel sections. APt=Draught of the shafts. APm=Piston effect due to the vehicles moving in the direction of the air (speed of air). APw=Action of the wind on the tunnel portals, on the intake or on the outlet sections of the shafts. APH=Variation in barometric pressure between the portals on the intake or outlet sections of the shafts. APBa=Pressure drop in the air cooling coils. Apyl=Pressure drop in the filtration stations. AP~=Pressure drop in the sound attenuators. Hv=Fan total pressure. HB=Booster fan total pressure. Equation (1) is valid for the case in which all of the aforementioned fluid dynamic resistances are in series. In evaluating the total fan pressure, the portion accounting for the Saccardo effect is included, and corresponds to the pressure required to introduce air into the tunnel section. The Saccardo effect induces a thrust on the air in the tunnel and is effective over certain calculated lengths. Booster fans are provided between precipitator stations to maintain
Volume 1, Number 3/4, 1986
the air flow along the tunnel. Booster fans are also provided in the sections of tunnel in which the air flows are normally induced by the Saccardo effect from the main supply fans and the precipitator station fans. Figure 6 shows a ventilation circuit for one tube section, from supply fan inlet to exhaust fan outlet, divided into segments each allotted segment number. Equation (1) may be written and solved for various segments of the section under consideration. Values are established for the allowable smoke concentrations and for the filtration efficiency of electrostatic precipitators along the tunnel. By applying the mass balance equations to Segment 4-5 of the tube, including the filtering station (see Fig. 6), it is possible to deduce values for the tube sections between the stations along the tunnel. Figure 5 represents a solution for one filtering station. The air in the tunnel is heated and its temperature raised due to heat released from: (1) the flow of cars and trucks; (2) the ventilation equipment (3) the electrical equipment in the tunnel; and (4) the lighting and signalling equipment. For the design traffic flow M=2000 Veh/h, the greatest heat is contributed by cars and trucks.
Though the solution provided by the thermal balance equation is written for an infinitesimal segment of the tube, it is possible to obtain the air temperature trend along the tube. In Fig. 7, line (a) represents the temperature distribution in one section of the tube. Since the air temperature in the tunnel would reach high values which could not be tolerated, it is necessary to provide a cooling plant to reduce the air temperature. This cooling process is performed by a chilled water system utilizing a refrigeration plant. The chilled water feeds coils provided at the intake points of the supply air fans and at selected filtering stations along the tube (see Fig. 7). Line (b) in Fig. 7 illustrates the air temperature trends due to this cooling process and identifies the position of the cooling stations necessary to obtain an air temperature of less than approx. 30°C. Safety and Operation Criteria Safety in road tunnels can be defined as the ability of the tunnel operator to inform the users properly of driving conditions in the tunnel; to obtain information quickly about any anomalous event occuring in the tunnel; and to .9o ~4 o.
(~ ~ F.A, fan. / /
D.A. fan (
Booster ~ Fitt stotion
__ 2 " L r
3 4 I AI ]
5 I
[
6 7 I' I AI I
~. II
"
;
-- ; 2
:1
!i ;:
3
2'
Figure 6. Ventilation scheme---reference sketch for equation (1).
59.3"C f
50.
J
E
E
(a)
O
40 ,.tO
/
OJ
30
/
,¢
28.7* ....
~
_39*
300
30*C
(b).' 20.
_
~15"C IO
o
18.5 °
3750 I
2
18.5"
18.5 °
150011500150C 150C 150011500 50C 1500 1500 too6 3
FiLtering stations Refrig. stations
I -=
2 -= 12
3-=
4-=
5° 22
6-=
7-=
8-= 9-= 3 -=
18 18.750 km
102
Figure 7. Mid-Channel section of tube 1: air temperature trends with (a) and without (b) refrigerating stations.
Volume I, Number 3/4, 1986
transmit information and instructions to meet the new, changed conditions of traffic, while at the same time adopting the appropriate measures to remove the causes of the trouble. The type and quantity of the equipment to be installed for this purpose are mainly related to the tunnel length and the traffic volume expected therein. It is evident that the longer a tunnel is and the heavier traffic conditions are, the higher are the risks of accident, fire traffic stoppages and slowdowns. Tunnels in Japan are classified into five classes according to their length and traffic volume. The longest and more trafficked tunnels belong to class AA: these need to be suitably equipped to provide the best protection to the users and service personnel, as well as to the tunnel structures and installations. The Channel Tunnel would belong to class AA. Each of the two tubes will be provided with two control rooms----one for each portal--manned around the clock. Safety equipment and signals--which are a constituent part of the safety facilities--would be placed along the tunnel, spaced at intervals equal to multiples or submuhiples of 500 m, this being the distance between the crosspassages connecting the two tubes of the road tunnel. Consequently, green arrows and red crosses above each land would be installed every 250 m--i.e, at every crosspassage and halfway between the crosspassages. The green arrows switched on advise that the lane is open, while the red crosses indicate that the lane is closed. Flashing amber arrows instruct the drivers to shift to the lane open to traffic. Whenever a lane is not usable because of road works or other obstructions, the prescribed signals for works are indispensable. Signs that must be repeated, e.g. speed limit, no parking or waiting will be installed every 2000 m. Telephones, essential for safey, would be installed in emergency recesses 2 m high, 2 m wide and 1 m deep, clearly marked and well-illuminated; and would be provided with dust-tight glass doors to keep them clean in the usually dusty and dirty road tunnel environment. Opening the door of a telephone recess switches on a flashing yellow light over it. One recess will be located near each cross-passage; another two will be placed between one cross-passage and the next; hence, a recess will be located every 167 m, i.e. at a distance equal to one-third of 500 m. The operator at the control room will be able to see on a display panel the location of the telephone where the call is coming from. It is also convenient to install alarm buttons, fire extinguishers, hydrants and power sockets into emergency recesses. Additional alarm buttons also could be installed halfway between recesses. In this case also, the operator in the control
TUNNELLING AND UNDERGROUNDSPACE TECHNOLOGY 267
room can pinpoint the location the alarm comes from. Another facility essential to safety is closed-circuit television. The TV camera would be installed at 250-m intervals, i.e. at every cross-passage and midway between cross-passages. This distance can allow a good general view of the traffic. Reduced spacing would require an excessive number of cameras. In each control room, a single monitor would show the pictures taken by 12 TV cameras, thus reducing to 16 the number of monitors, not counting those connected to the cameras located outside the tunnel• This CCTV system would be linked to other safety facilities (alarm buttons, telephones, fire extinguishers and detectors, traffic detectors). In the case of an alarm given by any of these facilities, the monitor--usually the one connected with an external camera-would automatically show the area involved. A radio installation would also be provided so that drivers in the tunnel can listen to two radio stations, one transmitting in English and the other in French. The installation would also be used for service communications (operation, fire brigade, ambulances, etc.). Signs at the tunnel entrance would give drivers information about the frequencies that can be tuned in inside the tunnel. The operator at the control room can introduce messages for the drivers on these same wave lengths, giving necessary information, advice and instructions. Listening to the radio can make less tedious the time spent driving in a tunnel. This becomes a very important factor when the tunnel is so long. For the same reason, two different types of lighting systems are to be provided which would alternate every 6 km (approx. 5 rain drive). One system consists of 36W fluorescent lamps arranged along two continuous rows; the other, of 250W high-pressure sodiumvapour lamps, placed 10 m apart, arranged alternately in two rows i.e. at 20-m intervals on every single row. The roadway and walls would be finished with light colours and the wall color would change every 6 kin. A 100-m-long transition zone separating each and a km-long tunnel section would be lit by means of 400W high-pressure sodiumvapour lamps arranged in three rows, thus creating intensely bright "sunlight windows (400 cd/m 2, as opposed to 14 and 15 cd/m 2 in the 6-kin-long tunnel sections). Thus, drivers would have--both physically and psychologically--the vivid impression of driving through a series of different tunnels. Two (2) fire extinguishers, of the power type and with a unit capacity of 6 kg, would be placed into the emergency recesses. Hydrants, connected to the water mains under pressure, would have a pressure at the outlets of 6-7 atm. and a flow of 1200 l/min. Fire detectors installed in separate single units would
send to the control room an alarm of any temperature rise exceeding a certain value. Nevertheless, this type of tunnel must have its own fire-fighting organization, with staff and equipment permanently available on the spot. At the beginning, a fire is almost always small: therefore, prompt action is essential• The presence at each portal of trained firefighters and special equipment can prevent, in most cases, the development of a dangerous fire. Naturally, in particularly serious contingencies, action by local fire brigades from both countries would be necessary• The operational staff for the Channel Tunnel would consist of 36 people at each tunnel portal for traffic control and assistance in case of accident or fire. Thus, every portal would be covered by a team of seven people during each of the three work shifts. Every hour the tunnel would be inspected alternatively by two patrols of two people each, who would drive a fast vehicle---a motorcycle or Land Rover-and carry temporary signs, as well as fire-fighting and rescue equipment. Therefore, during each eight-hour shift, four people would be in charge of surveillance for each portal. Another three people would be available at the portals, along with other specially equipped vehicles ready to intervene in case of emergency, e.g. fire or accident. The adoption of strict traffic regulations would limit the transit of hazardous material through the tunnel, allowing only those goods for which the level of risk is reasonably acceptable. A speed limit of 100 km/h was proposed for cars; and a speed limit of 80 km/h for trucks and for coaches with more than nine paying seats• The speed limit proposed for commercial vehicles carrying hazardous materials would be 60 km/h. A long tunnel such as this one inevitably implies the provision of two separate managing centers, at the English and the French portal, respectively. Each center would have its own operational department (equipment and installations, safety facilities) and administrative offices (accounting, purchase and warehouse, toll, EDP center). • The formation of operational teams including personnel from both countries is never--as our experience has proven-an advisable solution. This is due not only to the difficulties arising from having to move throughout such a long tunnel, but also to the actual differences in language, attitudes and work practices. Therefore, a fair distribution of functions among the personnel from both countries, assigning them duties and responsibilities in a well-balanced form, must be provided. In this and other areas the rule of reciprocality must be carefully respected. The staffworking at both portals must be numerically equal and their distribution, based on their specific duties, should be
268 TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
similar. Insofar as the operational services are concerned, the duties would be divided on the basis of common instructions, among the personnel assigned to each portal, who should look after the maintenance and safety of the tunnel mid-section adjacent to their respective portal. The operational procedures concerning the technical services and safety facilities, as well as those regarding trafic regulations, should, of course, be the same. Each control room will provide for the surveillance of the entire tunnel. Traffic controllers, who would be required to speak both languages, should maintain mutual contact and act in agreement. In addition, the administrative staff would follow common instructions despite the different accounting and fiscal procedures in force in the two countries. []
Acknowledgements Warmest thanks to Sea Containers Ltd for having allowed this presentation at the Seikan Colloquium, and personal thanks to company President Mr J. B. Sherwood and Vice-President Mr D. K. Bray for their contributions to the project.
References Baba, T. and Okano, K. 1982. Ventilation system of the Tsuruga Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield,
ed.) pp. 367-382, 403-420. Baba, T., Ohashi, H. and Nakamishi, F. 1979. A new longitudinal ventilation system using a electrostatic precipitator for long vehicular traffic tunnel. Third International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, 1SAVVT, Sheffield, 1979 (BHRA, Cranfield,
ed.), pp. 201-226. Baba, T., Ohashi, H. and Uesaki, K. 1982. Aerodynamic specialities in connection with the Tsuruga Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield, ed.).
pp. 403-420. Baba, T., Ohashi, H., Nakamichi, F•, Inami, E. and Akita, I. 1985. Recent trends in ventilation systems of long vehicle tunnels in Japan. Fij2h International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, Lille, 1985 (BHRA Cranfield, ed.), pp. 371-388. Channel Tunnel Study Group. 1966. Channel Tunnel: Site Investigations in the Strait of Dover 1964-1965, Vols. I-IV.
Destombes, J. P. and Shephard-Thorn, E. R. 1971. Geological results of the Channel Tunnel site investigations. 1964-1965 Report 71/ 11, pp. 1-11. Institute of Geol. Sciences, HMSO. European Economic Community, 1970. Directive 70/220/EEC, Journal L76. European Economic Community, 1985. Directive Proposal 85/C, 245/01. Gould. H. B., Jackson, G. O. and Tough, S. G. 1975. The design of the Channel Tunnel. Struct. Eng. 53: 45-62. Grance, A. and Muir Wood, A. H. 1970. The site investigations of the Channel Tunnel. Proc. Inst. Civ. Engrs 45: 103-123.
Volume 1, Number 3/4, 1986
Morgan, M., Barratt, D. A. and Tilley, D. H. 1977. The tunnelling system for the British section of the Channel Tunnel, Phase II Works. TRRL Laboratory Report 734, pp. 1-56.
Ohashi, H., Mizuno, A., Nakahori, I. and
Volume l, N u m b e r 3/4, 1986
Ueki, M. 1983. A new ventilation method for the Kan-Etsu Road Tunnel. Fourth International Symp. on the Aerodynamics and Ventilation of Vehicle Tunnels, York, 1982 (BHRA, Cranfield, ed.), pp. 31-47. Pischinger, R. and Schweiger, H. 1985a.
Determining exhaust emission of motor vehicles in tunnels. Fifth International Syrap. on the Aerodynamics and Ventilation of Vehicle Tunnels, Lille, 1985. (BHRA, Cranfield, ed.), p. 405. Pischinger, R. and Schwieger, H. 1985h. lbid, p. 395.
TUNNELLING AND UNDERGROUNDS,PACE T~'-CHNOLOGY 269