<p><p><figure id='attachment_3601' style='max-width:600px' class='caption aligncenter'><img class="wp-image-3601" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Plan view graphic showing general layout of the sewage treatment plant facilities." width="600" height="685" /><figcaption class='caption-text'> Sewage Treatment Plant General Layout. (Masse et al., 2001)</figcaption></figure></p><p><div><h2>Project Summary/Scope:</h2>Former rice fields underlain by highly compressible clay layers were improved using vacuum preloading in order to be used to support a sewage treatment plant. The area improved had a surface area of 80,000 m².</p><p>Subsurface Conditions: The site consisted of highly compressible clay layers with depths varying between 25 and 43 meters. There were three relatively uniform soil layers. The upper layer (4 to 7 meters thick) was a silt with sand. The intermediate layer (20 to 35 meters thick) was a compressible saturated clay. The bottom layer was a weathered rock 25 to 43 meters deep from the initial ground level. The preliminary soil investigation consisted of SPT, CPT, PMT, and laboratory tests, and included 24 quality control points located under future buildings. Design structural loads ranged from 3.3 to 15.5 tonne/m². Foundation depths ranged up to 7 meters below finished grade. The goal was a total average settlement of 3.6 meters.</p><p>The implementation of vacuum preloading was completed in the following phases:<br><ol> <li>Site preparation - placing a woven geotextile to stabilize the working platform and then placing a sand blanket with a height of 1 meter as the drainage layer</li> <li>Drainage - installation of vacuum transmission pipes and horizontal drains within the sand blanket</li> <li>Air/water tightness - an impervious slurry wall was installed outside the perimeter with a depth of 9 meters in addition to a peripheral trench system</li> <li>Primary fill - a 1.5-meter fill layer was placed above the sand layer and under the membrane</li> <li>Membrane/pumping system - the PVC membrane was laid out and welded together, then the vacuum pumps were turned on.</li></ol>The project was completed between January 1995 and April 1997. The vacuum preload was applied for 9 months.<br><h2>Complementary Technologies Used:</h2>Fill Surcharge</p><p><figure id='attachment_3603' style='max-width:764px' class='caption aligncenter'><img class="wp-image-3603 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic graph showing settlement with time and rebound post-vacuum." width="764" height="519" /><figcaption class='caption-text'> Graph showing settlement and post-vacuum rebound.</figcaption></figure></p><p>&nbsp;<br><h2>Performance Monitoring:</h2>Measurement of initial/final void ratios (e), effective stress (σ’_v), and compression index (c_c) with depth. Settlement gauges were also used.</p><p>The project was completed on a performance design basis.</p><p>The recorded settlement ranged from 314 to 548 cm for surcharge height varying from 6.5 to 15.5 meters during the vacuum preload/fill surcharge application. Once the vacuum was turned off and the fill surcharge removed, a slight rebound was recorded (less than 10 cm). Settlement stabilized in two weeks and no residual settlement was observed. Overall, the project was considered to be a success.<br><h2>Project Technical Paper:</h2>Masse, F., Spaulding, C.A., Wong, I.C. and Varaksin, S. (2001) “Vacuum consolidation: a review of 12 years of successful development.” Geo-Odyssey, ASCE, Virginia Tech, Blacksburg, VA<br><h2>Date Case History Prepared:</h2><strong> </strong>November 2012</p><p></div></p></p>