Dilatancy Relationship Research Articles

A stress dilatancy relationship for coarse-grained soils incorporating particle breakage

A stress dilatancy relationship for coarse-grained soils incorporating particle breakage

Auxiliary plastic potential approach in elastoplasticity for soils

The scope of this paper is to have an alternative to the use of an explicit plastic potential in elastoplastic models for soils. This is possible through the definition of a stress–dilatancy relationship and a simple expression for an auxiliary surface in lieu of a given expression of the plastic potential surface. This approach results in a flexible definition of the model and to very simple expressions of the auxiliary plastic potential derivatives.

Relation of the successful block regional anesthesia with increased peripheral venous circumference and peripheral skin temperature at distal part of the block

Introduction: Evaluating the success rate of regional anesthesia is performed with pinprick test, Bromage score and pain scales, where they act as indicators of success or otherwise of motor, sensory and nociceptive blockade. The sympathetic system is also affected by the regional anesthesia blockade. The present study evaluated the relationship of peripheral venous dilatation and the skin temperature of the block area, to be used as an additional tool. Methodology: An analytic, observational study was conducted in Dr. Soetomo Surabaya Hospital. 18 patients received peripheral nerve block (PNB) and 16 patients received subarachnoid block (SAB). Informed consent was obtained from all the participants. The peripheral venous circumference was measured by using linear probe of Sonosite® M–Turbo ultrasound, before the blocks and then one hour after PNB and SAB to assess the venous dilatation. The peripheral skin temperature was measured with a thermometer (Microlife NC-150 Bluetooth®) infrared thermometer before the blocks, and within the range of 5 min from the zero min after the block until the 30th min. The success rate of the blocks was performed with pain scale (VAS) and absence of motor, sensory and nociceptive response Results: No relationship was found of sex, age, weight and type of block with increased peripheral venous circumference and peripheral skin temperature (p > 0.05). The block's success was associated with the increased peripheral venous circumference and peripheral skin temperature (p ≤ 0.001) in both PNB and SAB blocks. The average PNB block succeeded in 20 min while SAB took only 5 min (p < 0.05) to affect both of the parameters. The delta value of the increased temperature's successful block was 0.7oC in the PNB, and 0.275oC in the SAB group. Conclusions: The success of the peripheral nerve block and the subarachnoid block is associated with an increase in the peripheral venous circumference and in the peripheral skin temperature in the block area. Key words: Regional anesthesia; Peripheral nerve block; Subarachnoid block; Sympathetic block. Abbreviations: RA – Regional anesthesia; PNB – Peripheral nerve block; SAB – Subarachnoid block Citation: Sumartono C, Sulistiawan SS, Wirabuana B, Putri HS, Johansyah A, Hidayati HB. Relation of the successful block regional anesthesia with increased peripheral venous circumferential length and peripheral skin temperature at distal part of the block. Anaesth. pain intensive care 2021;25(4):458-462. DOI: 10.35975/apic.v25i4.1383 Ethical Review Commission approval: No. 233/Panke.KKE/ III/ 2017. Received: October 13, 2020, Reviewed: February 4, 2021, Accepted: April 1, 2021

Mesoscale numerical investigation of the effects of fiber stiffness on the shear behavior of fiber-reinforced granular soil

Fiber reinforcement techniques can effectively optimize the engineering properties of ground soils. This study aims to investigate the influence of fiber stiffness on the shear behavior of fiber-reinforced granular soil. First, the particle shapes are automatically extracted based on the improved Viola–Jones algorithm. Subsequently, the fiber stiffness is calibrated considering the results of laboratory tensile tests. Moreover, a series of numerical biaxial tests are conducted considering different fiber stiffnesses and contents and a flexible boundary. The influence of the fiber stiffness on the strength and volumetric strain is analyzed, and the stress–dilatancy relationship of the fiber-reinforced soil is discussed. In addition, the interaction between the fibers and soil particles is clarified according to the internal structure and stress network, including the coordination number, contribution of the contact, sliding of the particles and mobilization of the tensile force in the fibers. The results of this study can help clarify the reinforcement mechanism of fibers with typical stiffness values.

Dilatancy Characteristics and Constitutive Modelling of the Unsaturated Soil Based on Changes in the Mass Water Content

Most soil mechanics theories are limited to strain hardening and shrinkage under high compressive stresses, and there are some shortcomings in the selection of suction or degree of saturation as the water content state varies in the constitutive models of unsaturated soil. Based on the triaxial shear tests of unsaturated compacted soil (a silt of high plasticity) with different water content and confining pressure (low-confining), a shear dilatancy model of unsaturated soil based on the mass water content is proposed in this paper. The influence of the water content on the shear deformation characteristics of the unsaturated soil is analysed. The stress–dilatancy relationship and the prediction equation of the minimum dilatancy rate of the unsaturated soil under different water content and different confining pressure are provided. Selecting the mass water content as the state variable, a constitutive model suitable for the dilatancy of unsaturated soil is established. The method of determining model parameters based on the mass water content is analysed. The applicability of the model is verified by comparisons between the predicted and experimental results.

Characterization of stress–dilatancy behavior for methane hydrate-bearing sediments

To evaluate the stability of seabed ground during gas hydrate exploitation, a constitutive model that can appropriately estimate the mechanical properties of methane hydrate-bearing sediments must be established. A better understanding of the stress–dilatancy characteristics is crucial in modeling the stress–strain behavior of methane hydrate-bearing sediments under complex loading paths. This study presents a compressive analysis of the effects of several factors on the stress–dilatancy behavior of methane hydrate-bearing sediments. The dilatancy behavior of methane hydrate-bearing specimens synthetized in the laboratory and natural hydrate-bearing samples acquired in the field are compared. Results show that the hydrate saturation, temperature, porosity, and hydrate formation pattern affect the peak stress ratio, dilatancy rate, and critical state stress ratio of methane hydrate-bearing sediments. However, the effect of effective confining pressure on the stress–dilatancy curve is minimal. Different hydrate formation methods yield different hydrate morphologies; consequently, the dilatancy behavior of methane hydrate-bearing sediments is altered significantly. Differences observed between synthetized specimens and natural samples may originate from various hydrate morphologies. The stress–dilatancy relationship of methane hydrate-bearing sediments is interpreted and described using Rowe's theory. Furthermore, the dilatancy behavior of methane hydrate-bearing sediments and cemented sands under similar test conditions is compared.

Stress–dilatancy behavior of cemented sand: comparison between bonding provided by cement and biocement

Biocement as an alternative to cement for soil improvement has been studied for the past decade. A comparative study on the cementation effect on the mechanical behavior of sand by biocement and Portland cement is presented. Drained triaxial tests were carried out on both cement- and biocement-treated sand. The yielding of cemented sand is largely associated with the breakage of bonding. Bonding ratio is defined in this paper to quantify the bonding effect. The bonding provided by biocement is stronger than that by cement, and as a result, the stress ratio at yielding for biocement-treated sand is higher than that for cement-treated sand given the other conditions the same. The shear resistance of cemented sand consists of bonding, dilation and friction. The stress–dilatancy relationship of biocement-treated sand is different from that of cement-treated sand or the Rowe’s stress–dilatancy equation. The increase in stress ratio with dilatancy ratio (1 − δev/δe1) is higher for biocement-treated sand.

Stress–Dilatancy Relationship of Erksak Sand under Drained Triaxial Compression

Analyzing the results of triaxial compression tests under drained conditions for Erksak sand published in the literature, the stress–dilatancy relationships were described using the frictional state concept. At all phases of shearing, the linear stress ratio–plastic dilatancy relationship can be expressed by the critical frictional state angle and two parameters of the frictional state concept. At failure, dense sand exhibits purely frictional behavior (α = 0, β = 1) and the stress ratio–dilatancy relationship may be correctly described by the Rowe, Bolton, and frictional state concept relationships. Very loose Erksak sand sheared under drained triaxial compression at the ultimate state reaches a stable condition, but the reached stress ratio is significantly smaller than the one at a critical state.

A simple model for sand–structure interface behaviour

This paper deals with the modelling of sand–structure interface behaviour under monotonic loading. In particular, the importance of the stress–dilatancy relationship is highlighted since volumetric behaviour strongly characterises the variation of the normal stress in constant normal stiffness direct shear tests. The procedure for the calibration of constitutive parameters is shown and the model is validated by comparison with different sets of sand–aluminium interface direct shear tests.

Dilatancy and Critical State of Calcareous Sand Incorporating Particle Breakage

Particle breakage has a crucial impact on the dilatancy and critical state of calcareous sand. This study performed several triaxial experiments on calcareous sand samples to describe the stress–dilatancy relationship of calcareous sand. The experimental results revealed that critical friction angle always is lower than the mobilized friction angle for calcareous sand. The shear resistance correlates with dilatancy and particle breakage. In addition, particle breakage highly affected the critical state line in the conducted tests. By introducing the concept of breakage parameters, this study established a modified dilatancy equation considering particle breakage under the theoretical framework of state parameters. The experimental results of this study exhibited a good correlation with the model results employing unique parameters.

Shear‐thinning behaviour of blood in response to active hyperaemia: Implications for the assessment of arterial shear stress‐mediated dilatation

What is the central question of this study? Quantitative values of shear rate-specific blood viscosity and shear stress in the human macrovasculature in response to exercise hyperaemia are unknown. What is the main finding and its importance? Using the handgrip exercise model, we showed that an increase in brachial artery shear rate led to a decrease in blood viscosity, despite concomitant haemoconcentration. This shear-thinning behaviour of blood, secondary to increased erythrocyte deformability, blunted the expected increase in brachial artery shear stress based on shear rate prediction. Our data yield new insights into the magnitude and regulation of macrovascular blood viscosity and shear stress in physiological conditions of elevated metabolic demand and blood flow in humans. Blood viscosity is a well-known determinant of shear stress and vascular resistance; however, accurate quantitative assessments of shear rate-specific blood viscosity in the macrovasculature in conditions of elevated blood flow are inherently difficult, owing to the shear-thinning behaviour of blood. Herein, 12 men performed graded rhythmic handgrip exercise at 20, 40, 60 and 80% of their maximal workload. Brachial artery shear rate and diameter were measured via high-resolution Duplex ultrasound. Blood was sampled serially from an i.v. cannula in the exercising arm for the assessment of blood viscosity (cone-plates viscometer). We measured ex vivo blood viscosity at 10 discrete shear rates within the physiological range documented for the brachial artery in basal and exercise conditions. Subsequently, the blood viscosity data were fitted with a two-phase exponential decay, facilitating interpolation of blood viscosity values corresponding to the ultrasound-derived shear rate. Brachial artery shear rate and shear stress increased in a stepwise manner with increasing exercise intensity, reaching peak values of 940±245s-1 and 3.68±0.92Pa, respectively. Conversely, brachial artery shear rate-specific blood viscosity decreased with respect to baseline values throughout all exercise intensities by ∼6-11%, reaching a minimal value of 3.92±0.35mPas, despite concomitant haemoconcentration. This shear-thinning behaviour of blood, secondary to increased erythrocyte deformability, blunted the expected increase in shear stress based on shear rate prediction. Consequently, the use of shear stress yielded a higher slope for the brachial artery stimulus versus dilatation relationship than shear rate. Collectively, our data refute the use of shear rate to infer arterial shear stress-mediated processes.

Geomechanical constitutive modelling of gas hydrate-bearing sediments by a state-dependent multishear bounding surface model

Natural gas hydrate in marine sediments and permafrost areas is considered as an important potential energy source. Since hydrate dissociation will reduce the stability of gas hydrate-bearing sediments (GHBS) and may cause wellbore failures and geological disasters during gas production, it is necessary to reveal the mechanical behavior of GHBS for the safe exploitation of natural gas hydrate. This paper proposes a geomechanical constitutive model of GHBS within the multishear bounding surface framework. Following the slip theory of plasticity, a constitutive formulation is obtained by splitting the macro constitutive response of sediments into a macro volume response and a series of micro shear responses in spatial distributions related to virtual microshear structures. Each microshear structure describes micro shear and dilatancy responses in three orthogonal orientations. A micro stress–strain relationship and a micro stress–dilatancy relationship are established for each orientation of the microshear structure. The model comprehensively describes the consolidation, hardening, softening, dilatation, collapse, and non-coaxial characteristics of gas hydrate-bearing sediments by introducing the multishear concept, state parameter, evolution law of hydrate bonding and debonding, and collapse strain caused by hydrate dissociation. The effectiveness of the model is confirmed by simulating the available published laboratory tests on the samples of synthetic and natural GHBS under different pore pressures, temperatures, initial void ratios, hydrate saturations, and initial effective confining stresses.

The relationship of atrial fibrillation and tricuspid annular dilation to late tricuspid regurgitation in patients with degenerative mitral repair

ObjectivesGuidelines do not address preoperative atrial fibrillation when considering adding tricuspid annuloplasty to mitral surgery. Our purpose was to determine the occurrence of late tricuspid regurgitation in patients with less than moderate tricuspid regurgitation undergoing surgery for degenerative mitral regurgitation and the importance of atrial fibrillation and tricuspid annular dilation. MethodsFrom 2004 to 2017, 1021 patients underwent surgery for degenerative mitral regurgitation; 869 (85%) had less than moderate tricuspid regurgitation, and 846 (97%) underwent repair. Preoperative atrial fibrillation was present in 199 patients and ablated in 194 patients (97%). Tricuspid annular diameter was measured in 657 of 869 patients (76%). ResultsFor patients who did not receive tricuspid annuloplasty, recurrent moderate or more late tricuspid regurgitation was 8% (45/576) in the no atrial fibrillation group and 25% (38/154) in the atrial fibrillation group (P < .001; odds ratio, 2.42). In 75.2% of patients (494/657), the tricuspid annulus was less than 4.0 cm; in 17% of patients (112), the tricuspid annulus was 4.0 to 4.4 mm (mean 41.1 mm); and in 7.8% of patients (51), the tricuspid annulus was 45 mm or more (47.8 mm). Only tricuspid diameter 45 mm or more was a risk for late tricuspid regurgitation (P = .002; odds ratio, 3.25). Progression to moderate or higher tricuspid regurgitation was associated with an increase in long-term mortality: unadjusted hazard ratio, 3.58 (2.04-6.29) (P < .001); adjusted hazard ratio, 2.37 (1.23-4.57) (P = .010). ConclusionsPreoperative atrial fibrillation is an important risk factor for late tricuspid regurgitation despite concomitant ablation surgery. Tricuspid annular dilation was not associated with late tricuspid regurgitation until the annulus was 45 mm or greater. Progression to moderate or greater tricuspid regurgitation was associated with an increase in late mortality.

Stress–dilatancy relationship for fiber-reinforced sand and its modeling

The stress–dilatancy relationship could be employed as the foundation to develop a constitutive model for polypropylene fiber-reinforced (PFR) soils. In this study, a number of triaxial compression tests were carried out to investigate the effect of uniform distributed fiber reinforcements on the stress dilatancy relationship of Nanjing sand. A new parameter representing the increase in the effective confining stress $$\sigma _{\rm FR}$$ was introduced to describe the stress–dilatancy of PFR sand, and a new stress–dilatancy relationship was proposed for PFR sand based on Rowe’s stress–dilatancy equation for granular materials. Moreover, the stress–dilatancy relationships in the conventional triaxial compression, extension and plane stain conditions were discussed in this paper. The stress–dilatancy relationship is validated against a series of triaxial tests on Nanjing sand and Hostun RF sand mixed with discrete polypropylene fibers. It is shown that the predicted results are in a good agreement with the experimental results.

A microstructure-based elastoplastic model to describe the behaviour of a compacted clayey silt in isotropic and triaxial compression

The paper focuses on the hydromechanical behaviour of an unsaturated compacted clayey silt, accounting for fabric changes induced by drying–wetting cycles occurring at low stress levels. The response along isotropic compression and triaxial compression (shear) at constant water content was investigated by laboratory tests on both as-compacted and dried–wetted samples. Compaction induces a microstructural porosity pertinent to clay peds and a macrostructural porosity external to the peds. Drying–wetting cycles decrease the microporosity and increase the macroporosity, which reduces the water retention capacity, increases the compressibility, and promotes higher peak strengths with more brittle behaviour during triaxial compression. A coupled double-porosity elastic–plastic model was formulated to simulate the experimental results. A nonassociated flow rule was defined for the macrostructure, modifying a stress–dilatancy relationship for saturated granular soils to account for the increase in dilatancy with suction observed in the experiments. The average skeleton stress and suction were adopted as stress variables. As correctly predicted by the model, the shear strength at critical state is not significantly influenced by the degree of saturation or by the hydraulic history. On the contrary, the higher peak strength, brittleness, and dilatancy of the dried–wetted samples are mostly explained by their reduced water-retention capacity.

Axial behavior of tapered piles using cavity expansion theory

This paper presents a procedure for evaluating the load–displacement behavior of tapered piles under static axial compressive loads. The response of tapered piles under elastic phase is evaluated using nonlinear load transfer method, whereas the increase in stresses due to slippage at the soil–pile interface is obtained from a developed drained cylindrical cavity expansion solution based on a nonlinear stress–dilatancy relationship. The governing differential equation is solved using the differential quadrature element method. The methodology is validated using two reported experimental model testing of the tapered pile in cohesive–frictional soil and soft soil. A comparative analysis between the different nonlinear load transfer models is also carried out. Further, the effect of the heterogeneity of the soil properties along the length of the pile on the axial response of the tapered pile is studied.

Multishear bounding surface modelling of anisotropic sands accounting for fabric and its evolution

This paper presents a multishear bounding surface model for sands that considers evolving fabric anisotropy. The model is formulated by decomposing the overall response into a macro volumetric response and a set of spatially distributed micro shear responses. The micro stress–strain and stress–dilatancy relationships are defined for each direction of the micro shear structure. The evolving fabric tensor and anisotropic state parameter are used to characterize changes in the anisotropic structure and to satisfy the anisotropic critical state theory. The model performance is validated by the test data under different confining pressures, densities, loading modes, and loading directions.

Stress-strain behaviour of Toyoura sand in undrained triaxial compression

The stress-plastic dilatancy relationship for Toyoura sand sheared under undrained triaxial conditions was analysed by use of Frictional State Theory. Under undrained conditions, plastic strain increments are counterbalanced by elastic strain increments. The linear stress ratio-plastic dilatancy relationships at different stages of sand shear were obtained by assuming that Poisson's ratio is a function of shear strain. Contrary to a drained condition, natural state parameter values are not special for characteristic points of sand behaviour under undrained conditions.

Stress–dilatancy relationship for railway ballast

Abstract Knowledge of the mechanical behaviour of ballast is very important for designing a railway track, especially for high-speed lines. The monotonic drained triaxial tests of scaled and fouled ballast presented in literature were analysed using the Frictional State Theory. The stress–plastic dilatancy relationship shows that four characteristic stages of shearing may be specified. The influence of stress level and water content may be quantified by the use of the Frictional State Theory.

Stress–Dilatancy For Crushed Latite Basalt

Abstract In this article, the stress–dilatancy relationship for crushed latite basalt is analysed by using Frictional State Theory. The relationship is bilinear, and the parameters α and β determine these two straight lines. At the initial stage of shearing, the mean normal stress increment mainly influences breakage, but at the advanced stage, it is shear deformation that influences breakage. At the advanced stage of shearing, the parameter αpt represents energy consumption because of breakage and βpt mainly represents changes in volume caused by breakage during shear. It is also shown that breakage effect is significant at small stress levels and the η-Dp plane is important to fully understand the stress–strain behaviour of crushed latite basalt in triaxial compression tests.