<p><p><h2>Project Summary/Scope:</h2>The Hokkaido Highway Construction Project was intended to improve the traffic connection between area towns. One section required the construction of a new embankment.</p><p>Subsurface Conditions: Thick, soft peat from the ground surface to a depth of about 6 meters had water contents ranging from 400 to 1,000%. The unconfined compressive strength of the peat material was around 10 to 20 kPa. Soft clay layers underlay the peat and have shear strengths increasing with depth.</p><p>Field tests were conducted on three test embankments: one with sand drains, another with sand compaction piles, and a third without either sand drains or sand compaction piles. The sand drain test embankment consisted of 40-cm sand drains in an equilateral triangle configuration at 1.5 meter spacing to a depth of 11.5 meters. The sand compaction pile test embankment consisted of 70 cm diameter sand compaction piles installed in a 1.5 meter square configuration to a depth of 11.5 meters, terminating before reaching the stiff layer. The embankments were constructed to a height of 8 meters.<br><h2>Complementary Technologies Used:</h2>Sand drains<br><h2>Performance Monitoring:</h2>The unimproved embankment settled during the consolidation period, failing with a crack and large horizontal deformation at a height of 3.5 meters. The embankments constructed with sand drains and sand compaction piles were both successfully constructed to the intended height of 8 meters. Nearly 300 cm of settlement occurred for the sand drain embankment and 224 cm occurred for the sand compaction pile embankment. Based on the measured settlement of the embankment with sand compaction piles and estimations by the hyperbola method, a settlement reduction factor of 0.75 was obtained for the sand compaction piles relative to the unimproved ground.</p><p><figure id='attachment_2624' style='max-width:572px' class='caption aligncenter'><img class="size-full wp-image-2624" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematics of the construction sequence for Sand Compaction Piles." width="572" height="326" /> Construction Sequence for Sand Compaction Piles<br /><figcaption class='caption-text'>(Figure from Barksdale (1987), after Tanimoto (1973))</figcaption></figure><h2>Project Technical Paper:</h2>Kitazume, M. (2005). “The Sand Compaction Pile Method.” Port and Airport Research Institute, Yokosuka, Japan, pp. 84-88.<br><h2>Date Case History Prepared:</h2>November 2012</p></p>