<p><p><figure id='attachment_3606' style='max-width:6876px' class='caption aligncenter'><img class="wp-image-3606 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagram of the generic vibrocompaction process." width="6876" height="4012" /><figcaption class='caption-text'> Generic vibrocompaction process. (Figure courtesy of FHWA, Elias et al. 2006).</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>The I-90 corridor through the Mt. Baker Ridge area was designed to carry an estimated 50,000 vehicles daily. Deep cut construction was used to allow for covered roadways and to have minimal impact on the surrounding residential communities. Massive footings were used to support the covered roadway on soils originally assumed to have an allowable bearing capacity of 285 kPa. It was later determined that the reported allowable bearing capacity was not adequate for settlement requirements. Vibrocompaction was selected to improve the bearing and settlement characteristics of the soil.</p><p>Subsurface Conditions: Fill overlying sandy glacial deposits.</p><p>Stone backfill was used during the vibrocompaction process. 540 points were compacted/densified to a depth ranging between 4.5 and 6.0 meters. The compaction points were spaced on a 1.8-meter grid spacing. The design was intended to limit settlements to 19.1 mm. A 120-kW vibrator was used for the compaction process.<br><h2>Alternate Technologies:</h2>Deep foundations and in-situ soil improvement were considered to improve the bearing and settlement properties of the soil.<br><h2>Performance Monitoring:</h2>Two plate load tests were performed at selected compaction points. A 1.8 by 1.8‑meter plate was loaded in increments to 930 kN, representing a pressure of 285 kN/m².</p><p>Average total settlement under working design load was approximately 12.5 mm. About 6.5 mm of plastic deformation was observed during the unloading of the plate load test.<br><h2>Summary Source:</h2>Elias, V., Welsh, J., Warren, J., Lukas, R., Collin, J.G., and Berg, R.B. (2006). “Ground Improvement Methods-Volume I and II.” Federal Highway Administration, Publication No. FHWA NHI-06-019 (Vol. I) and FHWA NHI-06-020 (Vol. II).<br><h2>Date Case History Prepared:</h2>November 2012</p></p>