Advanced Soil Constitutive Model Research Articles

A numerical study of deep excavations adjacent to existing tunnels: Integrating CPTU and SDMT to calibrate soil constitutive model

Accurate determination of parameters for an advanced soil constitutive model highly relies on laboratory testing, even though it is notoriously difficult to obtain undisturbed samples for soft soils. This study explores the potential use of in-situ tests, such as piezocone penetration tests (CPTU) and seismic dilatometer tests (SDMT), to estimate the constitutive model parameters. Based on a case history of a deep excavation adjacent to existing tunnels in silt/sand-dominated sediments, a calibration approach of a set of the HSSmall (Hardening Soil Model with Small Strain Stiffness) model parameters is presented, and the derived parameters are used to numerically compute the interactive responses of tunnels and deep excavations. Several comparisons against field monitoring data indicate that the numerical model with the CPTU/SDMT-interpreted HSSmall model parameters adequately reproduces observed deformation responses of deep excavations adjacent to tunnels. However, the use of laboratory tests with disturbed samples to estimate the stiffness parameters of the HSSmall model may lead to an overconservative solution. This finding supports the use of CPTU/SDMT to provide representative parameters for a range of soil layers, leading to the conclusion that tunnel linings may be beneficial to mitigate ground movements and wall deflections due to a barrier effect.

Performance of an advanced sand constitutive model in modelling soil and soil-structure interaction under seismic excitation

There is a growing number of available advanced soil constitutive models aimed at capturing soil cyclic behaviour and their subsequent use in seismic applications. Nevertheless, detailed validation studies of these soil constitutive models on benchmark experimental works including seismic soil-structure interaction are still rare. This work presents a short validation study of the seismic performance of an advanced elastoplastic sand constitutive model on a boundary value problem including kinematic and inertial soil-structure interaction. The results of the finite element numerical model for the free field and structural responses are compared with the experimental work on a group of piles analysed in a flexible soil container filled with dry sand and subjected to simplified seismic loading. In general, the comparisons show a satisfactory match between the results of the simulations and the experiments, with the exception of the numerical predictions of settlements. The computed results are discussed based on: i) the dominant stress-paths in soil; ii) parametric studies on the settlement evaluation; iii) the origin of the high frequency motion oscillations to simple sinusoidal input motions; all with respect to potential improvements in the formulation of the elastic behaviour of the constitutive model in the future.

Modeling the response of a shallow foundation using advanced soil constitutive models

Shallow foundations are a common type of foundation used for many significant structures. These foundations can be subjected to vertical loads, moments, and base shear, which induce stresses and strains in the supporting soil. Consequently, understanding soil behaviour is crucial in geotechnical engineering. This paper presents a numerical analysis of a shallow foundation using various soil behaviour laws, utilizing finite element methods implemented in Plaxis software. The primary objective of this study is to conduct numerical modeling of a foundation under a centered load. Specifically, it aims to compare the results obtained using different constitutive models, including the Mohr-Coulomb (MC) model, the Soft Soil model, and the modified Cam-Clay model. By employing these models, we aim to evaluate their effectiveness in predicting soil response under load and to identify the most accurate model for specific soil conditions. The comparative analysis provides insights into the advantages and limitations of each model, highlighting the importance of selecting appropriate soil behaviour laws for accurate geotechnical design. Furthermore, this study underscores the significance of advanced numerical tools in enhancing our understanding of soil-structure interaction and improving the reliability of foundation design. The findings contribute to the broader field of geotechnical engineering by offering guidance on the selection of constitutive models for various soil types and loading conditions, ultimately aiding in the design of safer and more efficient shallow foundations. This research also emphasizes the role of precise modeling in predicting settlement and bearing capacity, which are critical factors in the performance and longevity of shallow foundations. Overall, this study aims to improve foundation design practices significantly.

Optimal intensity measure for seismic performance assessment of shield tunnels in liquefiable and non-liquefiable soils

Relating the ground motion intensity measure (IM) and the structural engineering demand parameter is a crucial step in the performance-based earthquake engineering framework. This study investigates the selection of IM for development of probabilistic seismic demand model of urban shield tunnels subjected to earthquake ground motions in liquefiable and non-liquefiable soils. Nonlinear dynamic effective stress analyses are conducted to develop a database of the intensity measures and structural seismic responses exposed to ground shaking and soil liquefaction. Two advanced soil constitutive models (i.e., Pressure DependMultiYield03 and PressureIndependMultiYield for liquefiable and non-liquefiable soils, respectively) are employed to capture the nonlinear behavior. A suite of 23ground motion intensity measures is selected and assessed based on the evaluation criteria of correlation, efficiency, practicality and proficiency. Eventually, the multi-level fuzzy comprehensive evaluation method is employed to comprehensively consider the four evaluation criteria and establish the optimal ground motion IM suitable for probabilistic seismic demand analysis of shield tunnel structures. The obtained results show that the sustained maximum acceleration is the optimal IM for evaluating the structural seismic response, followed by the peak ground acceleration in both liquefiable and non-liquefiable soils. Peak pseudo velocity spectrum, displacement square integral and Housner spectral intensity are found to be not suitable for the probabilistic seismic demand analysis of shield tunnel structures.

Predictive models for assessment of buried pipeline response under seismic landslides in Iran

In seismic regions both in Iran and around the world, subterranean gas pipelines inevitably extend through high-risk areas prone to seismic landslides. The seismic landslide-pipe failure mechanism constitutes a continuum geomechanical challenge influenced by factors such as sliding mass configuration, pipe positioning relative to potential slope failure surfaces, and seismic input characteristics. In this study, response of steel pipeline buried in sand under seismic landslide action is analyzed by finite difference models using an advanced soil constitutive model. The numerical model is first validated based on the shaking table test results and then several dynamic analyses are performed using the selected records of the Iranian ground motions database. The outcomes of the dynamic analysis demonstrate that Arias Intensity (Ia) can be identified as an optimal intensity measure (IM) for predicting the seismic response of a slope-pipe system in terms of maximum pipe deflection, axial strain, and shear stress. Predictive models are then developed based on the optimal IM for estimating the pipe deflection, axial strain, and shear stress subjected to a seismic landslide. These proposed predictive models offer valuable insights for assessing the response of buried pipelines to seismic landslides in Iran within the framework of performance-based earthquake engineering.

Calibration of advanced soil constitutive models for liquefaction studies: application to an urban area on the eastern Sicily (Italy)

Calibration of advanced soil constitutive models for liquefaction studies: application to an urban area on the eastern Sicily (Italy)

Overconsolidated Stress and Strain Condition of Pavement Layers as a Result of Preloading during Construction

The stiffness and resilient behavior of soils are essential input properties when designing pavements. There are many material models that take into account the stress dependency of stiffness. In pavements, horizontal stresses generally differ from conventional soils because of the preloading of the pavement during construction. In this research, standardized pavement cross sections were analyzed using finite element software with advanced soil constitutive models, and equations describing their behavior were calibrated with the back-analysis of in-situ and laboratory measurements. The pavement was modelled as comprising 4 layers: asphalt pavement, well graded crushed stone base course, granular subbase course and fine-medium sandy subgrade. The ratio of horizontal and vertical stresses σ3/σ1 and strains ε3/ε1 were investigated and assessed in the function of depth and loading, and recommendations are given for the description of these functions. The recommendations give useful input data for future practical applications such as simplified calculation methods that are capable of determining the permanent settlement beneath flexible pavements without the use of finite element methods.

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.

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.

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.

Automated calibration of advanced soil constitutive models. Part II: hypoplastic clay and modified Cam-Clay

Automated calibration of advanced soil constitutive models. Part II: hypoplastic clay and modified Cam-Clay

Automated calibration of advanced soil constitutive models. Part I: hypoplastic sand

Automated calibration of advanced soil constitutive models. Part I: hypoplastic sand

Numerical modelling of the effect of horizontal drains in centrifuge tests on soil-structure interaction in liquefiable soils

The research presented herein was carried out in the framework of the H2020 LIQUEFACT project ( http://www.LIQUEFACT.eu/ ). This paper presents the results of a set of numerical analyses performed to study the soil-structure interaction in presence of a liquefiable soil. In the first part of the paper, the attention was focused on the ability of some advanced soil constitutive models to simulate the centrifuge tests carried out within the project. Two finite element codes, Plaxis 2D and OpenSees, were used for the computations. The results were analysed in terms of accelerations, displacements and pore pressures build up. In the second part of the paper the effects of the introduction of horizontal drains, as mitigation techniques against liquefaction, were shown and discussed in terms of their ability in reducing pore pressure build-up and building settlement. All the numerical predictions confirmed the experimental evidence that horizontal drains are able to reduce the excess pore pressure during shaking and the structural settlement. The amount of reduction depends on the water boundary condition at surface: a free seepage surface generally allowed a larger mitigation than where the liquefiable layer was topped by clay.

Coupled analysis of full flow penetration problems in soft sensitive clays

This study describes the development and implementation of a numerical procedure for the analysis of coupled geotechnical problems involving finite deformations, changing boundary conditions, multiphase porous media and softening behaviour. The numerical scheme is first validated through a benchmark problem concerning the laying of an on-bottom offshore pipeline, and then some further highlights of the effects of soil softening are presented. The scheme is then specifically employed to study the penetration process of a full flow cyclic T-bar test in soft sensitive clay. An advanced soil constitutive model has been implemented to capture the effects of soil structure and its progressive de-structuring as well as soil fabric anisotropy. Accordingly, the changing soil resistance due to the combined effects of soil softening, remoulding and reconsolidation is illustrated, by considering a T-bar undergoing large amplitude cyclic sequences interspersed with consolidation periods. The results from the numerical simulations reveal the effects of soil softening on the soil deformation pattern, the evolution of shear bands, the generation of excess pore pressures and the process of soil reconsolidation.

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

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

An AI‐based model for describing cyclic characteristics of granular materials

SummaryModelling cyclic behaviour of granular soils under both drained and undrained conditions with a good performance is still a challenge. This study presents a new way of modelling the cyclic behaviour of granular materials using deep learning. To capture the continuous cyclic behaviour in time dimension, the long short‐term memory (LSTM) neural network is adopted, which is characterised by the prediction of sequential data, meaning that it provides a novel means of predicting the continuous behaviour of soils under various loading paths. Synthetic datasets of cyclic loading under drained and undrained conditions generated by an advanced soil constitutive model are first employed to explore an appropriate framework for the LSTM‐based model. Then the LSTM‐based model is used to estimate the cyclic behaviour of real sands, ie, the Toyoura sand under the undrained condition and the Fontainebleau sand under both undrained and drained conditions. The estimates are compared with actual experimental results, which indicates that the LSTM‐based model can simultaneously simulate the cyclic behaviour of sand under both drained and undrained conditions, ie, (a) the cyclic mobility mechanism, the degradation of effective stress and large deformation under the undrained condition, and (b) shear strain accumulation and densification under the drained condition.

Effect of the constitutive material model employed on predictions of the behaviour of earth pressure balance (EPB) shield-driven tunnels

Abstract Earth pressure balance (EPB) shield-driven tunnelling involves a complex soil-structure interaction problem, where performance is heavily influenced by stress history and its development during construction. Numerical modelling must therefore focus on selecting appropriate constitutive models for soils and structures, simulating construction procedures and sequences, and modelling the soil/structure interface. Reliable numerical models to predict expected settlements, lining pressures and other design parameters are essential for safe tunnel design. This paper discusses these factors in detail by utilizing a well-documented case study of twin tunnels in Shanghai. A 3D finite element model of the behaviour of reinforced concrete tunnel linings is developed using the new PLAXIS concrete model. Predictions of four different advanced soil constitutive models are compared with measured field results to assess the model effectiveness and suitability. The undrained behaviour of the saturated soft silty clay soil at the tunnelling site is studied during and after advancement of the shield tunnelling machine. The comparison matrix includes surface settlement troughs along transverse sections, and changes developing in earth and pore water pressures around the tunnel. The HSSmall soil model, which accounts for increased soil stiffness at small strains, was found to be the most suitable for addressing these problems.

Constitutive model for predicting stress-strain behavior of fine-grained sediments using shear-wave velocity

The mechanical response of a sediment to an applied stress is significantly affected by variations of material properties, state conditions, and stress states. These stress state and conditions are utilized to infer input parameters for advanced soil constitutive models. Parameters such as void ratio and effective stresses have been readily inferred from shear-wave velocities under low-strain conditions. Thus, this research aimed to develop a shear-wave velocity-based constitutive model within a critical state soil mechanics framework to predict the undrained triaxial behavior of fine-grained sediments. Laboratory tests were performed for sediment samples ranging from silt-predominant to clay-predominant sediments. As result, a new two-term power function was developed that determined mean effective stress as a function of shear-wave velocity. By virtue of this new power function, the Original Cam Clay and Modified Cam Clay critical state models were adapted to estimate the stress-strain behavior and stress paths under undrained conditions, in terms of shear velocity. In addition, correlations were developed using the state and material properties to predict the input model parameters. The developed correlations allow broad application of the proposed framework to different sediment types in which clay and silt are the dominant deposits.

Investigations of pile–soil interaction under thermo-mechanical loading

Thermo-active piles that couple load bearing with ground source heat pump systems are one of the new technologies in geotechnical engineering. This paper investigates the pile–soil interaction behaviour of a thermo-active pile in overconsolidated London clay by conducting a thermo-hydro-mechanical finite element analysis using an advanced soil constitutive model. Negative and positive excess pore pressures are computed around the pile during cooling and heating, respectively. However, the difference in the radial effective stress acting on the pile–soil interface between the cooling and heating stages is small, and the pile–soil interaction is governed by the shear mobilization associated with thermally induced cyclic movements of pile expansion and contraction. During the first cooling stage, the shear stress at a small portion in the upper part of the pile reaches close to the yield values, which leads to an additional settlement about 3 mm from the original mechanical load–induced settlement of 2 mm. The shear stresses in subsequent heating and cooling cycles are much smaller than the ultimate shear stress values, because of the heavily overconsolidated nature of the London clay.

Subsidence estimation of breakwater built on loosely deposited sandy seabed foundation: Elastic model or elasto-plastic model

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.