<p><p><figure id='attachment_3553' style='max-width:640px' class='caption aligncenter'><img class="wp-image-3553 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of trench constructed to dampen vibration effects of using rapid impact compaction." width="640" height="480" /><figcaption class='caption-text'> Excavated trench above utility line to dampen impact of RIC. (Kristiansen and Davies, 2004; from www.nicee.org/wcee/)</figcaption></figure></p><p><div><h2>Project Summary/Scope:</h2>A combined fire station and office building complex designated as a post-disaster structure required a design to withstand a 1 in 475 year earthquake. The complex was constructed on a site containing liquefaction susceptible soils.<br>Subsurface Conditions: The soil conditions generally consisted of granular fill over interbedded sand and silt layers underlain by granular deposits. The fill thickness was typically about 1 ft (0.3 m). The underlying native granular deposit was typically encountered at about 10 ft (3 m) depth and consisted of sand with variable gravel content and minor silt content and occasional cobbles. The upper zone of this granular soil deposit was compacted to a very dense state, with typically equivalent SPT-N₆₀values of the order of 17 blows per ft (305 mm) or more to an approximately 21 ft (6.5 m) depth. However, loose compacted zones up to about 8 ft (2.5 m) thick existed between a 21 ft (6.5 m) and 33 ft (10 m) depth. Interpretation of BPT data indicated dense to very dense granular soil from about a 33 to 49 ft (10 to 15 m) depth over compact to dense granular soil to about a 66 ft (20 m) depth, which in turn was underlain by very dense granular soil.</p><p>Compaction was carried out at close spacing with many compaction locations within a 20 ft x 20 ft (6 m x 6 m) area. Due to wet weather conditions prior to and during the rapid impact compaction construction program, the top 1½ to 3 ft (0.5 to 1 m) of the soil was sub-excavated and backfilled with sand with minor gravel then compacted using a smooth drum ride-on vibratory compactor. After sub-excavation and replacement, rapid impact compaction works were carried out on the entire building footprint. The rapid impact compaction consisted of hydraulically dropping a 7.5 ton (7 tonne) weight from a controlled height onto a 5 ft (1.5 m) diameter tamper at a rate of 40 to 60 blows per minute. Each area was compacted with a minimum of two passes with each pass having a minimum of 13 compaction points. Each point was compacted by sufficient blows to achieve a final set (deformation) during the second pass of maximum 3/8 in (10 mm). Shallow trenches were excavated between vibration sensitive structures to dampen the impact of the rapid impact compaction.<br><h2>Alternate Technologies:</h2>The improvement alternatives to rapid impact compaction were excavation and replacement, stone columns, and dynamic compaction.<br><h2>Performance Monitoring:</h2>A data acquisition system was used to monitor the rapid impact compaction construction. Pre-treatment analysis included solid stem augers, Dynamic Cone Penetration Tests (DCPTs), CPTs and Becker Penetration Tests (BPTs). Post-treatment analysis using BPTs occurred approximately one month after treatment.</p><p>The method densified the in-situ soils appreciably to a depth of approximately 20 ft (6 m) below ground surface. It was judged that granular zones on the subject site with equivalent SPT-N₆₀ values of approximately 15 blows per foot (305 mm) or less between depths of 20 ft (6 m) and almost 30 ft (9 m) were densified to equivalent SPT-N₆₀ values of about 20 blows per foot (305 mm) or more.<br><h2>Project Technical Papers:</h2>Kristiansen, H. and Davies, M. (2003), “Results of Becker Penetration Testing, Chilliwack Fire Hall”, AMEC Earth &amp; Environmental, Inc., Burnaby, B.C., Canada, 10p.</p><p>Kristiansen, H. and Davies, M. (2004), “Ground Improvement Using Rapid Impact Compaction”, Proceedings from the 13^th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, Paper No. 496.<br><h2>Date Case History Prepared:</h2><strong> </strong>November 2012</p><p></div></p></p>