Search

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]

• 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]

• 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]

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]

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure. • The mechanical behavior and failure characteristics of FWCS are closely associated with the unloading stress path. • The volumetric expansion of FWCS under unloading conditions is notably pronounced due to the release of lateral stress. • The shear-tensile failure of FWCS under complex unloading stress paths is driven by rapid energy accumulation. • Microcracks in pore ice and cemented particles cause quartz and feldspar to separate, leading to macro-scale failure. [ABSTRACT FROM AUTHOR]

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]

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]

In order to study the deformation and non-coaxial characteristics of fiber cement modified iron tailing sand (FCIT) under different stress paths. The evolution law of the dynamic stress ratio (η) on the cumulative deformation and non-coaxial angle of FCIT under different tension-compression amplitude ratios (α) was explored through hollow torsional shear tests. The deformation behavior of FCIT is analyzed by using the stability theory. The research results show that: 1) The increase of dynamic stress level will deepen the cumulative deformation of FCIT, while the increase of α will make the deformation mode of FCIT develop into bulging failure-shear failure-tensile failure. 2) According to the development trend of cumulative strain and cumulative strain rate of FCIT, it can be divided into three stages: plastic stability, plastic creep and incremental collapse, and the cumulative strain rate development prediction model is established, and the prediction error distribution is within ±20%. 3) The stress path determines the non-coaxiality of FCIT to a certain extent, and the non-coaxial angle fluctuates and decreases with the increase of the principal stress direction angle. When α =0.125, the maximum and minimum values of the non-coaxial angle of FCIT are 1.5 rad and 0.4 rad respectively. 4) Cement hydration reaction generates calcium alumina and hydrated calcium silicate (C-S-H) to make FCIT structure more compact, fiber-matrix interfacial connections more dense, and play a role in filling the pores. • Effects of dynamic stress levels and stress paths on cumulative deformation and failure modes of FCIT. • Decomposition of deformation behavior of FCIT by stabilization theory. • Quantifying the change in the non-coaxial angle to explore the non-coaxiality of FCIT. [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 introduces a novel segmented lining model designed to mitigate the challenges associated with tensile cracking in reinforced concrete linings within underground rock caverns subjected to high internal pressure. The proposed model comprises prefabricated reinforced concrete segments interconnected by bolts, with selected connectors designed to facilitate retractability. This unique feature enables circumferential deformation, effectively preventing concrete cracking and the subsequent loss of bearing capacity under high internal pressure conditions. Key components of the proposed segmented lining include the utilization of prefabricated segments for improved construction efficiency and quality control, secured interconnection through bolts to ensure a flexible yet robust assembly, and the incorporation of retractable connectors for controlled circumferential deformation. The presence of predetermined seams in the lining facilitates the transmission of elevated air pressure within the cavern to the surrounding rock, thereby minimizing damage to the rock structure and ensuring optimal utilization of the surrounding rock's bearing capacity. The study employs a systematic approach, deriving simplified mechanical expressions for the rock masses encompassing a cavern with high internal pressure. The stress evolution and mechanical response of the surrounding rock during the internal pressure increase are examined across distinct stages: elastic–plastic, plastic unloading, plastic loading, and plastic expansion. Case studies are conducted to investigate the influence of various factors on the gas storage capacity of the cavern supported by the segmented lining. Parameters such as the quality of the surrounding rock, cavern burial depth, spring stiffness of the retractable connector, and preset seam width of the lining are evaluated. Results demonstrate that the segmented lining not only averts lining cracking and damage but also markedly enhances the gas storage pressure within the cavern compared to conventional reinforced concrete linings. [ABSTRACT FROM AUTHOR]

• Propose a methodology to reconstruct structured clays like its natural intact clays. • The developed method is based on natural structural process of marine clays. • Applicability of method is verified by macro and micro evaluation. Quantitative laboratory studies on the structural behavior of natural intact marine clays require a large number of identical natural samples leading to an expensive and challenging task. This study proposes a simple method to reconstruct an artificial structured marine clay as the state of its natural intact clay at both macro and micro levels. For this purpose, the Shanghai marine clay is selected and mixed with low cement contents (1–6%). The clay-cement slurry is mixed in a container with the ice-covered sides at a low temperature about 0 ± 2 °C to postpone the hydration reactions until consolidation began. The purpose of adding cement is to generate the inter-particle bonding and structure in reconstituted samples. Initially, the reconstituted samples are consolidated under the in situ stress of 98 kPa and then under the pre-consolidation pressure of 50 kPa. Mechanical characteristics such as compression index, yield stress, unconfined compression strength, shear strength ratio, and the stress paths from triaxial tests are compared with natural intact clay accordingly. Scanning electron microscope and mercury intrusion porosimetry analyses are also performed to analyze the microstructure of clays for comparison. Furthermore, the proposed method is also examined by using natural intact marine clays of different locations and characteristics. [ABSTRACT FROM AUTHOR]

Abstract Most models developed for hydraulic fracturing initiation of borehole are based on the elasticity mechanics, and tensile fracturing is considered as the mechanism of fracture initiation. However, the lab and field data show that these models cannot properly predict the fracturing mechanism of soft formations. We proposed an elasto-plastic model to analyze the fracturing mode and fracture initiation pressure in the soft formations that considers the effect of overburden pressure and fluid flow. The analytical stress solutions under six different stress state are obtained, thus the effective stress path on the borehole wall is analyzed to determine the fracturing mode. The effective stress path analysis indicate that both tensile and shear fracturing are considered as the fracturing mode. The fracturing mode and fracture initiation pressure are influenced by the burial depth significantly. The tensile fracturing is more likely to occur in the shallow formation, while the shear fracturing usually occurs in the deep formation. In addition, the formation strength and mud cake also affect fracturing mode and fracture initiation pressure. The shear fracturing is more easily to be induced in the formation with low strength and tight mud cake. The preyielding around the borehole due to the low strength will decrease the fracture initiation pressure without affecting the fracturing mode of the borehole wall. Highlights • Both Tensile and Shear Fracturing May Occur during Fracturing Due to the Low Strength of Soft Rocks. • Tensile and Shear Fracturing Tend to Occur in Shallow and Deep Layer, respectively. • Mud Cake on the Borehole Wall Makes the Formation More Difficult to Be Fractured. • The Preyielding Around the Borehole Due to the Low Strength Will Decrease the Fracture Initiation Pressure. [ABSTRACT FROM AUTHOR]

Abstract The traditional way of analyzing wellbore stability in depleted reservoirs is by assuming homogenous depletion and uniaxial strain. Then the analytical solution of stress path is obtained. Pore pressure depletion, however, is location and time dependent. The objective of this study is to develop a workflow for infill well design. More specifically, a wellbore stability analysis is developed for infill wells using a coupled geomechanics and reservoir simulator (CGRS) which considers lateral displacement and inhomogeneous depletion. Different shear failure criteria are utilized in a new CGRS wellbore stability model. The upper bounds of shear failure are given by Drucker-Prager Inscribes and Griffith Theory, while the lower bound is given by Drucker-Prager Circumscribe. CGRS wellbore stability model is compared with conventional wellbore stability model (based on the analytical solution of stress path). CGRS wellbore stability can quantify the influence of azimuth on minimum and maximum mud weight during the depletion when initial maximum horizontal stress equals minimum horizontal stress. In addition, CGRS can give the output of a location-dependent mud weight map for the entire reservoir. Neither of the above two functions can be realized by conventional wellbore stability model. Therefore, CGRS can provide dynamic information concerning where to drill, when to drill, and how to drill for infill wells. Highlights • Coupled geomechanics reservoir simulator (CGRS) is used in wellbore stability (WS). • Inhomogeneous depletion causes different mud weight windows for different azimuths. • CGRS-WS captures failures that cannot be diagnosed by traditional stress path. • CGRS-WS provides dynamic information concerning where/when/and how to drill. [ABSTRACT FROM AUTHOR]

Graphical abstract Strength Envelopes from DEM, UST, VE, MC and DP: Prediction and Comparison. Highlights • A new numerical true triaxial engine is developed for 3D granular material. • Stress-strength behavior in meridian and deviatoric stress space is well produced. • A demonstration of DEM study for real 3D granular material behavior modeling. Abstract A new numerical true triaxial engine based on discrete element method accounting for rolling resistance contact is developed. By this engine, we have simulated mechanical behavior of granular materials under complex stress loading path in this study. Stress-strain responses of a kind of typical granular sand under several stress loading path in meridian and deviatoric stress space are provided. The results show that the three dimensional effects like the intermediate principal stress play an important role in the modeling processes. Theoretical analysis in strength characteristic implies the strength criteria with three parameters such as unified strength criterion and van Eekelen strength criterion are capable of describing cohesionless granular material behaviors in three dimensional stress states. Moreover, the case study for Chende sand further demonstrates the numerical true triaxial engine, is a potential tool. As compared to conventional triaxial compression test, this new developed apparatus could be widely used to "measure" elastic-plastic behavior in three dimensional stress space for finite element analysis in geotechnical problems. [ABSTRACT FROM AUTHOR]

Underwater construction has gone to greater depths below the sea level for the extraction of resources such as oil and minerals. During different construction stages of deep-sea structures, different loading rates may be applied to deep-sea sediments. Generally, the strength of soil usually increases with the loading rate, and the sensitivity to strain rate effects may be more pronounced in deep-sea sediments. Previously, the strain rate effects were mainly studied on shallow marine deposits, but rarely on deep-sea sediments due to the difficulty of sampling. In this study, the strain rate effects on intact deep-sea sediments were investigated by a series of undrained triaxial tests with different strain rates of 0.5%/h, 2.6%/h and 13.2%/h under normally and over-consolidated conditions. In addition, scanning electron microscopy (SEM), nitrogen adsorption (NA) and mercury intrusion porosimetry (MIP) tests were conducted to illustrate the unique microstructure and pore size distributions of the deep-sea sediments, which showed a flocculent structure with abundant mesopores and macropores. It is found that higher strain rate leads to higher undrained shear strength due to the delay of increase of excess pore pressure as a result of low permeability. Strain rate effects are more obvious with the increase of confining pressure and then become less significant when the confining pressure is increased further. This change of trend is attributed to the increase of particle contact and more particle rearrangements when the confining pressure is first increased, but the particle rearrangement is suppressed under higher confining pressure. The sensitivity to strain rate effects increases with the overconsolidation ratio as more particle rearrangement is enabled under less confinement. • Strain rate effects are attributed to the delay of pore water pressure and particle rearrangement. • Mesopores and ink-bottle-shaped pores cause the delay of pore water pressure. • Higher strain rate leads to higher undrained shear strength. • Rate sensitivity increases with the increase of confining pressure and overconsolidation ratio. [ABSTRACT FROM AUTHOR]

The microstructure evolutions of natural marine clay during loading and unloading processes were investigated using undrained triaxial tests. The pore distribution and arrangement of soil particles and aggregates were measured by mercury intrusion porosimetry (MIP) and field emission scanning electron microscope (FESEM) tests, respectively. The results show that pores do not always collapse into smaller ones with stress levels increasing; the destruction of cemented soil structure will lead to the connection of small pores into large pores. In the consolidation process, as the consolidation pressure increased from 0 to 100 kPa, the total specific surface decreased from 20.01 mm2/g to 17.42 mm2/g. Conversely, the total specific surface increased from 17.42 mm2/g to 19.25 mm2/g as the confining pressure surpassed the preconsolidation pressure, indicating the formation of new surfaces. The rebound effect during the unloading process is another factor causing the increase in pore volume, but the destruction of the soil structure can significantly reduce this effect. The microscopic morphology at the point of soil failure under high stress levels in both loading and unloading processes tended to be similar, as the soil structure was completely destroyed. • Soil structural destruction creates larger connected pores. • Unloading process causes inter-aggregate pores to expand due to rebound effect. • Stress paths and levels determine soil microstructure evolution. • Cemented bonds influence the microstructure of natural marine clay. [ABSTRACT FROM AUTHOR]

Highlights • Effect of low cement content is significant on macro and micro structure of soft clay. • The fundamental parameters relationships for low and highly cemented clays are established. • This study can be helpful for the low cement-treated dredged clays land reclamation projects. Abstract The sustainable utilization of dredged soft clays for land reclamation requires a lower strength with lesser cement content as compared to traditional cement-treated clays. The mechanical behavior of soft clays at low cement content can differ from clays treated with higher content. For land reclamation, the required cement content is generally used up to 10%. Hence, this study is focused on analyzing the sustainable utilization of soft clays treated with cement content lower than 7%. Additionally, a comparison is drawn between a low-cement-treated soft clay with the highly cemented clays to determine the difference in mechanical behavior. Shanghai soft clay is reconstituted with cement content from 0 to 6%. The experimental investigation indicates that the low cement content has a significant effect on the microstructure, compression characteristics, compressive strength, undrained stress paths, and stress-strain behavior. However, the effect of curing time on such characteristics is limited. The mechanical behavior of low-cement-treated soft clay is similar to the highly cemented clays with respect to the relationships of compressive strength with strain at failure, yield stress and clay-water/cement ratio but is different with respect to deformation modulus versus compressive strength. The outcomes of this study can help to choose the minimum required cement content for the fill materials of land reclamation projects. [ABSTRACT FROM AUTHOR]

Abstract A nonlinear regression model for peak-failure strength prediction of rockfill materials is proposed. It is based on the relationship between the peak-failure stress ratio and the normalized confining pressure as well as the relationship between the normalized peak-failure stress ratio and the exponent function of the intermediate principal stress ratio. This model can well predict the variations of the peak-failure stress ratio with the initial confining pressure and the intermediate principal stress ratio for different rockfill materials under different general stress paths. Comparisons of the measured and predicted results show that the peak-failure strength under the constant- p ′ and constant- b path is larger than that under the constant- σ 3 ′ and constant- b path. The predictive capacity of the proposed model for the peak-failure stress ratio is better than that for the peak-failure friction angle. Graphical abstract Image 1 Highlights • A nonlinear regression model was proposed for strength of rockfill materials. • The regression model could consider the pressure and generalized stress. • The peak-failure strength was dependent on the general stress path. [ABSTRACT FROM AUTHOR]

Previous study has suggested that the stress paths of confined concrete in concrete-filled steel tube (CFT) stub columns influence the compressive strengths of the concrete, which, however, is based on the test of concrete-loaded CFT columns. In this paper, to fully understand the compressive strength of confined concrete in CFT column, the stress paths of confined concrete in the whole-section-loaded CFT columns are investigated. A detailed parametric study is conducted on the stress paths and their corresponding effects on compressive strength. Test results suggest that the lateral stress of the concrete in a whole-section-loaded CFT column generally occurred in a later stage and less significant than that in a concrete-loaded CFT column. The compressive strength of confined concrete in the whole-section-loaded CFT column with a small confinement coefficient is path-dependent, and the confinement effect of the concrete is generally weaker than that in concrete-loaded CFT column. With the increase of the confinement coefficient, the compressive strengths of confined concrete in whole-section-loaded CFT columns become path-independent. Based on the test results, a compressive strength model incorporating the stress path effect is developed for confined concrete in both whole-section-loaded and the concrete-loaded CFT columns. Good agreement between the experimental results and the ones predicted by the model is found, indicating a high performance of the proposed model. [ABSTRACT FROM AUTHOR]

The progressive process of brittle failure was studied using the results of laboratory damage-controlled tests on the samples of Lac du Bonnet granite and Indiana limestone under uniaxial and triaxial loading conditions. A similar trend of decreasing crack damage stress, peak stress and cohesion and increasing friction angle with increasing damage was observed for both rocks which confirmed the previous findings from the results of uniaxial tests. While the absolute strength of Lac du Bonnet granite is much higher than Indiana limestone, the normalized crack damage stress curves for both rocks were similar. It was shown that cohesion degradation is mainly a function of accumulated damage and is not sensitive to confining stress. Friction mobilization, on the other hand, dependents on both the damage level and confining stress and decreases with increasing confinement. A nonlinear Cohesion Weakening Friction Strengthening (CWFS) model was proposed to capture the process of brittle failure at the laboratory scale. The results of the model were in reasonable agreement with experimental stress-strain curves at different levels of confining stress. A simplified version of the CWFS model was proposed for in situ applications and implemented in the finite difference code, FLAC3D for numerical modeling of four underground excavations at the Underground Research Laboratory in Canada. In all cases, the CWFS model closely captured the observed zone of brittle failure around the excavation. The proposed in situ CWFS model eliminated the problematic behavior of the current linear CWFS models by using identical plastic strain thresholds for residual cohesion and residual friction angle. It was shown that the proposed CWFS model offers sufficient versatility to be applied to a wide range of geomaterials with strain softening and strain hardening behavior. Empirical guidelines were proposed for estimating the parameters of the proposed in situ CWFS model for good quality rock masses. [ABSTRACT FROM AUTHOR]

Two sets of strain-controlled cyclic triaxial tests were conducted to investigate soil liquefaction of clean sands. The first set involved conventional uniform strain amplitude cyclic tests, while the second set examined non-uniform strain amplitude cyclic tests. Comparisons were made between the two sets of results with respect to the generation of excess pore pressure and relationship between strain amplitude and stress path. In the case of uniform strain-controlled cyclic tests, larger strain amplitude produced more rapid generation of excess pore pressure. Conversely, for non-uniform strain-controlled tests, larger strain amplitudes may generate lower excess pore pressure instead. Such counter-intuitive phenomenon has design implications if irregular earthquake loadings in the field are incorrectly represented as equivalent uniform loading in the laboratory. Details are described in this paper. [ABSTRACT FROM AUTHOR]

Strain localization in a porous calcarenite facies of the Aren formation in the Tremp basin was studied. This Maastrichtian syn-tectonic formation exposed in front of the Boixols thrust, in the Central South Pyrenean Zone, hosts bedding perpendicular deformation bands. These bands are organized in two major band sets, striking East-West and N-020 respectively. Both populations formed during early deformation stages linked to the growth of the fold and thrust. A magnetic fabric study (Anisotropy of Magnetic Susceptibility, AMS) was carried out to constrain the shortening direction responsible for the deformation bands development during the upper Cretaceous-Paleocene N-S contraction in the region, which allowed us to define populations of Pure Compaction Bands (PCB) and Shear Enhanced Compaction Bands (SECB) regarding their orientations compared to the shortening direction. Both sets are formed by cataclastic deformation, but more intense in the case of SECBs, which are also thinner than PCBs. The initial pore space is both mechanically reduced and chemically filled by several cementation phases. We propose a geomechanical model based on the regional context of layer parallel shortening, thrusting and strike-slip tectonics considering the burial history of the formation, in order to explain the development of both types of bands at remarkably shallow depths. [ABSTRACT FROM AUTHOR]

Triaxial tests on back-saturated specimens using different controlled stress paths were conducted to study the influence of the stress path on the hydro-mechanical behavior of a clay shale. Opalinus Clay, a clay shale chosen for the disposal of high-level nuclear waste in Switzerland, was utilized. Three different stress paths approximating a tunnel excavation were applied: a two-dimensional stress path with isotropic initial stress conditions (i.e. pure shear compression), a two-dimensional stress path with anisotropic initial stress conditions, and a three-dimensional stress path. The influence of the stress path was investigated with respect to the specimens' geometry. Two end members were tested: specimens where the axial load was applied parallel to bedding (P-specimens) and specimens where the load was applied normal to bedding (S-specimens). Differences in the hydro-mechanical response were identified with respect to the specimens' geometry but also to the stress paths. When subjected to the two-dimensional stress paths, positive excess pore pressure was measured for S-specimens at low differential stresses whereas P-specimens showed negative excess pore pressure. The magnitudes of excess pore pressure were higher for the anisotropic two-dimensional stress path. Dilation associated with yielding was observed for all specimens. The application of the three-dimensional stress path revealed pore pressure responses that were conceptually comparable to the pore pressure response observed in situ. Pore pressure increase in front of the tunnel face can be related to poroelastic response of the rock mass to a change in differential and mean stress. Again, differences between P- and S-specimens were identified. Decrease in pore pressure before the tunnel face can be related to the dilation associated with yielding. No difference in peak strength between P- and S-specimens and the different stress paths was found. Nevertheless, it was shown that the state of failure is affected by the transversal isotropy as S-specimens fail at lower effective stresses compared to P-specimens. [ABSTRACT FROM AUTHOR]

Phase III of Harbin Metro Line #1 was constructed in low to medium plasticity silty clay. In the primary design, forepoles with a spacing of 0.8 m were used as pre-support. However, it was found in the practice that the drilling rate was low and the grouting diffusion range was limited when the water content was low in the silty clay. In order to determine the optimum forepole spacing in relation to water content of the silty clay subject to tunnelling, a method combining laboratory tests, numerical simulations with field monitoring was developed in this study. A series of laboratory tests were performed to relate the deformation and strength parameters of the silty clay with water content. The silty clay has been sub-classified according to liquid index the mechanical parameters at different sub-classes were suggested. The parameters were used in numerical simulations for the determination of the optimum forepole spacing for tunnels in soil mass with different water contents. Field monitoring was performed to calibrate the water content-dependent deformation and strength parameters used in the numerical simulations. Numerical simulations were performed to obtain the ground surface settlement, crown settlement and steel rib axial stress for the cases without pre-support, and with forepores in different spacing. Finally, a scheme for the determining the optimum forepole spacing in relation to water content of the silty clay was obtained. In the scheme, for the silty clay with liquid limits in the range of 0.05–0.20, the tunnel could maintain stability without forepoles for the silty clay with liquid limits in the ranges of 0.20–0.45, and 0.45–0.8, the tunnel could maintain stable with forepoles in spacing of 0.8 m and 1.6 m, respectively. This scheme was used in both the phase III of Harbin Metro Line #1 and Harbin Metro Line #3. The practices proved that the scheme was applicable to the pre-support for safe and economic tunnelling in the low to medium plasticity silty clay for Harbin Metro construction. [ABSTRACT FROM AUTHOR]

This paper introduces a new method for quantifying the morphological evolution of the strain response envelope (SRE). The Fourier series approximation was used to trace the morphological characteristics of SREs. Two SREs computed via numerical simulations using the Modified Cam Clay (MCC) model and three SREs obtained from stress-probing experiments on Chicago clay were used to validate the proposed method of Fourier series approximation. The results show that using a harmonic number of 1 or 2, the target shape of the SRE can be approximated within a 10% error. [ABSTRACT FROM AUTHOR]

That permeability is a critical parameter dictating the performance of naturally fractured reservoirs, like coalbed methane (CBM), is evident form the available field, experimental and permeability modeling information in the literature. Although modeling is often achieved at the expense of several input parameters, the exercise is typically unable to match sudden increases in coal permeability, encountered in deep coals after significant depletion. This paper is aimed at coupling stress and permeability in order to reduce the number of parameters required for modeling the permeability variation. Stresses in the reservoir are translated to invariants and stress path of coal is established in octahedral effective stress plane. Based on a detailed analysis of the stress path of three different coal types, a permeability model is presented in terms of stresses alone, that is applicable for elastic as well as inelastic deformations of coal. The model is validated using pressure-dependent-permeability experimental data for three coal types along with the geomechanical testing data used to develop the failure envelope. The primary implication of the study is improved capability to predict permeability of deep coal deposits, given that they are likely to undergo inelastic deformation or shear failure with continued depletion, using one parameter only. Finally, realistic constraints on the values of the parameter are provided to enable operators with the necessary tools to use the model for field applications, particularly in the new and upcoming CBM fields. [ABSTRACT FROM AUTHOR]

Rainfall-induced flowslides in soil slopes remain one of the most destructive natural hazards. To prevent and mitigate the hazard requires a good understanding of soil behavior under the constant shear drained (CSD) stress path. This stress path differs from typical triaxial compression stress paths that have been extensively studied in soil laboratories. Here we present an attempt to explore various behaviors of loose granular packings along different stress paths and the associated micromechanical mechanisms using a robust grain-scale modeling technique. Through systematic simulations of the CSD, constant-volume (CDCV), and conventional drained (CD) shearing stress paths, we show that the behavior under the CSD stress path conforms to critical state concepts at both macro- and micro-scale. The evolutions of the stress ratio (q / p'), coordination number (Z), and fabric anisotropy (a c) along the CSD stress path are highly similar to those along the CD stress path. A substantial plastic strain tends to develop once the second-order work becomes nonpositive along the CSD stress path, while a dramatic drop of shear strength will occur at the vanishing of second-order work along the CDCV stress path. In both cases, the second-order work vanishes at an almost identical stress ratio, which demarcates the lower boundary of the potential instability zone in the stress space. We establish an explicit relationship between this stress ratio and the initial state parameter of the packing. The significance of this relationship lies in its applicability for both CSD and CDCV loading paths and its root in the critical state theory. • We carry out systematic simulations of loose granular packings under the stress path pertinent to rainfall-induced slope failures. • We show that the packing behavior under this stress path complies with the critical state theory at both macro- and micro-scale. • We establish an explicit relationship between the stress ratio corresponding to packing instability and the initial state of the packing. [ABSTRACT FROM AUTHOR]

Compression testing schemes that induce failure in rock specimens primarily through a reduction in confining stress have become increasingly common in recent years. Despite this, the interpretation of the results from such studies are fraught with complications due to the large number of factors that can influence the outcome of such tests relative to standard compression tests that follow a loading path. Among these, unloading rate is especially significant, as it has the potential to both influence peak strength and total test time (i.e. time-dependent effects). In this study, we present a framework to convert unloading rates into equivalent loading rates to facilitate comparison with standard compression test results as well as comparisons across rock types. We then present the results of a suite of 39 compression tests, including strain-controlled standard UCS and triaxial tests, constant deviatoric stress unloading triaxial tests, diagonal stress path unloading triaxial tests, and load-controlled standard triaxial tests. Based on comparison of load-controlled and strain-controlled standard compression tests, it is concluded that strain-controlled tests produce appreciably lower peak strength values, even if relevant ISRM Suggested Methods and ASTM Standards are followed in both cases. Additionally, the different control modes produce different volumetric strain responses up to the point of peak strength. A detailed comparison of load-controlled test results from standard triaxial tests and unloading triaxial tests with failure points at σ 3 ≈ 1 MPa reveals that diagonal stress path unloading tests produce comparable peak strength values to standard load-controlled tests. Although the observed trend in the constant deviatoric stress unloading triaxial test data corresponds to lower peak strength values than those obtained using standard load-controlled tests, we attribute this discrepancy to time-dependent damage effects and/or minor damage accumulation during the initial loading phase of the tests rather than to the difference in stress paths. • Complexities of interpreting compression test data under unconventional stress paths are summarized. • A framework for characterizing unloading rates is proposed. • Constant deviatoric stress unloading tests are compared to standard tests. • Discrepancies between load- and strain-controlled test results are identified. • No stress path effects were identified. [ABSTRACT FROM AUTHOR]

The objective of this study is to characterize the damage evolution behavior of concrete under hydrostatic pressures varying from 30 MPa to 500 MPa for better understanding the concrete material properties at complex stress states. A series of uniaxial tests were carried out to evaluate the damage degree of concrete after hydrostatic tests and a number of microscopic observations were also provided to allow visualizing the changes of microstructures of the specimen after and before hydrostatic tests. The effect of stress path on compressive meridian and tensile meridian of concrete was also studied. Experimental results indicate that concrete suffers obvious damage if the applied hydrostatic pressure is higher than the uniaxial compressive strength of concrete specimen. The strength and Young's modulus of concrete decrease significantly after hydrostatic tests and the aggregate-mortar interfacial transition zone (ITZ) is the most obvious damage region. The stress path has insignificant effects on ultimate strength envelopes. But if the stress path involves a high hydrostatic pressure that damages the concrete specimens upon unloading, the strength envelope “shrinks” because of the damage to concrete due to high hydrostatic pressure. [ABSTRACT FROM AUTHOR]

While the Critical State Locus (CSL) determined from triaxial compression tests is commonly adopted for the constitutive modelling of soil, the validity of the locus for other stress paths needs to be proved. Several authors have tried to experimentally verify whether the classical CSL representation in the stress invariants – void ratio space could be considered as unique or should depend on the loading direction, but the question is still being debated and a unique conclusion has not been convincingly drawn. In order to clarify this issue, compression and extension triaxial tests are performed on granular materials with different characteristics, namely, two homogeneously distributed sands and an assembly of steel spheres prepared under different initial conditions. The procedure for identifying the CSL is reviewed and indicates the limitations arising from strain localization (shear bands and necking). All the tests show that the materials head to systematically different traces in the e - p ′ and p ′ -q planes when sheared under triaxial compression and extension. Searching for the reasons for this phenomenon, small samples of sand are subjected to the same tests quantifying the whole strain field with X-ray tomography and a digital image correlation. This analysis reveals an inhomogeneous pattern of deformation that is strongly affected by the presence of the two rigid frictional bases and the flexible side membrane, even for the samples deforming in an apparently uniform manner. The different localization observed for the compression and extension tests justifies the dependence of the CSL on the stress path seen on the global scale. On the other hand, a unique trace of the CSL is obtained in the volumetric e-p ′ plane when the void ratio is measured limitedly to the zones affected by the largest distortion. [ABSTRACT FROM AUTHOR]

The behavior of crushable rockfill sheared along different stress paths is studied using the discrete element method. Rockfill particles are modeled as breakable agglomerates, and reasonable consistency is found between the predicted and experimental results. The simulation highlights the influence of agglomerate breakage on both the macro- and micro-behavior of the assembly. The evolution of both the number and mode of agglomerate breakage during shearing is significantly influenced by the confining pressure, deviator stress ratio, and loading direction. The relationship between the deviator stress ratio on the macro-scale and the deviator fabric on the micro-scale along different stress paths is explored. [ABSTRACT FROM AUTHOR]

This paper presents a novel analytical solution for geotextile-wrapped soil based on a comprehensive numerical analysis conducted using the discrete element method (DEM). By examining the soil–geotextile interface friction, principal stress distribution, and stress–strain relations of the constituent soil and geotextile in the DEM analysis, a complete picture of the mechanical characterization of geotextile-wrapped soil under uniaxial compression is first provided. With these new insights, key assumptions are verified and developed for the proposed analytical solution. In the DEM analysis, a near-failure state line that predicts stress ratios relative to the maximums at failure with respect to deviatoric strain is uniquely identified; dilation rates are found to be related to stress ratios via a single linear correlation regardless of the tensile stiffness of the geotextile. From these new findings, the assumptions on the stress-state evolution and the stress–dilatancy relation are developed accordingly, and the wrapped granular soil can therefore be modeled as a Mohr–Coulomb elastoplastic solid with evolving stress ratio and dilation rate. The development of the proposed analytical model also demonstrates an innovative approach to take advantage of multiscale insights for the analytical modeling of complex geomaterials. The analytical model is validated with the DEM simulation results of geotextile-wrapped soil under uniaxial compression, considering a wide range of geotextile tensile stiffnesses. To further examine the predictive capacity of the analytical model, the stress–strain response under triaxial compression conditions is solved analytically, taking both different confining pressures and geotextile tensile stiffnesses into account. Good agreement is obtained between the analytical and DEM solutions, which suggests that the key assumptions developed in the uniaxial compression conditions also remain valid for triaxial compression conditions. [ABSTRACT FROM AUTHOR]

Fluid injection operations, such as CO 2 storage and enhanced oil recovery (EOR), imply reservoir pressurization, which changes the effective and total stresses due to poroelastic effects. These stress changes control the geomechanical stability of discontinuities like faults and fractures. Though the effect of these pre-existing discontinuities on stress path is sometimes neglected, the stress state is altered around them. We investigate the effect of a fault on the stress path evolution when pressurizing a reservoir using an in-house hybrid FEM-DEM code called “MDEM”. Simulation results indicate that the stress path is affected by the presence of faults considered to deform elastically, especially in the vicinity of the fault in the reservoir-caprock interfaces. The stress path perturbation is caused by the shear deformation of the fault plane, which is different in the reservoir and the caprock sections. Actually, the magnitude and the extension of the stress path perturbation around a fault become larger for faults with lower shear stiffness. The upper hanging wall and the lower footwall of the fault in the reservoir-caprock interface experience a higher stress path in the horizontal and the vertical directions. Furthermore, the stress paths decrease (negative in the vertical direction) in the upper footwall and the lower hanging wall in the reservoir-caprock interfaces. The fault effect on the stress path increases as the aspect ratio of the reservoir becomes lower. Moreover, the results indicated that both the caprock and the reservoir in the footwall experience a greater change for lower Poisson’s ratio of the caprock. These stress changes are independent of the in situ stress regime as long as the fault deforms elastically. However, the impact of the stress path perturbation on the stability of the reservoir and the caprock is different in a compressional (reverse faulting) and an extensional (normal faulting) stress regimes. The stress state becomes less stable in the vicinity of the fault in the reservoir and in the caprock in a compressional stress regime than in an extensional stress regime. Therefore, a compressional stress regime leads to a less stable situation due to the fault effect on the evolution of the stress path. Overall, the presence of faults alters the stress state around them, which may lead to a stress state that is closer to failure conditions than predicted by models that do not explicitly include faults. [ABSTRACT FROM AUTHOR]

The 1920 Haiyuan Ms 8.5 earthquake induced a large number of fluidized loess landslides in China, characterized by low slope angles, long run-out distances, and fluidized movement. The mechanism of these landslides has aroused considerable interest, although additional research is needed to understand more fully the behavior of the loess and the failure mechanism. Field investigation was conducted on the Shibeiyuan landslide, and loess samples collected for later laboratory analysis by conventional geotechnical tests, triaxial compression tests, and ring shear tests. The field survey revealed that the Shibeiyuan landslide occurred on a concave slope (< 5°) with a long run-out distance, indicating a small apparent friction angle. It was also found that standing water was present in the landslide area and that the loess had high porosity. Experimental results showed that application of cyclic shear stress to a loose and saturated loess specimen causes excess pore pressure to develop gradually, resulting in a decrease of effective stress until liquefaction. The steady state strength of the loess showed no correlation with stress path, but it was closely related to the degree of saturation, loading rate, and void ratio. This indicates that excess pore pressure can accumulate under seismic loading and that plastic deformation can develop rapidly within a shearing zone, resulting in loess liquefaction and a reduction of shear strength. In the Shibeiyuan landslide, the steady state strength was near zero with the large deformation related to the low angle, long distance, and fluidized movement. [ABSTRACT FROM AUTHOR]

In this paper, the general shear strain hardening and/or softening Drucker-Prager models based on the common triaxial compression test results have been introduced to model the mechanical behaviour of rock formations. These elastoplastic models are then adopted to develop rigorous analytical solutions for the drained wellbore drilling problem subjected to in-plane isotropic stress field, and to further predict the borehole collapse failure. The illustration numerical examples show the distributions of stress components and the progressive development of the plastic deviatoric strain, in addition to the effective stress trajectory for a rock point at the borehole surface due to the wellbore drilling. The advantage of the desired wellbore drilling curve presented lies in the fact that it can track the deformation responses of the borehole surface from elastic to elastoplastic states and down to the peak and ultimate/residual conditions, thus offering much more flexibility and more appropriate mud pressure design over the conventional elastic-brittle models. The critical (minimum) mud pressures, predicted by the current elastoplastic analysis based on different wellbore instability criteria, are compared with the value corresponding to the elastic theory. The solution procedure proposed can also be utilized for the tunnelling analysis and extended to the design of lining required to stabilize a tunnel. [ABSTRACT FROM AUTHOR]

The objective of this study is to examine the stress state of soils during deep excavation, in relation to the determination of appropriate soil parameters for deformation analysis of a deep excavation case using the finite element method. Two well documented case histories of a deep excavation were utilized for the validation of the analysis procedure and the selection of soil stiffness parameters. Results from the Hardening Soil model showed that the out-of-plane stress has significance influences to the direction of soil effective stress path. In addition, most of the soil inside and outside excavation zone is in the elastic behavior. Even though the effective stress path of soils adjacent to the diaphragm wall have undergone yield, but the characteristics of those soils are still dominated by the elastic behavior. Hence, the unloading/reloading parameters are predominant in a deformation analysis of an excavation case. When the undrained shear strength and unloading/reloading modulus were precisely specified, even the Mohr-Coulomb model could obtain good prediction of the wall deflections. Moreover, a hypothetical case was employed to investigate the performance of the computed ground surface settlements. The result showed that the computed ground settlement from Mohr-Coulomb model was close to the result from the Hardening Soil Small model if the layer of soft soil is deep enough and a layer of small strain stiffness zone is introduced at bottom of the model geometry. [ABSTRACT FROM AUTHOR]

• This study highlights the limitation of uniaxial strain assumptions in fault stability assessments for CO2 injection sites, revealing that this simplified approach underestimates the change in effective horizontal stress. • Discrepancies between 3D geomechanics simulations and uniaxial strain assumptions are largest when bounding faults are juxtaposed with softer materials, emphasizing stiffness contrast importance. • The uniaxial strain assumption overlooks critical scenarios for fault stability assessments due to its inability to account for lateral deformation on the fault/reservoir boundary. • To correct uncertainties caused by the uniaxial strain assumption, the study suggests calibrating the fault stability assessment by 30% for a base case and 60% for a conservative assessment when bounding faults are juxtaposed with low-stiffness shale formation under a normal stress regime. This study investigates the limitation of simplified stress path assumptions, particularly uniaxial strain conditions, in fault stability assessments for CO 2 injection sites. We conducted a 3D geomechanics simulation for the Smeaheia fault block in the Norwegian North Sea and compared the results with simplified stress path assumptions. Our results indicate that the uniaxial strain assumption underestimates the change in effective horizontal stress, particularly for bounding faults subjected to a significant change in pore pressure gradient with soft surroundings. Rotations of maximum horizontal stresses parallel to soft surroundings are also observed along the bounding faults due to the directional difference in stiffness contrast along faults. This underestimation results in overestimation of fault stability by up to 60% for an extreme case. Our study thus highlights that the uniaxial strain assumption, which limits to account for lateral deformation on the fault/reservoir boundary, overlooks critical changes in the effective horizontal stress and associated critical scenarios for fault stability assessments. When bounding faults are juxtaposed with low-stiffness shale formation under a normal stress regime, calibrating the fault stability assessment by 30% for a base case and 60% for a conservative assessment can provide a practical way to correct the uncertainties caused by using uniaxial strain assumption. [ABSTRACT FROM AUTHOR]

This paper uses 3D numerical analyses to investigate the stress path experienced by soil elements around large diameter piles in sand subjected to monotonic drained lateral loading. Inspection of the loading-induced stresses in the soil revealed the multiaxial nature of these stress paths, which are characterised by rotation of one or more principal stress axes. Based on the outcome of the finite element analyses, typical stress paths for different soil elements around the piles are extracted. Such stress paths are then evaluated against those enabled by conventional and advanced laboratory soil element testing. It is found that a combination of tests in the Hollow Cylinder Torsional Apparatus (HCTA) can reproduce most features of the numerically identified stress paths for soil elements around the pile. Unavoidable limitations in laboratory testing are discussed as well as the major challenge in replicating the loading direction with respect to the material axes. Some guidance for the experimental implementation of these stress paths in the HCTA are provided as well as a discussion on the use of conventional experimental equipment, such as the conventional triaxial or simple shear apparatus. [ABSTRACT FROM AUTHOR]

In this study, the accumulated plastic strain (APS) of granite residual soil (GRS) under traffic loading is investigated via cyclic hollow-cylinder and triaxial tests. GRS is a special type of soil that is found widely in the hot and rainy areas of southern China. Because of insufficient understanding of the cumulative plastic deformation of GRS, how the dynamic stress amplitude, degree of saturation, effective consolidation stress, and stress path affect the APS under loading cycles is explored and analyzed. The results show that the effective consolidation stress inhibits the development of APS, whereas the dynamic stress amplitude promotes it. The APS of GRS increases with the degree of soil saturation, and its noticeable water-softening characteristics become the least favorable factor for soil deformation. The combined action of water softening and principal stress rotation helps to increase the APS significantly, and it leads to the emergence of an APS developmental curve that differs from the stable curve. Accounting for the water-softening characteristics of GRS and various stress conditions, a simple and easily adopted APS model is developed to predict the evolution of APS with loading cycles. Although specific to GRS in China, the findings of this study are expected to apply more widely to other weathered geomaterials. •Water softening properties affect the cumulative plastic strain of residual soil. •Principal stress rotations lead to unprecedented types of cumulative deformation. •The proposed model is suitable for residual soil under different test conditions. •Structural strength causes different strain types in original and remodeled soils. [ABSTRACT FROM AUTHOR]

Wrapping granular soils in geosynthetic containers, such as soilbags, results in a considerable increase in the bearing capacity due to the effective restraint on the dilatancy of the soil. This paper numerically investigates the stress states and fabric anisotropies in the wrapped soil using the discrete element method, providing a novel perspective for new insights into the reinforcement mechanisms and the development of constitutive relations for soilbags. The two most anticipated loading conditions, namely, unconfined compression and simple shear, are considered, and numerical predictions are compared to experimental results. During unconfined compression, both global and local p – q stress paths evolve linearly, having the same slope until the global failure of the wrapping geosynthetic. Under simple shear, the global stress path approaches the critical state line first and then turns to the compression line of the wrapped soil. Some local loading–unloading stress paths are observed, which may account for the high damping of soilbags during cyclic shear. The reduced fabric anisotropies of the normal and tangential force chains suggest greater confinement from the lateral sides of the geosynthetic container in either loading course. The performance and mechanisms of the soilbag earth reinforcement method, i.e., confinement and interlocking, can be better understood based on these new findings on the stress states and fabric anisotropies. [ABSTRACT FROM AUTHOR]

A constitutive model for sand is derived based on a new theoretical framework that combines features of perfect elastoplasticity and smooth hysteresis. It resembles a bounding surface model with vanished elastic region, but with considerable modifications in that the plastic modulus is not explicitly defined, and the mapping rule is Bouc–Wen motivated and works equally well in monotonic as in stress-reversal loading. Among the proposed features, are: (a) critical state compatibility not only for monotonic but also for cyclic loading, and (b) novel plastic flow rule accounting for anisotropic distribution of the dilatancy strain ratio, d , to the normal plastic strain increments. The capability of the model in capturing complex aspects of sand behavior (e.g. cyclic mobility, static liquefaction, densification) is demonstrated through illustrative paradigms with emphasis on the physical meaning of each key-model parameter and comparisons with experimental data. [ABSTRACT FROM AUTHOR]

Production of hydrocarbons from geological reservoirs, and injection of fluids such as water or CO 2 into geological strata are accompanied with stress changes in the reservoir and in the cap rock. If the stress changes are large enough, they may reactivate faults or pre-existing natural fractures, or induce new fractures in the reservoir and/or the cap rock. Fractures in the cap rock caused by stress changes during CO 2 injection may threaten the cap rock integrity. Fractures within the reservoir may increase its injectivity, improve hydraulic communication and thereby facilitate spreading of the injected fluid. The objective of this work was to classify possible stress dynamics and fracturing scenarios that may take place under geological storage of CO 2 . A compendium of stress regimes and expected fracture patterns is compiled that can be used as a quick guide when evaluating the risk of fracturing under CO 2 injection into deep saline aquifers or depleted fields as well as when estimating geomechanical effects of reservoir stimulation. [ABSTRACT FROM AUTHOR]

Investigation of the volume change behavior of expansive soils typically utilizes conventional oedometer which provide estimates of vertical strain and swelling pressure under fully lateral restrained conditions. In this study, testing was conducted on compacted highly expansive clay using a thin-walled oedometer to evaluate the state of stresses during inundation in both vertical and lateral directions in addition to the vertical strain. First, calibration, correction, and verification of the thin wall oedometer were described. Second, an experimental program was developed to evaluate the volume change behavior during inundation for a wide range of vertical stresses at inundation (σ i ) under two conditions: (i) constant vertical stress at inundation and (ii) constant volume. Results of tests under constant vertical stress at inundation indicate the dependency of strain state of expansive soil on the inundation vertical stress. Moreover, the vertical stress at inundation (σ i ) was observed to affect the vertical stress state after inundation for constant volume condition. Investigating the equilibrium vertical stress state after inundation under constant volume condition showed that there is one relation termed as “Swell-Collapse Equilibrium Line, SCEL” that represents the equilibrium condition after inundation for specimens subjected to different initial sample conditions prior to inundation. General trends of strain softening behavior for the evolution of lateral stresses with time were observed, particularly for the swelling zone. Stress path followed by tested samples was depicted. Interpretation of results in light of Barcelona Expansive Model (BExM) was also performed. An enlargement of yield envelop after loading to stresses greater than past stress history was observed. [ABSTRACT FROM AUTHOR]

A truck–pavement–ground coupling model was established to study the dynamic responses of a saturated poroelastic half-space generated by a moving heavy truck on the uneven pavement. The ground was simulated as a fully saturated poroelastic half-space governed by Biot’s theory. The overlying pavement was simplified as a Kirchhoff thin plate. With the assumption of a sinusoidal pavement surface, the dynamic wheel–pavement force was obtained through a linear Hertizian contact model. The numerical results showed that this dynamic load could make considerable contributions to the stress and excess pore water pressure responses in the ground. Furthermore, the effective stress path of the soil unit beneath the pavement caused by the moving truck was firstly calculated and presented. It was found that the differences between the total stress path and the effective stress path became significant as the truck speed increased, thus the effective stress path was more suitable than total stress path to reflect the stress history of soil elements in the saturated ground during the passage of high-speed traffics. [ABSTRACT FROM AUTHOR]

Highlights: [•] A theoretical model was applied to characterise unloading responses under different paths. [•] The propagation of unloading perturbation was represented in 3D contour maps. [•] Numerical simulation was performed for the 2D unloading responses under different paths. [•] Results of numerical simulation were consistent with the mathematical physical model. [•] The effects of unloading rate and path were studied on excavation unloading responses. [ABSTRACT FROM AUTHOR]

Abstract: The influence of stress paths on the mechanical behavior and coupled permeability evolution of quartz sand packings and soft sandstone have been investigated. The proposed approach is mainly based on the performing drained compression tests keeping constant a stress path parameter K, defined as the ratio of the horizontal to vertical effective stress increments. Macroscopic mechanical data and the stress path dependency of permeability have been measured in the elastic, brittle and compaction regimes. The micro-structural characteristics of unconsolidated materials—coarse rounded grains (glass beads—GB) and angular grains (Durance sand—DS)—and a weakly consolidated sandstone (Otter Sherwood sandstone—OSS) have been quantified in intact and deformed states combining petrophysical core analysis and multi-scale imaging according to the feasibility of sub-sampling of the different materials. Two different types of hydro-mechanical behavior were evidenced for each material. The weakly consolidated OSS presents a mechanical behavior similar to the consolidated rocks with two distinct regimes of deformation; the transition between these two regimes is a function of the stress path. On the other hand, the sand shows a gradual transition regime requiring the use of a curvature criterion to pick yield stresses; this criterion has been validated on the basis of acoustic emissions analysis. The modified Cam-Clay model and the elliptical cap model allow capturing efficiently the yield envelopes. The permeability measurements were performed with intermediate pressure ports to measure accurately the high permeable sand and to avoid end-effects. For OSS, permeability evolutions follow closely the volumetric strain evolutions in both the elastic and plastic regimes and are mainly controlled by the mean pressure before yield. At these critical stresses, the permeability drops drastically under the influence of deviatoric stress. Conversely for DS, the correlation between strain and permeability is not obvious as permeability reduction is pronounced at an early stage of loading. [Copyright &y& Elsevier]

Abstract: In this article, we study the characteristics and spatial distribution of the deformation structures along the Kumano transect of the Nankai accretionary wedge, and use this information to interpret the stress path followed by the sediments. Deformation structures are identified from logging while drilling (LWD) resistivity images of the materials surrounding the drill hole and from 3-dimensional X-ray CT-images of cores acquired during the IODP NanTroSEIZE project. The relative resistivity of the structures identified on logs and the strike, dip, and density of structures identified on CT scan images are measured. The analysis of dip and strike of structures indicates that most of the resistive structures identified on logging data correspond to compactive shear bands. Results also indicate that conductive structures predominate at the toe of the prism and above the main out of sequence thrust, in locations where past and recent erosion occurred. We propose several mechanisms that could explain the relation between erosion and the absence of compactive shear bands. We conclude that sediments followed different stress paths depending on their location within the wedge, and that those differences explain the distribution of deformation structures within the wedge. We also show the coexistence of dilatant and compactant structures in fault zones including the frontal thrust and mega splay fault, and we interpret the coexistence of these structures as a possible consequence of a transient fluid pressure. [Copyright &y& Elsevier]

Viscous pressure forming has shown its advantages in precision forming of complex surface components. However, there are very few reports focusing on revealing the mechanism of springback control by viscous medium. This paper aims to study the effect of viscous medium on springback and the mechanism of springback control by viscous medium. The viscous pressure forming of a bulging axisymmetric geometry is studied. The effect of viscous medium on springback and stress path of sheet is analyzed in numerical simulation by unloading the sheet and viscous medium together. Then, the experiments are conducted using different kinds of viscous medium and loading speeds. The digital correlation image (DIC) technology is employed to measure the springback. The stress and membrane force of the bulging sheet are calculated and analyzed. Results show that non-uniformly distributed force of viscous medium changes the shape and stress path of the sheet. The viscous medium simultaneously possessing good strain rate sensitivity and viscosity can well control the springback. This is because the coupling effect of non-uniform normal force and tangential adhesion promotes the uniformity of stress distribution on the whole sheet and reduces the bending moment of sheet near the die corner. [Display omitted] • The mechanism of springback control by viscous medium is investigated. • The effect of viscous medium properties and loading speeds on springback is studied experimentally. • The viscous medium simultaneously possessing good strain rate sensitivity and viscosity can well control the springback. • The coupling effect of non-uniform normal force and tangential adhesion reduces the stress gradient and bending moment. [ABSTRACT FROM AUTHOR]

The quasi-static method was used to study the internal stress path in deep-sea sediment under the driving load of a crawler-type nodule collector. First, the instantaneous stress state of a soil element was calculated according to the theory of elasticity and was compared with the results of a numerical simulation. Next, the relative positions of the load imposed by the nodule collector and the soil element were changed to simulate the driving of the nodule collector to obtain the full-time stress path in the soil. Finally, the stress path and rotation of the principal stress axes in the soil at typical positions were analysed. The results showed that the spatial position of the soil had a significant influence on the stress path. In addition, the stress, peak value of the time-history curve for the principal stress and rotation mode of the principal stress axes showed correlations with the spatial position. Therefore, the stress-loading scheme should be selected according to the actual conditions of a given position in a laboratory test. A method was developed for representing the three-dimensional (3D) rotation of the principal stress axes based on a spherical projection of the direction vector. The proposed method can intuitively show the rotation law of the principal stress axes at any position in the soil during the driving of the crawler. • Presents mechanical models for predicting the stress in deep-sea sediments. • The models are developed using the mining vehicle's parameters. • The models predict the stress path of sediments under different depth. • Both the magnitude and direction of soil principal stress turned simultaneously. • A new three-dimensional stress path expression method is proposed. [ABSTRACT FROM AUTHOR]