Engineering Properties and Microscopic Mechanisms of Composite-Cemented Soil as Backfill of Ultra-Deep and Ultra-Narrow Foundation Trenches

The backfilling of lime soil in ultra-deep and ultra-narrow foundation trenches is a difficult construction link, ordinary-cemented has drawbacks, including poor strength, impermeability, frost resistance. To solve these problems, fly ash (FA)–water glass (WG)-composite-cemented developed based on background project. three-factor orthogonal tests are conducted the unconfined compressive strength (UCS) composite-cemented soil, optimal engineering mix proportion proposed for FA-WG-composite-cemented soil. Its UCS compared with that cemented only doped FA or WG (FA- WG-cemented soil). In addition, cyclic wetting–drying tests, freeze–thaw impermeability carried out to study endurance cold regions rich water. hydration products investigated through scanning electron microscopy (SEM) X-ray diffraction (XRD) analysis, curing mechanism discussed from microscopic perspective. research results indicate mixing ratio cement crucial development soil; greatly influences middle late stages; slightly affects strength. cement, FA, 9%:12%:3% Compared oil FA- shows significantly improved load-bearing capacity. permeability coefficient always obviously lower than after any period. Despite mass loss, superior ordinary one overall cycles. Through SEM XRD content found be higher period, hydrates exert stronger cementing action particles contents C-S-H gel Aft crystals apparently larger those Under alkali activation WG, produces free SiO32− AlO2−, which undergo polymerization reaction Ca2+ generate C-A-H gel, further promoting cement.