repairs or improvements. So what’ s an alternative? How about a walkable tunnel underneath the corridor to supply the steam, chilled water, compressed air, signal, and electric services so crucial for daily life on campus?
The University’ s East Campus Utility Improvements project involved the installation of this walkable utility tunnel – essentially a 10- by 12-foot-wide, 1,800-foot-long underground vault. To complete the project, the Wisconsin Department of Administration’ s Division of State Facilities( DSF) worked with a design team of Affiliated Engineers Incorporated( AEI), Ayres Associates, Bloom Companies, and JJR.
Such a proposed tunnel was bound to conflict with existing underground utilities, which meant that storm sewer and water mains, sanitary sewers, and other civil utilities would need to be relocated. Ayres Associates provided these relocation services, as well as traffic / pedestrian control, survey, and construction services. The high-profile, large-scale project was completed in phases over five years.
A major challenge of the project was installing a portion of the tunnel underneath West Johnson Street and University Avenue – two busy roadways connecting the east and west sides of Madison. So vital are these arteries that the City of Madison stipulated that the roads could never be closed during construction. Any lane closures were largely restricted to off-peak hours.
To deal with these limitations, the design team came up with several options, including boring( i. e., going underneath the majority of utilities) and using temporary bridges. A cost analysis revealed that the option of temporary bridges was the most cost-effective and offered the least surface disruption.
This approach involved constructing bridges to hold and maintain the existing street levels, allowing the tunnel to be constructed underneath the streets while traffic above could continue. Before the temporary bridges could be constructed, structures called H-piles were driven into the ground where the tunnel would be installed to support the bridge decking. A frame work was installed between the H-piles to keep soil from collapsing into the excavation. Over the course of numerous weekends, the existing surface on University Avenue and West Johnson Street was removed one lane at a time and then repaved with a bridge deck sitting on the H-piles.
The construction involved a true bridge deck design using reinforced bar – also known as rebar – and highearly-strength concrete so that traffic could be back on the surface by 7 a. m. each Monday. The bridge decks were used for two years while the tunnel was being constructed. When the tunnel was completed underneath these roadways, the bridge decks were removed and replaced with colored concrete.
But don’ t forget all that“ spaghetti.” Fred Klingbeil,
8│TRENDS