Three-Dimensional Finite Element Analysis of the Pile Foundation Behavior in Unsaturated Expansive Soil PDF Download
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Author: Xingyi Wu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Expansive soils, which are widely referred to as problematic soils are extensively found in many countries of the world, especially in semi-arid and arid regions. Several billions of dollars are spent annually for maintenance or for repairs to the structures constructed with and within expansive soils. The major problems of expansive soils can be attributed to the volume changes associated with the alternate wetting and drying conditions due to the influence of environmental factors. Pile foundations have been widely accepted by practicing engineers as a reasonably good solution to reduce the damages to the structures constructed on expansive soils. Typically, piles foundations are extended through the active layer of expansive soil to reach the bedrock or placed on a soil-bearing stratum of good quality. Such a design and construction approach typically facilitates pile foundations to safely carry the loads from the superstructures and reduce the settlement. However, in many scenarios, damages associated with the pile foundations are due to the expansion of the soil that is predominantly in the active zone that contributes to the pile uplift. Such a behavior can be attributed to the water infiltration into the expansive soil, which is a key factor that is associated with the soil swelling. Due to this phenomenon, expansive soil typically moves upward with respect to the pile. This generates extra positive friction on the pile because of the relative deformation. If the superstructure is light or the applied normal stress on the head of the piles is not significant, it is likely that there will be an uplift of the pile contributing to the damage of the superstructure. In conventional engineering practice, the traditional design methods that include the rigid pile method and the elastic pile method are the most acceptable in pile foundation design. These methods are typically based on a computational technique that uses simplified assumptions with respect to soil and water content profile and the stiffness and shear strength properties. In other words, the traditional design method has limitations, as they do not take account of the complex hydromechanical behavior of the in-situ expansive soils. With the recent developments, it is possible to alleviate these limitations by using numerical modeling techniques such as finite element methods. In this thesis, a three-dimensional finite element method was used to study the hydro-mechanical behavior of a single pile in expansive soils during the infiltration process. In this thesis, a coupled hydro-mechanical model for the unsaturated expansive soil is implemented into Abaqus software for analysis of the behavior of single piles in expansive soils during water infiltration. A rigorous continuum mechanics based approach in terms of two independent stress state variables; namely, net normal stress and suction are used to form two three-dimensional constitutive surfaces for describing the changes in the void ratio and water content of unsaturated expansive soils. The elasticity parameters for soil structure and water content in unsaturated soil were obtained by differentiating the mathematical equations of constitutive surfaces. The seepage and stress-deformation of expansive soil are described by the coupled hydro-mechanical model and the Darcy's law. To develop the subroutines, the coupled hydro-mechanical model is transferred into the coupled thermal-mechanical model. Five user-material subroutines are used in this program. The user-defined field subroutine (USDFILD) in Abaqus is used to change and transfer parameters. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. Except for the coupled hydro-mechanical model of unsaturated expansive soils, a soil-structure interface model is implemented into the user-defined friction behavior subroutine (FRIC) to calculate the friction between soil and pile. The program is verified by using an experimental study on a single pile in Regina clay. The results show that for the single pile in expansive soil under a vertical load, water infiltration can cause a reduction in the pile shaft friction. More pile head load is transferred to the pile at greater depth, which increases the pile head settlement and pile base resistance. In future, the proposed method can also be extended for verification of other case studies from the literature. In addition, complex scenarios can be investigated to understand the behavior of piles in expansive soils.
Author: Xingyi Wu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Expansive soils, which are widely referred to as problematic soils are extensively found in many countries of the world, especially in semi-arid and arid regions. Several billions of dollars are spent annually for maintenance or for repairs to the structures constructed with and within expansive soils. The major problems of expansive soils can be attributed to the volume changes associated with the alternate wetting and drying conditions due to the influence of environmental factors. Pile foundations have been widely accepted by practicing engineers as a reasonably good solution to reduce the damages to the structures constructed on expansive soils. Typically, piles foundations are extended through the active layer of expansive soil to reach the bedrock or placed on a soil-bearing stratum of good quality. Such a design and construction approach typically facilitates pile foundations to safely carry the loads from the superstructures and reduce the settlement. However, in many scenarios, damages associated with the pile foundations are due to the expansion of the soil that is predominantly in the active zone that contributes to the pile uplift. Such a behavior can be attributed to the water infiltration into the expansive soil, which is a key factor that is associated with the soil swelling. Due to this phenomenon, expansive soil typically moves upward with respect to the pile. This generates extra positive friction on the pile because of the relative deformation. If the superstructure is light or the applied normal stress on the head of the piles is not significant, it is likely that there will be an uplift of the pile contributing to the damage of the superstructure. In conventional engineering practice, the traditional design methods that include the rigid pile method and the elastic pile method are the most acceptable in pile foundation design. These methods are typically based on a computational technique that uses simplified assumptions with respect to soil and water content profile and the stiffness and shear strength properties. In other words, the traditional design method has limitations, as they do not take account of the complex hydromechanical behavior of the in-situ expansive soils. With the recent developments, it is possible to alleviate these limitations by using numerical modeling techniques such as finite element methods. In this thesis, a three-dimensional finite element method was used to study the hydro-mechanical behavior of a single pile in expansive soils during the infiltration process. In this thesis, a coupled hydro-mechanical model for the unsaturated expansive soil is implemented into Abaqus software for analysis of the behavior of single piles in expansive soils during water infiltration. A rigorous continuum mechanics based approach in terms of two independent stress state variables; namely, net normal stress and suction are used to form two three-dimensional constitutive surfaces for describing the changes in the void ratio and water content of unsaturated expansive soils. The elasticity parameters for soil structure and water content in unsaturated soil were obtained by differentiating the mathematical equations of constitutive surfaces. The seepage and stress-deformation of expansive soil are described by the coupled hydro-mechanical model and the Darcy's law. To develop the subroutines, the coupled hydro-mechanical model is transferred into the coupled thermal-mechanical model. Five user-material subroutines are used in this program. The user-defined field subroutine (USDFILD) in Abaqus is used to change and transfer parameters. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. Except for the coupled hydro-mechanical model of unsaturated expansive soils, a soil-structure interface model is implemented into the user-defined friction behavior subroutine (FRIC) to calculate the friction between soil and pile. The program is verified by using an experimental study on a single pile in Regina clay. The results show that for the single pile in expansive soil under a vertical load, water infiltration can cause a reduction in the pile shaft friction. More pile head load is transferred to the pile at greater depth, which increases the pile head settlement and pile base resistance. In future, the proposed method can also be extended for verification of other case studies from the literature. In addition, complex scenarios can be investigated to understand the behavior of piles in expansive soils.
Author: Amir M. Kaynia
Publisher: CRC Press
ISBN: 1000398587
Category : Technology & Engineering
Languages : en
Pages : 401
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Book Description
This book presents computational tools and design principles for piles used in a wide range of applications and for different loading conditions. The chapters provide a mixture of basic engineering solutions and latest research findings in a balanced manner. The chapters are written by world-renowned experts in the field. The materials are presented in a unified manner based on both simplified and rigorous numerical methods. The first four chapters present the basic elements and steps in analysis of piles under static and cyclic loading together with clear references to the appropriate design regulations in Eurocode 7 when relevant. The analysis techniques cover conventional code-based methods, solutions based on pile-soil interaction springs, and advanced 3D finite element methods. The applications range from conventional piles to large circular steel piles used as anchors or monopiles in offshore applications. Chapters 5 to 10 are devoted to dynamic and earthquake analyses and design. These chapters cover a range of solutions from dynamic pile-soil springs to elasto-dynamic solutions of large pile groups. Both linear and nonlinear soil behaviours are considered along with response due to dynamic loads and earthquake shaking including possible liquefaction. The book is unique in its unified treatment of the solutions used for static and dynamic analysis of piles with practical examples of application. The book is considered a valuable tool for practicing engineers, graduate students and researchers.
Author: Adrian R. Russell
Publisher: CRC Press
ISBN: 1000115356
Category : Technology & Engineering
Languages : en
Pages : 1400
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Book Description
This book contains the contributions to the Second European Conference on Unsaturated Soils, E-UNSAT 2012, held in Napoli, Italy, in June 2012, and includes more than one hundred papers, addressing three thematic areas: experimental, modelling, and engineering.
Author: Zeinab Bayati
Publisher:
ISBN:
Category :
Languages : en
Pages : 261
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Book Description
Piles should sustain the axial loads transmitted from the supported structure without failing in bearing capacity and/or undergoing structural damage, as well as limit excessive settlements. This is verified by examining the stability (strength) and serviceability (e.g. permissible settlements) of the pile foundation. Classical design frameworks (e.g. the AASHTO LRFD specifications) only address the pile design at the strength limit state, and the pile serviceability is typically checked after determining the design bearing capacity. Therefore, a more comprehensive and practical design framework is required to account simultaneously for the strength and serviceability limit states. An analysis approach based on predicting the load-settlement response can facilitate the incorporation of both strength and serviceability limit states in the routine design of axially loaded pile foundations. The research presented in this dissertation aimed at investigating the strength and serviceability limit states for the analysis and design of axially loaded steel tubular piles. The research was conducted over three major phases of study. The first phase investigated the stability of a pile having tubular steel square section. The model considered buckling of an axially loaded pile entrenched in a continuous medium. Three-dimensional finite element analyses were conducted by modelling partially embedded piles in typical clayey and sandy soils. Three-dimensional analyses were necessary in order to account for the influence of the surrounding soil elastic medium. In order to model the pile section as closely as possible to reality, no particular restrains were imposed on the pile tip. The influence of the pile head restraint, as well as lateral soil support, on the stability of a pile was investigated. Moreover, the effect of the pile-soil interface stiffness on the value of critical buckling load (Pcr) was brought to light for design purposes. The second phase of the study verified the stability of the pile-soil system against failure by considering the nonlinearity of the surrounding soil medium. The serviceability of the pilesoil system was also examined at this stage by means of the pile load-settlement relation in order to certify satisfactory control of the allowable deformations. The objectives of the second phase of the study were met through conducting two levels of analyses: (1) Continuum medium-based finite element analyses, and (2) one-dimensional load transfer analyses. The first level of analyses involved using two- and three-dimensional finite element simulations, that incorporated classical elasto-plastic (Drucker-Prager and Mohr-Coulomb), and nonlinear elastic (Duncan-Chang and Hyperbolic) soil models. The properties of such soils are generally obtained from lab tests. In this context, a new modelling strategy was proposed for the elasto-plastic analysis of steel tubular section piles having sharp corners embedded in a granular (sandy) soil medium. The second level of analyses introduced an approach based on the simultaneous use of the load transfer and finite element analysis methods. In this framework, an elasto-plastic finite element approach was implemented in order to conduct nonlinear finite element analyses with the load-settlement response curve of axially loaded single piles. This was achieved via the nonlinear pile-soil stress-displacement curves along the pile shaft (t-z curve) and a tip (qz curve). The plasticity algorithm considered strain hardening through the pile-soil interaction (t-z and q-z) curves. The load transfer analysis showed a significantly improved characterization for the pile load-settlement behavior compared to field test results. The computation of pile settlement was also improved by reproducing the interaction curves for both pile shaft and pile tip via the use of the so-called “Sublayer” or “Overlay” method. Finally, the third phase aimed at providing a practical design framework accounting simultaneously for the pile strength and serviceability limit states. The design framework accounts for the stability (buckling) of the pile section and can be extended to the design of different types of deep foundations such as steel tubular and concrete piles.
Author: Nasser Khalili
Publisher: CRC Press
ISBN: 1315749580
Category : Technology & Engineering
Languages : en
Pages : 1872
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Book Description
Unsaturated Soils: Research and Applications contains 247 papers presented at 6th International Conference on Unsaturated Soils (UNSAT2014, Sydney, Australia, 2-4 July 2014). The two volumes provide an overview of recent experimental and theoretical advances in a wide variety of topics related to unsaturated soil mechanics:- Unsaturated Soil Behavi
Author: Toufic Elias Smayra
Publisher:
ISBN:
Category : Finite element method
Languages : en
Pages : 180
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Book Description
The analysis of axially-loaded driven piles is examined in this study using a finite-element model. The three-dimensional model accounts for the nonlinear behavior of the soil undergoing large deformation. The simulation of the penetration of the pile in the soil in the course of driving has been attempted in a previous study; the computational cost was however found excessive, thus, limiting the study to the driving of piles that are already in place (prebored piles). In this research, the penetration of the pile is simulated by gradually expanding a cavity in the soil in the form of the pile, until the desired depth of penetration is reached. The pile is then placed in the cavity to reach equilibrium. The driving of the pile is then continued using a nonlinear time-domain dynamic analysis in which the hammer blows are simulated by a periodic forcing function. A comparison is made between the response of actually (computationally) driven piles and piles driven by the expansion simulation. The response of prebored piles will also be compared with driven piles. The evolution of the state of stress and deformation in the soil and the soil resistance against the pile will be traced at all stages of the analysis.
Author: Chandrakant S. Desai
Publisher:
ISBN:
Category : Columbia Lock
Languages : en
Pages : 29
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Book Description
Columbia Lock (on the Ouachita River near Columbia, Louisiana) was designed as a gravity-type structure in which the load is transferred essentially through the foundation piles. Results obtained using Hrennikoff's method did not agree closely with observed field data in terms of the distribution of loads in the piles. The finite element (FE) method was therefore used to predict the behavior of the lock structure. As an approximation and to avoid undue amounts of manpower and computer efforts, the three-dimensional system was idealized as a structurally equivalent two-dimensional plane strain system. The FE method simulated major steps of construction including the in situ stress condition, dewatering, excavation, construction of piles and lock, backfilling, filling the lock with water, and development of uplift pressures. Nonlinear behavior of soils and of interfaces between the lock and surrounding soils and between the piles and the foundation soils was introduced into the analysis. The distribution of load in piles in the FE analysis showed improved agreement with field data in comparison with the agreement shown by Hrennikoff's method. The FE computations verified the trend shown by the observed field data that the piles on the backfill side carried an increased share of the applied load.
Author: Lawrence D. Johnson
Publisher:
ISBN:
Category : Foundations
Languages : en
Pages : 112
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 10
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Book Description
A quasi-three-dimensional finite element method of analysis is proposed for the dynamic response analysis of pile foundations that is computationally feasible for practical applications. The method uses a simplified three-dimensional wave equation for describing the dynamic response of the soil. The response of the pile foundation is computed directly without having to use pile-soil-pile interaction factors. The quasi-three-dimensional solution greatly reduces the computational time for the direct analysis of pile groups. The method is presented here for an elastic response so that itcan be validated against existing more exact elastic solutions and low-amplitude field vibration tests. The method is extended to nonlinear dynamicresponse analysis in an accompanying paper.
Author: Ahmed Mohd
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659681172
Category :
Languages : en
Pages : 52
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Book Description
The design of foundation of the building structure should be given prime attention because building foundation is in contact with the material i.e. soil which is highly complex, particulate, poly-phase, heterogeneous, and stress and strain level dependent. The real behavior of structure in contact with soil involves an interactive process beginning with the construction phase and ending with a state of balance within the structure and within the ground influenced by the structure. The analysis of such combined piled-raft foundation is very challenging because of complexities involved in the interaction between soil, pile, raft slab and structure. The interaction between the soil, foundation and the structure affects the demands (loads and displacements) imposed on structure, and the analysis of interaction between the pile, the raft and the soil of combined piled-raft foundation and upper structure can only be possible effectively by means of an advanced three-dimensional non-linear finite element technique or using a computer code based on advanced computational techniques in which proper models are incorporated to simulate soil behavior and soil-structure interaction.
