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Show Overhaul scheduled for Zion Tunnel engineers will conduct a comprehensive examination of theentire length of the 1.1-mile-long tunnel and will develop a topographic map that will accurately chart the relation of the tunnel and its path to the canyon wall. The latter information is essential in considering alternatives to the tunnel issue. The tunnel will be closed to traffic between the hours of 7 p.m. and 6 a.m. daily during the work program. Installation In-stallation of the warning system will require about six weeks. The tunnel may be closed on an extended basis if the monitoring devices reflect significant distress occurs. The National Park Service announced today that a mile-long mile-long tunnel in Zion National Park in southern Utah will be closed during the nighttime hours only for perhaps a six-week period this fall to permit installation in-stallation of a traffic warning war-ning system and a detailed inspection of the tunnel. Superintendent Robert C. Heyder said contract documents and specifications are being prepared and the work should commence in mid-September. mid-September. Strain guages inplanted in the two-lane bore have shown increased loading along a 100 yard length of the roof near a point identified as Gallery No. 3. Data collected from the strain guages have shown an increase in stress over the past 18 years, although Superintendent Heyder said the rate of increase has diminished with time. There is also an annual cycle of stress that has been found to be directly correlated to seasonal temperatures. The 22-foot-wide tunnel was constructed between 1927 and 1930 to provide access from Mt. Carmel Junction to the Park from the east side. The bore parallels the face of a 600-foot-high cliff of Navajo sandstone. The outer wall is less than one foot thick in one place. Superintendent Heyder said Park Service representatives have consulted con-sulted at length with tunnel authorities and weighed the prospect of immediate closure. There is no evidence of imminent failure, however. The warning system to be installed will involve flashing red lights at both portals to the tunnel, and barriers located within the tunnel itself with appropriate ap-propriate signs. Both lights and barriers will be activated ac-tivated by electrical impulse. im-pulse. They will be connected con-nected to sensitive monitoring devices that will be implanted at key locations in the tunnel walls and roof. The tunnel is being monitored dai!y by Park personnel. At the same time the warning system is installed, mmHMXMMtmmaimmmMmm:- |