F &R provided a subsurface investigation and geotechnical evaluation in support of the $90.6 million, New Educational Building to be constructed on the campus of UNC at Chapel Hill, NC. The new, modern educational facility, will replace the 45 year old Berryhill Hall, which does not meet the needs of medical teaching/ learning, and can no longer accomodate the increasing medical student class size. The irregular shaped building is to be constructed on a concrete slab, with reinforced concrete pan and joists or skip joists, with an approximated 20,000 sf foot print.
A majority of the new building will overlap the footprint of existing Berryhill Hall, which presented challenges in assessing subsurface conditions on this site since traditional exploration techniques (i.e., test borings) could not be performed in a large portion of the proposed building footprint. This was further compounded by the erratic soil and rock conditions that are typical of the Carolina Slate belt, as well as the presence of boulders within the residual soils above the bedrock surface that is common throughout the UNC-CH campus.
Based upon F&R’s findings, foundation recommendations were provided. Conventional shallow spread foundations were considered, but ruled out as a viable support option because the variable consistency bearing soils are not conducive to using a relatively high bearing capacities. A mat foundation was not
viable largely as a result of the irregular building footprint. Ground improvement techniques were also not viable due to the presence of boulders within the overburden soil. As such, deep foundations needed to be considered. Most deep foundations systems (e.g., driven piles, ACIP piles, large diameter drilled shafts) were also not viable because of complications presented by boulders in the overburden. In order to install foundations through boulder-containing overburden and into suitable bearing strata, micro-piles were recommended since they can effectively penetrate boulders and other obstructions present in the overburden and readily extend down into competent parent bedrock bearing strata.