Strength and Stiffness of MICP Treated Sand Subjected to Various Stress Paths

As the global population grows, the demand for more infrastructure increases and the availability of competent soil decreases. Harnessing biological processes to improve soil properties satisfies the societal demand for ground improvement in a natural manner. The improved soil properties are achieved from chemical reactions catalyzed in situ by soil bacteria. Microbial induced calcite precipitation (MICP) increases the strength and stiffness of loose sand deposits, increasing resistance to seismically-induced soil liquefaction. Triaxial tests are used to evaluate the evolution of stiffness and strength in specimens subjected to various stress paths. The cementation process is monitored using non-destructive geophysical measurements (i.e. bender elements). Shear response of the treated and untreated samples are evaluated for drained and undrained triaxial specimens subjected to compression, extension, and constant p loading paths. A marked increase in peak normalized shear strength of up to about 1.5 times that of the untreated samples is observed in moderately cemented samples. Degradation of the cementation as reflected by changes in stiffness is observed using geophysical monitoring. The results are used to plan centrifuge tests that will evaluate the increased resistance to liquefaction triggering from microbial induced calcite precipitation treatment.