Critical Friction Angle Research Articles

Grading scalping and sample size effects on critical shear strength of mine waste rock through laboratory and in-situ testing

Geotechnical stability analyses of mine waste rock (WR) piles require the critical friction angle (ϕcr) of the coarse blasted rock. However, due to the presence of oversized rock clasts, shear strength can only be characterized on small samples prepared using grading scaling techniques, such as scalping. Thus, considering a testing device able to handle samples of characteristic size D, the material should be scaled down to a maximum particle size dmax given by the minimum sample aspect ratio α = D/dmax. However, a practical concern about how far the size scale can be reduced while keeping representative results remains a matter of debate in the geotechnical community. International standards do not agree on the minimum recommended α, and its effects on the mechanical behavior remain poorly understood. This paper aims to investigate the grading effects and sample size effects on ϕcr of WR materials using the scalping technique, to provide insights on the minimum recommended α. Triaxial tests were conducted on loose and dense samples of diameters D = 150 and 300 mm. Samples were scalped from field material having dmax = 75 mm, to allow a range of α from 4 to 30. Additionally, one of the world largest in-situ direct shear boxes (120 × 120 × 38 cm3) was developed to test the same WR material. The results show that scalping is an appropriate technique to assess the critical shear strength of WR. The minimum α for ϕcr assessment in triaxial testing is not sensitive to grading nor sample size, but it is affected by sample density. The aspect ratio was found to be α ≥ 12 and α ≥ 16 for loose and dense samples, respectively. This finding advocates that α values recommended by worldwide standards, such as ASTM D7181-20, might be too low and should be revisited after comprehensive testing.

Corrosion effects on axial pile capacity

Increase in surface roughness by corrosion processes has long been neglected as potential factor influencing pile setup. However, recently there has been an increasing number of studies who referred pile setups largely or solely to corrosion and sand incrustation. Only limited research has been conducted to assess the potential impacts of corrosion directly on pile capacity development. Therefore, we sampled steel and crust surfaces from a steel monopile having been aged for ∼four years in sand. Surface roughness measurements and interface direct shear testing were performed to quantify changes for friction angles. The impact of friction angle changes on pile capacity were calculated using ICP-05 and UWA-05 for a large- and small-diameter geometry and referenced by field data. We can show that corrosion can significantly contribute to temporal pile capacity gains. Evidence have been found that the maximum and critical interface friction angles evolve differently considering the same changes in roughness. Also, differences in shearing behavior to literature were observed, being potentially a result of the naturally corroded surfaces sheared in our study. A strong, maybe exaggerated sensitivity of the capacity prediction approaches to pile diameter was observed. Effects causing an increase in surface roughness, should be reconsidered as an important factor influencing pile setup.

Development of a modified hypoplastic model for calcareous sand considering particle crushing

In the field of ocean engineering, calcareous sand is frequently employed. However, particle breakage can significantly reduce its strength and dilatancy while increasing its compressibility, leading to potential safety and stability issues for foundations. Traditional constitutive models have limitations in accurately describing the mechanical behavior of calcareous sand. To address this issue, a modified hypoplastic model is proposed in this study, incorporating the quantified indicator of relative particle breakage rate, Br. The established stress-strain relationship is intricately linked to the Br index, effectively connecting it with the effective stress and deviatoric stress. The effect of particle crushing on the critical friction angle, CSL parameters and α parameter of the hypoplastic model were systematically analyzed. A VUMAT subroutine is developed to assess the precision and applicability of the proposed model by simulating triaxial drainage tests under three different densities. The simulation results exhibit good agreement with experimental data, demonstrating the superiority of the modified model over the conventional hypoplastic model. This modified model proves suitable for calcareous sands with varying densities, making it a valuable tool for enhancing stability and safety in ocean Engineering Geology.

Effect of heterogeneity of particle properties on the mechanical properties of sandy soil materials

The random arrangement of particle composition or the heterogeneity of the particles' inherent properties is what causes the variability of mechanical parameters in sandy soils. Combining the discrete element method with random field theory, a random discrete coupling modeling method is refined, in which a rolling resistance contact model was used to take into account the rolling friction characteristics of sand soil particles. Four random discrete element models (RDEM) are developed for typical working situations taking into account the two random field factors, i.e., the coefficient of variation and fluctuation range. The Monte Carlo method is employed to simulate the triaxial RDEM, and the stress-strain relations, parameters of strength and deformation are analyzed. The effects of the coefficient of variation (Cov) and fluctuation range (δ) on the variability of mechanical characteristics are studied. The results show that the mean shear modulus G, peak friction angle φp, and critical friction angle φc of random heterogeneous samples decline while the mean Poisson's ratio μ increases as the Cov increases. The mean values of parameters of deformation and strength of random heterogeneous samples eventually approach those of homogeneous samples as the δ increases.

A consistent calibration process for the Matsuoka–Nakai friction angle under direct simple shear conditions for clay hypoplasticity

In geotechnical engineering, direct simple shear (DSS) tests are used to determine strength and stiffness parameters of a material. DSS predictions of a constitutive model influence failure mechanisms in plane-strain, finite-element applications. In this article, we introduce a closed-form solution to determine the Matsuoka–Nakai equivalent critical friction angle from direct simple shear stress and normal stress data. In order to apply it to clay hypoplasticity (Mašín, 2013), we carry out DSS simulations to investigate rotations of principal stresses and the principal stress state at critical state for plane-strain conditions.Finally, we interpret DSS predictions of clay hypoplasticity for different overconsolidation ratios and demonstrate that the location of the CSL in the vertical stress–void ratio plane coincides with the location of the CSL in mean effective stress–void ratio plane.

Coupled effects of particle overall regularity and sliding friction on the shear behavior of uniformly graded dense sands

Particle morphology has been regarded as an important factor affecting shear behaviors of sands, and covers three important aspects, i.e. global form (overall shape), local roundness (large-scale smoothness), and surface texture (roughness) in terms of different observation scales. Shape features of different aspects can be independent of each other but might have coupled effects on the bulk behavior of sands, which has been not explored thoroughly yet. This paper presents a systematic investigation of the coupled effects of the particle overall regularity (OR) and sliding friction on the shear behavior of dense sands using three-dimensional (3D) discrete element method (DEM). The representative volume elements consisting of ideal spheres and irregular clumps of different mass proportions are prepared to conduct drained triaxial compression simulations. A well-defined shape descriptor named OR is adopted to quantify particle shape differences of numerical samples at both form and roundness aspects, and the particle sliding friction coefficient varies from 0.001 to 1 to consider the surface roughness effect equivalently in DEM. The stress-strain relationships as well as peak and critical friction angles of these assemblies are examined systematically. Moreover, contact network and anisotropic fabric characteristics within different granular assemblies are analyzed to explore the microscopic origins of the multi-scale shape-dependent shear strength. This study helps to improve the current understanding with respect to the influence of the particle shape on the shear behavior of sands from different shape aspects.

Study on the packing and shear characteristics ofgranular mixtures via the DEM

Granular mixtures are often encountered in civil engineering, but the micromechanical implications of their packing and shear characteristics are still unclear. In this study, the packing and shear characteristics of binary mixtures were studied using a three-dimensional discrete element method (DEM). The binary mixtures contained realistic gravel-shaped coarse particles and one of two tested fine particle shapes (namely, spherical or elongated particles). The densest isotropic samples were generated by using a frictionless condition. The initial void ratio and particle contacts of the packed samples were examined. This study shows that the particle shape of the fines affects the relationship between the initial void ratio and fines content (FC). The contact types in binary mixtures can be classified as coarse particle-coarse particle (CC contacts), coarse particle-fine particle (CF contacts) and fine particle-fine particle (FF contacts). A microscopic investigation of the particle contacts indicated that the coarse and fine particle shapes influenced the partial coordination numbers of the CC and CF contacts and the CF and FF contacts, respectively. All the samples were then subjected to numerical triaxial compression tests. The results show that the particle shape of the fines affected the magnitudes and evolutions of the peak (φp) and critical (φc) friction angles of the binary mixtures. Finally, an anisotropic analysis was performed to highlight the microscopic mechanisms that cause the shear strength to be dependent on the particle shape and FC.

Friction and maximum dilatancy angles of granular soils incorporating low plastic fines and depositional techniques effects

This paper addresses the effects of over consolidation ratio (OCR = 1–8), low plastic fines content (Fc = 0–40%) and depositional techniques (DFP and WD) on the stress-strain and volume change behaviours as well as maximum dilatancy, peak-state friction, critical state friction and excess friction angles through two series of drained triaxial compression tests. The first one, emphasizing the effect of the OCR and the second one analysing the influence of Fc on the mechanical behaviour of Chlef sand and Chlef sand-silt mixtures, respectively. All specimens were prepared at a medium density (Dr = 53%) and subjected to a confining pressure (σ′3 = 0.1 MPa). The obtained results indicate that the increase in the fines content of the DFP specimens leads to a decrease in the deviatoric stress and dilative character at the same axial strain, however, the reverse trend is observed for the WD ones. Moreover, it is observed that the deviatoric stress generally increases with the increasing of the OCR for both depositional techniques and the DFP specimens prepared exhibit higher values of the shear strength than the WD ones. Furthermore, the results show that Fc, OCR and depositional techniques influence significantly the mechanical characteristics (ϕ′ps, ϕ′cs, ψmax and ϕ′ex).

Hydro-mechanical behaviour of soil experiencing seepage erosion under cyclic hydraulic gradient

Numerous incidents and failures of earth slopes, dykes, levees and embankment dams are caused by internal erosion. At a time of global climate change, rapid pore-water pressure changes in soil masses are frequently induced by extreme rainfall, storm surges, waves, flash floods and so on. Under such complex cyclic hydraulic conditions, the soil erodibility, hydraulic conductivity and subsequent stress–strain behaviour may differ from those under the monotonic seepage condition, and are still poorly understood. In this study, preliminary laboratory tests have been conducted to investigate the development of internal erosion and changes in hydraulic conductivity under one-way cyclic seepage, and the post-erosion stress–strain behaviour. Representative internally stable and unstable soils were tested. The effects of mean hydraulic gradient and cyclic gradient amplitude were investigated in detail. Results show that the erosion development is significantly influenced by both the initial grain size distribution and the pattern of imposed cyclic hydraulic gradient. The cyclic seepage promotes the loss of fine particles and leads to larger hydraulic conductivity. For the internally unstable soil, the eroded soil mass and hydraulic conductivity increased significantly with increasing cyclic gradient amplitude. Nevertheless, the internally stable soil experienced a small amount of particle loss, even under large cyclic gradients. For both types of soil, a larger cyclic gradient amplitude corresponds to a stronger post-erosion contractive shearing behaviour and a smaller critical friction angle.

Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

Abstract. The Köfels rockslide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the (i) pre-failure and failure topography, (ii) failure volume and porosity of the sliding mass, and (iii) numerical models on initial deformation and failure mechanism, as well as shear strength properties of the basal shear zone obtained by back-calculations. Geographic information system (GIS) methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3100 and 4000 million m3, respectively, and a sliding mass porosity of 26 %. For the 2D numerical investigation the distinct element method was applied to study the geomechanical characteristics of the initial failure process (i.e. model runs without a basal shear zone) and to determine the shear strength properties of the reconstructed basal shear zone. Based on numerous model runs by varying the block and joint input parameters, the failure process of the rock slope could be plausibly reconstructed; however, the exact geometry of the rockslide, especially in view of thickness, could not be fully reproduced. Our results suggest that both failure of rock blocks and shearing along dipping joints moderately to the east were responsible for the formation or the rockslide. The progressive failure process may have taken place by fracturing and loosening of the rock mass, advancing from shallow to deep-seated zones, especially by the development of internal shear zones, as well as localized domains of increased block failure. The simulations further highlighted the importance of considering the dominant structural features of the rock mass. Considering back-calculations of the strength properties, i.e. the friction angle of the basal shear zone, the results indicated that under no groundwater flow conditions, an exceptionally low friction angle of 21 to 24∘ or below is required to promote failure, depending on how much internal shearing of the sliding mass is allowed. Model runs considering groundwater flow resulted in approximately 6∘ higher back-calculated critical friction angles ranging from 27 to 30∘. Such low friction angles of the basal failure zone are unexpected from a rock mechanical perspective for this strong rock, and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rockslide. In addition, the rock mass properties needed to induce failure in the model runs if no basal shear zone was implemented are significantly lower than those which would be obtained by classical rock mechanical considerations. Additional conditioning and triggering factors such as the impact of earthquakes acting as precursors for progressive rock mass weakening may have been involved in causing this gigantic rockslide.

Upscaling critical state considering the distribution of meso‐structures in granular materials

AbstractThe evolutions of meso structures of granular materials play important roles during shearing toward the critical state. This study aims to establish an extended analytical model based on a specific upscaling procedure considering the distributions of meso structures in granular materials. A general Gaussian distribution is applied when determining the relationship between meso critical state parameters and order n, and then a quantitative model of macro CSL is developed by taking the discrete case into a continuous function. The quantitative model is then related to interparticle friction μ and contact stiffness k for predicting the macro CSLs for ideal granular assemblies, and the analytical results have good agreement with DEM results. Furthermore, the influence patterns of contact properties on both meso and macro critical states are discussed in detail, which provides a roughly explanation on the variations of critical friction angle with μ.

Effect of the intermediate principal stress on the mechanical responses of binary granular mixtures with different fines contents

The effect of the intermediate principal stress (b quantifies its relative magnitude) on macroscale and microscale shear responses of binary granular mixtures with different fines contents (FCs) was investigated using the discrete element method. Mixtures were made up of coarse particles with real gravel shapes and fine particles with sphere shapes. True triaxial compression tests were conducted on their dense specimens. The shapes of coarse particles play an important role in the peak and critical friction angles and the peak dilatancy angles of binary granular mixtures. For mixtures with different FCs and an identical b, there is a linear relationship between the peak friction angle (or peak dilatancy angle) and the change in the void ratio. An acceptable equation was proposed to predict the peak dilatancy angle of a mixture. When b = 0.2 and 0.4, the coaxiality of strain increments and stresses is affected by the FC. A previous study classified mixtures as “underfilled”, “interactive-underfilled”, “interactive-overfilled” and “overfilled” based on the percentage contributions of coarse–coarse, coarse–fine and fine–fine contacts to the shear strength. This study shows that the b value has little effect on the classification of mixtures at the peak and critical states. Furthermore, it was observed that there is a linear relationship between the relative peak dilatancy angle and the difference between the partial coordination numbers based on the “subsphere–subsphere” approach at the peak and critical states.

Experimental and numerical analysis of axially loaded slender piles implementing a hypoplastic model

Multiple studies have been carried out to estimate uplift pile capacity, within three main categories: i) the experimental method, which is very costly; ii) a simpler method using load transfer mechanisms; and iii) the numerical finite element method (FEM). The predictive capacity of numerical simulation depends mainly on the constitutive model used to model the soil-structure interface at which the load transfers from the pile to the surrounding soil. A reliable constitutive model capable of capturing the main features of soil behaviour based on easily obtained parameters is thus required. The hypoplasticity model is a promising constitutive model in this respect, offering a particular class of rate non-linear constitutive model in which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model thus requires only eight material parameters (critical friction angle φc , e c0, e i0, e d0 (critical, maximum, and minimum void ratios, respectively), granular stiffness hs, and the model constants n, α, and β), with two additional parameters used to simulate the pile-soil interface (kr and ), which represent the surface roughness and the thickness of the shear zone, respectively. The performance of the model was verified in this work by comparing the numerical results with the experimental results for a single pile model under pull-out force with different surface roughnesses and confining pressures. The resulting good agreement between the numerical and the experimental results confirmed the ability of the hypoplastic model to simulate soil behaviour under complex conditions.

Fractional derivative in the elastic-viscoplastic stress-strain state model describing anisotropic creep of soft clays

A fractional elastic-viscoplastic (F-EVP) creep model describing the anisotropy of soft soil is established. A nonlinear viscoplastic creep expression is obtained by a fractional derivative and the Laplace transformation, which is extended by the definition of the reference yield surface. On this basis, the anisotropy of soil is considered in the model by a rotating hardening criterion, and the effect of anisotropic parameters on the stress-dilatancy ratio is discussed. The scalar multiplier in the form of stress ratio is described, and a critical friction angle is used to unify the modeling parameter. The validity of the model is examined by the existing triaxial creep results. The results indicate that the rotational anisotropy induces coaxial rotation as the result of the stress-dilatation relationship. The fractional viscoplastic model can reasonably describe the plastic behavior of soil before yielding, and accurately characterize the creep behavior of soil. From the comparison between the test results and the model calculation results, it is found that the model calculation results are basically consistent with the test results.

Effect of particle type on the shear behaviour of granular materials

In discrete element method (DEM) simulations, multi-sphere (MS) clumped and convex particles are two main particle models that are used to study the mechanical behaviours of granular materials. Of interest is the evaluation of the effect of multiple contacts between clumped particles or single contacts between convex particles on the mechanical behaviours of granular materials. In this context, a series of drained triaxial compression tests were conducted on convex true (CT) ellipsoids and MS ellipsoids with aspect ratios (ARs) ranging from 1.0–2.0. The microscale results indicate that at a given AR, the critical friction angle φc changes with the particle type, whereas the peak friction angle φp is nearly independent of the particle type. The anisotropic analysis provides underlying mechanisms of the shear strength evolution from two perspectives. First, the anisotropies of granular materials are essential to shear strength as the deviatoric (q)-to-effective mean (p′) stress ratio can be expressed as the sum of the anisotropies, i.e., q/p′ ≈ 0.4ac+ 0.4an + 0.6at, where ac, an and at are the normal contact anisotropy, normal contact force anisotropy and tangential contact force anisotropy, respectively. For all samples, ac and an underpin the shear strength and are influenced by the particle type. The similar φp displayed by the CT and MS ellipsoids does not translate to similar an and ac but similar ac+an for the two particle types. In addition, owing to their larger ac+an, the CT ellipsoids have a higher φc than the MS ellipsoids. Second, there is a satisfactory linear relationship between q/p′ and ac within strong and non-sliding (sn) contacts acsn (i.e., q/p′ = kacsn), where k is the fitting parameter. Accordingly, in the peak state, the subtle difference in shear strength is attributed to the greater acsn in the CT ellipsoids than in the MS ellipsoids that is counteracted by the smaller k. However, in the critical state, the greater difference in acsn between the CT and MS ellipsoids is partially offset by the smaller difference in k, causing a higher φc in the CT ellipsoids than in the MS ellipsoids.

UH model for granular soils considering low confining pressure

The mechanical behaviors including strength and isotropic compression of granular soils under low confining pressure are systematically analyzed. The compressive hardening parameter ps is introduced in semi-logarithmic coordinates to express the curved normal compression line of granular soils in the e-ln p plane, to describe the little compressibility of granular soils under low confining pressure. The nonlinear variation of critical friction angle with confining pressure is considered by introducing the interlocking strength parameter τ0 into strength criteria. Based on the unified hardening model for clays and sands (CSUH model), the unified hardening (UH model) for granular soils considering low confining pressure, called UH-L model, is established. The UH-L model behaves significantly different with the CSUH model under low confining pressure, while tends to be same as the CSUH model with increasing confining pressure. The relationship between parameter ps and τ0cotφ, as well as the effect of ps and τ0cotφ on model performance are analyzed. Good agreement with the experimental data shows that the UH-L model is capable of uniformly describing the stress–strain relations and strength of granular soils with interparticle locking over a wide confining pressure load range, especially at low confining pressure.

Influence of mineral dissolution on the mechanical behaviour of a granular assembly under complex stress states

Rock and soil are natural assemblies of mineral grains. Dissolution of mineral compositions in a granular assembly can dramatically disturb and change the microstructure. Once the soil fabric and inter-particle contacts change, large deformations can develop and the shear strength can decrease. Currently there is a lack of understanding and experimental evidence of geomaterial behaviour subjected to mineral dissolution under realistic complex stress conditions. In this experimental study, extensive laboratory tests were conducted to investigate changes in the stress-strain relation, shear strength and critical state of a granular assembly after experiencing a substantial loss of particles by salt dissolution. During the salt dissolution process, a larger shear stress or confining pressure leads to a smaller increase of void ratio, a smaller positive state parameter, and a weaker strain-hardening behaviour. After the salt dissolution, the material grading becomes narrower, the grading state index decreases and the specific void ratio increases, leading to an upward shift of the critical state line. However, the increase of void ratio is more than the upward shift of the critical state line, thus the stress state changes from the dense side to the loose side, accompanied by a change of shearing behaviour from strain-softening to strain-hardening. Nevertheless, as the critical friction angle is dominated by the inter-particle contacts among coarse particles, with almost no change in the coarse content of the post-dissolution materials, only a slight decrease of 2.3° in the critical friction angle is found.

Behaviour of Uniform Drava River Sand in Drained Condition—A Critical State Approach

Numerous triaxial tests on sand and sand-like materials have been performed worldwide during the past several decades. Their results provided a development of the advanced soil constitutive models and laboratory testing devices, as well as the establishment of a worldwide database of different types of uniform sandy materials. From such research, the critical state and steady state theory has emerged as one of the most useful tool for the modelling of a soil behaviour. This paper presents the results of static drained tests performed on the uniform Drava River sand from the Osijek region in Croatia. The main aim was to determine the shear behaviour and critical state, given that these characteristics are mostly unknown for the tested sand material. A series of detail triaxial tests were performed in drained conditions for three different initial relative densities, DR, and two different loading directions; e.g., axial compression and axial extension. In total, 18 drained tests were performed. The study indicated that the value of 33.75∘ is the critical friction angle for the tested sand. The relative density of 57% is determined as the critical relative density. Additionally, the study confirmed the difference in critical state for compression and extension loading. In addition, the results indicate that the sample preparation procedure has an important impact on the critical state of loosely prepared sandy samples. These results give the first insights into the behaviour of the Drava River sand, which can generally contribute to the worldwide sand behaviour knowledge base.

Shear behaviours of cohesionless mixed soils using the DEM: The influence of coarse particle shape

The coarse particles in mixed soils can be cobbles or gravels, with the main difference being their roundness (an indicator describing particle shape characteristics at an intermediate scale). The influence of coarse particle shape (i.e., roundness) on the macroscopic and microscopic shear behaviours of cohesionless mixed soils with various fines contents (FCs) was investigated via the discrete element method in this study. The shapes of coarse particles were formed using the rotation-invariant spherical harmonic method proposed by previous investigators. An equation was proposed to predict the initial void ratios of samples in this study. A decrease in the roundness of coarse particles can increase the peak friction angle (FC≤40%) and critical friction angle (FC≤30%). As the roundness of coarse particles decreases, the peak dilatancy angle initially increases and then decreases (FC≤20%). Furthermore, it was found that the roundness of coarse particles hardly affects the classification of cohesionless mixed soils, as determined by probing the percentage contributions of coarse–coarse, coarse–fine, and fine–fine contacts. When cohesionless mixed soils change from an underfilled structure to an interactive-underfilled structure at the critical state, the main forms of coarse–coarse contacts were discovered. Additionally, the force-fabric anisotropy mechanisms of the influences of the roundness and rolling resistance coefficient of coarse particles on the shear strengths of cohesionless mixed soils were found to be different.

Measurement and Calibration of the Parameters of Hypoplasticity Model for an Iraqi Soil

There are many constitutive models that have been used to model the mechanical behavior of soils. Some of these models are either unable to represent important features such as the strain softening of dense sand or required many parameters that can be hard to obtain by standard laboratory tests. Because of that, a more reliable constitutive model, which is capable to capture the main features of the soil behavior with easily obtained parameters, is required. The Hypoplasticity model is considered as a promising constitutive model in this respect. It is considered as a particular class of rate non-linear constitutive model at which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model required only eight material parameters (critical friction angle critical, maximum and minimum void ratio respectively), granular stiffness hs and the model constants n, α, β). The appealing feature of the hypoplastic model is that the material parameters are separated from the state variables (void ratio and the initial stresses). This feature enables the model to simulate the soil behavior under a wide range of stresses and densities with the same set of material parameters. In this research, a brief description of the Hypoplasticity model is presented. Detailed discussions regarding the measurement and calibration of the model parameters of an Iraqi soil are then exposed. It is concluded that only Consolidated Drained (CD) triaxial test, oedometer test, and the well-known limit density tests are needed to get all the parameters of the hypoplasticity model.