Yao Zhang

Loess is a distinctly structured soil. Undisturbed loess is prone to geological hazards, such as liquefaction and landslides under dynamic loads. There are also problems such as the inhomogeneity, anisotropy, and disturbance of in situ sampling. An artificial structural loess is prepared to accurately display the dynamic characteristics of undisturbed loess. This study took artificial structural loess as the study object, through dynamic triaxial tests, analyzed the effects of the confining pressure (σ₃), dry density (ρ_d), and cement content (D) on its dynamic strength. Then, a dynamic strength index model of artificial structural loess was established. Our results show that the dynamic strength of artificial structural loess rises with enhanced σ₃, ρ_d, and D. The dynamic cohesion (c_d) and dynamic friction angle (φ_d) increased with the rise of ρ_d, and D. The dynamic strength of artificial structured loess is closer to that of undisturbed loess when the ρ_d is 1.60 g/cm³ and D is 2%. The R² values of the φ_d and the c_d model were 0.97 and 0.98, respectively, fitting the dynamic strength index of artificial structural loess with different D, ρ_d, and σ₃. Our study outcomes can serve as references and guides for engineering construction in loess areas.

Due to the difficulties in sampling, high sensitivity to humidity, and inconvenience in storage, undisturbed loess is prone to changes in its original structure. Therefore, trace amounts of cement and salt are added to remolded soil to simulate the structure of undisturbed loess. The GDS dynamic three-axial test apparatus was used to investigate the influence of dry density, cement content, and confining pressure (CP) on the dynamic distortion characteristics of artificially structured soil. Based on dynamic triaxial tests, the Hardin–Drnevich (H-D) model was established through fitting analysis. The research findings indicate that increased dry density, cement content, and CP can enhance the soil’s resistance to distortion. Under dynamic loading, the higher the CP, the smaller the damping ratio of the soil. With a dry density of 1.20 g/cm³ and 2% cement, the dynamic modulus of the artificially structured loess is similar to that of undisturbed loess. With a dry density of 1.60 g/cm³ and 2% cement, the CP is 200 kPa, the soil’s dynamic modulus of elasticity (DM-E) peak value is 113.14 MPa, and the damping ratio is 0.258. The good agreement between trial data and the predicted results demonstrates that the H-D hyperbolic model is appropriate for representing the DM-E of artificially structured loess. A three-dimensional model of the dynamic deformation characteristics and microstructure of artificial structural loess under dynamic loads was established. The findings can guide the study of the mechanical properties of loess under dynamic loading.

Periodic freezing–thawing is recognized as a real threat to the mechanical properties of reinforced loess, which has been used in the recent construction of high-speed railways in northwest China; however, the performance of these materials under periodic freezing–thawing and dynamic loading has rarely been investigated. In this work, dynamic triaxial tests were conducted on fly ash- and polypropylene fiber-reinforced loess with different blend ratios and freeze–thaw cycles. The dynamic shear modulus and damping ratio were investigated. The results revealed that cyclic freezing–thawing had a remarkable effect on the dynamic shear modulus and damping ratio, which demonstrated considerable reductions and increases, respectively, after cyclic freezing–thawing. Additionally, the dynamic shear modulus increased notably with the fly ash content and confining pressure and decreased with the water content. Meanwhile, the damping ratio increased with the fiber content and water content and decreased with the fly ash content and confining pressure. Comparatively, the effects of polypropylene fiber on dynamic behavior were found to be not significant. Furthermore, novel models were established to predict the dynamic shear modulus and damping ratio for reinforced loess. The results provide more information towards infrastructure design in seasonal frozen regions.

The electro-dewatering technique is an effective method to reinforce soft clay. Electro-dewatering experiments were conducted to assess the impact of salt content on electro-dewatering behaviors and effects with copper and stainless steel anodes. The changes in the current, accumulated drainage volume, and electro-osmotic flow velocity reflect the “catch point” phenomenon between the copper anode and the stainless steel anode. Moreover, the higher the salt content was, the earlier the appearance of the “catch point,” which means that the effect of the copper anode was better in the early stages and then worse in the following stages than that of the stainless steel anode. Based on photographs of anode surface, SEM-EDS (Scanning electron microscopy-Energy dispersive spectrometry) and XRD (X-ray diffraction) results, we found that the copper anode surface produced green product, which observably decreased the conductivity of the copper anode and then reduced the effective electrical potential gradient. On the other hand, there were no added elements on the stainless steel anode surface after the electro-dewatering experiments, and the conductivity of the stainless steel anode was similar to its initial status. The above two points led to the appearance of the“catch point” phenomenon. The pH value of the stainless steel anode was lower than that of copper anode, and the concentration of Cl⁻ had the opposite relationship. Because the effective electrical potential gradient of the stainless steel anode was higher than that of the copper anode after the “catch point,” the water content of the stainless steel anode was lower than that of the copper anode.