<p><p><figure id='attachment_2575' style='max-width:1024px' class='caption aligncenter'><img class="wp-image-2575 size-large" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of the excavation of unsuitable material using an excavator in Columbus, Mississippi." width="1024" height="768" /><figcaption class='caption-text'> Excavation of Unsuitable Soil using Hydraulic Excavator in Columbus, Mississippi (Courtesy of David M. Coleman).</figcaption></figure><h2>Basic Function:</h2>Excavation and Replacement is a ground improvement method to increase the reliability and strength of soil beneath an embankment or pavement structure.<br><h2>Advantages:<em> </em></h2><ul> <li>Simplicity of the technology</li> <li>Reliability</li> <li>Equipment is readily available</li> <li>Contractors are readily available</li> <li>Specifying/Contracting is simple</li></ul><h2>General Description:</h2>Unsuitable soils beneath an embankment or pavement structure are replaced by good quality material such as sand or gravel that is easy to compact, strong, and relatively insensitive to moisture changes.<br><h2>Geologic Applicability:</h2><ul> <li>Decreases the effects of soft clays, expansive clays, highly organic soils, topsoil, and uncontrolled fill.</li> <li>Shallow unsuitable soils, generally up to about 15 to 20 feet deep.</li> <li>Poorly graded aggregates are a good replacement material.</li> <li>Generally used above the groundwater table.</li></ul><h2>Construction Methods:</h2>In Excavation and Replacement unsuitable material is removed and replaced by sand or gravel. All highly compressible material in the load path should be excavated. Sand or gravel is the preferred backfill. On-site soils or borrow is more economical. Chemically stabilized soils are generally not free draining, and are not recommended for areas with a high groundwater table. The backfill is placed in lifts and compacted. Moisture sensitive soils should have a water content near optimum for compaction. Geosynthetic materials can be used to improve the behavior of the replacement fill.<br><h2>Additional Information:</h2>The depth of the excavation is determined by the depth of the unstable soil, which with groundwater and the soil’s ability to support construction equipment dictates the type of construction equipment to use. Excavation construction equipment is readily available on most construction sites. The cost of the technology depends on the replacement material quality and availability. Cost generally can be $6 to $12 per cubic yard ($10 to $20/m²) of treated ground, but will vary with local and project conditions.<br><h2>SHRP2 Applications:</h2><ul> <li>New Embankment and Roadway Construction</li> <li>Roadway and Embankment Widening</li> <li>Stabilization of the Pavement Working Platform</li></ul><h2>Example Successful Applications:</h2><ul> <li>Considered as the baseline treatment approach for most projects.</li></ul><h2>Complementary Technologies:</h2>Typically not used in conjunction with other technologies. Nontraditional replacement materials and compaction technologies can be used in conjunction. Replacement materials can be improved with reinforcing technologies.<br><h2>Alternate Technologies:</h2>Many SHRP2 R02 technologies can be alternates.<br><h2>Potential Disadvantages:</h2><ul> <li>Requires excavation; hauling and disposal of materials; and hauling, placement and compaction of imported material versus in situ stabilization technologies.</li> <li>Often, but not always cost effective.</li> <li>Slower process than other technologies.</li> <li>Requires construction trafficking on exposed subgrade and replacement material, and may require dewatering, shoring, and/or disposal of waste materials.</li></ul><h2>Key References for this technology:</h2>Ariema and Butler (1990). “Embankment Foundations.” <em>State of the Art Report 8: Guide to Earthwork Construction</em>, Transportation Research Board, Washington, D.C.</p><p>Brown, R.W. (Editor) (2001). <em>Practical Foundation Engineering Handbook, </em>McGraw-Hill, Columbus, Ohio.</p><p>Greenfield, S. J., and Shen, C. K. (Editors) (1992). <em>Foundations in Problem Soils: A Guide to Lightly Loaded Foundation Construction for Challenging Soil and Site Conditions.</em> Prentice Hall, Englewood Cliffs, New Jersey.</p></p>