<p><p><strong>References:<br></strong><em> Schaefer et al. (2016)<br>Massarsch And Fellenius (2001)<br>Mitchell (1981)<br>SHRP 2-Phase I Technology Assessment (2008)</em></p><p><strong>Method Summary</strong></p><p>The Standard Penetration Test (SPT) is a field method to directly measure the soil resistance to penetration and obtain disturbed samples. The test is performed by hammering a standard “split-spoon” sampler into the ground in three six-inch increments. The number of blows which drives the sampler into the ground for the last two six inch increments is the SPT N-value which is correlated to give strength or modulus parameters. The best strength relationships are provided for SPTs performed in granular soils. This test is unable to provide a continuous profile.</p><p><strong>Accuracy and Precision</strong></p><p>This test is generally regarded as a crude, brute force method that is user‑dependent. This is a very common in‑situ test in geotechnical engineering and there are many empirical relations between SPT results and soil properties.</p><p><strong>Adequacy of Coverage</strong></p><p>The frequency of SPT tests is based on size of construction, number of machines in operation, complexity of ground, and importance of the structure being built. Depending on the importance of the project, more or less SPT tests can be performed.</p><p><strong>Implementation Requirements </strong></p><p>SPT tests are a simple and commonly performed procedure. SPT measurements should be taken at the center point between vibrocompaction points (i.e., at the center of the triangular or square grid shapes).</p><p><strong>General Comments</strong></p><p>The SPT results are an indicator of the ability of the soil foundation to support the service loads and prevent liquefaction. SPT N-values can be correlated to relative density values. The SPT N‑value can also be related to the strength or elastic modulus of the in-situ soil, which will provide an indication of the amount of expected settlement. A method to correct SPT N‑values for overburden is described by Massarsch and Fellenius (2001). Commonly, construction specifications will mandate a particular SPT N‑value for the in-situ cohesionless soil and will vary depending on the project.</p><p>Experience has shown that SPT blow counts can be misleading. This is because SPT data are subject to variability and the process is user dependent. The time frame in which testing occurs needs to be considered. Massarsch and Fellenius (2001) discuss why low test values can be obtained if the site is tested too soon. Verification testing procedures should be performed after pore pressure dissipation (Schaefer et al., 2016). This will allow the tester to obtain more accurate test values.</p></p>