<p><p><h2><img class="aligncenter wp-image-2544 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Cartoons showing the sequence of compaction grouting under a footing." width="1151" height="371" /></h2><h2>Basic Function:</h2>Compaction grouting strengthens and stiffens soils through densification by displacement of the soil as grout is injected into the soil.<br><h2>Advantages:<em> </em></h2><ul> <li>Effectiveness has been well proven in practice.</li> <li>Can be implemented in areas of low head clearance.</li> <li>Directly treats areas that need improvement.</li> <li>Can be installed under existing structures</li></ul><h2>General Description:</h2>Compaction grouting involves pumping a low mobility grout, typically 2 inch (50 mm) slump or less, at high pressures (100-400+ psi) into the soils that are to be treated as a means of displacing the soil to achieve higher densities. The grout forms a homogenous bulb at the point of application, and expands to weak areas in the soil strata. Unlike many other grout applications the grout does not strengthen the soil by cementation, but instead strength and stiffness are typically increased as the soil is displaced (i.e., compacted).<br><h2>Geologic Applicability:</h2><ul> <li>Can be applied successfully and economically in cohesionless granular soils, collapsible soils, and unsaturated fine grained soils</li> <li>Silts and well graded sands have higher success than clays and poorly graded sands and gravels</li> <li>May be used to fill voids in the soil stratum such as sinkholes in karst terrain or abandoned mine shafts</li> <li> Also used to arrest settlement under a structure, lift foundations that have settled, and mitigate liquefaction.</li></ul><h2>Construction Methods:</h2>Construction usually consists of driving or drilling the grout casing to the desired depth and location and pumping in grout until the design stopping criteria has been reached. Grout may be placed in either bottom up or top down applications and forms a bulb of grout or multiple linked bulbs of grout to displace the surrounding soils. The stage down method is used to densify a loose or soft top soil layer. This method is commonly used when overburden pressures are less than 1000 psf. Grout injections are placed in a predetermined pattern, and can be installed vertically or battered at an angle. Spacing can be between 3 and 15 feet, but 8 to 12 foot spacing is more typical. Grout bulbs are formed about every 1 to 3 feet depending on the application. Pumping rates can vary depending on the type of soils and the amount of compaction necessary, but are in the range of 0.5 to 1 cubic feet per minute. Diameter of the grout bulb can vary from around one foot up to approximately three feet.<br><h2>Additional Information:</h2>Different criteria are used to determine when to advance the grouting process, but it typically consists of grout pressure, volume of grout take, and ground heave. Secondary, and if necessary tertiary, grout holes are filled in sequence to achieve better results. These holes should take considerably less volume of grout than the first grout hole as the soil has already been densified and their purpose is to find any weak areas left untreated.<br><h2>SHRP2 Applications:</h2><ul> <li>New Embankment Construction</li> <li>Embankment Widening</li> <li>Stabilization of Working Platforms</li></ul><h2> <strong>Example Successful Applications:</strong></h2><ul> <li>Retaining Wall Repair Along I-70 in Western Colorado</li> <li>Repair of State Route 85 And I-70 Over Karst Terrain In Frederick, Maryland</li> <li>Liquefaction Mitigation of Laurel Street Bridge In Santa Cruz, California</li></ul><h2>Complementary Technologies:</h2><ul> <li>PVDs</li></ul><h2>Alternate Technologies:</h2>Jet Grouting, Deep Mixing, Deep Dynamic/Rapid Impact Compaction, Micropiles, Conventional piles, Chemical/Permeation Grouting, Vibrocompaction, Stone Columns<br><h2>Potential Disadvantages:</h2><ul> <li>Grout rheology has been tested but requires further investigation.</li> <li>Can cause a build-up of excess pore pressure in fine grained soils.</li> <li>QA/QC procedures need to be further developed</li> <li>Design methodology is not well articulated.</li></ul><h2>Key References for this technology:</h2>Elias, V., Welsh, J., Warren, J., Lukas, R., Collin, J. G., and Berg, R. R. (2006b). . Ground Improvement Methods, NHI-06-020 , Volume 2.</p><p>Schmertmann, J.H. and Henry, J.F., (1992). “A Design Theory for Compaction Grouting.” Proceedings of the Conference on Soil Improvement and Geosynthetics, New Orleans, Louisiana. GSP-30.</p><p>Warner, James (2004). Practical Handbook of Grouting - Soil, Rock and Structures. John Wiley &amp; Sons.</p></p>