<p><p><strong>Reference(s):</strong></p><p><em>Casagrande (1983)</em></p><p><strong>Method Summary</strong></p><p>Penetration tests such as Standard Penetration Tests (SPT), Cone Penetration Tests (CPT), and Dynamic Cone Penetration (DCP) tests can be used to assess the improvement in the soil strength by comparing post-treatment results with pre-treatment results. SPTs and CPTs are widely used for many geotechnical applications and can measure soil properties to deeper depths (&gt;30 meters), while DCP is generally used in pavement foundation layer construction QA process and can measure soil properties to relatively shallow depths (&lt;2 meters). In-situ test results using penetration tests for electro-osmosis treatment are not well-documented in the literature.</p><p>The SPT is described in ASTM D1586. The 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. At each testing depth, the number of blows required to drive the tube for three consecutive 150-mm (6-inch) intervals is recorded, and the values for the last two intervals are added to give the SPT penetration resistance, or N-value, in blows per foot. These blow count values have been correlated to soil shear strength parameters; however, correlations for cohesive soils are not reliable and not recommended (Kulhawy and Mayne 1990). Disturbed soil samples acquired from the tube are used to classify the soils and obtain soil stratigraphy information.</p><p>The CPT is described in ASTM D3441. CPT involves pushing an instrumented cone tip with following friction sleeve 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 that it can provide a more continuous profile of soil parameters. The sleeve friction and tip resistance values have been correlated to soil classification. Its major disadvantage is that it does not provide a soil sample for visual identification.</p><p>DCP test method is described in ASTM D6951. 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.</p><p><strong>Accuracy and Precision</strong></p><p>The accuracy of SPT values is highly variable, with a Coefficient Of Variation (COV) ranging from 15 to 100% depending on calibration of the equipment and type of soil (Kulhawy and Mayne 1990). However, the test is repeatable, provided the same equipment and crew are used, and thus can be used as a qualitative indication of improvement. CPT is much more reliable with a COV of 7 to 12 % (Kulhawy and Mayne, 1990) and the reliability of DCP lies somewhere in between CPT and SPT. All three methods are considered repeatable for comparing before and after blow count or penetration resistance values at specified depths.</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 tests at the surface (e.g., static and dynamic plate load tests). An SPT can take longer than CPT and DCP tests. DCP tests are more economical than SPTs and CPTs, but can only measure soil properties to a depth of about 1 meter and up to 2 meters with extension rods.</p><p><strong>Implementation Requirements </strong></p><p>Some experience and special equipment is necessary. DCP tests can be run by one or two persons. SPTs and CPTs require specialized equipment and trained personnel.</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., undrained shear strength, liquefaction potential, etc.). These test methods are useful for QA. If site-specific correlations are not available, these tests can be used to assess the relative improvement in the soils by conducting tests before and after treatment.<strong> </strong></p></p>