EDITORIAL

Balancing Risk and Innovation in Underground Construction

Richard Robbins

1. Innovation: the Route to Lower Costs Complex underground jobs with difficult or unexplored

geology are the projects where the greatest payoff will be realized by innovation, if the new concepts are designed to reduce the effects of encountering the unknown. The difficult geologic conditions, even the potential of their existence, belong to the owner of the project. Owners must recognize this fact and seek ways to mitigate the geologic risks. The cost of construction will always be reducedby the use of the highest s tandard of technology and the best use of expertise and mangement systems.

On tunnel jobs of ordinary dimensions and where the geologic conditiosn can be inferred accurately, the standard system &accepting the low bidder, especially from a group of qualified contractors, may result in the lowest cost to the owner. However, on mega-projects, the normal bidding and contracting system can turn against the owner. The use of the best technology and the best people on very large or very difficult jobs is the most certain way to reduce costs. To ensure tha t result, owners of these big jobs should consider negotiated contracts.

2. The Development Payoff Large and complicated underground works are becom-

ing more common as societal needs increase and as our technical ability to perform the work improves. The past forty years have witnessed steady, incremental improve- ments in tunnel construction techniques, especially me- chanical excavation methods. This evolutionary process has led to increased tunneling speed, improved safety records, and reduced costs.

Today, however, we are designing tunnel projects that cannot be built at an acceptable cost using state-of-the-art

Present address: Richard Robbins, President, The Robbins Company, Box 97027, 22445 - 76th Avenue South, Kent, WA 98031, U.S.A. This editorial was hrst presented as akeynote address at ~I2.1NCON '92: Design and Construction of Tunnels ~, held September 1992, in Maseru, Lesotho; and was published in the Proceedings of that conference. It is reprinted herein with permission.

technology. Two undersea tunnel projects illustrate this trend: the Channel Tunnel between France and England; and the Great Belt Crossing in Denmark.

The French side of the Channel Tunnel required the development of the first water-pressure bulkhead shield machines for rock boring. At the Great Belt, these features also were required, with the added complication of boring a clay and sand till containing large boulders.

The geologic conditions on these jobs are so severe that great dividends would accrue to the owner if advanced excavation and support systems could be made to work. The payoff has yet to come on the Great Belt, but it was there with dividends on the Channel Tunnel, where world records were broken and tunnel progress from both ends approached double the average tha t was expected for the job.

It is fortunate that very high advance rates were achieved on the Channel Tunnel, because the job got offto a slow and shaky star t on both the French and British ends. The slow start can be attributed to the untried prototype machines and the complexity of the systems involved in the simulta- neous construction of four or five tunnels from each under- ground work site.

3. Prototype Development on the Job These examples illustrate two things: first, the need and

potential for payoff of innovative tunneling systems; and second, the risks associated with on-the-job prototype de- velopment. The jobs needed the innovation to be sure, but the problems caused in the early and critical stages &these projects were almost more than they could stand. This is particularly dangerous when a large international consor- t ium of banks is providing most of the required capital.

How can development and innovation be encourage d and applied to such mega-projects without taking these high risks? Almost always, a job of this size and cost involves years of planning and financial arranging prior to the construction. This is when innovation should be encour- a g e d - a n d , in fact, should be required--by the owner.

One example of such successful innovation is described by Messrs. Gravesen and Rasmussen in their paper in this issue of T&UST commemorating the fiftieth anniversary of the Maas Tunnel in Rotterdam [pp. 413-424]. A contemporary example, the TARP project, is described in more detail below.

Tunnelling and Underground Space Technology, Vol. 8, No. 4, pp. 411-412, 1 9 9 3 . 0886-7798/93 $6.00 + .00 Printed in Great Britain. Pergamon Press Ltd 4 1 1

4. The Chicago TARP Experience

The Chicago TAB/' (Tunnel and Res- ervoir Plan) is an example of a mega- project on which the owner saw the potential for cost savings through the application ofadvanced technology. This water clean-up program for Greater Chi- cago was foreseen to require more than 25 years to construct, and at least $US4 billion of taxpayers' money. It was a progressive solution to the thunderstorm flooding that has seriously polluted the Chicago River and Lake Michigan.

The solution to the problem of sum- mer flooding was to provide a wide- spread network ofcollector tunnels and deep, 10- to 11-m-diameter tunnels to form a long underground reservoir with a capacity of 155 m 3. This reservoir temporarily stores the entire runoff from a thunderstorm, so that the run- off can be treated gradually over a period of time and within the capaci- ties of the treatment plants, while the reservoir is emptied.

The second phase of this project is now under construction. When completed, it will include more than 211 km of deep tunnels; 252 vertical drop shafts averaging about 90 m deep; 645 near-surface collecting structures; four pumping stations; and five surface reservoirs.

A project of this size--the world's largest dvil engineering underground project--is being built entirely under a densely populated urban area. The owner's Chief Engineer was aware when the designs were completed for the first phase, in 1976, that tunneling machines had been used successfully on many tunnel jobs in weaker rock, but the Chicago dolomite had strength to 200 MPa. There was no certainty that l l -m-diameter hard rock TBMs could be built that could bore the Chi- cago rock.

The Metropolitan Sanitary District (MSD) decided tha t the long-term economic and political success of the project might depend on convincing the cont rac tors t h a t a sys t em of machine boring could be employed. They felt they had to avoid blasting if any other means of excavation was possible. But they were also looking for a faster, cheaper and more efficient system of excavation.

The MSD decided to require boring for an important early tunnel project of moderate diameter. Many contractors objected, but the job was done success- fully and soon everyone was commit- ted to the fact tha t they mus t bid all the future work without explosives. The equipment manufacturers responded to the demand with powerful and reli- able machines.

As the tunnel contracts on the TARP project continue to be let, the contrac-

torslearn from one another. The equip- ment utilization has improved; the trailing eqiupment and shaft muck el- evating systems are more efficient; and knowedge and experience in the me- chanical and electrical maintenance and repair areas have been gained.

Now that the project is into the second phase of construction, the MSD--now called the Metropolitan Water Reclamation District of Great Chicago--has saved hundreds of mil- lions of dollars by forcing the technol- ogy in the early stages of the project. Production records have been set and new industry standards are influenc- ing tunnel construction around the world. I t must be borne in mind, how- ever, that very few projects will present the opportunity the TARP project did to develop expertise and equipment that would influence more than 30 tun- nel contracts over the coming 25 years--- all for the benefit of the same owner.

5. Development and Innovation for the Mega-Projects

The owner of a long and difficult tunnel will have plenty of opportunity to consider whether a developmental breakthrough could have a positive ef- fect on the outcome of the job. The preliminary studies, geological explo- ration and economic analysis takes years on truly large jobs. Consider the new Alp Transit tunnels now being planned. Four new routes for deep rail tunnels are being planned to connect Italy to northern Europ~ including at least one route through the Austrian A]ps, two new routes through Switzer- land, and one through the French Alps.

These rail tunnels will be longer than the Channel Tunnel, through very hard crystallline rocks and through condi- tions expected to include very bad rock. But the key feature of all these new routes is the depth below the rock sur- face. Overburden of 3 km is expected. The rock pressues will be so great that even in the best of conditions the rock may need immediate support to coun- teract rockburet, especially where high tectonic stress is combined with the overburden loads. In bad rock zones, squeeze can be anticipated, perhaps with substantial convergence.

These deep alpine crossings can be constructed with conventional tech- niques and equipment, but the cost and time to complete them will be very difficult to predict. This is a clear case where the development of advance tun- neling technology could pay attractive returns.

How could the development be car- ried out in advance of a major project such as the Alp Transit? The first step would be to identify the potential diffi- culties and decide what methods will

be used if curent technology is em- ployed. I f the results indicate there is a good chance for very high costs or program delays, perhaps something could be developed to overcome the difficulties. The owner should contact the industry innovators and ask them for their opinions. What can be devel- oped? Who can do it? If the payoff could justify the cost of development, the mega-project owner should con- sider making the investment and cov- eting the cost of its demonstation on other projects.

For example, the owner of a major transport project may decide that probe drilling should be developed so that the danger of an unexpected inundation could be avoided. How can probe drill- ing be done in a way tha t does not inhibit the advance of the tunneling work?

I f an attractive solution is conceived, the prototype eqipment or method could be tried out on a hydropower tunnel project i f the t ransprotat ion owner covers the risks and costs. Successful development and =debugging" on an independent tunnel could have an important impact on the future mega- project.

6. Conclusion Standard contracting practices have

served well to construct many difficult jobs in the past. The contracting in- dustry is well suited to take risks and to take the consequences of the success or failure of an innovative solution. That has been true, but only in cases when the value of the construction work and the potential losses on the job can be borne by the contractors without serious risk of bankruptcy. When the jobs become too large, the geology too uncertain, and the potential for ex- tremely high cost overruns escalate, the traditional system of contracting seems inappropriate.

The owner should select a designer and contractor to work closely together to develop innovative solutions to the high risk aspects of the job. The con- tractors and designer should select equipment developers and systems experts who can work with them to ensure the best possible results.

Wherever possible, major new equip- ment development projects should be built and tested prior to their use on a mega-project, especiallyifthe expected geology will require their success. Owners should use their own creative thinking to find means to encourage the innovation or development that will pay dividends on their projects.

--RICHARD ROBBINS President,

The Robbins Company Kent, Washington, U.S~%-

412TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY Volume 8, Number 4, 1993