This study examines the dynamic shear strength properties of expanded polystyrene lightweight soil (EPS LWS) samples through dynamic triaxial tests, focusing on the effects of EPS bead content, cement concentration, and confining pressure. The results indicate that increasing the cement content positively correlates with the dynamic strength of EPS LWS due to the formation of reticulate cement hydrates that bond soil particles. When the cement content is below 10%, EPS beads have minimal impact on dynamic shear strength. However, at cement contents of 15% or higher, increasing EPS bead content reduces dynamic strength because the low-strength EPS beads break under these conditions. Elastic deformation in EPS LWS remains stable, with elastic strain increasing as EPS particle content and confining pressure rise. This highlights the significant impact of these factors on elastic strain, which is crucial for achieving the desired density and strength in engineering applications. The nonlinear behavior under dynamic stress and strain, showing strain hardening at critical levels. Higher EPS content reduces the dynamic stress required for bearing capacity due to decreased stiffness. Additionally, the dynamic elastic modulus increases with cyclic loading frequency, while higher confining pressure enhances hoop stress effects, requiring more dynamic stress to achieve the same strain. This study provides insights into the dynamic shear strength properties of EPS LWS, emphasizing the critical roles of cement content, EPS bead content, and confining pressure in influencing its performance in engineering applications.

Saturated sand foundations are susceptible to liquefaction under dynamic loads. This can result in roadbed subsidence, flotation of underground structures, and other engineering failures. Compared with the traditional foundation reinforcement technology, enzyme-induced calcium carbonate precipitation technology (EICP) is a green environmental protection reinforcement technology. The EICP technology can use enzymes to induce calcium carbonate to cement soil particles and fill soil pores, thus effectively improving soil strength and inhibiting sand liquefaction damage. The study takes EICP-solidified standard sand as the research object and, through the dynamic triaxial test, analyzes the influence of different confining pressure (sigma 3) cementation times (CT), cyclic stress ratio (CSR), dry density (rho d), and vibration frequency (f) on dynamic strength characteristics. Then, a modified dynamic strength model of EICP-solidified standard sand was established. The results show that, under the same confining pressure, the required vibration number for failure decreases with the increase in dynamic strength, and the dynamic strength increases with the rise in dry density. At the same number of cyclic vibrations, the greater the confining pressure and cementation times, the greater the dynamic strength. When the cementation times are constant, the dynamic strength of EICP-solidified sand decreases with the increase in the vibration number. When cementation times are 6, the dynamic strength of the specimens with CSR of 0.35 is 25.9% and 32.4% higher than those with CSR of 0.25 and 0.30, respectively. The predicted results show that the model can predict the measured values well, which fully verifies the applicability of the model. The research results can provide a reference for liquefaction prevention in sand foundations.

The purpose of this study was to understand the dynamic behaviors of lignin-amended loess. Dynamic properties tests of lignin-amended loess with different contents and strength tests at optimum content were carried out by using a hollow cylinder torsion shear apparatus. Firstly, the effect of lignin fiber content (0%, 0.5%, 1%, 2%, 3% and 4%) on the dynamic properties of improved loess was investigated, and the results showed that the optimal lignin content for improved loess was 1%, at which time compared with pure loess the highest increase of the dynamic shear stress in the skeleton curve of the soil was 73.8%, the increase of dynamic shear modulus was 26%, and the decrease of dynamic damping ratio was 60%; Then, the effects of moisture content (12%, 17%, 21%) and consolidated confining pressure (100 kPa, 200 kPa, 300 kPa) on the dynamic strength of 1% modified loess were studied, and the subsidence characteristics of the improved loess were also focused on, the results indicated that the dynamic strength of the improved loess decreased with the increase of moisture content and increase with the confining pressure, and the seismic characteristics increase with the increase of dynamic shear stress and the number of cycles.

On July 20, 2021, over 2000 ground subsidence events and collapses occurred in Zhengzhou, China, after a heavy rainstorm. These events were mostly caused by the reduced mechanical properties of loess under moistening and repeated dynamic loading. After the conducted dynamic triaxial tests considering varying moisture content, envelope pressure and 10,000 vibrations, the dynamic properties evolution of undisturbed loess under moistening has been clarified. The experimental results showed that the dynamic strain of undisturbed loess under moistening conditions increases gradually with increasing dynamic stress, following the Hardin-Drnevich hyperbolic model. The initial dynamic shear modulus, maximum dynamic shear stress, and dynamic strength decrease linearly with increasing moisture, while the dynamic strain is the opposite, and the damping ratio is less affected by the increased moisture. The dynamic strain rises with increasing dynamic stress and moisture content considering the same vibrations. Increased vibrations and greater moisture content under identical dynamic stress cause a faster accumulation of dynamic strain in undisturbed loess, making it more susceptible to damage. The results are of guiding significance for the evaluation and analysis of the dynamic properties of loess and provide technical support for disaster prevention and mitigation in Zhengzhou.

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.