Enhancing the mechanical properties of washed recycled sand: Synergistic effects of EICP and geogrid reinforcement

The enzyme-induced carbonate precipitation (EICP) technique and geogrid reinforcement have each proven effective in enhancing the mechanical properties of sandy soils. However, the brittleness of EICP-treated sand and the limited interlocking between geogrids and sand particles limit their engineering applications. This study investigates the feasibility of integrating EICP with geogrid reinforcement to improve the mechanical performance of washed recycled sands. The effects of three critical variables including cementation-enzyme ratio ( X 1 ), median particle size D 50 ( X 2 ), and geogrid placement depth ( X 3 ) on sand treated with both EICP and geogrid (STEG) were evaluated using five performance indicators, i.e. unconfined compressive strength (UCS), calcium carbonate content, wave velocity, hydraulic conductivity, and surface crack pattern. The optimal conditions were further determined using response surface methodology. The results indicate that all three variables significantly influence the strength of the sand columns, with notable interactions among them. The optimal treatment conditions were identified as X 1 = 1:2.01, X 2 = 1.149 mm, and X 3 = 2.817 cm, yielding a maximum UCS of 4.59 MPa. EICP treatment facilitated the precipitation of calcium carbonate crystals, effectively filling soil pores, which enhanced both ultrasonic velocity and strength while reducing permeability. Furthermore, particle image velocimetry (PIV) test results confirmed that geogrid reinforcement improved the stability of the sand column by mitigating crack propagation and lateral deformation. This stabilization mechanism directly contributed to a significant increase in peak strength and toughness compared with the unreinforced sample. These findings provide valuable insights into the synergistic application of EICP and geogrid reinforcement to enhance the mechanical performance of sandy soils.