DFI Technical Committee Project on the Effect of Overburden Stresses (During Curing) on the Mechanical Properties of Soil-Cement Mixed Materials-Paper

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The study examines how overburden pressure during curing affects the strength of deep-mixed soil-cement materials, and why standard quality-control tests may underestimate their in-situ properties. Researchers combined laboratory bench tests, modified field-oedometer tests from seven sites, early-age in-situ stress measurements at two sites, and validated core-strength data.<br /><br />Results show a generally linear relationship between curing stress and unconfined compressive strength (UCS), with the size of the strength gain depending on soil type. Low-plasticity fine-grained soils, especially silts, gained substantially more strength under stress than granular soils. High-plasticity clays showed weaker gains, likely because slow drainage limits consolidation and particle contact. Core data broadly supported the strength-gain estimates developed from laboratory and oedometer tests.<br /><br />The authors propose empirical methods for estimating in-situ UCS from the uncured-stress UCS, overburden pressure, and a coefficient selected by soil classification. Measurements also showed that freshly mixed columns initially behave hydrostatically; as curing proceeds, drainage, consolidation, and chemical hardening alter internal stresses.<br /><br />Strength gains in fine-grained soils exceeded those attributable to changes in water-to-cement ratio alone, suggesting that particle rearrangement and interparticle interactions also contribute. Overall, the findings indicate that testing specimens cured at ambient pressure can undervalue field strength. The proposed coefficients and methods may improve practical strength estimates, although further research is needed to clarify stress evolution during curing.

Keywords

deep-mixed soil-cement

overburden pressure

curing stress

unconfined compressive strength

in-situ strength

field-oedometer tests

soil classification

low-plasticity silt

consolidation

core-strength data