John Reilly has actively worked on the question “How much should an owner be responsible for the definition of Tunnel Boring Machines (TBMs) including the degree to which their configuration and operating characteristics are specified”.
This question, and the related issue of the balance between, or choice of, prescriptive or performance specifications has been debated in several of John’s projects, including:
- The LA Metro, Segments 2, 3 and the East Side Extension
- The Toronto Rapid Transit Expansion Program
- The Sir Adam Beck Hydro project, Niagara Falls
This has also been the focus of discussions with International Associations in Mexico, Austria, Switzerland, Holland, UK, Germany, Australia, China, Sweden and Korea.
The prescriptive approach fully defines the type and characteristics of the TBM, and usually the sequence of tunneling and support operations such as cutter replacement and machine maintenance. This was the case for the Toronto Rapid Transit Expansion Program tunnel drives. The basis for the prescriptive approach is that the owner, advised by tunneling, geotechnical and other experts, has the time, knowledge and ability to determine the best machine type, machine characteristics and methodological requirements for the project. This also allows early TBM procurement, for significant time savings.
The performance approach requires only that the contractor(s) meet defined performance requirements and leaves substantial freedom of choice, to the contractor, regarding machine types, methods and sequence of operations – so long as they meet contractual performance requirements, including quality, cost and schedule. The basis for the performance approach is that the contractor, with his experience considering available equipment, is best able to determine the most appropriate methods and techniques, using practices that best suit his equipment and experience. This should result in a bid that represents the best price for the underground work. However, this approach is sometimes flawed in its application and consequently does not always produce the expected results – frequently leading to disputes, changes, claims and litigation.
There is discussion for a move to a position between the prescriptive and performance approaches – but, how to determine the correct balance in this regard? For more details on this question, see John’s paper on “Owner’s Responsibilities in the selection of Tunnel Boring Machines”, presented at the World Tunnel Conference, Vienna, 1997 and other papers listed in the publication section of this Website.