Advanced Constitutive Models Research Articles

Numerical investigation of pull-out capacity and failure mechanism of suction anchors with mooring line in sand

Suction anchor is a widely used anchorage foundation in taut or catenary mooring systems to fix floating structures. This paper aims to investigate the pull-out capacity and failure mechanism of suction anchors in sand using the finite element method which models the attached mooring line on the anchor padeye. The advanced critical state elastoplastic constitutive model SIMSAND is utilized which can well simulate the state-dependent peak strength and stress-dilatancy behavior of sand, and its accuracy and effectiveness are validated with centrifuge test results. A series of systematical parametric studies are then carried out to explore the effects of the mooring line, aspect ratio, padeye position and loading angle on the pull-out capacity and failure mechanism of the suction anchor. Based on the numerical results and those obtained in other researchers’ work, the optimal padeye position and the normalized V–H envelopes are explicitly discussed. Finally, a calculation framework is put forward for predicting the inclined pull-out capacity of suction anchor in sand considering the mooring line effect.

On the influence of cyclic preloadings on the liquefaction resistance of sands: A numerical study

Soil deposits may be subjected to preloading episodes due to different factors such as previous earthquakes, excavations, refilling, compaction, construction of overlying structures, storms under onshore/offshore conditions, among many others. It is well-known that preloading episodes remarkably influence the subsequent soil mechanical behavior and liquefaction resistance. In order to accurately describe the influence of cyclic preloadings, advanced constitutive models which are able to realistically reproduce the soil mechanical behavior are necessary. In this work, a numerical study was carried out to investigate the influence of cyclic preloadings on the liquefaction resistance of sands. The numerical analyses were performed considering three advanced and well established constitutive models, namely: the hypoplastic model for sands by Von Wolffersdorf (1996) with the Intergranular Strain extension by Niemunis and Herle (1997), the same hypoplastic model for sands extended with Intergranular Strain Anisotropy by Fuentes et al. (2020), and the bounding surface plasticity model Sanisand by Dafalias and Manzari (2004). The simulations were performed based on the experimental databases on Zbraslav sand by Duque et al. (2023a,b). Remarks about the model capabilities and limitations on tests with different types of cyclic preloadings and their repercussion on boundary value simulations are given at the end.

Evaluation of the optimal ground motion intensity measure in the prediction of the seismic vulnerability of earth dams

The large majority of existing earth dams were designed with old standards, which often accounted for the effects of earthquakes in a simplified manner. As a result, seismic re-evaluation of these structures is now becoming increasingly important for dam owners. The seismic performance of earth dams can be evaluated at different levels of resolution, typically ranging from simple sliding block analysis, to the use of advanced numerical models. Seismic inputs for these models are typically chosen using code-based or site-specific probabilistic seismic hazard analysis (PSHA). In this study, we analyze the seismic vulnerability of two major earth dams located in Southern Italy, a seismically active area. The two dam systems have different geotechnical characteristics: one of them is founded on potentially liquefiable materials, whereas the other one is not susceptible to liquefaction. Our analyses are based on finite difference numerical simulations using both simplified and advanced constitutive models. Seismic vulnerability of both dams is analyzed by means of analytical fragility functions for various damage mechanisms and ground motion intensity measures (IMs). Such fragility functions are based on nonlinear deformation analyses within the multiple stripe analysis framework. We analyze efficiency and predictability of various IMs in predicting different damage levels and mechanisms. We show that the cumulative absolute velocity is overall the optimal IM in predicting vulnerability of both earth dams. We also analyze the relative importance of PSHA inputs (i.e. alternative ground motion and earthquake rupture forecast models; GMMs and ERFMs, respectively) and numerical models (simplified vs advanced) in the seismic analysis of earth dams by means of tornado diagrams. We show that the choice of GMMs and ERFMs is always more important than that of the constitutive model. However, for dams prone to liquefaction, the choice of the constitutive model has a higher importance than for non-liquefiable earth dams.

Numerical investigation on the pull-out capacity of suction anchors in sand considering torsional and mooring line effects

Torsional pullout of suction anchors may occur during installation due to improper positioning or deviations caused by current forces, but less attention has been paid to the effect of torsion on the pull-out capacity of suction anchor in existing literatures. This paper therefore numerically investigates the pull-out capacity and failure mechanism of suction anchors in sand considering both torsional and mooring line effects using the advanced SIMSAND constitutive model. It is found that considering torsional influence causes a significant reduction in the pull-out capacity of suction anchor in sand under horizontal and inclined loading. The case with the optimal padeye depth of 0.7L produces the largest pull-out capacity and the greatest reduction in the pull-out capacity due to torsion. The dimensionless pull-out capacity for the case without mooring line is approximately 24% higher than or almost twice that of the case with mooring line in scenarios without or with torsional condition. Based on the findings, a new framework for estimation of the pull-out capacity of the suction anchor at the optimal padeye depth in sand considering torsional and mooring line effects is finally proposed which may benefit the design of suction anchor in scenarios with torsion in the real practice.

Centrifuge and numerical modeling of the behavior of homogeneous embankment on liquefiable soil subjected to dynamic excitation

Centrifuge and numerical modeling are developed to investigate the behavior of a homogeneous embankment constructed on a liquefiable sand ground, which was prepared with wet under-compaction method. The physical centrifuge modeling directly highlights the response of the centrifuge model in terms of excess pore pressure, acceleration response, settlement, and the deformation pattern of the embankment model. In parallel, a numerical simulation using FEM is conducted. The advanced constitutive model, PM4Sand, is adopted to simulate the liquefaction of the sand ground. The performance of the numerical model is then verified against the results of the centrifuge test. Overall, the numerical simulation aligns well with the centrifuge test. Finally, the verified numerical model is refined to include two improved boundaries, and the potential boundary effects in centrifuge and numerical models are discussed.

Behaviour of anchored sheet pile quay stabilized with deep cement mixing columns in soft soil: Centrifuge and numerical modelling

This paper describes research on the behavior of anchored sheet pile quay stabilized by deep cement mixing (DCM) columns in soft soil through a centrifugal test investigation to understand excavation-induced soil-structure interaction mechanisms. By employing an advanced soil constitutive model, three-dimensional (3-D) finite element (FE) simulations were subsequently performed to back-analyze the centrifuge test. Moreover, a numerical comparison analysis between this case and a null DCM columns case was performed to describe the shielding effect of the DCM columns composite foundation in the anchored sheet pile quay in terms of lateral earth pressure, bending moment, lateral deflection of the quay wall, and quay ground settlement induced by excavation. Finally, a parametric study was carried out to investigate the effect of DCM column arrangement and geometry on the quay wall lateral deflection. Results showed that the presence of DCM columns reduced the adverse effects on the quay wall in excavations, and they could effectively enhance the stability of the anchored sheet pile quay in soft soil, such as the shielding effect. In addition, the parametric study results indicate that length and the elastic modulus of the column are two critical factors affecting the shielding effect of DCM columns. This research provides reasonable explanations and valuable insights to understand the soil-structure interaction mechanism in anchored sheet pile quay and is of use in the preliminary design of sheet pile quay structures in soft soil.

Implementation of an Advanced Constitutive Models for Fine-Grained Soils

Implementation of an Advanced Constitutive Models for Fine-Grained Soils

Seismic responses of suction bucket foundation in liquefiable seabed considering spatial variability

The abundant wind energy happens to be distributed along the seismic regions with potential liquefaction. Offshore wind turbines have to be built in these regions for high power generation efficiency. The earthquake-induced liquefaction affected by the natural variability of the seabed makes the safety assessment of suction bucket foundations a challenge. The seismic responses of the laterally-loaded suction bucket foundation in spatially variable soil modeled by an advanced constitutive model were investigated using an FE- FD method. The SPT-(N1)60cs was considered a random variable and the seabed was modeled as a non-Gaussian random field by the Cholesky decomposition technique. The seismic responses were described by the Monte Carlo simulation and the FE-FD method. Statistics of the tilt and the liquefaction potential index influenced by the coefficient of variation and the scale of fluctuation were investigated. The stochastic model was compared with the deterministic model. The liquefaction mechanism and failure mechanism of the suction bucket foundation in random soil were investigated. The tilts and liquefaction may be underestimated without considering the soil spatial variability. Safety factors were introduced into the calculation of the failure probability of the suction bucket foundations. The simulations provide insight into the nonlinear behavior of suction bucket foundations considering the liquefaction of spatially variable soil.

Modelling the density homogenisation of a block and granular bentonite buffer upon non‐isothermal saturation

AbstractThis paper presents a numerical analysis of the mechanical performance of a bentonite clay buffer for the containment of nuclear waste in the context of deep geological disposal. The design of the buffer is based on the Swiss concept where the waste canisters are emplaced on pedestals of compacted bentonite blocks and the remaining space between the tunnel and the canister is backfilled with grains of highly compacted bentonite. A complete analysis of the long‐term performance of the repository requires a good understanding of the mechanical evolution of the bentonite upon heating from the radioactive waste and hydration from the host rock. Despite its importance, the implications of the initial heterogeneous bentonite layout, characterised by blocks and grains, on the final dry density at the repository scale in the steady state have not been previously studied. The present study aims to shed light into these processes by means of finite element modelling using an advanced constitutive model for the bentonite behaviour that considers several thermo‐hydro‐mechanical couplings. The constitutive model is shown to be able to reproduce several laboratory tests involving saturation of block and pellets at different dry densities. The model predictions, extended up to 100,000 years, indicate that the bentonite blocks and grains tend to homogenise in terms of dry density as the buffer reaches full saturation. Due to the different swelling potential of the block pedestal and the granular backfill, the canister is subjected to movements, although these remain relatively small. The impact of initial segregation of the granular bentonite is also studied and it is seen to not to affect substantially the mechanical evolution of the buffer, although it might reduce canister displacements.

A physics-informed deep neural network for surrogate modeling in classical elasto-plasticity

In this work, we present a deep neural network architecture that can efficiently surrogate classical elasto-plastic constitutive relations. The network is enriched with crucial physics aspects of classical elasto-plasticity, including additive decomposition of strains into elastic and plastic parts, and nonlinear incremental elasticity. This leads to a Physics-Informed Neural Network (PINN) surrogate model named here as Elasto-Plastic Neural Network (EPNN). Detailed analyses show that embedding these physics into the architecture of the neural network facilitates a more efficient training of the network with less training data, while also enhancing the extrapolation capability for loading regimes outside the training data. The architecture of EPNN is model and material-independent; it can be adapted to a wide range of elasto-plastic material types, including geomaterials; and experimental data can potentially be directly used in training the network. To demonstrate the robustness of the proposed architecture, we adapt its general framework to the elasto-plastic behavior of sands. We use synthetic data generated from material point simulations based on a relatively advanced dilatancy-based constitutive model for granular materials to train the neural network. The superiority of EPNN over regular neural network architectures is demonstrated through predicting unseen strain-controlled loading paths for sands with different initial densities.

3D numerical modeling of a rigid inclusion reinforced railway embankment under cyclic loading

Rigid inclusion reinforcements of embankments are increasingly used in traffic route engineering to ensure the long-term system sustainability and to enhance the soft subsoils load-bearing capacity under static and cyclic loading conditions in an economical and practical way. This paper presents a three-dimensional numerical finite difference model to assess the performance of a rigid inclusion reinforced railway embankment subjected to cyclic loading. A slice model of the railway embankment is considered based on full-scale physical tests. The advanced elasto-plastic SANISAND constitutive model is considered for the granular layer in the rigid inclusion reinforced railway embankment. The responses of the system under cyclic loading are outlined concerning settlements, stress distribution and axial–flexural response of the rigid inclusions.

Investigation on behavior of anchored sheet pile quay wall improved by cement-soil: Centrifuge and numerical modelling

By using the centrifuge test and three-dimensional (3-D) finite element (FE) simulation with an advanced soil constitutive model, this study investigated the suitability and reinforcement effect of cement deep mixing (CDM) for stabilizing the anchored sheet pile quay (ASPQ) in soft clay. Besides, a parametric study was designed to analyse the influence of three factors, including the excavation depth ratio, the slenderness ratio and the strength of the CDM block, on the responses of quay wall and quay-surface settlement. The results showed that the effectiveness of CDM was closely related to its strength, slenderness ratio, and excavation depth ratio. There existed a critical slenderness ratio of the CDM block to minimize the lateral deflection of the quay wall. The influence of CDM block strength on the response of the quay wall was significant only when it had low rigidity. As a result of material improvement, the reduction in maximum wall displacement became more significant as the excavation depth ratio increased. A CDM block-to-excavation-strength shape factor was proposed to characterise the lateral response of quay walls in cement-improved soil.

New perspectives on preshearing history in granular soils

The design of deep dump slopes for opencast mines usually requires information about the soil resistance to liquefaction during earthquakes. This resistance depends not only on the initial stress, the initial density, and the amplitude of the cyclic loading, but also on the preshearing, that is, the deviatoric stress path applied to the soil before the cyclic loading. To explore the influence of preshearing on the subsequent soil behaviour, a set of triaxial tests with a combination of undrained preshearing and drained stress cycles using two sample preparation methods is presented. It is shown that the preshearing as well as the preparation method have a major influence on the strain accumulation upon cyclic loading. Simulations of the experiments with four advanced constitutive models reveal that neither the long-lasting effect of preshearing nor the preparation method can adequately be captured by all of the models. This deficiency of the constitutive models can lead to unsafe designs due to the overestimation of the cyclic resistance to liquefaction and to the underestimation of long term settlements.

Some remarks on the performance of three advanced soil constitutive models in the small-strain region

ABSTRACT This short communication identifies some inconsistencies in the numerical predictions of three advanced soil constitutive models. The chosen constitutive models are subject to simple numerical tests in the small-strain range relevant to the cyclic response of soil in seismic, offshore and urban applications. The numerical tests comprise a cyclic simple shear test in the small-strain range, a simple shear test with very small strain unloading-reloading loops and a test on the dependence of the rate of the shear stiffness degradation on the changing mean confining stress. The results are briefly discussed and, in some cases, the reasons for the observed inconsistencies and potential improvements in the formulations of the investigated constitutive models are initially drafted.

State of the art on structural reinforced concrete design guidelines with non-linear analyses

Structural design rules of reinforced concrete structures for using non-linear analysis with MC2010 are presented in this article. The authors propose guidelines and good practice for using the non-linear analysis tools when performing structural design tasks. A brief resume of the state of the art in non-linear constitutive concrete models is presented as well. In general, Portugal’s structural design is based on linearized analysis, using the partial safety factor method. Although this methodology is validated and commonly used, it still presents several drawbacks: (i) it is uneconomic if the behavior is fragile, localized or unknown; (ii) it makes architectural solutions unfeasible with the reduction of constructed spaces; (iii) rendering existing structures design with outdated codes is unfeasible. The civil engineering industry widely accepted the linearized analyses, due to its easy and fast implementation with minimum material inputs and knowledge. On the contrary, in developed European countries, the non-linear analyses are already used in structural design to optimize the constructed space. Although the natural uncertainties arising from the properties of concrete are taken into account, the use of advanced constitutive models allows to promote structural solutions that enhance constructed space and satisfy the expectations of potential investments, either in the private and public sector rationally and safely.

Liquefaction assessment based on numerical simulations and simplified methods: A deep soil deposit case study in the Greater Lisbon

The accurate estimation of earthquake-induced liquefaction damage requires detailed ground response analysis, which does not generally consider liquefaction. This paper presents a well-documented pilot site where different approaches to estimate surface ground motion were compared. A simplified stress-based method and non-linear dynamic effective stress numerical analyses were used to identify liquefaction. HVSR curves were used to validate the numerical analyses and laboratory test results were employed to calibrate an advanced constitutive model capable of reproducing liquefaction stress-strain behaviour and pore water pressure generation.1D non-linear elastic numerical analysis evidenced high shear strains in weak soil layers where liquefaction may occur. When PM4sand model was used to simulate liquefaction behaviour in sandy layers, 1D and 2D model responses were rather similar, since liquefaction occurs predominantly at a sandy layer that extends across the valley. Therefore, 1D horizontally infinite layers seems to be a good approximation of the 2D response of this valley.

Evaluation of loading-path-dependent constitutive models for springback prediction in martensitic steel forming

In this study, the performance of conventional and advanced constitutive models to the prediction of springback for ultra-high strength steel was assessed. The elasto-plastic behavior of a martensitic steel sheet sample was characterized to assess the conventional stress-strain behavior in uniaxial tension. More advanced tests such as uniaxial compression and tension-compression experiments were conducted to assess the strength-differential (SD) effect and hardening fluctuations during non-linear loading paths (NLLP effect). Three constitutive plasticity models, namely, the conventional isotropic hardening, Yoshida-Uemori (YU) two surface kinematic hardening and pure distortional hardening (HAH20) models were calibrated using an optimization procedure. Then, these models were employed for finite element predictions of springback after forming. The isotropic hardening model does not consider both SD and NLLP effects and the YU model captures only the influence of the NLLP effect. On the other hand, the HAH20 model describes both effects simultaneously. The performance of these models with respect to springback prediction was evaluated using three forming applications: wiper bending, C-rail drawing and Roof-Side-Rail crush forming. This work indicates that the HAH20 model is the best candidate for the prediction of forming and springback for such martensitic steel because of its ability to consider both SD and NLLP effects. However, the conventional isotropic hardening model led to results in good agreement with those obtained using the HAH20 model in specific cases. The reason, discussed in detail in this article, is likely due to the compensation of the permanent softening due to load reversal by the higher flow stress due to the SD effect.

Calibration of an elastoplastic model of sand liquefaction using the swarm intelligence with a multi-objective function

According to post-seismic observations, spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction, where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a “liquid”. Therefore, correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field. In advanced elastoplastic models of sand liquefaction, certain fitting parameters have a remarkable effect on the computed results. However, the identification of these parameters, based on the experimental data, is usually intractable and sometimes follows a subjective trial-and-error procedure. For this, this paper presented a novel calibration methodology based on an optimization algorithm (particle swarm optimization (PSO)) for an advanced elastoplastic constitutive model. A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations. To overcome computational problem probably appearing in simulation of the cyclic triaxial test, two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions. The Dafalias model has been used as an example to demonstrate the main programme. With the calibrated parameters for the HN31 sand, the computed results were highly consistent with the laboratory experiments (including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes). Finally, an extension example is given for Ottawa sand F65, suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.

Numerical analysis of energy piles in a hypoplastic soft clay under cyclic thermal loading

AbstractThis work is a numerical investigation of the effect of thermally induced volumetric collapse of normally consolidated clays on the performance of energy piles. A series of coupled thermo‐hydro‐mechanical Finite Element simulations were carried out using the commercial software ABAQUS. These examined a single free‐head energy pile embedded in a normally consolidated clay layer subjected to a constant mechanical load and to a number of heating/cooling cycles, to reproduce operating conditions. The soil behaviour was described with two advanced hypoplastic constitutive models for clays, one of which incorporates the thermally induced volumetric collapse using an ad‐hoc algorithm developed by the authors. Both models predict a cyclic accumulation of settlement and excess pore water pressure, especially when the thermal collapse effect is considered. While the excess pore pressure distribution stabilises within a few cycles, the rate of settlement of the pile head does not show any tendency to decrease from one cycle to another. These results are in agreement with data from small scale tests on an isolated energy pile in normally consolidated clay, indicating that the numerical model developed in this study can be used to investigate the complex soil/pile/raft interaction processes occurring in real piled foundations incorporating energy piles.

Numerical inspection of Miner’s rule and drained cyclic preloading effects on fine-grained soils

The prediction of soil cyclic behaviour is relevant for several geotechnical applications. In order to obtain accurate predictions of settlements and pore water pressure build-up on boundary value simulations, robust constitutive models which are able to realistically reproduce the soil mechanical behaviour under monotonic and cyclic loading are necessary. To have confidence on their predictions, their capabilities and limitations should be very well known. In this article, the prediction capabilities and limitations of two advanced constitutive models for fine-grained soils, namely: CAM and AHP+ISA were inspected considering undrained cyclic triaxial tests with more complex and realistic nature than ”conventional” undrained cyclic tests usually considered in the literature for the calibration and validation of constitutive models but not representative of many real loading scenarios. In particular, the influence of drained cyclic preloadings and packages of cycles with different deviatoric stress amplitudes in different sequences (inspection of Miner’s rule) was evaluated. For that purpose, simulation results with the models were qualitatively as well as quantitatively compared against several experimental results under monotonic and cyclic loading on Malaysian kaolin reported by Duque et al. (2022a).