Small-Strain Behaviour of Artificially Cemented Sand in Deep Mixing Application-Paper

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This study examines the small-strain stiffness and decementation of lightly cemented sand relevant to deep soil mixing (DSM). The researchers assessed whether low-calcium fly ash (FA), activated with sodium silicate, could provide a lower-carbon alternative to Portland cement, and how soil density and curing stress affect performance.<br /><br />Uniform quartz sand was mixed with binders and tested in an oedometer under at-rest lateral-pressure conditions. Bender elements measured shear-wave velocity as an indicator of stiffness, while volume change indicated collapse and loss of cementation. Specimens were prepared in loose and dense states and cured under different confining pressures. Separate unconfined-compression tests examined FA and activator contents and moisture conditions.<br /><br />Higher FA content generally increased compressive strength; strength also depended strongly on moisture and activator dosage. In the oedometer tests, cementation initially increased stiffness, but loose FA-stabilized sand could soften abruptly and collapse as loading exceeded its yield stress. Greater curing pressure delayed this softening. Dense specimens were stiffer and showed less visible collapse, although unloading results suggested some cementation loss. Portland-cement-treated sand did not decement under the same loading range as the lightly FA-stabilized sand.<br /><br />The findings show that binder type and amount, initial density, and stress history all influence cemented-sand behaviour. High shear-wave velocity alone does not guarantee a strong deposit: lightly cemented soil may fail progressively and brittly. Optimized alkali-activated FA could offer a practical alternative binder for DSM, but its design requires accounting for potential stiffness degradation and collapse.

Keywords

small-strain stiffness

decementation

lightly cemented sand

deep soil mixing

low-calcium fly ash

sodium silicate

shear-wave velocity

oedometer testing

soil density

alkali-activated binder