<p><p><h2>Preferred QC/QA Procedures</h2>There is no FHWA published guidance on QC/QA procedures for mass mixing methods of shallow soil mixing (SSM) and mass stabilization (MS). However, detailed QC/QA procedures for deep soil mixing are presented in the FHWA Deep Soil Mixing Design Manual (Bruce et al., 2013). Several QC/QA methods have been employed on SSM and MS projects to verify material properties and monitor construction processes. These methods include construction monitoring, penetration resistance tests, sampling, and laboratory tests. A combination of these methods is recommended for use in a QC/QA program.</p><p>There are three primary goals of the QC/QA program:<br><ul> <li>ensure mixing processes conform to specifications</li> <li>verify improvement in shear strength and/or settlement characteristics of the stabilized soil</li> <li>verify that mixing achieved adequate homogeneity of the stabilized volume</li></ul>Quality Control (QC) and Quality Assurance (QA) are terms applied to the procedures, measurements, and observations used to ensure that construction satisfies the requirements in the project plans and specifications. Herein, Quality Control refers to procedures, measurements, and observations used by the contractor to control the construction quality such that all applicable requirements are satisfied. Quality Assurance refers to measurements and observations by the owner or the owner's engineer to provide assurance to the owner that the facility has been constructed in accordance with the plans and specifications.</p><p>Quality Control and Quality Assurance are related and may impact each other. These definitions for Quality Control and Quality Assurance are used within. Note that not all literature adheres to these conventions, and sometimes the terms are used interchangeably. Sometimes the term Quality Assurance is used to refer to both contractor and owner methods and procedures. The following procedure summaries use the conventions of the source literature, sometimes referring to QC/QA measures collectively as quality control, etc. Commentary provided by the SHRP 2 R02 documents use QC and QA in accordance with the convention noted above. Quality control and quality assurance procedures include construction monitoring and both in situ and laboratory testing methods. Common in situ quality assurance methods include cone penetration tests (CPT), column penetration tests (KPS), and field vane shear tests for strength and homogeneity. Settlement plates and settlement hoses to monitor settlement are also used. Shear strength, stiffness, and permeability can be evaluated in the laboratory using samples taken from the stabilized soil volume. Although it is not commonly used on mass mixing projects, a brief discussion of x-ray fluorescence is provided. X-ray fluorescence can be applied before, during, and after mixing to monitor the binder content and homogeneity of the soil mix. Table 1 shows the components of QC/QA monitoring programs for SSM and MS. The entries in the table are a list of typical items, not a list of all methods that could be used for QC/QA. Some QC procedures and measurement items may also serve as QA procedures and measurement items.<br><h3>Table 1. Typical components of QC/QA monitoring programs.</h3><table class='tablepress' id='tablepress-2008'><thead><th><center>Topics </th><th>#colspan#</th><th>#colspan#</th><th><center>Items</th></thead><tbody><tr><td ><center>Existing
QC/QA
Procedures &
Measurement
Items</td><td rowspan=2 ><center>Q
C</td><td ><center>Material
Related
</td><td >• Binder quality
• Water quality (for slurried binder)
</td></tr><tr><td ><center>QC</td><td ><center>Process
Control
</td><td >•Binder dosage
•Binder mix proportions
•Mixing time
•Mixing tool configuration
•Rotation/penetration rate
•Number of passes
•Stabilization/mixing pattern
•Mixing depth
•Column spacing
•Block size/layout</td></tr><tr><td ><center>QA</td><td rowspan=2 ><center>Q
A</td><td ><center>Material
Related</td><td >• CPT resistance for strength
• Sampling for strength tests
• KPS resistance
• Binder content
</td></tr><tr><td ><center>QA</td><td ><center>Process
Control</td><td >• CPT resistance for homogeneity
• Sampling for homogeneity
</td></tr><tr><td rowspan=2 ><center>Performance
Criteria
</td><td ><center>Material
Parameters
</td><td >#colspan#</td><td >•Unconfined compressive strength
•Compressibility
•Density
•Permeability
•Homogeneity</td></tr><tr><td ><center>System
Behavior</td><td >#colspan#</td><td >•Settlement
•Lateral displacement
•Piezometric levels, flow rates to wells</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2>SSM and MS are employed to improve the strength and settlement characteristics of soft soils within 40 ft. (12 m) of the ground surface. Though MS typically has been used to depths of about 13 ft. (4 m), depths up to 23 ft. (7 m) have been reported. SSM has been applied to greater depths, depending on the depth of soft soils to be treated. Achieving the desired improvements requires that a sufficient quantity of the correct binder be mixed thoroughly and uniformly throughout the stabilized soil volume. Quality control of materials and processes during mixing are employed by the contractor to achieve these requirements.</p><p>The most important quality control methods for shallow soil mixing and mass stabilization are the control of the binder delivery rate, mixing energy, and the mixing geometry. The success of the project is dependent on the mixing practices employed during stabilization. Design binder quality and dosage, determined in the laboratory and often adjusted in field mixing tests, should be carefully controlled to achieve the specified results. The adequacy of mixing, and therefore the homogeneity of the stabilized volume, will be evaluated through quality assurance activities. Penetration tests, sampling, and laboratory tests verify that the design properties were achieved uniformly over the stabilized volume.</p><p>Construction observations, daily logs, and record keeping are essential QC/QA activities for all technologies. These activities help to ensure and/or verify that:<br><ul> <li>Good construction practices and the project specifications are followed.</li> <li>Problems can be anticipated before they occur, in some cases.</li> <li>Problems that do arise are caught early, and their cause can oftentimes be identified.</li> <li>All parties are in good communication.</li> <li>The project stays on schedule.</li></ul>Additional technology-specific details for construction observations, daily logs, and record keeping QC/QA activities are provided in the Individual QC/QA Methods section below. The Quality Control/Quality Assurance document for Deep Mixing Methods (within GeoTechTools) provides additional information on QC/QA that may also be applicable to mass mixing methods. Summaries of individual QC/QA methods are presented on the following pages.</p></p>
<p><p><h2>References</h2>Aldridge, C.W. and Naguib, A. (1992). “In situ mixing of dry and slurried reagents in soil and sludge using shallow soil mixing.” 85th Annual Meeting & Exhibition, Air and Waste Management Association, Kansas City. 14p.</p><p>ALLU. (2007). Mass Stabilisation Manual, ALLU Finland Oy, Orimatilla. 57p. <a href="http://www.allu.net/products/stabilisation-system">http://www.allu.net/…; (June 24, 2014).</p><p>ASTM D2166 - 13 “Standard Test Method for Unconfined Compressive Strength of Cohesive Soil,” ASTM International, West Conshohocken, PA, 2013. 7p.</p><p>ASTM D2573 - 08 “Standard Test Method for Field Vane Shear Test in Cohesive Soil,” ASTM International, West Conshohocken, PA, 2008. 8p.</p><p>ASTM D5084 - 10 “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter,” ASTM International, West Conshohocken, PA, 2010. 24p.</p><p>ASTM D5778 - 12 “Standard Test Method for Electronic Friction Cone and Piezocone Penetration Testing of Soils,” ASTM International, West Conshohocken, PA, 2012. 20p.</p><p>ASTM D6067 - 10 “Standard Practice for Using the Electronic Piezocone Penetrometer Tests for Environmental Site Characterization,” ASTM International, West Conshohocken, PA, 2010. 11p.</p><p>Axelsson, M. and S. E. Rehnman. (1999). “Field Methods for Quality Control at the Dry Jet Mixing Method.” Proc. International Conference on Dry Mix Methods for Deep Soil Stabilization, Stockholm.</p><p>Bredenberg, H., Holm, G., and Broms, B.B. (1999). Dry Mix Methods for Deep Soil Stabilization, Balkema, Rotterdam. 370p.</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>Bruce, M.E.C., Berg, R.R., Collin, J.G., Filz, G.M., Terashi, M. and Yang, D.S. (2013). Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support, FHWA-HRT-13-046, U.S. DOT, Federal Highway Administration, Washington, D.C., 244p.</p><p>Burke, G.K., Sehn, A.L., Hussin, J.D., Hull, V.E., and Mann, J.A., (2007). “Dry Soil Mixing at Jewfish Creek.” Proceedings, GeoDenver 2007, ASCE GSP 172 Soil Improvement, Denver, Colorado, February 18-21. 11p.</p><p>Dunnicliff, J. (1998). Geotechnical Instrumentation Reference Manual, FHWA-HI-98-034, Federal Highway Administration, Washington, D.C., 238p.</p><p>Forsman, J., Maijala, A., and Järvinen, K. (2008). “Case stories, harbours - mass stabilisation of contaminated dredging mud in Sörnäinen, Helsinki.” Proc., International mass stabilisation conference. Lahti, Finland.</p><p>Garbin, E. and Mann, J.A. (2010). “Mass Stabilization for Environmentally Sensitive Projects in Florida.” Transportation Research Record: Journal of the Transportation Research Board, No. 2201, Transportation Research Board of the National Academies, Washington D.C., 2010, pp. 62–69.</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>Havukainen, J., Piispanen, A., and Leppänen, M. (2011). Stabilisation of tributyltin-sediment in a harbour in Helsinki.” Ground Improvement, 164(3), pp. 139-150.</p><p>Hayward Baker Inc. (2009). “Dry Soil Mixing.” Publication U14, Hayward Baker.</p><p>Holm, G, Ruin, M, and Hakansson, S. (1999). “Column Penetration Tests and Extraction of Lime/Cement Columns.” Dry Mix Methods for Deep Stabilization, Proc. International Conference on Dry Mix Methods for Deep Soil Stabilization, Stockholm.</p><p>Jelisic, N. and Leppanen, M. (1999). “Mass stabilization of peat in roadway and railway construction.” Proc., International conference on dry mix methods for deep soil stabilization, Stockholm, pp. 59-64.</p><p>Jelisic, N. and Leppanen, M. (2003). “Mass Stabilization of Organic Soils and Soft Clays.” Grouting and Ground Treatment, Geotechnical Special Publication 120, ASCE, pp. 553-561.</p></p>