Unified equivalent intergranular void ratio for biotreated binary soils in characterising liquefaction resistance

Both calcareous silt and calcium carbonate (CaCO₃) precipitation crystals generated by microbially induced calcium carbonate precipitation (MICP) are fine-grained but exhibit distinct properties. The combined effect of these two components on the liquefaction resistance of biotreated binary soils is rarely reported. In this study, systematic undrained cyclic triaxial tests and bender element tests were conducted on reconstituted calcareous sand specimens, varying in two density parameters, four levels of fines content and three biotreatment levels. The results reveal that packing density, fines content and biotreatment levels significantly affect the cyclic behaviour, liquefaction resistance and shear wave velocity of biotreated soils. In addition, low-boundary curves were established to improve the accuracy of liquefaction assessments at sites with high shear wave velocity. Furthermore, the relative contributions of fines and calcium carbonate crystals were incorporated using the concept of the unified equivalent intergranular void ratio (EIVR). The utility of this approach in characterising the liquefaction resistance of biotreated binary soils was validated through the data from both this study and previous research. The new unified EIVR concept can be used to estimate the complex liquefaction resistance of cemented binary soils, which further enhances the theoretical framework for dynamic liquefaction of non-cemented or cemented sandy soils.