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Design of the shield tunnel for the trans-Tokyo bay highway
TUNNELS AND DEEP SPACE
Design of the Shield Tunnel for the Trans-Tokyo Bay Highway Keinosuke Uchida, YuJirou Wasa and Makoto Kanal
A b s t r a c t - - T h e Trans- Tokyo Bay Highway projeet is the first phase of an ambitious plan to connect Kawasaki and Chiba by a 15-kin crossing of Tokyo Bay. The crossing invovles a 5-kin bridge, a 10kin undersea tunnel, and a manmade island in the middle of the bay. The construction method for the undersea tunnel must take into account the large external diameter of the primary lining (approx. 14 m) ; the extremely soft ground under the sea; the extremely high water pressure to which the tunnel will be subjected;and active seismic conditions in the Tokyo Bay area. This paper discusses the slurry shield tunnelling method adopted for the undersea tunnel portion of the project.
1. Introduction T he Trans-Tokyo Bay Highway (TTBH) is a 15-kin toll road, exclusively for vehicles, that will connect Kawasaki City with Kisarazu City by tunnel, bridge and manmade island across Tokyo Bay (see Fig. 1). The Highway structure will consist of two 10-km-long undersea tunnels and a 5-km long bridge, with two manmade islands in between. The trunk highway system in the Tokyo metropolitan area is composed of the Tokyo Bay Coastal Highway, the Metropolitan Central ConnectingHighway, the Tokyo Outer Loop Highway, and the Higashi Kanto Expressway (see Fig. 1). As the keystone ofamajor highway network, the Trans-Tokyo Bay Highway willcomplete the loop ofhighways circlingTokyo Bay; and will also function as a by-pass around the central Tokyo area. The entirestructurewillform part of a planned ~figure-eightYroad concept aimed at solving problems of overcrowded housing, physicaldistribution, and lifestyleresultingfrom Tokyo's con centrated urban structure. The construction of the T]?BH will contribute
Present address: K. Uchida and Y. Wasa, Tunnel Design Section, Design Department, Trans-Tokyo Bay Highway Corporation, Ichibancho NN Bldg., 15-5 Ichibancho, Chiyoda-ku, Tokyo 102, Japan; M. Kanai, TTB Kisarazu Tunnel J.V., Ohbayashi Corporation, 2-3, Kanda-tsukasa, Chiyoda, Tokyo 101, Japan
greatly to increased economic activity in the south Kanto area, especially among manufacturers and service industry firms. This wide-ranging vision takes in the entire Tokyo Bay area. The Trans-Tokyo Bay Highway is an offshore project in which factors such as the unprecedented construction scale,difficultnatural conditions (including geological, meteorological, and seismicproblems),and severe planning restrictions(including congested marine navigation and environmental protection) must be overcome. The project is outlined in Table 1. Constructionon the SUS8.5-billionproject began in 1989, and is scheduled for completion in 1996. The undersea tunnels will be built from the Kawasaki side,where navigation trafficis congested. The shallow section on the Kisarazu side, where boat trafficis sparse,willbe crossed by a bridge (see tunnel-bridge profilein Fig. 2). The Kisarazu m a n m a d e island willform the junction between the tunnel and the bridge. This island also will provide the launching base for the shield-driventunnel, and will support the highway transitionfrom tunnel to bridge. Ventilationtowers willbe built on the Kisarazu island. At the center of the tunnel section, the Kawasaki m a n m a d e islandwillform a launching base for the shield tunnel (see Fig. 3). A ventilationtower and monument will be erected on this island. The Ukishima vertical shaft will be built at the landfall on the Kawasald side. This shaft will serve as a launch-
Tunnelhngand UndelgroundSpaceTechnology,Vol. 7, No. 3, pp. 251-261, 1992. Printed in Great Britain.
Rdsumd---L'autoroute Trans-Tokio-Bay est la premiere ~tape d'un plan ambitieux qui a pour but de connecter Kawasaki 6 Chiba, en trauersant la bale de Tokyo. Le projet inclut un pont de 5 kin, un tunnel sous-marin de 1Ohm et u ne ZleartificieUe au milieu de la bale. La m~thode de construction utilis~e pour le tunnel dolt tenir compte du diam~tre int~rieur important du rev@tement primaire (d peu pros 14 m); du terrain extr~ment peu consolid~; de la pression d'eau considerable ~ laquelle le tunnel sera soumis; et des conditions sismiques actives dans la bale de Tokyo. Le present article discute la m~thode de creusemen t util is~epour la partie sous-marins du projet, savoir un bouclier ~ la bentonite.
0886-7798/92 $5.1t(t + .00 © 1992 Pergamon Press Ltd
ing base for the shield tunnel, and will also have a ventilation tower.
2. Natural Restrictions and Planning Conditions 2.1. Topography and Geology (Fig. 4) The topography of the seabed along the planned highway link is extremely gentle, generally conforming to the shape of a ship's hull, with a maximum depth of approximately 28 m. Geologically, from Ukishima on the Kawasaki side to the center of the Bay, there is a very soft 20- to 30-m-deep layer of alluvial soil, known as the Yurakucholayer; on the Kisarazu side, a relatively dense sand layer has accumulated from the surface. The upper stratum of the Kazuza formation, a sandy layer with an N-value greater than 70 at depths belowTP-80 to-90 m, is considered tobe a suitable bearing stratum for engineering designs. Along the tunnel route, the geolog~ mainly consists of alluvial and diluvial clay soil layers on the Kawasaki side, with a diluvial sandylayer sandwiched between the two. The Ukishima and Kisarazu ramp sections are on reclaimed land.
2.2. Marine Navigation Tokyo Bay encompasses four ports of special importance (Tokyo, Kawa-saki, Yokohama, and Chiba ports), as well as other ports (Yokosuka and Kisarazu ports). There are many vessel movementsbetween various ports within the Bay, in addition to the vessels entering
251
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Figure 1. Tokyo's metropolitan highway network (Trane-Tokyo Bay road in center).
Table 1. Main features of Trans-Tokyo Bay Highway. Name of road: Route designation: Section: Total length: Design speed: Design load: Width, number of lanes: Construction: Total project cost: Construction period: Planned traffic volume:
Trans-Tokyo Bay Highway National Highway 409 From Ukishima in Kawasaki to Nakajima in Kisarazu 15.1 km 80 km TL-20t and "1-1"-43t 3.5 m x four lanes; two lanes in each direction, to be expanded to six lanes (three lanes in each direction) in future Tunnel, bridge and artificial island Approx. Y1,150 billion About 10 years from fiscal 1986 64,000 vehicles/daytwenty years after construction (33,000 vehicles/day upon initially entering service)
252 TUNN~J.~a ANDUNDE~ROUND SPACETECHNOLOGY
2.3. Earthquake Activity Earthquake activity is common in the Tokyo Bay area. It is believed that 32 major earthquakes occurred in the Bay area in the period from 818 to 1867 A.D.; since 1868, 23 damage-causing earthquakes have occurred. The great K a n t • earthquake of 1923 is representative ofthese major earthquakes. Figure 5 shows the epicenters of large earthquakes (i.e., those having a magnitude greater than 6.5) t h a t occurred between 1885 and 1979 within 300 k m of the TI~BH site.
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and leaving the bay. The ports handle nearly 450,000 vessels ~nnually. The types and shapes of the vessels are also diverse. In 1982, about 744 boats per day passed through the Uraga strait, and this figure has remained constant in recent years. A survey on the actual conditions in the Bay counted 1274 boats per day in the area in November 1982; more than 90% of these were concentrated in the 10-kin section on the Kawasaki side.
3. Outline of the Project 3.1. Selection of Tunneling Method Highway tunnels under the seabed traditionally have been constructed using the sunken tube method. However, the enormous advances in shield tnnneling techniques as a means of b~nnelingin urban areas in recent years suggested t h a t this method might be feasible, particularly given the following conditions for this tunnel site: • Large tTmnel diameter (13.9 m external dia.). • Great water depth, resulting in very high water pressure (5-6 kg/cm').
° Small overburden ( 6 . 4 - 9 . 4 m at access slope). ° E x t e n d e d l e n g t h of t u n n e l (2,000-3,000 m). Other advantages of the shield tunneling method are the ease of constructing additional tunnels, and the relatively minor disruption of navigation, fisheries and the environment during construction. In consideration of all these factors, the shield t~mnel method was chosen for this project instead of the submerged method, bearing in mind possible future traffic volumes and overall profitability. To ensure face stability and safe t~mneling operations with no danger of water influx, the slurry shield method was selected from the variety of tunneling tech nlques available, because it is the most compatible with the construction plan. The plan involves using the two-way advance method and launching t - n n e l s from different locations using eight shield m a c h i n e s - two each from the U k i s h i m a and Kisarazu vertical shafts, and four from
Volume 7, Number 3, 1992
Plan Ukishima access K a w a s a~ l k i c i ~ y~ /
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Figure 2. Plan and profile of the Trans-Tokyo Bay Highway project. the Kawasaki ventilation tower, meeting under the bay at points midway between the shafts. 3.2. Basic Construction
3,2.1. Longitudinal alignment and tunnel dimensions The longitudinal alignment (see Fig. 4) was chosen to ensure stability of the required overburden against upli~ing, as well as to maintain the drAinsge slope in the t-nnel. In addition, the gradient of the ramps was fixed at 4% to suit the approach road alignment,
the size of the rnAnrn~de island, the flow ofvehicles, and other factors based on road construction standards. The plane alignment was determined to be 1.0 D (D ffi outside diameter of tnnnel) in clearance for the general section, in consideration of the effect from the juxtaposed tlmnel; and 0.5 D in clearance for the joint section to the vertical shait of both slipways, in consideration of the quality of the mAnmAE]e ground. The tnnnel section (see Fig. 6) is designed to accommodate a two-lane carriageway and the ventilation facili-
ties, etc., as well as to include road safety equipment such as emergency parking zones. The provision of extra emergency parking zones, involving partial widening of the tnnnel, presented problems not only in terms of design and construction, but also from the point of view of construction cost andperiod. Therefore, instead of emergency parking zones, a 2.5-m-wide left shoulder will be created throughout the length of the tlmnel. In further consideration of the need for traffic information signs and accident prevention systems, and after
Figure 3. Artist's rendering of a cutaway view of the Trans-Tokyo Bay Highway tunnel, as it passes through the Kawasaki manmade island.
Volume 7, Number 3, 1992
Tu~-~.~.ma ANDUNDERGROUNDSPACETECHNOLOGY253
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absorb deformations of the tunnel in the axial direction resulting from ground settlement and earthquakes. It will be necessary to develop a method of lining the joints between vertical shafts and the tunnel, and the other undersea joint. Stable progress of parallel shields must be maintained (separation:0.5 D at ramps and 1 D over the seabed section) with a large face (about 14 m in diameter) under conditions ofhigh water pressure (5-6 kg/cm~), extremely thin overburden (0.7 D at the ramps and 1.0 D over the seabed section), and extended length (2,000-3,000 m), even with two-way advance). This will require fabrication of large-diameter shields that are durable and that have good abrasion resistance and watertightness. Finally, the work must be accomplished rapidly and automatically in order to adhere strictlyto the construction schedule.
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Figure 5. Earthquakes of magnitude >_6.5 that have occurred within a 300-km radius of the center of Tokyo Bay from 1885 to 1990. adding an inspection walkway, the final internal diameter of the tunnel was determined to be 11.9 m (13.9 m external diameter). This diameter provides a highway with the same width inside and outside the tunnel, unlike conventional tunnels, so t h a t driving into and through it should be a very comfortable experience.
The lining system and joint construction must minimize the possibility of problems such as deformation, and cracking, and must provide improved watertightness and durability. In addition, the lining system must
A stable shield operation must be ensured under a thin overburden and through reclaimed ground to prevent uplifting of the tunnel. The mechanical constants of the reclaimed ground will have to be determined in order to calculate the external force on the lining. Because the tunnel excavation has to proceed through filled ground, particular problems with abrasion resistance of the face plate rim and the outer bit m u s t be resolved.
650 350
3.2.2. Ventilation system
The tunnel will be ventilated through towers to be built at the Ukishima access section,on Kawasaki m a n m a d e island, and on Kisarazu m a n m a d e island (See Fig. 7). Taking advantage of the technologicalinnovations of recent years, a vertical shaft air feed and exhaust ventilation system using electricdust collectorswill be fitted (see Fig. 8), as has been done in other large tunnels such as the Kanetsu Tunnel. This system has resulted in reduced maintenance and management costs. 3.3. Tunnel Features
The main features of this tunnel with respect to design and construction are described below. 3.3.1. Long, parallel tunnels, constructed under difficult conditions
The large-diameter tunnel isin deep water, with only a small overburden in soft ground.
Volume 7, Number 3, 1992
Invert
Figure 6. Tunnel section configuration.
TUNNELLING AND UNDERGROUND SPACE TECHNOIX)Gy
255
Figure 7. Construction of the Kawasaki manmade island, which will include a ventilation tower.
3.3.3. Ventilation system Additional study will be required to determine the enclosure, layout, methods of maintenance, control, and ventilation efficiency of the various aspects of the vertical flow ventilation system with circular shield section.
4. Tunnel Design Tunnel design conditions are shown in Table 2. The Trans-Tokyo Bay Tunnel is without precedent in the sense that it is very large in both physical and technical scale. In addition, construction is in extremely soft ground under deep water in an earthquakeprone area. In order to succeed with this colossal project, we dare not simply extend past design principles. Nevertheless, careful study of past experiences has been undertaken. An examination committee was established for each structure to undertake technological surveys and studies. These committees selected the optima] structure type, fixed the design criteria, examined the seismic response, elucidated the normal behaviors, and chose the optimal design and construction method for each item, while also surveying and examining the technological problems arising from the special regional characteristics of Tokyo Bay.
4.1. Design Method for Primary Lining This tunnel has a large cross-section in comparison to conventional tun-
nels, and is to be constructed near the border between the soft alluvial and the diluvial undersea layers. Therefore, in designing the lining, it was necessary to verify the assumed value ~ ~, as commonly usedin calculations (assuming a ring with uniform flexural rigidity) using the beam spring model (i.e., a ring model including spring in the joint to represent the dynamic properties of the joint). The spring constants KO and Ks were chosen by referring to the results of a full-size bending test on a segment joint (with axial force) and a shearing test. Basedon theseresults, asegment with a core-type joint (joint reinforced with a ribbed anchor plate) and a long bolt was found to be sufficiently safe, despite using the conventional TI assumption in the calculation. Figure 9 shows the structural analysis model of the lining selected.
4.2. Load Conditions (see Table 3) The pressure of the ground in the tunnel periphery was assumed to be soil and water combined against clayey soil layer for original ground; soil and water separately against the sandy layer; and soil and water combined for manmade ground, to give the design a safety margin. The ramp tunnel passes through reclaimed ground. Although the overburden is small, the ground strength is high; therefore, resistance can be anticipated. To consider the reclaimed ground and the natural ground around it, a
256 TUNNELLINGANDUNDERGROUNDSPACETECHNOIA)GY
two-dimensional elastic FEM analysis was undertaken with the maximum bending moment as a parameter, and the coefficient ofsubgrade reaction and the coefficient of lateral pressure were found to be *c= 3.5 kg/cm and k = 0.6, respectively. To verify experimentally the magnitude and distribution of the external forces acting on the tunnel and the level of ground stress and deformation, the liningload was tested usingamodel, to determine the degree of loosening of the natural ground, the effects ofbackfillinginjection, the magnitude of coefficient of lateral pressure, and the difference in improved ground strength. The tunnel passes through natural ground over the flat seabed section, and the means of reflecting the effects of high water pressure in the calculation of combined lateral soil and water pressure in the clayey soil is open to question. However, the strength of the clayey soil led to the following judgment of lining stress conditions: Full section Ac layer > alternate Ac and De layers > full section De layer. By referring to the literature on soil properties, design experience and spedfications, the coefficient of subgrade reaction and the coefficient of lateral pressure were found to be k = 0.800.75 and ~ = 0 (kgf/cmS), respectively, for the Ac layer; and k = 0.65 and ~ = 1.5-2.5 (kgf/cma), respectively, for the De layer.
Volume 7, Number 3, 1992
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Figure 8. Tunnel utility plan. In addition, field measurements of parallel tunnels in similar clayey ground (¢ 7.25, slurry shield, clearance 0.5 D) were carried out, verifying the above assumption from data regarding the primary lining (in transverse and longitudinal directions) and the disturbance in the peripheral ground.
5. The waterproofing of the tunnel basically consists of backfilling injection of the primary lining. Secondary measures involving waterproof sheeting will be contemplated if water leakage occurs. The mix of backfilling injection material, the number of sealing stages, the shape, the type, and the material will be determined after oh-
4.3. Lining Construction
Figure 10 shows a section through the t u n n e l The primary lining of the tunnel basically consists of reinforced concrete plate segments 13.9 m in outside diameter, 1.5 m high, 0.65 m thick, and divided into 11 sections (the key segment is the axial insert type). The secondary lining is 0.35-m-thick castin-place reinforced concrete, mainly for the purpose of adding weight and protecting the primary lining from fire or explosion. The lining design is based on the following basic concepts: 1. Full-size segmentjoint tests were conducted on several types of joints to find a joint t h a t was highly rigid and durable and t h a t could be assembled automatically. A core-type joint section reinforced with a ribbed anchor plate, assembled using a long bolt was found to meet these conditions economically. 2. The primaryliningis designedto resist the total load. 3. Both the primary lining and the secondary lining are to be corrosionresistant construction type 2. Based on the results of durability tests, it has been determined t h a t half the weight of the necessary cement for the RC segment will be replaced by blast furnace slag. 4. The secondary lining is designed to resist dead weight and water pressure only.
Volume 7, Number 3, 1992
taining the results of waterproofing tests on the tunnel. 4.4. Effects on the Tunnel of Ground Deformations under the Tunnel
In the Ukishima r a m p section, it is considered possible t h a t bending deformation m a y occur in the axial direction of the tunnel ai~cercompletion as a
Table 2. Design conditions for the Trans-Tokyo Bay Highway.
Internal section: Lining:
Length: Alignment:
Clearance: Uplift safety factor: Overburden: Water Depth: With Pressure: Excavated Soil:
Final inside diameter, 12.6 m Primary lining; outside diameter 13.9 m, inside diameter 12.6 m, thickness 1.5 m Secondary lining, thickness 0.35 m 9.1 km (4,600 m on Kawasaki side; 4,510 m on Kisarazu side) Longitudinal: Ramp section 4% (maximum highway gradient) Flat seabed section 0.2% (for drainage) Curved grade section: R=10,000 m (for mitigation of congestion) Plane; R=3,400 m (one location each on Kawasaki side and Kisarazu side) Seabed section 1.0 D (D: outside diameter of tunnel); Both ramp sections before vertical shaft 0.5 D More than 1.25 when completed; More than 1.1 during construction Ramp section, 6.4 m-9.4 m; flat seabed section, 16.0 m (average) At seabed section, 27.5 m on average At tunnel center, 6 kgf/cm 2 Reclaimed land at ramps Flat seabed section: alternating layers of alluviai and diluvial clayey soil and sandy soil
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY2 5 7
result of the deformation of the diluvial clayey soil layer under the filling due to the load from the stabilization filling. Therefore, deformation at the tunnel center and a cross-sectional force on the lining are expected to occur. It was calculated that elastic deformation and primary consolidation deformation would be complete by the time the shields are launched, and that the residual deformation resulting from secondary consolidation would reach about 6 crn one hundred years after completion of the tunnel at the access section of the vertical shaft. The maximum bending moment resulting from this deformation and from an earthquake will occur at the access section of the vertical shaft. However, it was discovered that if a flexible design is implemented at that point, durability would be assured because the maximum bending moment would be about 60 times the bending strength of the tunnel. To absorb the deformation at this point, a flexible segment will be used in the primarylining, and a bridging construction in the secondary lining and floor slab.
4.5. Peripheral Ground and Stability of the Tunnel At the accesssection of the Ukishima vertical shaft, a minima] overburden of only H = 6.4 m (H/D = 0.46) can be secured as a result of the tunnel alignment. Therefore, it was decided to secure the required safety factor (Fs > 1.1) against lifting during construction by considering shearing resistance of the manmade and natural ground. The required safety factor at the time of completion (Fs > 1.25) was found to be secured by considering the deadweight and the weight of overburden only.
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Figure 9. Tunnel analysis model. To ensure stable shield excavation through the ground, and based on past data in these construction conditions, the unconfined compressive strength q u and wet unit volume weight were . . . selected as the determining properties of the reclaimed ground. These were prescribed as 6 kgf/cm2< q < 30 kgf/cm~ (target approx. 10 kgf/cm2), ~t > 1.8 tf/m 3.
1. Earthquake motion anticipated within the life of the structure (L1). 2. Earthquake motion likely to occur only very rarely (L2), such as the Great Kanto Earthquake. The structure should not suffer any damage that impairs its transportation function when an L1 earthquake occurs, and it should not suffer damage that results in flooding or total collapse in an L2 situation. As a result of aseismic studies on the tunnel thus far, the following basic policy for aseismic design of the tunnel has been prescribed: • The ground in the tunnel area will not liquefy or turn into siurry. Therefore, no special measures, such as groundimprovement, will be necessary on the existing ground.
5. Earthquake R e s i s t a n c e Because of the active seismic nature of the site area, an aseismic tunnel design was chosen. In addition, earthquake response analysis usingthe response displacement method was necessary to ensure tunnel safety. In choosing the earthquake characteristics to input into the earthquake response analysis, two concepts were introduced:
Table 3. Soil properties and load factors at the tunnel location.
Soils A A D D D D D Manmade
Legend:
N Blow
q kg/cm
E kg/cm
0 0 12 15-5 20 54 78
0.44 0.87 0.96
4.8-9.6 5.7-22.9 35.9-289.0 25.0-204.0
2.11 1.57
296.2 195.5
7.5-21.3
A: Alluvial C: Clayey soils N: Number of Blows by SPT q~:::Unconfined Compressive Strength Modulus of Elasticity
258 rI~JNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
ton/m 3 1.3-1.5 1.6-1.7 1.4-1.8 1.6-1.8 1.7-1.8 1.8-1.9 1.7 1.6-1.8
D: S: ~: K; k:
Water in Soils
K
0 0 1.5 0.5-4.0 2.0 4.0 5.0 3.5
0.75 0.75 0.65 0.35-0.55 0.65 0.35 0.35 0.6
Combined Do. Do. Separated Combined Separated Do. Combined
Diluvial Sandy soils Unit Weight of Soils Modulus of Subgrade Reaction Earth-pressure Coefficient
Volume 7, Number 3, 1992
Connections between the tunnel and vertical shafts will have a flexible construction in order to absorb the deformations resulting from an earthquake. To clarify the behavior of the tunnel at the border between the improved ground on the tip of Ukishimaramp andthe soft original ground during an earthquake, vibration tests were conducted using a r a m p tunnel model. As a result of these tests, it was decided to increase the strength of a certain section of the tunnel at this point using axial-strain-absorbing washer at both ends of the long belt between segmental rings, or other means, as well as to design the tunnel with a flexible structure in the axial direction. To clarify the mutual behavior of the primary lining and the secondary lining and its effect on the tunnel's seismic response, a shield tunnel lining seismic test (No. 1) was conducted. The test results led to a decision to avoid concentration of deformation in a certain joint of the primary lining by adjusting the amount of rebar in the secondary lining and by making it continuous in the axial direction. Although rigidity in the axial direction of the tunnel is increased by the secondary lining and the sectional force on the whole tunnel m a y be higher, the sectional force borne by the primary lining is somewhat lower than in a case where there is no secondary lining. However, to give a m a r g i n of safety, the joint between rings
6. Shield Tunneling Although the aim is to construct the tunnel safely and without incident using the p r e s s u r i z e d s l u r r y shield method, if any unforeseeable circumstances should arise or major changes should be needed, considerable difficulties may be encountered as a result of the high subsurface water pressure. For this reason, the shield tunneling procedure is being studied carefully to grasp accurately the present state of the technology, and to anticipate problems that may arise in the future and solutions to them. The problems faced in this design are described below. 6. I. Technological Problems Related to the Largo Tunnel Diameter
6.1.2. Design, fabrication and assembly of large-dlameter shield machlnes The premise of this tunnel design is that pressurized slurry shieldmachines will be used. The largest such machine in past experience, which was 11.22 m in diameter, was used for the construction of an adjustment pond tunnel under a street in the Hirano river water system. The main technological problems in the design, fabrication, and assembly of a shield machine with an outside diameter of 14.14 m concern: • Reliability of the soil seal and bearing that are to be fabricated in sections and then assembled. • Supporting the cutter face plate so that it does not impose an
6.1.3.Controlllng the stablllty of • large face Because the diameter of the tunnel is large, the face consists of diverse soil layers. These layers differ not only in mechanical and physical properties, such as water pressure, strength, stability, and particle size composition, but also in the direction of excavation. In addition, because the excavation has to be carried out under a thin overburden, the usual ratio of water level to ground depth is reversed. To maintain stable progress under these conditions, itis considered essential to have a highly automated statistical management method that can measure, analyze, and display a variety of excavation dataon-line andinreal time, so that decisions can be made about: • Optimum slurry pressure. • Factors t h a t govern the quality of slurry. • Volume of excavated soil • Optimum excavation standards t h a t satisfy requirements of face stability and excavation speed. In some special locations ground freezing techniques will be used to: 1. Secure stability of the face in the launching section and ensure tightness until the shield passes the entrance packing. 2. Secure stability and water tightness where underground junctions are opened. Backfill grout hole
3 969.83 -/
excessive load on the soil seal, bearing, or bulkhead. The need for rapid assembly in the vertical shaft, and ensuring accuracy aider assembly.
will be designed to resistthe sectional force, which would not be on the primary lining only.
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Volume 7, Number 3, 1992
a~
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TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY2 5 9
However, because it takes time to achieve these effects, a combination of ground freezing and the mechanical underground junction method is now being investigated as a way to shorten the construction period without compromising reliability.
6.1.4. Construction technology for a deep, large-diameter shield method The construction techniques t h a t need to be developed and improved in the construction of this t - nnel include: • Automation (e.g., in advancing and excavation, transport and disposal of excavated material, assembly of lining, alignment control, material flow control). • Disposal of excavated material (continuous removal of sand and gravel from the cutter, continuous discharge of sand and gravel from the b-lkhead, transport and disposal ofvol-ml-ous excavated material). • High-speed construction (highspeed advance, high-speed lining). • Lining construction with ratiohal joints (adequate rigidity and strength for the ground conditions, easy and quick assembly, compatible with automation).
6.2. Technological Problems Related to Tunnel Depth 6.2.1. Pressure proofness and waterUghtness of shield machine Until now, the greatest depth experienced with a closed-face shield machine was in construction of a water conveyance tunnel for the Waterworks Bureau of N a r a Prefectural Office (shield diameter 3.950 ram), with a maximum overburden of 135 m and a 110-m mAximuIn head. Because the mRximllIn head in this case is about 60 m, the factors t h a t have to be taken into consideration in the design and fabrication of the shield machines are: Strength of shield body. In the case of the adopted segments, because the ring width is 1.5 m and the key segment is inserted in the axial direction, sufficient rigidity and strength are necessary in the tail plate, which is the weakest point in terms of external pressure. In addition, the b - l k h e a d must be able to withstand the high slurry pressure and fluctuations in pressure. Supports for moving parts. The cutter support must be such that no excess load is imposed on the b-ll~head or bearing. The bearing must be able to withstand huge face resistance. Watertightness ofmovingparts. The watertightness of moving parts such as the cutter bearing and seal is typically secured by a number of layers of urethane rubber lip-type soil seals. Although it is possible to cope with a
water pressure of about 10 kg/cm 2 at a sliding speed below 20 m/s using soil seals, when the shield diameter is large and the seal sliding speed is higher, a device that applies a bacldng pressure to the soil seal will be needed.
Watertightness of tail seal. The tail seal must be watertight and durable under high water pressure. The number of stages, the material used, the shape, and the clearance remain to be researched.
6.2.2. Waterproofing of lining construction Conventionally, linings are waterproofed at the watertight seal of the pr~mRry lining, but this technology seems inadequate for this case. At great depths and with large-diameter shields, emphasis must be placed on watertightness and corrosion resistance from the viewpoint of economy of maintenance, creating a series of waterproofing and corrosion-proof steps from the secondary lining through the primary and secondary lining interface, to the primary lining and the backfilling injection. The work described below will be necessary. In the secondary lining, the concrete must be thoroughly cured to prevent cracking due to thermal shrinkage and drying shrlnksge. At the interrace between primary lining and secondary lining, waterproofing sheets must be installed. The construction should allow easy passage of leaking water, should it occur. In the primary lining, a combination of shapes and materials for waterfight seals m u s t ensure durability. Waterproofing measures may also need to be taken in a potential water channel. The concrete must be dense and tight, w i t h r e d u c e d p e r m e a b i l i t y achieved by thorough curing. Finally, a waterproofing additive must be developed that reacts with water infiltrating through segmental joints. For the backfilling injection, a reliable instantaneous/simultaneous injection system for baclcfilling material in quantity must be developed. An additive t h a t demonstrates water-resistance even after the main member has hardened also must be developed. 6.2.3. Coping with unexpected situations near the face In the case of a closed shield construction, it is necessary for workers to operate outside the b , ikhead if any unexpected situation arises. Thus, itis absolutely essential to secure a safe worldng space despite the high water pressure. The most reliable auxiliary method possible at present is ground freezing, although this m a y result in a longer construction period. In the future, it
260 TU~TJ~n~G ANDUNDERGROUNDSPACETECHNOLOGY
will be necessary to devise a means of reducingtheinstallation time for freezing pipes and to reduce the time required for freezing to occur.
6.2.4. Removal of spoil and watertightness of the conveyance system When using the pressurized shield method of construction, the high face pressure m a y be reduced to atmospheric pressure during the process of removing spoil. Therefore, it is necessary for the removal and conveyance system to have the same degree of pressure-proofness/water tightness/ durability as specified above.
6.3. Technological (Excavation) Problems Related to Tunnel Length It is no exaggeration to say that the limit oft~mnel length is determined by the durability of the shield machine and the conveyance and disposal facilities for slurry. The m a x i m u m l~mnel length excavated in the past using a closed shield machine was in construction of the gas piping t - n n e l for the Kawagoe thermal power plant of Chubu Electric Power Company, i.e., 2.500 m (¢ 4,200 m m shield outside diameter). Because the radius of the installation, the sliding speed of the soil seal, and the cutting rate of the bit tend to increase at greater depths and with large-diameter shields, a m a x i m u m t - n n e l l e n g t h of about 3 k m i s probably realistic. A tunnel larger than this may have to be designed with an underground junction To improve the durability of deep, large-diameter shield machines, it will be necessary to: • Improve the abrasion resistance and durability of the cutter face plate and the peripheral surface. • Improve the abrasion resistance and durability of the cutter bit. • Improve the abrasion resistance and durability of all movable parts, such as the agitator. • Improve the durability of the soil seal and tail seal at high pressure. • Improve the durability of each part of the shield machine (moving parts and parts under electrical or mechanical load) • Reduce wear in the conveyance and disposal system for spoil. • Improve the technology for replacing worn parts. • Develop a highly accurate alignment control system to t~mnel accordingto the planned alignment. In the case of the T T B H t11nnel,the plan is to t-nnel for 4,700 m between the vertical shafts using shield t~mnels 2,000-3,000 m long by means of an underground junction.
Volume 7, Number 3, 1992
Fiscal Work area/ year
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6.4.2. Development of an underground jointing method In the shield work, advancing in parallel from Ukishima, Kawasaki and Kisarazu vertical shafts aims to reduce the construction period. Underground jointing is a necessary part of this plan. However, if ground freezing is adopted as an auxiliary method in the main jointing work, as in conventional practice, the period required forjointing would amount to about 10 months on the critical path. Hence, the development of new auxiliary methods and a mechanical undergroundjointing method are currently being studied to further reduce the construction period.
7. Conclusion Bridoo
Figure 11. Work schedule for the Trans-Tokyo Bay Highway Project. 6.4. New Tunneling Technology The construction of this tunnel faces unprecedented difficult conditions, involving a large-diameter tunnel (13.9 mdia.), excavated over a distance of about 9 km under the seabed of Tokyo Bay, about 60 m below water level. Because the shields will be launched from vertical shafts at Ukishima, Kawasaki, and Kisarazu in a parallel advance and will be connected by means of an underground junction, the latest shield technology will have to be used. In addition, because the tunneling work lies on the critical path for the whole project, the establishment of rapid construction technology to reduce the construction period is a major issue. Within the construction industry, there have been continuing social demands for improved safety. To meet these demands and to overcome our skilled l a b o r s h o r t a g e a n d a g i n g workforce, it is essential to standardize, increase efficiency, and reduce labor in all operations; and quality control must alsobe applied. Additionally, there is a need to improve environmental and working conditions and to avoid hazardous operations. The TTBH tunnel project is no exception to these requirements. In consideration of these circumstances, thorough research and investigation have focused on reducing the
Volume 7, Number 3, 1992
construction period (see Fig. 11) and minimizing labor requirements in the following areas: 1. Rapid construction (improvement ofexcavation speed, simultaneous and parallel work by different trades, prefabrication of structural members). 2. Use of robots. 3. Mechanical underground jointing on the basis of a highly accurate alignment control system. 4. Simultaneous construction ofprim a r y a n d secondarylinings, in order to shorten the construction period. Items 2 and 3 are discussed below.
6.4.1. Use of robots Work on automating the assembly of segments, an operation that takes place at an elevation of about 14 m, has been progressing, with the aim of completingthe operation safelyand quickly. This work involves the development of an automated conveyance and assembly system for the segments, which weigh about 10 tons each. The use of robots for piping work, which is simple and repetitive, is also considered an important issue. Particularly important is coping with the automation of segment construction, and joint construction in particular. Further research is continuing into improved methods of matching the sections.
This paper has outlined the structure, design and construction methods for the Trans-TokyoBay Highwayshield tunnel. In bringing the tunnel structure to completion, there are m a n y problems that require study, such as rational aseismic design in the soft ground, rust prevention, and an corrosion-resistant design. Amethod of interior finishing that makes driving comfortable, and formulation of a safe, accurate, and economical construction plan, are also necessary. These technical issues have been studied by the committee of the Trans-Tokyo Highway Shield Tunnel and, based on the results of their efforts, designs and redesigns for the project have been carried out. The Trans-Tokyo Bay Highway project is the core route in an expansive trunk highway network designed to handle the traffic functions of the capital region and to promote balanced development of the area. Reduced travel distances and time spent commuting will have a significant direct economic effect, and the Highway will greatly ease traffic congestion in the entire Tokyo Bay region. The TTBh has become a commercial reality twenty years after it was first proposed by taking advantage of the private sector. In carrying out this project, we are aiming at early completion while paying thorough attention to the natural environment, the city environment, transportation n e e ~ and works safety.
Acknowledgment The authors wish to t h a n k the mem bers of the Examination Committee and members of the organizations concerned for their guidance and assistance on various technical problems.
TUNNELLINGANDUNDERGROUNDSPACE TECHNOLOGY261
Design of the Shield Tunnel for the Trans-Tokyo Bay Highway Keinosuke Uchida, YuJirou Wasa and Makoto Kanal
A b s t r a c t - - T h e Trans- Tokyo Bay Highway projeet is the first phase of an ambitious plan to connect Kawasaki and Chiba by a 15-kin crossing of Tokyo Bay. The crossing invovles a 5-kin bridge, a 10kin undersea tunnel, and a manmade island in the middle of the bay. The construction method for the undersea tunnel must take into account the large external diameter of the primary lining (approx. 14 m) ; the extremely soft ground under the sea; the extremely high water pressure to which the tunnel will be subjected;and active seismic conditions in the Tokyo Bay area. This paper discusses the slurry shield tunnelling method adopted for the undersea tunnel portion of the project.
1. Introduction T he Trans-Tokyo Bay Highway (TTBH) is a 15-kin toll road, exclusively for vehicles, that will connect Kawasaki City with Kisarazu City by tunnel, bridge and manmade island across Tokyo Bay (see Fig. 1). The Highway structure will consist of two 10-km-long undersea tunnels and a 5-km long bridge, with two manmade islands in between. The trunk highway system in the Tokyo metropolitan area is composed of the Tokyo Bay Coastal Highway, the Metropolitan Central ConnectingHighway, the Tokyo Outer Loop Highway, and the Higashi Kanto Expressway (see Fig. 1). As the keystone ofamajor highway network, the Trans-Tokyo Bay Highway willcomplete the loop ofhighways circlingTokyo Bay; and will also function as a by-pass around the central Tokyo area. The entirestructurewillform part of a planned ~figure-eightYroad concept aimed at solving problems of overcrowded housing, physicaldistribution, and lifestyleresultingfrom Tokyo's con centrated urban structure. The construction of the T]?BH will contribute
Present address: K. Uchida and Y. Wasa, Tunnel Design Section, Design Department, Trans-Tokyo Bay Highway Corporation, Ichibancho NN Bldg., 15-5 Ichibancho, Chiyoda-ku, Tokyo 102, Japan; M. Kanai, TTB Kisarazu Tunnel J.V., Ohbayashi Corporation, 2-3, Kanda-tsukasa, Chiyoda, Tokyo 101, Japan
greatly to increased economic activity in the south Kanto area, especially among manufacturers and service industry firms. This wide-ranging vision takes in the entire Tokyo Bay area. The Trans-Tokyo Bay Highway is an offshore project in which factors such as the unprecedented construction scale,difficultnatural conditions (including geological, meteorological, and seismicproblems),and severe planning restrictions(including congested marine navigation and environmental protection) must be overcome. The project is outlined in Table 1. Constructionon the SUS8.5-billionproject began in 1989, and is scheduled for completion in 1996. The undersea tunnels will be built from the Kawasaki side,where navigation trafficis congested. The shallow section on the Kisarazu side, where boat trafficis sparse,willbe crossed by a bridge (see tunnel-bridge profilein Fig. 2). The Kisarazu m a n m a d e island willform the junction between the tunnel and the bridge. This island also will provide the launching base for the shield-driventunnel, and will support the highway transitionfrom tunnel to bridge. Ventilationtowers willbe built on the Kisarazu island. At the center of the tunnel section, the Kawasaki m a n m a d e islandwillform a launching base for the shield tunnel (see Fig. 3). A ventilationtower and monument will be erected on this island. The Ukishima vertical shaft will be built at the landfall on the Kawasald side. This shaft will serve as a launch-
Tunnelhngand UndelgroundSpaceTechnology,Vol. 7, No. 3, pp. 251-261, 1992. Printed in Great Britain.
Rdsumd---L'autoroute Trans-Tokio-Bay est la premiere ~tape d'un plan ambitieux qui a pour but de connecter Kawasaki 6 Chiba, en trauersant la bale de Tokyo. Le projet inclut un pont de 5 kin, un tunnel sous-marin de 1Ohm et u ne ZleartificieUe au milieu de la bale. La m~thode de construction utilis~e pour le tunnel dolt tenir compte du diam~tre int~rieur important du rev@tement primaire (d peu pros 14 m); du terrain extr~ment peu consolid~; de la pression d'eau considerable ~ laquelle le tunnel sera soumis; et des conditions sismiques actives dans la bale de Tokyo. Le present article discute la m~thode de creusemen t util is~epour la partie sous-marins du projet, savoir un bouclier ~ la bentonite.
0886-7798/92 $5.1t(t + .00 © 1992 Pergamon Press Ltd
ing base for the shield tunnel, and will also have a ventilation tower.
2. Natural Restrictions and Planning Conditions 2.1. Topography and Geology (Fig. 4) The topography of the seabed along the planned highway link is extremely gentle, generally conforming to the shape of a ship's hull, with a maximum depth of approximately 28 m. Geologically, from Ukishima on the Kawasaki side to the center of the Bay, there is a very soft 20- to 30-m-deep layer of alluvial soil, known as the Yurakucholayer; on the Kisarazu side, a relatively dense sand layer has accumulated from the surface. The upper stratum of the Kazuza formation, a sandy layer with an N-value greater than 70 at depths belowTP-80 to-90 m, is considered tobe a suitable bearing stratum for engineering designs. Along the tunnel route, the geolog~ mainly consists of alluvial and diluvial clay soil layers on the Kawasaki side, with a diluvial sandylayer sandwiched between the two. The Ukishima and Kisarazu ramp sections are on reclaimed land.
2.2. Marine Navigation Tokyo Bay encompasses four ports of special importance (Tokyo, Kawa-saki, Yokohama, and Chiba ports), as well as other ports (Yokosuka and Kisarazu ports). There are many vessel movementsbetween various ports within the Bay, in addition to the vessels entering
251
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Figure 1. Tokyo's metropolitan highway network (Trane-Tokyo Bay road in center).
Table 1. Main features of Trans-Tokyo Bay Highway. Name of road: Route designation: Section: Total length: Design speed: Design load: Width, number of lanes: Construction: Total project cost: Construction period: Planned traffic volume:
Trans-Tokyo Bay Highway National Highway 409 From Ukishima in Kawasaki to Nakajima in Kisarazu 15.1 km 80 km TL-20t and "1-1"-43t 3.5 m x four lanes; two lanes in each direction, to be expanded to six lanes (three lanes in each direction) in future Tunnel, bridge and artificial island Approx. Y1,150 billion About 10 years from fiscal 1986 64,000 vehicles/daytwenty years after construction (33,000 vehicles/day upon initially entering service)
252 TUNN~J.~a ANDUNDE~ROUND SPACETECHNOLOGY
2.3. Earthquake Activity Earthquake activity is common in the Tokyo Bay area. It is believed that 32 major earthquakes occurred in the Bay area in the period from 818 to 1867 A.D.; since 1868, 23 damage-causing earthquakes have occurred. The great K a n t • earthquake of 1923 is representative ofthese major earthquakes. Figure 5 shows the epicenters of large earthquakes (i.e., those having a magnitude greater than 6.5) t h a t occurred between 1885 and 1979 within 300 k m of the TI~BH site.
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and leaving the bay. The ports handle nearly 450,000 vessels ~nnually. The types and shapes of the vessels are also diverse. In 1982, about 744 boats per day passed through the Uraga strait, and this figure has remained constant in recent years. A survey on the actual conditions in the Bay counted 1274 boats per day in the area in November 1982; more than 90% of these were concentrated in the 10-kin section on the Kawasaki side.
3. Outline of the Project 3.1. Selection of Tunneling Method Highway tunnels under the seabed traditionally have been constructed using the sunken tube method. However, the enormous advances in shield tnnneling techniques as a means of b~nnelingin urban areas in recent years suggested t h a t this method might be feasible, particularly given the following conditions for this tunnel site: • Large tTmnel diameter (13.9 m external dia.). • Great water depth, resulting in very high water pressure (5-6 kg/cm').
° Small overburden ( 6 . 4 - 9 . 4 m at access slope). ° E x t e n d e d l e n g t h of t u n n e l (2,000-3,000 m). Other advantages of the shield tunneling method are the ease of constructing additional tunnels, and the relatively minor disruption of navigation, fisheries and the environment during construction. In consideration of all these factors, the shield t~mnel method was chosen for this project instead of the submerged method, bearing in mind possible future traffic volumes and overall profitability. To ensure face stability and safe t~mneling operations with no danger of water influx, the slurry shield method was selected from the variety of tunneling tech nlques available, because it is the most compatible with the construction plan. The plan involves using the two-way advance method and launching t - n n e l s from different locations using eight shield m a c h i n e s - two each from the U k i s h i m a and Kisarazu vertical shafts, and four from
Volume 7, Number 3, 1992
Plan Ukishima access K a w a s a~ l k i c i ~ y~ /
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3,2.1. Longitudinal alignment and tunnel dimensions The longitudinal alignment (see Fig. 4) was chosen to ensure stability of the required overburden against upli~ing, as well as to maintain the drAinsge slope in the t-nnel. In addition, the gradient of the ramps was fixed at 4% to suit the approach road alignment,
the size of the rnAnrn~de island, the flow ofvehicles, and other factors based on road construction standards. The plane alignment was determined to be 1.0 D (D ffi outside diameter of tnnnel) in clearance for the general section, in consideration of the effect from the juxtaposed tlmnel; and 0.5 D in clearance for the joint section to the vertical shait of both slipways, in consideration of the quality of the mAnmAE]e ground. The tnnnel section (see Fig. 6) is designed to accommodate a two-lane carriageway and the ventilation facili-
ties, etc., as well as to include road safety equipment such as emergency parking zones. The provision of extra emergency parking zones, involving partial widening of the tnnnel, presented problems not only in terms of design and construction, but also from the point of view of construction cost andperiod. Therefore, instead of emergency parking zones, a 2.5-m-wide left shoulder will be created throughout the length of the tlmnel. In further consideration of the need for traffic information signs and accident prevention systems, and after
Figure 3. Artist's rendering of a cutaway view of the Trans-Tokyo Bay Highway tunnel, as it passes through the Kawasaki manmade island.
Volume 7, Number 3, 1992
Tu~-~.~.ma ANDUNDERGROUNDSPACETECHNOLOGY253
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absorb deformations of the tunnel in the axial direction resulting from ground settlement and earthquakes. It will be necessary to develop a method of lining the joints between vertical shafts and the tunnel, and the other undersea joint. Stable progress of parallel shields must be maintained (separation:0.5 D at ramps and 1 D over the seabed section) with a large face (about 14 m in diameter) under conditions ofhigh water pressure (5-6 kg/cm~), extremely thin overburden (0.7 D at the ramps and 1.0 D over the seabed section), and extended length (2,000-3,000 m), even with two-way advance). This will require fabrication of large-diameter shields that are durable and that have good abrasion resistance and watertightness. Finally, the work must be accomplished rapidly and automatically in order to adhere strictlyto the construction schedule.
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Figure 5. Earthquakes of magnitude >_6.5 that have occurred within a 300-km radius of the center of Tokyo Bay from 1885 to 1990. adding an inspection walkway, the final internal diameter of the tunnel was determined to be 11.9 m (13.9 m external diameter). This diameter provides a highway with the same width inside and outside the tunnel, unlike conventional tunnels, so t h a t driving into and through it should be a very comfortable experience.
The lining system and joint construction must minimize the possibility of problems such as deformation, and cracking, and must provide improved watertightness and durability. In addition, the lining system must
A stable shield operation must be ensured under a thin overburden and through reclaimed ground to prevent uplifting of the tunnel. The mechanical constants of the reclaimed ground will have to be determined in order to calculate the external force on the lining. Because the tunnel excavation has to proceed through filled ground, particular problems with abrasion resistance of the face plate rim and the outer bit m u s t be resolved.
650 350
3.2.2. Ventilation system
The tunnel will be ventilated through towers to be built at the Ukishima access section,on Kawasaki m a n m a d e island, and on Kisarazu m a n m a d e island (See Fig. 7). Taking advantage of the technologicalinnovations of recent years, a vertical shaft air feed and exhaust ventilation system using electricdust collectorswill be fitted (see Fig. 8), as has been done in other large tunnels such as the Kanetsu Tunnel. This system has resulted in reduced maintenance and management costs. 3.3. Tunnel Features
The main features of this tunnel with respect to design and construction are described below. 3.3.1. Long, parallel tunnels, constructed under difficult conditions
The large-diameter tunnel isin deep water, with only a small overburden in soft ground.
Volume 7, Number 3, 1992
Invert
Figure 6. Tunnel section configuration.
TUNNELLING AND UNDERGROUND SPACE TECHNOIX)Gy
255
Figure 7. Construction of the Kawasaki manmade island, which will include a ventilation tower.
3.3.3. Ventilation system Additional study will be required to determine the enclosure, layout, methods of maintenance, control, and ventilation efficiency of the various aspects of the vertical flow ventilation system with circular shield section.
4. Tunnel Design Tunnel design conditions are shown in Table 2. The Trans-Tokyo Bay Tunnel is without precedent in the sense that it is very large in both physical and technical scale. In addition, construction is in extremely soft ground under deep water in an earthquakeprone area. In order to succeed with this colossal project, we dare not simply extend past design principles. Nevertheless, careful study of past experiences has been undertaken. An examination committee was established for each structure to undertake technological surveys and studies. These committees selected the optima] structure type, fixed the design criteria, examined the seismic response, elucidated the normal behaviors, and chose the optimal design and construction method for each item, while also surveying and examining the technological problems arising from the special regional characteristics of Tokyo Bay.
4.1. Design Method for Primary Lining This tunnel has a large cross-section in comparison to conventional tun-
nels, and is to be constructed near the border between the soft alluvial and the diluvial undersea layers. Therefore, in designing the lining, it was necessary to verify the assumed value ~ ~, as commonly usedin calculations (assuming a ring with uniform flexural rigidity) using the beam spring model (i.e., a ring model including spring in the joint to represent the dynamic properties of the joint). The spring constants KO and Ks were chosen by referring to the results of a full-size bending test on a segment joint (with axial force) and a shearing test. Basedon theseresults, asegment with a core-type joint (joint reinforced with a ribbed anchor plate) and a long bolt was found to be sufficiently safe, despite using the conventional TI assumption in the calculation. Figure 9 shows the structural analysis model of the lining selected.
4.2. Load Conditions (see Table 3) The pressure of the ground in the tunnel periphery was assumed to be soil and water combined against clayey soil layer for original ground; soil and water separately against the sandy layer; and soil and water combined for manmade ground, to give the design a safety margin. The ramp tunnel passes through reclaimed ground. Although the overburden is small, the ground strength is high; therefore, resistance can be anticipated. To consider the reclaimed ground and the natural ground around it, a
256 TUNNELLINGANDUNDERGROUNDSPACETECHNOIA)GY
two-dimensional elastic FEM analysis was undertaken with the maximum bending moment as a parameter, and the coefficient ofsubgrade reaction and the coefficient of lateral pressure were found to be *c= 3.5 kg/cm and k = 0.6, respectively. To verify experimentally the magnitude and distribution of the external forces acting on the tunnel and the level of ground stress and deformation, the liningload was tested usingamodel, to determine the degree of loosening of the natural ground, the effects ofbackfillinginjection, the magnitude of coefficient of lateral pressure, and the difference in improved ground strength. The tunnel passes through natural ground over the flat seabed section, and the means of reflecting the effects of high water pressure in the calculation of combined lateral soil and water pressure in the clayey soil is open to question. However, the strength of the clayey soil led to the following judgment of lining stress conditions: Full section Ac layer > alternate Ac and De layers > full section De layer. By referring to the literature on soil properties, design experience and spedfications, the coefficient of subgrade reaction and the coefficient of lateral pressure were found to be k = 0.800.75 and ~ = 0 (kgf/cmS), respectively, for the Ac layer; and k = 0.65 and ~ = 1.5-2.5 (kgf/cma), respectively, for the De layer.
Volume 7, Number 3, 1992
n
LI-'-
- - J J
. . . .
.l~t f a n
........
" ign ;g
Emergency Air speed and direction se Visibility Fire Fire h Alarm Fire Extin[
y exit sign
CO e Mull Emergency
ation cable
L,
Figure 8. Tunnel utility plan. In addition, field measurements of parallel tunnels in similar clayey ground (¢ 7.25, slurry shield, clearance 0.5 D) were carried out, verifying the above assumption from data regarding the primary lining (in transverse and longitudinal directions) and the disturbance in the peripheral ground.
5. The waterproofing of the tunnel basically consists of backfilling injection of the primary lining. Secondary measures involving waterproof sheeting will be contemplated if water leakage occurs. The mix of backfilling injection material, the number of sealing stages, the shape, the type, and the material will be determined after oh-
4.3. Lining Construction
Figure 10 shows a section through the t u n n e l The primary lining of the tunnel basically consists of reinforced concrete plate segments 13.9 m in outside diameter, 1.5 m high, 0.65 m thick, and divided into 11 sections (the key segment is the axial insert type). The secondary lining is 0.35-m-thick castin-place reinforced concrete, mainly for the purpose of adding weight and protecting the primary lining from fire or explosion. The lining design is based on the following basic concepts: 1. Full-size segmentjoint tests were conducted on several types of joints to find a joint t h a t was highly rigid and durable and t h a t could be assembled automatically. A core-type joint section reinforced with a ribbed anchor plate, assembled using a long bolt was found to meet these conditions economically. 2. The primaryliningis designedto resist the total load. 3. Both the primary lining and the secondary lining are to be corrosionresistant construction type 2. Based on the results of durability tests, it has been determined t h a t half the weight of the necessary cement for the RC segment will be replaced by blast furnace slag. 4. The secondary lining is designed to resist dead weight and water pressure only.
Volume 7, Number 3, 1992
taining the results of waterproofing tests on the tunnel. 4.4. Effects on the Tunnel of Ground Deformations under the Tunnel
In the Ukishima r a m p section, it is considered possible t h a t bending deformation m a y occur in the axial direction of the tunnel ai~cercompletion as a
Table 2. Design conditions for the Trans-Tokyo Bay Highway.
Internal section: Lining:
Length: Alignment:
Clearance: Uplift safety factor: Overburden: Water Depth: With Pressure: Excavated Soil:
Final inside diameter, 12.6 m Primary lining; outside diameter 13.9 m, inside diameter 12.6 m, thickness 1.5 m Secondary lining, thickness 0.35 m 9.1 km (4,600 m on Kawasaki side; 4,510 m on Kisarazu side) Longitudinal: Ramp section 4% (maximum highway gradient) Flat seabed section 0.2% (for drainage) Curved grade section: R=10,000 m (for mitigation of congestion) Plane; R=3,400 m (one location each on Kawasaki side and Kisarazu side) Seabed section 1.0 D (D: outside diameter of tunnel); Both ramp sections before vertical shaft 0.5 D More than 1.25 when completed; More than 1.1 during construction Ramp section, 6.4 m-9.4 m; flat seabed section, 16.0 m (average) At seabed section, 27.5 m on average At tunnel center, 6 kgf/cm 2 Reclaimed land at ramps Flat seabed section: alternating layers of alluviai and diluvial clayey soil and sandy soil
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY2 5 7
result of the deformation of the diluvial clayey soil layer under the filling due to the load from the stabilization filling. Therefore, deformation at the tunnel center and a cross-sectional force on the lining are expected to occur. It was calculated that elastic deformation and primary consolidation deformation would be complete by the time the shields are launched, and that the residual deformation resulting from secondary consolidation would reach about 6 crn one hundred years after completion of the tunnel at the access section of the vertical shaft. The maximum bending moment resulting from this deformation and from an earthquake will occur at the access section of the vertical shaft. However, it was discovered that if a flexible design is implemented at that point, durability would be assured because the maximum bending moment would be about 60 times the bending strength of the tunnel. To absorb the deformation at this point, a flexible segment will be used in the primarylining, and a bridging construction in the secondary lining and floor slab.
4.5. Peripheral Ground and Stability of the Tunnel At the accesssection of the Ukishima vertical shaft, a minima] overburden of only H = 6.4 m (H/D = 0.46) can be secured as a result of the tunnel alignment. Therefore, it was decided to secure the required safety factor (Fs > 1.1) against lifting during construction by considering shearing resistance of the manmade and natural ground. The required safety factor at the time of completion (Fs > 1.25) was found to be secured by considering the deadweight and the weight of overburden only.
Interactive awing between Linings
/ Shear sprin~
~LlbgYa(]C
r~';icti(}iI
/,
~:
lining
/ ~ -
-'}
/
- Rotatior, spri,l~
[h-in~ary linin~ ]'4[. I'iN~
/I]d. l'll)~
Figure 9. Tunnel analysis model. To ensure stable shield excavation through the ground, and based on past data in these construction conditions, the unconfined compressive strength q u and wet unit volume weight were . . . selected as the determining properties of the reclaimed ground. These were prescribed as 6 kgf/cm2< q < 30 kgf/cm~ (target approx. 10 kgf/cm2), ~t > 1.8 tf/m 3.
1. Earthquake motion anticipated within the life of the structure (L1). 2. Earthquake motion likely to occur only very rarely (L2), such as the Great Kanto Earthquake. The structure should not suffer any damage that impairs its transportation function when an L1 earthquake occurs, and it should not suffer damage that results in flooding or total collapse in an L2 situation. As a result of aseismic studies on the tunnel thus far, the following basic policy for aseismic design of the tunnel has been prescribed: • The ground in the tunnel area will not liquefy or turn into siurry. Therefore, no special measures, such as groundimprovement, will be necessary on the existing ground.
5. Earthquake R e s i s t a n c e Because of the active seismic nature of the site area, an aseismic tunnel design was chosen. In addition, earthquake response analysis usingthe response displacement method was necessary to ensure tunnel safety. In choosing the earthquake characteristics to input into the earthquake response analysis, two concepts were introduced:
Table 3. Soil properties and load factors at the tunnel location.
Soils A A D D D D D Manmade
Legend:
N Blow
q kg/cm
E kg/cm
0 0 12 15-5 20 54 78
0.44 0.87 0.96
4.8-9.6 5.7-22.9 35.9-289.0 25.0-204.0
2.11 1.57
296.2 195.5
7.5-21.3
A: Alluvial C: Clayey soils N: Number of Blows by SPT q~:::Unconfined Compressive Strength Modulus of Elasticity
258 rI~JNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
ton/m 3 1.3-1.5 1.6-1.7 1.4-1.8 1.6-1.8 1.7-1.8 1.8-1.9 1.7 1.6-1.8
D: S: ~: K; k:
Water in Soils
K
0 0 1.5 0.5-4.0 2.0 4.0 5.0 3.5
0.75 0.75 0.65 0.35-0.55 0.65 0.35 0.35 0.6
Combined Do. Do. Separated Combined Separated Do. Combined
Diluvial Sandy soils Unit Weight of Soils Modulus of Subgrade Reaction Earth-pressure Coefficient
Volume 7, Number 3, 1992
Connections between the tunnel and vertical shafts will have a flexible construction in order to absorb the deformations resulting from an earthquake. To clarify the behavior of the tunnel at the border between the improved ground on the tip of Ukishimaramp andthe soft original ground during an earthquake, vibration tests were conducted using a r a m p tunnel model. As a result of these tests, it was decided to increase the strength of a certain section of the tunnel at this point using axial-strain-absorbing washer at both ends of the long belt between segmental rings, or other means, as well as to design the tunnel with a flexible structure in the axial direction. To clarify the mutual behavior of the primary lining and the secondary lining and its effect on the tunnel's seismic response, a shield tunnel lining seismic test (No. 1) was conducted. The test results led to a decision to avoid concentration of deformation in a certain joint of the primary lining by adjusting the amount of rebar in the secondary lining and by making it continuous in the axial direction. Although rigidity in the axial direction of the tunnel is increased by the secondary lining and the sectional force on the whole tunnel m a y be higher, the sectional force borne by the primary lining is somewhat lower than in a case where there is no secondary lining. However, to give a m a r g i n of safety, the joint between rings
6. Shield Tunneling Although the aim is to construct the tunnel safely and without incident using the p r e s s u r i z e d s l u r r y shield method, if any unforeseeable circumstances should arise or major changes should be needed, considerable difficulties may be encountered as a result of the high subsurface water pressure. For this reason, the shield tunneling procedure is being studied carefully to grasp accurately the present state of the technology, and to anticipate problems that may arise in the future and solutions to them. The problems faced in this design are described below. 6. I. Technological Problems Related to the Largo Tunnel Diameter
6.1.2. Design, fabrication and assembly of large-dlameter shield machlnes The premise of this tunnel design is that pressurized slurry shieldmachines will be used. The largest such machine in past experience, which was 11.22 m in diameter, was used for the construction of an adjustment pond tunnel under a street in the Hirano river water system. The main technological problems in the design, fabrication, and assembly of a shield machine with an outside diameter of 14.14 m concern: • Reliability of the soil seal and bearing that are to be fabricated in sections and then assembled. • Supporting the cutter face plate so that it does not impose an
6.1.3.Controlllng the stablllty of • large face Because the diameter of the tunnel is large, the face consists of diverse soil layers. These layers differ not only in mechanical and physical properties, such as water pressure, strength, stability, and particle size composition, but also in the direction of excavation. In addition, because the excavation has to be carried out under a thin overburden, the usual ratio of water level to ground depth is reversed. To maintain stable progress under these conditions, itis considered essential to have a highly automated statistical management method that can measure, analyze, and display a variety of excavation dataon-line andinreal time, so that decisions can be made about: • Optimum slurry pressure. • Factors t h a t govern the quality of slurry. • Volume of excavated soil • Optimum excavation standards t h a t satisfy requirements of face stability and excavation speed. In some special locations ground freezing techniques will be used to: 1. Secure stability of the face in the launching section and ensure tightness until the shield passes the entrance packing. 2. Secure stability and water tightness where underground junctions are opened. Backfill grout hole
3 969.83 -/
excessive load on the soil seal, bearing, or bulkhead. The need for rapid assembly in the vertical shaft, and ensuring accuracy aider assembly.
will be designed to resistthe sectional force, which would not be on the primary lining only.
Radial joint bolt hole
Backfillgr°uth°le \ Segment grip hole
~
~ t ~ ~o--~ ~..~~
i g h ~'~" ~ J ~ J Ring joint bolt hole
'
t \
gasket
D~amageprotective gasket
Segment grip hole
a-a
Segment support hollow \
I IIg__[i "' i[
Backfillgrout / hole
/ ' Segment grip hole Figure 10. Tunnel lining structure.
Volume 7, Number 3, 1992
a~
[i \u ii__lll i
/ aJ Position mark for assembly robot
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY2 5 9
However, because it takes time to achieve these effects, a combination of ground freezing and the mechanical underground junction method is now being investigated as a way to shorten the construction period without compromising reliability.
6.1.4. Construction technology for a deep, large-diameter shield method The construction techniques t h a t need to be developed and improved in the construction of this t - nnel include: • Automation (e.g., in advancing and excavation, transport and disposal of excavated material, assembly of lining, alignment control, material flow control). • Disposal of excavated material (continuous removal of sand and gravel from the cutter, continuous discharge of sand and gravel from the b-lkhead, transport and disposal ofvol-ml-ous excavated material). • High-speed construction (highspeed advance, high-speed lining). • Lining construction with ratiohal joints (adequate rigidity and strength for the ground conditions, easy and quick assembly, compatible with automation).
6.2. Technological Problems Related to Tunnel Depth 6.2.1. Pressure proofness and waterUghtness of shield machine Until now, the greatest depth experienced with a closed-face shield machine was in construction of a water conveyance tunnel for the Waterworks Bureau of N a r a Prefectural Office (shield diameter 3.950 ram), with a maximum overburden of 135 m and a 110-m mAximuIn head. Because the mRximllIn head in this case is about 60 m, the factors t h a t have to be taken into consideration in the design and fabrication of the shield machines are: Strength of shield body. In the case of the adopted segments, because the ring width is 1.5 m and the key segment is inserted in the axial direction, sufficient rigidity and strength are necessary in the tail plate, which is the weakest point in terms of external pressure. In addition, the b - l k h e a d must be able to withstand the high slurry pressure and fluctuations in pressure. Supports for moving parts. The cutter support must be such that no excess load is imposed on the b-ll~head or bearing. The bearing must be able to withstand huge face resistance. Watertightness ofmovingparts. The watertightness of moving parts such as the cutter bearing and seal is typically secured by a number of layers of urethane rubber lip-type soil seals. Although it is possible to cope with a
water pressure of about 10 kg/cm 2 at a sliding speed below 20 m/s using soil seals, when the shield diameter is large and the seal sliding speed is higher, a device that applies a bacldng pressure to the soil seal will be needed.
Watertightness of tail seal. The tail seal must be watertight and durable under high water pressure. The number of stages, the material used, the shape, and the clearance remain to be researched.
6.2.2. Waterproofing of lining construction Conventionally, linings are waterproofed at the watertight seal of the pr~mRry lining, but this technology seems inadequate for this case. At great depths and with large-diameter shields, emphasis must be placed on watertightness and corrosion resistance from the viewpoint of economy of maintenance, creating a series of waterproofing and corrosion-proof steps from the secondary lining through the primary and secondary lining interface, to the primary lining and the backfilling injection. The work described below will be necessary. In the secondary lining, the concrete must be thoroughly cured to prevent cracking due to thermal shrinkage and drying shrlnksge. At the interrace between primary lining and secondary lining, waterproofing sheets must be installed. The construction should allow easy passage of leaking water, should it occur. In the primary lining, a combination of shapes and materials for waterfight seals m u s t ensure durability. Waterproofing measures may also need to be taken in a potential water channel. The concrete must be dense and tight, w i t h r e d u c e d p e r m e a b i l i t y achieved by thorough curing. Finally, a waterproofing additive must be developed that reacts with water infiltrating through segmental joints. For the backfilling injection, a reliable instantaneous/simultaneous injection system for baclcfilling material in quantity must be developed. An additive t h a t demonstrates water-resistance even after the main member has hardened also must be developed. 6.2.3. Coping with unexpected situations near the face In the case of a closed shield construction, it is necessary for workers to operate outside the b , ikhead if any unexpected situation arises. Thus, itis absolutely essential to secure a safe worldng space despite the high water pressure. The most reliable auxiliary method possible at present is ground freezing, although this m a y result in a longer construction period. In the future, it
260 TU~TJ~n~G ANDUNDERGROUNDSPACETECHNOLOGY
will be necessary to devise a means of reducingtheinstallation time for freezing pipes and to reduce the time required for freezing to occur.
6.2.4. Removal of spoil and watertightness of the conveyance system When using the pressurized shield method of construction, the high face pressure m a y be reduced to atmospheric pressure during the process of removing spoil. Therefore, it is necessary for the removal and conveyance system to have the same degree of pressure-proofness/water tightness/ durability as specified above.
6.3. Technological (Excavation) Problems Related to Tunnel Length It is no exaggeration to say that the limit oft~mnel length is determined by the durability of the shield machine and the conveyance and disposal facilities for slurry. The m a x i m u m l~mnel length excavated in the past using a closed shield machine was in construction of the gas piping t - n n e l for the Kawagoe thermal power plant of Chubu Electric Power Company, i.e., 2.500 m (¢ 4,200 m m shield outside diameter). Because the radius of the installation, the sliding speed of the soil seal, and the cutting rate of the bit tend to increase at greater depths and with large-diameter shields, a m a x i m u m t - n n e l l e n g t h of about 3 k m i s probably realistic. A tunnel larger than this may have to be designed with an underground junction To improve the durability of deep, large-diameter shield machines, it will be necessary to: • Improve the abrasion resistance and durability of the cutter face plate and the peripheral surface. • Improve the abrasion resistance and durability of the cutter bit. • Improve the abrasion resistance and durability of all movable parts, such as the agitator. • Improve the durability of the soil seal and tail seal at high pressure. • Improve the durability of each part of the shield machine (moving parts and parts under electrical or mechanical load) • Reduce wear in the conveyance and disposal system for spoil. • Improve the technology for replacing worn parts. • Develop a highly accurate alignment control system to t~mnel accordingto the planned alignment. In the case of the T T B H t11nnel,the plan is to t-nnel for 4,700 m between the vertical shafts using shield t~mnels 2,000-3,000 m long by means of an underground junction.
Volume 7, Number 3, 1992
Fiscal Work area/ year
U k •
-
'89
'90
'91
'92
'93
'94
J
-
Access
Kawasaki Man-made Island-
/
Kisarazu Man-made Island-
/
Shielded Tunnel
6.4.2. Development of an underground jointing method In the shield work, advancing in parallel from Ukishima, Kawasaki and Kisarazu vertical shafts aims to reduce the construction period. Underground jointing is a necessary part of this plan. However, if ground freezing is adopted as an auxiliary method in the main jointing work, as in conventional practice, the period required forjointing would amount to about 10 months on the critical path. Hence, the development of new auxiliary methods and a mechanical undergroundjointing method are currently being studied to further reduce the construction period.
7. Conclusion Bridoo
Figure 11. Work schedule for the Trans-Tokyo Bay Highway Project. 6.4. New Tunneling Technology The construction of this tunnel faces unprecedented difficult conditions, involving a large-diameter tunnel (13.9 mdia.), excavated over a distance of about 9 km under the seabed of Tokyo Bay, about 60 m below water level. Because the shields will be launched from vertical shafts at Ukishima, Kawasaki, and Kisarazu in a parallel advance and will be connected by means of an underground junction, the latest shield technology will have to be used. In addition, because the tunneling work lies on the critical path for the whole project, the establishment of rapid construction technology to reduce the construction period is a major issue. Within the construction industry, there have been continuing social demands for improved safety. To meet these demands and to overcome our skilled l a b o r s h o r t a g e a n d a g i n g workforce, it is essential to standardize, increase efficiency, and reduce labor in all operations; and quality control must alsobe applied. Additionally, there is a need to improve environmental and working conditions and to avoid hazardous operations. The TTBH tunnel project is no exception to these requirements. In consideration of these circumstances, thorough research and investigation have focused on reducing the
Volume 7, Number 3, 1992
construction period (see Fig. 11) and minimizing labor requirements in the following areas: 1. Rapid construction (improvement ofexcavation speed, simultaneous and parallel work by different trades, prefabrication of structural members). 2. Use of robots. 3. Mechanical underground jointing on the basis of a highly accurate alignment control system. 4. Simultaneous construction ofprim a r y a n d secondarylinings, in order to shorten the construction period. Items 2 and 3 are discussed below.
6.4.1. Use of robots Work on automating the assembly of segments, an operation that takes place at an elevation of about 14 m, has been progressing, with the aim of completingthe operation safelyand quickly. This work involves the development of an automated conveyance and assembly system for the segments, which weigh about 10 tons each. The use of robots for piping work, which is simple and repetitive, is also considered an important issue. Particularly important is coping with the automation of segment construction, and joint construction in particular. Further research is continuing into improved methods of matching the sections.
This paper has outlined the structure, design and construction methods for the Trans-TokyoBay Highwayshield tunnel. In bringing the tunnel structure to completion, there are m a n y problems that require study, such as rational aseismic design in the soft ground, rust prevention, and an corrosion-resistant design. Amethod of interior finishing that makes driving comfortable, and formulation of a safe, accurate, and economical construction plan, are also necessary. These technical issues have been studied by the committee of the Trans-Tokyo Highway Shield Tunnel and, based on the results of their efforts, designs and redesigns for the project have been carried out. The Trans-Tokyo Bay Highway project is the core route in an expansive trunk highway network designed to handle the traffic functions of the capital region and to promote balanced development of the area. Reduced travel distances and time spent commuting will have a significant direct economic effect, and the Highway will greatly ease traffic congestion in the entire Tokyo Bay region. The TTBh has become a commercial reality twenty years after it was first proposed by taking advantage of the private sector. In carrying out this project, we are aiming at early completion while paying thorough attention to the natural environment, the city environment, transportation n e e ~ and works safety.
Acknowledgment The authors wish to t h a n k the mem bers of the Examination Committee and members of the organizations concerned for their guidance and assistance on various technical problems.
TUNNELLINGANDUNDERGROUNDSPACE TECHNOLOGY261