A numerical study of the suitability of rigid inclusion ground reinforcement beneath caisson quay walls

The objective of this study was to determine whether rigid inclusions are suitable for reinforcement of the foundation of a caisson quay wall functioning as a container terminal. Apart from their brittle behaviour under lateral loading, rigid inclusions are well suited to the large uniform loads and stringent post-construction deflection tolerances associated with container terminal structures. Their inherent strength and stiffness means they have certain advantages over other stiffening columns commonly used for ground reinforcement in port expansion projects. Their mechanical properties allow construction to unrestricted heights at any construction rate and, in theory, RIs can be applied to all soil types. Additionally the locations of many ports coincide with rivers, deltas and estuaries which are associated with poor soil conditions often requiring ground improvement. Their suitability is of practical significance to port planners and engineers who are faced with the challenge of providing satisfactory foundation performance that is cost effective. The addition of RI ground reinforcement for this structural application would allow for greater flexibility in meeting these challenges. The literature review for this study was broad in its scope with emphasis placed on describing the mechanics of the problem, analysis methods and suitable installation methods for execution in the marine environment. One of the key outcomes of the literature review was identifying the problem of lateral loading due to "free-field" lateral ground movements. In light of this, suitable strategies for limiting and accommodating lateral loading of the RIs were proposed. A numerical study of the proposed ground improvement scheme was undertaken using the 3D finite element method. The key model outputs were caisson deflections and RI forces, moments and stresses, for the various simulated construction phases up to operational conditions. The model results were assessed in terms of the key foundation performance criteria which were related to STS crane rail tolerances and limiting tensile stresses in the RIs. This study found that for a firm clay subsoil condition the proposed RI ground reinforcement scheme met the foundation performance criteria for this structural application provided (i) strategies to limit lateral loading were implemented and (ii) the RIs were reinforced over the length where they were not fully compressed. While this study provided insights into the behaviour of RIs for this structural application, ultimately suitability is a function of range of factors, in addition to the limited technical performance criteria derived for this study

BEST SOIL: Soft soil modelling and parameter determination

The report aims to give advice on parameter derivation for standard and advanced constitutive (soil) models, with focus on soft soil models. The soil models concerned include several strain-hardening models that are commonly used by geotechnical practitioners, installed in the Plaxis finite element (FE) suite, such as the Soft Soil model and the Hardening Soil model. These are referred to as the standard models. In addition, an advanced creep model developed at Chalmers, soon available for practicing engineers, is considered. Firstly, key features of the models are introduced, highlighting the main differences of the models. This is followed by recommendations for testing needed for reliable model parameter determination. It is highlighted that whilst for some of the models the determination of model parameters can be done easily based on typical Swedish site investigation and lab testing, for some models, this is not the case. Finally, advice on laboratory testing programme when intending to use geotechnical FE analyses is done

3D Finite Element Modelling of Sheet Pile Wall Excavation: A Case study in Bangkok

Sheet pile wall has been used extensively as a soil retaining structure during the excavation process in soft ground. Meanwhile, finite element method (FEM) has been widely used as a numerical tool to predict wall movements due to soil excavation. In FEM, many factors including soil parameters, structures’ parameters and construction stages simulation influence the analysis results. This paper presents a modelling of sheet pile wall at deep excavation using 3D FEM. The study focuses on the structures’ stiffness modelling and the stages of construction simulation. The hardening soil model and its parameters adopted from previous study was employed in the analysis. To validate the model, an excavation site located in the center of Bangkok was selected to model. PLAXIS 3D – a commercial software for solving finite element problem was employed in this study. In overall, the results of wall movements from 3D FEM agree well with the instrumented data confirming that the modelling could reflect the real behavior of sheet pile walls at deep excavation in soft soils in Bangko

Back Calculation from Geotechnical Structures Response around Kuala Lumpur

It is well recognized that uncertainties are abundant in geotechnical engineering which may result in failure of geotechnical structures. Achieving an idealized parameters' literature has become a form of approach analysis but the accurate determination of soil parameters is rather difficult. The main focus of this study is to evaluate aspects of computational geotechnics through inverse analysis to deduce design parameters through correlation with field monitoring data of various high rise residential developments around Kuala Lumpur, mainly focusing on soil-structure interaction during Simulation of Basement Excavation and Constructio

Vertical facing panel-joint gap analysis for steel-seinforced soil walls

This paper reports the results of a numerical parametric study focused on the prediction of vertical load distribution and vertical gap compression between precast concrete facing panel units in steel-reinforced soil walls ranging in height from 6 to 24 m. The vertical compression was accommodated by polymeric bearing pads placed at the horizontal joints between panels during construction. This paper demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill and foundation soil stiffness. The summary plots in this study can be used to estimate the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, to demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or as a benchmark to test numerical models used for project-specific design. The paper also demonstrates that although the load factor (ratio of vertical load at a horizontal joint to weight of panels above the joint) and joint compression are relatively insensitive to foundation stiffness, the total settlement at the top of the wall facing is very sensitive to foundation stiffness. This paper examines the quantitative consequences of using a simple linear compressive stress–strain model for the bearing pads versus amultilinear model that is better able to capture the response of bearing pads taken to greater compression. The study demonstrates that qualitative trends in vertical load factor are preserved when a more advanced stress-dependent stiffness soil hardening model is used for the backfill soil as compared with the simpler linear elastic Mohr–Coulomb model. Although there were differences in vertical loads and gap compressionwith the use of both soilmodels for the backfill, the differenceswere small and not of practical concern.Peer ReviewedPostprint (author's final draft

Evaluation of Lateral and Axial Deformation for Earth Pressure Balance (EPB) Tunnel Construction Using 3 Dimension Finite Element Method

Mass Rapid Transit Jakarta (MRTJ) phase 1 tunnel construction using the earth pressure balance method has been completed and surface settlement and lateral displacement data according to elevation and inclinometer readings has been collected to evaluate the effect of tunnel’s construction on surrounding infrastructure. Soil stratification along the research area, defined according to boring logs and soil parameters for the hardening soil model (HSM) and the soft soil model (SSM), was determined by optimization of stress-strain curve fitting between CU triaxial test, consolidation test and soil test models in the Plaxis 3D software. Evaluation of the result of surface settlement measurements using an automatic digital level combined with geodetic GPS for elevation and position control points showed that the displacement behavior was affected by vehicle load and stiffness of the pavement. Lateral displacement measurements using inclinometers give a more accurate result since they are placed on the soil and external influences are smaller than surface settlement measurement. The result of 3D finite element modeling showed that surface settlement and lateral displacement during TBM construction can be predicted using HSM with 2% contraction. SSM and the closed-form solutions of Loganathan and Poulos are unable to provide a good result compared to the actual displacement from measurements

Numerical analysis of Double-O-Tube shield tunnelling

Underground tunnels play an important role in the mass transportation systems in modern cities. The ground movements induced by tunnel excavation in short term and long term are of great concern due to their potentially irrecoverable impact on the surrounding buildings and services. The numerical modelling, in conjunction with well documented case studies to validate the modelling approach, is an efficient methodology for adequate and robust predictions of the ground response caused by tunnelling. The Double-O-Tube (DOT) shield tunnelling is a new technology developed since 1989, and has been applied in over 20 engineering cases in China and Japan. Due to its unique double tube cross-sectional shape, the DOT tunnel is expected to perform differently in mechanical terms compared to traditional twin tunnels. Therefore, a systematic study of its engineering behaviour, of the ground response and of tunnel lining is necessary. This research involves numerical simulations and investigation of DOT construction in soft clay and stiff clay conditions, represented by Shanghai clay and London clay respectively, using Imperial College Finite Element Program (ICFEP). In the first part of the thesis, the Shanghai clay and the whole ground profile are characterised referring to the laboratory data and field experimental evidence. A numerical model is developed in ICFEP for the case of DOT tunnel in the Shanghai Metro system, applying an extended Modified Cam Clay (MCC) model to represent the ground conditions and discretising the tunnel lining with elastic beam elements. The predicted short-term settlement troughs achieve good agreement with the field monitoring data, validating the reliability of the numerical model. Additional sensitivity studies investigate the conditions of the tunnel lining joints and the effects of the pressure exerted by grouting in the constructions process. The second part of the thesis focuses on the modelling of the reinforced concrete segments of tunnel lining using an advanced elasto-plastic concrete model. The model validation is performed with the simulation of loading tests on a single lining segment performed in the laboratory, demonstrating very close agreement between the predicted and measured segment deflections under applied load and an accurate onset of cracking in concrete. Such a concrete model is applied in the analysss of DOT tunnelling in Shanghai to investigate its merits against a simpler lining representation. Finally, the application of DOT tunnelling is explored in stiff clay ground conditions, utilising the Jubilee Line Extension and the Crossrail case studies in London clay, and applying an advanced kinematic surface hardening model for soil behaviour. The comparison of numerical predictions against field monitoring data demonstrates comparable magnitudes of ground movements mobilised by DOT tunnelling with respect to conventional twin tunnelling.Open Acces

Modelling and Validation of 3D FEM for Laterally Loaded Single Pile

At present, researchers are increasingly in favour of Three-Dimensional Finite Element Method (3D FEM) during design process to better understand ground mechanisms and soil-structure interactions. Subsequently, it is essentially a back-analysis modelling procedure for applications in design and post-construction or failure investigation. This research aims to use 3D FEM to validate laterally loaded single pile response. Two different case studies are selected, Firstly, a published case study comparing the p-y method and finite element method for the behaviour of single pile subjected to the horizontal forces is investigated. The second case is one of published centrifuge data and finite element method for the behaviour of pile behind retaining wall subjected to excavation-induced soil movement. Through comparison with the results from case studies, 3D FEM is in good agreement with the general trend observed in field or centrifuge measurements and gives better validation or prediction of lateral deflection characteristics compared to other conventional methods

Behavior of Walls and Piles in Cohesive Soils Under Cyclic Loads

The nonlinear cyclic behavior of a soil-structure system has a significant influence on the mechanical response of this system. The cyclic response of soil-structure system has been studied experimentally and analytically. However, the results of these studies are not yet reproducing the applicability of key aspects of soil-structure behavior concepts in practice. A key prerequisite is to model the cyclic response in a facilitative and realistic way. There are several constitutive models in the literature that are available for cumulative responses, but they need many soil tests for calibration and they can be used under specific numerical codes and can be only executed by specialists. To overcome these difficulties, this research develops a simplified constitutive model (a kinematic hardening constitutive model with Von Mises failure criterion) for analyzing nonlinear plastic response of a soil-structure system subjected to cyclic loading. In addition, cumulative deformations are an essential aspect of the performance of walls and piles/caissons under cyclic loading. Therefore, reasonable estimates of the cumulative plastic displacements of structures in cohesive soils are necessary, particularly for soils which the cyclic influence may be significant. For example, the cumulative wall displacements that increase over time as the system is subjected to repeated live loading from trains passing near wall, in addition to the vertical settlements under the train track. Studying the effects of cyclic loading of railroads on the soil-wall system is necessary to improve train safety when a soil-wall system is near the tracks. As a second example, while pile and caisson anchors and foundations for offshore structures, such as wind turbines and the oil/gas exploration and production facilities have been the focus of considerable attention with respect to monotonic load capacity, much less attention has been given to cumulative displacements under cyclic loading. This issue is particularly crucial for inclined loading, since cumulative displacements can lead to loss of embedment of the caisson or pile. Since stress-strain behavior of soils is inelastic even at small strains, analyses based on linear elasticity, or on elastoplastic models that assume purely elastic behavior beneath the ultimate yield surface, cannot predict the cumulative soil deformations. Hence, an analysis that takes inelastic soil behavior at low stress levels into account, such as a bounding surface plasticity model, is required to predict cumulative displacements under cyclic loading. A cyclic nonlinear elastoplastic soil spring model has been applied to predict the monotonic and cyclic nonlinear p-y curve of piles in soft clay during the cyclic loading. Predictions of pile performance based on the kinematic hardening constitutive model used in this research are shown to match the centrifuge test results better than predictions based on the widely used API soil springs. This proposed spring model can overcome the limitations of the API clay model and can be implemented with either MATLAB or as UEL (User-defined elements) subroutine in ABAQUS/Standard. Predictions based on the spring model developed in this research shows good agreement with the measurements of cumulative displacement and soil stiffness from centrifuge tests involving cyclic loading of a single pile in soft clay

The Role of Soil Stiffness in Reverse Fault Rupture Propagation

A nonlinear Mohr-Coulomb constitutive model with a strain dependent yield surface and non-associated flow was employed to study the plastic soil properties which affect the rate of surface fault rupture propagation in reverse events. These numerical simulations show a trend for soils with higher stiffness to have a higher rate of rupture propagation. Additionally the study shows the effects of strain softening and hardening on the rate of rupture propagation. Soils which strain harden exhibiting ductile behavior typically require more basal offset to rupture to the surface than soils which strain soften exhibiting brittle behavior. These results agree with our previous fault box studies, which showed that soils with higher near surface shear wave velocity were more likely to propagate rupture to the surface for a given reverse event. The numerical modeling allowed for a more comprehensive evaluation of material types and fault angles than the fault box, and provided confidence in these findings