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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]

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 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]

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]

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.

Accurately predicting stress-strain characteristics is crucial to ensuring the regulated capacity and controlled deformation of the tubes during and after construction. However, research on the shear strength of geotextile tubes under surcharge loading, especially after dewatering, is insufficient. This study proposes an analytical model with a Stress-State Boundary (SSB) and Yield Function to comprehensively describe the stress-strain behavior of Load-Bearing Geotextile Tubes (LGTs). The SSB is designed to predict the initial state of stress in the infill soil prior to load application, while the Yield Function is formulated to express the shear stress path experienced by the LGT before fabric failure. The model considers various factors that affect LGT behavior, including diverse soil mechanical parameters, nonlinear fabric stiffness, initial tension due to self-weight and principal stress axes rotation. Results show that a decrease in Poisson's ratio corresponds to an increase in failure stress. Moreover, it was demonstrated that the axial failure strain can be influenced by the geotextile linear or nonlinear behavior. Notably, the study highlights that tube height and inclination angle significantly affect the geotextile's confining effect. Beyond theoretical contributions, the analytical model serves as a valuable tool for optimizing geotextile tube design and execution, contributing to project success and longevity through enhanced structural stability. • Stress-Strain Model of a Large Geotextile Tube capable of accommodating various soil and encasing fabric parameters. • Soil compressibility and non-linear seam effects influence the stress experienced by the soil at various axial strain levels. • Stress-state boundary predicts stresses during consolidation, and yield function characterizes stress paths during loading. [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.

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]

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]

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]

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]

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]

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]

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]

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]

• 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]

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.

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.

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]

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]

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]

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]

• 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.

Fault reactivations induced by deep excavation can pose significant challenges to underground construction or resource extraction. Laboratory experiments on rock faults demonstrate that unloading‐induced fault reactivations obey the Coulomb failure criterion derived from loading‐induced events. However, the effect of stress path during unloading on the failure criterion and rupture dynamics of fault reactivations remains poorly understood. Here, we present findings from a series of laboratory experiments aimed at elucidating the effect of the unloading path on the failure criterion and rupture dynamics of fault reactivations. We conducted experiments under various stress conditions, examining two cases of unloading paths. In Case I, we unloaded the minimum principal stress, while in Case II, the maximum principal stress was unloaded. Strain gauges and high‐speed photography were employed to capture the transient dynamic rupture process. Our investigations have yielded new insights into the effect of unloading path on the rupture dynamics when the fault is reactivated. In Case I, we observed fault reactivations resembling those loading‐induced events characterized by forward sliding. Conversely, in Case II, fault reactivations associated with stress reversal produce mild reversed sliding with lower stress drop and rupture velocity. Furthermore, we find that there is a remarkable reduction in static friction for reversed sliding, indicating that the failure criterion for fault reactivation is influenced by the stress path. We demonstrate that enhanced stress heterogeneity, caused by stress reversal, serves as a mechanism for reduced static friction. These findings contribute to our understanding of the mechanisms underlying fault reactivations, particularly those involving reversed sliding. Plain Language Summary: It is known that underground excavation, accompanied by stress release, can trigger fault reactivation, resulting in induced earthquakes. Understanding how unloading affects the activation and rupture dynamics of these induced events is crucial. To investigate the role of unloading path, we conducted laboratory experiments to simulate unloading‐induced fault reactivation on analog material containing a fault. Loadings are applied biaxially at the boundary. We observed that unloading the minimum principal stress (i.e., reducing the minimum loading) could reactivate the fault, generating forward sliding resembling loading‐induced rupture events. Conversely, unloading the maximum principal stress (i.e., reducing the maximum loading) induces reversed sliding, featuring smaller stress drop, coseismic slip, and rupture speed compared to forward sliding. Moreover, the static friction coefficient is reduced prior to reversed sliding. We also found that enhanced stress heterogeneity prior to unloading‐induced reversed sliding can account for the difference in static friction coefficient. Therefore, it is necessary to incorporate the effect of loading path into the studies of fault reactivation. Key Points: Rupture process of unloading‐induced fault reactivation is dictated by the initial stress state and stress pathThe static friction of fault is reduced for the unloading‐induced reversed slidingEnhanced stress heterogeneity caused by stress reversal contributes to reduced static friction [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Loading and unloading effects are common in all kinds of geotechnical engineering. In order to study the mechanical response and damage evolution law of rock mass loading and unloading under different stress paths, the damage variable function of the bond was introduced into the traditional bond-based peridynamics constitutive model to reflect the nonlinear stage of strain hardening and then strain softening in the stress-strain curve of rock materials. The mechanics and damage evolution of fine sandstone under different loading and unloading paths were studied by using the improved bond-based peridynamics model and the laboratory loading and unloading test. The results show that the improved bond-based peridynamics constitutive model can simulate the mechanical properties of strain hardening and then strain softening of rock materials and the mechanical response and damage development trend under different stress paths. Under the conventional triaxial path, the compressive strength and confining pressure of rock show a strict positive correlation. The defined damage value can intuitively compare the damage development of rock under different loading and unloading paths and conventional triaxial compression. Compared with conventional triaxial compression, the unloading path speeds up the failure of rock materials, and the damage degree of ascending axial pressure > constant axial pressure > unloading axial pressure. [ABSTRACT FROM AUTHOR]

Causal mechanisms for fluid injection-induced seismicity are characterised by various stress paths to drive slippage of underlying fractures. Investigation into the role of stress paths on the fracture slip behaviour and seismic response is crucial for understanding causal mechanisms for induced seismicity. In this work, novel experimental stress and pressure paths were proposed to induce fracture slip in a fashion that decouples fracture normal and shear stresses, whilst maintaining the same rate to approach slippage (the same Coulomb stress change rate). Laboratory experiments were carried out on a shale sample to simulate slippage along a pre-existing fracture under three fluid injection-related stress and pressure paths, i.e. pore pressure elevation, fracture normal stress relaxation, and fracture shear stress increase. Seismic stable fracture slip characterised by frictional strengthening occurred in these experiments, and the time-varying friction of the fracture was reasonably described by the rate-and-state friction law. The pore pressure elevation and fracture normal stress relaxation paths at the same stressing rate caused similar fracture slip and seismicity behaviour, and can be considered to be equivalent. Results have shown a transition from quasi-static to dynamic fracture slip under both fracture effective normal stress relaxation paths, but not under the fracture shear stress increase path. This indicates that the fracture effective normal stress relaxation tends to cause accelerating slip, whilst the fracture shear stress increase initiates prolonged gradual slip. Accumulative seismic moment scales linearly with fracture slip duration, which implies that fracture shear stress increase causes larger seismic moment than fracture effective normal stress relaxation paths. Highlights: Novel stress paths that isolate normal and shear stresses under the same Coulomb stress change rate are designed to promote fracture slip. Fracture effective normal stress relaxation is more inclined to promote slip acceleration than fracture shear stress increase. Seismic moment scales linearly with slip duration, and shear stress increase causes larger moment than effective normal stress relaxation. [ABSTRACT FROM AUTHOR]

Coal and gas outburst is a type of coal mine dynamic disaster with complex causes and serious consequences. In China, the number and scale of outburst disasters are among the highest in the world. It is an inevitable stage for outburst that the mechanical instability of the combination of intact coal and tectonic coal (CICTC) in strata. The dip angle of the interface has an important influence on the instability of CICTC-containing gas. To further understand the instability process of CICTC, the uncoordinated deformation of CICTC was defined. According to this, three strain conditions were delimited. The variations of stress under three strain conditions were analyzed, the expressions of additional interfacial stress were established. Then, based on the Mohr–Coulomb criterion, the strength characteristics and failure forms were analyzed. It was found that the dip angle deflects the principal stress in the interface, and the influences of additional stresses on the value of principal stress are opposite. These two reasons make the principal stress state and instability process of the combination complicated. Finally, combined with actual parameters, the instability processes of CICTC under different stress paths and buried depths were studied. It can be found that the failures of CICTC under different stress paths were concentrated appearing in the tectonic coal body, intact coal interface, and tectonic coal interface. With the increase of buried depth, the initial maximum principal stress increases and the reduction from additional stresses to the strength of intact coal interface enhances, which makes the combination damage easily and the failure form change. The research results in this paper can provide a theoretical basis to prevent and control the outburst of the combination containing gas considering the dip angle of the interface. Highlights: The uncoordinated deformation of combination considering the dip angle was first defined. The expressions of additional interfacial stress of combination considering the dip angle were established The influences of different stress paths and buried depths for the instability of combination were discussed quantificationally. [ABSTRACT FROM AUTHOR]

The fracture of the surrounding rock in deep hard rock engineering is influenced by the stress path during excavation. Taking the stress path as the only variable, a true triaxial experimental system was used to study the loading–unloading stress path during excavation and the loading stress path with constant stress state after excavation, and combined with acoustic emission, 3D laser scanning and SEM to investigate the differential mechanisms of the two stress paths on the strength, energy storage and fracture of the rock. The results show that the strength, deformation and ultimate energy storage capacity of the rock under the loading−unloading stress path are greater than those under the loading stress path with constant stress state. Compared with the loading stress path with constant stress state, with the loading−unloading stress path, the rock fractures are more fragmented, the failure angles are slightly smaller, and the development of shear cracks is delayed, occurring closer to rock failure. This is due to the influence of the true triaxial stress state on rock fracture expansion. The changing direction and location of rock fracture expansion under the loading−unloading stress path inhibits crack penetration, which in turn delays the development of shear cracks. The effect of the stress path is influenced by the rate of loading and unloading; the greater the rate of loading and unloading of the rock is, the greater the strength and ultimate energy storage of the rock. Finally, the evolution characteristics of the tensile and shear cracks formed in the rock under the loading−unloading stress paths during excavation provide new understanding for the prevention and control of deep engineering hazards. [ABSTRACT FROM AUTHOR]

The mechanism of flow liquefaction in granular soils under drained conditions compared with that under undrained conditions is a subject of great interest. This paper discusses the diverse views in relation to the initiation of instability and the conceptual difficulties brought by the discrepancies. It is shown that the constant shear drained (CSD) stress path is not a conventional stress-controlled test, and overlooking this fact may result in misleading conclusions. The difficulties inherent in the CSD tests have resulted in different criteria for the detection of the onset of instability in experiments and thereafter to different views. Through systematic simulations for the CSD, ACU and ICU stress paths under a range of initial states, it is shown that the instability line in the stress space is state dependent, and its gradient can be well related to the state parameter defined using the critical state concepts. For a given soil, the relationship is nearly unique regardless of the CSD, ACU or ICU stress path, and the critical state concepts and the second-order work criterion work well. Theoretically, it is shown that the conditions for instability under the drained and undrained stress paths are the same, regardless of the constitutive models chosen. [ABSTRACT FROM AUTHOR]

For the rock burst disaster problems caused by unloading disturbance of deep roadway excavation, the study on the deformation and fracture mechanism of roadway surrounding rock under different unloading conditions was carried out. Taking the coal-rock combination as the object of research, the true triaxial testing machine for rock mechanics and acoustic emission monitoring system was used to carry out the unidirectional unloading test of constant axial pressure and unloading lateral pressure, explore the mechanical properties of coal-rock combination under the influence of unloading initial confining pressure and unloading rate, invert the propagation laws of different types cracks in the coal-rock combination through the acoustic emission signal characteristics, and quantify the damage of coal-rock combination during loading and unloading with the ringing count. The results showed that coal-rock combination had obvious failure characteristics of tensile and shear composite under the condition of unidirectional unloading, macroscopically the coal was dominated by shear failure and the rock was dominated by tensile failure; the increase of the unloading initial confining pressure led to aggravating the failure of coal-rock combination, and the increase of unloading rate promoted the expansion of tensile cracks along the stress unloading direction of rock samples; the change of RA–AF of acoustic emission parameter accurately described the proportion of different types cracks in the coal-rock combination, coal-rock combination mostly expanded in the form of shear cracks during the loading and unloading process, the proportion of shear cracks decreased with the increase of the unloading initial lateral stress, and the increase of unloading rate promoted the increase of the proportion of tensile cracks in the stress unloading stage, the proportion of shear cracks decreased; it was found that unloading initial lateral stress and unloading rate were the main factors affecting the damage development of coal-rock combination in unloading stage through studying the damage calibrated by acoustic emission ringing count during the loading stage; after unloading initial lateral stress exceeded 20 MPa, it basically had no effect on the damage of coal-rock combination in unloading stage. The research results could provide reference for the occurrence mechanism and disaster prevention of rock burst in deep roadway excavation.

The disposal of mining tailings has increasingly focused on the use of dry stacks. These structures offer more security since they use filtered and compacted material. Because of the construction method and the heights achieved, the material that compounds the structure can be subjected to different stress paths along the failure plane. The theoretical framework considered in the design of these structures generally is the critical state soil mechanics (CSSM). However, the data in the literature concerning the uniqueness of critical state line (CSL) is still controversial as the soil is subjected to different stress paths. With respect to tailings, this question is even more restricted. This paper studies two tailings with different gradings due to the beneficial processes over extension and compression paths. A series of drained and undrained triaxial tests was conducted over a range of initial densities and stress levels. In the q-p′ plane, different critical stress ratio (M) values were obtained for compression and extension stress paths. However, the critical state friction angle is very similar with a slightly higher critical state friction angle for extension tests. Curved stress path dependent CSLs were obtained in the ν-lnp′ plane with the extension tests below the CSL defined in compression. Regarding the fines content, the studied tailings presented very similar M and critical state friction angle values. However, the fines content affects the volumetric behavior of the studied tailings and the CSLs on the ν-lnp′ plane shift downwards with the increasing fines content for compression and extension tests. In relation to dilatancy analysis, the fines content did not present an evident influence on the dilatancy of the materials. However, different values of mean stress ratio N were obtained between compression and extension tests and can corroborate the existence of non-unique CSLs for these materials.

This paper attempts to expand the graphical analysis concept proposed by Chen and Abousleiman (Géotechnique, 2022. https://doi.org/10.1680/jgeot.21.00172) to deduce the undrained expansion solution of a cylindrical cavity in shear strain-hardening Drucker–Prager frictional soil. Based on the geometrical representation of the stress state/path and strain increments in the deviatoric planes, it is shown that the deviatoric stress-Lode angle stress path can be desirably determined by solving a first-order differential equation for the stress ratio (deviatoric stress over mean effective stress) in term of the Lode angle. The essential cavity expansion curve may also be readily constructed by calculating the internal cavity pressure and the corresponding expanded cavity radius, respectively, through simple numerical integrations with respect to the same variable of stress ratio. In particular, the ultimate cavity pressure can be easily evaluated by directly integrating the expression for cavity pressure with the stress ratio up to its limiting value. Some numerical results obtained from the proposed graphical method are presented to illustrate the impacts on the cavity responses of the earth pressure coefficient at rest, K 0 , and the key plasticity hardening parameters, which have also been compared with alternative solutions that require dealing with a system of coupled differential equations involving three principal effective stress components. [ABSTRACT FROM AUTHOR]

Particle breakage, which is affected by the stress path, is a key factor influencing the mechanical properties of granular geomaterials. According to the results of triaxial tests conducted on granular geomaterials under different stress paths, a particle breakage model considering the effects of the stress path was established in this study, and a mathematical expression of the model and a method to determine the model parameters were established. The results indicated that the integral function of the plastic strain increment can be used to describe the variation in the particle breakage of granular geomaterials under different stress paths; however, the influence of the stress path on the plastic strain increment should be eliminated by introducing a stress-path-related parameter. Because it was difficult to obtain such a parameter directly, particle breakage models under a proportional loading path and a triaxial compression test path were established, and functional expressions of the particle breakage model of granular geomaterials under different stress paths were derived by combining the concepts of constant-breakage surface and stress path decomposition. A comparison of the calculated results with the experimental results showed that the proposed model can not only reasonably predict the particle breakage under different shear strains applied in the loading process but can also describe the variation in the particle breakage under different stress paths, thus validating the proposed model. [ABSTRACT FROM AUTHOR]

Sixteen Reduced Triaxial Compression (RTC) triaxial tests were conducted to investigate the reinforcement effect of fibered clay in this paper. Palm fiber with four different fiber lengths (5 mm, 10 mm, 15 mm, and 20 mm) and four different fiber contents (0.3%, 0.5%, 0.7%, and 0.9% in mass) were utilized. Accordingly, three additional groups of triaxial tests were performed to analyze the stress path effects with four different stress paths, including RTC, Conventional Triaxial Compression (CTC), Reduced Triaxial Extension (RTE), and isotropic Triaxial Compression (TC). Three samples were tested, including fibered clay with a fiber length of 10 mm and a fiber content of 0.7% (referred to as 10 mm 0.7%), fibered clay with a fiber length of 20 mm and a fiber content of 0.5% (referred to as 20 mm 0.5%), and bare clay, which was used to reveal the fiber reinforcement of clay. All samples were tested under consolidated undrained conditions. The test results showed that in RTC conditions, the deviator stress increased to a greater extent with 0.3% mass content of fibers according to the same higher confining pressures of bare clay. Fibers primarily increased the cohesion of fibered clay, a shear strength parameter, in terms of total stress, whereas they also increased the friction angle of fibered clay in terms of effective stress. For short fibers, the coefficient of strength reinforcement of the fibered clay increased with fiber content. However, for long fibers, this reinforcement may lead to a weakening of the clay's strength, as the long fibers may cluster or weaken along their longitude. Among the four stress paths (CTC, TC, RTC, and RTE) examined, the reinforcement took effort mainly in the CTC condition. In contrast, in unloading conditions, the fibers had little contribution to reinforcement. Consequently, in unloading conditions, such as deep excavating and slope cutting, the stress path should be considered to obtain a reliable parameter for geotechnical engineering applications. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)