<p><p><figure id='attachment_2608' style='max-width:598px' class='caption aligncenter'><img class="wp-image-2608 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematics of the equipment and process used for shallow soil mixing (left) and mass stabilization (right)." width="598" height="164" /><figcaption class='caption-text'> Schematics of the equipment and process used for shallow soil mixing (left) and mass stabilization (right) (Broomhead and Jasperse 1992, with permission from ASCE; Courtesy of ALLU Finland Oy 2007).</figcaption></figure><h2>Basic Function:</h2>Mass mixing methods refer to two technologies, shallow soil mixing (SSM) and mass stabilization (MS). These technologies are used to stabilize and strengthen soils at shallow to moderate depths using a binder material. Mass mixing methods can be used to treat soft clays, peats, and sludges for roadway, railway, and support of structures.<br><h2>Advantages:</h2><ul> <li>Can be used to stabilize peat and other soft soils, and to treat contaminated soils</li> <li>Can stabilize large blocks of soil</li> <li>Quicker and less expensive than many alternatives</li> <li>Lower environmental impact than many alternate solutions</li> <li>Traditional binders of Portland cement, lime and lime-cement mixtures can be used</li> <li>Industrial byproducts such as flyash and ground granulated blast furnace slag also can be used as part or all of the binder</li></ul><h2>General Description:</h2>SSM uses a wet slurry binder or dry powder binder and an auger to construct a series of laterally overlapping columns, which when completed can form a single treated volume or a project-specific geometry. Typically, the auger for SSM is crane-supported. MS uses an excavator-mounted mixing tool and either a pneumatically-delivered dry binder or a wet slurry binder to create a large stabilized mass. These two mass mixing methods differ from deep mixing by providing more economical soil treatment for depths less than about 40 ft. (12 m), and the design strength of the mixture is usually lower than that for deep mixing. Additionally, mass mixing methods are often installed in block geometries for nearly 100% coverage of the treated soil. Mass mixing methods are different from surface stabilization, in which admixtures are blended with soil and compacted in lifts.<br><h2>Geologic Applicability:</h2><ul> <li>Peat, soft clay, dredged soil, sludges, contaminated soils, soft silt.</li> <li>SSM and MS processes can be used below the groundwater table.</li></ul><h2>Construction Methods:</h2>Shallow soil mixing uses mixing tools to mix either water-binder slurry or dry powder binder with native soil to create a column of stabilized soil in situ. This<br>process can be repeated with overlapping columns to achieve adequate coverage and to create a stabilized soil mass up to 40 ft. (12 m) below the surface. Mass stabilization uses an excavator-mounted mixing tool, which can be maneuvered laterally and vertically to mix a wet or dry binder into the soil to depths up to 23 ft. (7 m); the binder is delivered through the mixing tool. The area to be treated is often divided into blocks and treated a block at a time. In both the SSM and MS methods, the stabilized soil is often topped with a preload embankment, placed immediately after mixing, to induce consolidation of the treated soil<br>while curing.<br><h2>Additional Information:</h2>QC/QA methods evaluate strength, homogeneity, and compressibility characteristics. Cone penetration tests (CPT), column penetration tests, and<br>field shear vane tests are used to evaluate strength and homogeneity; if necessary, samples are collected for laboratory testing. Settlement and lateral movement are monitored using settlement plates, settlement hoses, and inclinometers. Settlement is most rapid during the preload period immediately following stabilization as the air mixed into the soil is pushed out and excess pore pressures dissipate. In environmental applications, permeability of the stabilized mass and fixation of any contaminants are also of interest. SSM or MS of organic soils may require particular attention to soil-binder interaction.<br><h2>SHRP2 Applications:</h2><ul> <li>New Embankment over Unstable Soils</li> <li>Embankment Widening</li></ul><h2>Example Successful Applications:</h2><ul> <li>Stabilization to support US 1 expansion– Florida</li> <li>Peat stabilization for industrial complex –Helsinki</li> <li>Shallow mixing to support spill tanks –Vancouver Island, British Columbia</li></ul><h2>Complementary Technologies:</h2><ul> <li>Deep mixing methods or other column technologies</li> <li>Geosynthetic reinforcement</li></ul><h2>Alternate Technologies:</h2><ul> <li>Excavate and replace</li> <li>Preloading and PVDs</li> <li>Column-supported embankment</li> <li>Deep mixing methods</li></ul><h2>Potential Disadvantages:</h2><ul> <li>Limited treatment depth</li> <li>Organic soils may require higher binder contents and specific binder types</li> <li>Cost-effectiveness depends on accurate measurement of binder quantity</li> <li>Subsurface obstructions such as boulders or logs can disrupt construction</li></ul><h2>Key References for this technology:</h2>ALLU. (2007). Mass Stabilisation Manual, ALLU Finland Oy, Orimatilla. 57p. http://www.allu.net/products/stabilisationsystem (June 24, 2014).</p><p>Broomhead, D., and Jasperse, B.H. (1992). “Shallow Soil Mixing – A Case History.” ASCE Geotechnical Division Specialty Conference Grouting, Ground Improvement and Geosynthetics, ASCE, New Orleans. 12p.</p><p>Garbin, E., Mann, J.A., McIntosh, K.A., Dasai, K.R. (2011). “Mass Stabilization for Settlement Control of Shallow Foundations on Soft Organic Clayey Soils.” Geotechnical Special Publication 211, ASCE, pp. 758 – 767.</p><p>Jelisic, N. and Leppanen, M. (2003). “Mass Stabilization of Organic Soils and Soft Clays.” Grouting and Ground Treatment, Geotechnical Special Publication<br>120, ASCE, pp. 553-561.</p></p>