<p><p><strong>References:<br></strong><em>Axelsson and Rehnman (1999)<br>Burke et al. (2007)<br>Forsman et al. (2008)<br>Garbin and Mann (2010)<br>Garbin et al. (2011)<br>Havukainen et al. (2011)<br>Hayward Baker Inc. (2009)<br>Holm et al. (1999)<br>Jelisic and Leppanen (1999)</em></p><p><strong>Method Summary</strong></p><p>The column penetration test (KPS, from the original Swedish name) is an in situ quality assurance method that is similar to the CPT. However, the test was developed to measure average shear strength across a larger volume than by CPT. KPS testing is performed after mixing operations to verify that the specified level of improvement has been achieved. The KPS apparatus is similar to the cone penetrometer, but two vanes are attached to the probe at 180-<br>degrees from one another (Figure 1).</p><p><figure id='attachment_7377' style='max-width:913px' class='caption aligncenter'><img class="wp-image-7377 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of the head of a KPS vane used to measure the shear strength of shallow-mixed or mass stabilized soils." width="913" height="626" /><figcaption class='caption-text'> Figure 1. KPS vane is used to evaluate the shear strength of shallow-mixed or mass stabilized soils (Garbin and Mann, 2010).</figcaption></figure></p><p>The vanes increase the surface area of the probe, measuring average shear strength over a larger area of improved soil. A load cell measures the force required to push the vane through the soil or soilcrete while an encoder tracks depth. The force can be converted directly to undrained shear strength by using a bearing capacity factor of 10:<br><p style="text-align: center;"><em><strong>T=(1/10) X (Q/A)</strong></em></p><p style="padding-left: 330px;">where<br><em>T</em>= shear strength (psi)<br><em>Q</em>= penetration resistance (lbs)<br><em>A</em>= cross sectional area of the probe (in²)</p>More information on column penetration testing is available from Axelsson and Rehnman (1999) and Holm et al. (1999).</p><p><strong>Accuracy and Precision</strong></p><p>Data from the KPS is more reliable than data from traditional CPTs in shallow-mixed or massstabilized soil because of the larger volume engaged by the probe. The test provides a continuous profile with depth. The pushing force and depth are electronically monitored and are therefore as accurate as the monitoring equipment allows. The accuracy of the shear strength values is dependent on the accuracy of the bearing capacity factor.</p><p><strong>Adequacy of Coverage</strong></p><p>Adequate coverage is dependent on the number of tests performed. Engineering judgment should be used when determining the number of tests to perform. Frequency should be determined considering the size of the area to be treated, subsurface variations, mixing procedures, and other factors that may affect the representativeness of a single test, as well as the type and performance expectations of the proposed facility. Garbin and Mann (2010) recommend one test per 2,500 sq. ft. of improved area. Locations where test results do not meet the requirements should be retested within 2 ft. of the original test location to determine if the failure was due to an isolated inclusion or if additional improvement is required.</p><p><strong>Implementation Requirements</strong></p><p>The KPS vane is not readily available in the United States and will likely need to be specially constructed according to specifications in literature (see Garbin and Mann 2010).</p><p><strong>General Comments</strong></p><p>Due to the larger surface area of the KPS vane, tests may meet refusal at shallow depths if the post-improvement shear strength is high. In such cases, CPTs may be used to profile deeper depths of the improved volume (Garbin et al. 2011).</p></p>