This presentation explores the current trends in tunneling procurement and delivery being used across the Americas. This includes a comparison between conventional and alternative delivery methods as they have been applied to tunnel projects in transportation and water/wastewater. The paper will illustrate methods such as design-build, progressive/modified design build, construction management at risk and public-private partnerships and how alternative delivery methods have been successfully used and challenges faced as they are applied to a wide range of tunnel projects across the USA.
A formal risk management process is widely implemented in our industry and this process is acknowledged as being a benefit to projects. However, risk management has descended to the level of a box-checking exercise for some projects. This session will present a framework of the basic needs and tools for project risk management. it will go on to provide tips for re-energizing and engaging the project team to get the maximum benefits from these processes, both for the project and for all project participants.
Dr. Brierley will discuss a nine-step process that is required in order to produce good designs and good contract documents for tunneling projects. In general, tunneling projects are radically different as compared to all other types of civil engineering projects because 100% of a tunnel comes into contact with the ground and because 75% of the risks associated with a tunneling project are related to construction procedures rather than the finished facility. As a result of the above, an enormous amount of thought must be given both to how the ground is “described” and to how the ground will “react” to proposed construction procedures, and, finally, to how the ground is “indicated” in the contract document via the Geotechnical Data and Baseline Reports. It is also important to note that the contract document must paint a “consistent” picture of construction procedures among the geotechnical documents and the plans and specifications.
Factors that make tunneling difficult are generally related to instability, which inhibits timely placement or maintenance of adequate support at or behind the tunnel face; heavy loading from the ground which creates problems of design as well as installation of a suitable support system; natural and man-made obstacles or constraints; and physical conditions which make the work place untenable unless they can be modified. In many cases special approaches or arrangements must be made to safely and efficiently excavate and stabilize the tunnel as it passes through this “Difficult Ground”. In this lecture, emphasis will be placed on creating and maintaining stable tunnel excavation in ground in TBM and SEM construction. Examples projects such as Chinatown Station in San Francisco, Istanbul Strait Crossing, and Alaskan Way tunnel will be used to illustrate the challenges.
NATM Design and Construction” introduces the tunnel design principles for the application of the Sequential Excavation Method (SEM). The presentation addresses the main aspects of SEM tunneling including: Ground Classification, Definition of SEM Excavation and Support Classes, Ground Support Elements, Structural Design, Instrumentation and Monitoring, Contractual Aspects, and Risk Management. Selected case histories are provided to demonstrate the range of applications ranging from shallow soft ground tunneling in urban settings to tunneling in rock.