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Dilatancy is commonly defined as the ratio of the rates of plastic volumetric strain to plastic deviatoric strain, denoted as Dp. Owing to the high modulus of elasticity, the elastic volumetric and deviatoric strain rates under shear stress in conventional cohesionless materials are negligible. Therefore, using the ratio of the rates of total volumetric to deviatoric strain (Dt) as an approximation is common in studying stress–dilatancy behavior and calibrating dilatancy model parameters. This approach is also common in the study of rubber-added cohesionless materials (RCM). However, RCM with a common range of rubber content exhibit a significantly lower modulus of elasticity compared to conventional cohesionless materials. Further research is needed to evaluate the potential impact of elastic strain rates in RCM on stress–dilatancy analysis. Therefore, comparisons were conducted on the stress–dilatancy responses of a series of tests on RCM, where dilatancy is calculated by Dp and Dt, respectively. Furthermore, a modified method for calibrating the parameters of a state-dependent dilatancy model considering Dp is presented. It turns out that Dp is better suited and more precise for dilatancy analysis on highly elastic RCM. Additionally, the dilatancy model can more precisely capture the test results of RCM with parameters calibrated by the proposed method. [ABSTRACT FROM AUTHOR]

Highlights: A relaxation test data set is reinterpreted with a focus on radial strain Specimens loaded below the crack damage stress contracted more than predicted by elasticity theory The rate of lateral contraction increased when the stress had dropped by between 50% and 80% of the total stress relaxation observed at the end of the test One specimen loaded just above crack damage changed from dilation to contraction at the transition from primary to secondary relaxation [ABSTRACT FROM AUTHOR]

The anisotropic microstructure of granular materials has a profound effect on their macroscopic behaviour and can be characterised using a fabric tensor. To include of fabric in the critical state theory (CST), anisotropic critical state theory (ACST) was proposed by modifying the state parameter (ψ) of CST to a fabric-dependent dilatancy state parameter (ζ) . Noteworthy that ψ showed a very strong correlation with characteristic features (e.g. instability, phase transformation and characteristic state) of macroscopic behaviour and, as a result, it has been adopted in many constitutive models. While ζ aided the inclusion of fabric in ACST models, the correlation between ζ and characteristic features has not been evaluated in detail yet, although a large number of works are found on micromechanics and fabric only. In this study, a large number of discrete element method simulations for drained and undrained triaxial were conducted to evaluate the correlation between ζ and characteristic features. To this purpose, the correlation between stress ratio and both classic and dilatancy state parameter (ψ and ζ ) were studied in important characteristic features (e.g. instability, phase transformation and characteristic state). It was found that this correlation was improved using ζ which might be due to the inclusion of fabric in our model. This observation is new and significant for inclusion of fabric evolution in constitutive modelling. [ABSTRACT FROM AUTHOR]

Lack of investigation into the tensile strength characteristics of unsaturated tailings hinders their recycling as construction materials in bulk earthworks. Here, the strength characteristics and strength-dilatancy relation in the tensile stress regime of unsaturated tailings were investigated via flattened Brazilian and direct shear tests. A nonlinear variation of tensile strength with water contents was observed. The unsaturated tailings with water contents below the plastic limit were strain softening and dilative under low normal stress. Furthermore, an analytical equation was proposed to predict the tensile strength of compacted tailings via the soil water characteristics curve (SWCC) and corroborated via experiments. [ABSTRACT FROM AUTHOR]

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

The study aims to investigate and find natural fiber as concrete reinforcement using the self-compacting concrete method. Methods of adding fiber and self-compacting concrete methods are exciting because these two methods have different characteristics and advantages. Therefore, the performance of the fresh-state flow capability of the self-compacting concrete method, which contains various fibers, was observed. Coconut fiber, pineapple leaf fiber, ijuk sugar palm fiber, and artificial polypropylene fiber were used with varying compositions of 0.3, 0.5, and 0.7% by mass of binder. The results show that coconut and pineapple fiber concrete met the European Guidelines for Self-Compacting Concrete standards. The coconut and pineapple fiber concrete performed admirably in all tests. [ABSTRACT FROM AUTHOR]

Injection-induced seismicity and aseismic slip often involve the reactivation of long-dormant faults, which may have extremely low permeability prior to slip. In contrast, most previous models of fluid-driven aseismic slip have assumed linear pressure diffusion in a fault zone of constant permeability and porosity. Slip occurs within a frictional shear crack whose edge can either lag or lead pressure diffusion, depending on the dimensionless stress-injection parameter that quantifies the prestress and injection conditions. Here, we extend this foundational work by accounting for permeability enhancement and dilatancy, assumed to occur instantaneously upon the onset of slip. The fault zone ahead of the crack is assumed to be impermeable, so fluid flow and pressure diffusion are confined to the interior, slipped part of the crack. The confinement of flow increases the pressurization rate and reduction of fault strength, facilitating crack growth even for severely understressed faults. Suctions from dilatancy slow crack growth, preventing propagation beyond the hydraulic diffusion length. Our new two-dimensional and three-dimensional solutions can facilitate the interpretation of induced seismicity data sets. They are especially relevant for faults in initially low permeability formations, such as shale layers serving as caprock seals for geologic carbon storage, or for hydraulic stimulation of geothermal reservoirs. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]

Abstract—The hydrogeology of fault zones, especially at considerable depth, is perhaps a most underdeveloped field in earthquake source mechanics. This is due to both the lack of the data on the filtration characteristics of the geomaterial at large depths and to the complexity of the processes of mass transfer, fracture formation and healing under high temperatures and pressures. In this case, the strong influence of fluid on both the friction characteristics and the stress conditions in the vicinity of the slip zone is obvious. Fluids are carriers of dissolved matter and thermal energy, an effective catalyst for various types of metamorphic transformations. According to some models, fluid flows can be triggers for the initiation and arrest of seismogenic ruptures. The current trend in world seismology to constructing a complex computational model that adequately describes the processes of preparation, initiation, and arrest of various fault slip modes requires developing the ideas about fluid dynamics of seismogenic faults. This review considers the information on hydrogeology of fault zones obtained in recent years. Models and ideas involving field data, laboratory and field experiments and numerical calculations regarding the role of fluids at different stages of the seismic cycle are analyzed. [ABSTRACT FROM AUTHOR]

Slowing down translocation dynamics is a crucial challenge in nanopore sensing of small molecules and particles. Here, it is reported on nanoparticle motion‐mediated local viscosity enhancement of water‐organic mixtures in a nanofluidic channel that enables slow translocation speed, enhanced capture efficiency, and improved signal‐to‐noise ratio by transmembrane voltage control. It is found that higher detection rates of nanoparticles under larger electrophoretic voltage in the highly viscous solvents. Meanwhile, the strongly pulled particles distort the liquid in the pore at high shear rates over 103 s−1 which leads to a counterintuitive phenomenon of slower translocation speed under higher voltage via the induced dilatant viscosity behavior. This mechanism is demonstrated as feasible with a variety of organic molecules, including glycerol, xanthan gum, and polyethylene glycol. The present findings can be useful in resistive pulse analyses of nanoscale objects such as viruses and proteins by allowing a simple and effective way for translocation slowdown, improved detection throughput, and enhanced signal‐to‐noise ratio. [ABSTRACT FROM AUTHOR]

Design of geosystems built on coarse-grained soils with broader gradations are typically based on methodologies developed for clean sands without explicit consideration of the effects of gradation, potentially leading to uncertainty in performance predictions. This study investigates the effect of changes in gradation on the shear strength, stress-dilatancy behavior, critical state parameters, and fabric evolution of coarse-grained soils using three-dimensional (3D) discrete element method (DEM) simulations. The simulations of monotonic isotropically-consolidated drained and undrained triaxial tests were conducted on specimens with coefficients of uniformity (CU) between 1.9 and 6.4 composed of nonspherical particles following the calibration of parameters against experimental triaxial data. Results are used to evaluate the peak and critical state shear strengths, dilatancy responses, critical state lines, shear-induced pore pressures, and fabric evolution. Notably, an increase in CU leads to increases in peak shear strength, total dilation, rate of dilation, negative pore pressure magnitude, and rate of pore pressure generation. The results show that the state parameter better captures the effect of gradation than the relative density because the former accounts for the difference between the initial and critical states. The trends in triaxial parameters are compared with established frameworks to highlight the differences in response resulting from variations in CU. The particle-level measurements indicate that gradation affects the packing characteristics and contact force transmission, where broader gradations result in greater interlocking between coarser particles, and the presence of coarser particles increases the anisotropy of the strong force networks. The finer particles provide resistance to buckling within these strong force networks. Additionally, particles smaller than D10 are inactive in stress transmission, and the percentage of particles inactive in stress transmission decreases with an increasing CU. The combination of macro- and microresults contributes to understanding the mobilization of stress and its dependency on dilatancy in soils of varying gradation. [ABSTRACT FROM AUTHOR]

To clarify the stress–strain behaviour, strength on the deviatoric plane, shear band formation, and dilatancy characteristics of aeolian sand under three-dimensional loading conditions, a series of true-triaxial tests with various intermediate principal stress coefficients b ∈ [0.0, 1.0] at constant effective mean principal stress p' were conducted under drained and undrained conditions. The results presented that the variations of the stress–strain, strength, and effective internal friction angle show its significant dependence on the relative magnitude of the intermediate principal stress expressed in terms of the b value. Because a clear penetrating shear band was produced in the prismatic specimen at b = 0.2 and b = 0.4, the stress–strain response exhibits softening, and its peak shear stress and effective internal friction angle are reduced. Besides, shear bands often appear in the hardening regime. Moreover, the dilatancy was the weakest at b = 0.0 and the strongest at b = 0.4, which depended on the stress path in terms of the b value. The peak shear stress on the deviatoric plane decreased in a transverse "S" shape with the b value varying from 0.0 to 1.0, correspondingly, the effective internal friction angle increased first and then decreased. But in the case of increasing p' value, aeolian sand has a unified critical state line and phase transformation line at constant b value. [ABSTRACT FROM AUTHOR]

To appropriately connect good simulation of rockfill material stress–strain behavior at element level with good simulation of dam deformation, a practical nonlinear elastic EBD constitutive model is developed by introducing dilatancy into the traditional Duncan–Chang EB model. Based on the dam deformation monitoring data of the 164.8 m high Aertashi concrete face rockfill dam and particle swarm optimization, five inversion cases are designed to obtain the optimal EB and EBD model parameters that achieve the best fit with monitoring data. The traditional EB model is shown to have difficulties in achieving good simulation for both settlement and horizontal displacement of rockfill dams, especially in terms of their distribution, whereas the EBD model can simulate both settlement and horizontal displacement well. More importantly, the EB model parameters that allow for acceptable simulation of dam deformation result in poor simulation of element level stress–strain behavior of the gravelly sand, rockfill, and overburden materials. In contrast, the EBD model can achieve good simulation of dam deformation and element level stress–strain behavior simultaneously, paving the way for accurate dam deformation prediction based on model parameters calibrated via triaxial tests. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University 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.)

The deformation characteristics and constitutive behavior of granular materials under normal forces acting on particles are dependent on the geometry of the grain structure, fabrics and the inter-particle friction. In this study, the influence of particle morphology on the friction and dilatancy of five natural sands was investigated using deep learning (DL) techniques. A Three-dimensional (3D) imaging technique using computed tomography was utilized to compute the morphology (roundness and sphericity) of collected natural sands. Triaxial tests were conducted on the five different natural sands at different densities and confinement stresses (σ3). From the triaxial results, peak friction angle (φp), critical state friction angle (φcs), and dilatancy angle (ψ) were obtained and modeled using conventional multiple linear regression (MLR) models and DL techniques. A total of 100 deep artificial neural networks (DANN) models were trained at different sizes of first and second hidden layers. The use of MLR resulted in R2 of 0.709, 0.565, and 0.795 for φp, φcs and ψ, respectively, while the best performed DANN (30 and 50 neurons for the 1st and 2nd hidden layers, respectively) had R2 of 0.956 for all outputs (φp, φcs and ψ) combined. Using the best-performed DANN model, the weight partitioning technique was used to compute an importance score for each parameter in predicting φp, φcs and ψ. The σ3 had the highest importance followed by relative density, roundness, and sphericity with a relative importance of more than 10%. In addition, sensitivity analysis was conducted to investigate the effect of each parameter on the shear parameters and ensure the robustness of the developed model.

Dilatant hardening is one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro‐computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ∼10 MPa, while varying confining pressure (10–130 MPa) and pore fluid pressure (1–120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior. Plain Language Summary: When rocks are breaking, the pore spaces and developing fractures dilate, resulting in a decrease in pore fluid pressures. This decrease can strengthen the rock from ongoing deformation in a process known as dilatant hardening. We conducted experiments to better understand how this strengthening effect works, in particular looking at the ratio of pore fluid pressure to the external confining pressure (simulating rocks buried at depth), and also analyzed how the fractures that develop can vary from dilatant hardening. We found a threshold pressure at which the strengthening peaked, and increasing pore fluid pressure did not change how strong the rocks got from continuing deformation. We also observed a drastic increase in how damage was distributed due to this hardening effect at both a large (visible to the naked eye) and small scale (only visible in a high‐magnification microscope). These results indicate that dilatant hardening can increase how much energy must be expended to break the rock and to cause faults to slip when pore fluid pressures are high enough, and likely plays a role in stabilizing fault slip, causing earthquakes to slow down and be less dynamic. Key Points: We measured the transition between dynamic and stable rupture as a result of dilatant hardeningWe observed differences in microstructural development tied to the shift in rupture styleWe developed a model of fracture nucleation and propagation at different pore fluid pressures [ABSTRACT FROM AUTHOR]

Copyright of Revue Française de Géotechnique is the property of EDP Sciences 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.)

Constitutive models in the literature for creep of frozen soil are based on the direct use of time counted from the onset of creep. An explicit time dependence in a constitutive equation violates the principles of rational mechanics. No change in stress or temperature is allowed for during creep, using the time-based formulations. Moreover, the existing descriptions need much verification and improvement on the experimental side as well. Creep behaviour of artificially frozen sand was evaluated experimentally. Novel testing methods were used, and new insights into the creep behaviour of frozen soil were gained. Creep rate under uniaxial compression was examined with different kinds of interruptions, like unloadings or overloadings. Experimental creep curves were presented as functions of creep strain. They were brought to a dimensionless form which describes the creep universally, despite changes in stress or temperature. Possible anisotropy of frozen soil was revealed in the creep tests on cubic samples with changes of the loading direction. Using the particle image velocimetry (PIV) technique, information on the lateral deformation and the uniformity of creep were obtained. Volumetric creep of unsaturated frozen soil under isotropic compression was demonstrated to be due to the presence of air bubbles only. [ABSTRACT FROM AUTHOR]

Calcareous sand is the main geomaterial available for island-reef reclamation construction projects in the South China Sea. To clarify the effect of particle breakage on the dilatancy of calcareous sand, multiple consolidated-drained triaxial shear tests were conducted on calcareous gravelly sand (CGS) under different conditions. On this basis, dilatancy assessment indices were constructed from the perspectives of stress ratio and dilatancy ratio, and their relationships with the initial physical parameter and stress level of CGS were established. Next, the variations in particle breakage of CGS with compactness and stress level were explored, and a physical model was proposed to predict particle breakage according to plastic work. Finally, the relationship between dilatancy and particle breakage was established for CGS. The results lay a research foundation for developing an elastoplastic constitutive model considering the effect of particle breakage for CGS. In this study, the dilatancy of calcareous sand was investigated under varying relative densities and effective confining pressures. Then, the variations in the particle breakage of calcareous sand with compactness and stress level were revealed. Finally, the relationship between dilatancy and particle breakage of calcareous sand was established. [ABSTRACT FROM AUTHOR]

Beyond a threshold applied compressive stress, porous rocks typically undergo either dilatant or compactant inelastic deformation and the response of their physical properties to deformation mode is key to mass transport, heat transport and pressure evolution in crustal systems. Transitions in failure modes—involving switches between dilatancy and compaction—have also been observed, but to date have received little attention. Here, we perform a series of targeted mechanical deformation experiments on porous andesites, designed to elucidate complex post-failure deformation behaviour. By investigating a sample suite and effective pressure range that straddles the transition between positive and negative volumetric responses to compression, we show two post-failure critical stress states: a transition from compaction to dilation ([Formula: see text]), and a transition from dilation to compaction, which we term [Formula: see text]. We demonstrate that multiple switches in deformation mode can be driven by stress application under conditions relevant to the shallow crust. While the effect on fluid flow properties of compaction-to-dilation switching may be masked by a net reduction in sample porosity, samples that underwent dilatant-to-compactant failure mode switching exhibited an increase in permeability of approximately two orders of magnitude, despite only slight net volumetric change. Such a substantial permeability enhancement underscores the importance of post-failure deformation in influencing solute and heat transfer in the crust, and the generation of supra-hydrostatic fluid pressures in volcanic environments.

A modelling approach consisting of best-fit relations to estimate the post-yield strength parameters is presented for simulating post-peak behavior beyond the point of residual strength of coal pillars having different w/h ratios. The model was developed based on back-analysis of the complete stress-strain behavior of specimens belonging to six different Indian coal seams with different w/h ratios of 0.5–13.5. It was found that the simultaneous degradation of the cohesion and friction angle of the Mohr-Coulomb rock material characterizes the post-peak strength behavior of the rock. The resulting expressions are simplistic as they require parameters that can be easily determined using uniaxial and triaxial compression results. Eventually, the developed model was validated by simulating the triaxial tests of coal specimens with different sizes under varying confining stresses and comparing its findings with the published test results. The study showed that its implementation in the numerical model could reproduce laboratory-observed mechanical response, deformation behavior, and failure mechanism very closely.

Dilatancy is commonly defined as the ratio of the rates of plastic volumetric strain to plastic deviatoric strain, denoted as Dp. Owing to the high modulus of elasticity, the elastic volumetric and deviatoric strain rates under shear stress in conventional cohesionless materials are negligible. Therefore, using the ratio of the rates of total volumetric to deviatoric strain (Dt) as an approximation is common in studying stress–dilatancy behavior and calibrating dilatancy model parameters. This approach is also common in the study of rubber-added cohesionless materials (RCM). However, RCM with a common range of rubber content exhibit a significantly lower modulus of elasticity compared to conventional cohesionless materials. Further research is needed to evaluate the potential impact of elastic strain rates in RCM on stress–dilatancy analysis. Therefore, comparisons were conducted on the stress–dilatancy responses of a series of tests on RCM, where dilatancy is calculated by Dp and Dt, respectively. Furthermore, a modified method for calibrating the parameters of a state-dependent dilatancy model considering Dp is presented. It turns out that Dp is better suited and more precise for dilatancy analysis on highly elastic RCM. Additionally, the dilatancy model can more precisely capture the test results of RCM with parameters calibrated by the proposed method.

Pore fluids are ubiquitous throughout the lithosphere and are commonly invoked as the cause of induced seismicity and slow earthquakes. We perform lab experiments to address these questions for drained fault conditions and low pore pressure. We shear simulated faults at effective normal stress σn′ $\left({\sigma }_{n}^{\prime }\right)$ of 20 MPa and pore pressures Pp from 1 to 4 MPa. We document the full range of lab earthquake behaviors from slow slip to elasto‐dynamic rupture and show that slow slip can be explained by the slip rate dependence of the critical rheologic stiffness without dilatancy hardening or other fluid effects. Our fault permeabilities ranges from 10−18 to 10−17 m2 with an initial porosity of 0.1 and estimated fluid diffusion time ≈1 s. Slow slip and quasi‐dynamic fault motion may arise from high Pp at higher pressures but dilatancy strengthening is not a general requirement. Plain Language Summary: Earthquakes begin and propagate within the fluid‐saturated rocks of Earth's crust. Many investigators have suggested that high pore fluid pressure (Pp) is essential for slow earthquakes and tremor. These studies rely on the idea that changes in Pp can impact rupture propagation speed by dilatant volume increase during faulting with concurrent increases in fault effective normal stress. Thus, understanding the processes that produce slow‐slip versus dynamically propagating rupture is integral to seismic hazard forecasting. Here, we describe experiments on granular faults that produce the full spectrum of slip observed in nature. We measure the mechanical and hydraulic behavior of the faults and determine that frictional and fluid‐driven processes occur in conjunction. Importantly, we demonstrate that frictional processes are sufficient to explain slow‐slip when fluid migration is not inhibited. We demonstrate that for low pore fluid pressures, the full transition from slow slip to dynamic rupture events can be explained as a frictional effect via the critical rheologic stiffness. Key Points: The frictional stability transition does not require dilatant hardening for granular fault zones sheared at low pore pressuresSlow earthquakes and quasi‐dynamic fault slip can be explained by the strain‐rate dependence of the critical fault stiffness (Kc)For the effective normal stresses studied, pore pressure has a negligible impact on frictional stability and the mode of fault slip [ABSTRACT FROM AUTHOR]

Within the strain level attainable in drained triaxial tests, it is not uncommon for dense cohesionless soil to be sheared insufficiently to reach the critical state. Linear fitting of the correlative data from the maximum stress ratio or minimum dilatancy to the end of the test, and then extrapolating these fitted lines to the critical stress ratio or zero dilatancy has been frequently used to estimate the critical state void ratio. However, the linear extrapolation method is empirical and involves different choices of correlative test data, which leads to different estimates. Therefore, a series of simulations of drained tests on dense Toyoura sand are performed using a state-dependent model. Multiple data sets are generated, including void ratio e, volumetric strain εv, stress ratio η, and dilatancy D. The linear extrapolation accuracy of the e–η, e–D, and εv–D data sets is examined. It turns out that the e–η data set is best suited. The goodness of the e–η data set is examined against 18 sets of experimental data on dense sand. In addition, the selection of the start point for extrapolation is shown to influence the estimates. The latter 50% of the post-peak data is found to be reliable. [ABSTRACT FROM AUTHOR]

The mathematical modeling of creep and long-term strength of rocks uses the non-associated flow rule. The authors propose a unified approach to the plasticity and creep processes. The theoretical calculations are compared with the testing data of different materials. In creep deformation in rocks, the applied problems on limit state of rock mass in plain strain are considered: pressure applied by a solid die block with flat bottom on rock mass limited by a horizontal plane and occupying the bottom part of a half-space; instability of pit wall or natural slope under different loads. These problems evaluate stresses in the limit state zones and the times-to-failure in rocks mass with regard to internal friction. [ABSTRACT FROM AUTHOR]

In this paper, we provide a brief overview of certain fundamental concepts which can be used to derive constitutive relations for the stress tensor of granular materials. These include concepts such as dilatancy, cohesion, yield criterion, shear banding, etc. The focus will be on the constitutive relations which are used in the so-called 'frictional flow' or 'slow flow' regime as opposed to the rapid flow regime; in the slow flow regime the material is about to yield or has just yielded and the flow has been initiated. This type of flow occurs in the storage of grains, etc., in silos and bins or hoppers after the valves/gates are opened. The techniques of continuum mechanics are used to discuss constitutive relations where the effects of non-linearities such as yield stress, dilatancy, density gradients, etc., are important. [ABSTRACT FROM AUTHOR]

The impact dynamics of dilute debris flows (typically volumetric solid fractions<50%) have been extensively investigated within the framework of hydraulics. For dense debris flows, the impact mechanisms have been poorly studied. From a geotechnical viewpoint, the feedback between granular dilatancy and pore‐pressure response may play an important role in the dense debris‐flow regime. In this study, the impact behavior of dense and dilute debris flows in an instrumented flume is analyzed. The basal stresses (normal/shear stresses, pore‐fluid pressure) and impact pressure on a rigid barrier are measured. A time‐dependent creeping mode is observed for the impact process of slow‐moving dense debris flows, which cannot be accurately estimated using current debris‐flow load models. At the grain scale, this macroscopic creeping mode is a result of the feedback between granular dilatancy and pore‐pressure response. This feedback can be further characterized by examining the timescales associated with pore‐pressure generation and dissipation. The regulation of pore‐pressure feedback on basal shear stress, impact load, and state of static deposit is revealed. Finally, a tentative phase diagram is proposed for dense and dilute debris‐flow impact. The proposed framework complements the theory for debris‐flow impact loads. Plain Language Summary: The destructive power of fast‐moving debris flows has been continuously emphasized in the scientific literature and the public media. However, a substantial portion of debris flows are actually slow‐moving and seem less destructive, even if their real destructiveness remains unknown. We conducted flume experiments of dilute (low solid‐fraction) and dense (high solid‐fraction) debris flows impacting a rigid obstacle. Our findings highlight the effect of the interplay between granular void change and interstitial fluid‐pressure evolution on the mobility and impact behavior of debris flows. Especially for dense debris flows, the high solid fraction results in an ultralow rate of pore‐pressure dissipation and a high basal shear stress. For these flows, the impact is reflected in the stoppage of the material and its creeping deformation. In addition, it may not be possible to accurately estimate the impact load using fast‐flow load models, indicating that existing models for estimating the destructive power of these flows should be cautiously considered when assessing and mitigating the associated risks. Key Points: Comprehensive experimental measurements reveal the impact‐pressure characteristics of dense and dilute debris flowsA time‐dependent creeping mode is observed for dense debris‐flow impact, which is regulated by the pore‐pressure feedback in the impact processA tentative phase diagram is proposed for dense and dilute debris‐flow impact [ABSTRACT FROM AUTHOR]

Abstract Dilatant hardening is one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro‐computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ∼10 MPa, while varying confining pressure (10–130 MPa) and pore fluid pressure (1–120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.

In this paper, we provide a brief overview of certain fundamental concepts which can be used to derive constitutive relations for the stress tensor of granular materials. These include concepts such as dilatancy, cohesion, yield criterion, shear banding, etc. The focus will be on the constitutive relations which are used in the so-called ‘frictional flow’ or ‘slow flow’ regime as opposed to the rapid flow regime; in the slow flow regime the material is about to yield or has just yielded and the flow has been initiated. This type of flow occurs in the storage of grains, etc., in silos and bins or hoppers after the valves/gates are opened. The techniques of continuum mechanics are used to discuss constitutive relations where the effects of non-linearities such as yield stress, dilatancy, density gradients, etc., are important.

Abstract Pore fluids are ubiquitous throughout the lithosphere and are commonly invoked as the cause of induced seismicity and slow earthquakes. We perform lab experiments to address these questions for drained fault conditions and low pore pressure. We shear simulated faults at effective normal stress σn′ of 20 MPa and pore pressures Pp from 1 to 4 MPa. We document the full range of lab earthquake behaviors from slow slip to elasto‐dynamic rupture and show that slow slip can be explained by the slip rate dependence of the critical rheologic stiffness without dilatancy hardening or other fluid effects. Our fault permeabilities ranges from 10−18 to 10−17 m2 with an initial porosity of 0.1 and estimated fluid diffusion time ≈1 s. Slow slip and quasi‐dynamic fault motion may arise from high Pp at higher pressures but dilatancy strengthening is not a general requirement.

Pumice sand of volcanic origin contains a high fraction of non-plastic fines (>40 % for Satozuka pumice sand in Sapporo, Japan). Suffusion in such soil can wash away a portion of the fine particles and alter the soil microstructure. The moisture content and degree of compaction can affect the suffusion characteristics of soil deposits, however their effect has not yet been evaluated. Future construction sites in growing Sapporo City, consisting of pumice sand, will require a high degree of compaction (over 90 % and preferably over 95 %) as this sand is prone to suffusion in spite of its dense state. The aim of this study is to assess the impact of suffusion on densely compacted pumice sand with a high proportion of fines, based on its mechanical properties, with an emphasis on shear strength and dilatancy. Firstly, the suffusion characteristics of Satozuka pumice sand were evaluated. Subsequently, undrained triaxial tests (CU¯ tests) under monotonic loading were conducted on high-density specimens, with suffusion and without suffusion, to study the impact of suffusion. It is seen in the results that the hydraulic conductivity, shear strength, stress paths, and dilatancy are all noticeably affected by suffusion. The specimens with suffusion exhibit an increase in residual shear strength and maximum deviator stress under shearing and experience an earlier occurrence of phase transformation from contraction to dilation during shearing. This tendency implies that suffusion has no significant negative impact on the deterioration of earth fill made from pumice sand and non-plastic fines, and that it persists at degrees of compaction between 80 % and 100 %.

We formulate and test different Voellmy-type mixture rheologies that can be introduced into two-layer debris flow models. The formulations are based on experimental data from the Swiss Illgraben test site as well as on mathematical constraints in steady flow conditions. In agreement with the ideas of Iverson, we show that the uniform, fixed rheological models cannot accurately represent the changing frictional resistance when debris flows undergo spatial and temporal changes in solid–fluid composition. Indeed, the experimental results of Illgraben indicate that flow friction decreases with increasing volumetric fluid concentration; however, the degree of reduction depends on both the pore pressure and the solid particle agitation. The interplay between these processes makes friction in debris flows highly nonlinear and difficult to quantify. Changing the friction according to the flow composition must be carefully executed, because it can lead to numerical instabilities, which is a recurrent problem in two-layer debris flow models. We test the different rheological formulations using a real event documented with differential topographic data collected using unmanned aerial vehicles (UAVs). The model is able to reproduce the correct erosion pattern and exhibit the right density profile. The event includes de-watering at the front and deposition of sediment, which causes a change from debris flow to debris flood or hyperconcentrated flow, which indicates that two completely different flow states can be modeled with a single Voellmy-type mixture rheology. [ABSTRACT FROM AUTHOR]

Shear rupture and fault slip in crystalline rocks like granite produce large dilation, impacting the spatiotemporal evolution of fluid pressure in the crust during the seismic cycle. To explore how fluid pressure variations are coupled to rock deformation and fault slip, we conducted laboratory experiments under upper crustal conditions while monitoring acoustic emissions and in situ fluid pressure. Our results show two separate faulting stages: initial rupture propagation, associated with large dilatancy and stabilized by local fluid pressure drops, followed by sliding on the newly formed fault, promoted by local fluid pressure recharge from the fault walls. This latter stage had not been previously recognised and can be understood as fluid‐induced afterslip, co‐located with the main rupture patch. Upscaling our laboratory results to the natural scale, we expect that spontaneous fault zone recharge could be responsible for early afterslip in locally dilating regions of major crustal faults, independently from large‐scale fluid flow patterns. Plain Language Summary: Faults in rock form during what is known as rupture; rupture is followed by sliding along the newly formed fault. If this occurs quickly, we speak of an earthquake. When creating the fault during rupture, small cracks are formed in the intact rock that grow and link up. This creates local void spaces in the nascent fault zone. Pore fluids, which typically reside at pressure everywhere within the Earth's crust, will expand in this newfound space so that the pore pressure drops in the rupture zone. Such a drop may slow down the rupture and fault slip—an earthquake may be postponed. Here, we measure this so‐called dilatancy effect in unprecedented detail: We observe how the rupture is controlled by the dilatancy effect, and we discover that after rupture fluids from further away flow into the void spaces in the newly formed fault, thereby increasing pressure again and driving fault slip. This pore fluid control on fault behavior is a fundamental mechanism that can explain why faults continue slipping just after an earthquake. Key Points: We observe two stages during faulting in the presence of fluids: Dilatancy‐dominated shear rupture and slip accommodated by fluid rechargeFault formation by shear rupture evolves non‐linearly with stress drop and may be stabilized by dilatancy‐induced local pore pressure dropsSlip accommodated by local fluid recharge might be responsible for early afterslip following coseismic slip observed in nature [ABSTRACT FROM AUTHOR]

The dilatancy equation ignores the noncoaxiality of granular soil for the coaxial assumption of the direction of the stress and strain rate in conventional plastic potential theory, which is inconsistent with extensive laboratory tests. To reasonably describe the noncoaxial effects on dilatancy, the energy dissipation of plastic flow is derived based on the property-dependent plastic potential theory for geomaterials and integrates the noncoaxiality, the potential theory links the plastic strain of granular materials with its fabric, and the noncoaxiality is naturally related to the mesoscopic properties of materials. When the fabric is isotropic, the dilatancy equation degenerates into the form of the critical state theory, and when the fabric is anisotropic, it naturally describes the effects of noncoaxiality. In the plane stress state, a comparison between a simple shear test and prediction of the dilatancy equation shows that the equation can reasonably describe the effect of noncoaxiality on dilatancy with the introduction of microscopic fabric parameters, and its physical significance is clear. This paper can provide a reference for the theoretical description of the macro and micro mechanical properties of geomaterials. [ABSTRACT FROM AUTHOR]

It is of practical significance to investigate the dilatancy and seepage characteristics of tight sandstone gas under different confining pressures for its efficient development. Therefore, fluid–solid coupling triaxial loading experiments with gas-bearing sandstone were conducted. The results showed that the gas-bearing sandstone exhibited brittle characteristics with tensile–shear composite failure. The dual logarithmic model can better characterize the sandstone strength (R2 = 0.9952), whereas the fitting effect of the linear Mohr–Coulomb criterion is poor (R2 = 0.9294). The dilatancy capacity of sandstone was negatively correlated with confining pressure, and the dilatancy index decreased by 38.4% in the form of its convex power function with the increasing confining pressure. The sandstone underwent significant damage dilatancy during the yielding stage, resulting in a significant permeability recovery, with an increase of 67.0%~70.4%, which was greater than the decrease of 9.6%~12.6% in the elastic stage. In view of the different dominant factors of permeability reduction induced by pore compaction and recovery induced by crack development, the permeability model was established with volumetric strain and radial strain as independent variables, which could better reflect the whole process of permeability evolution. [ABSTRACT FROM AUTHOR]

In this study, compressive loading tests of pile-overlapping backfilled soil were performed to investigate the effect of the dimensions and location of backfilled sand with different densities on the shaft resistance of the pile. The results showed that when the backfilled soil is dense sand, the shaft resistance is affected by the dimensions and location of the sand. The earth pressure at which the maximum value of the shaft resistance is reached is shown to be related to the distance from the outer surface of the pile to the outer edge of the backfilled sand (i.e., the width of the backfilled sand). Thereafter, a method was developed to evaluate the earth pressure related to the shaft resistance of the pile according to the width of the backfilled sand by dividing the sand into several segments in the circumferential direction. Based on these results, a calculation method was developed to calculate the maximum axial resistance of the pile considering various conditions (dimensions, location, and density) of the backfilled sand. [ABSTRACT FROM AUTHOR]

The long-term response and stability of underground mining works are crucial for ensuring the safety of workers, preventing costly accidents, and maintaining efficient operations. This is primarily due to the critical role these structures play in various industries, including mining, construction, and transportation. Understanding the long-term response and stability of such structures is an important factor for ensuring their durability and safety. Additionally, advancements in technology and engineering practices have allowed for more accurate assessments and predictions of long-term behaviour, leading to improved design and maintenance strategies. By examining the creep and relaxation behaviour, scientists can gain insights into the mechanical properties and stability of rocks under different conditions. The time-dependent experiments involve subjecting the rocks to varying rates of loading or deformation to understand their behaviour under different conditions. These methods provide valuable insights into the time-dependent properties of rocks, allowing researchers to better understand their response to various geological processes and engineering applications. This study was carried out in order to determine the rheological characteristics of the rock salt from Slanic Prahova mine, horizon XIV, and to analyse the local stability and the general stability of the resistance structures. The results of the experimentally determined rheological characteristics showed that the analysed salt has a pronounced tendency to creep, being able to be classified in creep category 5, which is a pronounced creep. The values obtained for the dilatancy threshold confirm the fact that salt is a material system that exhibits dilatancy. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on state-dependent behavior of weathered sands incorporating progressive particle breakage by a number of drained triaxial tests to interpret the characteristics of particle breakage, the friction–dilatancy behavior, the critical-state behavior, and the state-dependent dilatancy. Weathered sands were pre-produced by temperature weathering under the weathering number N = 0, 20, and 40 within a designated range of temperatures (− 20 °C and + 110 °C). Particle breakage was quantified by Hardin's relative breakage. Particle breakage increased with increasing axial strain, confining pressure, or weathering number. For a given initial confining pressure, a characteristic void ratio of sand existed to cause a maximum particle breakage in comparison with looser or denser void ratio for silica sand no. 3 N = 0. However, with increasing weathering number N, e.g., N = 20 and N = 40, particle breakage increased while decreasing void ratio. The characteristic void ratio of sand yielding the maximum particle breakage was also state dependent. A hyperbolic model was proposed to correlate relative breakage with plastic work per unit volume, showing more particle breakage in weathered sands with larger weathering number. Particle breakage impaired the peak-state friction resistance and dilatancy of weathered sands. For a given initial void ratio, particle breakage caused a v-shape change of peak-state basic friction angle. However, for a given initial confining pressure, the evolution of peak-state basic friction angle against particle breakage depended on the initial void ratio of sand. In the q-p′ plane, particle breakage rotated anticlockwise the dilatancy lines of weathered sands, but rotated clockwise the failure lines of weathered sands. In the e-p′α=0.7 plane, particle breakage resulted in downward translation and clockwise rotation of critical-state lines of weathered sands. In the q-p′ plane, particle breakage caused up-convex nonlinearity of critical-state lines of weathered sands that evolved diversely against weathering number. Particle breakage resulted in rotation and translation of the linear relation of peak-state dilatancy and peak-state stress ratio or peak-state state parameter. A friction–dilatancy relation was proposed to interpret the behavior of weathered sands incorporating progressive particle breakage. [ABSTRACT FROM AUTHOR]

Natural disasters pose global challenges and can result in social, economic, and environmental damage, substantial loss of life, and even pose a threat to geopolitical stability. The study of such disasters through deformation modeling and analyses has found application in the disciplines of Geodesy and Geodynamics. The strain method has in fact been used to model deformation. The strain deformation parameters, namely, dilatancy, total shear strain and differential rotation, of this finite elemental model were calculated by using the baseline ratios of the coordinates of a classical traverse observed using the Global Positioning System (space technique), in the Minna datum platform. Computation was undertaken in a MATLAB programme and a MONTE CARLO environment, after the ill-conditioned triangles in the network were excluded. Statistical analysis was used to determine the significance levels of the respective deformation parameters at the 95%, 97.5% and 99.5% confidence intervals. After the statistical testing of the deformation parameters, it was observed that some of the controls were unstable in terms of their computed dilatancy and their total shear strain values. For the differential rotation of the network, the significance levels at the 95%, 97.5% and 99.5% confidence intervals were found to be 1.8743908, 0.9651796 and 0.4338522, respectively, while, on the other hand, the controls or centroids that did not respond to the network rotation had a mean value of approximately -0.99999. The minimal and maximal principal strain levels occurring at Centroids 11 and 36 with their triangulated station identities were found to be (36-12, 30-84, 43-34A) and (34-30A, 34-32A, 34-36A), respectively. The method adopted for this research proved to be very effective for a deformation study and analysis. [ABSTRACT FROM AUTHOR]

Studies show that the shear strength of angular-shaped calcareous sand is mainly affected by dilatancy, interparticle locking, and particle breakage. In the present study, a series of consolidated-drained triaxial compression tests on calcareous sands are carried out to investigate the strength impacts of dilatancy, interparticle locking, and particle breakage. It is found that as the stress level increases, the friction angle difference reflecting the effect of the particle breakage increases. In contrast, the friction angle difference reflecting the interparticle locking and dilatancy effect decreases gradually. Moreover, the critical stress ratio of the high-angled calcareous sands decreases, which may be attributed to particle breakage. The obtained results demonstrate that when the stress level exceeds a certain value, the critical stress ratio remains constant. Then the correlation between the particle breakage, interparticle locking, and dilatancy effects in the shear strength is studied. Finally, based on the performed analysis on energy dissipation in calcareous sands, a dilatancy model is proposed that covers the particle breakage effect. The performed analyses demonstrate that the proposed model can accurately explain the experimental data. [ABSTRACT FROM AUTHOR]

Considering the high vulnerability of existing masonry buildings, which often have strategic or cultural value, professionals and specialized engineers are frequently required to model complex historical buildings. The approaches proposed by National Building Codes may not always be suitable for such cases, but more detailed approaches are necessary, relying on FEM continuum modeling and inelastic constitutive law. There are many constitutive laws proposed in the literature that allow us to accurately reproduce the mechanical behavior of masonry. However, they require the identification of several parameters that are not easy to determine. In this study, a sensitivity analysis of the parameters of a nonlinear constitutive law very popular for masonry modeling (the "Concrete Damage Plasticity—CDP" model) is conducted, considering literature tests of masonry panels under shear stress as the benchmark. The aim is to assess the influence of the main parameters of the model and compare them to one of the more commonly used Mohr–Coulomb failure criteria. [ABSTRACT FROM AUTHOR]