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Quantifying the effects of curing stresses and soil type on the in-situ compressive strength of cement-treated soils via deep mixing method
Onorato, George A.
Onorato, George A.
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2023
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Abstract
The Deep Mixing Method (DMM) is an ever-growing ground improvement technique used worldwide to improve in-situ soils using cementitious binders and/or other types of admixtures to either increase the strength and/or decrease the permeability of soils for various types of civil and/or environmental engineering applications. The process involves using specialized high torques drilling equipment with specially design augers or cutters that allow for the injection of flowable grout (suspension) through the auger or cutter to liquify the soil in-situ while blending in the cementitious suspension. When the suspension and soil mixture solidify, the designed engineering material properties are achieved. This study investigates the curing conditions in which in-situ materials are exposed to and how these conditions influence the strength of the deep mixed materials. The findings of this study reveal that the curing conditions for in-situ materials, particularly the applied stresses and temperatures, differ significantly from the conditions under which typical quality control specimens are cured. Consequently, these conditions can lead to a significant underestimation of the strength of the in-situ materials if curing conditions are not considered.
This study incorporates field and laboratory data collected from various studies that directly or indirectly studied the influences of curing stresses on deep mixed material’s mechanical properties. The data compiled for this investigation included strength and temperature data derived from specially designed laboratory bench test studies, field conducted modified oedometer tests, in-situ instrumentation tests from deep mixed columns, and a review of independent coring data results from datasets collected from deep mixed project across north America. Upon reviewing these collective studies, it becomes evident that there exists a correlation between curing stress and unconfined compressive strength (UCS). The observed rate of strength gains follows a linear pattern and is influenced by the type of soil being treated. Notably, fine-grain soils exhibit a higher rate of strength gain when subjected to in-situ curing stress (with depth) in comparison to granular soils. Additionally, this study puts forth several hypothesized physio-chemical mechanisms that could potentially explain the varying strength gains observed based the influence of the treated soil’s particle size.
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