<p><p><strong>References:<br></strong><em>Briaud and Seo (2003)<br>NCHRP 21-09 (2010)<br>Peterson et al. (2006)<br>Rahman et al. (2008),<br>Ryden and Mooney (2007)<br>White et al. (2007a, 2008d, 2009d)</em></p><p><strong>Method Summary</strong></p><p>Soil stiffness gauge (SSG), Briaud compaction device (BCD), and seismic methods fall under this category. These tests typically involve calculating modulus at relatively low strains.</p><p>BCD test is performed by placing a 150 mm diameter plate on the ground, applying the load (a minimum load of 223 N), and measuring the applied load and the bending strain in the plate to determine the modulus. SSG device weights about 10 kg, is 28 cm in diameter, and 25.4 cm in height, and rests on a ring-shaped foot on the soil surface. The SSG produces high frequency vibrations (100 to 200 Hz) which produces small changes in vertical force and deflections which are used to determine stiffness and modulus values. Seismic methods involve estimating Young’s or shear moduli using different wave propagation methods: (a) impact echo, (b) impulse response, (3) spectral analysis of surface waves, (4) ultrasonic survae wave, and (5) ultrasonic body wave velocity.</p><p><strong>Accuracy and Precision</strong></p><p>All these test methods are generally considered repeatable. Correlation results between these test methods and conventionally used modulus test methods (e.g., PLT) are limited, but are promising.</p><p><strong>Adequacy of Coverage</strong></p><p>Sufficient evaluation requires many tests. These tests are relatively fast to perform (approximately &lt; 5 min per test).</p><p><strong>Implementation Requirements</strong></p><p>Specialized equipment and trained personnel are necessary to conduct the test and analyze the results.</p><p><strong>General Comments</strong></p><p>This test method provides a direct measure of elastic modulus and can serve as a good QA tool.</p></p>