Effect of freeze–thaw cycling on mechanical properties of Na-montmorillonite modified EICP-treated silty sand

Enzyme induced carbonate precipitation (EICP) has been developed as a new soil improvement technology. In this study, Na-montmorillonite (Na-Mt) was introduced into traditional EICP to improve the curing efficiency. In order to examine the applicability of the proposed method in seasonal frozen soil area, the mechanical properties of Na-Mt modified EICP treated soil subjected to freeze-thaw (FT) cycling were analyzed. The effects of different number and temperature ranges of FT cycles on the stress-strain curve, unconfined compressive strength (UCS), secant modulus, and strain corresponding to peak stress of silty sand were studied by UCS test. Then, the porosity and microstructure of silty sand under different FT cycling numbers and FT temperature ranges was measured by scanning electron microscope. When not subjected to FT cycling, Na-Mt modified EICP can reduce the apparent porosity of silty sand, and increase UCS and secant modulus by 4.9 and 3.1 times respectively compared with untreated soil; the increase in FT cycling numbers and FT temperature ranges generally reduces the soil particle size, increases the porosity and decreases the UCS; the silty sand solidified by Na-Mt modified EICP still has the most compact structure, the smallest porosity, the highest strength and the best toughness and stiffness compared with other methods even after FT cycling in extreme environment. Na-Mt can effectively fill the newly formed pores in EICP treated soil during FT cycling, thereby offsetting part of the pore changes. Na-Mt modified EICP is suitable for soil reinforcement in seasonal frozen soil area