Research on the Effect of Curing Stresses on the Mechanical Properties of Soil-Cement Mixed Materials-PDF

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This report investigates how overburden stress during curing affects the unconfined compressive strength (UCS) of deep mixing method (DMM) soil-cement materials. The research combines controlled laboratory bench tests, field oedometer tests, validated core data from completed projects, and in-situ measurements of horizontal stress and temperature at two sites.<br /><br />Results show that curing under stress generally increases UCS, meaning standard quality-control samples cured without field stresses may underestimate in-situ strength. Strength gains were greater in fine-grained soils than in granular soils. A low-plasticity silt showed a strong, approximately linear increase in strength with applied stress, while a high-plasticity clay showed no clear trend. The clay’s limited drainage and consolidation, together with difficulties achieving uniform mixing, may explain its inconsistent results.<br /><br />Field oedometer and core data broadly confirmed the laboratory findings. The authors propose empirical relationships and soil-type-specific coefficients for estimating strength at depth from unstressed wet-grab sample results. These coefficients should not be used for overburden stresses above 30 psi, where the relationship has not been verified. Analysis also suggests that strength gains cannot be explained solely by water loss and a reduced water-to-cement ratio; consolidation and changes in particle interactions likely contribute.<br /><br />In-situ measurements indicated that freshly mixed material initially behaves approximately like a fluid, with horizontal stress near hydrostatic levels, followed by changing stresses during curing. Because measurements came from only two sites, these observations are preliminary.<br /><br />The report recommends developing practical guidance for applying the proposed adjustments and conducting further research, particularly on complementary in-situ testing such as cone penetration testing.

Keywords

overburden stress

curing

unconfined compressive strength

deep mixing method

soil-cement

field oedometer

in-situ measurements

soil type

consolidation

cone penetration testing