Critical timepoint of cementation transition in MICP treated sand of Soan River, Pakistan

The time-dependent changes in the mechanical properties of poorly graded sandy soil from the banks of the Soan River, Pakistan, treated with microbially induced calcite precipitation (MICP) using indigenous Bacillus species, have been evaluated. MICP treatment has been applied over a period of six weeks. The results reveal that the critical time of two weeks of MICP treatment is needed to induce a dramatic change in the mechanical properties of treated soil. At this point, calcite content exceeds 17% and the cementation transitions from non-effective to effective. The angle of internal friction increases drastically during the first two weeks of treatment while the drained cohesion, undrained shear strength, and unconfined compressive strength (UCS) increase significantly after two weeks’ time. A consistent reduction trend is observed in both void ratio and permeability, indicating improved soil densification and reduced flow paths. The drained and undrained cohesion of the soil increased from 0 to 11.32 and 60 kN/m2, respectively, over a period of six weeks. The drained angle of friction increased from 33° to 36.16° while UCS achieved the final value of 120 kN/m2. The findings provide insights into the critical timing and calcite content required for achieving optimal mechanical performance.