Degradation of EICP and Biopolymer Treated Calcareous Silt Under Dry-wet Cycles

Biopolymer (BP) is an emerging environment-friendly biomaterial for soil reinforcement in recent years. However, due to its water solubility, the strength of BP-stabilized soil gradually deteriorates under cyclic dry-wet conditions. Therefore, it is very important to improve the water resistance of BP-strengthened soil. In this paper, the calcareous silt in the South China Sea was reinforced by plant urease-induced calcium carbonate precipitation (EICP) combined with xanthan gum (XG). The unconfined compression test and shear wave velocity test were carried out on the solidified silt under different drying and wetting cycles. EICP and XG-EICP solution precipitation tests were carried out as well, and the microscopic pore structure of the combined solidified soil and pure precipitate without soils were analyzed by scanning electron microscopy (SEM) and X-ray energy spectrum analysis (EDS). The test results show that: with the increase of xanthan gum content and plant urease concentration, the unconfined compressive strength of xanthan gum (XG) stabilized soil and joint (XG-EICP) stabilized soil increased significantly; With the increase of dry-wet cycles, the strength decrease of xanthan gum-stabilized soil is greater than that of joint-stabilized soil, and joint-stabilized soil has better resistance to dry-wet cycles. Xanthan gum exists in a fibrous network structure in the pores of silt particles, and the EICP solution provides sufficient Ca2+ for the cross-linking modification of xanthan gum, and the mineralized crystallization of EICP also provides more connection sites for xanthan gum, making the mechanical properties of the combined solidified soil more stable. The test results of EICP and XG-EICP solutions show that: XG can form a water-insoluble gel-like precipitate in EICP solution, and the calcium carbonate particles attached to the XG-EICP precipitate are larger than those produced by pure EICP. This experiment verified the feasibility of EICP to improve the erosion resistance of biopolymer-solidified soils against dry-wet cycles, and is expected to provide new ideas and methods for marine soil reinforcement.