Soil Deformation Mechanisms Research Articles

Effect of tunnel-building separation distance on the dynamic soil-structure interaction response

Understanding how buried structures respond to cyclic loading is crucial for designing earthquake-resistant underground infrastructure. The complexity of the dynamic response of these underground structures is accentuated when accounting for their interaction with adjacent buildings. This study focuses on the impact of the lateral distance between a shallow rectangular tunnel and an adjacent residential structure on dynamic soil-structure interaction, employing two dynamic centrifuge tests. Particle Image Velocimetry technique was adopted to observe the developed mechanisms of liquefied soil deformation, tunnel uplift, and foundation settlement. Results show the pronounced effects on soil deformation above the tunnel crown with a reduction in the tunnel-building separation distance. The distribution of excess pore pressure along the tunnel lining will be presented. Tunnel manifested additional lateral movement and reduced uplift when the adjacent building was in close proximity. A decrease in the tunnel-building distance contributed to a reduction of building rotation, primarily due to the significant mitigation of non-uniform settlement under the footing. Overall, the soil deformation mechanism around the tunnel and the building will be shown to change depending on the separation distance between them.

Development of dynamic centrifuge models for measurement and visualization of deformation mechanisms in liquefiable soils

Recent advancements in geotechnical physical modeling have enabled visualization and analysis of deformation mechanisms in soil sections through the integration of Particle Image Velocimetry (PIV) in dynamic centrifuge modeling. PIV requires a rigid wall container. In this paper, we summarize the design considerations that enable reliable measurement and visualization of soil deformation mechanisms at the University of Colorado (CU) Boulder’s 400 g-ton, 5.5 m radius centrifuge facility. The primary objective of this system is to investigate the response of complex and stratigraphically variable, saturated granular soil deposits beneath shallow-founded structures, though it can also be used for other configurations that benefit from advanced visualization in the centrifuge. The setup aims to enable quantification and visualization of different deformation mechanisms, including shear, volumetric, and soil ejecta formation, near and away from structures. The paper provides detailed design considerations for the system components, including a rigid container with a transparent Perspex wall and duct seal inclusions, a linear-elastic single-degree of freedom (SDOF) structure, soil texture, a potential ground improvement technique, and a high-speed camera system. Through fully-coupled, three-dimensional (3D) nonlinear finite element analyses, we investigate the influence of container type, domain size, and duct seal geometry on boundary effects, with consideration of nonlinearities within various soil profile configurations with and without the presence of a building model. The findings highlight the critical impact of proximity to lateral boundaries of the container on accelerations, excess pore pressures, foundation settlement, tilt, and shear strains, as well as the benefits of duct seal in reducing those boundary effects. The results also show that the extent of boundary effects on key performance measures depends on the properties of the container, soil layers, and ground motion. The simulations also show that surface ejecta potential within stratigraphic soil profiles is highly sensitive to the depth of the groundwater table and variations in soil permeability, which must be considered in designing experimental programs that investigate the development of soil ejecta.

The Horizontal Bearing Characteristics and Microscopic Soil Deformation Mechanism of Pile-Bucket Composite Foundation in Sand

The pile-bucket composite foundation represents an innovative foundation form that surpasses the horizontal bearing performance of both single bucket-shaped foundations and pile foundations. The intricate interplay between piles and buckets introduces the complexity of the factors influencing the bearing performance of composite foundations under horizontal loads. In this paper, the indoor model tests were conducted to investigate the effects of relative density and pile-to-barrel diameter ratio on the horizontal bearing capacity and surrounding soil pressure of the pile-bucket composite foundation. A sensitivity analysis on the bearing characteristics of the pile-bucket foundation was performed using ABAQUS/CAE 2020 software. The results reveal a consistent variation in load–displacement curves across diverse diameter ratios of piles to buckets. The pile-bucket diameter ratio significantly impacts the horizontal bearing characteristics of the composite foundation. Reducing the pile-bucket diameter ratio improves the horizontal bearing capacity of the composite foundation. When the diameter ratio of piles to buckets diminishes to ≤0.317, the influence of this ratio on bearing performance becomes markedly pronounced. The displacement range of the surface soil decreases with an increase in relative density, while the influence depth of the surrounding soil of the composite foundation significantly decreases as the pile-to-barrel diameter ratio decreases.

A rigorous analytical approach to the pile-soil interaction of torsionally loaded piles in saturated SANICLAY soils

The paper proposes a rigorous analytical approach to predict interaction between torsionally loaded piles and saturated clay soils. The soil deformation mechanism around the pile is determined using the non-associated and anisotropic constitutive model, SANICLAY, along with the axisymmetric condition, equilibrium equation, and boundary conditions. By solving the derived governing equations, the hoop shear stress against rotation curve is obtained, including elastic, elastoplastic, and critical state processes. Taking advantage of the finite-difference method, the torque-rotation behavior of the pile and the stress-strain state of the soil around the pile are figured out. The proposed approach is compared with a FEM simulation and a parametric analysis is conducted to investigate the effect of overconsolidation ratio and in-situ coefficient. Model pile tests and field tests are used to manifest the validity and capacity of the model. The results demonstrate that the present approach can well predict the torque-rotation response of the pile and can reflect some important phenomena observed in pile tests.

Earth pressure distribution on laterally loaded offshore monopiles

Unlike conventional pile foundations, a monopile is a large diameter open-ended steel tube driven into the seabed. Accurate quantification of the earth pressure distribution along a monopile due to lateral loads plays a pivotal role in the design of offshore wind turbines and remains a problem of great interest. This paper presents an attempt to address the problem by means of three-dimensional (3D) finite element modeling, with focus on the effect of pile slenderness on earth pressure distribution and the associated soil deformation mechanisms. The study shows that as pile diameter increases, the deformation mode of the pile will change from flexural to rotational deflection while the deformation pattern of the surrounding soil varies from being the wedge-type to a combination of the wedge-type and the rotation-type. The magnitude of either normal contact stress or shear stress at a pile section decreases with increasing pile diameter, but the distribution pattern of the normalized contact stress (either normal or shear stress) is nearly the same. The implications of these findings for engineering practice are two-fold: (a) Use of the p-y relationship established from field tests on piles of reduced scales in the design of large-diameter piles may still result in a potential risk of overestimating the lateral bearing capacity if the test pile diameter is not large; and (b) a unified factor independent of pile diameter can be introduced to average the contact stress across the pile section in the development of simplified methods.

Investigation of rocking mechanism of shallow foundations on sand via PIV technique

AbstractAdoption of the rocking isolation concept in foundation design is considered as an effective method in reducing seismic loads of structures. Despite much research conducted on the rocking behavior of foundations, concerns regarding the practical application of the rocking foundation design concept still prevail. The concerns primary stem from the lack of accurate understanding and knowledge associated with the soil‐foundation deformation mechanisms during rocking motions. Determination of deformation mechanisms and soil mass failure modes during foundation rocking helps to gain insight into the rocking behavior, recognize influential factors on foundation settlement or uplift, and propose appropriate improvement strategies to control foundation deformations. The primary objective of this study is to investigate the deformation behavior and failure modes of the soil mass beneath a rocking foundation with various initial static vertical factors of safety (F.S.v) and embedment depths. To this end, a series of reduced‐scale slow‐cyclic tests under 1g condition have been conducted using a single degree of freedom (SDOF) model. To determine soil deformation mechanisms, soil displacement fields have been measured using Particle Image Velocimetry (PIV) technique. Soil deformation mechanisms during loading and unloading paths, as well as causes leading to the foundation settlement or uplift have been evaluated and discussed. Additionally, changes in the effective soil‐foundation contact area in different loading cycles have been examined based on the PIV results. Based on the results, soil deformation mechanisms in the loading portions include soil densification, wedge deformation and scoop deformation. As the footing embedment depth increases, wedge deformation mechanism becomes limited, while scoop deformation mechanism becomes stronger. Additionally, as the foundation F.S.v increases, the depth of influenced zone of the rocking foundation decreases and the soil displacement occurs to a more limited depth.

Numerical study on stress paths in grounds reinforced with long and short CFG piles during adjacent rigid retaining wall movement

Abstract Ensuring the safety of existing structures is an important issue when planning and executing adjacent new foundation pit excavations. Hence, understanding the stress state conditions experienced by the soil element behind a retaining wall at a given location during different excavation stages has been a key observational modelling aspect of the performance of excavations. By establishing and carrying out sophisticated soil–structure interaction analyses, stress paths render clarity on soil deformation mechanism. On the other hand, column-type soft ground treatment has recently got exceeding attention and practical implementation. So, the soil stress–strain response to excavation-induced disturbances needs to be known as well. To this end, this paper discusses the stress change and redistribution phenomena in a treated ground based on 3D numerical analyses. The simulation was verified against results from a 1 g indoor experimental test conducted on composite foundation reinforced with long and short cement–fly ash–gravel (CFG) pile adjacent to a moving rigid retaining wall. It was observed that the stress path for each monitoring point in the shallow depth undergoes a process of stress unloading at various dropping amounts of principal stress components in a complex manner. The closer the soil element is to the wall, the more it experiences a change in principal stress components as the wall movement progresses; also, the induced stress disturbance weakens significantly as the observation point becomes farther away from the wall. Accordingly, the overall vertical load-sharing percentage of the upper soil reduces proportionally.

Utilisation of extrusion method in geotechnical tests: conception and theoretical analysis

Extrusion method has been utilised in a variety of product-processing units such as metal casting and food processing. The process of extruding is relatively fast and reproducible, and more importantly, can benchmark shear resistance of extruded materials. These advantages have propelled researchers to practice the extrusion method to determine soil properties, e.g. Atterberg limits and shear strength. Although the mechanics behind the extrusion process remains less understood, studies have verified the feasibility of the benchmarking. This study presents the theoretical basis underpinning the extruding process by extending the conventional slab analysis method to model the entire process of extruding. The developed analytical method is original in assessing the extrusion of the dead material zone and considering the dynamic move of extruded materials. The novel theoretical analysis enhances a more accurate estimation of extruding pressure and builds a solid foundation for developing extrusion tests in geotechnical engineering. In addition, the described extrusion mechanics explains reasons for observing some discrepant correlations to other geotechnical parameters due to the different soil deformation mechanisms among the test methods.

From cyclic sand ratcheting to tilt accumulation of offshore monopiles: 3D FE modelling using SANISAND-MS

Serviceability criteria for offshore monopiles include the estimation of long-term, permanent tilt under repeated operational loads. In the lack of well-established analysis methods, experimental and numerical research has been carried out in the last decade to support the fundamental understanding of monopile–soil interaction mechanisms, and the conception of engineering methods for monopile tilt predictions. With a focus on the case of monopiles in sand, this work shows how step-by-step/implicit, three-dimensional (3D) finite-element (FE) modelling can be fruitfully applied to the analysis of cyclic monopile–soil interaction and related soil deformation mechanisms. To achieve adequate simulation of cyclic sand ratcheting and densification around the pile, the recently proposed SANISAND-MS model is adopted. The link between local soil behaviour and global monopile response to cyclic loading is discussed through detailed analysis of model prediction. Overall, the results of numerical parametric studies confirm that the proposed 3D FE modelling framework can reproduce relevant experimental evidence about monopile–soil interaction, and support future improvement of engineering design methods.

Quantifying the influence of pile diameter on the load transfer curves of laterally loaded monopile in sand

Although the load transfer curves (i.e., p-y curves) recommended by the current industry standards are regarded as questionable for the recently emerging large diameter monopile, the influence of pile diameter and bending stiffness on the p-y curves in sand has not been systematically quantified. Nor have the underlying mechanisms of the diameter dependent p-y curves been well understood. This study presents a series of well calibrated three-dimensional finite-element (FE) analyses, aiming to quantify p-y curves of laterally loaded piles with different pile diameters and bending stiffness in sand, and to reveal the underlying mechanisms. It is found that the p-y curves in the API [6] code, which are valid for piles with a small diameter (D = 1 m), overestimate the initial stiffness while underestimates the soil resistance of a large-diameter pile (D = 5 m) by more than 90%. The numerical analyses further reveal that the modification of the p-y curves with the increasing pile diameter is mainly associated with the altered soil deformation mechanisms around the increasingly stiff pile. On the other hand, the influences of the skin friction, base shear and base moment of the large-diameter pile (with D up to 5 m) on the p-y curves are almost negligible. New p-y curves considering the effect of failure mechanism of large diameter monopile in dense sand is proposed, which are shown to yield better predictions for large-diameter piles than the existing p-y curves.

Mechanisms beneath rectangular shallow foundations on sands: vertical loading

This paper details analysis of deformation behaviour of silica and carbonate sands under a rectangular foundation subject to uniaxial vertical load based on results from a series of centrifuge model tests. A multiscale particle image velocimetry/digital image correlation (PIV/DIC) technique was used to record and analyse the foundation tests with high resolution and measurement precision. Cone penetrometer and pressuremeter tests provide in situ soil characterisation of the tested sand sample in the centrifuge environment. The soil behaviour is analysed through foundation load–settlement response and the observed soil deformation measurements. Different soil deformation mechanisms and strain behaviours were observed in the different sands tested, and the particle shape effect is considered, with data from scanning electron microscopy, to explain the differences. The results and analyses contribute towards better understanding of different soil behaviours under shallow foundations in different sands.

Effect of particle roundness and morphology on the shear failure mechanism of granular soil under strip footing

This study investigates the effect of particles roundness and morphology on the shear failure mechanism of soil. A strip footing was modeled under laboratory conditions. Calcareous soil was tested with three roundness classes: angular, rounded and well-rounded shapes with sizes of 0.30 mm to 4.75 mm. These were divided into six different groups at three relative densities of 30%, 50% and 70%. A series of photographs was taken during the tests and analyzed using the particle image velocimetry (PIV) method to understand the soil-deformation mechanism. The results showed that increasing the sample sizes increased the affected area of the soil. At the same time, increasing the relative density caused a punching failure mechanism that went towards the general failure. The shear failure mechanism of the soil changed from general toward punching shear failure with increasing particle roundness. This effect was larger with the smaller materials. Underneath the affected layers of soil, the angular samples were deeper than the rounded and well-rounded samples. The affected depth in the angular soil was approximately 1.5B in the smallest size group. This was more than 3B and near 4B in the largest size group. Both the sides and the underlying soil layers should be considered on angular soils. The area under the footing becomes more important than the side parts after increasing the roundness of the particles.

A novel analytical approach for predicting the noncylindrical pile penetration‐induced soil displacement in undrained soil by combining use of cavity expansion and strain path methods

SummarySince development of cavity expansion theory and strain path method, almost all the conventional analyses of pile penetration problem have been based on circular cross section penetrometer. However, noncylindrical pile (with noncircular cross section) is also required in geotechnical engineering such as rectangular cross‐sectional pile, X‐sectional cast‐in‐place concrete pile, H‐shaped steel pile, prefabricated vertical drains, and flat dilatometer. This paper presents a novel and general analytical approach for capturing the soil deformation mechanism around the pile with arbitrary cross section. The penetration problem is simulated by a new 2‐dimensional (radial and circumferential) cavity expansion model. Based on the theoretical framework of strain path method, the kinematics (velocity field) of the noncylindrical cavity expansion is reduced to solve the Laplace equation with arbitrary velocity boundary conditions by using the conformal mapping technique. Then, solutions for the strain and displacement, which could consider the large deformation effect, are obtained by the integration of the strain rate and velocity along the streamline. The analytical solution is validated by comparing the degenerate solution of this study with conventional circular (cylindrical) cavity expansion theory. Subsequently, typical numerical examples for the deformation mechanism of elliptical and rectangular cavity expansion are presented to prove the advantage of the proposed new solution particularly in capturing the noncylindrical symmetric displacement field. A brief application of the proposed new analytical solution to the interpretation of the smear effect of prefabricated vertical drain installation confirms its useful in geotechnical engineering.

Study on deformation law of circular foundation under combined loading

The foundations of some ocean engineering structures are built to withstand not only the vertical gravity load V, but also the horizontal load H induced by sea waves and current. The horizontal load includes the concentrated force load, the moment load M, and the torque load T termed also as combined loading. It is of academic and engineering significance to study the deformation law of submarine seabed due to combined loading. On the basis of the three-dimensional elastic mechanics solution of circular foundation, numerical methods are used to analyze the deformation law of submarine soil under circular foundation with six degrees of freedom. The finite element analysis results give the elastic deformation law of soil in three dimensional spaces, modify the theoretical elasticity solution, and presents nonlinear soil deformation mechanism under the circular foundation with six degrees of freedom.

Analysis of Bearing Capacity of Suction Bucket Foundation Subjected to Horizontal and Moment Loadings

The suction bucket foundation is not only supporting the vertical loading such as the sea platform and weight itself, but also subjecting to horizontal and moment loading due to wind and wave. The response of bucket foundation to combined Horizontal (H) and Moment (M) loading has been studied using 3D finite element analysis Then the proposed method is numerically implemented in the framework of the general-purpose FEM software ABAQUS. Relationship curve between the coefficient of ultimate bearing capacity and displacement is obtained by the application of load-displacement controlled method in homogeneous soft foundation the failure envelope of foundation in the M-H is obtained by the application of swipe testing. The behavior is explained using upper bound plasticity mechanisms suggested by the soil deformation mechanisms observed in the finite element analysis. The numerical results computed by the proposed method will be helpful in engineering practices.

The horizontal-moment capacity of embedded foundations in undrained soil

The bearing capacity of embedded foundations subject to combined horizontal and moment loading in undrained soils is of interest particularly to the offshore geotechnical engineer. These loadings can be experienced by monopod foundations and offshore manifolds and often take the form of a horizontal load applied at a lever arm height above the foundation base. Previous design methods using the failure envelope approach have suggested that peak moment capacity of a foundation is mobilized with positive horizontal loads, but that peak horizontal load is mobilized with no additional moment loading. This paper reports numerical work specifically investigating the effects of the embedment ratio on the horizontal-moment foundation capacity under no vertical load in both uniform strength and "normally consolidated" undrained soil. It is shown that the embedment ratio significantly affects the eccentricity of the M–H failure envelope so that the shape varies when normalized by the pure moment (M0) and pure horizontal load (H0) capacity. The reasons for the eccentricity of the failure envelopes are understood by investigating soil deformation mechanisms calculated during FE analysis and by accompanying upper bound plasticity analysis. This mechanistic understanding is used to suggest load reference point translations that ease curve-fitting of the complex failure envelopes for use in design.Key words: bearing capacity, foundations, numerical modelling and analysis, plasticity.

Numerical analysis on dynamic deformation mechanism of soils under blast loading

Soil is considered as a three-phase medium consisting of solid particles, water and air. Its behavior is very difficult to predict, especially under high rate blast loading. In this study, a new three-phase soil model for shock loading is employed to facilitate a full simulation of explosion and the subsequent stress wave propagation in soils. Upon validating the model, extended numerical calculations are carried out and the results are analyzed to demonstrate the change of characteristic parameters of the soils, the inherent distribution of the pressure on individual phases and hence the deformation mechanisms of the soils under blasting loading. Two primary deformation mechanisms exist, one is the deformation of the soil skeleton formed by the solid particles; the other is the deformation of all individual soil phases. It is found that the response of soil near the charge is dominated by the second mechanism while the first mechanism dominates in areas beyond a certain scaled range. The location of the transition zone depends primarily on the initial state of the soil. The results are useful for establishing rational and practical soil models for engineering applications concerning blasting.

Finite Element Modelling of Excavation and Advancement Processes of a Shield Tunnelling Machine

During shield tunnelling operation, a shield machine is driven forward by applying mechanical jack forces behind the machine tail and excavating the soil in front of the machine with its cutting face. In this study, the advancement and excavation processes of the shield tunnelling operation are modelled using the finite element method in order to investigate the effect of these construction processes on the ground response. A new excavating finite element, which models the disturbed soil in front of the cutting face, is introduced. The operation of shield advancement and of soil excavation is simulated using the finite element remeshing technique at each time step of the analysis. The accuracy of the finite element remeshing technique is discussed by analysing one-dimensional consolidation of an isotropic elastic medium. The proposed modelling techniques of shield tunnelling construction are applied to simulate a tunnelling project in Tokyo and the numerical results are compared with the field measurements. The soil deformation mechanism associated with the shield tunnelling operation is examined in detail.

Selection of load–transfer functions for passive lateral loading of pile groups

Abstract A finite element study has been carried out to determine the pile–soil–pile interaction behaviour for closely spaced pile rows and groups under passive lateral loading from soil movement. A horizontal section close to the piles was studied to determine the effects of pile spacing and soil constitutive law on the load–transfer relationships of the piles. The study has revealed links between the soil stress–strain law, the soil deformation mechanism and the pile load–transfer curves. Interaction behaviour was seen to depend on the prevailing deformation mechanism which in turn was governed by the soil constitutive law. Elastic-plastic and power law soil models were applied. Interaction factors suitable for design use to account for increasing lateral pressure on piles during passive lateral loading have been produced for a range of pile spacings and power law soil exponents. Interaction between piles increased both with reduction of pile spacing and with increase of soil exponent—the less soil stiffness degradation with shear strain, the greater the interaction between piles at a given spacing. This suggests that the passive interaction factors calculated using elastic methods are likely to overestimate the effects of pile–soil–pile interaction.

Combined loading of skirted foundations

>The response of skirted offshore foundations to combined vertical (V), moment (M) and horizontal (H) loading has been studied using two-dimensional finite-element analysis and upper-bound plasticity analysis assuming the soil to be undrained. New information has been gained about the shape of the yield locus and the soil deformation mechanisms occurring at yield from the finite-element analysis. The shape of the yield locus was found to be similar to that predicted by previous workers in V—M and V— H space but differed significantly in M—H space. This behaviour is explained using upper-bound plasticity mechanisms suggested by the soil deformation mechanisms calculated in the finite element analysis. This procedure is then used to give a good approximation to the shape of the yield locus and thus may form the basis for future design methods. Additionally, a simplifying transformation is suggested for the yield locus in H—M space based on plasticity analysis, which allows use of simple mathematical expressions to form a design envelope. Nous 6tudions la réponse de fondations offshore à jupe à une combinaison de charge verticale (V), instantanée (M) et horizontale (H) en utilisant des analyses d'é1éments finis en deux dimensions et une analyse de plasticité de limite supérieure en supposant un sol non drainé. Nous drons de Panalyse d'é1éments finis de nouveaux renseignements sur la forme du lieu d'é1asticité limite et sur les mécanismes de déformation du sol qui se produisent à la limite é1astique. La forme du lieu se révèle comme similaire à celle présagée par les travaux précédents dans les espaces Vmdash;M et V—H mais considérablement différente dans Pespace M—H. Nous expliquons cc comportement en utilisant les mécanismes de plasticité de limite supérieure qui sont suggérés par les mécanismes de déformation du sol calcu1és dans 1'analyse d'é1éments finis. Cette procédure est alors utilisée pour donner une bonne approximation de la forme du lieu qui pourra ainsi former la base des futures méthodes de design. De plus, nous suggérons une transformation simplificatrice pour le lieu d'é1asticité limite dans Pespace H—M sur la base de 1'analyse de plasticité qui permet Putilisation d'expressions mathématiques simples pour former une enveloppe de design.