Abstract:

The microbially induced calcite precipitation (MICP) technique can effectively enhance the mechanical properties of coral sand. To investigate the small-strain dynamic characteristics of MICP-treated coral sand, resonant column tests were conducted on specimens with varying biocementation cycles N_b and effective confining pressures σ₀ and the development laws of dynamic shear modulus G and damping ratio γ were comparatively analyzed. The test results reveal that: at small strains, the dynamic shear modulus G increases significantly with both N_b and σ₀. The maximum dynamic shear modulus G_max exhibits a linear correlation with N_b and a power-law correlation with σ₀. A significant power-law relationship exists between G_max and unconfined compressive strength (q_ucs). As N_b increases, the reference strain γ₀  decreases gradually while the G/G_max-γ_d curves shift downward, indicating enhanced nonlinearity. Both minimum and maximum damping ratios increase, with the γ-γ_d curve moving upward and characterized by greater energy dissipation. In contrast, increasing σ₀ produces opposite trends in both G/G_max-γ_d and γ-γ_d curves, exhibiting reduced nonlinearity and energy dissipation. Empirical relationships are established to quantify the nonlinear dynamic behavior and energy dissipation characteristics of MICP-treated coral sand. Scanning electron microscope (SEM) observations reveal that stiffness improvement primarily results from three mechanisms: contact cementation between sand grains, grain coating by calcite precipitates, and matrix supporting through pore filling.

Key words: coral sand, microbially induced calcite precipitation, resonant column tests, dynamic shear modulus, damping ratio