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The Cone Penetration Test (CPT) is a widely used site investigation tool due to its accuracy and wealth of data at a relatively low cost. Virtually all CPT interpretations explicitly or implicitly depend on how the in-situ state parameter is correlated to the tip resistance. Accurate interpretation of the state parameter from CPT is the basis for evaluating strength and liquefaction susceptibility of granular soils. The handful of interpretation methods used in the industry range between empirical and semi-empirical. As is the case for all empirical methods, extrapolating these methods outside of the original database, especially to significantly different soils such as silt-rich tailings, brings about significant risk. This paper presents a new method of interpreting the state parameter from a fully validated model of the cone penetration in sand. The method has no empirical elements and produces soil-specific correlations between the tip resistance and the state parameter. It can be easily implemented in a spreadsheet and does not require complicated analyses. The method differentiates among soils through calibration of a critical state based constitutive model, Norsand, through triaxial compression tests. The potential errors induced by not measuring soil properties are quantified. [ABSTRACT FROM AUTHOR]

In order to improve the understanding on static liquefaction phenomenon, this paper presents an insight into the instability mechanism of a silty sand originating from the Sakarya region (Turkey). Monotonic undrained simple shear tests were performed in either strain-controlled or stress-controlled modes. The interpretation of the experimental results allowed us to draw three interesting conclusions on instability conditions: (1) Hill's stability postulate can be conveniently used to identify the onset of instability for strain-controlled tests, whereas in stress-controlled conditions, an alternative new parameter η* (modified apparent viscosity) was introduced. Depending on the strain rate, η* allows to identify stability conditions more clearly than second-order work; (2) the value of the pore pressure ratio at the onset of instability (ru,is), ranging between 0.30 and 0.50, is linearly linked to the state parameter ψ ; and (3) at the onset of instability, the dependence of both the major and minor principal stress directions (αis and βis) and Lode's angle (θis) on ψ was also observed. These findings are expected to be of some help for a more consistent approach to the constitutive modeling of the static instability mechanism. [ABSTRACT FROM AUTHOR]

The state parameter (ѱ) accounts for both relative density and effective stress, which influence the cyclic stress or liquefaction characteristic of the soil significantly. This study presents a ѱ‐based probabilistic liquefaction evaluation method using six soft computing (SC) techniques. The liquefaction probability of failure (PL) is calculated using the first‐order second moment (FOSM) method based on the cone penetration test (CPT) database. Then, six SC techniques, such as Gaussian process regression (GPR), relevance vector machine (RVM), functional network (FN), genetic programming (GP), minimax probability machine regression (MPMR) and multivariate adaptive regression splines (MARS), are used to predict PL. The performance of these models is examined using nine statistical indices. Additionally, plots such as regression plots, Taylor diagrams, error matrix and rank analysis are shown to assess the SC model's performance. Finally, sensitivity analysis is performed using the cosine amplitude method (CAM) to assess the influence of input parameters on output. The current study demonstrates that SC models based on state parameter predict PL effectively. RVM and MPMR models closely follow the GPR model in terms of performance, which is superior to the other models. Notably, two equations are generated using GP and MARS models to predict PL. The results of the sensitivity analysis reveal the magnitude of earthquake (Mw) as the most sensitive parameter. The outcomes of this research will offer risk evaluations for geotechnical engineering designs and expand the use of state parameter‐based SC models in liquefaction analysis. [ABSTRACT FROM AUTHOR]

Results of torsional shear hollow cylinder (TSHC) tests carried out on a reconstituted sand maintaining a constant direction of major principal stress relative to the vertical axis (α) and intermediate principal stress ratio (b) during shearing are presented. Tests were undertaken following the constant shear drained (CSD) stress path, which simulates stress conditions under a rising phreatic surface. The test programme was complemented by undrained TSHC tests to provide further insight regarding the behaviour of the sand when sheared under a range of α values. Various reconstitution methods (i.e. moist tamped (MT), dry pluviated (DP) and wet pluviated (WP)) were included to examine the effects of fabric on CSD triggering. Only MT and DP specimens could be prepared loose enough to exhibit liquefaction behaviour; hence the focus of this study was on these preparation methods. The programme indicated that the instability stress ratio (ηIL) under the CSD stress paths decreases as α increases, suggesting that cross-anisotropy strongly influences the shearing behaviour of sands under this trigger mechanism. In addition, the DP sand showed a greater decrease of ηIL with increasing α compared to the MT sand, consistent with other studies examining the effect of fabric and preparation methods on inherent anisotropy. The results of this study suggest that ignoring the effect of cross-anisotropy on the CSD trigger mechanism will lead to unconservative slope stability assessments. [ABSTRACT FROM AUTHOR]

This study adopts three-dimensional discrete element method to examine how particle shape affects the cyclic liquefaction resistance of granular materials. A family of superquadric particles is employed to model different particle shapes by varying two shape parameters: aspect ratio (AR) and blockiness (B). Five smooth and convex particle shapes are considered in this study, with AR ranging from 0.5 to 1.5, and B varying from 2 to 8. These particles are used to create isotropically compressed samples at an initial confinement of 100 kPa and two relative densities ( D r ) of 20 % and 50 % , resulting in ten samples. These samples are then subjected to constant-volume cyclic simple shearing with various levels of cyclic stress ratios until initial liquefaction occurs in 41 simulations. The results of these simulations reveal that at D r = 20 % , the spherical particles exhibit the highest liquefaction resistance compared to the non-spherical particles. However, this trend is reversed for the samples with D r = 50 % . By employing the overall regularity (OR) as a synthetic descriptor of particle shape, it is observed that liquefaction strength generally increases with higher OR at D r = 20 % , while it demonstrates an approximately decreasing trend at D r = 50 % . Furthermore, the initial coordination number and two critical state parameters based on the void ratio and the coordination number at the pre-shearing state of the samples, demonstrate a strong correlation with the cyclic liquefaction resistance within the ranges of particle shape and D r considered in this study. [ABSTRACT FROM AUTHOR]

There are many geotechnical applications involving dams, embankments and slopes where the presence of an initial static shear stress prior to the cyclic loadings plays an important role. The current paper presents the experimental results gathered from undrained cyclic simple shear tests carried out on non-plastic silty sand with fines content in the range 0-30% with the consideration of sustained static shear stress ratio (α). Two distinct parameters, namely the conventional state parameter Ψ, and the equivalent state parameter Ψ*, are introduced in the context of critical state soil mechanics (CSSM) framework to predict failure mode and undrained cyclic resistance (CRR) of investigated soils. It is proved that the failure patterns for silty sands are related to (a) the initial states of soils (Ψ or Ψ*) and (b) the combination of initial shear stress with respect to cyclic loading amplitude. At each α, the CRR-Ψ (or Ψ*) correlation can be well represented by an exponential trend which is practically unique for both clean sands and silty sands up to a threshold fines content (fthre≅24.5%). Varying α from low to high levels simply brings about a clockwise rotation of the CRR-Ψ (or Ψ*) curves around a point. This CRR-Ψ (or Ψ*) platform thus provides an effective methodology for investigating the impact of initial shear stress on the cyclic strength of both clean sands and silty sands. The methodology for estimating Ψ (or Ψ*) state parameters from in-situ cone penetration tests in silty sands is also discussed. [ABSTRACT FROM AUTHOR]

This paper presents an appropriate physical parameter for cement admixed clay, termed as the state parameter that combines the influence of void ratio, stress level, and cement content reference to an ultimate (steady) state. Data from a triaxial testing program on Pasak Clay with different stress paths was presented and demonstrated to be dependent on the state parameter. The strength and pore water pressure at the failure of cement mixed clay were directly associated with mean stress and decreasing state parameters. The 3-D surface for deviatoric stress, mean stress, and state parameter at certain distortional strains was proposed based on a stress path triaxial test. The stiffness of cement-treated clay increased with a decreasing state parameter and increase in mean stress. The concept of state parameter is a basic physical concept and has broad application as an empirical normalising parameter and constitutive modelling of soil behaviour. [ABSTRACT FROM AUTHOR]

In the current study, we proposed a novel fractional-order thermo-mechanical constitutive model within the framework of critical state theory to depict the coupling effect of fine content and temperature on shear behaviors of sand–clay mixtures. The direction of the non-orthogonal plastic strain increment was derived by taking the fractional derivative of the yield surface without introducing an additional plastic potential function, which provided a unified description of the associated and non-associated flow rule. In addition, the fines- and temperature-dependent critical state was also considered. Subsequently, the performance of the fractional-order thermo-mechanical model was analyzed through parametric investigation. Comparisons between the predicted and experimental results demonstrate that the proposed model can effectively reproduce the strain-softening, dilatancy, and thermal softening behaviors of sand–clay mixtures with different confining pressures, fine contents, and temperatures. [ABSTRACT FROM AUTHOR]

This paper has been prepared to detail the main theme of the published paper in the journal of Marine Georesources and Geotechnology; entitled "Liquefaction susceptibility of beach sand containing plastic fines" for enhancing the content integrity to be considered as a discussion paper of Hamza Saeed, Zalihe Nalbantoglu & Eris Uygar (2021). [ABSTRACT FROM AUTHOR]

The state parameter allows the evaluation of the in situ state of soils, which can be particularly useful in tailings impoundments where flow liquefaction is the most common failure model. Positive state parameter values characterize a contractive response during shearing and, for non-plastic soils, can indicate flow liquefaction susceptibility. This paper presents a methodology to classify and estimate the state parameter (Ψ) for non-plastic silty soils based on seismic cone penetration measurements. The method expands on a previous methodology developed for sands that use the ratio of the small strain shear modulus and the cone tip resistance G0/qt for classification and Ψ assessment. For non-plastic silty soils, drainage conditions during cone penetration must be accounted for and are used to allow soil classification and correct the cone tip resistance. An empirical formulation is proposed to correct qt for partial drainage measurements and predict Ψ for non-plastic silty soils. Mining tailings results of in situ and laboratory tests were used to validate the proposed methodology producing promising responses. The Ψ value estimated through the proposed methodology are in the range of those obtained from laboratory tests, indicating an adequate prediction of behavior for non-plastic silty soils.

The state parameter allows the evaluation of the in situ state of soils, which can be particularly useful in tailings impoundments where flow liquefaction is the most common failure model. Positive state parameter values characterize a contractive response during shearing and, for non-plastic soils, can indicate flow liquefaction susceptibility. This paper presents a methodology to classify and estimate the state parameter (Ψ) for non-plastic silty soils based on seismic cone penetration measurements. The method expands on a previous methodology developed for sands that use the ratio of the small strain shear modulus and the cone tip resistance G0/qt for classification and Ψ assessment. For non-plastic silty soils, drainage conditions during cone penetration must be accounted for and are used to allow soil classification and correct the cone tip resistance. An empirical formulation is proposed to correct qt for partial drainage measurements and predict Ψ for non-plastic silty soils. Mining tailings results of in situ and laboratory tests were used to validate the proposed methodology producing promising responses. The Ψ value estimated through the proposed methodology are in the range of those obtained from laboratory tests, indicating an adequate prediction of behavior for non-plastic silty soils. [ABSTRACT FROM AUTHOR]

This study presents a novel formulation for incorporating anisotropy into the generalized plasticity constitutive model. Generalized plasticity is a hierarchical framework allowing for extensibility, in order to encompass new phenomena and improve its predictive capabilities. Anisotropy formulation is based experimentally on the phase transformation state and considers explicitly the direction of the maximum principal stress and the magnitude of the intermediate principal stress, through an anisotropy state variable that contributes to the state parameter. Additionally, the model incorporates the fabric using an evolving fabric variable that reflects initial fabric due to sample preparation method for granular soils. The formulation is simple and introduces three constitutive parameters, allowing for straightforward implementation into the constitutive model and direct application in finite element analysis. The model is validated with undrained triaxial tests conducted on Toyoura sand, covering a wide range of initial conditions with a unique set of constitutive parameters, and yielding overall satisfactory results despite some limitations. [ABSTRACT FROM AUTHOR]

This paper presents a new interpretation procedure to estimate the initial state parameter from cone penetration testing (CPTu) in undrained conditions based on the results from a comprehensive set of numerical simulations of CPTu in low permeability liquefiable soil. CPTu simulations are performed using the Particle Finite Element Method, whereas the material response is modelled with the Clay and Sand Model. The effects of soil constitutive parameters and roughness of the soil–steel interface are examined. It turns out that the numerical results are correctly summarized by an analytical relation derived from undrained cavity expansion results in critical state soils, as long as the constraints resulting from cone geometry are taken into account. The resulting adapted analytical formulation is notable for its simplicity and ease of use, comparing favorably with existing alternatives. [ABSTRACT FROM AUTHOR]

The state parameter (ψ) is based on a framework of critical state soil mechanics, which reflects the influences of soil compactness and stress level and has significant advantages for liquefaction analysis. In engineering practice, a simplified procedure based on the cone penetration test (CPT) to assess the liquefaction potential in the field involves model and parameter uncertainties. Furthermore, the use of limited CPT measurements involves project-specific test uncertainties, and the spatial variability of soil properties has a remarkable effect on soil liquefaction. To tackle these challenges, this study develops a ψ-based liquefaction probability framework to integrate the prior information of project-specific CPT, and uses limited tests to characterize the 2D spatial distribution of liquefaction potential with proper consideration of various uncertainties and soil spatial variability. The framework is developed based on simulation of Gaussian stationary random fields and Markov Chain Monte Carlo simulation. The proposed method is demonstrated using real CPT data from the 2011 Tohoku-Oki earthquake in Japan. The results indicate that the ψ-based evaluation performs well and can reasonably assess the liquefaction phenomenon of heterogeneous soils. This study incorporating the spatial variability of ψ into the liquefaction probability framework provides valuable information for geotechnical engineering design. [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]

Cyclic liquefaction failure modes are directly related to the consequence of liquefaction and important for mitigation strategies. Two common failure modes, cyclic mobility (CM) and cyclic instability (CI), are well reported in the literature. However, recent experimental studies revealed three other failure modes, i.e. plastic strain accumulation (PSA) and two hybrid failures: CI followed by CM and CI followed by PSA. This study used discrete element method (DEM) which demonstrated all five different failure modes for cyclic loadings. The mechanics involved in these failure modes were evaluated in light of the Critical State Soil Mechanics (CSSM) framework using a series of drained and undrained triaxial simulations after isotropic and K0 consolidation. The state parameter (ψ) showed a good correlation with phase transformation (PT) and instability (IL) states. It was found that cyclic failure modes, particularly CM and CI, are closely linked with the PT and IL states, respectively. Some previous studies reported that the hybrid failure mode depends on the soil fabric influenced by the sample preparation method. However, all five different failure modes were observed for the assemblies prepared by the same technique. It was found that the failure modes depended on the location of the initial states of soil with respect to the critical state line in the classical e-log(p′) space, where e is the void ratio and p′ is mean effective stress. Also, distinct zones for failure modes were observed in the SSR/CSR-ψ space, which confirmed that the cyclic behaviour was strongly dependent on ψ; where CSR is cyclic stress ratio and SSR is static stress ratio. Such observation allows the prediction of cyclic failure modes within the CSSM framework. [ABSTRACT FROM AUTHOR]

Results from both laboratory and in-situ cone penetration tests (CPTs) on predominantly sandy silt platinum tailings from an operational mine in South Africa are reported. The CPTs were conducted with four different cone diameters at varied penetration rates. With the results interpreted in terms of the normalized tip resistance and the initial state parameter, in addition to dissipation tests, it was possible to identify the CPTs affected by significant partial drainage effects. A review of the partial drainage concept enabled the formulation of a novel characteristic surface approach, which uses a unified continuous equation to estimate the state parameter from the CPT data from drained to partially drained and undrained regimes and from contractive to dilative states. A review of different methods for the estimation of the coefficient of consolidation, and hence the normalized penetration velocity, enables a comparison of the estimated state parameter with independent values calculated from recovered saturated samples, showing the ability of this technique to infer the state parameter from CPT tests where partial drainage occurs. [ABSTRACT FROM AUTHOR]

A new state parameter that is capable of characterizing the mechanical properties of cement-treated clays with different mixing proportions, curing time, and stress conditions is developed in this study. The development is conducted by combining the effect of stress level based on the critical state theory with the effective void ratio. Based on the experimental data of cement-treated Bangkok clay performed in this study together with those of cement-treated Singapore marine and Ariake clays reported in previous studies, the analyses reveal that the state parameter is proven to be an efficient parameter for characterizing the mechanical properties of cement-treated clays with different base clays under various mixing proportions and curing times tested under various stress conditions. Furthermore, empirical equations to assist the establishment of the effective void ratio on the critical state locus from the plastic limit value of the base clay are suggested based on regression analyses. The state parameter can thus be computed and the engineers can preliminarily estimate the mechanical properties of cement-treated clay in the planning stage. [ABSTRACT FROM AUTHOR]

Based on the frictional state concept, the natural state parameter for sands is defined as an extension of the state parameter defined by Been and Jefferies. The proposed definition of the natural state parameter is the sum of the distance between the normalised difference of the current stress ratio and the critical frictional stress ratio and the difference between the current and critical frictional state void ratio for the same mean principal stress. Therefore, it combines the difference between the current and critical frictional state in the q ‒ p’ and e ‒ p’ planes and can be treated as an extension of Been and Jefferies’ definition of the state parameter in the e ‒ p’ plane. The results of drained triaxial compression tests for Toyoura sand and Dog’s Bay sand, presented in the literature, are analysed. The values of the natural state parameter at failure for these sands are equal to zero. Therefore, the critical state in the q ‒ p’ and e ‒ p’ planes can be determined by analysing the conditions at failure. At failure, the deformations of the samples are almost homogeneous, and the stresses and deformations (void ratios) can be correctly determined. Additionally, the critical frictional state and critical state are very similar for these sands. The relationship between the dilatancy and the state parameter at failure, similar to that given by Been and Jefferies, was obtained directly by using the frictional state concept and the proposed definition of the natural state parameter. The natural state parameter, like the state parameter, can be used for modelling of sands in the future.

Standardization is essential for innovation (on the impacts on design, manufacturing, and operation processes) and its dissemination, both within a country and internationally. A phenomenological information model has been developed for the system of standards, which will be used as an information base for integrated quality management systems, environmental safety, and energy saving depending on the type of products, requirements of technical regulations, and conformity assessment procedures. Phase portraits of the life cycle system of complex products were constructed, and a general expression for the Lyapunov exponents characterizing the overall behavior of the dynamic system in phase space was obtained. The presence of particular areas to which, regardless of the initial conditions, all phase trajectories rapidly evolve has been established. The critical conditions for the control parameters were found. A diagram was constructed that determines the stability of the system states of the life cycle of complex products. It was found that the processes of the life cycle of complex products are carried out in two stages: in the first, there is a rapid evolution of components and parameters of technical and software tools, as well as energetic elements of functional subsystems, which is reflected in a specific attractive section of phase portraits, in the second, further slow development along it.

Several widely used field methods for estimating postliquefaction ground deformation are based on the laboratory data from one series of cyclic simple shear tests performed on one uniform clean sand reconstituted to three relative densities. It is not clear if the trends of this one data set are applicable to other clean sands, nonplastic silty sands, and nonplastic silts. A database of 579 test results on postliquefaction volumetric strain, including 299 test results that relate maximum shear strain to the factor of safety against liquefaction triggering, was compiled and used to examine trends for these soils. The database includes postcyclic test data on 10 clean sands, 2 gravels, 3 silty sands, 5 silts, and 3 clayey soils. The enlarged cyclic testing database was used to develop models that estimate postliquefaction volumetric strain and maximum shear strain as a function of soil type, state, and seismic demand. The models are applicable to uniform nonplastic soil. The state parameter was used in addition to relative density and void ratio to characterize the state of the soil. Correlations between these parameters enable the full data set to inform the models. [ABSTRACT FROM AUTHOR]

This article presents an experimental program under the constant volume condition to investigate the influence of over-consolidation on flow instability of clean and silty sand specimens prepared by a systematic increase in fines content (FC), where fines are particles smaller than 0.075 mm of non-plastic minerals. An extensive series of constant volume Direct Simple Shear (DSS) tests on normally and over-consolidated clean and silty Firoozkuh No. 161 sand specimens were carried out. The testing program covers a range of initial void ratios, effective vertical stresses, and FCs. Analysis of the laboratory data indicates that over-consolidation history leads to an increase in the slope of the instability line and a rise in normalized constant volume shear strength at the onset of flow instability. Furthermore, at the same normalized constant volume shear strength, brittleness index and maximum excess pore-water pressure ratio increase with over-consolidation. Even though an increase in FC leads to a family of non-unique critical state lines in the void ratio versus effective vertical stress plane, it is observed that the slope of the instability line and normalized constant volume shear strength vary almost uniquely with state parameter at the onset of flow instability irrespective of FC. [ABSTRACT FROM AUTHOR]

This paper presents the potential of scrap tire in controlling the onset of instability of sand in the constant shear drained (CSD) stress path. A series of triaxial tests in the constant shear drained stress path was conducted on the sand and sand––tire chip (STCh) mixtures. All the tests were performed following the conventional consolidated drained (CD) test up to a predefined deviator stress (onset of CSD). The CSD test then was carried out on samples at the onset of CSD by reducing the confining pressure while maintaining the deviator stress and backpressure constant. The effect of different deviator stress (qCSD), initial mean stress (po′) levels, and tire chip content (TCh) on the onset of instability were investigated. The instability of sand and sand–tire chip mixtures was determined based on the decrease in the constant deviator stress (dq<0) and second-order work criteria (d2W<0). Both approaches were found to be consistent in determining the onset of instability of STCh mixtures. The onset of instability of sand is influenced by the TCh content and qCSD. On other hand, a unique value of pf′ was found for different values of po′. The optimum performance in controlling the onset of instability of sand was found for TCh=20% for the tire chip considered in this study. The mobilized effective friction angle also exhibited improved performance for TCh = 20%. In addition, the modified state parameter had good correlation with the mobilized effective friction angle in the CSD stress path. [ABSTRACT FROM AUTHOR]

Increase in seismic events around the world has necessitated the evaluation of soil liquefaction potential since it adversely influences the stability of adjacent structures and poses a threat to lives and property. The first step in evaluating the liquefaction potential involves the estimation of the in situ state of sand and the state parameter as an index to characterize the behavior of sand. Due to the difficulty in obtaining high-quality undisturbed sandy samples for laboratory testing and evaluation, simplified equations based on the cone penetration test (CPT) are used for reasonable estimation of field behavior. In the present study, an optimized group method of data handling (GMDH)-type neural network was proposed to estimate the state parameter from CPT data obtained from the historical liquefaction database. A comparison was made between the measured and the predicted values of the state parameter to evaluate the performance of the proposed GMDH neural network method. A sensitivity analysis of the proposed model was also carried out to study the effect of input variables on the output variable of the proposed model. Additionally, the evaluation of in situ state and liquefaction potential of sand based on the state parameter was also presented and compared with the existing methods. Overall, the use of the GMDH model in evaluating the in situ state of sand and subsequent liquefaction potential assessment has shown promising results. [ABSTRACT FROM AUTHOR]

In order to study the changes of steam state parameters and the interaction between hydraulic calculation and thermal calculation during the long-distance heating of steam, a variety of working conditions were simulated by the compressible fluid pipe network analysis software AFT arrow combined with the control variable method. The results show: The steam outlet pressure obtained by traditional calculation methods is lower than the outlet pressure when considering the change of steam state parameters. The density change of steam is related to the flow velocity and pipe diameter of steam. When the maximum flow rate of steam in a long straight pipe is 20 m/s, the temperature drop of steam per kilometer gradually decreases. When the maximum steam flow rate is 40 m/s, 60 m/s, the temperature drop of steam per kilometer decreases first and then increases. This shows, there is still a certain error between the traditional method of calculating steam pressure drop and the actual, especially for small pipe diameters, heating pipes where the flow rate of steam changes greatly during the heating process, heating pipes where the flow rate of steam changes greatly during the heating process.

Abstract The effects of fibre (0–3 %) and cement (0–3 %) additives, on Toyoura sand were examined under consolidated drained compression and extension loading conditions. All samples were prepared to a target dry density value (e.g., $${\rho }_{d}$$ ρ d = 1.489 g/cm3) of Toyoura sand using under-compaction moist tamping technique. In compression, the unreinforced specimens exhibited a behavior of medium dense sand and reached a peak deviator stress (q p ) at approximately 4 % axial strain ( $${\epsilon }_{a}$$ ϵ a ) for the varying mean effective stresses, pʹ (i.e. 50–400 kPa). The peak drained strength increases in fibre reinforced cemented specimens were found to be up to 132 % (lower effective stresses) and 243 % (higher effective stresses), while, the drained strength increases at critical state for the fibre reinforced cemented specimens were found to be up to 105 % (lower effective stresses) and 245 % (higher effective stresses). Overall, the fibre and cement additives increased the stiffness, peak and strength at critical state of pure Toyoura sand but were found to be least effective in extension loading. Moreover, the stress ratio, peak and critical state stress ratios increase with the addition of fibres and cement. The secant modulus shows limited increases for the fibre reinforced specimens. However, a significant improvement in the secant modulus is observed for the fibre reinforced cemented specimens. For both unreinforced and reinforced specimens there is a decrease in volumetric strain with greater effective stresses or in other words, the rate of dilation decreases with increases in effective stresses. The fibre and cement additives also increased the strength parameters (frictional angle, cohesion), dilatancy angle, slope of the critical state line, and decreased the state parameter of pure Toyoura sand.

Fabric anisotropy and fines content (fc) in sands modify significantly their mechanical behaviour, particularly as related to static liquefaction under undrained conditions. The fabric anisotropy aspect, expressed by means of an evolving fabric tensor F, has been addressed in the recently developed Anisotropic Critical State Theory (ACST) that enhances the two critical state conditions on stress ratio (η) and void ratio (e) of the classical Critical State Theory by an additional condition on the critical state value of F in relation to loading direction; based on this concept it introduces the dependence of dilatancy on fabric anisotropy. Various models have been successfully developed within this framework for clean sands. The fc aspect has been addressed within the Equivalent Granular State Theory (EGST) that substitutes a properly defined equivalent granular void ratio (e*) for e in any model for clean sand in order to obtain the response of sand with fines without any other change of the model structure and constants. Along these lines, a constitutive model is constructed in this work in order to address the effect of both F and fc simultaneously, by a combination of these two powerful propositions. The idea is very simple: one takes a constitutive model developed within ACST for clean sands, hence it accounts for fabric anisotropy, and substitutes the e* for e, as well as the derivative quantities of such substitution, hence it accounts for fc. The result yields a model that can simulate data on the undrained response for a range of fc, with emphasis on static liquefaction. It is shown that the inclusion of fabric anisotropy improves previous similar simulations made within the EGST but without the framework of ACST. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of gassy sand is rather complex owing to the inherent complex nature of sand and the occluded/dissolved gas. For better understanding of the behaviour of gassy sand under monotonic loading, a numerical model is presented in this paper. By considering the gas–water mixture in gassy sand as a homogenous pore fluid, the theory of two-phase saturated porous media is employed. Based on this theory, the impact of the occluded/dissolved gas is characterized by the relationship between the compressibility of pore fluid and the degree of saturation as well as the pore fluid pressure, derived from Boyle's and Henry's Laws. Then an advanced constitutive model for sand is combined with the porous media theory to capture the complex stress–strain behaviour of sand, using a single set of model parameters. Through the spatial and temporal discretization of the governing equations by the finite element method and the well-known θ-method, the porous model is numerically implemented as a user-defined element subroutine provided by ABAQUS, in which the implicit constitutive integration algorithm is used. Finally, the influences of gas type, degree of saturation, pore fluid pressure level, and physical state (void ratio and stress level) on the behaviour of gassy sand are studied by the numerical model. The model is validated by comparing the simulated results with laboratory test data from literature. [ABSTRACT FROM AUTHOR]

This research consists of two main parts. First, some laboratory and field tests have been conducted on a specific soil. Therefore, a series of laboratory and field data have been obtained that can be used to evaluate numerical analyses. In the second part, an elastoplastic constitutive model is introduced based on Duncan-Chang constitutive model. The steady state concept has been added to this constitutive model using the state parameter. The mentioned constitutive models have been calibrated using laboratory data for the soil. Then, these constitutive models have been applied in the numerical analysis of an excavation problem monitored during construction. Thus, the effect of the state parameter and steady-state concept on the numerical results has been evaluated with a comparison between the numerical analyses and field observation. Finally, according to the numerical analyses and field data, it has been concluded that the steady state concept in constitutive models can play a significant role to improve the numerical simulations of geotechnical structures. [ABSTRACT FROM AUTHOR]

When soil particles break, the particle size distribution (PSD) becomes a variable in the same way as other variables like void ratio, soil structure and anisotropy, etc. To consider particle breakage in a constitutive model, we need three key components: (i) quantification of PSD in a realistically simple manner, (ii) evolution of PSD during particle breakage, and (iii) influences of PSD on other soil properties like strength and stiffness. This paper firstly summarizes the latest advances in the first two components, discusses new ways of quantifying PSD effects, and finally presents a new critical state model where the PSD is treated as a variable. In discussing the PSD effects, we focus on the movement of the critical state line (CSL) due to particle breakage. We introduce a new state parameter and a new evolution law of the CSL. We assume that the CSL shifts downwards in the v—lnp space with increasing particle breakage under relatively low stresses, but all the CSLs for different PSDs converge to a steady state at high stresses where particle breakage eventually stops and is no longer the main mechanism for soil deformation. The proposed model is compared with other constitutive model in the literature and validated against experimental data, which demonstrates its satisfactory performance. [ABSTRACT FROM AUTHOR]

Volcanic pyroclastic deposits generally have a metastable and collapsible structure, which may lead to their liquefaction under monotonic, cyclic, and dynamic loading. Their structure could be partly attributed to the nature of the pyroclastic particles, especially their lightweight, fragile and porous features. In comparing the results of monotonic and cyclic undrained triaxial tests performed on Cervinara soil, the steady-state concept is used to define the occurrence of liquefaction. A significant part of the experimental program on Rangiriri soil is carried out to highlight the role of the fragility of pyroclastic particles on the occurrence of liquefaction. The comparison between the results obtained on the two types of pyroclastic soils shows the possibility of explaining the undrained mechanism of pore pressure buildup using the state parameter ψ. The parameter ψ seems to be useful also in comparing the results obtained on pyroclastic soils with those on ordinary sands. The state parameter has a clear physical significance that could be used to define a more reliable model of undrained pore pressure buildup for soils of different natures. [ABSTRACT FROM AUTHOR]

Tailings are the reservoirs containing a high proportion of saturated silts that may be extremely difficult to sample in their undisturbed condition. This is mostly due to the fabric disturbance and densification that can alter soil behavior. Meanwhile, assessing the in situ state of deposits is indispensable to stability analyses. A useful parameter defining states of soils is state parameter (Ψ), usually determined using the results of the cone penetration test. In this study, several series of numerical analyses of the piezocone penetration test (CPTu) were carried out for saturated tailing silts to evaluate the resistance against penetration for different soil properties and initial states. The numerical simulation adopted the Norsand model as an appropriate constitutive law to capture silt behavior. Analyses indicated that the familiar methods for determining the initial state of soils from CPTu results fail to precisely estimate the initial state parameter (Ψ0) in saturated tailing silts. Therefore, the numerical model was applied to tailing silts to propose relationships using cone penetration resistance to predict the initial state parameter. In addition, the numerical model procedure and the proposed relationships are validated with available numerical and field -piezocone soundings measurements. [ABSTRACT FROM AUTHOR]

Sand‐fines mixtures are commonly used engineered materials, and their mechanical behavior is significantly affected by density, confining pressure, as well as fines content. Although many laboratory tests have been performed on sand‐fines mixtures, few works have been conducted on its constitutive law. To adequately describe the mechanical behavior of sand with different fines content, a novel elastoplastic constitutive model was developed for sand‐fines mixtures by incorporating an equivalent granular state parameter into Rowe's stress‐dilatancy equation, plastic modulus, and in conjunction with the correlation between the critical state and fines content. Subsequently, the Runge‐Kutta schemes with automatic error control are adopted for the proposed model and implemented in a finite element code. The performance of the fines‐state‐dependent model with the Runge‐Kutta schemes, in terms of accuracy, efficiency and convergence, is verified by analyzing element scale tests and boundary value problems. The comparisons of simulated and experimental results demonstrate that the fines‐state‐dependent model can effectively capture the strain hardening (or softening) and contraction (or dilatancy) behaviors of sand‐fines mixtures under drained conditions. In addition, the key features under undrained conditions, such as flow, limited flow, and non‐flow behaviors can also be reasonably reproduced. [ABSTRACT FROM AUTHOR]

The effects of fibre (0–3 %) and cement (0–3 %) additives, on Toyoura sand were examined under consolidated drained compression and extension loading conditions. All samples were prepared to a target dry density value (e.g., ρ d = 1.489 g/cm3) of Toyoura sand using under-compaction moist tamping technique. In compression, the unreinforced specimens exhibited a behavior of medium dense sand and reached a peak deviator stress (qp) at approximately 4 % axial strain ( ϵ a ) for the varying mean effective stresses, pʹ (i.e. 50–400 kPa). The peak drained strength increases in fibre reinforced cemented specimens were found to be up to 132 % (lower effective stresses) and 243 % (higher effective stresses), while, the drained strength increases at critical state for the fibre reinforced cemented specimens were found to be up to 105 % (lower effective stresses) and 245 % (higher effective stresses). Overall, the fibre and cement additives increased the stiffness, peak and strength at critical state of pure Toyoura sand but were found to be least effective in extension loading. Moreover, the stress ratio, peak and critical state stress ratios increase with the addition of fibres and cement. The secant modulus shows limited increases for the fibre reinforced specimens. However, a significant improvement in the secant modulus is observed for the fibre reinforced cemented specimens. For both unreinforced and reinforced specimens there is a decrease in volumetric strain with greater effective stresses or in other words, the rate of dilation decreases with increases in effective stresses. The fibre and cement additives also increased the strength parameters (frictional angle, cohesion), dilatancy angle, slope of the critical state line, and decreased the state parameter of pure Toyoura sand. [ABSTRACT FROM AUTHOR]

The state parameter is a fundamental component of critical state compatible, bounding surface plasticity models. Several definitions for the state parameter exist, expressing how far the current state is from critical. However, there is rarely the opportunity to directly assess the chosen state parameter definition within a given model. Here, we use a plasticity model of the SANISAND family to simulate partially drained paths in triaxial space, by imposing a constant ratio of volumetric to axial strain. We show that for such paths, the locus of post-phase transformation and post-peak stress ratio points where instability is triggered represents a constant state parameter curve in e − p ′ space. We then present results from a series of partially drained triaxial compression experiments on Hostun sand, where volumetric and axial strains are coupled. We demonstrate that the chosen constitutive model does not recreate the experimentally observed paths well and more specifically is unable to match the experimentally obtained locus of constant state instability points. Consequently, we propose an updated state parameter definition through which the selected bounding surface plasticity model is shown to not only capture the desired locus of instability points, but to also achieve an overall improved performance in simulating partially drained paths. [ABSTRACT FROM AUTHOR]

This article presents a fuzzy controller for autonomous vehicle to intelligently recognize running environment and avoid an obstacle, which is constructed by rough sets (RSs) and an adaptive neuro-fuzzy inference system (ANFIS). Firstly, RSs are considered to propose a pyramid normalization (PN) method for normalizing state parameters (SPs) which are defined to recognize relative position such as distance and angle among a vehicle, an obstacle and target pathway, to improve the adaptability of complex environment and optimize the database of driving knowledge. Secondly, ANFIS is employed to design a controller with self-position azimuth correction (SPAC) for performing trajectory tracking and obstacle avoidance. Finally, the proposed methods have been implemented on the model vehicle called “RoboCar”, and compared with various fuzzy control approaches such as the initial SPs with ANFIS, the normalized SPs with fuzzy neural network (FNN), and the initial SPs with FNN. Time, maximum tracking error and mean tracking error are calculated to evaluate the performance. The experimental results with four kinds of target pathways have shown that the PN-ANFIS-based controller has saved time (7.6%), reduced maximum tracking error (8.1%) and mean tracking error (8.5%).

Particle breakage is a typical characteristic of crushable granular soil under high pressure, which has great effects on its stress–strain behaviors. The phenomenon of the critical state line (CSL) shifting downward in the compression plane caused by particle breakage was depicted by a breakage-dependent critical state plane (BCSP). Particle breakage was incorporated into a void ratio–pressure state parameter to modify Rowe's stress–dilatancy equation, and then, the state parameter was incorporated into the bounding stress ratio and plastic modulus. Due to the impact of high pressure on particle breakage, the pressure-dependent plastic modulus parameters were introduced. A breakage-dependent bounding surface plasticity model was proposed to capture the influence of particle breakage on the state-dependent stress–strain behaviors for silica and coral sands, and the transition of complex breakage-dependent critical states resulted from the competition between the contraction due to particle breakage and the dilatancy due to particle rearrangement. [ABSTRACT FROM AUTHOR]

Based on the existing unified hardening model, the double-state parameters unified hardening (DPUH) model is proposed, which can take into account the initial density and confining pressure dependent characteristics and stress-induced anisotropy of geotechnical materials. The DPUH model uses 11 material parameters, whose physical significance is clear. It has the following characteristics: (1) the state parameter χ is introduced to reflect the effect of initial density on deformation and shear strength under monotonic loading; (2) the stress state parameter R is used to reflect the influence of stress history on the current elastoplastic modulus and strength; (3) in order to reflect the influence of stress-induced anisotropy on the stress–strain relationship, the rotational hardening rules are introduced to establish the mixed hardening parameters that meet the critical state condition and take into account the isotropic compression and rotation-hardening characteristics; (4) the double-state parameters model can be used to describe the cyclic mobility phenomenon under cyclic loading conditions. By comparing the test data with prediction results of sand, it can be adopted to simulate the stress–strain relationship for sand with a different initial density and confining pressure under complex loading conditions. [ABSTRACT FROM AUTHOR]

There are two important conditions for the wide application of constitutive models for soil in contemporary engineering practice: a) the model should predict sufficiently well the soil behaviour at different stress paths; b) the material constants of the model can be determined from standard laboratory tests. Taking into account both conditions, a HASP model has been formulated to describe the mechanical behaviour of the overconsolidated clays, using the critical state theory and the boundary surface concept. The HASP model in a simple way overcomes many deficiencies of the Modified Cam Clay model, without introducing any additional material parameters. The formulation of the hardening rule in the function of the state parameter and overconsolidation ratio, allows the description of numerous elements of the mechanical behaviour of the overconsolidated clays. The HASP model has been implemented in software Abaqus using the Governing Parameter Method for the numerical integration of constitutive relations. The paper presents validation of the HASP model in comparison with the published results of triaxial tests as well as the possibilities of the model to adequately predict the behaviour of the overconsolidated clays through the analysis of the boundary value problem using the finite element method. The problem of the clay settlements due to phased construction of the embankment on the saturated clay surface was analyzed, assuming different overconsolidation ratios.

The state parameter (ψ) measures the distance from the current state to the critical state line (CSL) in the compression plane. The existence of a correlation between both the peak angle of shearing resistance (ϕp′) and peak dilatancy and ψ is central to many constitutive models used to predict granular soil behavior. These correlations do not explicitly consider particle crushing. Crushing-induced evolution of the particle size distribution influences the CSL position, and recent research supports the use of a critical state plane (CSP) to account for changes in grading. This contribution evaluates whether the CSP can be used to calculate ψ and thus enable the prediction of the peak angle of ϕp′ and peak dilatancy where crushing takes place. The data considered were generated from a validated DEM model of Fontainebleau sand that considers particle crushing. It is shown that where ψ is calculated by considering the CSL of the original uncrushed material, there can be a significant error in predicting the material response. However, where the CSP is used, there is a significant improvement in our ability to predict behavior irrespective of whether the CSP is accurately determined using a large number of tests or approximated using crushing yield envelopes. It is shown that the state parameter calculated using the previously available definition can give a false sense of security when assessing the liquefaction potential of potentially crushable soils. This contribution also highlights the stress-path dependency of the relationship between ϕp′ and ψ whichever approach is used to determine ψ. [ABSTRACT FROM AUTHOR]

Crushing of grains can greatly influence the strength, dilatancy, and stress-strain relationship of rockfill materials. The critical state line (CSL) in the void ratio versus mean effective stress plane was extended to the breakage critical state plane (BCSP). A state void-ratio-pressure index that incorporated the effect of grain crushing was proposed according to the BCSP. Rowe's stress-dilatancy equation was modified by adding the breakage void-ratio-pressure index, which was also incorporated into the formulations of the bounding stress ratio and plastic modulus. A BCSP-based bounding surface plasticity model was proposed to describe the state-dependent stress-strain behaviors and the evolution of grain crushing during shearing process of rockfill materials, and was shown to sufficiently capture the breakage phenomenon. Image 1 • A breakage critical state plane was established for rockfill materials. • Rowe's stress-dilatancy was modified by incorporating grain crushing. • Breakage-dependent plasticity model was proposed for rockfill materials. [ABSTRACT FROM AUTHOR]

There have been significant advances in the application of critical state, CS, in liquefaction potential assessment. This was done by comparing state parameter, ψ with estimated characteristic cyclic stress ratio, CSR due to an earthquake. A cyclic resistance ratio, CRR curve, which can be determined from cyclic liquefaction tests, separates historical liquefied and non-liquefied data points (ψ , CSR). On the other hand, the concepts of equivalent granular state parameter, ψ *, which was developed for sands with fines, can be used in lieu ψ to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines, irrespective of fines content (f c). The present work combines these two propositions, and by merely substituting ψ * for ψ into the aforementioned CS approach to capture the influence of f c. A series of static and cyclic triaxial tests were conducted, separately and independently of the concept of ψ *, for sand with up to f c of 30%. The clean sand was collected from Sabarmati river belt at Ahmedabad city in India which was severely affected during the Bhuj earthquake, 2001. The experimental data gave a single relation for CRR and ψ * which was then used to assess liquefaction potential for a SPT based case study, where f c varies along the depth. The prediction matched with the field observation. Image 1 • A cyclic resistance ratio, CRR curve, which can be determined from cyclic liquefaction tests, separates historical liquefied and non-liquefied data points (ψ , CSR). • The concepts of equivalent granular state parameter, ψ *, which was developed for sands with fines, can be used in lieu ψ to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines, irrespective of fines content f c. • The present work combines these two propositions, and by merely substituting ψ * for ψ into the aforementioned CS approach to capture the influence of f c. • CRR and ψ * was used to assess liquefaction potential for a SPT based case study, where f c varies along the depth. [ABSTRACT FROM AUTHOR]

Featured Application: In this paper, the influence of two model parameters a and b of critical state line on sand dilatancy behaviour are discussed. However, the emphasis is still put on liquefaction behaviour of clean loose sand. Moreover, a large number of real field studies have indicated that the presence of silt is very common at the liquefied sites during earthquakes. Therefore, this study could also be extended to investigate the potential influence of fine fraction of silty sand mixture on the critical state line and its instability behaviour. In sand constitutive models, it is of cardinal importance to consider a state parameter to distinguish the real dilatancy for cohesionless soils (sand), which is different from cohesive soils (clay). Thus, one of the key issues in simulating the sand behaviour is the better representation and parameter calibration of critical state line (CSL) for estimating contraction in loose state and dilatancy in dense state, respectively. For this purpose, a new exponential form for CSL with two model constants a and b has been presented in the literature. This paper provides a valuable insight into the two model constants, controlling the shape of the critical state line by simulating a uniform quartz reference sand (Hostun RF) in loose and dense states under undrained triaxial conditions. It can be concluded that the liquefaction behaviour in loose state is fundamentally affected by even a minor variation in model constant a , but insensitive to model constant b. Moreover, the linear fitting calibration of CSL recommended in the literature is complicated in consideration of the non-unified critical state line. Thus, the maximum void ratio in the natural state could be considered as a comparison basis on which to evaluate the liquefaction potential as an alternative. The numerical results showed good agreement with real experimental data. However, in dense state, the dilatant behaviour of sand was found to be mainly controlled by model parameter b. In addition, the influence of a non-unified critical state under various confining pressures on the determination of b should not be neglected. With the correction of b , the numerical results were found to be consistent with the experimental data concerning Hostun RF sand. [ABSTRACT FROM AUTHOR]

Unsaturated soil-continuum interfaces determine the behavior of structures such as friction piles embedded in unsaturated soil and retaining walls with unsaturated backfill. Developing accurate constitutive models for these interfaces is essential for innovative computational design and analysis in geotechnical engineering. This study presents a rigorous mathematical derivation to quantify the bonding effect at interparticle and pore space contact zones, introducing a bonding variable and a state parameter based on the ratio between current and critical void ratios. The novelty lies in introduction of a hydraulic-mechanical (HM) coupling constitutive model for unsaturated soil-continuum interfaces, incorporating the bonding effect and critical-state concept. Despite the 16 parameters in proposed model, all are methodically calibrated using suction-controlled interface shear tests. Effectiveness of the model is demonstrated through predictions in interface shear tests involving unsaturated Toyoura sand, smooth/rough steel, and published tests with unsaturated Minco silt and steel. The model's applicability is extended to diverse conditions, including structural stiffness, interface thickness, counterface roughness, and drying- wetting (D-W) cycles. This model provides a unified framework for analyzing volume changes and stress-displacement responses in unsaturated soil-continuum interfaces, providing valuable insights for design of pile foundations in unsaturated soils. [ABSTRACT FROM AUTHOR]