B09_-_Amend_0002_-_Attachment_12_-_1991_GEI_Geotechnical_Report_-_SBT_0002.pdf

This is an engineering assessment report and cost estimate for remedial work at the Staple Bend Tunnel, a historic 160-year-old railroad tunnel located in Johnstown, Pennsylvania, constructed between 1831 and 1834. The report was prepared by GEI Consultants, Inc. and submitted to Sellards & Grigg, Inc. on March 29, 1991 (Project 90259).

The report documents field investigations conducted August 20-24, 1990, including geological mapping, test pit excavation, and stability evaluation of the tunnel structure. The tunnel, approximately 900 feet long, consists of five distinct sections: masonry-lined portal areas (150 feet west, 100 feet east), an unlined bedrock section (600 feet), and a concrete-lined section (50 feet). Priority remedial work identified includes replacing lost masonry blocks at two locations (Sta. 0+58 and 1+03), repointing masonry joints above the springline, removing unstable rock blocks from the crown, stabilizing major overhangs in tunnel walls through steel shoring posts or breaking back overhangs, and stabilizing the west portal facade through tree removal and earth backfill restoration. Secondary priority work includes general cleanup and optional grouting. The engineer's cost estimate (Table 1) provides Class B level estimates with 15% contingency, ranging from $3,500 for east portal facade cleanup to $69,000 for breaking back major overhangs in the bedrock section. The report recommends a combined unit price and time-and-material contract approach for interior tunnel work to accommodate site-specific conditions and reduce engineering conservatism during construction.