<p>Bioslurry is a promise biomineralization technology used in several projects. However, the mechanical behavior of bioslurry-treated soils does not exhibit a consistent trend with calcium carbonate content, in contrast with biogrout-treated soils. This phenomenon arises from calcium carbonate precipitation during bioslurry and biogrout processes exerts a distinct impact on the mechanical response. Several undrained triaxial shear tests were conducted to investigate the impact of calcium carbonate on the mechanical behavior of bioslurry-treated sands, comprising two categories: sand-inactive bioslurry mixtures and sand-active bioslurry mixtures by biotreatment. Two factors—the filling of bioslurry and the cementation by calcium carbonate precipitated during the biogrout process—have been identified as influencing the mechanical behavior of bioslurry-treated soils. The deviatoric stress–axial strain and excess pore water pressure–axial strain relationships are systemically analyzed under varying conditions. Furthermore, we conducted a comprehensive investigation of the normalized maximum excess pore water pressure, the normalized excess pore water pressure at the critical state, the normalized hardening parameter, the resistance to further deformation, and the critical state lines to characterize the mechanical response of bioslurry-treated sands under varying initial mean effective stresses, inactive bioslurry contents, and cementation levels, illustrating the distinct role of calcium carbonate in bioslurry-treated soils.</p>