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Tunnelling machine development for undersea projects—a review of the issues
0886-7798(94)00033-6
Tunnelling Machine Development for Undersea Projects--a Review of the Issues Richard Robbins and Martin Kelley
Abstract--The decisions that lend up to the start of a major undersea tunnel will be the principal factors in determining the degree of succses of the project. This is especially true if the geologic conditions are difficult. Many factors can conspire against success, including some which might at first appear to benefit the owner. This paper covers issues from the uiewpointd of a tunnel machine manufacturer and a contractor. The uses of undersea tunnels are discussed, as are the types of machines that should be considered, us determined by the geologic conditions. Probe drilling, considered the most reliable method of detecting hazardous conditions ahend of the face, is reviewed. The state-ofthe-art in pressure bulkhead shields is detailed. The contractor's viewpoint focuses on issues of risk sharing. The categories of risk and proper allocation of these risks are discussed, us well as the most effectiue methods of Umiting and resolving disputes. The authors describe the contractor's expectations of the tunneling machine supplier, both before the construction contract is signed and after the selection of a machine.
Viewpoint of a Tunneling Machine Manufacturer s is the case w i t h most b]nnel
ing jobs, the project cost and time to completion for an undersea t - n n e l is determined by what happens at the headln~. Although the job may involve a very large investment in capital and expert manpower, all of the effort is concentrated at the t~]nnel heading. If it isn't happening there, it isn't happenin~ anywhere. This me~nR that the design criteria for the job and the selection of methods and equipment must be done with great care. In a major undersea tnnnel, the job becomes highly committed to the successful use of the systems selected. Unlike a subway tunnel, the solution
Present address: Richard J. Robbins, Vice Chairman, The Robbins Company, Box 97027, 22445 - 76th Ave. So., Kent, Wa~hin~on 98031, U.S~..; Martin Kelley, Vice-President (retired), Engineering and Estimating, Kiewit Construction Group, do 25070 N.E. Graham Road, Aurora, OR 97002, U.S.A.
of grouting from the surface or sinlring an extra repair shaft is usually out of the question. The contracting practices currently in use often encourage unjustified risk-tRklng by the contractor. Furthermore, the competitive naturo of the bidding process supports the tendency to rely on optimistic assumptions. Another hazard presented by large prestigious undersea projects such as the Channel tunnel, the Trans-Tokyo Bay highway, and the Seikan tunnel is the prestige of being associated with a world-class tunnel project. This prestige is sometimes viewed as justifying either a very low price or otherwise unacceptable contracting conditions and special risks. Even though the prestige and advertising value m a y be worth a substantial amount, the owner and/or the contractor m u s t consider w h e t h e r accepting a bargain price m e a n s compromising the success of the job. In today's economic environment, a bargain price is hard to pass up; however, in the highly committed tunnel business, experience or a proven track record m a y be worth more in completing the project on schedule.
Uses of Undersea T u n n e l s The major undersea tunnels t h a t have attracted the most international publicity have been transportation facilities, and mainly railways. Examples have been Seikan tunnel in Japan, the ChRnnel tunnel linking Groat Britain and France, and the Great Belt tunnel in Denmark. Highway tunnels such as the Trans-Tokyo Bay project are occasionally built, as are strait and i~ord crossings in locations such as Norway. Non-transportation tunnel projects include major offshore sewer outfall tunnels such as those in Boston H a r beur and Sydney, Australia; cooling water tunnels for power plants such as the Seabrook nuclear power plant in New Hampshire; and freshwater intake tunnels such as the Lake Michigan water tunnels for Chicago, Illinois, and the Port Huron tunnel for Detroit, Michigan.
TBM Selection T - n n e l bering machines (TBMs) have been used to excavate m a n y undersea tunnels and tunnels under great bodies of fresh water.
Tunnellingatul UndergroundSpace Technology, Vo[. 9, No. 3, pp. 323-328, 1994 Elsevier Science Ltd Printed in Great Britain 0886-7798/94 $7.00 + .00
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All types of T B M s have been used, from open gripper machines to pressure bulkhead shield machines. The choice depends on the geology. Most major undersea jobshave been in rock. As would be expected,most of the machines have been normal open gripper type,hard rock tunnel borers. Rock Tunnels Undersea tunnels in rock should be approached as normal reck tunnels, with the obvious caution to keep in mind that an unlimited quantity of water at high pressure is available to flood the tunnel from above. The best way to cope with this threat depends on the rock conditions to be encountered. The problem should be dealt with in the plavning stages by Prediction, Preparation, and Detection. Prediction is the use of the best geologic expertise available, based on appropriate exploration techniques. Prediction should be divided into each major geologic block and should inchide a statement of how the rock and the waterwill react to having the tunnel opening bored t h r o u g h it. This information should provide the basis for a Geotechnical Design Summary Report (GDSR) and for the methods a n d e q u i p m e n t selected by t h e contractor. Preparation involves the design of the TBM and the other equipment, including the rolling stock and trailing gear or back-up system. It includes determination of the rock support and lining systems, and defining appropriate measures to be used when the detection system employed indicates the presence of high water permeability or unstable rock ahead of the machine. Preparation work must Rnawer questions related to the amount of water inflow that can be tolerated during the construction period, and whether it will be salt water. Corrosion protection and specifications of all equipment, particularly electrical equipment, should be agreed upon in advance. Preparation also includessafety designand trainingforalltunnel workers. Emergency evacuation plans should be practiced. Detection is the one area of tunnel technology that has not been developed to keep pace with the needs for undersea tunneling. What do we need to know? We must be able to detect bad or worsening geologic conditions well in advance of the tunnel heading. The detection system should tell us about the water inflow to be expected, rock stability, flammable gas, and any other hazardous conditions. In reck tunneling, it is fair to assume that we will depend on ground treatment, particularly grouting from within the machine or from a position
FOUR TARGET AREAS TUNNEL LININ
Figure 1. 1974 Channel tunnel probe drilling pattern. just behind it for the drilling and injection. These procedures should be carried out from a position in relatively good rock or previously treated ground. This means that the detection system should identify hazards a minimum of four or five diameters ahead of the machine or up to twenty to thirty diameters ahead, or as far ahead as is practical. Probe drilling must be done systematically and in a pattern to detect lowangle faults that could cause flooding. In 1974, at a previous start of the Channel Tunnel, the designers required four probe holes to maintain a pattern of protection, as shown in Figure 1. The probe holes had to enter the target areas within a limited distance ahead of the tunnel face and remain in the target for a specified distance. It can be argued that the lower two probe holes are not required in undersea tunneling, since any fiat-lying fault coming up from below is not likely to be connected directly with the water source above the tunnel. On the other hand, it might be wise to put down some shorter (four to five tunnel diameter) steep holes in areas of serious concern. Each of these probe holes should be drilled through a sealable packer inserted into a drilled oversize starting hole. Detection of serious water problems well ahead of the TBM is an essential feature of bored undersea tunnels in rock. However, the most important and most difficult task is interpreting the information that is available from the probe drilling. This remains the commission of an experienced drilling superintendent or geo-technician, who should be on duty whenever the probe drilling is being carried out.
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In the future we may see practical systems of continuous detection based on geophysics for mapping ground features ahead of the TBM as it bores forward. Watching the research work that is being carried out by numerous organizations around the world gives us hope, but for the foreseeable future we must continue to rely on probe drilling for reliable detection.
Long Probe Holes An interesting possible development that would be welcome is accurate long hole probe drilling ahead of a TBM. A system can be developed to bore long horizontal holes that can be steered accurately while drilling. The advantage of such a system would be a probe drilling operation that would not interfere with the tunnel bering. Oil well drilling is turning more frequently to horizontal drill holes to drain difficult production areas. Holes as long as 2 km have been drilled. A horizontal bore hole would start behind the tunneling machine, perhaps as far back as 100 m or more. It would enter the wall of the tunnel at a fairly acute angle of about 20 degrees. The drill must then turn through a 20degree arc to parallel the centerline of the tunnel and stay within a target area of perhaps 1 m to 2 m diameter while bering out 1 or 2 km ahead of the machine. With a drill hole on either side of the area above the tunnel alternating, we could have continuous probe information weeks before the machine headed into a bad ground area. As the machine approached the dangerous zone, a more complete pattern of probe holes could be bored ahead to gain the detailed information needed to design a grouting program. A schematic de-
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sign of such a system is shown in Figure2. Long horizontal probe holes require the development of a drilling system that can be driven around a fairly short radius curve of about 10 m radius around arc angles of up to 30 degrees. A very accurate surveying system will have to be developed to determine the position and attitude of the drill head, either providing continuous "Position While DrillinL~ information or periodic information that can be obtained rapidly without too much interruption of the probe dri|ling.
Undersea Tunnels in Mixed Geology and Wet Conditions Although the French side of the Channel tunnel was a rock tnnnel, the weak rock was severely faulted with open joints. The joints provided a direct connection between the tunnel face and the open sea above. The choices were to grout it all solid or to drive the tunnel with a water pressure b,dkhead shield and a sealed segmental liner, as if it were a subaqueous, sell-ground t u n n e l In 1974 the decision was made to grout. The TBM that was built for the service tunnel had an open cutterhead with special previsions for probe drilling and grouting. It was the only practical choice, given the state of t , nneliug technology at that date. In 1987 the decision was made to drive the tunnel as a pressure bulkhead shield--a system that had never before been used in rock. The key technical question was how to remove cut rock debris from the seawater pressurized chamber of the cutterhead. The choices included slurry pumping, double screw conveyors with or without a plug zone between the screws, rotary discharge chambers or carrousels, twin pressure hoppers, and twin piston discharger. Only the twin pressure hoppers had been used before in a rock tunnel--the 10.3-m-diameter RER rail tlmnel in Paris from the Etoile to Defense. That rail tunnel was driven with a pressure bulkhead shield, the first in the world; however, the muck removal system from the cutterhead was in compressed air, and not under water pressure. The large diameter provided the large vertical height required for the pressure hoppers. This method did not seem practical for the 5.8-m driven pilot tunnel for the Chnnne] t-nnel. The other systems of muck removal had all been used in both small- and large-scale soil hmnels, but not in rock. The final decision was to use a cutterhead with a centrally located hopper and a center-supported primary screw conveyor to bring the muck from the cutterhead to the rear of the shield while under pressure. The screw would
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move the muck and at the same time consolidate it, so that the solid muck made up the large majority of the volume at the discharge point of the screw. For dry boring conditions or in areas of low water inflow, the screw was designed to discharge into a flight feeder conveyor that fed directly onto a belt for loading muck cars. In high water flow and high pressure areas, the screw fed pressurized muck into a twin piston discharger, which took the muck down to atmospheric pressure in the controlled released of a positive displacement pump. This system was secure againat water blow-through. A third alternative muck removal system--a conventional slurry pumping system--was provided and built into the machinery but never used. All of the slurry equipment was designed and procured to accept the muck from the machines screw, mix it and pump it to the shaft discharge point continuously while the machine borod the tunnel. The slurry system also eliminated the need for the muck car haulage system. This complex and relatively slow muck removal system was to be used only if the piston discharge system could not be developed to operate effectively. Fortunately, it was never needed. The two rl]nn~llg tunnel machines of 8.5-m diameter for the French side of the tunnel were built in a joint venture between Robbins and Kawasaki Heavy Indlmtries. Kawasaki was convinced that it could make a double screw system with a plug zone work effectively as the means to bring the muck from high pressure to atmospheric pressure. This conviction was based on full-scale testing of a double screw in the labora-
tory at the manufacturing plant in Japan, using tunnel muck t h a t was shipped from the Channel Tunnel. These machines were therefore built with the double screw instead of the piston discharger. In operation at the Channel Tunnel, the rock chips cut by the rlmnin E t, mnel machines did not develop the proper consistency to form a pressure plug or the proper pressure differential along the screws. As a result, water and fines would blow through the screws out ofcentrol. Fort-nntely, the service t-nnel provided the possibility to grout the area ahead of the running bmnel machines; and there-
fore, it became ,mnecoesary to run the
big machines under water pressure. The B#tish Side Inundation Protection An unusual feature of the three machines that bored under the Channel from the British side, eastward toward France, was the use of special inundation seals. There was concern that one of the hundreds of bore holes which had been drilled for exploration over a period ofmore than one hundred years might have been leit open and would be bored through by the tunneling machine. Even a near rni~ could break through into the tunnel behind the cutterhead. The required solution was a ring seal around the outside periphery of the shield that could be expanded to imbed a sharp edge into the material of the bored t-nnel to create an outer seal around the machine. This seal was quits an engineering feature, since it was required to withstand a 10-bar pressure. The interior of the machine was
TUNNEL~UNN IG -~
f
TBM
TOP VlEW
TWO TARGET AREAS TUNNEL UNING SEC]ION ~IEW
Figure 2. Long horizontal probe holes.
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designed with a pressure bulkhead and the conveyor w a s r e t r a c t a b l e . A pressure door was designed to quickly close the conveyor opening at the pressure bulkhead when the conveyor was retracted. This a r r a n g e m e n t effectively closed off the front portion of the machine. It also required that the machine be designed with the same s t r u c t u r a l c a p a b i l i t y of a normal pressure bulkhead shield. All structural components and openings, including the main bearing seal system, had to be designed to withstand 10bar pressure. The design of the sides and the rear portion of the shield was another question. The British tunnel segments were not designed to be sealed. In fact, the key segment placed at the top was trapezoidal wodge-shaped and was shorter than the normal segments, in order to provide for variable expansion of the rings against the ground. There was no practical way to seal the tail against a non-sealing segment system, especially one with a large opening r e m a i n i n g at e v e r y ring. Nonetheless, the owner insisted that some form of a flexible sealing system be devised and b u i l t - - a t a very substantial cost. No a m o u n t of argument could dissuade the owner from this decision, even when it was clearly pointed out that it was impossible to develop a working seal t h a t would be effective. T h e n o r m a l o p e r a t i o n throughout the tunnel was without a shield tail and the rings were built directly on the cut rock.
The State-of-the-Art in Pressure Bulkhead Shield Tunneling Hundreds of tunneling machines have been operated successfully below the water table by using slurry or EPB systems of muck removal and face support. This technology transfers directly from the urban environment for which it was developed to subsea tunneling, especially in soil formations. Pressure shields have been used successfully in recent years in mixed ground conditions and in fractured rock, as was demonstrated at the Channel Tunnel. However, future subsea tlmnels will be driven at much greater depth than the Channel tunnel or D e n m a r k ' s Great Belt tunnel. One limitation of the pressure shield technology will be its pressure capacity.
Pressure Capacity Although the Channel tunnel pressure shields were built to operate at 10 bar, the design and test pressures were greater. Specifications required aleakage rate at the tail seals of less than 9 liters per second at 9.4 b a r pressure and, of course, zero leakage at the
main bearing seals at 10 bar. At the time those machines were designed, no machine had operated at those high pressure levels, which are equivalent to 100 m of w a t e r pressure. We believe this remains the general state of the art, although some machines for Japanese tunnels m a y have been built to operate at somewhat higher pressures in recent years. A short study of the question has led us to conclude that future machines might be built to operate at pressures up to 20 bar. This appears to be feasible, beth structurally and in seal technology; however, it is likely that special tail seals would have to be built and tested. Special segments, with very smooth outer surfaces and special inter-segment seals, also may be required. One problem t h a t will be increasingly difficult to solve at high water pressure will be changing the tail seals when they become damaged or worn. It m a y be possible to develop an inflatable ring seal mounted at the very back of the tail. Such a seal would allow all rows of tail seals to be exposed for changing seals from within the tail skin. Another problem, which is already beyond solution at 10 bar, is changing cutters when the machine is operating under high w a t e r pressure. The only reasonable solution to this problem is to build a protected area around the machine with grout. With the ground consolidated, the pressure can be reduced to zero in the cutterhead cavity so that the machine can be entered for repairs, as p u m p s take care of leakage. This situation is one of the main reasons for having very small or closable openings in the cutterhead and a very capable grouting system.
Cutters for Mixed Conditions In soils and some mixed ground conditions, it m a y not be possible to create an effective solidified zone around the machine. This provides an extra incentive for the development of very reliable long-life cutters. Most ground, including most soil conditions, can be bored using disc cutters that will give the same results that would be achieved with drag pick cutters. However, in mixed rock and soil or beulders or in solid rock, drag pick cutters simply will not work. They cRnnot take the wear and shock without breaking. They hook onto large pieces of reck or boulders and rip them out of their embedded position in the matrix material, causing the large rocks to tumble around the face and become jammed into the bucket openings. The big pieces of rock also may find their way into the cutterhead cavity, where they m u s t then be dealt with. This may mean crushing the rocks before bring-
326 TUNNELLINGAND UNDERGROUNDSPACETECHNOLOGY
ing them out of the cutterhead by a screw or slurry system. A cutterhead with all disc cutters and small bucket openings can deal with all of these conditions effectively, particularly if the bucket lips are retractable in unstable conditions. Boulders can be broken into normal-size rock chips and ingested through small b u c k e t openings, where t h e y are handled without difficulty by a screw conveyor or even a slurry system. There is a need to develop very reliable disc cutters with longer-life cutting edges. The technology is available, including pressure compensation for cutter bearings and tungsten carbide discs.
Muck Removal Systems For subsea tunnels under very high pressure, the muck removal from the pressurized cutterhead chamber to atmospheric pressure within the t~mnel is a critical element. As mentioned above, dual screw conveyor systems have failed to operate reliably at relatively moderate pressures unless the soil conditions are ideal. Even adding polymers and bentonite will not provide the consistency needed when boring in rocky formations. This means t h a t some type of positive displacem e n t or compartmentalized system is required. Such systems include: • Piston dischargers. • Double hopper tAnk.q. • Rotary hopper. These systems are illustrated schematically in Figure 3. All of these systems m u s t be further developed, particularly for use with large-diameter tunnels. Slurry systems can be used effectively at very slow advance rates and high expense. It is clear t h a t considerable room remains for continued development of tunneling machines for undersea tunnels. In soft ground and mixed conditions, there m a y be some tunnels that will be too deep to be practical. If the pressure will be too high for pressure bulkhead type machines, it is hard to imagine other methods that could be more risk-free. In rock bering, the emphasis should be on development ofprebe drill detection systems and effective groutlng from within the machine at the heading. The area t h a t m a y have the greatest potential payoffto the tunnel owners in t e r m s of reduced costs and completion times is the best use of modern contracts between the owner, the contractor and the equipment suppliers. The guidelines for contracting practice and disputes resolution that the International Tunnelling Association (ITA) has produced should be serionsly considered.
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The basic economics of the contract, such as labour cost, material cost, and equipment type, quantity, and cost, are best controlled by the contractor and therefore are his risl~ Maintaining a construction schedule is the contractor's risk, unless the schedule is influenced by factors outside the contractor's control. Labor strikes at the job site are the contractor's risk, although contractors should be entitled to time extensions. A contractor who chooses to subcontract work is responsible for managing the subcontractors, and bears the risk associated with their performance.
PISTON DISCHARGER
DOUBLE HOPPER TANKS MUCK FLOW ROTARY HOPPER
Figure 3. Pressurized muck removal systems.
Viewpoint of a Tunnel Contractor Risk Shanng in the Construction Process When an owner m a k e s a decision to construct a project, he bears all of the risk flowing from t h a t decision. The owner continues to bear all of the risks until he has transferred them to another party for a fair and equitable compensation. The principal guidelines in transferring risk should be whether the receiving party: • has the ability to control or minimize the risk; • has the competence to be able to assess the risk; and • is best able to bear the cost. For the purposes of this paper, the major risks can be grouped into four main categories, with comments on the party most likely to be able to deal with them. Physical Risk Access to the site and reasonable room to construct a project are part of the owner's basic planning and must be provided by the owner. Because subsurface conditions are of prime impertance on all underground projects, they should be set forth in a complete Geotechnical Design S u m m a r y Report (GDSR). This report should set forth the designer's anticipated subsurface condition and its impact on both design and construction. The report should establish the geotechnical baseline for all anticipated conditions. This single c o n t r a c t u a l i n t e r p r e t a t i o n of the geotechnical conditions will generally provide for more uniform bid prices and less misinterpretation of the subsurface data.
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The GDSR baseline is used during construction to measure whether conditions differ materially from those described. I f they do, and the contractor can demonstrate a financial impact, the contractor should be entitled to additional compensation. Thus, the owner receives bids based on a uniform intorpretation with appropriate bid prices, and accepts the risk if conditions turn out to be more difficult. A detailed description and an eT~mple of a GDSR report can be found in the pamphlet entitled =Avoidln~ and Resolving Disputes During Construction" (American Society of Civil Engineers 1990), and therefore will not be covered heroin. Weather conditions are normally the contractor's risk. The contractor should be relieved of time loss caused by extremely abnormal weather phenomena. Other extreme physical conditions, such as flood and earthquake, should fall under =Acts of God~ and remain as an owner risk.
Economic Risk Two major risks in this group are inflation and currency variations. Because these items CRnnot be determined or controlled by the contractor, they must remain with the owner. Other types of economic disruption, such as nationwide strikes, new taxes, and new government regulations, are all beyond the control of the contractor and, again, remain the owner's risk. The owner's project funding m u s t allow for covering the risk assumed, as well as the defined project cost. I f the owner uses lack of funds as a reason not to pay the contractor when additional compensation is due, it puts the owner in the position of not following his own contract.
~LL~O
Political and Social Risk Today, environmental risks are becoming a major factor in all construction projects. The owner may find some design options decided by the environmental impact rather than cost. The contract should detail all known environmental problems so that they m a y be included in the contract bid. Contractors should be responsible for any environmental problems caused by their operations. Any new environmental problems or new government agency regulations must remain the owner's risk.
Design Risk The project design is usually contracted to a project designer or team. The designer must exercise due diligence using skills normally provided by peers in the profession. The design must meet and provide for all codes, regulations, safety requirements, and constructability. The risk transferred to the designer should be within the designer's ability and financial resources and be proportional to the fee. Workmanship is the contractor's responsibility unless it is related to a defective design. Even when it is thought that all risk has been allocated in the contract, it is quite possible for significant disputes to arise. In the past, these disputes were settled by litigation. This became a very long and protracted way of settling such disputes, typically t~klng five, ten, or more years. On all projects, but particularly on mega-projects, this time delay can be fatal to one or more of the parties involved. In an attempt to improve the settlements of disputes and shorten the time required to settle them, the construction industry turned to arbitration associations or groups. This arrangement helped for awhile, but over time arbitration lost its innovation and became bound by many of the rules and time-consuming formalities, delays, and costs that had discouraged the use of the courts. In an attempt to reduce disputes and speed up their settlement, new alternative methods are being tried,
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including Partnering, Mediation, and Disputes Review Boards. For the settlementof disputes, the
referenced American Society of Civil Engineers publication (ASCE 1990).
Disputes Review B o a r d (DRB) has become quite popular in the United
What the Contractor Expects from the TBM Supplier
States. The board consists of three members selected w h e n the project starts. The owner and the contractor each appoint one m e m b e r to the beard, and the two appointees choose the third member. All beard members need to be approved by both the owner and the contractor. The board members are chosen for their knowledge, technical expertise, independence, and objectivity in the type of project to be constructod. The members' experience frequently reflects engineering design, construction, contract administration, and a legal background. The D R B holds meetings at the job site every three to four months, depending on the activity, in order to keep members current and up to date with construction progress and administration. At the meetings, the owner and the contractor beth present their views of the current job progress and situation. A n y items that look as though they m a y develop into a dispute will be discussed at these meetings in order to provide a background for any future resolution. One of the key elements of the D R B is that the members are knowledgeable about allthe detailsof the project and the conditions at the job site. Ifa dispute arises, each party prepares a position paper for presentation to the beard and to the other party. This paper will be provided to the board and other parties prior to a job site hearing. A formal hearing is then held at the job site, where each party gives an oral explanation of its position and rebuttal of the position of the other party. The DRB members can ask questions or request additional detail at such meetings. After all presentations have been submitted to the DRB, the beard meets in private to formulate and write its recommendations. These recommendations are submitted to beth parties to the contract. They are prepared as quickly as possible, usually within two to three months. On very urgent current operational matters, they have been completed in three to seven days. The great advantage of the DRB is in the engineering, construction, administration, and legal backgrounds of the group members and their current knowledge of the project and all circumstances related to the background of the dispute. A complete discussion of the DRB process can be found in the
During the bidding period, the contractor expects the TBM supplier to review the project and its requirements. The supplier must become familiar with the ground conditions, as described in the GDSR, and how his equipment can best be made to fit the project. The supplier should review ideas for the TBM with the contractor and incorporate as many of the contractor's suggestions as possible. The proposed delivery schedule should be compatible with the contract construction schedule, as well as the TBM supplier's ability to deliver the machine in accordance with his schedule. The contractor needs to realize that at bid time, the TBM supplier cannot completely tailor his quotation to the contractor's requirement, since there can be five or more bidders and the supplier cannot quote to each one's detailed specifications. After the bid, the successful contractor will usually talk to two or three TBM suppliers who are considered to have the best price, machine, and delivery schedule. The contractor will review in more detail the machine and delivery requirements, incorporating experience from operating other TBMs on other tunnel projects. At this time the TBM supplier will submit new prices based on the adjusted information, and the contractor will then pick the supplier that most nearly meets the job requirements. After the TBM purchase contract has been signed, the contractor will continue to work very closely with the TBM supplier during the design and early fabrication stages. The contractor will want the supplier to incorporate his ideas into the detailed design. However, contractors must be aware of the impact--on beth time and cost--of incorporating their ideas. During the fabrication of the machine, the contractor may have a full-time representative at the factory, depending on the complexity of the TBM and the newness of the design to the contractor. The contractor will want the TBM to be designed to the latest state-ofthe-art, on the one hand; but on the other hand, he will also want it to be as reliable as possible. The TBM design must take into account that a tunneling operation is usually one of the most crowded and hostile environments in which a piece of construction
328 TUNbrZ~G ANDUNDERGROUNDSPACETECHNOLOGY
equipment has to operate. A machine must not be so complex that it takes too many people to service it, and thereby lose more time in servicing than is gained in production by using a state-of-the-art machine. As the fabrication and assembly near completion, all operating components should be shop-tested and operated. Since these tests cannot be performed under load conditions, they must be carefully planned and thoroughly run in order to establish that everything has been designed and assembled properly. The shipment to the job site must be planned and coordinated so that the TBM will arrive in proper order for assembly and to ensure that no parts or components will be damaged in shipment. After the TBM parts start to arrive at the job site, the contractor will expect the manufacturer to furnish experienced technical staff to assist and help direct the assembly of the machine. The contractor will also expect this staffto test the machine at the job site and to help familiarize the field operating people with its operation and maintenance. During the start-up and shakedown of the TBM, the supplier should maintain qualified staff at the job site to assist in solving any problems that develop during this stage. After the machine has completed its shakedown period and is in operation, it is usually not necessary to have the manufacturer's representative at the job site. Depending on the complexity of the machine and its continuing operating situation, there will be times when a technical representative from the manufacturer should be available at the job site to help solve problems of operation as they develop. While contractors realize that the TBM manufacturer is not experienced in the driving of tunnels, they do expect manufacturers to bring all of their experience to bear on developing the most efficient machine possible for the ground conditions expected to be encountered. In order for the tunnel project to be a success, the TBM manufacturer and the contractor must have a mutual respect for each others' ideas and integrity. []
References American Society of Civil Engineers. 1979. Construction Risk and Liability Sharing, Volumes 1 and 2 (January, 1979). New York: ASCE. American Society of Civil Engineers. Avoiding and Resolving Disputes During Construction. 1989. New York: ASCE.
Volume 9, Number 3, 1994
Tunnelling Machine Development for Undersea Projects--a Review of the Issues Richard Robbins and Martin Kelley
Abstract--The decisions that lend up to the start of a major undersea tunnel will be the principal factors in determining the degree of succses of the project. This is especially true if the geologic conditions are difficult. Many factors can conspire against success, including some which might at first appear to benefit the owner. This paper covers issues from the uiewpointd of a tunnel machine manufacturer and a contractor. The uses of undersea tunnels are discussed, as are the types of machines that should be considered, us determined by the geologic conditions. Probe drilling, considered the most reliable method of detecting hazardous conditions ahend of the face, is reviewed. The state-ofthe-art in pressure bulkhead shields is detailed. The contractor's viewpoint focuses on issues of risk sharing. The categories of risk and proper allocation of these risks are discussed, us well as the most effectiue methods of Umiting and resolving disputes. The authors describe the contractor's expectations of the tunneling machine supplier, both before the construction contract is signed and after the selection of a machine.
Viewpoint of a Tunneling Machine Manufacturer s is the case w i t h most b]nnel
ing jobs, the project cost and time to completion for an undersea t - n n e l is determined by what happens at the headln~. Although the job may involve a very large investment in capital and expert manpower, all of the effort is concentrated at the t~]nnel heading. If it isn't happening there, it isn't happenin~ anywhere. This me~nR that the design criteria for the job and the selection of methods and equipment must be done with great care. In a major undersea tnnnel, the job becomes highly committed to the successful use of the systems selected. Unlike a subway tunnel, the solution
Present address: Richard J. Robbins, Vice Chairman, The Robbins Company, Box 97027, 22445 - 76th Ave. So., Kent, Wa~hin~on 98031, U.S~..; Martin Kelley, Vice-President (retired), Engineering and Estimating, Kiewit Construction Group, do 25070 N.E. Graham Road, Aurora, OR 97002, U.S.A.
of grouting from the surface or sinlring an extra repair shaft is usually out of the question. The contracting practices currently in use often encourage unjustified risk-tRklng by the contractor. Furthermore, the competitive naturo of the bidding process supports the tendency to rely on optimistic assumptions. Another hazard presented by large prestigious undersea projects such as the Channel tunnel, the Trans-Tokyo Bay highway, and the Seikan tunnel is the prestige of being associated with a world-class tunnel project. This prestige is sometimes viewed as justifying either a very low price or otherwise unacceptable contracting conditions and special risks. Even though the prestige and advertising value m a y be worth a substantial amount, the owner and/or the contractor m u s t consider w h e t h e r accepting a bargain price m e a n s compromising the success of the job. In today's economic environment, a bargain price is hard to pass up; however, in the highly committed tunnel business, experience or a proven track record m a y be worth more in completing the project on schedule.
Uses of Undersea T u n n e l s The major undersea tunnels t h a t have attracted the most international publicity have been transportation facilities, and mainly railways. Examples have been Seikan tunnel in Japan, the ChRnnel tunnel linking Groat Britain and France, and the Great Belt tunnel in Denmark. Highway tunnels such as the Trans-Tokyo Bay project are occasionally built, as are strait and i~ord crossings in locations such as Norway. Non-transportation tunnel projects include major offshore sewer outfall tunnels such as those in Boston H a r beur and Sydney, Australia; cooling water tunnels for power plants such as the Seabrook nuclear power plant in New Hampshire; and freshwater intake tunnels such as the Lake Michigan water tunnels for Chicago, Illinois, and the Port Huron tunnel for Detroit, Michigan.
TBM Selection T - n n e l bering machines (TBMs) have been used to excavate m a n y undersea tunnels and tunnels under great bodies of fresh water.
Tunnellingatul UndergroundSpace Technology, Vo[. 9, No. 3, pp. 323-328, 1994 Elsevier Science Ltd Printed in Great Britain 0886-7798/94 $7.00 + .00
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All types of T B M s have been used, from open gripper machines to pressure bulkhead shield machines. The choice depends on the geology. Most major undersea jobshave been in rock. As would be expected,most of the machines have been normal open gripper type,hard rock tunnel borers. Rock Tunnels Undersea tunnels in rock should be approached as normal reck tunnels, with the obvious caution to keep in mind that an unlimited quantity of water at high pressure is available to flood the tunnel from above. The best way to cope with this threat depends on the rock conditions to be encountered. The problem should be dealt with in the plavning stages by Prediction, Preparation, and Detection. Prediction is the use of the best geologic expertise available, based on appropriate exploration techniques. Prediction should be divided into each major geologic block and should inchide a statement of how the rock and the waterwill react to having the tunnel opening bored t h r o u g h it. This information should provide the basis for a Geotechnical Design Summary Report (GDSR) and for the methods a n d e q u i p m e n t selected by t h e contractor. Preparation involves the design of the TBM and the other equipment, including the rolling stock and trailing gear or back-up system. It includes determination of the rock support and lining systems, and defining appropriate measures to be used when the detection system employed indicates the presence of high water permeability or unstable rock ahead of the machine. Preparation work must Rnawer questions related to the amount of water inflow that can be tolerated during the construction period, and whether it will be salt water. Corrosion protection and specifications of all equipment, particularly electrical equipment, should be agreed upon in advance. Preparation also includessafety designand trainingforalltunnel workers. Emergency evacuation plans should be practiced. Detection is the one area of tunnel technology that has not been developed to keep pace with the needs for undersea tunneling. What do we need to know? We must be able to detect bad or worsening geologic conditions well in advance of the tunnel heading. The detection system should tell us about the water inflow to be expected, rock stability, flammable gas, and any other hazardous conditions. In reck tunneling, it is fair to assume that we will depend on ground treatment, particularly grouting from within the machine or from a position
FOUR TARGET AREAS TUNNEL LININ
Figure 1. 1974 Channel tunnel probe drilling pattern. just behind it for the drilling and injection. These procedures should be carried out from a position in relatively good rock or previously treated ground. This means that the detection system should identify hazards a minimum of four or five diameters ahead of the machine or up to twenty to thirty diameters ahead, or as far ahead as is practical. Probe drilling must be done systematically and in a pattern to detect lowangle faults that could cause flooding. In 1974, at a previous start of the Channel Tunnel, the designers required four probe holes to maintain a pattern of protection, as shown in Figure 1. The probe holes had to enter the target areas within a limited distance ahead of the tunnel face and remain in the target for a specified distance. It can be argued that the lower two probe holes are not required in undersea tunneling, since any fiat-lying fault coming up from below is not likely to be connected directly with the water source above the tunnel. On the other hand, it might be wise to put down some shorter (four to five tunnel diameter) steep holes in areas of serious concern. Each of these probe holes should be drilled through a sealable packer inserted into a drilled oversize starting hole. Detection of serious water problems well ahead of the TBM is an essential feature of bored undersea tunnels in rock. However, the most important and most difficult task is interpreting the information that is available from the probe drilling. This remains the commission of an experienced drilling superintendent or geo-technician, who should be on duty whenever the probe drilling is being carried out.
324 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
In the future we may see practical systems of continuous detection based on geophysics for mapping ground features ahead of the TBM as it bores forward. Watching the research work that is being carried out by numerous organizations around the world gives us hope, but for the foreseeable future we must continue to rely on probe drilling for reliable detection.
Long Probe Holes An interesting possible development that would be welcome is accurate long hole probe drilling ahead of a TBM. A system can be developed to bore long horizontal holes that can be steered accurately while drilling. The advantage of such a system would be a probe drilling operation that would not interfere with the tunnel bering. Oil well drilling is turning more frequently to horizontal drill holes to drain difficult production areas. Holes as long as 2 km have been drilled. A horizontal bore hole would start behind the tunneling machine, perhaps as far back as 100 m or more. It would enter the wall of the tunnel at a fairly acute angle of about 20 degrees. The drill must then turn through a 20degree arc to parallel the centerline of the tunnel and stay within a target area of perhaps 1 m to 2 m diameter while bering out 1 or 2 km ahead of the machine. With a drill hole on either side of the area above the tunnel alternating, we could have continuous probe information weeks before the machine headed into a bad ground area. As the machine approached the dangerous zone, a more complete pattern of probe holes could be bored ahead to gain the detailed information needed to design a grouting program. A schematic de-
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sign of such a system is shown in Figure2. Long horizontal probe holes require the development of a drilling system that can be driven around a fairly short radius curve of about 10 m radius around arc angles of up to 30 degrees. A very accurate surveying system will have to be developed to determine the position and attitude of the drill head, either providing continuous "Position While DrillinL~ information or periodic information that can be obtained rapidly without too much interruption of the probe dri|ling.
Undersea Tunnels in Mixed Geology and Wet Conditions Although the French side of the Channel tunnel was a rock tnnnel, the weak rock was severely faulted with open joints. The joints provided a direct connection between the tunnel face and the open sea above. The choices were to grout it all solid or to drive the tunnel with a water pressure b,dkhead shield and a sealed segmental liner, as if it were a subaqueous, sell-ground t u n n e l In 1974 the decision was made to grout. The TBM that was built for the service tunnel had an open cutterhead with special previsions for probe drilling and grouting. It was the only practical choice, given the state of t , nneliug technology at that date. In 1987 the decision was made to drive the tunnel as a pressure bulkhead shield--a system that had never before been used in rock. The key technical question was how to remove cut rock debris from the seawater pressurized chamber of the cutterhead. The choices included slurry pumping, double screw conveyors with or without a plug zone between the screws, rotary discharge chambers or carrousels, twin pressure hoppers, and twin piston discharger. Only the twin pressure hoppers had been used before in a rock tunnel--the 10.3-m-diameter RER rail tlmnel in Paris from the Etoile to Defense. That rail tunnel was driven with a pressure bulkhead shield, the first in the world; however, the muck removal system from the cutterhead was in compressed air, and not under water pressure. The large diameter provided the large vertical height required for the pressure hoppers. This method did not seem practical for the 5.8-m driven pilot tunnel for the Chnnne] t-nnel. The other systems of muck removal had all been used in both small- and large-scale soil hmnels, but not in rock. The final decision was to use a cutterhead with a centrally located hopper and a center-supported primary screw conveyor to bring the muck from the cutterhead to the rear of the shield while under pressure. The screw would
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move the muck and at the same time consolidate it, so that the solid muck made up the large majority of the volume at the discharge point of the screw. For dry boring conditions or in areas of low water inflow, the screw was designed to discharge into a flight feeder conveyor that fed directly onto a belt for loading muck cars. In high water flow and high pressure areas, the screw fed pressurized muck into a twin piston discharger, which took the muck down to atmospheric pressure in the controlled released of a positive displacement pump. This system was secure againat water blow-through. A third alternative muck removal system--a conventional slurry pumping system--was provided and built into the machinery but never used. All of the slurry equipment was designed and procured to accept the muck from the machines screw, mix it and pump it to the shaft discharge point continuously while the machine borod the tunnel. The slurry system also eliminated the need for the muck car haulage system. This complex and relatively slow muck removal system was to be used only if the piston discharge system could not be developed to operate effectively. Fortunately, it was never needed. The two rl]nn~llg tunnel machines of 8.5-m diameter for the French side of the tunnel were built in a joint venture between Robbins and Kawasaki Heavy Indlmtries. Kawasaki was convinced that it could make a double screw system with a plug zone work effectively as the means to bring the muck from high pressure to atmospheric pressure. This conviction was based on full-scale testing of a double screw in the labora-
tory at the manufacturing plant in Japan, using tunnel muck t h a t was shipped from the Channel Tunnel. These machines were therefore built with the double screw instead of the piston discharger. In operation at the Channel Tunnel, the rock chips cut by the rlmnin E t, mnel machines did not develop the proper consistency to form a pressure plug or the proper pressure differential along the screws. As a result, water and fines would blow through the screws out ofcentrol. Fort-nntely, the service t-nnel provided the possibility to grout the area ahead of the running bmnel machines; and there-
fore, it became ,mnecoesary to run the
big machines under water pressure. The B#tish Side Inundation Protection An unusual feature of the three machines that bored under the Channel from the British side, eastward toward France, was the use of special inundation seals. There was concern that one of the hundreds of bore holes which had been drilled for exploration over a period ofmore than one hundred years might have been leit open and would be bored through by the tunneling machine. Even a near rni~ could break through into the tunnel behind the cutterhead. The required solution was a ring seal around the outside periphery of the shield that could be expanded to imbed a sharp edge into the material of the bored t-nnel to create an outer seal around the machine. This seal was quits an engineering feature, since it was required to withstand a 10-bar pressure. The interior of the machine was
TUNNEL~UNN IG -~
f
TBM
TOP VlEW
TWO TARGET AREAS TUNNEL UNING SEC]ION ~IEW
Figure 2. Long horizontal probe holes.
TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY325
designed with a pressure bulkhead and the conveyor w a s r e t r a c t a b l e . A pressure door was designed to quickly close the conveyor opening at the pressure bulkhead when the conveyor was retracted. This a r r a n g e m e n t effectively closed off the front portion of the machine. It also required that the machine be designed with the same s t r u c t u r a l c a p a b i l i t y of a normal pressure bulkhead shield. All structural components and openings, including the main bearing seal system, had to be designed to withstand 10bar pressure. The design of the sides and the rear portion of the shield was another question. The British tunnel segments were not designed to be sealed. In fact, the key segment placed at the top was trapezoidal wodge-shaped and was shorter than the normal segments, in order to provide for variable expansion of the rings against the ground. There was no practical way to seal the tail against a non-sealing segment system, especially one with a large opening r e m a i n i n g at e v e r y ring. Nonetheless, the owner insisted that some form of a flexible sealing system be devised and b u i l t - - a t a very substantial cost. No a m o u n t of argument could dissuade the owner from this decision, even when it was clearly pointed out that it was impossible to develop a working seal t h a t would be effective. T h e n o r m a l o p e r a t i o n throughout the tunnel was without a shield tail and the rings were built directly on the cut rock.
The State-of-the-Art in Pressure Bulkhead Shield Tunneling Hundreds of tunneling machines have been operated successfully below the water table by using slurry or EPB systems of muck removal and face support. This technology transfers directly from the urban environment for which it was developed to subsea tunneling, especially in soil formations. Pressure shields have been used successfully in recent years in mixed ground conditions and in fractured rock, as was demonstrated at the Channel Tunnel. However, future subsea tlmnels will be driven at much greater depth than the Channel tunnel or D e n m a r k ' s Great Belt tunnel. One limitation of the pressure shield technology will be its pressure capacity.
Pressure Capacity Although the Channel tunnel pressure shields were built to operate at 10 bar, the design and test pressures were greater. Specifications required aleakage rate at the tail seals of less than 9 liters per second at 9.4 b a r pressure and, of course, zero leakage at the
main bearing seals at 10 bar. At the time those machines were designed, no machine had operated at those high pressure levels, which are equivalent to 100 m of w a t e r pressure. We believe this remains the general state of the art, although some machines for Japanese tunnels m a y have been built to operate at somewhat higher pressures in recent years. A short study of the question has led us to conclude that future machines might be built to operate at pressures up to 20 bar. This appears to be feasible, beth structurally and in seal technology; however, it is likely that special tail seals would have to be built and tested. Special segments, with very smooth outer surfaces and special inter-segment seals, also may be required. One problem t h a t will be increasingly difficult to solve at high water pressure will be changing the tail seals when they become damaged or worn. It m a y be possible to develop an inflatable ring seal mounted at the very back of the tail. Such a seal would allow all rows of tail seals to be exposed for changing seals from within the tail skin. Another problem, which is already beyond solution at 10 bar, is changing cutters when the machine is operating under high w a t e r pressure. The only reasonable solution to this problem is to build a protected area around the machine with grout. With the ground consolidated, the pressure can be reduced to zero in the cutterhead cavity so that the machine can be entered for repairs, as p u m p s take care of leakage. This situation is one of the main reasons for having very small or closable openings in the cutterhead and a very capable grouting system.
Cutters for Mixed Conditions In soils and some mixed ground conditions, it m a y not be possible to create an effective solidified zone around the machine. This provides an extra incentive for the development of very reliable long-life cutters. Most ground, including most soil conditions, can be bored using disc cutters that will give the same results that would be achieved with drag pick cutters. However, in mixed rock and soil or beulders or in solid rock, drag pick cutters simply will not work. They cRnnot take the wear and shock without breaking. They hook onto large pieces of reck or boulders and rip them out of their embedded position in the matrix material, causing the large rocks to tumble around the face and become jammed into the bucket openings. The big pieces of rock also may find their way into the cutterhead cavity, where they m u s t then be dealt with. This may mean crushing the rocks before bring-
326 TUNNELLINGAND UNDERGROUNDSPACETECHNOLOGY
ing them out of the cutterhead by a screw or slurry system. A cutterhead with all disc cutters and small bucket openings can deal with all of these conditions effectively, particularly if the bucket lips are retractable in unstable conditions. Boulders can be broken into normal-size rock chips and ingested through small b u c k e t openings, where t h e y are handled without difficulty by a screw conveyor or even a slurry system. There is a need to develop very reliable disc cutters with longer-life cutting edges. The technology is available, including pressure compensation for cutter bearings and tungsten carbide discs.
Muck Removal Systems For subsea tunnels under very high pressure, the muck removal from the pressurized cutterhead chamber to atmospheric pressure within the t~mnel is a critical element. As mentioned above, dual screw conveyor systems have failed to operate reliably at relatively moderate pressures unless the soil conditions are ideal. Even adding polymers and bentonite will not provide the consistency needed when boring in rocky formations. This means t h a t some type of positive displacem e n t or compartmentalized system is required. Such systems include: • Piston dischargers. • Double hopper tAnk.q. • Rotary hopper. These systems are illustrated schematically in Figure 3. All of these systems m u s t be further developed, particularly for use with large-diameter tunnels. Slurry systems can be used effectively at very slow advance rates and high expense. It is clear t h a t considerable room remains for continued development of tunneling machines for undersea tunnels. In soft ground and mixed conditions, there m a y be some tunnels that will be too deep to be practical. If the pressure will be too high for pressure bulkhead type machines, it is hard to imagine other methods that could be more risk-free. In rock bering, the emphasis should be on development ofprebe drill detection systems and effective groutlng from within the machine at the heading. The area t h a t m a y have the greatest potential payoffto the tunnel owners in t e r m s of reduced costs and completion times is the best use of modern contracts between the owner, the contractor and the equipment suppliers. The guidelines for contracting practice and disputes resolution that the International Tunnelling Association (ITA) has produced should be serionsly considered.
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The basic economics of the contract, such as labour cost, material cost, and equipment type, quantity, and cost, are best controlled by the contractor and therefore are his risl~ Maintaining a construction schedule is the contractor's risk, unless the schedule is influenced by factors outside the contractor's control. Labor strikes at the job site are the contractor's risk, although contractors should be entitled to time extensions. A contractor who chooses to subcontract work is responsible for managing the subcontractors, and bears the risk associated with their performance.
PISTON DISCHARGER
DOUBLE HOPPER TANKS MUCK FLOW ROTARY HOPPER
Figure 3. Pressurized muck removal systems.
Viewpoint of a Tunnel Contractor Risk Shanng in the Construction Process When an owner m a k e s a decision to construct a project, he bears all of the risk flowing from t h a t decision. The owner continues to bear all of the risks until he has transferred them to another party for a fair and equitable compensation. The principal guidelines in transferring risk should be whether the receiving party: • has the ability to control or minimize the risk; • has the competence to be able to assess the risk; and • is best able to bear the cost. For the purposes of this paper, the major risks can be grouped into four main categories, with comments on the party most likely to be able to deal with them. Physical Risk Access to the site and reasonable room to construct a project are part of the owner's basic planning and must be provided by the owner. Because subsurface conditions are of prime impertance on all underground projects, they should be set forth in a complete Geotechnical Design S u m m a r y Report (GDSR). This report should set forth the designer's anticipated subsurface condition and its impact on both design and construction. The report should establish the geotechnical baseline for all anticipated conditions. This single c o n t r a c t u a l i n t e r p r e t a t i o n of the geotechnical conditions will generally provide for more uniform bid prices and less misinterpretation of the subsurface data.
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The GDSR baseline is used during construction to measure whether conditions differ materially from those described. I f they do, and the contractor can demonstrate a financial impact, the contractor should be entitled to additional compensation. Thus, the owner receives bids based on a uniform intorpretation with appropriate bid prices, and accepts the risk if conditions turn out to be more difficult. A detailed description and an eT~mple of a GDSR report can be found in the pamphlet entitled =Avoidln~ and Resolving Disputes During Construction" (American Society of Civil Engineers 1990), and therefore will not be covered heroin. Weather conditions are normally the contractor's risk. The contractor should be relieved of time loss caused by extremely abnormal weather phenomena. Other extreme physical conditions, such as flood and earthquake, should fall under =Acts of God~ and remain as an owner risk.
Economic Risk Two major risks in this group are inflation and currency variations. Because these items CRnnot be determined or controlled by the contractor, they must remain with the owner. Other types of economic disruption, such as nationwide strikes, new taxes, and new government regulations, are all beyond the control of the contractor and, again, remain the owner's risk. The owner's project funding m u s t allow for covering the risk assumed, as well as the defined project cost. I f the owner uses lack of funds as a reason not to pay the contractor when additional compensation is due, it puts the owner in the position of not following his own contract.
~LL~O
Political and Social Risk Today, environmental risks are becoming a major factor in all construction projects. The owner may find some design options decided by the environmental impact rather than cost. The contract should detail all known environmental problems so that they m a y be included in the contract bid. Contractors should be responsible for any environmental problems caused by their operations. Any new environmental problems or new government agency regulations must remain the owner's risk.
Design Risk The project design is usually contracted to a project designer or team. The designer must exercise due diligence using skills normally provided by peers in the profession. The design must meet and provide for all codes, regulations, safety requirements, and constructability. The risk transferred to the designer should be within the designer's ability and financial resources and be proportional to the fee. Workmanship is the contractor's responsibility unless it is related to a defective design. Even when it is thought that all risk has been allocated in the contract, it is quite possible for significant disputes to arise. In the past, these disputes were settled by litigation. This became a very long and protracted way of settling such disputes, typically t~klng five, ten, or more years. On all projects, but particularly on mega-projects, this time delay can be fatal to one or more of the parties involved. In an attempt to improve the settlements of disputes and shorten the time required to settle them, the construction industry turned to arbitration associations or groups. This arrangement helped for awhile, but over time arbitration lost its innovation and became bound by many of the rules and time-consuming formalities, delays, and costs that had discouraged the use of the courts. In an attempt to reduce disputes and speed up their settlement, new alternative methods are being tried,
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including Partnering, Mediation, and Disputes Review Boards. For the settlementof disputes, the
referenced American Society of Civil Engineers publication (ASCE 1990).
Disputes Review B o a r d (DRB) has become quite popular in the United
What the Contractor Expects from the TBM Supplier
States. The board consists of three members selected w h e n the project starts. The owner and the contractor each appoint one m e m b e r to the beard, and the two appointees choose the third member. All beard members need to be approved by both the owner and the contractor. The board members are chosen for their knowledge, technical expertise, independence, and objectivity in the type of project to be constructod. The members' experience frequently reflects engineering design, construction, contract administration, and a legal background. The D R B holds meetings at the job site every three to four months, depending on the activity, in order to keep members current and up to date with construction progress and administration. At the meetings, the owner and the contractor beth present their views of the current job progress and situation. A n y items that look as though they m a y develop into a dispute will be discussed at these meetings in order to provide a background for any future resolution. One of the key elements of the D R B is that the members are knowledgeable about allthe detailsof the project and the conditions at the job site. Ifa dispute arises, each party prepares a position paper for presentation to the beard and to the other party. This paper will be provided to the board and other parties prior to a job site hearing. A formal hearing is then held at the job site, where each party gives an oral explanation of its position and rebuttal of the position of the other party. The DRB members can ask questions or request additional detail at such meetings. After all presentations have been submitted to the DRB, the beard meets in private to formulate and write its recommendations. These recommendations are submitted to beth parties to the contract. They are prepared as quickly as possible, usually within two to three months. On very urgent current operational matters, they have been completed in three to seven days. The great advantage of the DRB is in the engineering, construction, administration, and legal backgrounds of the group members and their current knowledge of the project and all circumstances related to the background of the dispute. A complete discussion of the DRB process can be found in the
During the bidding period, the contractor expects the TBM supplier to review the project and its requirements. The supplier must become familiar with the ground conditions, as described in the GDSR, and how his equipment can best be made to fit the project. The supplier should review ideas for the TBM with the contractor and incorporate as many of the contractor's suggestions as possible. The proposed delivery schedule should be compatible with the contract construction schedule, as well as the TBM supplier's ability to deliver the machine in accordance with his schedule. The contractor needs to realize that at bid time, the TBM supplier cannot completely tailor his quotation to the contractor's requirement, since there can be five or more bidders and the supplier cannot quote to each one's detailed specifications. After the bid, the successful contractor will usually talk to two or three TBM suppliers who are considered to have the best price, machine, and delivery schedule. The contractor will review in more detail the machine and delivery requirements, incorporating experience from operating other TBMs on other tunnel projects. At this time the TBM supplier will submit new prices based on the adjusted information, and the contractor will then pick the supplier that most nearly meets the job requirements. After the TBM purchase contract has been signed, the contractor will continue to work very closely with the TBM supplier during the design and early fabrication stages. The contractor will want the supplier to incorporate his ideas into the detailed design. However, contractors must be aware of the impact--on beth time and cost--of incorporating their ideas. During the fabrication of the machine, the contractor may have a full-time representative at the factory, depending on the complexity of the TBM and the newness of the design to the contractor. The contractor will want the TBM to be designed to the latest state-ofthe-art, on the one hand; but on the other hand, he will also want it to be as reliable as possible. The TBM design must take into account that a tunneling operation is usually one of the most crowded and hostile environments in which a piece of construction
328 TUNbrZ~G ANDUNDERGROUNDSPACETECHNOLOGY
equipment has to operate. A machine must not be so complex that it takes too many people to service it, and thereby lose more time in servicing than is gained in production by using a state-of-the-art machine. As the fabrication and assembly near completion, all operating components should be shop-tested and operated. Since these tests cannot be performed under load conditions, they must be carefully planned and thoroughly run in order to establish that everything has been designed and assembled properly. The shipment to the job site must be planned and coordinated so that the TBM will arrive in proper order for assembly and to ensure that no parts or components will be damaged in shipment. After the TBM parts start to arrive at the job site, the contractor will expect the manufacturer to furnish experienced technical staff to assist and help direct the assembly of the machine. The contractor will also expect this staffto test the machine at the job site and to help familiarize the field operating people with its operation and maintenance. During the start-up and shakedown of the TBM, the supplier should maintain qualified staff at the job site to assist in solving any problems that develop during this stage. After the machine has completed its shakedown period and is in operation, it is usually not necessary to have the manufacturer's representative at the job site. Depending on the complexity of the machine and its continuing operating situation, there will be times when a technical representative from the manufacturer should be available at the job site to help solve problems of operation as they develop. While contractors realize that the TBM manufacturer is not experienced in the driving of tunnels, they do expect manufacturers to bring all of their experience to bear on developing the most efficient machine possible for the ground conditions expected to be encountered. In order for the tunnel project to be a success, the TBM manufacturer and the contractor must have a mutual respect for each others' ideas and integrity. []
References American Society of Civil Engineers. 1979. Construction Risk and Liability Sharing, Volumes 1 and 2 (January, 1979). New York: ASCE. American Society of Civil Engineers. Avoiding and Resolving Disputes During Construction. 1989. New York: ASCE.
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