SHN provided a geotechnical evaluation for the new Humboldt State University Behavioral and Social Sciences Building located in Arcata, CA.

The geotechnical report for the project included descriptions of site subsurface conditions and the results of field and laboratory tests, slope stability analysis, and recommendations for site development and foundations (including a recommended foundation type). The report included appropriate geotechnical criteria and recommendations for design and construction of the foundations, floor slabs-on-grade, retaining walls, and subdrainage. The report also included analyses and discussion of settlement potential, slope stability analyses, and corrosion potential.

SHN’s previous experience on the site allowed the geosciences group to significantly reduce the estimated work scope. Because the bedrock was shallower than a previous geologist anticipated, the depth of borings was significantly reduced; there was no need to drill large distances into the basement rock at the site, which would have been slow and expensive and would not have yielded useful data. Furthermore, based on evolution of industry standards since completion of the 1993 geologic study, SHN replaced some rotary machine borings with Cone Penetrometer Test (CPT) soundings. CPT soundings are extremely quick and cost-effective relative to machine borings, and provide accurate, continuous subsurface data. CPT soundings measure variations of soil type, soil strength and density, with depth. They also provided an indication of groundwater levels. In particular, they provided a continuous log of penetration resistance that is directly correlated with SPT (Standard Penetration Test) blow counts. By selecting an appropriate drill rig, SHN was able to combine geotechnical boring (mud rotary or hollow stem auger), rock coring, and CPT soundings.

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