<p><p><figure id='attachment_3343' style='max-width:965px' class='caption aligncenter'><img class="wp-image-3343 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Diagram of layout of blast holes for a liquefaction study at the National Geotechnical Experimentation Site" width="965" height="542" /><figcaption class='caption-text'> Test layout for pilot liquefaction study (Ashford et al. 2004; With permission from ASCE)</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>A pilot liquefaction study was conducted to determine the optimal charge size, pattern, and delays required to liquefy the soil. A second objective of the pilot program was to confirm that liquefaction is repeatable (i.e., that a second blast at the same site would provide similar results). The treatment area was 15.2 by 19.8 meters. Treatment depth was approximately 5 meters.</p><p>Subsurface Conditions: The site consisted of hydraulically placed fill (loose fine sand or sandy silt with interbedded layers of lean clay) and native shoal sands to a depth of 4.5 to 6 meters. The water table at the site was about 0.5 meters below the ground surface. The average hydraulic conductivity of the sand was 3.5 x 10^-3 cm/s. The initial relative density of the sand layer ranged from 20 to 70%.</p><p>A series of test blasts were performed at the site to define the relationship between induced excess pore pressure ratio and scaled distance. The pilot tests were conducted after successful completion of the test blast program. Vibrating wire transducers were destroyed during the test blasts. More robust piezoresistive transducers were used for the pilot tests.</p><p>Two blasts were conducted, each with a total of 16 0.5-kg TNT-equivalent charges. The charges were located at the perimeter of two 2.1-meter radius circles. Two-part explosives, composed of ammonium nitrate and nitro-methane, were placed at a depth of 3.6 meters below the ground surface (3.1 meters below the water table). The borehole was backfilled with pea gravel. Charges were detonated two at a time with a 250 ms delay between explosions. Three days after the initial blasts, identical blasts were detonated.<br><div><h2>Performance Monitoring:</h2>Pore pressure transducers were installed to provide information regarding pore pressure response as a function of depth and distance from the blast points. CPT tests were conducted before the blasts, two days after the blasts, and 42 days after the blasts.</p><p>Although pore pressure transducers indicated that liquefaction occurred just a few seconds after detonation, surface manifestation of liquefaction occurred after a period of 3 to 5 minutes. Settlement was typically about 2.5% of the liquefied thickness and about 85% of the settlement occurred within 30 minutes after the blast. Two days after blasting, a decrease in CPT resistance was observed. A significant increase in CPT resistance was observed 42 days after blasting.<br><h2>Project Technical Paper:</h2>Ashford, S.A., Rollins, K.M. and Lane, J.D. (2004). “Blast-Induced Liquefaction for Full-Scale Foundation Testing.” <em>Journal of Geotechnical and Geoenvironmental Engineering</em>, ASCE, 130(8), pp. 798-806.</p><p><a href="http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282004%29130… Case History Prepared:</h2>November 2012</p><p>&nbsp;</p><p></div></p></p>