<p><p><strong>References:<br></strong><em>Aboshi et al. (1991)<br>Barksdale (1987)<br>Kitazume (2005)<br>Kuroda and Kanada (1983)<br>SHRP 2-Phase I Technology Assessment</em></p><p><strong>Method Summary</strong></p><p>The Standard Penetration Test (SPT) is a field method to indirectly measure the soil strength 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 necessary to drive the sampler into the ground for the last two six inch increments is the SPT N-value which is correlated to give strength parameters. The best strength relationships are provided for SPTs performed in granular soils. This test does not provide a continuous profile and is often unreliable in clayey soils.</p><p><strong>Accuracy and Precision</strong></p><p>Data are subject to variability and the process is user dependent.</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 subsurface variability, and importance of the structure being built. Depending on the importance of the project, more or less SPTs can be performed. Barksdale (1987) suggests testing one SPT for every 3,280 linear feet of SCP, while Kitazume (2005) recommends one SPT per every 200 to 500 piles.</p><p><strong>Implementation Requirements </strong></p><p>SPT tests are a simple and common procedure.</p><p><strong>General Comments</strong></p><p>Commonly, construction specifications will mandate a particular SPT value for either the SCPs or for the in-situ soil for sites with cohesionless soils. For sand compaction piles in cohesive soils, the SPT penetration resistance is typically measured down the center of the pile. Barksdale (1987) states that if low permeability layers are present in the soil, the SPT penetration resistance should be taken as long after construction as possible due to temporary loss of strength caused by disturbance and remolding of soil surrounding the SCP. SPT tests should be performed after excess pore pressure has dissipated. This will allow more accurate test values to be obtained post-construction. For sand compaction piles in cohesionless soils, SPT N-values are measured in the center of the SCP and in the inter-pile sandy soil. The SPT penetration resistance obtained during QC/QA is a function of confining pressure and the presence of other piles installed nearby. Correction factors are provided to account for these effects in Kuroda and Kanada (1983). The SPT values are an indicator of the ability of the soil foundation to support the service loads, reduce settlement, and prevent liquefaction.</p></p>