CPT Interpretation in Highly Organic Soils and Soft Clay Soils: Fid-Bau Portal

CPT Interpretation in Highly Organic Soils and Soft Clay Soils

Merani, Jay M. / Hunt, Christopher E. / Donahue, Jennifer L. / Bray, Jonathan D.

A planned environmental remediation construction project in Northern California requires constructing a containment cover over existing dredge spoils deposited over a former marsh. Key geotechnical concerns with the cover construction include short- and long-term stability concerns and potentially large total and differential settlements. The soft subsurface soils include highly organic silts and clays (organic soils) and San Francisco Young Bay mud (YBM). Differentiation between these soils is critical for evaluation of edge stability and anticipated differential settlement across the site because the strengths and primary and secondary compression responses of the organics and YBM differ significantly. A 5-ton cone (calibrated for high sensitivity in soft soils) was used for cone penetration testing (CPT) during this investigation to enhance the resolution of the measured tip resistance and the associated friction ratio in an attempt to distinguish between the two materials. Using the 8 CPT/boring pairs, criteria were established to distinguish reliably between the organic soils and the YBM, and these criteria were extrapolated to 31 CPTs across the site to establish baseline site stratigraphy and material properties for use in design.