Search

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office 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.)

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.

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.

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]

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]

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.

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]

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.

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.

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.)

Calcareous sand is widely observed in the foundation of off-shore infrastructure. Although a lot of research has been carried out on the mechanical properties of calcareous sand, study into the influence of the stress–strain path on the mechanical behaviour of calcareous sand is very limited. In this study, a series of triaxial tests were performed on calcareous sand under three different stress paths. The particle morphology of calcareous sand before and after the tests, the stress–strain relationship under different stress paths, and the characteristics of shear strength and deformation were investigated. The results show that the consolidation pressure and stress path have significant effects on the volume strain, strength, and particle breakage of calcareous sand. In addition, the underlying mechanisms of the different behaviours of calcareous sand observed in this study were discussed.

Understanding the mechanical characteristics of frozen soil is critical for engineering projects in cold regions. A series of case studies were conducted to explore the macroscopic and microscopic mechanical behavior of frozen soil during four different stress paths, i.e., isotropic, constant stress ratio, conventional triaxial, and true triaxial compression tests, using the distinct element method (DEM). The particle-scale mechanism and temperature effect of frozen soil are also taken into account in the DEM simulation. The results indicate that the peak stress/yield stress of frozen soil decreases with the increase of temperature or decrease of stress ratio or decrease of intermediate principal stress ratio b, which is related to the evolutions of bond breakage, bond stress, mechanical coordination number, and deviatoric fabric. When 0.25 ≤ b ≤ 0.75, the direction of strain increment deviates from the direction of stress. In addition, the relationship between the damage variable B and the volumetric strain εv or shear stain εs can be expressed as B = 1 - exp (- a · ε v n) or B = 1 - exp (- a · ε s n) under different stress paths. The simulation results and revealed microscopic mechanism will be valuable in developing breakage-mechanics-based constitutive models for frozen soil. [ABSTRACT FROM AUTHOR]

Investigation of the swelling pressure of buffer/backfill materials is a critical aspect in the design of high-level radioactive waste (HLW) disposal repositories. In this study, to clarify the swelling pressure–suction relation for compacted bentonite upon the hydration path, constant-volume swelling pressure tests with suction control were conducted. The swelling pressure–suction curves indicated that the swelling pressure of the specimens increased significantly with increasing dry density, while the shape of the curves during hydration depended on the dry density. Moreover, the swelling pressure–suction curves exhibited a distinction between unsaturated and saturated segments divided by the critical saturated state (CSS) curve, which proves the unique existence of a CSS curve in the stress space independent of the stress path. With the introduction of the CSS curve into the s–p space, the conventional stress space of unsaturated soil could expand to that of unsaturated expansive soil. The results obtained in this study could provide the mechanical parameters for the construction of disposal repositories. In addition, the stress space with CSS curve proposed in this study provides a new approach to building constitutive models of bentonite materials. [ABSTRACT FROM AUTHOR]

Salt layers and domes have been used to store hydrocarbons and to dispose of nuclear wastes. One of the most important properties of rock salt is its good deformability, which can neutralize the deviatoric stress and heal damage. Structural stability is one crucial requirement in salt cavern design and construction. Various criteria and methods have been proposed for salt cavern design and stability analysis. This paper investigated the advantages and limitations of various stability criteria. The results suggest that the stability criterion proposed by De Vries et al. is the most suitable approach for stability analysis. However, the effects of the stress path and history are not considered in this criterion. To overcome this shortcoming and to integrate effects of the stress path and history within the criterion, an updatable dilatancy criterion is proposed. In the proposed dilatancy criterion, a representative parameter is defined based on the healing and damage that occurred in a previous cycle of loading and unloading, which takes into account the stress path and history and their effects on the behavior of rock salt in subsequent cycles. The new criterion gives deeper insight into the strength of rock salt based on previous damage-healing background, and is useful in appropriate design and operation of salt cavern. [ABSTRACT FROM AUTHOR]

In order to investigate the compaction behavior of tight shale and obtain the apparent preconsolidation stress and critical stress of brittle-ductile transition, uniaxial strain tests were conducted at various temperatures. This method utilizes a cold-stretched 45# carbon steel sleeve to restrain the lateral deformation of tight shale, which successfully simulates the rigid constraints of rock stratum and overcomes the challenging issues of measuring the apparent preconsolidation stress and brittle-ductile transition based on existing tests. The results show that (1) the test curve can be divided into three stages: the pore compaction stage, the elastic compaction stage, and the cataclastic flow stage; (2) there is no obvious relationship between the front in situ stress coefficient and temperature, whereas the middle and later in situ stress coefficients increase at elevated temperatures; and (3) the apparent preconsolidation stress and critical stress of brittle-ductile transition decrease as the temperature rises, as does the elliptical yield surface of tight shale. In addition, the thermal stress distribution law of rock units was thermodynamically analyzed. The average increase in axial thermal stress is nearly equivalent to the decrease in apparent preconsolidation stress at various temperatures, and thermal stress has a compensating effect on the axial load. A new method is provided for studying the compaction behavior of tight rock under various coupling conditions. [ABSTRACT FROM AUTHOR]

In this study, we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir. Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County (California, USA), which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production. In our simulations, the geomechanical behavior of the sand reservoir is modeled using two models: (1) a linear elastic model (non-hysteretic stress path) that does not take into consideration irreversible deformation, and (2) a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction (hysteretic stress path). It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude. Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure. Moreover, this irreversible compaction may bring the nearby faults closer to reactivation. However, regardless of the two models applied, the geomechanical analysis shows that for the estimated stress conditions applied in this study, the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.

The mechanical properties of soil often vary with stress state and stress paths. In order to investigate the mechanical properties of saturated soil under vertical loading and constant shear stress path, saturated remolded loess samples are prepared. Through consolidated undrained (CU) triaxial tests and constant shear stress drained (CSD) triaxial tests, the corresponding stress-strain curves, pore water pressure curves and stress path curves are measured. The results show that the saturated remolded loess has obviously different deformation characteristics under the two paths. In CU tests, the stress-strain curves are softening weakly. The pore water pressure rises rapidly and tends to be stable gradually. In CSD tests, the deviator stress is a constant and the pore water pressure is applied. The deformation of samples is small for a long time at the beginning. When the pore water pressure increases to 60%−75% of the confining pressure, the samples are destroyed rapidly. Because there is no peak value of deviator stress in CSD path, the equivalent peak failure line is defined according to the axial strain-mean effective stress curves. By comparison, it is found that the effective peak strength indexes of the saturated remolded loess are significantly different under the two paths. However, the effective residual strength indexes are similar, indicating that the effective residual strength indexes are the internal attribute of the remolded loess and are not affected by the stress path. This study can provide reference for selecting the correct stress path test in practical engineering.

This work aims to investigate the influence of structural damage to natural soft clay on its mechanical behavior. K0 consolidated triaxial tests with loading and unloading stress paths were conducted, and field emission scanning electron microscopy (FESEM) and mercury intrusion porosimetry (MIP) were utilized for microstructural investigation. Macroscopic properties of soil were analyzed by microstructure evolution and damage theory. A pore size distribution index (S) was proposed that collectively accounts for the effect of pore size distribution and pore volume. Damage variables were determined based on the S to evaluate the damage degree of soft clay after K0 consolidation. The soil structure is obviously damaged when the confining pressure exceeds the preconsolidation pressure (119 kPa), with damage variables reaching 0.5 ~ 0.6 between 150 and 250 kPa. The initial tangent modulus and ultimate deviator stress of soft clay by reduced triaxial compression (RTC) tests are lower than those by conventional triaxial compression (CTC) tests. It is associated with relatively different microstructure failure modes, i.e., a loose uniform failure mode for RTC specimens and a locally dense non-uniform failure mode for CTC ones. However, the natural structure is slightly damaged after consolidation, and marginal macro and micro differences were observed between CTC and RTC test results when the confining pressure is less than the preconsolidation pressure. Therefore, the mechanical behavior of soft clay is strongly affected by stress paths and damage to the natural structure during consolidation and shearing processes on the macroscopic and microscopic views. [ABSTRACT FROM AUTHOR]

Aeolian sand is a special roadbed filler, but its three-dimensional mechanical properties are rarely studied. To obtain the characteristic of its deformation, strength on the deviatoric plane, and failure in three dimensions, a series of triaxial drained tests on aeolian sand in the Tengger Desert, under the condition of the constant average principal stress, p, were conducted by an equivalent alternative method to achieve a true triaxial stress path by a pseudo-triaxial apparatus. The results show that the method can better determine the strength. The peak shear stress decreases gradually with the increase of the intermediate principal stress coefficient, b, at the same p. Compared with the SMP and Mohr–Coulomb criteria, the peak shear stress is near the strength lines predicted by both criteria. At a lower p, the specimen exhibited strain-softening behaviours, but at a higher p, it showed hardening behaviours. Under the conditions of a higher p and lower b, the specimen exhibited contraction first and then dilatancy. The specimen deformation is greatly affected by anisotropy, and as the p-value increases, the effect of the initial anisotropy on the specimen begins to weaken. The εs (generalized shear strain)/η (stress ratio)-εs curves, can be expressed by a linear equation, of which the slope is affected by the b-value. The experiment verifies the feasibility and rationality of the equivalent method. The test data provide support for the maintenance of desert roadbeds and the sustainable development of the economy and society in ecologically fragile areas. [ABSTRACT FROM AUTHOR]

Engineering rock structures containing joints and fissures are frequently subjected to discontinuous periodic disturbances of varying amplitudes. To attain the quantitative relationship between the crack angle and the mechanical and deformation properties of rock under complex stress paths, uniaxial cyclic loading and unloading tests with increasing stress gradients were conducted on sandstone specimens containing a single crack of different angles. Our results showed that the bearing capacity of the sandstone increased as the crack angle increased. The irreversible strain and elastic moduli of the rock presented a sudden increase when entering the next cycle of the stepped loading. However, the entire loading process can be divided into three stages according to their respective trends. These three stages correspond to the three stages of rock deformation, i.e., the pore crack compaction stage, the elastic deformation to the stable micro-elastic crack development stage, and the unstable crack development stage. In addition, the crack angle of sandstone showed a negative correlation with the irreversible strain, but a positive correlation with the elastic modulus. With the increasing crack angle, the failure mode of the rock changed from the tensile-shear failure to the shear failure, and then to the interlayer dislocation failure. [ABSTRACT FROM AUTHOR]

Triaxial tests were employed to investigate palm-fiber-reinforced sand under consolidated drained conditions in this study. Sixteen series of triaxial tests were carried out to investigate the properties of palm-fiber-reinforced sand. One series of pure sand was also employed for comparison. The deviator stress, stress path, shear strength, volume change, void ratio, and enhanced coefficient of fiber-reinforced sand were studied with different fiber lengths varying from 8 mm to 20 mm and fiber contents varying in mass from 0.3% to 0.9%. The test results indicate that palm fibers were beneficial for enhancing the shear strength of the sand. Compared to the peak shear strength increase of about 10% to 20%, the critical shear strength increased much more, by a little over 100%. Therefore, the fibers played a key role in enhancing the critical shear strength of the sand but not the peak shear strength of the sand. The addition of fiber to sand resulted in prolongation of the axial strain required to reach the critical void ratio and improved the sand's ability to resist larger deformations, enhancing its toughness. Furthermore, the critical shear strength of the sand was positively correlated with both fiber content and fiber length, and the axial strain required to reach the critical shear strength increased with increasing fiber content and length. This study provides valuable experimental data and serves as a reference for temporary reinforcement in geotechnical engineering. [ABSTRACT FROM AUTHOR]

It is known that rock cores drilled from high-stress environments experience a complex stress path. The induced tensile stresses within the cores may result in the formation of micro-cracks, potentially leading to incorrect estimation of their laboratory properties. In this research, the influence of coring stress path on damage formation and the consequent changes in the laboratory properties of intact rocks were investigated using a 2D numerical program based on the hybrid Finite-Discrete Element Method. For this purpose, two models with distinct grain geometries (triangular and Voronoi) were generated. They were initially calibrated against the laboratory properties of the undamaged Lac de Bonnet granite. The calibrated models were then subjected to a coring stress path to generate damage in the form of micro-cracks. The calibration process also involved the laboratory properties of damaged granite, focusing on capturing the nonlinearity in the stress–strain response due to crack closure during uniaxial loading. It was concluded that both models can effectively capture the formation and opening of micro-cracks during unloading, their closure during compressive loading, and the nonlinearity in the stress–strain response. However, the model with Voronoi grains more accurately represented the reduction in peak strength and Young's modulus resulting from unloading-induced damage. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office 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.)

Although rock mechanical behaviour has a long record of study, attempts to understand the role of fractures on rock deformation still have unresolved issues. Due to technical and/or economic challenges, natural rock fractures are often dealt with crudely, without detailed consideration of fracture geometry and heterogeneity in many geoscience applications. Veined rocks that are ubiquitous in the upper Earth crust fall in that category where sustained efforts are needed to offer key information for rock mechanics and geomechanics applications. Following on from a recent study on the rupture of veined rocks (DOI: 10.1029/2019JB019052), we further examine stress path constraints on the deformation of veined rocks (i.e., stress-path-dependent behaviour of veined rocks) under polyaxial conditions. The Discrete Element Method is used to establish a calcite veined model where constant mean stress (σm) and constant least principal stress (σ3) paths that are representative in the subsurface activities are considered. The results reveal the stress-path dependency of brittleness for models under different loading paths. Models tested under constant-σm conditions exhibit no brittleness, compared to cases where constant-σ3 is applied. Sliding along the strike of an inclined vein is evident under constant-σm deformation, irrespective of the level of stress. Shear bands along the dominated (inclined) veins exhibit apparent particle trajectory anisotropy for the constant-σm deformations which is demonstrated by the evident colour contrast of the adjacent rock matrix and the displacement dispersion of the particles forming the shear bands. We envisage that the reactivation of veins is of relevance to Enhanced Geothermal Systems (EGS) development in terms of seismicity mitigation and multiphysics control of fracture and reservoir permeability. [ABSTRACT FROM AUTHOR]

A novel test method for analyzing the influence of stress path and roughness of structure on the strength characteristics of saturated sand-structure interface by using triaxial apparatus is presented. By making a triaxial specimen with a slope structure with a certain inclination angle, the soil slides along the preset failure surface during the shearing process, and the slope surface roughness of the structure can be controlled and adjusted. A triaxial instrument is used to control the changes in axial pressure,confining pressure to achieve loading in different stress paths. The soil slides along the structure surface with a certain angle during shearing when preformed failure surface exists. The roughness of the structure can be controlled and adjusted. The triaxial apparatus is used to control the confining pressure change of the sample to realize loading under different drainage conditions and stress paths. To verify the effectiveness of the method, direct shear test and triaxial shear tests are carried out on the specimen composed of Fujian sand and steel structures with different roughness and different stress paths. The results show that at the beginning of sliding, the friction angle of the interface in the interfacial constant normal stress path is smaller than that in the conventional shear path. Under smooth conditions, the interface friction angle obtained by direct shear test is 30% to 40% lower than that obtained by triaxial test. Under rough conditions, the interface friction angle obtained by direct shear test is slightly smaller than that obtained by triaxial test, and closer to the friction angle in normal stress shear paths.

Sand roughness is now accessible to measurement. Incorporating this parameter into sand models using the discrete element method (DEM) is known to improve bulk small strain response. In this work we explore the effect on problems where particle crushing takes place. A well-established DEM particle crushing model and a rough Hertzian contact model are here combined to incorporate both effects in a single contact model. Including contact roughness results in stronger particles whilst all other material parameters being equal. The model is then used to simulate high pressure oedometric compression tests on a strong silica sand. It is shown that including realistic values of surface roughness enables to correctly capture both load-unload behaviour and particle size distribution evolution while using realistic values of elastic bulk properties for the sand grains. Roughness is then a model refinement that may result in simpler, more objective DEM calibrations.

Studying train-induced response characteristics is essential for safely operating permafrost railway subgrades. A three-dimensional thermal-mechanical coupling nonlinear dynamic model of train-track-subgrade-ground relationships was established to analyse the train-induced dynamic stress, acceleration and stress path characteristics of a permafrost railway subgrade, and field monitoring data were used to verify this model. The differences between the 2D and 3D models are also discussed, along with the seasonal changes, train speed, axle load, and train type affecting permafrost subgrades. The main results are as follows. First, the vibration load significantly impacts the subgrade 6 m below the sleeper, producing distinct vertical dynamic stress waves due to the wheels and bogies. Dynamic compression stress dominates the subgrade and is influenced by the train structure, speed, and sleeper spacing. While the 2D model tends to underestimate the dynamic stress in shallower layers, it concurs with the 3D model in deeper subgrade dynamics within a 10% margin of error. Then, the principal stress axis of the subgrade soil rotates synchronously with train movements, exhibiting regular stress paths in the YZ plane (longitudinal section) with depth-dependent variations in the stress cycles and deviatoric stress. Finally, predominantly originating from sleeper-induced vibrations, the subgrade vibration acceleration varies with the train speed, sleeper spacing, and season and is most pronounced in the vertical direction. This study provides theoretical guidance for the vibration response of permafrost subgrades on the Qinghai-Tibet Railway (QTR). • Proposed a 3D train-track-subgrade-ground dynamic model of permafrost subgrade. • Compared 2D and 3D simulation results. • Discussed seasonal and train effects on permafrost subgrade vibration. [ABSTRACT FROM AUTHOR]

Engineering rock structures containing joints and fissures are frequently subjected to discontinuous periodic disturbances of varying amplitudes. To attain the quantitative relationship between the crack angle and the mechanical and deformation properties of rock under complex stress paths, uniaxial cyclic loading and unloading tests with increasing stress gradients were conducted on sandstone specimens containing a single crack of different angles. Our results showed that the bearing capacity of the sandstone increased as the crack angle increased. The irreversible strain and elastic moduli of the rock presented a sudden increase when entering the next cycle of the stepped loading. However, the entire loading process can be divided into three stages according to their respective trends. These three stages correspond to the three stages of rock deformation, i.e., the pore crack compaction stage, the elastic deformation to the stable micro-elastic crack development stage, and the unstable crack development stage. In addition, the crack angle of sandstone showed a negative correlation with the irreversible strain, but a positive correlation with the elastic modulus. With the increasing crack angle, the failure mode of the rock changed from the tensile-shear failure to the shear failure, and then to the interlayer dislocation failure.

In order to study the influence of stress path on the true triaxial macroscopic and mesoscopic deformation characteristics of rocks, a calibrated granular flow numerical specimen was established using the discrete element method, and the loading planes were selected as meridian plane, n-plane and the fixed-axis plane. Numerical experiments with different stress paths were conducted on the numerical specimen to analyze the true triaxial deformation evolution of rocks from the macroscopic and mesoscopic viewpoints, and the numerical simulation results were compared with the D-P yield criterion to verify the correctness of the results. The research results showed that: for the same stress increment, the anisotropy of strain increment was the lowest when loading along the meridian plane, and the stress reached the yield plane fastest when loading along the n-plane, resulting in the largest strain increment and the two-way unloading in fixed-axis plane produced the largest strain increment in all stress path loading processes. The elastic-plastic deformation characteristics were analyzed using the relative imaging of stress space and yield surface, defining deformation anisotropy parameters; the correlation between stress and strain increment paths was quantitatively analyzed at the mesoscopic view level, and it was concluded that the number of contact force chain transformations and strain increment deflection angle were negatively correlated, and the numerical model produced the largest number of microcracks with the most obvious internal damage when loaded along the n-plane, and the smallest number of microcracks with the least internal damage when loaded along the fixed-axis plane. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature 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.)

It is important to determine the volumetric change properties of hydrate reservoirs in the process of exploitation. The Skempton pore pressure coefficient A can characterize the process of volume change of hydrate-bearing sediments under undrained conditions during shearing. However, the interrelationship between A value responses and deformation behaviors remain elusive. In this study, effects of hydrate saturation and effective confining pressure on the characteristics of pore pressure coefficient A are explored systematically based on published triaxial undrained compression test data of hydrate-bearing sand and clay-silt sediments. Results show that there is a higher value of the coefficient A with increasing hydrate saturation at small strain stage during shearing. This effect becomes more obvious when the effective confining pressure increases for hydrate-bearing sand sediments rather than hydrate-bearing clayey-silt sediments. An increasing hydrate saturation leads to a reduction in A values at failure. Although A values at failure of sand sediments increase with increasing effective confining pressure, there are no same monotonic effects on clayey-silt specimens. A values of hydrate-bearing sand sediments firstly go beyond 1/3 and then become lower than 1/3 at failure even lower than 0, while that of hydrate-bearing clayey-silt sediments is always larger than 1/3 when the effective confining pressure is high (e.g., >1 MPa). However, when the effective confining pressure is small (e.g., 100 kPa), that behaves similar to hydrate-bearing sand sediments but always bigger than 0. How the A value changes with hydrate saturation and effective confining pressure is inherently controlled by the alternation of effective mean stress. [ABSTRACT FROM AUTHOR]

Based on the changes of total stress and pore water pressure in the spring model, the mechanism of vacuum preloading consolidation is studied by theoretically discussing the consolidation behavior of soil in vertical and horizontal directions with different boundary conditions. The variation of effective stress and development of deformation are analyzed for the soil under vacuum preloading under stress paths of K0 consolidation and isotropic consolidation based on the boundary conditions, respectively. Meanwhile, the theoretical earth pressure coefficient (K0MC) at rest for soft soil is deduced based on modified Cam-clay model. With engineering applications, the correctness and effectiveness of the mechanism is confirmed by the application in large area of ground improvement for soft soil and statistical analysis of some engineering cases. It is found that the drainage boundary condition and the scale of treated area have effects on deformation of soil mass. For the middle part of the treated zone under large-area vacuum preloading, the variation of effective stress is not isotropic, but following the pattern of one-dimensional compression. According to the statistic results from some site investigations, one-dimensional compression equation (Cc-Cr method) can be applied to predict the settlement at the center of the treated zone when the one dimensional condition is found in the center of treated zone as the ratio between treated breadth and length of vertical drains larger than 4-5.

In this study, we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir. Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County (California, USA), which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production. In our simulations, the geomechanical behavior of the sand reservoir is modeled using two models: (1) a linear elastic model (non-hysteretic stress path) that does not take into consideration irreversible deformation, and (2) a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction (hysteretic stress path). It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude. Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure. Moreover, this irreversible compaction may bring the nearby faults closer to reactivation. However, regardless of the two models applied, the geomechanical analysis shows that for the estimated stress conditions applied in this study, the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.

The critical damage value of rock is an important parameter of stability analysis when engineering rock mass. Based on the previous single test method, this paper, combined with the deformation characteristics of rock residual phase under different stress paths, proposed a single specimen repeated loading method to measure the critical damage value of rock based on different damage variables. The paper also proposed to modify the critical damage value based on residual constitutive energy and to improve the definition of damage variables based on constitutive energy dissipation. According to the microstructure characteristics of the rock sample, the mechanism of the single specimen method to determine the critical value of rock sample damage is revealed. The results show that: 1) Comparing the results of triaxial failure test of rock under different stress paths and single specimen repeated loading test, the residual strength of rock sample is mainly controlled by the confining pressure of loading, which is not an obvious relationship with initial confining pressure and stress path; 2) The number of repeated compressions has little effect on the internal structure, particle flatness, and particle surface smoothness of their specimens, which is reflected at the macroscopic level that the residual strength of sandstone tends to achieve a stable value; and 3) The corrected critical damage value based on residual strain energy is closer to the theoretical value. Test methods in this paper can provide useful references for determination of critical damage value.

Stress path tests in plane strain (PS) conditions with varying stress ratios have been carried out using a newly developed flexible boundary (FB) multiaxial testing device. It employs electro-pneumatic control and allows the application of independent principal stresses on each face of a 96-mm cubical soil specimen through a closed-loop feedback control system. Different stages of testing have been automated for both deformation and stress-controlled loading. It also has provisions for local deformation field estimation from the images acquired on the transparent rigid PS boundary. The friction angle for different stress paths in compression and extension mode is found to have minimal variation in PS conditions. The experimentally observed yield points match well with a simplified two-dimensional (2D) yield criterion resembling the shape of a "tear-drop." Local shear strain profiles under FB-PS conditions imply nearly uniform material behavior, while the emergence of instabilities is found to be minimal and mostly at the specimen corners. [ABSTRACT FROM AUTHOR]

Geotechnical investigation and design show that when evaluating the settlement of ground with soft soil ground, the use of a single stress path results in a larger error than in the case of a multistress path. To understand the influence of a multistress path on the deformation properties and microstructure characteristics of soil, a two-stage stress path (corresponding to three stress states: the in situ state, unloading-loading state, and grouting pressure state) of soil was examined by analytical solution. Then, a series of triaxial tests was conducted to analyze macroscopic deformation properties considering four influencing factors, i.e., the relative distance between the soil and tunnel, stress paths, type of silty clay, and drainage conditions. The results show that axial strain of silty clay caused by the two-stage stress path increases by 31.6% with the relative distance decreasing from 1.67R (R means tunnel radius) to 1.25R on tunnel side, while the volume strain increases by 80% with the relative distance decreasing from 1.21R to 1.06R on tunnel bottom. In addition, the deformation caused by the two-stage stress path (or reconstituted soil or undrained condition) is larger than that caused by the one-stage stress path (or undisturbed soil or drained condition). Finally, through scanning electron microscopy and mercury intrusion porosimetry, the pore size, distribution, shape, and arrangement of silty clay on the bottom and sides of the tunnel were investigated. The research shows that under the two-stage stress path, the number of large pores decrease and that of small pores increase. The probability entropy of pore orientation ranges from 0.834 to 0.971 when silty clay is subjected to a two-stage stress path. This illustrates that the pore order of the soil on tunnel side is better than that on the tunnel bottom. [ABSTRACT FROM AUTHOR]

The post-peak response of elasto-plastic material is dependent upon the stress path it is subjected to. This paper analyses and compares the stress path and strain response of advancing tunnel, using two-dimension:1al plane strain (2D PS) and full three-dimensional step by step excavation and support (3D SBS) finite difference numerical model (FDM). Stress paths for 3D SBS model indicate higher stress relaxation and straining at unsupported spans as well as elastic recompression behind applied supports; these features are not evident in 2D PS models. Implications of these differences on tunnel response are discussed. The complex 3D stress evolution with tunnel construction is greatly simplified by considering major and minor principal stresses only, for the purpose of stress path generation. To verify that the formulation of stress path adopted here is sufficient to describe stress–strain evolution of 3D SBS tunnel model, a numerical simulation of "stress path following triaxial unloading test" is conducted using "simplified loading conditions." Results show that the suggested test methodology has potential to map stress path of 3D SBS tunnel model for ideal geomaterial behavior. Also, improvement in measured strain response, as compared to 2D PS models, is observed. [ABSTRACT FROM AUTHOR]

An analytical solution for elastoplastic responses of an underground lined rock cavern for compressed air energy storage under initial hydrostatic pressure and high internal air pressure is proposed. In the analytical solution, the stress paths during cavern excavation and operational stages are considered. A numerical simulation is performed by using the finite element software Abaqus to verify the analytical solution. The concept of "high-pressure plastic zone" is proposed and the evolution of "high-pressure plastic zone" is analyzed. Furthermore, taking the occurrence of "high-pressure plastic zone" and failure of the sealing layer as the critical states, the calculation methods for critical internal pressure p c r 1 and ultimate internal pressure p u are proposed. Sensitive analyses are conducted to study the key parameters affecting the "high-pressure plastic zone" and the critical internal pressure. The research indicates that the proposed analytical solution can accurately predict the elastoplastic responses of an underground lined rock cavern. The radius of "high-pressure plastic zone" are mainly related to the surrounding rock quality, magnitude of air internal pressure and buried depth of cavern. The critical internal pressure p c r 1 and ultimate internal pressure p u are mainly related to the surrounding rock quality, cavern size, buried depth and thickness of concrete layer. [Display omitted] • An analytical solution for elastoplastic responses of an underground lined cavern for CAES is proposed. • The evolution of "high-pressure plastic zone" is analyzed. • The calculation methods for the critical internal pressure and ultimate internal pressure are proposed. [ABSTRACT FROM AUTHOR]

Sand roughness is now accessible to measurement. Incorporating this parameter into sand models using the discrete element method (DEM) is known to improve bulk small strain response. In this work we explore the effect on problems where particle crushing takes place. A well-established DEM particle crushing model and a rough Hertzian contact model are here combined to incorporate both effects in a single contact model. Including contact roughness results in stronger particles whilst all other material parameters being equal. The model is then used to simulate high pressure oedometric compression tests on a strong silica sand. It is shown that including realistic values of surface roughness enables to correctly capture both load-unload behaviour and particle size distribution evolution while using realistic values of elastic bulk properties for the sand grains. Roughness is then a model refinement that may result in simpler, more objective DEM calibrations. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the influences of grain shape and gradation on stress-dilatancy parameters. For this purpose, consolidated-drained triaxial tests are conducted on five different granular materials. Specimens are sheared following two different stress paths; axial compression and lateral extension, in order to monitor the influence of stress path on the investigated problem. For each soil, grain shapes, sizes and stress-dilatancy parameters are experimentally determined. Moreover, available data in literature for other sands are compiled with the data of this study. This allows the investigation of the dependence of stress-dilatancy parameters on gradation and grain shape characteristics. Especially with this study, variations of stress-dilatancy constants with grain characteristics are examined. Statistically significant relationships are obtained for predicting stress-dilatancy parameters as functions of average grain shapes. On the other hand, influences of stress path and gradation on stress-dilatancy response are experimentally considered. Finally, compiled and determined data used in the development of the relationships are provided in the form of tables. [ABSTRACT FROM AUTHOR]