To establish the hysteresis model of EPS particles amended light weight soil under multi-step cyclic loading, the dynamic deformation characteristics of light weight soil were studied by consolidated undrained dynamic triaxial tests. The results showed that the backbone curve of light weight soil is hyperbolic and has strain hardening characteristics. With the increase of dynamic stress, the hysteresis curve shape of light weight soil gradually transforms from spindle-shaped to crescent-shaped, showing nonlinearity, hysteresis and strain accumulation. Based on the Hardin-Drnevich model and Masing rules, a modified unloading and reloading rule for the hysteresis model of light weight soil is proposed. The maximum dynamic shear modulus correction coefficient k1 and dynamic shear modulus attenuation coefficient k2 are introduced to establish the modified hysteresis model of light weight soil. Based on the modified hysteresis model, the physical meanings of k1 and k2 are defined. The influence of k1 and k2 values on the shape of hysteresis curve is discussed, and the empirical formulas of k1 and k2 about the dynamic shear strain are obtained. Through the verified dynamic triaxial tests of light weight soil by changing stress state, it is found that the relative error between the predicted values of modified hysteresis model and measured values is between 3.19% and 19.41%, which indicates that the model can describe closely the mechanical response process of light weight soil under complex dynamic conditions. The modified hysteresis model can predict the complex mechanical response mechanism in the progressive evolution of structural soil from convex to concave-convex hysteresis loop.

This paper quantitatively analyses the macroscopic characteristics of soil hysteretic curves under dynamic loading and examines the elastic properties, viscosity, meso-damage degree and energy consumption of soil from a macroscopic perspective. Given the lack of research on the hysteresis characteristics of bioenzyme-modified silty soil, a series of dynamic triaxial tests were conducted under varying bioenzyme dosages, confining pressures, loading frequencies, and other conditions. The analysis focused on several parameters: the slope of the major axis of the hysteretic curve k, the ratio of the major to minor axes alpha, the distance between the central points of adjacent hysteretic curves d, and the area enclosed by the hysteretic curve S. These were used for quantitative analysis of the morphological characteristics, influencing factors, and changing patterns of the hysteresis curve in bioenzyme-modified silty soil. The results showed that the hysteresis curve of the bioenzyme-improved silty soil resembled an inclined ellipse. Under the influence of different bioenzymes dosages, confining pressures, and loading frequencies, k and alpha decreased as dynamic stress increased, while d and S increased exponentially with rising dynamic stress. When the bioenzyme dosage was 0.01%, the k value was largest, and alpha, d and S were smallest. With increasing confining pressure, k increased, while alpha, d, and S decreased. As the loading frequency increased, k, alpha, and d decreased, while S gradually increased. At a bioenzyme dosage of 0.01%, the bioenzyme had the greatest effect on improving the silty soil.

A dynamic triaxial test was conducted to assess the deformation characteristics of sodium silicate modified EPS (expanded polystyrene) particle lightweight soil (SCS) under cyclical loading. The hysteresis curves, dynamic elastic modulus, damping ratio, and cumulative strain were obtained for SCS samples with varying EPS particle content. We found that the samples' stress-strain hysteresis curves, became crescent-shaped for different dynamic stress situations, and were largely elastic in the latter phases. Furthermore, there was a progression from dense to sparse as EPS content increased. With increasing dynamic stress, the dynamic elastic modulus and damping ratio of SCS also rose. The damping ratio of SCS rose as the EPS particle content increased, whereas the dynamic elastic modulus decreased. Notably, increases in the PS particle content and dynamic stress largen the deformation of the SCS samples. Moreover, we found that when the cumulative strain curve becomes stable, varying the contents of EPS particles under different dynamic stresses leads to a power function relationship with the logarithm of the number of cyclic loading cycles. In cases where the cumulative strain curve reaches a critical or destruction point, the cumulative damage variable displays a power function relationship with the vibration count.

Expanded polystyrene (EPS) particle-based lightweight soil, which is a type of lightweight filler, is mainly used in road engineering. The stability of subgrades under dynamic loading is attracting increased research attention. The traditional method for studying the dynamic strength characteristics of soils is dynamic triaxial testing, and the discrete element simulation of lightweight soils under cyclic load has rarely been considered. To study the meso-mechanisms of the dynamic failure processes of EPS particle lightweight soils, a discrete element numerical model is established using the particle flow code (PFC) software. The contact force, displacement field, and velocity field of lightweight soil under different cumulative compressive strains are studied. The results show that the hysteresis curves of lightweight soil present characteristics of strain accumulation, which reflect the cyclic effects of the dynamic load. When the confining pressure increases, the contact force of the particles also increases. The confining pressure can restrain the motion of the particle system and increase the dynamic strength of the sample. When the confining pressure is held constant, an increase in compressive strain causes minimal change in the contact force between soil particles. However, the contact force between the EPS particles decreases, and their displacement direction points vertically toward the center of the sample. Under an increase in compressive strain, the velocity direction of the particle system changes from a random distribution and points vertically toward the center of the sample. When the compressive strain is 5%, the number of particles deflected in the particle velocity direction increases significantly, and the cumulative rate of deformation in the lightweight soil accelerates. Therefore, it is feasible to use 5% compressive strain as the dynamic strength standard for lightweight soil. Discrete element methods provide a new approach toward the dynamic performance evaluation of lightweight soil subgrades.

A new composite material of polyurethane-bonded rubber particle-sand mixture (PolyBRuS) is presented here. A series of cyclic triaxial tests were carried out the hysteresis curves under different confining pressures, temperatures, and freeze-thaw cycles, and then the morphological characteristics and evolution law of hysteresis curves under low-temperature conditions were analyzed. The results indicate that the dynamic strain amplitude, temperature, and number of freeze-thaw cycles have a great influence on the hysteresis curve, while the confining pressure has little influence on the hysteresis curve. While the temperature (T) is -15 degrees C and the number of freeze-thaw cycles (N) is 25, the long-axis slope K, i.e., the elastic properties and stiffness of the PolyBRuS material, decreases with increasing dynamic strain amplitude, tends to increase with higher confinement pressures. While N = 25 and the confining pressures (sigma(3)) is 25 kPa, the distance between the center point of the adjacent hysteresis curve d, i.e., fine microscopic damage of the PolyBRuS material, grows with increasing dynamic strain amplitude, rises with lower temperature. While T = -10 degrees C and sigma(3) = 25 kPa, hysteresis curve area S, i.e., energy dissipation of the PolyBRuS material, increases non-linearly in relation to the dynamic strain, and reduces with the enlarge of the number of freeze-thaw cycles, however, this reduction is negligible. Further research should focus on the quantitative analysis of the morphological characteristics and evolution law of hysteresis curves.