Dynamic behaviors of MICP-treated calcareous sand in cyclic tests

The calcareous sands from an island of the South China Sea are cemented by the microbially induced calcite precipitation (MICP) method. A series of cyclic tests and SEM tests are carried out to investigate the evolutions of the dynamic strength, dynamic deformation, dynamic pore pressure and effective stress path under different degrees of bio-cement as well as the micromechanism of the MICP-treated calcareous sands. The results show that the cyclic stress ratio and resistance to deformation of the calcareous sands are obviously improved due to the MICP method, implying that the MICP method can significantly improve the dynamic properties of calcareous sands. The evolution of the dynamic pore pressure can be divided into four stages: initial phase, stable development phase, rapid development phase and complete liquid phase. The sample begins to collapse when the pore pressure is developed at the later period of the rapid development phase, and the groove appears in the pore pressure curve. In the whole phase, the soil deformation and the change in soil strength are closely related to the development trend of the effective stress path and dynamic pore pressure, and then, the effective stress path exhibits cyclic mobility. The particles of the MICP-improved calcareous sands are wrapped or filled by the calcite precipitation, leading to the changed properties of calcareous sands, which increases the cohesion and internal friction angle of soils.