Depressing Traffic Top-Down

by Dan Burroughs, Parsons De Leuw, Inc., 1700 Broadway, Suite 800, Denver, CO 80290,
Shyi-Shyong Jiang, Parsons De Leuw, Inc., 1700 Broadway, Suite 800, Denver, CO 80290,
Henrie Henson, Parsons De Leuw, Inc., 1700 Broadway, Suite 800, Denver, CO 80290,


Serial Information: Civil Engineering—ASCE, 1994, Vol. 64, Issue 1, Pg. 62-64


Document Type: Feature article

Abstract:

Top down construction will permit the City and County of Denver to maintain traffic at two congested intersections while a tunnel is driven below them. The project, which will carry Speer Blvd. under Sixth Ave., Broadway and Lincoln St., will cost $24 million and be completed in December 1994. The three-lane, 49 ft wide, 1,800 ft depressed roadway, split by a 710 ft tunnel, combines several structure types. The tunnel consists of exterior load-carrying diaphragm slurry walls integral with a post-tensioned concrete tunnel lid. Both walls and the lid are put in place prior to tunnel excavation. This top-down construction method allows rapid construction,imum dewatering, reduced interference with traffic and minimum disturbance to adjacent structures. The deeper part of the depression approaching the tunnel has cantilevered slurry walls tied with compression struts beneath the roadway. The shallower depression consists of a tie-down tub section and standard retaining walls. The tunnel lid, set 2 ft below finished grade, is a haunched slab cast directly on the existing soil. It is cast in stages at the roadway intersections, with traffic allowed over the completed sections, which are post-tensioned after lid completion but before excavation.

Subject Headings: Tunnels | Traffic congestion | Highways and roads | Construction methods | Traffic management | Tension | Retaining structures

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