<p><p><strong>Reference(s):</strong></p><p><em>Åhnberg et al. (2009)<br>Larsson (2005)<br>Staab et al. (2005)</em></p><p><strong>Method Summary</strong></p><p>Geophysical methods consist of both seismic and electromagnetic imaging methods. Geophysical tests are able to determine general properties of an entire column of treated soil as opposed to a small sample from within a column. Seismic testing methods include down-hole and cross-hole logging. This process involves the use of a source and receivers in the treated soil to measure the average P- and S-wave velocities. Correlations have been developed between these wave velocities and the unconfined compressive strength of core samples, but correlations seem to be site-specific and are not always strong (Larsson 2005). Bender element tests have also shown capability in measuring shear wave velocity in lab samples, and site-soil specific correlations to unconfined compressive strength have been developed (Åhnberg et al. 2009). An advantage of seismic methods is that tests can be performed at various ages of the treated soil, and strength increase can be monitored with time. Electromagnetic imaging consists of electrical resistivity and cross-borehole ground penetrating radar tomography. These imaging techniques seek to verify the homogeneity of mixing and identify defects within the column profile due to poor mixing (Staab et al. 2005).</p><p>In current practice, geophysical methods are considered an area of ongoing research and development, but they show promise for application in future QC/QA practices.</p><p><strong>Accuracy and Precision</strong></p><p>The need for refinement and continued research of many geophysical methods hinder them from being applied as a primary means to verify improved soil properties.</p><p><strong>Adequacy of Coverage</strong></p><p>Geophysical tests can be applied to a significant area of improved soil and give average properties of the entire volume.</p><p><strong>Implementation Requirements </strong></p><p>Many engineers and technicians are not familiar with geophysical methods. Although commercially available, there is significant cost to acquire the necessary equipment and training.</p><p><strong>General Comments</strong></p><p>Geophysical methods show promise but are not widely used in current practice for QC/QA of deep mixing methods. Their usefulness is limited in most applications.</p></p>