To address scour hazards surrounding offshore foundations, a new method employing novel alkali-activated cementitious grout (AACG) has been proposed for improvement of seabed soil. Ground granulated blastfurnace slag (GGBFS) was replaced by fly ash (FA), steel slag (SS) or FA + SS to prepare precursors, the replacement amounts were 10 %, 20 %, 30 % and 40 %. Fresh-state and mechanical properties, minerals and microstructures were investigated. A novel scour simulation test device was developed to simulate engineering conditions of scour and remediation. Flow-soil coupled scour resistance tests were conducted, shear tests and SEM measurements of solidified soil were carried out. The results showed that the optimal ratio of GGBFS:FA:SS was 6:2:2 for AACG. The optimized AACG has better fluidity and lower brittleness, and its 28 d unconfined compressive strength (UCS) achieves 13.5 MPa. For AACG solidified soil, the maximum scour depth was reduced by 33.3 % and the maximum sediment transport amount was decreased by 53.2 %, which were compared to those of cement - sodium silicate (C-S) double slurry. Moreover, the increase degrees of internal friction angle, cohesion and critical shear stress were 700 %, 7.9 % and 786 %, respectively. The scour resistance of AACG solidified soil was superior. The inherent relationship between UCS and critical shear stress was discussed. UCS can be used to rapidly assess the scour resistance of consolidated soil. This study introduced an eco-friendly AACG as an innovative stabilizer for soil reinforcement around offshore structural foundations, offering significant application and environmental values for scour control.

Salt-frost heaving of canal foundation saline soils is the primary cause of damage to the lining structures of water conveyance channels in the Hetao Irrigation District, China. Chemical solidification of saline soils can mitigate frost heave; however, application studies exploring the salt-frost heave resistance of saline soils solidified through the synergistic use of multiple industrial solid wastes in the Hetao remain limited. This study employs a sustainable solidifying material composed of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate activator. The optimal mix ratio was determined using Response Surface Methodology (RSM). Unidirectional freezing tests evaluated the effects of solidification material content, curing period, and salt content on salt-frost heave development. Unconfined compressive strength tests assessed salt-frost heave durability of high-salinity solidified saline soils. Microstructural characteristics were analyzed using Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TG) to investigate resistance mechanisms. Results indicated that the industrial waste materials exhibited synergistic effects in an alkaline environment, with the optimal mix ratio of slag, fly ash, coal gangue, coal-based metakaolin, carbide slag, and potassium silicate at 21:25:33:8:7:6. Increasing solidified material content and curing time significantly enhanced salt-frost heave resistance, as evidenced by improved freezing temperature stability, deeper freezing front migration, and reduced salt-frost heave rate. The optimal group (35 % solidifier, 7 days curing) showed a 5.53 degrees C increase in stable freezing temperature, a 3.78 cm upward migration of the freezing front, and a 3.94 % reduction in salt-frost heave rate. Salt-frost heave durability of highsalinity soils improved post-solidification, with a gradual decrease in the degradation of unconfined compressive strength, achieving a minimum weakening of 21.13 %. Hydration products C-S-H, C-A-H, and AFt filled voids between soil particles, restricting water and salt migration. Hydration of industrial wastes reduced free water and SO24 content, decreasing water-salt crystallization and mitigating salt-frost heave. The findings provide an engineering reference for in-situ treatment of salt-frost heaving in saline soils of water conveyance channels in the Hetao Irrigation District.

Endophytic Fusarium oxysporum strain V5w2 has been suggested to offer the ecosystem service of suppressing Cosmopolites sordidus and other pests that attack tissue culture banana plants in agroecosystems. The effects of endophytic F. oxysporum V5w2 and nutrient supply on C. sordidus in potted tissue culture banana plants were investigated. In the screenhouse, rhizome damage by C. sordidus larvae was lower in F. oxysporum V5w2-inoculated plants than in non-inoculated ones. Banana plants inoculated with F. oxysporum V5w2 were larger and suffered less rhizome damage but with low chlorophyll content. Weights of C. sordidus larvae were not different between those reared on F. oxysporum V5w2-inoculated banana plants and the non-inoculated ones. Larval C. sordidus from nutrient-treated plants had lower weight than those that fed on plants that did not receive nutrients. In the field, fewer adult C. sordidus were found on F. oxysporum V5w2inoculated banana plants than on non-inoculated plants 12 h after insect release. The number of adult C. sordidus and their eggs did not vary between F. oxysporum V5w2-inoculated banana plants and controls at the end of the experiment. Adult C. sordidus did not discriminate between nutrient-treated banana plants and those without nutrient treatment. However, non-beneficial interactions between F. oxysporum V5w2 and plant-parasitic nematodes negate the chances of its application as an endophytic biological control agent. In conclusion, while F. oxysporum V5w2 is not quite viable for application as an endophytic biological control agent for C. sordidus and other banana pests, this fungus may still have some potential to offer alternative ecosystem services through the provisioning of pest-inhibitive organic compounds.