<p><p><strong>Reference(s):</strong></p><p><em>Broms (2003)<br>Esrig et al. (2003)<br>Hughes et al. (2001)<br>Larsson (2005)<br>Porbaha and Puppala (2003)</em></p><p><strong>Method Summary</strong></p><p>The pressuremeter test is used to evaluate the strength and compression modulus in treated columns. Pressuremeter tests are typically performed by inserting the apparatus into a pre-drilled hole at the center of the column to the desired depth. The pressure and displacement of the expanded membrane is measured in radial directions. The quality of mixing is determined by evaluating the variation in displacements measured from transducers within the apparatus. If the variation between displacement readings is greater than 20%, the column is considered to be non-homogeneous. The strength properties are evaluated using cylindrical cavity expansion models (Porbaha and Puppula 2003). Measurement of the compressibility of columns allows for estimation of expected settlements (Broms 2003).</p><p><strong>Accuracy and Precision</strong></p><p>Pressuremeter tests have been performed as a quality assurance method on several projects in the U.S., including the Boston CA/T and the Salt Lake City I-15 reconstruction (Esrig et al. 2003). In the Salt Lake City I-15 reconstruction project, compression moduli and calculated settlements from pressuremeter tests showed good agreement with measured settlements (Esrig et al. 2003). However, in the Boston CA/T project, strengths determined from pressuremeter tests showed no correlation with unconfined compressive strengths of core samples taken from the same borehole (Hughes 2001). Larsson (2005) points out that this is a common problem when comparing results from tests with differences in the testing conditions and objectives. Pressuremeter testing is considered a relatively accurate method of determining the compressibility of improved columns; however, the accuracy of pressuremeter testing for determining the shear strength of improved soil is questionable. A larger number of test records would help determine the adequacy of using pressuremeter testing to measure shear strength.</p><p><strong>Adequacy of Coverage</strong></p><p>The tests are time consuming and do not provide a continuous record of strength within the column. However, the measurement of displacement in multiple directions allows for the determination of treated soil properties for a relatively large volume of soil (Larsson 2005). Overall, the amount of soil that can be tested with the pressuremeter is small because the test is slow, specialized, and expensive.</p><p><strong>Implementation Requirements </strong></p><p>Performing tests and properly interpreting results requires an experienced engineer. Tests also require a pre-drilled hole. However, according to Esrig et al. (2003), the cost to perform pressuremeter tests is less than coring and testing core samples in the lab.</p><p><strong>General Comments</strong></p><p>Pressuremeter testing can be an effective tool to measure the compressibility of improved columns, but the reliability of this test for determining column strength is not well established. The difficulty of performing tests and interpreting the results coupled with the relatively few number of case histories of its use in DMM QC/QA limits the usefulness of pressuremeter testing in current practice.</p></p>