True triaxial tests were conducted on artificially frozen sand. The effects of the intermediate principal stress coefficient, temperature and confining pressure on the strength of frozen sand were studied. The stress-strain curves under different initial conditions indicated a strain hardening. In response to increases of either the intermediate principal stress coefficient or the confining pressure or to a decrease of temperature, the strength typically increased. Furthermore, a new strength criterion was proposed to describe the strength of artificially frozen sand under a constant b-value stress path, combining the strength function in the p-q and pi planes. Considering the low confining pressure, the strength criterion in the p-q plane fitted the linear relationship in the parabolic strength criterion well. The strength criterion in the pi plane was combined with stress invariants, and a new strength criterion was established. This criterion considers unequal tension and compression strength, and integrates temperature. Test results indicated its validity. All parameters of the strength criterion could be easily determined from the triaxial compression and triaxial tensile tests.

The deformation behaviors of soft clay under cyclic loading were investigated with constant loading frequency; however, the response frequency of the subgrade soil varied when the train passed by. Moreover, both deviator stress and confining pressure varied cyclically. Hence, two types of cyclic triaxial tests were conducted on saturated soft clay, in which the differences in deformation behaviors between constant and composite loading frequencies were analyzed, and the impacts of cyclic confining pressure and drained conditions were considered. The strain increment continuously decreased with the progress of the test under cyclic loading with constant loading frequency, while that first decreased, achieving the minimum value at the third loading stage, and then increased under cyclic loading with composite loading frequencies. Nevertheless, compared with the test results of cyclic triaxial tests with composite loading frequencies, the strain with constant loading frequency increased by 65.4% and 117.9% under undrained and partially drained conditions, respectively. The cyclic triaxial tests with constant loading frequency overestimated the strains under cyclic loading. The strain increments were greater in the first loading stage under undrained and partially drained conditions; however, the differences in strain increments between undrained and partially drained conditions in other loading stages can be ignored. Moreover, the effect of cyclic confining pressures was clarified under cyclic loading with composite loading frequencies: the strain ratio of cyclic confining pressures to constant confining pressures decreased from 0.870 to 0.723 as eta increased from 1.00 to 2.00 under undrained conditions, while it increased from 1.227 to 1.837 under partially drained conditions. Nevertheless, the ratios increased linearly with increasing eta under partially drained conditions, and decreased linearly under undrained conditions.

The effects of confining pressure and particle breakage on the mechanical behavior of tailings were investigated using the discrete-element method to simulate conventional triaxial tests. The particle breakage was simulated using the octahedral shear stress breakage criterion and 14 Apollonian fragments replacement method. The macroscopic behavior of tailings revealed that the peak shear stress ratio is sensitive to confining pressure and the critical shear stress ratio is less sensitive to particle breakage. Confining pressure and particle breakage affect shear expansion, leading to changes in shear damage patterns. The quantitative study shows that particle breakage is the main factor influencing the nonlinear variation of the tailing strength. However, the influence proportion of particle breakage is gradually decreasing with the increase in the confining pressure. Microscopic analysis reveals a positive correlation between the overall anisotropy and the shear stress ratio, with the anisotropy of the normal contact force distribution contributing the most. The variation of the overall anisotropy is caused by the variation of the contact state, in which the sliding contact state is the main influencing factor.

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 (sigma 3), dry density (rho 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 sigma 3, rho d, and D. The dynamic cohesion (cd) and dynamic friction angle (phi d) increased with the rise of rho d, and D. The dynamic strength of artificial structured loess is closer to that of undisturbed loess when the rho d is 1.60 g/cm3 and D is 2%. The R2 values of the phi d and the cd model were 0.97 and 0.98, respectively, fitting the dynamic strength index of artificial structural loess with different D, rho d, and sigma 3. Our study outcomes can serve as references and guides for engineering construction in loess areas.

Silty clay is a common compressible soil found in many engineering projects, where its deformation behavior is particularly complex under cyclic loading. This study uses the GDS dynamic triaxial testing system to examine how silty clay deforms under different moisture contents, confining pressures, and cyclic stress ratios (CSR). The results show that the cumulative strain of silty clay follows a three-phase pattern: an initial rapid increase (N = 0-300), followed by a slower rise (N = 300-1000), and finally reaching a stable state (N > 1000). Among the factors tested, CSR has the most significant impact on cumulative strain, with moisture content coming second, while confining pressure has a relatively minor effect. After 1000 cycles, cumulative strain shows a clear linear growth trend. Linear fitting analysis indicates that the uncertainty in the fitted curve is influenced by moisture content, confining pressure, and CSR. Uncertainty is greater at both low and high moisture content levels, while it is lower under moderate moisture conditions. These findings provide valuable insights into predicting soil deformation in engineering applications, helping to improve our understanding of silty clay behavior under cyclic loading.

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.

Cyclic triaxial tests with intermittent cyclic loading are usually used to investigate the deformation behaviors of soil; however, both deviator stress and confining pressure vary cyclically under traffic loading. Moreover, the pore water in soil can be dissipated throughout the test, affecting the mechanical behaviors of soils. Therefore, in this study, three test modes were applied to saturated soft clay to analyze the deformation behaviors, in which different cyclic confining pressures were used during cyclic loading periods, and different drained conditions during cyclic loading and intermittent periods were considered. The variations in strain increment were similar in all cases: as the loading stages progressed, the strain increment gradually diminished. The distinct variation in strain increment became evident in the initial loading stage, but it became negligible in subsequent loading stages. Furthermore, the change in strain increment with respect to cyclic confining pressure was influenced by drained conditions during the cyclic loading period: it increases as the cyclic confining pressure increased under partially drained conditions and decreases under undrained conditions. Moreover, the strain increased under partially drained conditions during intermittent periods, companying with the discharge of pore water, while it decreased for the recovery of specimen deformation under undrained conditions. The greater strain increment was caused under partially drained conditions during cyclic loading periods compared with the corresponding strain increment under undrained conditions. Besides, an empirical model was developed to forecast accumulated axial strain of soil subjected to intermittent cyclic loading, and the variations of parameters under different drained conditions were studied.

The occurrence of earthquake-induced soil liquefaction poses a significant threat, leading to extensive damage to building foundations and other structures, resulting in substantial economic repercussions. The seismic performance of geotechnical systems is markedly influenced by the saturation level of the soil. This study examines the impact of dynamic response on Palar sand. Cyclic triaxial tests were conducted on partially saturated finegrained loose sand with a relative density of 35 % and a degree of saturation ranging from 65 % to 75 %. These tests were carried out at a strain rate of 0.1 % and confining pressures of 50 and 75 kPa. The study findings reveal that an increase in back pressure corresponds to a rise in the excess pore water pressure ratio of the sand. Additionally, the sand undergoes liquefaction as the number of cycles increases, and the degree of saturation decreases for different confining pressures at frequencies of 0.75 and 1 Hz. It was observed that soil liquefies more rapidly at lower strain rates with an increase in effective confining pressure. Conversely, at higher frequencies, soil liquefaction occurs in a smaller number of cycles. Comparing the effects of confining pressure and frequency, a damping ratio of 13 % and a shear modulus of 40 MPa were achieved at a frequency of 0.75 Hz and a confining pressure of 50 kPa. The shear modulus of partially saturated sand decreases with an increase in the initial degree of saturation due to specific characteristics of the Palar sand and the loading conditions.

Ground deformation induced by frost heave is a matter of concern in cold region engineering construction since it affects surrounding structures. Frost heave, which is related to the heat-water-stress interaction, is a complicated process. In this study, a heat-water-stress coupling model was established for saturated frozen soil under different stress levels to quantify the water redistribution, heat transfer, frost heave, and water intake. An empirical formula for the soil permeability considering the confining and deviator pressures was employed as an indispensable hydraulic equation in the coupling model. The Drucker-Prager yield criterion matched with the Mohr-Coulomb criterion was employed in the force equilibrium equation to investigate the deformation due to the deviator and confining pressures. The anisotropic frost heave during unidirectional freezing was further considered in the coupling model by introducing an anisotropic coefficient. Subsequently, based on the above coupling relationship, a mathematical module in COMSOL Multiphysics was applied to calculate the governing equation numerically. Finally, the proposed model was validated through an existing frost heave experiment conducted under various temperature gradients and stress levels. The results of the freezing front, water redistribution, water intake, and frost heave ratio predicted using the proposed model were found to be consistent with the experimental results.

The traffic loading is a typical cyclic loading with variable confining pressure and always lasts long, and is believed to have a significant effect on the subgrade soil, especially for the subgrade filled with soft clay. However, the mechanics have yet to be fully understood. Given that the duration of traffic loading lasts long enough, the partially drained conditions should be considered for the soft clay under the long-term cyclic loading, rather than the undrained conditions adopted commonly by most previous researches. In this study, 28 cyclic tests were conducted on the remolded saturated soft clay, utilizing both constant confining pressure and variable confining pressure under partially drained and undrained conditions. The effect of cyclic confining pressure and different drainage conditions is analyzed in relation to the evolution of pore pressure and deformation behaviors. Incorporating both the cyclic confining pressure and cyclic stress ratio, a concise pre-diction model of permanent strain is proposed and validated by the experimental results.