<p><p><strong>Reference(s):</strong></p><p><em>Broms (2003)<br>Bruce (2001)<br>Cali et al. (2005a)<br>CDIT (2002)<br>Lambrechts (2005)<br>Terashi and Kitazume (2009)</em></p><p><strong>Method Summary</strong></p><p>Installation and testing of field test columns is a key pre-production QC/QA process for many DMM projects. Lambrechts (2005) notes that field test column installation allows all involved parties to observe the deep mixing process and to see the data collected by monitoring equipment during installation. Samples taken from field test columns and in-situ testing can verify that desired strength improvement and mixing uniformity have been achieved and confirm the adequacy of the mix design (CDIT 2002). In addition, the adequacy and performance of selected QCQA methods and sampling methods can be assessed for use during production installation as well as identifying unforeseen construction challenges as noted by Cal et al. (2005a).</p><p>Field test columns are recommended for many DMM projects. Bruce (2001) advises installation of field test columns on large jobs (&gt;1,000 columns) or when there is a lack of previous experience in the area of proposed DMM column placement. Lambrechts (2005) identifies three scenarios for which field test columns may not be necessary:<br><ul> <li>“The contractor has other recent nearby experience in similar soils from which to demonstrate adequate performance;</li> <li>The volume of the project is small and the contractor would propose to add ‘more than enough’ reagent to accomplish the soil stabilization; or</li> <li>The contractor accepts the responsibility to do more deep mixing as may be needed if the first installation does not come up to required strength.”</li></ul>The number of test columns or test sections to be installed should be set forth in the project specifications. In some cases, the contractor may choose to install additional columns to test different mix designs in the field. Broms (2003) recommends the installation of test columns in groups of six to ten.</p><p><strong> </strong><strong>Accuracy and Precision</strong></p><p>Installing field test columns is an important step to verify the lab mix trials and confirm the expected degree of improvement in field conditions. The field test allows for the demonstration and calibration of monitoring equipment for the amount of stabilizing agent, rotation speed of mixing blades, and penetration and withdrawal speeds (CDIT 2002). Other QC/QA techniques described later in this document, such as penetration/pullout methods, core and wet grab sampling, and excavation or extraction can also be performed on test columns to provide further indication of the level of field improvement.</p><p><strong>Adequacy of Coverage</strong></p><p>Test columns provide an accurate estimate of soil improvement expected from construction; however, the number of test columns is only a small fraction of the total number of columns installed on ordinary DMM projects. Installing more test columns allows for acquisition of more data, leading to better calibration of monitoring equipment and an increased number of tests which provides a more reliable range of expected improvement values. The location of the test section(s) is also an important consideration for determining how representative that area is of the soil conditions across the site.</p><p><strong>Implementation Requirements </strong></p><p>The main obstacle to installing test columns during the design phase is the high cost of mobilizing equipment for a relatively small number of columns. When test or demonstration columns are installed as part of the construction contract but prior to installation of the production columns, no additional mobilization costs are incurred, but equipment operating costs and personnel costs do apply. Adequate time for curing and testing of the columns should be provided prior to the start of installing production columns.</p><p><strong>General Comments</strong></p><p>Installation of test columns during the design phase can be relatively expensive and is best suited for large projects. Test or demonstration columns at the beginning of construction are more common. Test columns are important for verifying the adequacy of the design mix and for calibrating deep mixing equipment. Test columns can be particularly useful for verification of the vertical bearing capacity for support of structures and support of embankments. They also may be useful in establishing correlations between multiple strength verification methods.</p></p>