As a new type of granular backfill material, calcareous sand is widely used in the construction of marine transportation infrastructure. And they are subjected to complex irregular long-term dynamic loading such as that from waves, traffic and even earthquakes. In this paper, 22 groups of undrained cyclic shear tests were performed with calcareous sand under various cyclic stress ratios and cyclic stress paths. The influence mechanism of stress path on the cyclic shear behavior of calcareous sand was investigated. The results show that the ultimate residual pore pressure at critical state was not affected by cyclic stress ratios and paths. But the cyclic shear behaviors of calcareous sand including failure pore water pressure and long-term deformation were changed significantly. Axial load plays a dominant role in each stress path. A stress path parameter omega was proposed to characterize the vertical shaking impact of cyclic stress paths with different initial orientation of the sigma 1 axis to vertical alpha sigma 0. And a power function of omega was used to describe the involvement level of soil skeleton in anti-liquefaction. This parameter performs well in representing cyclic stress paths with different orientation to the vertical. A series of formulas were proposed to predict the failure residual pore pressure and the long-term cumulative deformation behavior of calcareous sand. More accurate shakedown discriminant boundaries suitable for almost unbroken calcareous sand were proposed.

Currently, studies on the permeability evolution characteristics of overlying aquiclude protective layers caused by coal mining focus on single lithological protective layers and assume the permeability coefficient remains constant. However, these studies fail to consider the variation characteristics of the combination protective layer structure and permeability coefficient. Therefore, an analytical method is proposed to study coal seam leakage under mining conditions in the blown-sand beach region based on the structure and permeability coefficient of the combination protective layer. First, the stress path of the overlying combination aquiclude under coal mining disturbance is comprehensively considered. Based on this, triaxial loading and unloading seepage creep experiments are conducted with different proportions of overlying combination aquiclude. The analytical relationship between the permeability coefficient of the samples and loess proportion, stress level, and soil depth in the stress recovery stage is determined, leading to the establishment of a creep permeability coefficient evolution model for the overlying combination aquiclude of the coal seam under the stress path of coal mining. Second, the creep permeability coefficient evolution model is integrated with a fusion algorithm in COMSOL numerical simulation software. Numerical simulations are then performed to examine the evolution law of phreatic leakage during coal seam mining and recovery, revealing a relationship curve in which leakage gradually decreases over time before stabilizing in the post-mining recovery stage. Finally, based on mathematical and statistical methods, a phreatic leakage evolution model is developed for both mining and post-mining stages to provide a theoretical basis for environmental protection.

Frozen soil is a common foundation material in cold region engineering. Therefore, the control and prediction of cumulative plastic strain for frozen soil materials are essential for the construction and long-term stability of actual foundation engineering under complex dynamic loadings. To investigate the influence of complex cyclic stress paths on frozen soil, a series of complex cyclic stress paths were conducted using the frozen hollow cylinder apparatus (FHCA-300).These cyclic stress paths included the triaxial cyclic stress path (TCSP), directional cyclic stress path (DCSP), circular-shaped cyclic stress path (CCSP), elliptical-shaped cyclic stress path (ECSP), and heart-shaped cyclic stress path (HCSP).The results indicated that the cumulative plastic strain under the five cyclic stress paths at three temperatures (-1.5,-6,and-15 degrees C) can be ranked as follows: DCSP>ECSP>HCSP>CCSP>TCSP. The cyclic stress paths are quantified based on the combined effects of the maximum shear stress (q(max)) and the principal stress axis angle (a). A developed model predicting cumulative plastic strain, considering complex cyclic stress paths, is introduced and demonstrates excellent predictive performance. The study's findings can offer insights into foundation engineering's deformation characteristics and settlement predictions under diverse complex dynamic loadings

Research on the dynamic response of subgrades is essential for designing heavy-haul railway subgrades. Therefore, a dynamic stress field test was carried out on the Daqin Railway using a three-dimensional dynamic soil pressure box capable of measuring the total stress component of soil elements. Then, a train-track-subgrade coupling finite-element model (FEM) considering the track irregularity and infinite element boundary conditions was established, and the validity of the model was verified using field test results. Subsequently, based on the field test results, the actual three-dimensional dynamic response and stress path of the subgrade under a train load were analyzed. Based on the FEM results, the effects of the train axle load, train speed, subgrade stiffness, and subgrade thickness on the three-dimensional dynamic response of the subgrade were analyzed, and a prediction model of the vertical dynamic stress was proposed. Finally, the influence of the depth of the heavy-haul train loads on the subgrade was studied. Research has shown that the normal stress caused by two wheelsets under the same bogie has a superposition effect, and each peak value of the normal stress corresponds to the center position of the bogie. When the train passes through the test section, the stress path of the soil element directly below the track is fairly elliptical, and the principal stress axis of the soil element rotates by 180 degrees. The normal stresses sigma x, sigma y, and sigma z increase proportionally with the speed and axle load of the train but decrease inversely proportional to the thickness of the ballast layer. The subgrade stiffness significantly influences the normal stress sigma x and sigma y but has no apparent influence on the normal stress sigma z. The influence depth of the train load in the subgrade is related to the axle load, train speed, and thickness of the ballast layer, but is unrelated to the stiffness of the subgrade surface layer. This study provides practical and theoretical data for analyzing the dynamic performance of heavy-haul railway subgrades.

Shield tunneling inevitably disturbs the surrounding soil, primarily resulting in changes in stress state, stress path, and strain. Modifications to certain parameters, such as shield thrust, shield friction, and soil loss, are made based on the elastic mechanics Mindlin solution and the mirror method, and a calculation expression for additional soil stresses induced by tunneling was derived. Additional soil stresses are calculated using the parameters of the Hangzhou Metro Kanji section. 3D principal stress paths and deviations of the principal stress axes near the tunnel crown, waist, and invert during shield tunneling were obtained by applying a transition matrix orthogonal transformation. These results are compared with experimental data to validate the theoretical solution's accuracy. The stress distribution along the tunneling direction and the 3D principal stress paths and deviations of the principal stress axes in the surrounding soil are determined. The results are as follows: The additional soil stresses along the tunneling direction follow a normal distribution and an S-shape. Under the combined influence of three construction mechanics factors, the shear stress component is approximately 1/3 to 1/2 of the normal stress and should not be neglected. During shield tunneling, the deviation angle of the principal stress axis at the tunnel crown changes from 90 degrees to 180 degrees, with little change in the magnitude of the principal stress. At the invert, the magnitude of the principal stress rapidly increases from 0.25 kPa to 8 kPa, with minimal deviation in the principal stress axis. At the shoulder, the principal stress variation and axis deviation are small. At the foot of the arch, the deviation angle of the major and minor principal stress axes is larger, while the magnitude of the principal stress slightly changes. At the waist, the deviation angle of the major principal stress is larger, and the magnitude of the minor principal stress significantly changes. A strategy for addressing changes in soil stress paths during shield tunnel construction is also proposed.

Stress-induced anisotropy, the directional variation in soil properties under applied loads, significantly influences the soil behavior and stability of geotechnical structures. This review critically examines its impact on shear strength, pore pressure, stiffness, and stress-strain behavior of soils, offering insights into its fundamental mechanisms. Advancements in experimental methods, including bender element tests, true-triaxial testing, and hollow cylinder apparatus, are critically analyzed alongside analytical and numerical models that capture complex anisotropic responses under varied loading conditions. The study highlights the practical significance of incorporating the anisotropic behavior of soils in geotechnical design. From the literature, it can be concluded that neglecting stress-induced anisotropy can overestimate the factor of safety (FOS) of slopes up to 33% and underestimate displacements of foundations by 25-40%, leading to critical inaccuracies in the design. A case study of slope failure under anisotropic stress highlights the necessity of accounting for these effects. Challenges such as replicating realistic stress paths in laboratory tests and integrating anisotropic parameters in numerical frameworks are identified. Future directions include developing predictive models, automating analysis using machine learning, and validating findings through large-scale field studies. This review bridges theoretical advancements with practical applications, advocating for integrating stress-induced anisotropy, wherever applicable, into geotechnical practice to enhance infrastructure safety and resilience.

The plastic strain of calcareous sand is related to its stress path and particle breakage, rendering the hardening process complex. An expression for the stress-path-dependence factor was developed by analyzing the variations in plastic strain across different initial void ratios. A stress-path-independent hardening parameter was derived from the modified plastic work and was subsequently validated. Constant-proportion loading tests on calcareous sands confirmed the applicability of this hardening model. The results indicated that under isotropic compression, the plastic volumetric strain increased with increasing average effective stress, albeit at a decreasing growth rate. A positive linear relationship was observed between the volumetric strain modulus and relative breakage index. The proposed hardening parameter effectively captured the particle breakage and stress path effects in calcareous sand and was validated through theoretical calculations and laboratory tests, offering valuable insights into the mechanical behavior of fragile granular soils.

Seismic events and wave action can induce volumetric strain (ev) accumulation in saturated sandy soils, leading to damage to the ground surface and structures. A quantifiable relationship exists between the generation of ev in sandy soils under drained conditions and the development of pore water pressures under undrained conditions. In this study, the impact of relative density (Dr), cyclic stress path, and stress level on the characteristics of volumetric strain (ev) generation in saturated coral sands (SCS) was evaluated through drained tests employing various cyclic stress paths. The test findings demonstrate that the rate of ev accumulation in SCS is notably affected by the cyclic stress path. The rise in peak volumetric strain (evp) in SCS, as a function of the number of cycles, conforms to the arctangent function model. The unit cyclic stress ratio (USR) was employed as an indicator of complex cyclic loading levels. It was determined that coefficient (evp)u is positively correlated with USR at a specific Dr. At the same Dr, coefficient CN1 exhibits a positive correlation with USR, while coefficient CN2 displays a negative correlation with USR, following a power-law relationship. Irrespective of cyclic loading conditions, evp rises with an increase in generalized shear strain amplitude (yga). A power function model was established to represent the relationship between evp and yga. The coefficient 41 decreases as Dr increases. Comparisons were drawn between evp and yga for Ottawa sand and SCS. The results indicate that, as Dr of Ottawa sand increases from 30 % to 70 %, the coefficient 41 decreases from 1.54 to 0.73, representing a reduction of approximately 53 %. In contrast, under identical conditions, the coefficient 41 of SCS exhibits a less pronounced decrease, from 1.16 to 0.79, corresponding to a reduction of roughly 32 %. These observations suggest that variations in Dr have a more substantial impact on generating evp in Ottawa sand compared to SCS.

This study investigates the strain development of saturated silty soil of Yellow River under varying initial consolidation inclination angles zeta by principle stress rotation tests. The results revealed that distinct patterns in axial, circumferential and torsional shear strains show the influence of zeta on the mechanical response of silty soil. Notably, the axial strain exhibits compressive behaviour at zeta=90 degrees during the first cycle, while the circumferential strain displays tensile behaviour. Anisotropy initiates at zeta=90 degrees and around 60 degrees for other zeta angles. Different values of zeta exhibit stabilization trends in strain fluctuations, with zeta=90 degrees and zeta=75 degrees showing intriguing similarities. The case of zeta=45 degrees stands out, with the highest fluctuation and strain amplitude. Torsional shear strain similarities are observed among most zeta angles except for zeta=90 degrees and zeta=60 degrees. Volumetric strain emphasizes the significant impact of consolidation angle inclination on anisotropic characteristics. With the increase of the initial solidification angle, the hysteresis curve shifts to the left, indicating cyclic creep characteristics, with negligible shear strain for the case of zeta=60 degrees. As the cycle period increases, the hysteresis loop contracts, indicating the continuous strengthening and eventual stabilization of shear stiffness. This comprehensive exploration provides valuable insights into the complex behaviour of saturated silty soil under rotational stress conditions, highlighting the role of initial consolidation inclination angles in shaping its mechanical response.

Gassy soil is prevalent in coastal regions, and the presence of gas bubbles can significantly alter the mechanical properties of soil, potentially leading to various marine engineering geological hazards. In this study, a series of triaxial tests were conducted on fine-grained gassy soils under different consolidation pressures (pc'), stress paths, and initial pore water pressures (uw0). These tests were also used to verify the applicability of a newly proposed constitutive model. According to the test results, the response to excess pore pressure and the stress-strain relationship of fine-grained gassy soils strongly depend on the initial pore water pressure (uw0), with the degree of variation being influenced by the consolidation pressure (pc') and stress path. As uw0 decreases, the undrained shear strength (cu) of fine-grained gassy soils gradually increases, and this is lower under the reduced triaxial compression (RTC) path compared to the conventional triaxial compression (CTC) path, which can be attributed to the destruction of the pore structure due to an increase in gas volume. The newly proposed model accurately predicts the pore pressure and stress-strain relationship of fine-grained gassy soils at low consolidation pressures (pc'), but it falls short in predicting the mechanical behavior during shear progression under high pc' or the RTC path. Although the model effectively predicts the excess pore pressure and deviator stress at the shear failure point (axial strain = 15%), further improvement is still required.