Precast Solutions - November/December 2008 - (Page 18) BEBO ARCH CONSTRUCTION PROCESS After the initial project consultation, the CONTECH process for the BEBO Arch System encompassed the following steps: 1. Design: Precast structure is designed to meet any code, loading or geometrical requirements. 2. Manufacture: Quality is assured through controlled conditions at precast concrete facilities. 3. Transportation: Arch units are placed horizontally and arrive on flat-bed trucks ready for installation. 4. Arch units: Bridge units are lifted off the truck, rotated into vertical position and set on strip footings, a base slab or a deep foundation system. 5. Foundation: Shims set the arch in place on the footing until the keyway is grouted. Hardwood wedges prevent the precast arches from spreading under self weight. 6. Twin-leaf arches: Larger twin-leaf arches are joined by the patented BEBO crown joint. 7. Joint seal: Arch units are grouted in the keyway and joints are sealed using a commercial joint wrap. 8. Walls: Precast concrete headwalls and wingwalls often facilitate an entire structure being set in one day. 9. Backfill: Concrete arch stiffness allows backfill to be placed and compacted quickly and effectively. 10. Finished bridge: The completed bridge is an attractive, economical, durable and easily installed solution that is ready for traffic. WORKING The BEBO Arch System uses the fundamentals of soil-structure interaction to achieve superior strength and stability. WITH LIVE TRACKS AND not the only factors making constructability the greatest challenge at the site. The builder had to ensure accuracy in all phases – from surveying to footing construction to erecting the precast arches. Everything had to fit together perfectly when the arches were set in place. The tolerance for the precaster was one-fourth inch in fabricating the BEBO arches. On this project, 444 precast concrete pieces had to fit together at the crown to form 222 full arches, side by side; this meant that 221 joints needed to meet exacting tolerances. The 1,332-foot-long tunnel structure was installed in 13½ days. Crews installed the final 26 arch units in just 11 TIGHT TOLERANCES Construction projects that involve live train tracks present many unique challenges for contractors. At the U.S. 395 crossing of BNSF, train traffic must be maintained during construction and BNSF’s specifications The primary concern for BNSF Railway Co. was maintaining uninterrupted rail service on the Kettle Falls Subdivision for customers from regions north of the tunnel. for excavating and trenching had to be followed carefully. A full-time BNSF flagman was present at the site during installation to provide advance notice of approaching trains. Trains run twice per day and can be up to 7,000 feet in length at this location. For the contractor, restrictive operating conditions were hours. 18 PRECAST SOLUTIONS | NOVEMBER/DECEMBER 2008
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