Statics of SPT

by John H. Schmertmann, (F.ASCE), Consultant; Schmertmann and Crapps, Inc., Prof. of Civ. Engr., Univ. of Florida, Gainesville, Fla.,

Serial Information: Journal of the Geotechnical Engineering Division, 1979, Vol. 105, Issue 5, Pg. 655-670

Document Type: Journal Paper


The theory presented permits an engineer to estimate the static end bearing and side friction resistance stress components to the penetration of the SPT sampler from only SPT data. This theory follows from the proportionality between SPT and quasi-static Dutch cone test (CPT) resistance components, demonstrated by parallel quasi-static SPT sampling and CPT. The theory seems well confirmed by its correct predictions of the relative magnitude of blow counts over the three successive 6-in. increments of the SPT, the major importance of sampler side friction to the determination of the blow count N—especially in cohesive soils, the magnitude of the decrease in N and increase in sample recovery when removing the liners from an SPT sampler designed for liners, and the energy required for SPT sampling. This paper also demonstrates the importance of both vertical and horizontal effective stress on N-values, and that N depends inversely on the energy per blow delivered to the sampler by the drill rig hammer-anvil-rod-sampler system.

Subject Headings: Statics (mechanics) | Friction | Load and resistance factor design | Penetration tests | Linings | Effective stress | Permits | Sustainable development

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