Predicting Shear Strength Properties for Low-Sensitivity Granular-Cohesive Soils from SPT Results

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by Simon C. Murley, P.E., Project engineer; Soil and Materials Engineers, Inc., 43980 Plymouth Oaks Blvd., Plymouth, MI 48170.,,
Hiroshan Hettiarachchi, P.E., Ph.D., Assistant Professor; Department of Civil Engineering, Lawrence Technological University, 21000 W 10 Mile Rd., Southfield, MI 48075.,,

Document Type: Proceeding Paper

Part of: Geo-Frontiers 2011: Advances in Geotechnical Engineering

Abstract: Several correlations between the standard penetration test (SPT) N-values and internal friction angle (φ') have been developed for granular soils. Some correlations have also been developed for un-drained shear strength of saturated clays. However, in many instances soils do not behave as either saturated clay or sand. Sometimes it is important to find the contribution of φ' in clays with higher silt and sand content; and cohesion in sands that has sufficient clay and silt content. It is incorrect to classify these soils as cohesive soils with no friction angle, or as granular soils with no cohesion, and is thus the focus of this research. This paper describes a research effort to develop practical relationships between φ', effective cohesion (c') and SPT N-values for granular-cohesive soils. Considering the SPT analogous to a miniature pipe pile, an energy-balance approach was taken to derive a relationship between φ', c', N-values and effective overburden pressure (σ'). A second relationship was derived between φ', c', σ' and the liquidity index (LI) of low-sensitivity granular-cohesive soils. The two relationships were then graphically solved to formulate direct correlations between field N-values and c' and φ'.

Subject Headings: Granular soils | Soil strength | Shear strength | Cohesive soils | Saturated soils | Soil classification | Penetration tests | Correlation | Friction |

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