Strength and durability of biocemented sands: Wetting-drying cycles, ageing effects, and liquefaction resistance

Abstract

Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentially sound technique for biocementation of granular soils. The method is based on the metabolic activity of urease-producing microbes. Bioaugmentation through individual microorganisms has been investigated till now, and synergistic effect of bacteria mixtures (hybrids) for bioaugmentation is under-explored yet. Durability aspect of biocemented soils in terms of wetting–drying resistance and ageing also requires special attention and thorough investigation before adopting in field application. Thus, considering these limitations of MICP, present study has been carried out to aim multiple objectives, including optimization of cementation solution injection strategy. Poorly graded liquefiable sand was treated in polyvinyl chloride (PVC) tubes by augmenting it with Sporosarcina pasteurii, Bacillus sphaericus, and their mixed culture for hybridized activity. The biotreatment was continued by using 0.50 M cementation solution using injection frequency 12 and 24 h, and injection pore volumes (PV) 1, 0.75, and 0.5 up to 18 days. Permeability and calcite content of biocemented specimens were determined after treatment. For durability analysis, biocemented specimens were subjected to 0, 5, 10, 15, and 20 wetting–drying (W-D) cycles and kept in an uncontrolled temperature environment for 0, 1.5, 3, 4.5, and 6 months to investigate ageing effects. After W-D cycles and ageing time, samples were tested for ultrasonic pulse velocity (UPV), shear modulus, unconfined compressive strength (UCS), and split tensile strength (STS). The mass-loss rate of biocemented specimens was also determined after cyclic W-D actions. The liquefaction resistance of biotreated sand was compared with untreated dense sand specimen using dynamic cyclic simple shear (DCSS) tests. The results showed W-D resistance of biocemented sand even after 20 W-D cycles, and ageing effects showed more than two times increase in mechanical properties. The DCSS test results showed that excess pore pressure ratio was not reached to 1 in biocemented sands up to 100 cycles.