<p><p><strong>Reference(s):</strong></p><p><em>Broms (2003)<br>Cali et al. (2005a)<br>Larsson (2005)<br>Porbaha and Puppala (2003)<br>Terashi and Kitazume (2009</em></p><p><strong>Method Summary</strong></p><p>The penetration and pullout category encompasses several in-situ methods of testing treated soil. Among the most notable penetration and pullout methods are the Swedish column penetration and reverse column penetration tests (KPS and FOPS), the Standard Penetration Test (SPT), Dynamic Cone Penetration Test (DCPT), combined static-dynamic penetration test, Cone Penetration Test (CPT), rotary penetration sounding test, and the weight-sounding test (Terashi and Kitazume 2009).</p><p>Several of these methods have been successfully applied in Scandinavian and Japanese practice as primary methods of shear strength verification, but they have had somewhat limited use in U.S. practice. In Sweden, the column penetration test (KPS) and/or reverse column penetration test (FOPS) are used for testing the shear strength of dry-method DMM columns. Broms (2003) reports that the shear strength determined by unconfined compression tests on cores from the columns is about the same as the shear strength determined by FOPS (used for shear strengths up to 600 kPa) and that the shear strength from CPT with a cone factor of 20 agreed closely with the results from KPS (used for shear strengths up to 200 kPa). A disadvantage of the reverse penetrometer is that the contractor knows in advance which columns will be tested and therefore could take additional measures to ensure high quality of columns where reverse penetrometer testing will take place. Other methods allow a random column selection at the owner/agency’s discretion based on analysis of installation monitoring data or other factors. Also, the reverse penetrometer test and pullout tests are limited by the tensile strength of the cable attachment to the probe as noted in Cali et al. (2005a), however the immediacy of the results as compared with other methods was beneficial. In a survey conducted by Puppala and Porhaba (2005), the CPT method was found to be the preferred in-situ method for its ability to provide continuous data throughout the testing interval. The CPT is most effective when the shear strength of stabilized soil is less than 1,000 kPa and the treated depth is 10 meters or less (Porbaha and Puppala, 2003). Broms (2003) notes that the disadvantages of CPT are that only a small volume of the stabilized soil is tested and that the penetrometer has a tendency to deviate from the column at a depth of 4 to 6 meters. The SPT has been used in Japan to check the bearing capacity of columns. The main disadvantages of SPT are the small size of the sampler, a weak correlation with shear strength, and that the penetration resistance measured is not continuous.</p><p>In US practice, specified values of unconfined compressive strength are often in the range of 100 to 150 psi, and contractors tend to produce mixtures that have average and maximum strengths several times higher than the specified strength to account for variability. Consequently, penetration methods are generally not very useful because they encounter refusal or deviate outside of the column.</p><p><strong>Accuracy and Precision</strong></p><p>Penetration and pullout methods can be used to determine the in-situ shear strength of improved soil through correlations, but they are limited by strength and depth of columns.</p><p><strong>Adequacy of Coverage</strong></p><p>Broms (2003) recommends that 0.5 to 2% of columns should be tested, depending on soil conditions, factor of safety, and the total volume of improved soil.</p><p><strong>Implementation Requirements </strong></p><p>Many of the penetration methods are common worldwide and equipment and experienced personnel are readily available. In the cases of several of the penetration/pullout methods, such as the KPS and FOPS, which are specific to Sweden, specialty equipment and training is required. There may be significant cost and training associated with obtaining and using this equipment.</p><p><strong>General Comments</strong></p><p>Penetration and pullout tests can be a very useful indicator of column strength provided that the strength is low enough such that the column can be penetrated. Penetration and pullout methods provide a correlation to the shear strength and stiffness of the column and are therefore an indicator of the column shear strength. Since US practice tends towards relative high strengths, penetration methods are less useful than in Scandinavian practice where lower mixture strengths are more common. Penetration and pullout testing can only be performed for the dry deep mixing method</p></p>