J02a RB Geotech Report from 300 feet away.pdf

This is a Site Exploration and Geotechnical Engineering Report for a proposed Tracker Mounted Array Solar system installation at Rosebud IHS Hospital in Rosebud, South Dakota, prepared by Twin Rivers Testing & Environmental, LLC, dated October 20, 2014.

The project involves installing twelve Tracker Mounted Array Solar units in an area measuring 154 feet by 219 feet northwest of the IHS Hospital. The site subsurface exploration identified Sandy Lean Clay, Clayey Sand, and Poorly Graded Sand with Clay materials. The solar panels will be supported by helical pile foundation systems installed to a depth of ten feet below existing grade, with site grading requiring approximately one foot of cut/fill. The geotechnical engineer recommends lateral bearing pressures of 180 PSF for Sandy Lean Clay (with notation that this material should be neglected due to frost action) and 250 PSF for Clayey Sand and Poorly Graded Sand. No groundwater was encountered during drilling on August 27, 2014, though the report notes that groundwater levels may fluctuate seasonally. The field investigation consisted of two soil test borings drilled to 15 feet below ground surface using standard penetration testing and laboratory analysis including natural water content, unconfined compression, sieve wash, and Atterberg limits tests.

The report provides detailed site preparation, fill placement, excavation, utility trenching, seismic design, and drainage recommendations for construction. Site Class "D" is recommended for seismic design calculations per the 2003 International Building Code. All fill materials require geotechnical engineer approval and testing prior to placement, with specified compaction standards and moisture content requirements. The contractor bears sole responsibility for designing and constructing stable temporary excavations in accordance with OSHA regulations (29 CFR Part 1926). The report emphasizes that boring logs depict subsurface conditions only at specific drilling locations and variations should be expected between locations.