<p><p><strong>References:<br></strong><em>Aldridge and Naguib (1992)<br>ALLU (2007)<br>Broomhead and Jasperse (1992)<br>Bruce et al. (2013)<br>Burke et al. (2007)<br>Forsman et al. (2008)<br>Garbin and Mann (2010)<br>Hayward Baker Inc. (2009)</em></p><p><strong>Method Summary</strong></p><p>Laboratory testing is a quality assurance technique performed after mixing operations to verify that the specified level of improvement was achieved. The most common tests used to verify field results are the unconfined compressive strength test (ASTM D2166) and the flexible wall permeameter test (ASTM D5084). Other tests to determine shear strength in the laboratory (i.e. triaxial tests) may be appropriate in some cases, but they will be more expensive than unconfined compression tests, and fewer can be performed. Given the cemented consistency of the mixed soil, unconfined tests are generally considered sufficient. Laboratory tests can be performed on samples of treated soil obtained from pushed thin-walled tubes after the mixture has set, if the mixture is not too strong, or from wet grab samples prior to the mixture setting. Grab samples are taken using a bucket sampler designed to take discrete samples from specific depths in the soil volume, and placed in a mold for curing (Aldridge and Naguib, 1992).</p><p>Thin-walled sampling may not be possible in soil with high post-treatment strength. Grab sampling may be difficult if the mixed soil is especially viscous. Coring may be a suitable alternative for high-strength soils and/or viscous soil-binder mixtures. Burke et al. (2007) describe the use of two- and three-barrel coring tools to obtain samples. Coring is typically performed after the soilcrete has reached its 28-day strength. Coring has been shown to provide high recovery rates in wet- and dry-mixed soils. More information on coring and wet grab sampling for quality assurance can be found in the GeoTechTools QC/QA <em>Procedures for Deep </em><em>Mixing Methods</em> and in the FHWA Deep Soil Mixing Design Manual (Bruce et al. 2013).</p><p><strong>Accuracy and Precision</strong></p><p>Laboratory test procedures and results are typically governed by standards (ASTM, AASHTO, etc.). These standards are meant to ensure tests are performed with standardized procedures that produce repeatable results. Tests performed in accordance with these standards should yield accurate verification of treated soil properties of the samples tested. Discussion of the anticipated precision and bias of a test is usually included in the ASTM standard test method. Accuracy may be affected by damage to the specimens while sampling, additional mixing energy being applied during sampling and forming of specimens, and differences in laboratory and in situ curing conditions.</p><p><strong>Adequacy of Coverage</strong></p><p>Tests are performed on specimens from a single location of the treated volume. To adequately verify the properties of the entire soil mass, tests should be performed on specimens sampled from different locations throughout the treated volume. Engineering judgment should be used when determining an appropriate number of tests. Testing and sampling frequency should consider the size of the area to be treated, variability in subsurface conditions, and the type and performance expectations of the proposed facility. The FHWA Deep Soil Mixing Design Manual (Bruce et al. 2013) suggests that frequency for coring samples can be selected as a percentage of elements (applicable to SSM) or percentage of elements and treatment area (applicable to SSM and to MS). For wet grab sampling, the manual suggests that one sample be taken for every 2,000 yd³(1,500 m³) of soil treated for embankment and foundation support applications with a minimum of one sample for every two production days.</p><p><strong>Implementation Requirements</strong></p><p>Tests to measure strength, compressibility or stiffness, and permeability are typical geotechnical engineering tests that can be performed at most geotechnical testing laboratories. Chemical tests such as leachate tests for environmental stabilization applications may require environmental testing laboratories.</p><p><strong>General Comments</strong></p><p>Various laboratory tests can be performed for quality assurance on shallow-mixed or massstabilized soil, depending on the project-specific objectives. The most common tests are performed to verify post-treatment shear strength, but tests may also be performed to determine post-treatment permeability or chemical composition for environmental applications. Results of laboratory testing must show that the treated soil meets acceptance criteria for strength and<br>uniformity. Comparing the test results from different locations in the treated volume can provide another indication of homogeneity of the soil.</p></p>