The City and Borough of Juneau (CBJ) performed an analysis which showed that there would be a lower operating and maintenance cost if a new library was constructed versus continuing to rent facility space for a public library. A municipal election was held and voters approved the construction of a new library. PDC Engineers (previously R&M Engineering) was retained by NorthWind Architects to provide geotechnical subsurface exploration and report for the new Mendenhall Valley Public Library. The library is a 20,000 square feet one-story building located adjacent to Riverside Drive and Dimond Park Aquatic Center with public library spaces, offices, restrooms, meeting room and mechanical room.
To accurately assess the existing subsurface conditions at the site two types of field exploration methods were employed; CME-55 truck mounted drill test holes and excavator machine dug test pits. Four (4) drill test holes to 30’ below ground surface were drilled with our in-house CME-55 drill truck. Test holes were advanced using 8” hollow-stem auger boring methods with standard 2inch O.D. split spoon sampler driven into the bottom of the borehole with 140-lb automatic trip hammer with an impact height of 30-inches. Soil samples were obtained at frequent intervals and selected representative samples were tested in PDC’s in-house laboratory. Samples collected were analyzed for pertinent physical and engineering properties of the soil relative to the proposed construction. Eight (8) machine dug test pits were also performed on the site to provide a visual representation of subsurface soil conditions and true ground water conditions. Representative bulk samples were collected for each soil layer encountered in the test pits from either the undisturbed test pit wall, or from the excavator bucket. Samples collected were analyzed for pertinent physical and engineering properties of the soil relative to the proposed construction.
The geotechnical report included seismic analysis, allowable bearing capacity and settlement analysis, liquefaction potential analysis, retaining wall/basement load factors, dewatering, frost protection, building site preparation, parking/access preparation, underground site utilities and corrosion resistant construction recommendations. PDC performed periodic Special Inspection services for monitoring the building foundation excavation, proof rolling and structural fill placement beneath the building.