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Valley Admin Building Temporary Stair Installation and Geotech Borings

Yosemite National Park » Valley Admin Building Temporary Stair Installation and Geotech Borings » Document List

This project is needed in response to an Occupational Health and Safety Administration (OSHA) violation issued July 27, 2012 which referenced the need for the building to have a secondary egress stair and a fire alarm system. The nature of the violation was "serious" and immediate action was required to avoid an evacuation requirement. Through a petition process the NPS was successful in separating the requirements into an immediate interim solution and a long term solution. The immediate solution required construction of a second story stair on the north side of the building. The stair is wood construction framed on pier blocks and has a 48" by 48" by 3.5" deep concrete landing pad on the ground level. The stairs are painted Wosky brown and are predominately self-standing. The stairs connect to the existing building at the second story deck which is centered on the north gable end of the building. This deck was constructed in the early 1990s and is not part of the historic structure. This interim construction configuration is not fully code compliant and is only allowed by OSHA through spring of 2014. The final requirement of the interim solution requires a two-step stair and grab bar to be installed at the second story exit window for emergency access to the deck and stairs. The long term solution will be evaluated under a separate design and compliance process. Design will evaluate three alternatives including a fully code compliant second story stair and alarm system, a three story stair, and an internal stair. Construction for the long term solution is targeted for fall of 2013, with compliance beginning in January 2013 and completed by mid-spring of 2013.

Stair design for the long-term solution needs to be informed by a soil investigation. This will be accomplished by drilling three bore holes near the building to determine the soil profile. The results of the boring will be evaluated by a geotechnical engineer to inform the foundation design for the alternatives that propose an exterior stair. More specifically, the borings will be accomplished using a drill rig mounted on a freightliner chassis (28' long by 10' wide), having a mast height of 27 feet. Up to a 9" diameter hollow stem auger will be drilled. Soil cuttings produced by auguring would generally fill 2 to 3 wheelbarrow loads if the 50 foot depth is achieved, and are typically used for backfilling the excavated boring after drilling is completed. Disturbance will be limited to the 9" diameter boring, with care taken moving the rig into and out of position. Area #1 (see Geotech Map) is the preferred drill location and may be the only area affected. However, if refusal is encountered prior to reaching the required depth, the drill rig will move to the other areas to achieve the deepest possible boring (up to 50').