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Continuous shear wave velocity measurements are conducted on cylindrical triaxial sandy specimens consolidated with isotropic and anisotropic stress histories to characterize the evolution of the elastic shear modulus under different stress paths. The shear wave velocity is measured using an automatic device capable of consecutive measurements of travel time. All specimens were prepared using the Water Sedimentation (WS) method, and after undergoing a stress-controlled path representing the stress history of the specimens, they were subjected to stress-controlled drained shearing along eight different paths. The stress components used in the existing correlations estimating the shear moduli are specified under different stress paths. The results demonstrate that the existing empirical correlations can appropriately be used within the elastic region or the loading surface. However, the accuracy of such models estimating shear moduli might be depreciated as shearing commences, particularly if the stress path involves deviatoric stress, diverging from the expected trends at a specific stress ratio, which is strongly linked to the consolidation stress state. A criterion at which the shear modulus is diverted is also suggested, found to be directly related to the initial stress anisotropy. [ABSTRACT FROM AUTHOR]

Stratified soil is a type of widely distributed special soil, consisting of alternating interlayered soils with distinct properties in both terrestrial and marine sedimentation conditions. It is endowed with anisotropic physical properties and mechanical behavior by its unique laminar structure features. So far, its mechanical behavior has not been fully understood. To systematically investigate the laminar structure effects of stratified soil, artificially prepared stratified soil samples of silty clay interlayered by silty sand were studied. First, the laminar structure features of stratified soil in Yangtze River floodplain deposits at Nanjing, China, were summarized. Then, based on the laminar structure features, preparation method for stratified soil samples was proposed by stacking soil layers one by one, which was basically an integration of soil paste plus consolidation method for silty clay layer preparation and water pluviation plus freezing method for silty sand layer preparation. After verification of the sample preparation method, a series of consolidated-undrained triaxial compression tests were carried out to study the mechanical behavior of stratified soil. The effects of thickness of constituent layers, consolidation conditions (isotropic or anisotropic consolidation), and loading paths (conventional triaxial compression, constant-p compression, and lateral extension) were investigated. The results show that the mechanical behavior of stratified soil (including stress–strain curves, excessive pore pressure accumulation, sample failure modes, and strength index) generally falls in between the behavior of the two constituent layers of soil, i.e., a normally consolidated silty clay and a medium-dense silty sand. The silty clay layer thickness (with fixed silty sand layer thickness), consolidation conditions, and loading paths together determine the stratified soil behavior, either silty sand dominant or silty clay dominant. Laminar structure can improve volumetric dilation trend and thus increase undrained shear strength of stratified soil. The presence of silty clay layer would suppress shear banding development in stratified soil. The strength of stratified soil can be underestimated by experiments using disturbed or remolded samples where the laminar structure is partially or completely lost. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, geological disasters on loess fill slopes have occurred from time to time, which has attracted widespread attention. In order to deeply understand its deformation and failure laws and promote the disaster prevention and mitigation work, this paper takes remolded loess as the research object, systematically explores the effects of three different stress paths (conventional triaxial compression test (CTC), triaxial compression test with constant average principal stress (TC), and triaxial compression test with reduced confining pressure (RTC)) on its mechanical properties, and observes and analyzes its microstructural characteristics by scanning electron microscopy (SEM). The results show that the soil is strain hardening under the CTC path, while it is strain weak hardening under the TC and RTC paths. In the order of CTC, TC, and RTC paths, the shear strength and volume shrinkage of the soil are reduced in turn, and its deformation has both shear reduction and shear expansion plastic deformation. In the order of CTC, TC, and RTC paths, the degree of particle crushing decreases in turn and the pore content increases in turn. It is inferred that in the initial deformation of loess under loading, the soil is compressed and compacted, and its strength is improved to a certain extent. As the loading continues to increase, the deformation rate increases steadily, and the soil deformation develops gradually, which is mainly axial compression deformation, while the lateral bulging deformation is small until it is destroyed. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the beginning, and the deformation is very small. When the lateral constraint is reduced to a critical state, the structure is completely unstable, and the deformation develops rapidly in a short time until it is destroyed. This study is of great significance for reducing the occurrence of geological disasters on fill slopes in loess areas. [ABSTRACT FROM AUTHOR]

Calcareous sand has been used in reclamation for constructing artificial islands. It suffers different stress paths with varying constant incremental stress ratios (Δq/Δp'), exhibiting diverse mechanical characteristics with grain crushing. However, previous experimental studies mainly focused on conventional triaxial stress path (Δq/Δp' = 3). This study aims to investigate more unconventional shear stress paths, such as constant ratios of Δq/Δp' ( = - 0.5 , - 1.5 , 2 , where negative ratio corresponding to p'-decreasing, and vice versa) and constant p' (Δq/Δp' = infinite) on both anisotropically and isotropically consolidated calcareous sand. For comparison, the conventional triaxial tests under constant confining pressure (Δq/Δp' = 3) are also performed. For all tested samples, the grain size distribution is measured to quantify the particle breakage after loading. It is found that shear stress path plays a significant role in the mechanical of calcareous sand. Despite varying degrees of particle breakage caused by different stress paths, the relationship between the peak state friction angle with the maximum dilatancy angle and state parameter is unique. Irrespective of the consolidation/shear stress path, the peak friction angle consistently exhibits a monotonic increase with the maximum dilatancy angle, while exponentially decreases with the increasing of state parameter. Additionally, particle breakage causes a downward curvature of the critical state line (CSL) in the e–lnp' plane. However, irrespective of the stress path, the CSL remains linear when plotted in e–(p'/pa)ξ and the e–ln(p' + pr) plane. The findings are helpful for understanding the mechanical behavior and modeling of crushable calcareous sand under complex loads. [ABSTRACT FROM AUTHOR]

Small strain properties of subgrade fill material are essentially required for the accurate estimation of deformation behavior of railway subgrade. Many attentions have received on small strain properties of soils under the isotropic stress state or low shear stress level. The high level of shear stress and stress ratio induce reduction in small strain stiffness and thus present the potential challenge to the deformation stability of the subgrade. However, there is not much attempt to investigate the small strain properties under high stress ratio. This paper explores the effects of stress path and stress state on small strain stiffness Gmax and Poisson’s ratio v of heavily compacted fully weathered red mudstone (FWRM) under a broad range of stress ratio, via a series of stress-controlled triaxial and bender element tests. Three stress paths, named as constant stress ratio (SSP), constant confined pressure (VSP), constant axial stress (HSP) with stress ratio up to 33.0 were considered. Low level of shear stress slightly promotes Gmax, while a significant reduction of Gmax is triggered as the stress ratio exceeds a critical value. A unified correlation between the critical stress ratio and confined pressure is developed. The evolution of Poisson’s ratio is also described by a unified three-dimensional feature surface, which influence of stress path is identified by the location and shape of the surface. [ABSTRACT FROM AUTHOR]

This study examines the effects of fibre (0–3%) and cement (0–3%) additives on poorly graded Toyoura sand under consolidated undrained (CIU) compression and extension conditions. Compression tests revealed that dense sands exhibit increased peak strength, stiffness, and a steady decline from peak to post-peak strength. Cemented and fibre-cemented specimens demonstrated stiffer responses and strain-hardening post-peak behavior compared to pure sand. Adding fibres and cement significantly enhanced peak deviatoric stresses, while their impact under extension loading was less pronounced. Fibre and cement combinations, particularly at higher percentages, improved the strength of pure sand under extension conditions. Randomly oriented fibres increased friction angle, cohesion, and compressive strength, while cemented and fibre-cemented specimens exhibited higher secant moduli. The additives enhanced strength parameters, the slope of the critical state line, and the state parameter, with the stress ratio (q/p') rising for both peak and critical states. [ABSTRACT FROM AUTHOR]

Previous studies on the undrained deformation behavior of saturated soft clay under traffic loading usually ignored the effect of cyclic confining pressure. In the present study, a series of undrained constant confining pressure (CCP) and variable confining pressure (VCP) cyclic triaxial tests were conducted on Wenzhou soft clay through GDS cyclic triaxial test system to investigate the deformation behavior of saturated soft clay subgrade under different stress paths due to traffic loading. Special attention was paid to the effects of cyclic stress ratio (CSR) and stress path (α) on the dynamic resilient modulus as well as axial accumulated strain. The test results show that under undrained conditions, the dynamic resilient modulus decreases with the increase of CSR and α, while the axial accumulated strain increases with the increase of CSR and α. It suggests that cyclic confining pressure can improve the stiffness and restrain the axial strain accumulation of saturated soft clay under cyclic loading. Based on the test results and the existing empirical models, a dynamic resilient modulus empirical model and an axial strain accumulation model were established, respectively, which consider the influence of stress paths due to traffic loading, and can be used to calculate and analyze the long-term deformation of soft clay soil foundation under traffic loading.

Abstract Stone fill materials are widely used in engineering projects such as earth-rock dams, railways, and highway embankments. Nevertheless, they are susceptible to particle breakage, which can lead to a decline in engineering performance. A complete set of studies on crushed stone aggregates was carried out to investigate particle crushing characteristics under various stress path conditions. To quantify the amount of particle crushing, the relative particle crushing rate was utilized as an indicator. The plastic work performed during the trials was compared across different stress routes, and the relationships between particle crushing and average stress p and generalized shear stress q were investigated. In triaxial testing, the differences in particle crushing behavior under different stress routes were thoroughly examined. The results show that particle crushing is substantially lower in the modelling of a rockfill dam constructed with a core wall and subjected to reservoir water pressure pathways than in conventional triaxial tests. A clear relationship was discovered. Across several stress routes, a clear link between plastic work and the relative particle crushing rate was detected, which was successfully characterized by a power function. Notably, the contributions of different stress components to the overall plastic work varied significantly. The plastic work exerted by the generalized shear stress q accounted for a large percentage of traditional triaxial testing, although the proportion of plastic work given by p and q changed significantly in complex stress path tests. This research enhances the understanding of the particle breakage characteristics of stone fill materials under complex stress paths.

The secondary utilization of iron tailings solid waste meets the green development requirements of road construction in the new era. Currently, there is a lack of research on the equivalent confining pressure effect of fiber, the influence of complex stress paths on the mechanical properties of modified soil, and the internal damage in soil based on energy dissipation theory. The effects of different polypropylene fiber content, confining pressure, curing age, and complex stress path on the mechanical properties of fiber cement–modified iron tailings (FCIT) were investigated by triaxial tests and energy angle. Combined with the actual subgrade engineering, the stress path test is set up, and the strength index of the FCIT under different working conditions is obtained. From the thermodynamic point of view, the failure process for the FCIT is further revealed. The results show that: (1) the optimal fiber content of FCITs is 0.75%. At this time, the mechanical properties of FCIT are optimal, the strength is high, and shear failure is not easy. The fiber has the equivalent confining pressure effect, which could provide better shear performance for FCITs so that the FCIT is resistant to collapse in embankment construction; (2) the influence of multislope stress path on the secant modulus of the FCIT is worse than that of a single-slope stress path. The influence of curing age on the secant modulus of these two kinds of stress path is consistent, and the secant modulus of the FCIT at 28-day curing is 1.2 times that at 7-day curing; (3) after 7 and 28-day curing, the dissipation energy of the FCIT was consistent when the fiber content was 1%. Due to the equivalent confining pressure of the fiber, the fiber dissipation energy of the FCIT is not affected by the curing age. The total dissipated energy of the FCIT with a stress path slope of 1.5 is 5–6 times that with a stress path slope of 2.5. The total dissipated energy of the single-slope and multislope stress paths decreases with the increase in curing age. [ABSTRACT FROM AUTHOR]

Current research on rock damage in mining floors primarily focuses on the seepage‐stress coupling effect, overlooking the fact that rock masses in coal measure strata are predominantly layered. To address this gap, cyclic loading and unloading triaxial tests were conducted. Additionally, theoretical analysis, mathematical statistics, and other methods were used to investigate the damage evolution law of layered rock masses in coal measures. This investigation was carried out under the coupled effects of a specific stress path, characterized by 'stress concentration‐stress unloading‐stress recovery', and a high confined water seepage field. The results show that the compression modulus increases with the increase in confining pressure and osmotic pressure, but its increasing trend gradually slows down. Within a certain range, increasing the confining pressure and osmotic pressure helps to close rock fractures and increase stiffness. [ABSTRACT FROM AUTHOR]

The "yield-resist" combined support measure is a widely employed control measure in soft rock tunnels for controlling large deformation, particularly in high geostress conditions. For strain-softening rock masses, the strength parameters in the plastic zone are coupled with the support reaction. Due to the complexity of the interaction mechanism between yielding support and strain-softening surrounding rock, the majority of current solutions are based on the plane–strain model. However, the advancement of the tunnel is a three-dimensional problem. Therefore, the longitudinal effect is worthy of discussion when analyzing the mechanical behaviors of strain-softening rock and yielding support. A new two-stage method is proposed to describe the interaction between strain-softening rock mass and yielding support based on the generalized Zhang–Zhu (GZZ) strength criterion. Firstly, a simplified mechanical model of the yielding support structure is suggested to describe the mechanical response of the surrounding rock and support. Subsequently, a semi-analytical solution to three-dimensional ground–support interaction is proposed, taking into account the longitudinal effect. The results of the proposed solution are compared with those of a finite element simulation, and a high degree of agreement is observed. Finally, the mechanical behaviors of different yielding supports are discussed. The findings indicate that postponing the support timing by means of yielding technologies is essential, as otherwise the support would bear a very large load. The second stage of support reaction can be significantly reduced by implementing the "control-yield-resist" (CYR) support. The research offers novel insights and methodologies for investigating the three-dimensional interaction between the surrounding rock and various tunnel supports in high geostress conditions. [ABSTRACT FROM AUTHOR]

Stress path is a key factor affecting the particle breakage of calcareous sand. In this study, the effects of stress path variations on calcareous sand particle breakage were investigated through triaxial compression tests across four distinct stress paths. Additionally, the gradation evolution of calcareous sand during particle breakage was analyzed. Furthermore, the correlation between the total input energy and characteristic particle size was investigated through energy dissipation analysis. The results indicated that the relative breakage index increases gradually with an increase in the maximum deviatoric stress and final volumetric strain, irrespective of the stress path. However, the dilatancy of calcareous sand is related to the relative breakage index as well as the stress path. Notably, the relationship between the relative breakage index and the total input energy can be represented using a power function. A gradation evolution model was formulated based on the results of energy dissipation analysis, and its validity was verified. The results confirmed the model's effectiveness in predicting the particle breakage evolution in both single-gradation and continuous-gradation calcareous sand specimens, accounting for the effects of the various stress paths. [ABSTRACT FROM AUTHOR]

A rigorous analytical solution is developed for undrained cavity expansion problems in non-associated Mohr–Coulomb soil, based on a novel graphical analysis approach and on the Lagrangian description through tracking only the responses of a soil particle at the cavity surface. The mathematical difficulties involved with the flow rate calculation when the stress state lies on the corner/edge of two adjacent (Mohr–Coulomb) yield surfaces, for both cylindrical and spherical cases, are tackled by using the generalised Koiter theory for non-associated plasticity. In particular, through the unique geometrical formulation, the effective stress path pertaining to the cylindrical cavity problem can be very conveniently directly determined, and is found to consist of simple, piecewise straight lines in the deviatoric stress plane with the orientations dependent of the relative magnitude of Poisson's ratio and the friction angle. This thus renders possible the removal of the stringent intermediacy assumption for the vertical stress that is commonly adopted in previous formulations, and hence the development of a complete cylindrical cavity expansion solution in Mohr–Coulomb soil under undrained loading conditions. The stress and deformation responses of the cavity, including the typical pressure–expansion curves and limiting cavity pressure, are finally analytically obtained along with the Lagrangian form of the radial equilibrium equation in completely explicit forms. The closed-form solution provided in this paper is the first rigorous one of its kind, thus completing the analytical analysis of the cavity expansion problem with the classical Mohr–Coulomb model; this is deemed to be essential for the interpretation of in situ test results pertaining to cohesive-frictional soils. [ABSTRACT FROM AUTHOR]

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In order to reveal the influence of stress paths on the stress-strain characteristics of natural sedimentary soft soil, physical and mechanical properties, conventional triaxial and stress path tests were carried out on the undisturbed soft soils of Tianjin and Hengshui Lake. The systematical investigation was conducted on the stress-strain characteristics and influencing factors of natural sedimentary soft soil under different stress paths. The main conclusions are as follows: stress-strain characteristics of soft soil are changed by the variation of the structural and bonding characteristics. Under the drainage shear, Tianjin soft soil with weaker structural and bonding characteristics reveals the strain hardening characteristics similar to remolded soil, while Hengshui Lake soft soil with stronger structural and bonding characteristics exhibits the strain softening characteristics of undisturbed soil. Due to the presence of structural and bonding characteristics, natural sedimentary soft soil can hear tensile stress and show expansion deformation. The content of clay particles and colloidal particles of Hengshui Lake soft soil are higher than Tianjin soft soil, exhibiting obvious bonding characteristics, higher shear strength and more significant expansion deformation under the axial unloading stress paths. The conclusions can provide reference for the design calculation and constitutive model of natural sedimentary soft soil. [ABSTRACT FROM AUTHOR]

In order to explore the applicability of the hardening soil constitutive model for numerical analysis of soft soil underground engineering in the Pearl River Delta region, and based on four different stress path triaxial tests, the mechanical properties and variation of constitutive model parameters of hardening soil were analyzed for the typical silty soil in this region. Research results have shown that lateral unloading and drainage conditions have significantly impact on the partial parameters of constitutive model, such as the strength parameters of c' and φ ', the stiffness parameters such as Eref 50, E ref ur and m, but the impact on the failure ratio Rf is relatively small. For the consolidated undrained lateral unloading condition, the main parameters of the constitutive model for typical silty soil in the Pearl River Delta region are shown as the reference secant modulus Eref 50 is 2.34 MPa, with reference to tangent modulus Eref oed is 1.59 MPa, with reference to the loading unloading modulus E ref ur is 11.67 MPa, with a failure stress ratio of Rf is 0.98, and the power exponent m related to stiffness stress level is 1.84; Among them: Eref 50 is 1.47 times of Eref oed, E ref ur is 7.34 times of Eref oed. The practice of a deep foundation pit of soft soil in the Pearl River Delta has proven that the constitutive model of hardening soil is suitable for simulating the mechanical properties of soft soil in this region. [ABSTRACT FROM AUTHOR]

This study conducted a cyclic loading–unloading (CLU) test on broken coal samples with three particle sizes (0–5 mm, 5–10 mm, and 10–15 mm) under four different stress path conditions. The evolution permeability characteristics of samples during repeated compaction were investigated. The dimensionless permeability and the porosity variation law were obtained under CLU conditions. The permeability loss difference (PID) index was defined, and the permeability damage was analyzed. The permeability evolution model under mining influence conditions was constructed. Results indicate that an increase in maximum loading stress (MLS) exacerbates the seepage network channel destruction of broken coal. As the MLS increases, there is a decrease in permeability recovery rate during the unloading stage and an increase in permeability loss rate during the loading stage. The first stress loading results in a rapid reduction in the porosity, while the subsequent CLU has a minor impact on porosity variation. Results of the PID analysis show positive correlation between the permeability attenuation degree and the MLS. Furthermore, both the permeability recovery rate and the permeability loss rate increase with increase in particle size, indicating that the effects of pressure relief and stress recovery have a greater influence on larger particles. Theoretical permeability values of model were verified with test results, and their high consistency proves the permeability evolution model's feasibility. The results will help provide theoretical guidance for gas extraction in goaf. [ABSTRACT FROM AUTHOR]

This study uses a hollow cylindrical apparatus to explore the effects of principal stress rotation on saturated silty soil, focusing on the static characteristics affected by cycle counts, intermediate principal stress coefficient (b), and rotational angle (a). As the principal stress axis rotates, strain fluctuations decrease and stabilize, with consistent strain trends observed across various b values. Anisotropy appears around 60° during the first cycle, significantly impacting radial strain while torsional shear strain remains less affected. Distinct hysteresis loops in shear stress-strain relationships reveal initial unclosed forms due to plastic strain accumulation, transitioning to closed loops with increased cycling, and showing noticeable variations in shear stiffness. As b values rise, stiffness degrades, influenced by both b values and a angles. Volumetric strain shows a linear increase for two cycles before decelerating, with b=1 demonstrating anisotropy at 60° and other values at 90°. Minimal contraction occurs for b=0 after the tenth cycle, while b=0.5 sees significant volume reduction. Higher b values also reduce non-coaxial behavior, linked to the initial principal stress orientation. These findings enhance the understanding of silty soil behavior under stress rotation, offering valuable insights for geotechnical engineering applications. [ABSTRACT FROM AUTHOR]

In recent years, geological disasters on loess fill slopes have occurred from time to time, which has attracted widespread attention. In order to deeply understand its deformation and failure laws and promote the disaster prevention and mitigation work, this paper takes remolded loess as the research object, systematically explores the effects of three different stress paths (conventional triaxial compression test (CTC), triaxial compression test with constant average principal stress (TC), and triaxial compression test with reduced confining pressure (RTC)) on its mechanical properties, and observes and analyzes its microstructural characteristics by scanning electron microscopy (SEM). The results show that the soil is strain hardening under the CTC path, while it is strain weak hardening under the TC and RTC paths. In the order of CTC, TC, and RTC paths, the shear strength and volume shrinkage of the soil are reduced in turn, and its deformation has both shear reduction and shear expansion plastic deformation. In the order of CTC, TC, and RTC paths, the degree of particle crushing decreases in turn and the pore content increases in turn. It is inferred that in the initial deformation of loess under loading, the soil is compressed and compacted, and its strength is improved to a certain extent. As the loading continues to increase, the deformation rate increases steadily, and the soil deformation develops gradually, which is mainly axial compression deformation, while the lateral bulging deformation is small until it is destroyed. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the beginning, and the deformation is very small. When the lateral constraint is reduced to a critical state, the structure is completely unstable, and the deformation develops rapidly in a short time until it is destroyed. This study is of great significance for reducing the occurrence of geological disasters on fill slopes in loess areas.

Despite its vital importance to the contemporary economy, some drawbacks are mainly associated with waste derived from mining activity. This waste consists of tailings that are hydraulically disposed of in large impoundments, the tailings dams. As the dams are enlarged to accommodate higher amounts of materials, the stress states at which the deposited tailings are submitted change. This may be a concern for the stability of such structures once the geotechnical behavior of this material may be complex and challenging to predict, considering the existing approaches. Thus, the present study concerns the mechanical response of bauxite tailings under a wide span of stresses, ranging from 25 kPa to 4000 kPa. One-dimensional compression tests and isotropically drained and undrained triaxial tests were carried out on intact and remolded samples of the bauxite tailings. The after-shearing grain size distribution was characterized via sedimentation analysis. The results have shown a stress-dependency of the critical state friction angle for the intact material, which may be related to fabric alterations derived from structure deterioration and particle breakage. Overall, this research provides valuable insights into the response of structured and de-structured bauxite tailings, which are helpful for future constitutive modeling of such material.

The mechanical properties of granular soils are significantly influenced by stress paths and particle breakage. In this study, a four-modulus incremental nonlinear model that incorporates the effects of the stress path and particle breakage was established based on an analysis of triaxial compression test results conducted on calcareous sands subjected to varying stress paths. A mathematical expression for this model and the process of determining its parameters was proposed. Subsequently, the model was experimentally verified. Our findings revealed that the isotropic compression consolidation volumetric strain modulus exhibited a curvilinear relationship with the average effective principal stress, whereas it demonstrated a linear correlation with the relative breakage index. Furthermore, a four-parameter nonlinear model was constructed, integrating the dilatancy equation to consider stress path effects and establishing a functional relationship between the stress ratio and shear strain. By comparing the experimental results with the calculated results for calcareous sands and rockfill materials, the model effectively simulated the stress ratio-axial strain behavior of granular soils under different stress paths. However, it failed to fully capture the volumetric strain-axial strain characteristics of granular soils after reaching the peak stress ratio. Therefore, further research is necessary to develop a more comprehensive correction method for incremental nonlinear models. [ABSTRACT FROM AUTHOR]

Coral sand is known to have stress path dependence and fragility. In this research, a series of drained triaxial tests were conducted to explore stress path effects on the mechanical and particle breakage characteristics of coral sands. Several mechanical characteristics, such as critical state, strength, and dilatancy characteristics were studied. The results revealed that the dilatancy behaviors, stress-strain responses, and crushing of coral sands were strongly affected by consolidation stress and stress path. The critical state lines of coral sands were straight in p'-q space and e-(p'/Pa)0.44 plane regardless of stress path. Based on these characteristics, a dilatancy equation was derived and validated through test results. The developed dilatancy equation could predict the dilatancy relationships of coral sands under various stress paths. [ABSTRACT FROM AUTHOR]

Despite its vital importance to the contemporary economy, some drawbacks are mainly associated with waste derived from mining activity. This waste consists of tailings that are hydraulically disposed of in large impoundments, the tailings dams. As the dams are enlarged to accommodate higher amounts of materials, the stress states at which the deposited tailings are submitted change. This may be a concern for the stability of such structures once the geotechnical behavior of this material may be complex and challenging to predict, considering the existing approaches. Thus, the present study concerns the mechanical response of bauxite tailings under a wide span of stresses, ranging from 25 kPa to 4000 kPa. One-dimensional compression tests and isotropically drained and undrained triaxial tests were carried out on intact and remolded samples of the bauxite tailings. The after-shearing grain size distribution was characterized via sedimentation analysis. The results have shown a stress-dependency of the critical state friction angle for the intact material, which may be related to fabric alterations derived from structure deterioration and particle breakage. Overall, this research provides valuable insights into the response of structured and de-structured bauxite tailings, which are helpful for future constitutive modeling of such material. [ABSTRACT FROM AUTHOR]

A shear‐transformation‐zone (STZ) model is proposed for time‐dependent behaviours of clay, in which the viscoplastic deformation is described by the evolution of a temperature‐like state variable. The model is featured by rate‐dependent dilatancy and a unique critical state stress ratio. In its present form, it has nine parameters, most of which can be handily calibrated, and can predict the rate‐dependent undrained shear strength, primary, and secondary creep, as well as stress relaxation for normally consolidated clay under complex stress paths using a single set of parameters. The capabilities of the model have been verified by available experimental results on five different clays. [ABSTRACT FROM AUTHOR]

Geomechanics tests and theories have confirmed that soil exhibits noncoaxial behavior under the rotation of principal stress. A series of hollow torsional shear tests were conducted in this study on fiber-reinforced soil using a hollow cylinder apparatus (GDS-SSHCA). Factors including deviatoric stress, q, the coefficient of intermediate principal stress, b, and fiber content, FC, potentially influencing the shear strain, volumetric strain, and noncoaxiality of fiber-reinforced aeolian soil were evaluated in the tests. The results revealed that both shear and volumetric strains of the fiber-reinforced aeolian soil samples increased as deviatoric stress and the coefficient of intermediate principal stress increased. However, the impact of fiber content initially decreased and then increased. Maximum shear strain and volume strain values were measured at 0.44% and 0.517%, respectively, with an optimum soil content of 3‰. During pure principal stress axis rotation, the fiber-reinforced aeolian soil exhibited noncoaxial characteristics and a fluctuating noncoaxial angle. The average noncoaxial angle decreased to a minimum of 23.59° as the deviatoric stress, the coefficient of intermediate principal stress, and the fiber content increased. Based on the range-analysis method, deviatoric stress was found to have the most pronounced effect on the average noncoaxial angle, followed by the coefficient of the intermediate principal stress and the fiber content. A shear strain prediction equation considering noncoaxiality under pure principal stress axis rotation was established and verified against previously published data. The equation's accuracy was further confirmed through comparison with monitoring data. These findings may serve as a valuable theoretical reference for preventing geological engineering disasters. [ABSTRACT FROM AUTHOR]

Results of torsional shear hollow cylinder (TSHC) tests carried out on a reconstituted sand maintaining a constant direction of major principal stress relative to the vertical axis (α) and intermediate principal stress ratio (b) during shearing are presented. Tests were undertaken following the constant shear drained (CSD) stress path, which simulates stress conditions under a rising phreatic surface. The test programme was complemented by undrained TSHC tests to provide further insight regarding the behaviour of the sand when sheared under a range of α values. Various reconstitution methods (i.e. moist tamped (MT), dry pluviated (DP) and wet pluviated (WP)) were included to examine the effects of fabric on CSD triggering. Only MT and DP specimens could be prepared loose enough to exhibit liquefaction behaviour; hence the focus of this study was on these preparation methods. The programme indicated that the instability stress ratio (ηIL) under the CSD stress paths decreases as α increases, suggesting that cross-anisotropy strongly influences the shearing behaviour of sands under this trigger mechanism. In addition, the DP sand showed a greater decrease of ηIL with increasing α compared to the MT sand, consistent with other studies examining the effect of fabric and preparation methods on inherent anisotropy. The results of this study suggest that ignoring the effect of cross-anisotropy on the CSD trigger mechanism will lead to unconservative slope stability assessments. [ABSTRACT FROM AUTHOR]

Underground soil in coastal areas is often affected by various dynamic effects such as earthquakes, construction, and waves. In order to study the influence of stress path on the dynamic characteristics of silty clay, resonance column tests were conducted on undisturbed samples of silty clay at different depths in the Yancheng area under cyclic stress paths. The results show that stress history has a significant impact on the response of soil dynamic parameters, and there is a significant difference between the maximum dynamic shear modulus Gmax and dynamic shear modulus G of the soil between loading and unloading paths; When the confining pressure is between 0~80 kPa, Gmax rapidly increases and variability decreases; The geological age and burial depth play an important role in the variation of soil dynamic parameters. As the burial depth increases, the difference between Gmax under different stress paths and G when the confining pressure changes continuously expands. When the geological age changes, G shows a significant increase; Propose a fitting relationship between the maximum dynamic shear modulus and confining pressure based on experiments, and provide fitting results for silty clay with different stress histories, providing reference for engineering design and construction in Yancheng and related coastal areas. [ABSTRACT FROM AUTHOR]

Both the magnitude and direction of principal stress will change during roadway excavation, while the direction often ignored in traditional rock mechanics, leads to large deformation of surrounding rock. To investigate the deformation and failure modes under principal stress rotation during roadway excavation, a numerical calculation model was established to study the evolution law of the magnitude and direction of the principal stress in the surrounding rock during excavation process. The results reveal significant disturbances in principal stress within a range of three times the roadway diameter, with a 1.66-fold increase in the major principal stress and a 41.61° rotation angle change. Then, hollow torsional shear tests were conducted under the assumption of in-plane principal stress rotation. Key parameters such as spherical stress (p), generalized deviatoric stress (qJ), intermediate principal stress coefficient (b), and principal stress rotation angles (α, β, γ) were controlled in the tests. Experimental results indicate that the strong disturbance zone is primarily influenced by deviatoric stress, intermediate principal stress coefficient, and principal stress direction. The major failure modes observed include main shear and torsional shear cracks, with larger principal stress rotation angles leading to more significant torsional shear cracking. The roof exhibits the most severe cracking, while the floor shows the least. These findings underscore the importance of considering changes in principal stress during the design and construction of roadway excavations to prevent instability and cracking. [ABSTRACT FROM AUTHOR]

This paper aims to reveal the inherent interaction mechanism between stress path and dilatancy equation for rockfill materials. The stress-strain response relationships among isotropic compression tests, conventional triaxial tests, and constant p test is analyzed. By employing theoretical analysis and experimental verification methods, a new method for constructing dilatancy equation is proposed within the framework of an elastoplastic constitutive model and was validated through triaxial tests of rockfill materials under various stress paths. The prediction results show that the proposed dilatancy equation can capture stress path effect, especially the effect for constant stress ratio loading paths. The conclusion reveals the importance of isotropic compression tests and constant p-tests. It is suggested to use these two types of tests when establishing dilatancy equation and constitutive model that consider stress path effect. [ABSTRACT FROM AUTHOR]

• The optimal plastic content for MSW is 6–9 %. • Stress path influences the optimal plastic content. • The influence patterns of particle size distribution on MSW. • Traditional well-graded criteria are unsuitable for MSW. Plastics within municipal solid waste (MSW) are non-degradable. As MSW continues to degrade, the relative content of plastics rises, and particle gradation may also change. Moreover, throughout the landfilling process, MSW is subjected to various stress conditions, potentially influencing its mechanical properties. This study explored the effects of varying plastic contents, different particle gradations, and distinct stress paths on the mechanical properties of MSW, and consolidated drained triaxial tests of 42 groups of reconstituted MSW specimens were conducted. The results showed that there was an optimal plastic content of 6–9 % for MSW, where the shear strength of MSW was higher than that of MSW with other plastic contents. When the stress path changed from TC45 to TC72, the optimal plastic content of MSW changed from 6 % to 9 %. As the plastic content increased, both the cohesion and internal friction angle of the MSW initially increased, then subsequently decreased. The impact of plastic content on cohesion was more pronounced than on the internal friction angle, especially at larger strains. Under various stress paths, MSW with distinct particle size distributions demonstrated diverse stress–strain behaviors. Traditional criteria for evaluating well-graded conditions in soils are not suitable for MSW. The effect of gradation on the cohesion of MSW is essentially due to the predominant role of fiber content; the relationship between gradation and the internal friction angle in MSW is complex and correlates closely with the content of both coarse and fine particles, as well as fibers. This study serves as an essential reference for predicting deformations in landfills and analyzing the stability of landfill slopes. [ABSTRACT FROM AUTHOR]

Viscoelastic plastic solutions for tunnel excavation in strain-softening rock mass and tunnel-rock interaction are proposed based on the Mohr-Coulomb and the Generalized Zhang-Zhu (GZZ) strength criterion considering stress path. The solutions are verified by numerical simulations, results show that the theoretical solutions are close to the simulated data. The evolutions of rock stresses, strains, displacements and support pressure were investigated and the influences of residual strength parameter, support stiffness, support timing, initial support pressure and viscosity coefficient on the rock deformation and the support pressure are discussed by proposed solution. It is found that strain-softening results in large deformation and high support pressure, with stiffer support and a larger viscosity coefficient contributing to even greater support pressure. Ductile support is recommended at the first stage to release the energy and reduce the support pressure by allowing a relatively large deformation. The support pressure, especially the additional support pressure at the second stage will be much smaller if a higher initial support pressure is applied at the first stage. This can not only control the displacement rate of surrounding rock and improve the tunnel stability at the first stage by exerting sufficient support pressure immediately after tunnel excavation, but also greatly reduce the pressure acted on permanent support and improve the structure stability at the second stage. Therefore, to avoid the instability of support structure, ductile support, which could not only deform continuously but also provide sufficient high support pressure, is recommended at the first stage. [ABSTRACT FROM AUTHOR]

Stress path change has a great relationship with the effect of deformation and strength of rock. However, the underground rock body is in the engineering environment where the stress field, seepage field, and other fields are coupled to change, the law of fluid flow in the rock body is complex and variable. The change in the stress field has an important effect on the seepage characteristics of rock body; therefore, it is necessary to study the pattern of rock permeability evolution pattern by different stress paths. This study is based on the study of limestone, conducting triaxial unloading seepage mechanics experiments, the evolution of permeability properties of limestone specimens was analyzed based on the test results. The results show that in the conventional triaxial loading seepage test, the permeability of the limestone decreases before the rock stress reaches the peak intensity and increases after that. Increasing axial pressure unloading surrounding pressure compression section, permeability loss rate and effective stress are in line with the changing law of Gaussian distribution function. Under the action of constant axial pressure unloading surrounding pressure, with the increase in unloading amount, the permeability rate of change appears to increase slowly, and in the late stage of unloading section, the permeability rate of change appears to surge. Unloading section permeability change rate and cumulative unloading amount are in line with the law of change of the exponential function. Creep unloading pressure seepage test found that unloading pressure stage strain-time and permeability-time evolution characteristics are in line with the exponential rule of change. The experimental results of this study can provide an important experimental and theoretical basis for the permeability analysis of low-permeability rock body under complex stress conditions in underground engineering.

Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation. In this study, to reveal the mechanical parameters of deep surrounding rock under different stress paths, a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed, and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied, including the deformation modulus, elastic deformation increment ratios, fracture degree, cohesion and internal friction angle. Additionally, stress path coefficient was defined to characterize different stress paths, and the functional relationships among the stress path coefficient, rock fracture degree difference coefficient, cohesion and internal friction angle were obtained. The results show that during the true triaxial cyclic loading and unloading process, the deformation modulus and cohesion gradually decrease, while the internal friction angle gradually increases with increasing equivalent crack strain. The stress path coefficient is exponentially related to the rock fracture degree difference coefficient. As the stress path coefficient increases, the degrees of cohesion weakening and internal friction angle strengthening decrease linearly. During cyclic loading and unloading under true triaxial principal stress direction interchange, the direction of crack development changes, and the deformation modulus increases, while the cohesion and internal friction angle decrease slightly, indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks. Finally, the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.

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.

Although end-bearing energy pile foundations subjected to symmetrical thermal cycles have been extensively studied in the laboratory and in the field, the mechanisms underlying the thermo-hydro-mechanical (THM) interactions in floating energy pile groups and rafts, especially when subjected to asymmetrical thermal loads, are not well understood. In this study, an advanced thermo-mechanical bounding surface model was implemented in finite-element (FE) code to investigate the THM interactions of a two-by-two floating energy pile group and pile raft, focusing on asymmetrical thermal cycles. Computed results are compared with published centrifuge model test results in soft clay. It is revealed that the irreversible volumetric contraction of the soil adjacent to the energy piles accumulates with each thermal cycle, resulting in a decrease in the horizontal stress and hence shaft resistance of the floating piles. During thermal cycles, the stress states of the soil around the energy pile shaft and the soil beneath the pile toe approach the critical state line along different paths. The induced temperature in the soil adjacent to the non-energy pile (NEP) is 5°C lower than that in the soil at the energy pile EP1, which is flanked by the other two energy piles EP2 and EP3. Consequently, the induced excess pore pressure in the soil at the NEP is approximately 20% smaller than that in the soil at EP1. The irreversible volumetric soil contraction at the NEP is about half that at EP1, resulting in approximately 45% less toe settlement. The thermally induced ratcheting settlements of the head and toe of the NEP are less than those of the energy piles, resulting in unacceptable ratcheting tilting of the floating energy pile group. However, the excessive tilting can be reduced by the use of a pile raft. [ABSTRACT FROM AUTHOR]

The mechanical properties of rockfill materials are not only influenced by microscopic factors such as particle morphology and gradation, but also closely related to different loading stress paths. It is of great significance to study the microscopic mechanical properties of rockfill materials under different stress paths for revealing the macroscopic mechanical properties as well as the microscopic deformation and failure mechanisms of rockfill materials. In this paper, based on the results of triaxial tests, a series of numerical triaxial simulation tests under different stress paths were carried out using the discrete element particle flow method, and the deformation, strength change rules, and fine structure evolution mechanism under three stress paths were explored. The results demonstrated that there were significant differences in the effects of stress paths on the stress–strain and strain-volume change characteristics of the rockfill materials. Stress paths exhibited little effect on the strength characteristics. The anisotropy of strong contact number and strong contact force was the microscopic source of macroscopic strength. The contact situation between the particles was the main microscopic factor affecting the macroscopic deformation. The intrinsic mechanism of macroscopic deformation properties could be revealed by the average coordination number and porosity. The stress path affected the growth rate of the number of bond failures and the total number of failures. The relationship between macroscopic mechanical properties and microstructural evolution under different stress paths was also discussed. The findings can provide meaningful insights into the deformation control and stability analysis of rockfill engineering. [ABSTRACT FROM AUTHOR]

This study employs the Discrete Element Method (DEM) to investigate the influence of initial fabric anisotropy on the cyclic liquefaction behavior of granular soils. Static and cyclic biaxial compression tests under undrained condition are simulated using two-dimensional elongated sharp-angled particles. Initial fabric anisotropy is introduced by considering a pre-defined inclined angle of elongated particles inside the sample. Results from the simulations reveal that varying fabric anisotropy affects the stress paths, resulting in a significant decrease in the maximum internal friction angle; however, the critical state internal friction angle is less affected. When subjected to cyclic loading, anisotropic samples exhibit distinct behavior influenced by initial fabric anisotropy. Comparison of the results with those of limited experiments in the literature confirms the simulations validity. The effective confining stress diminishes, leading to progressive liquefaction. The number of cycles required for initial liquefaction varies due to inherent anisotropy, and fabric anisotropy causes a shift in the concentration of compression or extension strains within the samples. Lower values of cyclic stress ratio amplifies the influence of inherent anisotropy on excess pore water pressure ratios. In addition to stress approach, the strain-based liquefaction resistance is also investigated by defining double amplitude strain values. It is found that when the double strain level is relatively small, the impact of inherent anisotropy becomes more noticeable. This study enhances the understanding of the role of initial fabric anisotropy in cyclic liquefaction behavior and provides insights for engineering design and mitigation strategies in seismic-prone areas. [ABSTRACT FROM AUTHOR]

Stress and deformation analysis of a cavity in an infinite/finite medium is a fundamental applied mechanics problem of interest in multiple physics and engineering disciplines. This paper develops a complete semianalytical solution for the cylindrical cavity expansion in nonassociated Mohr–Coulomb materials, by using the graphical approach and Lagrangian formulation of the cavity boundary value problem (through tracing the responses of a single material point at the cavity wall). The novelty of the new solution framework lies not only in the relaxation of the stringent intermediacy assumption for the vertical stress as usually adopted in the previous analyses, but also in the comprehensive consideration of nonhydrostatic initial stress conditions via arbitrary values of K0 (the coefficient of earth pressure at rest defined as the ratio between the horizontal and vertical initial stresses). The essence of the so-called graphical method, i.e., the unique geometrical analysis and tracking of the deviatoric stress trajectory, is fulfilled by leveraging the deformation requirement that during cavity expansion the progressive development of the radial and tangential strains must maintain to be compressive and tensile, respectively. With the incorporation of the radial equilibrium condition, the problem is formulated to solve a single first-order differential equation for the internal cavity pressure with respect to a pivotal auxiliary variable, for all the distinct scenarios of K0 being covered. Some selected results are presented for the calculated cavity pressure-expansion curve and limit cavity pressure through an example analysis. The definitive semianalytical solution proposed will be not only substantially advancing the current state of knowledge on the fundamental cavity expansion theory, but also able to serve as a unique benchmark for truly verifying the correctness and capability of the classical cornered Mohr–Coulomb constitutive model built in commercial finite element programs. [ABSTRACT FROM AUTHOR]

• Analytical solution is developed for deeply tunnelling in viscoelastic-plastic geomaterials, considering actual loading path. • The solutions are compared with the previous ones without considering stress path, and the difference is identified. • The influence of supporting time etc. on the time-dependent responses of surrounding rock is investigated. The rock rheology and time process of tunnel construction make the mechanical responses of rock a function of time and are closely related to the loading path, however, these factors are not properly or correctly considered in analytical studies. The analytical study for deep tunnels in rheological rock is performed in this study, strictly taking into account the viscoelastic‒plastic characteristic of surrounding rocks and the actual loading path during excavation and supporting stages. The plane-strain problem of a circular tunnel in infinite plane under hydraulic far-field stress is simplified, with the time-dependent supporting pressure exerted at a specific time to consider the effect of delay installation of yielding support. The solving procedure as well as the time-dependent analytical solution of displacement, stress, and plastic radius in the excavation and supporting stages are presented in detail when the rocks satisfy the Unified strength theory and perfect plasticity. The analytical solutions agree very well with the numerical results, where the time procedure of tunnel excavation and support is simulated in the numerical model. Furthermore, the proposed solution can predict well the long-term deformation of the Shangxinzhai tunnel, which validates its applicability in real engineering. It is found that the tunnel deformation is underestimated if the unloading stage is not correctly considered. Based on the analytical solution, the influence of the supporting time, start time of the yielding stage and viscosity coefficient on the time dependence of tunnel convergence and stresses is investigated. [ABSTRACT FROM AUTHOR]

The use of natural river silt treated as a 'waste material' has become the focus of research in the Yellow River flooded area, especially in the field of highway engineering. It is therefore of great significance to study the deformation and stiffness degradation of Yellow River silt (YRS) under long-term cyclic loads. To this end, a series of undrained cyclic triaxial tests on YRS for a large number of cycles (10 000) was carried out using a triaxial apparatus and the effects of confining pressure and cyclic stress ratio on the resilient strain of the YRS were explored. The critical cyclic stress and the critical cyclic stress ratio between the plastic shakedown state and incremental collapse state of the YRS were determined, and the modulus-softening behaviour of the YRS was assessed. The results of this study not only provide theoretical support for the long-term engineering performance of YRS, but also provide theoretical guidance for the cyclic response of all similar types of subgrade soils. [ABSTRACT FROM AUTHOR]

Abstract The laws of acoustic emission (AE) before and during rock failure are different under different stress states. In this article, a new multi-functional true triaxial geophysical (TTG) apparatus was applied to analyze the AE law of sandstone under different stress paths. The results show that (1) with the increase of Lode angle, the tensile fractures in the sandstone increase initially, followed by a decrease. The number of AE decreases initially, followed by an increase, while the average energy of AE signal increases initially, followed by a decrease. (2) During the loading process, the IB values of rock can be divided into wave type, band type and mixed type, which represent crack propagation process driven by external force, self-driving and mixed driving. It can provide a basis for early warning of underground engineering construction disasters. (3) The variation characteristics of RA and AF in rock failure process show the corresponding relationship with IB value. The RA value corresponding to the IB value of band, wave and distribution type distribution mainly concentrated around 0.05, 0.03 and widely distributed, respectively. According to the value of RA, the types of cracks show different characteristics under different driving forces. (4) With the increase of Lode angle, the failure types of rocks change from single oblique fracture (− 30°) to double-X-type fracture (10°), and finally changes to single-X-type fracture when Lode angle is 30°. The fracture angle of rock decreases initially, followed by an increase with the increase of Lode angle. Therefore, it is important to explore the AE law of rock failure process under different stress states for the early warning of underground engineering construction disasters, and can provide a guidance for the application of human underground space.