<p><p><figure id='attachment_3615' style='max-width:475px' class='caption aligncenter'><img class="wp-image-3615 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagram of vibro-concrete column construction." width="475" height="630" /><figcaption class='caption-text'> Diagram of vibro-concrete column installation. (Figure courtesy of FHWA, Elias et al. 2006).</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>New Jersey DOT replaced an aging bridge built in 1927 with a new 1,220-meter long bridge to the west of the existing structure. The new bridge approach consisted of embankment fill up to 6 meters high, 27 meters wide, and 150 meters long. A 55‑meter long retaining wall is located at one of the bridge abutments to prevent wetlands encroachment. The new embankment has a slope of 2H:1V.</p><p>Subsurface Conditions: Fill and natural sand overlying organic soils with compression ratios of 0.3 to 0.5. The undrained shear strength was 38 kPa and the long-term effective friction angle was 26°.</p><p>Design considered slope stability, settlement, and liquefaction. A series of PVDs and preloading was used. However, this construction program stopped short of the bridge abutment. Static factors of safety for the short- and long-term condition were 1.7 and 2.7 respectively. Primary consolidation under 6 meters of embankment was estimated to be as high as 1.1 meters and as much as 160 mm of long-term secondary compression. For liquefaction calculations, a reduced strength was used for the liquefiable sands which resulted in a factor of safety less than 1. Right-of-way, drainage, and wetlands prevented a flattening of the slope.</p><p>VCC columns were used to support a Load Transfer Platform (LTP) and the overlying embankment. The VCC columns consisted of a 45-cm diameter shaft and 90-cm diameter bulb at the top of the column. Standard bearing capacity analysis was used, which resulted in a factor of safety greater than 3. Columns were spaced 7 feet center-to-center and the distance was optimized based on the cost of VCCs compared to the cost of geosynthetics of various strengths. The geosynthetic reinforcement design was based on British Standard BS 8006. The granular mat above the geosynthetic was 0.9 meters thick. A timeline of two to three months per bridge approach was used for construction (four to six months total).<br><h2>Complementary Technologies Used:</h2>Column supported embankment with high strength geosynthetic reinforcement.<br><h2>Alternate Technologies:</h2>Two alternatives to vibro-concrete columns were considered: preload/surcharge and vibro compaction of the liquefiable soils. Time allotted for design and construction did not allow for the use of PVDs and surcharging.<br><h2>Cost Information:</h2>Estimated cost of $1.6M compared to $1.4M for PVDs/surcharge and $2.0M for vibro‑compaction.<br><h2>Project Technical Paper:</h2>Zamiskie, E.M., Lambrechts, J.R., Yang, K., Rodriguez, J.M., and McDonnell, M. (2004). “Vibro Concrete Columns Solve Problems for Victory Bridge Approach Fill.” Geotechnical Engineering for Transportation Projects, Proceedings of Geo-Trans 2004, ASCE, Los Angeles, CA. <a href="http://ascelibrary.org">http://ascelibrary.org</a><h2>Date Case History Prepared:</h2>November 2012</p></p>