United States Department of Transportation
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Alternative Title:Evaluation of a Lime-Fly Ash Cement Slurry Pressure Injection of a Roadway Embankment
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Edition:Initial Report
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Abstract:The use of lime and lime-fly ash mixtures to increase the shear strength and to decrease the plasticity of clay soils is widely accepted. However, the difficulties involved with treating large quantities of in-situ soils or embankment soils in the traditional manner are also recognized. A relatively new technique for treating troublesome clays in place is through the pressure-injection of a lime-fly ash slurry into the ground. A slurry of lime, fly-ash, cement and water was pressure injected into an interstate embankment that was experiencing stability problems. The Woodbine Corporation of Fort Worth, Texas was contracted to perform the slurry injection. Hollow steel probes were pushed into the ground by mechanical equipment to a depth of about 10 feet. The slurry was pumped into the ground at intervals of 12 to 18 inches. This process was carried out on a grid wi.th five foot spacings. Then the entire operation was repeated on a similar grid offset halfway between the holes of the first injection. Since in classical soil mechanics theory it is believed that the shear strength of an unstable soil mass must be increased (or driving forces reduced) to increase the mass's stability, relatively undisturbed samples were removed from the embankment to determine the soil's shear strength before and after treatment of the embankment. The "after" samples were removed following an approximate 30 day in-situ curing period. Laboratory strength tests indicate that the shear strength of the embankment decreased rather than increased. In fact, additional movement of the embankment was initiated during the treatment or injection phase of the project. However, laboratory tests performed prior to treatment indicated that the soils were, by definition, lime-reactive (qu>50psi) with the addition of 6% lime. Additional tests indicated that the addition of 1½% lime (the maximum amount that can be injected with the system) did not increase the unconfined compressive strength of laboratory specimen, but did alter the Atterberg limits of the soil. It is hypothesized that subsurface curing at a somewhat suppressed temperature (65°F) for 30 days is not sufficient to allow the necessary pozzolanic compounds to form. It is recommended that future research be instituted that would allow longer term (perhaps several years) monitoring of strength gains due to this potentially slow curing process.
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