Tunnel Business Magazine

AUG 2018

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Issue link: http://digital.tunnelingonline.com/i/1014911

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Page 26 of 43

TUNNELINGONLINE.COM 2 7 TBM: TUNNEL BUSINESS MAGAZINE // AUGUST 2018 The existing Downtown Tunnels (I- 264) carries the highest traffic volume of any tunnel in the Hampton Roads area. The first tunnel, the westbound tunnel, opene y 23, 1952, and is 3,350 ft long. The second tunnel, the eastbound tunnel, opene ch 4, 1987, and is 3,813 ft long. Since the opening of the first tunnel, the average vehicles per day in- creased over 500% to an average of 67,228 vehicles per day. Rehabilitation of the Existing Midtown & Downtown Tunnels The rehabilita - town and Downtown tunnels included the removal of the ceiling divider slab, inspection and repair of structural lin- ing, addressing leaks and concrete deg- radation, tunnel structural fireproofing protection, new electrical with LED tun- nel lighting, tile and concrete repair, exit and safety signage. The existing venti- lation was a transverse ventilation sys- tem which was replaced by longitudinal ventilation system. The contract documents allowed ei- ther board or spray fire protection solu- tions to be installed during nightly single lane closures and full tunnel closures over the weekend. The board solution considered was a calcium silicate matrix engineered board with a minimum thickness of 22 mm to meet the 2-hour RWS time/tem- perature curve. This type of board can be post-curved and post fixed directly to the existing concrete lining using stainless steel me specialty installation contractor or spe- cial preparation of the tunnel lining is required prior to installation. The spray fire protection solution considered was a high-density cementi- tious spray material with a minimum thickness of 30 mm. The spray solution requires a specialty spray fire protection installation contractor. The lining of the tunnel also requires power washing to remove all contamination as spray fire protection solution relies on the chemi- cal bond to the tunnel structure to stay in place. The spray solution also requires a reinforcement mesh anchored with stainless steel anchors. Because of 15 mm being the maximum thickness that can be applied in one pass, the spray solution required two passes. Another consideration in the evaluation was the spray fire protection is temperature and humidity sensitive, which limited the time of year it could be applied without special control measures. After evaluation of the cost of instal- lation and special preparations, the de- sign-build team chose Promat T calcium silicate matrix engineered board solu- tion using the post curved-post fixed method. There are limitations to the flexibility of the calcium silicate boards, however, and the existing tunnel's radii were too severe to post curve one layer of 22 mm, so the contractor chose the minimum thickness the manufacture could make, which was 15 mm. The additional 8 mm of fire protection above the minimum re- quired was a thermal value added to the solution. All calcium silicate boards are manufactured in a 1,200 x 2,500 mm for- mat. For ease of handling and post curv- ing, half size boards (1,200 x 1,250 mm) were chosen for light weight (32 lbs). The first layer was post curved and temporarily anchored using a type of flat head spike anchors (0.25 x 2 in.) with six required per sheet. The second layer was post curved and staggered over the first layer, so joints are not in line. This second layer was permanent- ly anchored with 9 each 0.25 x 3.25 in. 316 stainless mechanical expansion an- chors (non-cut back anchors), including stainless steel nut with nylon insert and 30 mm (1.125 in.) washers. The permanent anchors go through both layers of boards anchoring directly into the concrete lining to a depth specified by the anchor manufacturer. The number and spacing of anchors required are deter- mined not on the live and dead load the boards will experience during daily opera- tions of the tunnel, but determined from full scale fire testing for a 2-hour RWS fire event. Because of the closer spacing re- quired during a fire event, the possibility of the boards detaching from the ceiling during operation is negligible. Thermal justification of the Post Curved/Post Fixed System To comply with the requirements of A 502-2011, existing fire test data provided sufficient thermal information on the proposed system thermal perfor- manc - lation was provided from software devel- oped and validated for the manufacture by an independent testing laboratory. Because of the double layer of boards and staggering the joints between the first and second layer, gaps were not a critical part of the thermal justification. Due to the "Buy America Act" contract requirement for steel components, the U.S.-manufac- tured anchors selected were fire tested to 2-hour RWS time/temperature curve to satisfy the thermal performance for the double layer of fire protection boards and anchors as a system. A full-scale fire test for validation of any fire protection system is always highly recommended. Experiences Existing Midtown and Downtown Tunnels After the ceiling divider slabs were removed, the ceilings were inspected. Several areas in the tunnels had leaks with localized concrete degradation. The leaking areas were sealed and grouted, and the degraded concrete was removed and patched. The aggregate used in the original tunnel lining was locally available river aggregate quartz varying in size. The quartz aggregate was very abrasive which increased the drill bit usage. The fire pro- tection overlapped onto the existing tile. Void areas were filled with a trowel grade fire protection mortar. In areas where leaks could not be stopped, a stainless-steel channeling system was installed to direct the water around the tunnel structure to the storm drain on the sides. These channels were overlapped as shingles on a roof. The cal- cium silicate boards were boxed around drainage channel sections, providing fire protection in this area. In areas where new jet fan ventilation and signage systems were to be installed, the areas were left blank until equipment was installed. The fire protection boards were then built up around and over the mounting plates to protect the mounting plates from localized heating sink into the concrete during a fire event. At each end of the tunnel, the portal ceiling areas transitioned from a curved ceiling into a flat tunnel ceiling. These ar-

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