<p><p><figure id='attachment_856' style='max-width:816px' class='caption aligncenter'><img class="wp-image-856 " style="border: 2px solid #696969;" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Diagram showing a tunnel protection scheme using injected grout under the tunnel to improve the soils underlying the tunnel." width="816" height="816" /><figcaption class='caption-text'> Tunnel Protection Scheme (Illustration courtesy of Munfakh, G.A., 1991. Deep Chemical Injection for Protection of an Old Tunnel, Deep Foundation Improvements: Design, Construction, and Testing, ASTM STP 1089, ASTM International, West Conshohocken, PA)</figcaption></figure><h2>Basic Function</h2>Chemical grouting is used to seal off water intrusion into tunnels or deep excavations or to pretreat relatively coarse soils when tunneling.<br><h2>Advantages:</h2><ul> <li>Chemical grouts can be used in soils with low permeability</li> <li>Computer monitoring of grouting shows real-time analysis of construction process</li></ul><h2>General Description:</h2>Chemical grouts are a mixture of materials where all the elements of the grout are a pure solution with no suspended particles. The grouts are used in highly specialized applications including sealing water intrusions into tunnels, deep excavations, or through abutments. Sodium silicate based grouts can be used to pretreat coarse soils in advance of tunneling.<br><h2>Geologic Applicability:</h2><ul> <li>Loose liquefiable sands.</li> <li>Sand and gravel underlain by sedimentary bedrock.</li> <li>Highly variable, weakly cemented rock-fill materials.</li> <li>Soils with permeability as low as 10-4 cm/s and fines contents less than about 20%.</li> <li>Practical maximum depth of significant improvement is about 100 feet (30.5 meters).</li></ul><h2>Construction Methods:</h2>Chemical grouts used in injection systems range from sodium silicate (colloidal), to true solution grouts such as polyurethanes, resins, acrylates, and lignins, to exotic materials such as precipitation grouts. These grouts are used in specialized applications such as sealing off water intrusions into tunnels, deep excavations, or through abutments. Sodium silicate grouts are used to permeate sands and increasing strength and reducing permeability. The grout is often injected through a tube à manchette or packer system. Grouting has a maximum depth of 100 feet (30 meters). Discrete flow paths with an expansive and/or flexible material are filled using simple drill and inject principles.<br><h2>Additional Information:</h2>Chemical grouting takes significant of time to let the grout set but this also gives more time for the grout to permeate into the soil. The chemical grout method can be more expensive than other grouts. Chemical grouting has minimal application to SHRP 2 projects, as it is limited by the nature of the virgin soil and the cost and time for completion.<br><h2>SHRP2 Applications:</h2><ul> <li>Embankment and roadway construction over unstable soils</li> <li>Stabilization of pavement working platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Lexington Market Section MD Metro – Baltimore, MD</li> <li>Grouting of Backfill Kidd Creek Mines – Timmins, Ontario</li> <li>Outwash Sands Light Rail Transit Tunnel – Edmonton</li></ul><h2>Complementary Technologies:</h2>Chemical grouting is usually used independently<br><h2>Alternate Technologies:</h2>Jet grouting<br><h2>Potential Disadvantages:</h2><ul> <li>Experienced contractors are needed.</li> <li>Projects need many weeks to set up and complete.</li> <li>Some chemical grouts are found to break down over time and may reduce capacity to improve the soil and release toxic materials into the soil.</li> <li>The location of the grout in the soil is often difficult to determine without extensive investigation.</li></ul><h2>Key References for this Fact Sheet:</h2>Waller, M. J., Hue, P. J., and Baker, W. H. (1983). “Design and Control of Chemical Grouting. Vol. 1 - Construction Control,” Federal Highway Administration Report FHWA/ RD-82/036, FHWA, Washington, DC.</p><p>Krizek, R. J. and Baker, W. H. (1983). “Design and Control of Chemical Grouting. Vol. 2 – Materials Description Concepts,” Federal Highway Administration Report FHWA/ RD-82/037, FHWA, Washington, DC.</p><p>Baker, W. H. (1983). “Design and Control of Chemical Grouting. Vol. 3 – Engineering Practice,” Federal Highway Administration Report FHWA/RD-82/038, FHWA, Washington, DC.</p><p>Karol, R. H. (2003). Chemical Grouting and Soil Stabilization. Marcel Dekker, New York, NY.</p></p>