Although the root can enhance the soil's strength, vegetation cover landslide still occurs frequently under the rainfall. To elucidate the mechanism underlying the degradation of the shear strength of root-soil composites under the influence of moisture, we investigated trees from hilly slopes in southeastern China. The tensile mechanical properties of roots were tested under varying moisture conditions.The results of previous work on the friction characteristics of the root-soil interface under different soil water content were also considered. Furthermore, large-scale direct shear tests were performed to assess the strength characteristics of root-soil composites under different root cross-sectional area ratios (RAR) and moisture contents. Based on the widely used Wu model, and incorporating the failure modes of roots in root-soil composites and the mechanism of root-soil interface friction, a root-soil composite strength degradation model was established considering the effects of moisture. Moisture significantly affected the tensile strength of fine tree roots, with the tensile strength of fine roots being lower in the saturated state than in the fresh state. In contrast, coarse roots were almost unaffected by moisture. As the moisture content increased, the additional strength provided by the roots decreased, and the root efficiency (REp) decreased significantly. The model was validated against experimental data, and the calculated results were accurate. In root-soil composites, as moisture infiltrates, the tensile strength of the roots, soil shear strength, and root-soil interface shear strength decrease to different degrees. This results in reduced resistance to deformation in the root-soil composites, leading to a decrease in its strength.

In Australia, trifluralin is one of the commonly used herbicides to manage annual grasses and some broadleaf weeds. However, it may have some ecosystem impacts such as high toxicity to terrestrial and aquatic life, so it is vital to monitor the degradation of trifluralin for a considerable period for environmental safety. For risk assessment purposes, it is necessary to estimate the half-life of trifluralin, which is often evaluated using derived mathematical dissipation models. In the literature, bi-exponential (BEXP) and gamma models were suggested for modelling the dissipation of trifluralin in soil. Both models provide the half-life estimate without discussing the uncertainty of the estimate, which is a shortcoming in the literature. In this paper, we used simulation to illustrate the importance of estimate's uncertainty (standard error) and demonstrated a method to compute the standard error for the half-life estimate mathematically for kinetic dissipation models. Later, we evaluated the performance of the two suggested models using statistical indices. The computation of the half-life and the standard error of the half-life estimate were discussed. This allows us to describe the inference of the half-life parameter and determine whether the half-life estimates are significantly different against the co-variate (moisture) levels. We demonstrated the method to calculate the standard error of the half-life of trifluralin, which allows us to determine the statistical difference between the estimates. In this study, we found that the half-life of trifluralin in soil tends to increase with increasing moisture levels, and the half-life of trifluralin in soil with 100% moisture level is significantly greater than 40% and 70% moisture levels. Our findings suggest that soil moisture levels should be carefully considered before trifluralin application to minimize the non-target environmental damage.

Monopile foundations of offshore wind turbines embedded in soft clay are subjected to the long-term cyclic lateral loads induced by winds, currents, and waves, the vibration of monopile leads to the accumulation of pore pressure and cyclic strains in the soil in its vicinity, which poses a threat to the safety operation of monopile. The researchers mainly focused on the hysteretic stress-strain relationship of soft clay and kinds of stiffness degradation models have been adopted, which may consume considerable computing resources and is not applicable for the long-term bearing performance analysis of monopile. In this study, a modified cyclic stiffness degradation model considering the effect of plastic strain and pore pressure change has been proposed and validated by comparing with the triaxial test results. Subsequently, the effects of cyclic load ratio, pile aspect ratio, number of load cycles, and length to embedded depth ratio on the accumulated rotation angle and pore pressure are presented. The results indicate the number of load cycles can significantly affect the accumulated rotation angle of monopile, whereas the accumulated pore pressure distribution along the pile merely changes with pile diameter, embedded length, and the number of load cycles, the stiffness of monopile can be significantly weakened by decreasing the embedded depth ratio L/H of monopile. The stiffness degradation of soil is more significant in the passive earth pressure zone, in which soil liquefaction is likely to occur. Furthermore, the suitability of the accumulated rotation angle and accumulated pore pressure design criteria for determining the required cyclic load ratio are discussed.

In salt-rich soft soil regions, as a backfill material, foamed lightweight soil (FLS) is often subjected to long-term chemical erosion of groundwater, which would lead to a continuous degradation of strength properties, and ultimately causes a risk to the long-term safety of infrastructures. Combining sulfate chemical soaking test and dry-wet cycle test, this paper investigates the durability changes of FLS under different densities of FLS, sulfate concentrations, and cation types of sulfate. The results indicate that the dynamic strength degradation of FLS under dry-wet cycles is much greater than that under sulfate soaking. When other influencing factors remain unchanged, the corrosiveness of Na2SO4 solution is greater than that of MgSO4 solution. Moreover, this paper establishes a dynamic strength degradation prediction model for FLS based on the experimental results, which can scientifically guide the durability changes of FLS under different influencing factors.