<p><p><strong>References:<br></strong><em>Auzins and Southcott (1999)<br>Avalle and Carter (2005)<br>Avalle and Grounds (2004)<br>Avsar et al. (2006)<br>Clegg and Berrangé (1971)<br>Jumo and Geldenhuys (2004)<br>Landpac (2008b)<br>Pinrad (1999, 2001)<br>Scott and Suto (2007)</em></p><p><strong>Method Summary</strong></p><p>Use of penetration tests, such as Standard Penetration Test (SPT), Cone Penetration Test (CPT), and Dynamic Cone Penetration (DCP) test, are documented in the references listed above to assess the compaction improvement depth by comparing pre-compaction and post-compaction results. SPT and CPT are widely used for many geotechnical applications and can measure soil properties to deeper depths (greater than 30 meters), while DCP is generally used in pavement foundation layer construction as a QA process and can measure soil properties up to about 2 meters. Difficulties with these test procedures are documented in the literature when large particles or boulders are encountered in the subsurface, which may require drilling to continue the tests (Avalle and Grounds 2004).</p><p>SPT is described in ASTM D1586 or AASHTO T-206. SPT is a dynamic in-situ penetration test, which uses a thick-walled sampling tube (with outside diameter of 50 mm, inside diameter of 35 mm, and length of about 650 mm) that is driven into the ground by a slide hammer (about 64 kg) falling from a height of about 760 mm. The number of blows required to drive the tube to about 150 mm is typically recorded. These blow count values have been correlated to soil shear strength parameters. Disturbed soil samples acquired from the tube are used to classify the soil stratigraphy.</p><p>CPT is described in ASTM D3441. CPT involves pushing an instrumented cone tip into the ground at a controlled rate, and recording the sleeve friction and tip resistance of the cone almost continuously (about every 2 cm). Some modern electronic CPT cones now employ a pressure transducer to record pore water pressure data and is commonly referred to as CPTU method. One advantage of CPT over SPT is a more continuous profile of soil parameters. The sleeve friction and tip resistance values have been correlated to soil classification.</p><p>The DCP test method is described in ASTM D6951. The DCP test method involves driving a cone tip into the soil by lifting an 8 kg sliding hammer to 575 mm drop height and then releasing it. The total penetration for a given number of blows is then measured and recorded as mm/blow (penetration resistance). ASTM D6951 provides correlations between California bearing ratio (CBR) and mm/blow for different soil types. Correlations between DCP and undrained shear strength and modulus are documented in the literature (e.g., White et al. 2009).</p><p><strong>Accuracy and Precision</strong></p><p>These test methods are generally considered repeatable for comparing before and after blow count or penetration resistance values at specified depths. For subsurface conditions with large boulders or rocks, testing may be difficult. ASTM D6951 indicates that the repeatability standard deviation of the DCP test is less than 2 mm/blow. Accuracy and precision of CPT tests are not reported in ASTM D3441-05. Gui et al. (1998) reported that for CPT tests conducted by different laboratories on same soil a variation of about ±10% has been reported in the literature. ASTM 1586 indicates that the coefficient of variation in SPT N-values is about 100% or more when using different SPT equipment and drillers for adjacent borings of the same soil type. The coefficient of variation can be reduced to about 10% if same equipment and driller are used with energy calibration. Duncan (2000) reported a coefficient of variation of about 15% to 45% for SPT N-values.</p><p><strong>Adequacy of Coverage</strong></p><p>Sufficient evaluation requires many tests. The number of tests depends on the variability in subsurface conditions. Penetration tests are advantageous in assessing improvement in soil properties to greater depths than other surface tests at surface (e.g., static and dynamic plate load tests). The Landpac (2008b) specification recommends performing three DCP tests every 10 passes over a trial compaction section with dimensions of about 40 meters by 4 meters.</p><p><strong>Implementation Requirements </strong></p><p>Some experience and special equipment is necessary. DCP tests can be performed by one or two people. SPT and CPT require specialized equipment and personnel with training.</p><p><strong>General Comments</strong></p><p>Empirical correlations can be used to relate results from the penetration tests to soil engineering properties (e.g., soil strength, bearing capacity, stiffness/modulus, liquefaction susceptibility, etc.). These test methods are useful for QA. These methods can also be used for QC to assess improvements in subsurface conditions with increasing passes.</p></p>