Soil Constitutive Model Research Articles

Elastic-Viscoplastic Constitutive Model of Soil under Cyclic Loading

The creep problems are often involved in soil under cyclic loading, and its behaviors of soil under cyclic loading sparks many arguments in current research field. To propose one new model to demonstrate these creep behaviors of soil under cyclic loading, the cyclic loading was simplified equivalently, and the elastic-viscoplastic model (EVPM) for soil under cyclic loading was established based on the Bingham model. The yield criterion for soil under cyclic loading with constant amplitude was proposed following the simplified load. A constitutive equation based on the EVPM was constructed by using the flow criterion related to the yield criterion. Meanwhile, the parameters of EVPM were identified and discussed. In addition, the case analysis of the EVPM was also performed. The results indicate that the stable and destructive creep behaviors of soil under cyclic loading could be well described by the recommended EVPM, and the obtained parameters in the model exhibited a clear regularity with the increase of dynamic stress amplitude. Besides, the established model could be selected to predict the stable and destructive creep behavior of soil under cyclic loading.

A comparative study of the effect of the soil constitutive model on the seismic response of buried concrete pipes

No attention has been given in previous studies to understand the influence of the sophistication of the soil constitutive model on the response of buried concrete pipes subjected to transverse seismic effect. This research, therefore, has been conducted to address this gap in knowledge by analyzing the behavior of a buried concrete pipe subjected to transverse seismic shake employing the linear elastic (LE) model, elasto-plastic Mohr-Coulomb (MC) model, hardening soil (Hs) model, and hardening soil model with small strain stiffness (Hs small) to provide a benchmark study that helps the designers and the researchers to select the most suitable and less computationally demanding soil constitutive model. The cases of good and poor installation conditions have been considered in the analyses. In addition, numerous earthquake records have been used to allow the consideration of wide range of earthquake intensities to aid general conclusions. It was found that all of the considered constitutive models produce the same trend of the circumferential bending moment (BM) that is developed around the pipe. In general, the maximum BM produced using the LE and MC models is significantly lower than that produced using the Hs and Hs small models with one exception for the LE model for a predominant frequency of 0.66 Hz. Furthermore, the maximum BM produced using the LE and MC models is not sensitive to the increase of the peak ground acceleration (PGA). More importantly, the Hs and Hs small models produce almost similar results with a percentage difference ranges between 1% to 9%. In addition, the Hs and Hs small models show a decrease of the maximum BM as the predominant frequency rises and an increase of the maximum BM as the PGA rises.

The influence of face and shield annulus pressure on tunnel liner load development

Three dimensional (3D) finite-difference analysis simulations together with rare field data from strain gauges installed in segmental lining rings at the Seattle Sound Transit Northgate Link tunnel project are examined to provide a better understanding of segmental liner loading developed during earth pressure balance shield tunneling. A simplified 3D numerical model is presented for pressure balanced mechanized tunneling, where the annulus between the shield and excavated ground is full of pressurized material, simplifying the shield shape, and the modeling of the annular gap. This simplified model is based on the assumption that the shield annulus pressure controls the tunnel convergence prior to lining installation. While the presented model simplifies the modeling of the TBM shield, it captures the important components in shield tunneling, including the jointed segmental lining, grout injection pressure, time-dependent grout hardening, and the non-liner soil behavior using the hardening soil constitutive model. The results of this study show that the final lining loads are controlled by the chamber pressure for pressure balance TBMs with pressurized material in the shield annulus. In the case study presented here, pressure drops of the chamber pressure (common in EPB tunneling due to excavation standstill), result in a significant influence on tunnel lining loads.

Seismic Interaction of Adjacent Structures on Liquefiable Soils: Insight from Centrifuge and Numerical Modeling

In urban environments, structures are often built in close proximity to each other. Seismic coupling and structure-soil-structure interaction (SSSI) are known to affect system accelerations, settlement, and tilt with consequential impact on structural damage. Yet, the extent and nature of these interactions are poorly understood, particularly on ground susceptible to liquefaction. In this paper, we use dynamic centrifuge and numerical modeling of isolated and neighboring, similar and dissimilar, shallow-founded structures on layered, level, saturated, and liquefiable soils to provide insight into (1) the mechanisms of SSSI; and (2) the relative influence of key parameters on system performance. Fully-coupled, nonlinear finite-element analyses of the centrifuge experiments indicated that in addition to a comprehensive calibration of the soil constitutive model parameters, use of higher-order elements and a sufficiently large domain size in three dimensions (3D) were critical ingredients to predicting the general trends in system response compared to centrifuge recordings. A limited numerical sensitivity analysis was performed subsequently. The results identified the key parameters affecting SSSI as spacing between the two foundations (S) in relation to their width (W) as well as the contact stress and geometry of the neighboring foundation-structure system. SSSI slightly decreased the permanent settlement of structures at the expense of a notable increase in their permanent tilt, particularly when S≤W. The foundation’s spectral accelerations were observed to amplify at shorter periods when near a taller and heavier building at S≤W/3, which was attributed to the added confinement. Increasing the uniform thickness of the critical liquefiable layer increased both adjacent structures’ permanent settlement, while not affecting their residual tilt or SSSI. Importantly, the impact of SSSI on foundation tilt and accelerations remained significant for building spacings exceeding 2.5W. The results point to the importance of considering the impact of SSSI on structure’s key engineering demand parameters and the urgent need for improved guidelines when assessing and treating liquefaction in urban settings.

Numerical modelling of interaction between aluminium structure and explosion in soil

In this paper, a graphics processing unit-accelerated smoothed particle hydrodynamics solver is presented to simulate the three-dimensional explosions in soils and their damage to aluminium structures. To achieve this objective, a number of equations of state and constitutive models required to close the governing equations are incorporated into the proposed smoothed particle hydrodynamics framework, including the Jones-Wilkins-Lee equation of state for explosive materials, the Grüneisen equation of state for metals, the elastic-perfectly plastic constitutive model for metals, and the elastoplastic and elasto-viscoplastic constitutive models for soils. The proposed smoothed particle hydrodynamics methodology was implemented using the Compute Unified Device Architecture programming interface on an NVIDIA graphics processing unit in order to improve the computational efficiency. The various components of the proposed methodology were validated using four test cases, namely, a C4 detonation and an aluminium bar expanded by denotation to validate the modelling of explosion, a cylindrical Taylor bar impact test case to validate the modelling of large deformation in metals, a sand collapse test for the modelling of soils. Following the validation, the proposed method was used to simulate the detonation of an explosive material (C4) in soil and the concomitant deformation of an aluminium plate resulting from this explosion. The predicted results of this simulation are shown to be in good conformance with available experimental data. Finally, it is shown that the proposed graphics processing unit-accelerated SPH solver is able to model interaction problems involving millions of particles in a reasonable time.

Numerical simulation of suction bucket foundation response located in liquefiable sand under earthquakes

The suction bucket foundation is considered as an effective option for offshore wind turbines because of its advantages in rapid installation and recyclability. However, the depth of the suction bucket inserted into the seabed is shallower compared to the monopile. Earthquakes and liquefaction threaten the safety and stability of suction bucket foundations in the North Sea of Europe and the Chinese offshore where earthquakes are active and the seabed is prone to liquefaction. This paper investigated the behavior of the suction bucket foundation located in the liquefiable sand under earthquakes using an advanced liquefaction model. The FE-FD method with the cyclic mobility constitutive model for soil was used to carry out the nonlinear dynamic analyses. Responses of the excess pore water pressure ratio, acceleration, displacement, and rotation were studied under different earthquake magnitudes and sand density. The distribution of excess pore water pressure of the suction bucket foundation from the results show strong space-time characteristics. The failure mechanism of the suction bucket foundation after liquefaction was revealed. The numerical results indicate that offshore wind turbines will be subjected to permanent displacements and tilt to reach 40% of the safety threshold due to earthquakes and liquefaction. Thus, seismic load and liquefaction of the foundation must be considered in the design.

Investigation of three sophisticated constitutive soil models: From numerical formulations to element tests and the analysis of vibratory pile driving tests

The performance of three advanced constitutive models has been evaluated based on element tests and on a comparative study on the simulation of vibratory pile driving tests in saturated sand. The inspected constitutive models are the Sanisand model and Hypoplasticity with Intergranular Strain (Hypo+IGS) as well as with Intergranular Strain Anisotropy (Hypo+ISA) extension. The performance of the constitutive models is first evaluated by the simulation of element tests used for the parameter calibration of the sand used in the model tests. The constitutive models are then applied for the simulation of a vibratory pile driving test. The pile penetration, the driving force, the pore water pressure development and the incremental displacement in the vicinity of the pile tip are compared to the measurements in the model tests. The strengths and weaknesses of the different constitutive models are assessed. Generally, the model predictions showed good agreement with the experimental results. Despite different constitutive formulations (hypoplastic vs. elasto-plastic), all three models were able to reproduce the main mechanisms of the driving process properly. It may be concluded that all three models allow a proper prediction of vibratory pile driving as long as a proper calibration of the material parameters is secured.

Physical and Mechanical Properties of Turfy Soils under Confining and Axial Pressure Increases Stress Paths in Jilin Province, Northeast China

In recent years, highways have been built rapidly in China’s turfy swamp areas to accommodate economic development. Turfy soil is a type of special soil with high humus and incompletely decomposed plant contents, so its properties are complex and unique. Both the axial and confining pressures of turfy soil increase during embankment filling. Therefore, in this study, three soil tests for analysing the decomposition degree, organic matter content, and triaxial compression under confining and axial pressure increases stress paths were performed to achieve insights into the stress-strain properties of turfy soil. The volumetric and deviatoric strains of turfy soil were summarised to reveal the inner mechanisms of turfy soil, culminating in the establishment of a constitutive model for turfy soil. The results of the constitutive model were compared with the experimental test results to verify the accuracy of the constitutive model. The results showed that the stress-strain and strength of turfy soil are closely related to the organic matter content and decomposition degree. The calculated stress and strain results are also consistent with the experimental results, indicating that this constitutive model can be used to better indicate the original deformation state and strength characteristics of the turfy soil.

Simplified kinematic hardening plasticity framework for constitutive modelling of soils

A simplified kinematic hardening plasticity framework for the constitutive modelling of soils is presented. In contrast to conventional kinematic hardening plasticity, the yield surfaces do not enter explicitly into the governing equations but are used only for the purpose of computing an effective hardening modulus. This leads to models reminiscent of conventional nonlinear elastic/perfectly plastic models, thus facilitating an efficient numerical implementation. The framework is detailed both with respect to total and effective stress analysis. Its capabilities are illustrated by the development of a simple model for undrained total stress analysis of clays.

Optimum Open Cell Sheet Pile (OCSP) Quay Wall System in Port Said, Egypt

The principal intent of this paper was to propose a new quay wall system, whose validity was verified; to play the same role of the existing diaphragm quay wall at East Port Said Port in Egypt as an optimum quay wall. Firstly, the background information of the proposed Open Cell Sheet Pile (OCSP) was introduced. Then, a parametric study was conducted including 24 cases using soil constitutive Hardening Soil Model (HSM) by the PLAXIS 3D Finite Element Software. The behavior of the proposed system was presented graphically, and the effectiveness of the OCSP system was found satisfactory with the possibility to increase the seabed depth in front of the wall up to four meters. The system also was consisted of a bored piles group to carry the heavy loads generated by the gantry crane. Finally, the construction cost of the OCSP was compared to the existing quay wall structure system for evaluating the system design optimization.

Numerical Implementation of a Hydro-Mechanical Coupling Constitutive Model for Unsaturated Soil Considering the Effect of Micro-Pore Structure

An unsaturated soil constitutive model considering the influence of microscopic pore structure can more accurately describe the hydraulic–mechanical behavior of unsaturated soil, but its numerical implementation is more complicated. Based on the fully implicit Euler backward integration algorithm, the ABAQUS software is used to develop the established hydro-mechanical coupling constitutive model for unsaturated soil, considering the influence of micro-pore structure, and a new User-defined Material Mechanical Behavior (UMAT) subroutine is established to realize the numerical application of the proposed model. The developed numerical program is used to simulate the drying/wetting cycle process of the standard triaxial specimen. The simulation results are basically consistent with those calculated by the Fortran program, which verifies the rationality of the developed numerical program.

Dynamic site response analysis in the face of uncertainty–an approach based on response surface method

AbstractAlthough advanced modeling techniques such as the finite element method (FEM) have been used successfully in dynamic site response analysis, the high computational expense has hindered the incorporation of input parameter uncertainty in such analysis. Thus, when the variation of the peak ground acceleration (PGA) at the ground surface, which is the outcome of the site response analysis, has to be evaluated in the face of uncertainty, a surrogate model such as Response Surface Method (RSM) model is often used in lieu of the FEM model. In this paper, the RSM surrogate model was implemented in the context of seismic site response analysis to evaluate the variation (or uncertainty) of the PGA due to the propagation of input parameter uncertainty. The engineering implication of the variation of the surface PGA is significant as this knowledge is required for such tasks as reliability analysis of soil liquefaction and probabilistic seismic risk analysis. To derive the RSM model specifically for a site response analysis, a parametric study of the dynamic site responses using FEM code ABAQUS with the modified Davidenkov soil constitutive model implemented as a user‐defined material subroutine is first conducted. The input parameters, including the soil profile, soil properties, and input ground motion, in a typical dynamic site response analysis are then characterized and screened for their suitability to be included in the RSM model. For a given site response problem in the face of uncertainty, representative “samples” are taken for site response analysis using ABAQUS, and the analyses are carried out and finally the response surface is constructed using the outcomes of the ABAQUS numerical experimentations. The accuracy of the developed RSM model is then validated using the results of ABAQUS on cases not used in the development of the RSM model. Once the RSM model is deemed satisfactory, the reliability‐based formulation for evaluating the mean and standard deviation of the surface PGA is established. Example is provided to illustrate the RSM approach for dynamic site response analysis in the face of input parameter uncertainty.

Load-settlement response of piled raft foundations in sand

ABSTRACT The load-settlement behaviour of piled raft foundations (PRFs) resting on sand subjected to vertical uniformly distributed load is studied using three-dimensional elasto-plastic finite element (FE) analyses. The unified Clay and Sand Model (CASM), based on the critical state soil mechanics, is used as the soil constitutive model. In the present study, 38 rectangular, strip, and circular raft connected to different pile configurations resting on four different types of sands in their loose, medium, and dense states are considered. The accuracy of the finite element analysis is confirmed through verification and validation with other numerical and experimental studies. A detailed parametric study is conducted, which includes soil elastic and critical state parameters as well as different dimensions of PRFs. A guideline chart is provided, which will be helpful for a design practitioner to choose the suitable PRF configurations considering serviceability limit states of safety and economical design aspect. This flow chart is based on (i) combined effects of various parameters on PRF load settlement behaviour, (ii) load sharing between the raft and the pile groups, and (iii) a preliminary cost analysis.

Finite element implementation of an isotach elastoplastic constitutive model for soft soils

An isotach elastoplastic constitutive model devised by Yang et al. (2016) and referred to as the Hunter Clay (HC) model attempts to capture a number of key behaviours of soft soils within a critical state framework, namely destructuration, fabric anisotropy and rate dependency, the latter often manifesting in creep settlement. Finite element implementation of the HC model is a useful means by which its application to practical problems can be facilitated. However, there are a number of significant challenges associated with the translation of isotach elastoplastic models into a finite element setting. In this paper, a detailed discussion of these challenges is undertaken and a new finite element implementation of the HC model is subsequently developed. This includes sophisticated numerical integration algorithms which employ automatic time substepping for solution of the governing finite element equations. The ability of the implemented HC model to predict the mechanical behaviour of soft soils under 1D compression is investigated via simulation of laboratory tests carried out on Ballina clay by Pineda et al. (2016) and Parkinson (2018).

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

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

Application of a Simplified Anisotropic Constitutive Model for Soft Structured Clay on Embankment Failure

The design and maintenance of embankments is still a challenge in practical geotechnical engineering because of some features of soft sensitive soil behavior that are not considered in conventional methods. These features originate from the soil structure, including soil anisotropy, interparticle bonding, and decay as a result of the loading and deformation process. In recent years, many efforts have been made to incorporate the aforementioned features in various soil constitutive models. However, their application in practical geotechnical engineering is limited, owing to the complexity of the models, a number of parameters, and difficulties in the implementation in a computer code. The aim of this study is to modify a simple anisotropic constitutive model (SANICLAY) in order to take into account destructuration, named SANICLAY-D, and its implementation in computer code with a simple and robust algorithm. The capability of the proposed soil model in simulating the effects of the aforementioned soil features on the behavior of the well-known Test Embankment A constructed at Saint-Alban, Quebec, Canada, is explored. This model predicts, with sufficient accuracy, the effect of anisotropy on embankment failure behavior, especially the height and the failure surface, despite its simplicity.

Laboratory Assessment of the Mechanical Properties of an Unsaturated Mid-Atlantic Silty Sand

Natural soil formation processes involve variable particle size distributions that vary spatially within a deposit, giving rise to an array of soils that transition from one general soil type to another within essentially similar deposits. Characterization of such transition soils in the active zone is something past research has largely overlooked. An evaluation of the unsaturated strength behavior of a transition soil was carried out on a native mid-Atlantic silty sand. A suite of unsaturated consolidated drained axisymmetric triaxial shear tests was performed, and the stress–strain and volume change characteristics of the transition silty sand under different values of matric suction, confining pressure, strain rate, and fines content were investigated. It is found that the triaxial shear strength increases with increasing matric suction, confining pressure, strain rate, and fines content. The volumetric strain increases with increase in matric suction and confining pressure, and it decreases as fines content and strain rate are increased. The experimental results are used to further validate a state-dependent constitutive model for unsaturated soils that was recently proposed based on the theory of bounding surface plasticity and the framework of hyperelasticity. It is shown that the model simulations are in good agreement with the experimental data.

Geocell Reinforced Slope Behavior under Seismic Loading Using Calibrated Hypoplastic Soil Constitutive Model

This study evaluates geocell reinforced slope behavior under seismic loading using calibrated hypoplastic soil constitutive model. The constitutive soil model used in this simulation was calibrated for poorly graded dense sand by conducting a series of triaxial and odometer tests. A three dimensional analysis is carried out to simulate geocells and this soil model using the finite element software PLAXIS3D. To investigate the geocell seismic behavior, the lateral displacement, induced tensile force in geocell, slope stability and frequency content effect have been assessed. Furthermore, a comparison has been made among hypoplastic, Hardening soil with small strain and Mohr-Coulomb model. The obtained results indicated that the volumetric plastic strain and intergranular strain consideration by hypoplastic model had a significant effect on the lateral displacement of the reinforced and unreinforced slope. Using the geocell layers leaded to decrease the plastic points. This behavior caused to decrease the estimated results difference when performing three constitutive models as soil failure criterion. Also, the tensile force showed hypoplastic model was not sensitive to the earthquake reversible force. In addition, it was found that the geocells lost their effect when the PGA increased and the slope was apt to fail.

Construction strategies for a NATM tunnel in São Paulo, Brazil, in residual soil

Due to the fast growth of urban areas worldwide, the demand for tunnels in developed areas is increasing. The design and construction of those tunnels are complex because of their shallow depths and their interaction with existing aboveground and buried structures, which results in rather limited allowable ground deformations induced by the tunnel excavation and support. In tropical regions, residual porous soils near the surface are common. Those soils are highly deformable; thus, tunneling may induce large ground deformations that may damage nearby structures. The new Austrian tunneling method (NATM) and the sprayed concrete lining (SCL) technique are being widely employed in several big cities in tropical regions, but little research has been conducted to assess the induced ground deformations in residual soils, common in tropical areas. This paper provides insight into this issue. A well-documented metro tunnel in São Paulo, Brazil, in a residual red porous clay, was analyzed using 3D finite element method (FEM). The behavior of the residual red porous clay was approximated by an advanced constitutive soil model calibrated with triaxial tests on intact samples extracted at the site. Predictions of the tunnel deformations during construction matched the field data. The calibrated model was then used to explore the tunnel performance under different construction strategies. The influence of partial face excavation, unsupported span length, support stiffness and pipe roof umbrella were assessed. The numerical results showed that partial face excavation was effective to reduce ground deformations ahead of the face of the tunnel and to improve face stability; however, the settlements behind the face increased because of the delay in closing the primary lining. The installation of a stiffer liner closer to the face reduced the ground deformations significantly. The pipe roof umbrella was the most effective technique to reduce the ground deformations around the tunnel; however, the numerical results did not consider deformations that could be induced by the drilling and grouting operations. The results shown in this paper provide both qualitative and quantitative information about the ground deformations induced by NATM tunneling in residual porous soils, that could help designers and contractors choose the optimum support and construction methods to minimize ground deformations.

Bayesian inference of spatially varying parameters in soil constitutive models by using deformation observation data

AbstractParameters of soil constitutive models are usually identified through laboratory tests. The spatial variability of these parameters is generally not considered due to the limitation of the test scale. This study proposes a data‐driven approach to infer the spatially varying parameter of the modified Cam‐clay model from limited field observations and subsequently improves soil settlement predictions. The observation data and numerical results of random finite element method are assimilated in an inverse modeling process based on the iterative Ensemble Kalman filtering (iEnKF). Different unknown variables and number of observations are used to study their effects on parameter estimations and settlement predictions. The effectiveness of the proposed approach is illustrated through a synthetic partial‐loading test. The results show that the site‐specific spatial variability can be estimated reasonably, and predictions of settlement can be improved by using the inferred parameter field. When the variables to be inferred change from all 60 variables to the selected 17 important variables, the average error of the estimated fields increases, but the variance decreases. A reduction in the observation spacing and an increase in the number of observations lead to a slightly smaller error of the mean and considerably reduced uncertainties of soil parameters. Although the inferred results of parameter field show different accuracies, the corresponding calculated settlements are generally similar and satisfactory.