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Standard Penetration Test

Geotechdata.info - Updated 2.7.2016

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The Standard Penetration test (SPT) is a common in situ testing method used to determine the geotechnical engineering properties of subsurface soils. It is a simple and inexpensive test to estimate the relative density of soils and approximate shear strength parameters.

Standard Penetration Test, SPT, involves driving a standard thick-walled sample tube into the ground at the bottom of a borehole by blows from a slide hammer with standard weight and falling distance. The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is reported as SPT blowcount value, commonly termed  "standard penetration resistance" or the "N-value".

The N-value provides an indication of the relative density of the subsurface soil, and it is used in empirical geotechnical correlation to estimate the approximate shear strength properties of the soils.

Correlation between SPT-N value, friction angle, and relative density

Correlation between SPT-N value and friction angle and Relative density (Meyerhoff 1956)

[Blows/0.3 m - 1 ft]

Soi packing
Relative Density [%]
Friction angle
< 4
Very loose
< 20
< 30
4 -10
20 - 40
30 - 35
10 - 30
40 - 60
35 - 40
30 - 50
60 - 80
40 - 45
> 50
Very Dense
> 80
> 45


  • BS 1377-7:1990
  • ASTM D3441 - ASTM D1586 - 08a Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils Link


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  1. Meyerhof, G. (1956). Penetration tests and bearing capacity of cohesionless soils. J Soils Mechanics and Foundation Division ASCE, 82(SM1).

External Links

  1. Presentation of Standard Penetration Test, equipment layout, correlation between SPT and soil properties Ch. Baxter, UNiversity of Rhode Island
  2. Detailed description of Standard Penetration Test and parameters with figures J David Rogers, Lecture notes, Advanced Engineering Geology & Geotechnics, Missouri University of Science and Technology
  3. Standard Penetration Test on Wikipedia
  4. Standard Test Procedure Manual for SPT Saskatchewan Highways & Transportation, Canada
  5. SPT-CPT Correlations Peter K. Robertson, Richard G. Campanella, A. Wightman. 1983. Journal of Geotechnical Engineering, Vol. 109, No.11. ASCE. Available by Prof. P. Robertson's website.
  6. Subsurface Exploration using the Standard Penetration Test and the Cone Penetrometer Test J.D. Rogers. 2006. The Geological Society of America. Environmental and Engineering Geoscience, Vol. XIII, No.2, pp. 161-179.
  7. Engineering and Design: Standard Penetration Test1988. Technical Letter No. ETL 1110-1-138, (1988). U.S. Army Corps of Engineers, Washington, D.C.

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