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Geometry assessment and strength/stiffness monitoring of lime and cement modified soils via characterization of curing-induced property changes estimated from seismic wave propagation techniques and electrical resistivity
Bearce, Richard G.
Bearce, Richard G.
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2015
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2016-03-24
Abstract
Soil modification via binding additives such as lime and cement grout is a commonly used practice for improving the engineering properties of soil in civil and underground construction applications. Such additives change the properties of the soil by forming cementing agents that bond soil grains together. This cementing process increases the strength/stiffness and reduces the hydraulic conductivity of the modified soil. To ensure adequate performance of chemically modified soil, assessment of both engineering properties and the spatial extent of modification is vitally important. A variety of performance verification techniques are used to assess engineering properties and geometry by industry, but these techniques have inherent limitations. For roadway subgrade soil stabilized with lime and/or cement, an improved performance verification approach would utilize non-destructive monitoring of strength/stiffness growth of subgrade soils cured under field temperature conditions. This research employs wave propagation techniques to monitor the strength/stiffness growth of lime/cement stabilized subgrade and formulates a maturity function to predict modulus growth as a simultaneous function of both time and temperature. The maturity function is able to capture experimentally observed modulus growth from specimens cured at both constant (laboratory) and variable (field) temperature environments. A time/temperature dependent maturity function for lime/cement stabilized subgrade soils advances the current state of understanding and practice. For soils modified with cement grout via in-situ applications such as jet grouting, an improved performance verification test would allow for immediate non-destructive assessment of production column geometry. DC resistivity testing is used to estimate soilcrete column diameter in a laboratory-scale study and validated via computational modeling. The computational modeling approach is extended to field geometries and a DC electrical resistivity push probe is developed. The push probe is tested on several deep soil mixed and jet grout columns on active construction sites. Computational modeling is used to interpret the experimental results and develop a procedure for estimating column geometry. The probe is able to estimate column geometry with an accuracy of ±5% of the as-constructed column diameter. Furthermore, the probe is a reusable/recoverable device that non-destructively evaluates fresh soilcrete column diameter within 1 hour of construction. This diameter verification approach is an improvement over any technique currently available.
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