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<br /> <br /> <br /> <br />4 <br />overburden and riprap. The gradation specifics depend <br />on the character of the surrounding soils. Proper <br />compaction is required for all layers. See Figure 2 for <br />an example reverse filter. <br />Geotextile, Geosynthetic Clay Liner, or Geomembrane <br />- Similar to the clay blanket and reverse filter, <br />engineered liners and fabrics can be used after <br />excavation of the sinkhole. Native material should be <br />placed over the liner or fabric. Liners and fabrics can be <br />used in conjunction with reverse graded filters as <br />another layer of protection. <br />Grouting - Grouting is a repair option especially <br />effective if widespread cracks, voids, and joints are <br />found within the foundation or embankment. Grout is <br />generally applied with low pool and under dry <br />conditions so that the grout can set up. Various mixes <br />are available for grouting and selection of properties is <br />dependent on soil conditions, size of sinkhole, and <br />environmental conditions. Mixtures with fluid-like <br />consistency (low viscosity) take longer to set up but are <br />likely to penetrate more deeply and into smaller voids. <br />Thicker, more viscous mixtures are quicker to set up <br />but may not be as effective at filling the void. A <br />combination of mixes can be used to fill the smaller <br />and deeper areas with fluid grout and then the larger <br />void with more viscous grout. Depending on the size of <br />the sinkhole, soil conditions, and the grout material, <br />the grout can be gravity fed (pipe placed in hole for <br />funneling) or injected under pressure. The hole and <br />pipe are often flushed with water to remove debris <br />and loose material prior to application of grout. When <br />setup is complete, the area should be backfilled with <br />native soil and rocks/riprap placed to protect the grout <br />near the surface. <br />There are two general families of grout: cement grouts <br />and chemical grouts. Each family has primary grout <br />sub-types. Primary types of cement grout include <br />ordinary Portland cement (OPC) and ultrafine cements. <br />Primary types of chemical grouts include silicates <br />(typically sodium silicates), acrylic gels (acrylamide, <br />acrylic, and acrylates), and polyurethane foams <br />(hydrophilic or hydrophobic). Each grout type varies in <br />appropriate application based on their unique <br />characteristics including viscosity, set-up time, <br />expansion, flexibility, strength, life span, and cost. Due <br />to the wide array of grout products available and the <br />complexity of selecting the appropriate grout mix, a <br />qualified grouting engineer or contractor should be <br />engaged to provide site-specific recommendations. <br /> <br />Photo 4: Application of chemical urethane grout (Big Battlement <br />Dam) <br />Below is a list of grout types commonly used in <br />geotechnical void-filling applications: <br />• Acrylamide Grout – Highly impermeable and <br />low viscosity. Changes from liquid to a solid in <br />a controllable set-up time. Acrylamides <br />generally have a long life span (100 years+). [5] <br />• Polyurethane Chemical Resin Grout – <br />Hydrophilic foams react with water to form an <br />expansive flexible foam or non-expansive gel <br />that hardens. It can be used for grouting <br />applications where dry conditions are not <br />possible or too costly. Hydrophobic expansive <br />foams require little water to react and easily <br />withstand wet/dry cycles. Polyurethane foam <br />generally has a life span between 75 and 100 <br />years. [5] <br />• Epoxy Grouts – Suitable for underwater <br />applications <br />• Ultrafine Cementitious Grout – Cement grouts <br />generally cost less than chemical grouts and <br />have higher strength. Cement grouts have <br />higher viscosity and faster set-up times, which <br />can be controlled to a degree with water and <br />additives. Life span is typically 100 years+. [5]