AUA features outstanding Underground Project currently under construction, highlighting their unique aspects in terms of technology, location, function, etc. Contact UCA of SME to nominate projects.
This month's Featured Underground:
NUETRINOS AT MAIN INJECTOR (NUMI) PROJECT
DESCRIPTION OF PROJECT
The Neutrinos at the Main Injector (NuMI) project was constructed at Fermi National Accelerator Laboratory in Batavia, Illinois, as the centerpiece of an expanding neutrino physics program for the U.S. Department of Energy. The project provides underground and above-ground facilities to create and study the sub-atomic particles known as neutrinos.
Since the existence of neutrinos was first postulated in the 1930’s, the particle has proven highly elusive to study on account of its negligible mass and electric charge. As part of the world’s first high-energy, long-baseline neutrino experiment, the NuMI facility will harness the power of Fermilab’s Main Injector to generate a beam of neutrinos that will travel 435 miles through solid bedrock to an underground detector facility in Soudan, Minnesota. The experiments and research conducted will play a key role in our understanding of matter and the universe.
The facilities for the NuMI project consist of an interconnected system of tunnels and shafts with three major underground experimental caverns connected to two surface buildings by vertical access shafts. At one end, the project is connected to an existing particle accelerator and descends to 360 ft below ground over a length of approximately 4,200 lineal feet. The surface buildings provide assembly areas for the experimental facilities and permanent access, as well as utilities and operation and maintenance components.
PLANNING, DESIGN AND CONSTRUCTION
Fermilab scientists and engineers, together with engineers from MWH and Fluor Daniel, were responsible for planning and designing the underground facilities for the NuMI project. The scope of work included conceptual designs, feasibility studies, final design, cost estimating, and preparation of contract documents. The planning and design phase of the project was performed between 1995 and August 1999.
Tunneling and underground construction was subcontracted to S.A. Healy and completed between April 2000 and November 2002. MWH provided construction management services throughout the duration of the underground construction.
After construction of the underground work was completed, Fermilab began construction of the service buildings, final outfitting and installation of equipment and experiment components. In March 2005, the NuMI project was officially inaugurated by Hon. J. Dennis Hastert Jr. (Speaker of the U.S. House of Representatives) and Dr. Raymond L. Orbach (Director of the DOE Office of Science). The Speaker unveiled the beam to send the first pulses of neutrinos on a path through the earth from Fermilab to the far detector located in the historic Soudan iron mine in northeastern of Minnesota.
COMPLEXITY
As with all underground projects, there is an additional element of design complexity due to the inherent space limitations and the need to rely on the natural ground as an integral part of the structures. Furthermore, the unique end-user requirements of the NuMI project necessitated designs for a variety of complex conditions, including:
- Cut-and-cover, soft ground, “mixed face”, and hard rock excavations;
- Large caverns up to 60-ft high and 34-ft wide with less than 30-ft of rock cover;
- Large-diameter shafts up to 340-ft deep;
- Tunnels on steep declines of up to 15% grade; and
- Excavations in rock materials susceptible to deterioration upon exposure to air.
In addition to the challenges involved with the various types of underground structures and site conditions, the project alignment required extreme precision in order to “aim” the neutrino beam at a target nearly 455 miles away. Layout of the project necessitated detailed alignment studies with precise corrections for the earth’s shape and curvature.
ORIGINAL/INNOVATIVE APPLICATION
Numerical Modeling: The design of the underground facilities for the NuMI project involved the use of the latest state-of-the-art numerical modeling techniques to evaluate the stability and behavior of the excavations and structures under various ground conditions and loads. The main objectives of the numerical models were to:
- Determine the stability of excavations under variable rock conditions;
- Evaluate the influence of low rock cover on large-span excavations;
- Determine the effect of multiple excavation openings in close-proximity to each other;
- Determine deformations and redistribution of stresses upon excavation; and
- Optimize the sequence of excavations and support installation.
The numerical modeling was performed using 2-dimensional and 3-dimensional models solved by discrete element and finite difference methods. Results of the modeling were used to refine the dimensions, locations and layout of key project structures, and to optimize the appropriate sequence of excavations. As part of the detailed design, the underground structures were equipped with several types of geotechnical instruments to monitor and evaluate the performance of the structures with respect to the anticipated behavior as determined by numerical modeling.
Controlled Environment: During the conceptual design studies, emphasis was placed on defining the end-user’s requirements, particularly the need for a controlled underground environment with respect to groundwater infiltration, humidity, and radiation shielding. The strict project requirements were, in part, necessary to protect the sensitive electrical and mechanical components of the physics experiments, and to prevent the surrounding groundwater from becoming slightly radioactive. Therefore, the design challenge was to provide a relatively dry environment and to maintain a positive inflow of groundwater into the excavations.
The solution to these special requirements was achieved by designing a unique system of composite linings and underdrains. The linings for tunnels and experiment halls primarily consisted of reinforced shotcrete with an under-layer of various geotextile membranes and fabrics. For the Decay Tunnel, a 78-inch diameter steel pipe (through which the particle beam would travel) was backfilled with up to 8-feet of a controlled low-strength cementitious material (CLSM) to contain radiation emitted from decay of the particle beam during operation of the experiment. A dimpled sheeting membrane was placed between the CLSM backfill and the rock surface to collect groundwater infiltration from bedrock and channel the inflows into a downstream collection sump.
Special provisions were also required to achieve relative humidity levels of 60% to 80% in parts of the underground facilities. Dessicated air is supplied from the surface to the underground facilities and local dehumidification units are provided to alleviate humidity levels. The HVAC system is designed to allow decay of radiation to acceptable levels.
Cavern Design:In addition to the strict user’s requirements, several unique techniques and materials were required because of the anticipated ground conditions. For example, a large-span excavation was located in an area with only 27-feet of rock cover. Based on the results of numerical modeling, a particular sequence of excavation and support was determined necessary to control ground deformations. In other areas, the bedrock consisted of siltstones and shales that were susceptible to deterioration upon exposure. Provisions were allowed for installing a protective layer of a flexible spray-on waterproofing sealant to be applied immediately after excavation to prevent the rock from deterioration. Final linings were later placed on the protected rock surface.
Constructibility Review:Prior to the final design stage, several “constructability” meetings were held with specialty underground contractors to evaluate appropriate layouts, construction sequencing and construction methods. The outcome of these meetings was a preliminary design specifically suited for the complex arrangement of underground facilities. Later in the design process, after a comprehensive cost estimate had been developed, a Value Engineering (VE) workshop was held. At this workshop, an outside engineering agency (U.S. Army Corps of Engineers) was invited to brainstorm and formulate alternate engineering solutions to various aspects of the project. The workshops were followed by the involvement of a technical Underground Advisory Committee, comprised of industry experts, to provide input to the final design. This construction-minded approach to design was taken to better define the project and to minimize project cost, while meeting the unique requirements dictated by the experiment.
HONORS AND AWARDS
The NuMI project is particularly unique in that it is one of the first deep underground facilities specifically designed for the purpose of high-energy physics research in the United States. Other similar types of deep underground facilities are now in various stages of planning and development at Fermilab and other research institutions around the world. The knowledge and experience gained from the NuMI project will likely be instrumental for these future projects.
Since its completion, the NuMI Project has earned the 2005 Honor Award from the American Council of Engineering Companies (ACEC) of Illinois and was a National Finalist for the 2005 ACEC Engineering Excellence Awards.
NUMI PROJECT FACT SHEET
Project Name: Neutrinos at Main Injector (NuMI) Project
Location: Batavia, Illinois
Contracting Agency: Universities Research Associates (under contract to the U.S.Department of Energy)
Leah Consultants: Fluor Daniel and MWH (formerly Harza Engineering Co.)
Contractor: S.A. Healy
Construction Management: MWH (formerly Harza Engineering Co.)
Purpose: High-energy physics research facilities
Special Features:
- Carrier Tunnel: 415-LF at 15% grade in soil, mixed-face and rock; pre-cast concrete and reinforced shotcrete linings, minimum 6-ft ID.
- Construction Shaft: 26-ft ID temporary shaft.
- Target Shaft: 22-ft ID, 120-ft-deep; cast-in-place concrete lining.
- Support Rooms, Access Passageways and Labyrinth: various dimensions; with reinforced shotcrete composite lining systems.
- Target Hall: 225-LF, 45 to 60-ft height by 27-ft width; reinforced shotcrete composite lining system.
- Decay Tunnel: 2100-LF TBM excavation at 5.8% grade, 21.5-ft ID with drill-and-blast enlargements; 78-in steel Decay Pipe with drainage membrane and CLSM backfill.
- Absorber Hall: 60-LF, 20-ft height by 27-ft width; reinforced shotcrete composite lining system.
- Muon Alcoves (3): 45-LF ea, 8 to 12-ft height by 8-ft width; reinforced shotcrete composite lining system.
- Absorber Access Tunnel: 700-LF TBM excavation at 10%grade, 21.5-ft ID.
- MINOS Access Shaft: 22-ft ID, 340-ft-deep; cast-in-place concrete lining.
- MINOS Hall: 235-LF, 32-ft height by 36-ft width; reinforced shotcrete composite lining system.
Cost:Due to the extraordinary complexity of the project - and the refinements and modifications made throughout the planning, design and construction phases - the construction costs for the tunnels and halls were approximately 15% higher than the final budgeted cost of $34 million.
Schedule:The design of the NuMI Project was completed in August 1999, allowing for construction of the underground facilities to be substantially completed in November 2002. The service buildings, final outfitting and installation of equipment were completed on schedule in January 2005. In March 2005, the NuMI project was officially inaugurated.
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