scholarly journals Generalized framework to predict undrained uplift capacity of buried offshore pipelines

2016 ◽  
Vol 53 (11) ◽  
pp. 1841-1852 ◽  
Author(s):  
Shubhrajit Maitra ◽  
Santiram Chatterjee ◽  
Deepankar Choudhury
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Small Strain ◽  
Unit Weight ◽  
Soil Parameters ◽  
Burial Depth ◽  
Uplift Capacity ◽  
Finite Element Analyses ◽  
Simple Method ◽  
Offshore Pipelines

Estimation of undrained uplift capacity is essential for the determination of optimal burial depth of buried offshore pipelines. However, a generalized prediction model that incorporates various factors influencing this capacity is scarce in the literature. In this paper, results from a series of small-strain finite element analyses are presented that explore the effects of pipe embedment, pipe–soil interface roughness, interface tensile capacity, soil shear strength, and unit weight on pipe uplift response. From the study, a simple method to predict the undrained upheaval resistance of buried pipelines for any practical range of pipeline and soil parameters is proposed. Factors associated with transition in failure mechanism with embedment are also examined. The numerical model is validated by comparing the results with available analytical and experimental data. Large-deformation finite element analyses have also been performed independently for a few cases to justify the applicability of small-strain methods in modelling pipe upheaval. Accuracy of the model for generalized shear strength profile is then examined by considering practical values of parameters over broad ranges. The proposed methodology gives results with maximum error less than 8% for all ranges of parameters and hence can be adopted in design practices.

Finite Element Modeling of a Mechanically Stabilized Earth Trial Wall

2021 ◽  
pp. 036119812110164
Author(s):  
Andrew Lees ◽  
Michael Dobie
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Retaining Wall ◽  
Back Analysis ◽  
Soil Parameters ◽  
Failure Behavior ◽  
Valuable Insight ◽  
Deformation And Failure ◽  
First Case ◽  
Soil Shear Strength

Polymer geogrid reinforced soil retaining walls have become commonplace, with routine design generally carried out by limiting equilibrium methods. Finite element analysis (FEA) is becoming more widely used to assess the likely deformation behavior of these structures, although in many cases such analyses over-predict deformation compared with monitored structures. Back-analysis of unit tests and instrumented walls improves the techniques and models used in FEA to represent the soil fill, reinforcement and composite behavior caused by the stabilization effect of the geogrid apertures on the soil particles. This composite behavior is most representatively modeled as enhanced soil shear strength. The back-analysis of two test cases provides valuable insight into the benefits of this approach. In the first case, a unit cell was set up such that one side could yield thereby reaching the active earth pressure state. Using FEA a test without geogrid was modeled to help establish appropriate soil parameters. These parameters were then used to back-analyze a test with geogrid present. Simply using the tensile properties of the geogrid over-predicted the yield pressure but using an enhanced soil shear strength gave a satisfactory comparison with the measured result. In the second case a trial retaining wall was back-analyzed to investigate both deformation and failure, the failure induced by cutting the geogrid after construction using heated wires. The closest fit to the actual deformation and failure behavior was provided by using enhanced fill shear strength.

Reliability analysis of static liquefaction of loose sand using the random finite element method

2015 ◽  
Vol 32 (7) ◽  
pp. 2100-2119 ◽  
Author(s):  
Ali Johari ◽  
Jaber Rezvani Pour ◽  
Akbar Javadi
Keyword(s):  
Finite Element ◽  
Pressure Ratio ◽  
Monotonic Loading ◽  
Unit Weight ◽  
Soil Parameters ◽  
Loose Sand ◽  
Element Analysis ◽  
Content Type ◽  
Static Liquefaction ◽  
Random Finite Element

Purpose – Liquefaction of soils is defined as significant reduction in shear strength and stiffness due to increase in pore water pressure. This phenomenon can occur in static (monotonic) or dynamic loading patterns. However, in each pattern, the inherent variability of the soil parameters indicates that this problem is of a probabilistic nature rather than being deterministic. The purpose of this paper is to present a method, based on random finite element method, for reliability assessment of static liquefaction of saturated loose sand under monotonic loading. Design/methodology/approach – The random finite element analysis is used for reliability assessment of static liquefaction of saturated loose sand under monotonic loading. The soil behavior is modeled by an elasto-plastic effective stress constitutive model. Independent soil parameters including saturated unit weight, peak friction angle and initial plastic shear modulus are selected as stochastic parameters which are modeled using a truncated normal probability density function (pdf). Findings – The probability of liquefaction is assessed by pdf of modified pore pressure ratio at each depth. For this purpose pore pressure ratio is modified for monotonic loading of soil. It is shown that the saturated unit weight is the most effective parameter, within the selected stochastic parameters, influencing the static soil liquefaction. Originality/value – This research focuses on the reliability analysis of static liquefaction potential of sandy soils. Three independent soil parameters including saturated unit weight, peak friction angle and initial plastic shear modulus are considered as stochastic input parameters. A computer model, coded in MATLAB, is developed for the random finite element analysis. For modeling of the soil behavior, a specific elasto-plastic effective stress constitutive model (UBCSAND) was used.

Modelling the applied vertical stress and settlement relationship of shallow foundations in saturated and unsaturated sands

2011 ◽  
Vol 48 (3) ◽  
pp. 425-438 ◽  
Author(s):  
Won Taek Oh ◽  
Sai K. Vanapalli
Keyword(s):  
Finite Element ◽  
Bearing Capacity ◽  
Characteristic Curve ◽  
Friction Angle ◽  
Vertical Stress ◽  
Shallow Foundations ◽  
Surface Settlement ◽  
Soil Parameters ◽  
Finite Element Analyses ◽  
Unsaturated Sands

The bearing capacity and settlement of foundations are determined experimentally or modelled numerically based on conventional soil mechanics for saturated soils. In both methods, bearing capacity and settlement are estimated based on the applied vertical stress versus surface settlement relationship. These methods are also conventionally used for soils that are in an unsaturated condition, ignoring the contribution of matric suction. In this study, a methodology is proposed to estimate the bearing capacity and settlement of shallow foundations in unsaturated sands by predicting the applied vertical stress versus surface settlement relationship. The proposed method requires soil parameters obtained under only saturated conditions (i.e., effective cohesion, effective internal friction angle, and modulus of subgrade reaction from model footing test) along with the soil-water characteristic curve (SWCC). In addition, finite element analyses are undertaken to simulate the applied vertical stress versus surface settlement relationship for unsaturated sands. The proposed method and finite element analyses are performed using an elastic – perfectly plastic model. The predicted bearing capacities and settlements from the proposed method and finite element analyses are compared with published model footing test results. There is good agreement between measured and predicted results.

Estimation of Stress Intensity Factors due To Welding Residual Stresses for Circumferentially Cracked Pipes

2012 ◽  
Author(s):  
Chang-Young Oh ◽  
Ji-Soo Kim ◽  
Yun-Jae Kim ◽  
Young-Jin Oh ◽  
Kyoungsoo Lee ◽  
...  
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Residual Stresses ◽  
Stress Intensity Factors ◽  
Finite Element Analyses ◽  
Intensity Factors ◽  
Crack Face ◽  
Simple Method ◽  
Weld Geometry ◽  
Nonlinear Stress

This paper proposes a simple method to estimate stress intensity factors due to welding residual stresses. In this study, finite element analyses for circumferentially cracked pipe are performed to calculate stress intensity factors. Four cracked geometries and two types of weld geometry are considered. KI-solutions for the nonlinear stress distribution on the crack face were determined in accordance with codes and standards. The results are compared with KI-solutions from finite element results. It is found that proposed simple method agrees well with FE results.

Finite element modeling of partially embedded pipelines in clay seabed using Coupled Eulerian–Lagrangian method

2015 ◽  
Vol 52 (1) ◽  
pp. 58-72 ◽  
Author(s):  
Sujan Dutta ◽  
Bipul Hawlader ◽  
Ryan Phillips
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Strain Rate ◽  
Deep Water ◽  
Strain Softening ◽  
Mesh Size ◽  
Undrained Shear Strength ◽  
Band Formation ◽  
Offshore Pipelines ◽  
Undrained Shear

Vertical seabed penetration and lateral movement of deep-water offshore pipelines are simulated using the Coupled Eulerian–Lagrangian (CEL) approach in Abaqus finite element (FE) software. Abaqus CEL has been used in some previous studies to simulate large-deformation behavior of offshore pipelines; however, the effects of strain rate and strain-softening on undrained shear strength (su) have not been considered. In this study, the effects of these factors are critically examined. The available built-in models in Abaqus CEL cannot account for these factors directly, especially the strain rate; therefore, the development of user subroutines is required. In the present study, a simple but realistic soil constitutive model (published by Zhou and Randolph in 2007) that considers the effects of strain rate and strain-softening on su is implemented in Abaqus CEL. The effects of FE mesh size and shear band formation on penetration resistance are discussed based on a comprehensive FE simulation. Lateral analyses are performed for “light” and “heavy” pipes in clay seabed having a linearly increasing undrained shear strength profile for smooth and rough pipe–soil interface conditions. The FE results are compared with previous theoretical, numerical, and centrifuge test results. Based on the present FE analyses, it is shown that, similar to the remeshing and interpolation techniques with small strain (RITSS) technique developed at the The University of Western Australia, the Abaqus CEL can successfully simulate the response of partially embedded pipelines in deep-water clay seabed, provided strain rate and softening dependent clay models are implemented. A methodology to implement such a model using Abaqus user subroutine is also presented.

A method for the measurement of residual stresses using a fracture mechanics approach

1989 ◽  
Vol 24 (1) ◽  
pp. 23-30 ◽  
Author(s):  
K J Kang ◽  
J H Song ◽  
Y Y Earmme
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Distribution ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Residual Stress Distribution ◽  
The State ◽  
Two Dimensional ◽  
Finite Element Analyses ◽  
Simple Method

A simple method for measuring residual stresses in a plate is described. In this method residual stresses are evaluated using a fracture mechanics approach, that is, the strains or displacements measured at a point on the edge of a plate as a crack is introduced and extended from the edge are used to deduce the state of stresses that existed in the uncracked plate. Through finite element analyses and experiments this method is shown to be valid and effective for measuring the two-dimensional residual stress distribution of a welded plate.

scholarly journals Numerical Modeling of Pipe-Soil Interaction Under Transverse Direction

2014 ◽  
Author(s):  
Bahar Farhadi ◽  
Ron C. K. Wong
Keyword(s):  
Finite Element ◽  
Transverse Direction ◽  
Soil Parameters ◽  
Burial Depth ◽  
Soil Behavior ◽  
Finite Element Software ◽  
Failure Envelopes ◽  
Winkler Method ◽  
Pipe Deflection ◽  
Resultant Forces

Based on the Winkler method, a pipe can be treated as a beam, and pipe-soil interactions can be represented by soil springs in the axial, horizontal and vertical directions. Pipe deflection and resultant forces are correlated by coefficient K in the equation F=Kδ, where F is the resultant force and δ is the pipe displacement. This paper studies pipe-soil interaction for pipelines buried in clay and sand subjected to displacements in oblique directions. The objective is to measure the effect of soil parameters on coefficient K as well as the maximum soil resistance. Pipe-soil behavior has been studied using the finite element software ABAQUS/CAE. There are 48 models in total with varying soil parameters, pipe burial depth and pipe-soil interaction friction for the investigation of the effect of each variable on pipe-soil behavior. In addition, the finite element results have been compared to the analytical results from American Lifelines Alliance guideline (ALA, 2001) and proposed failure envelopes in previous studies.

Strain Softening and Rate Effects on Soil Shear Strength in Modeling of Vertical Penetration of Offshore Pipelines

2012 ◽  
Author(s):  
Sujan Dutta ◽  
Bipul Hawlader ◽  
Ryan Phillips
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Strain Softening ◽  
Undrained Shear Strength ◽  
Lateral Movement ◽  
Offshore Pipelines ◽  
Finite Element Software ◽  
Deformation Problem ◽  
Rate Effects ◽  
Undrained Shear

Offshore pipelines play a vital role in the transportation of hydrocarbon. In deep seas, pipelines laid on the seabed usually penetrate into the soil a certain amount. These pipelines might experience significant lateral movement during the operational period. The resistance to lateral movement depends on vertical penetration and berm formation around the pipe. Vertical penetration is a large deformation problem. Finite element modeling of vertical penetration of offshore pipeline in soft clay seabed in deep water is presented in this study. The modeling was performed using ABAQUS finite element software. Soil was modeled in an Eulerian framework and the pipe in a Lagrangian framework. Strain softening behavior and strain rate effects on undrained shear strength of clay was incorporated in ABAQUS FE software using user subroutines written in FORTRAN. The variation of undrained shear strength with depth is also considered. The results are compared with centrifuge test results and also with available solutions.

Effect of Preloading on the Response of a Shallow Skirted Foundation

2014 ◽  
Author(s):  
Cristina Vulpe ◽  
Susan Gourvenec
Keyword(s):  
Finite Element ◽  
Bearing Capacity ◽  
Small Strain ◽  
Significant Gain ◽  
Finite Element Analyses ◽  
Foundation Design ◽  
Degree Of Consolidation ◽  
Insight Into

The effect of preloading on the vertical settlement and bearing capacity of a circular skirted foundation was investigated as a function of relative preload and degree of consolidation by means of small strain finite element analyses. Significant gain in bearing capacity was observed for practical levels of preloads and duration of consolidation, offering an insight into potential efficiencies in foundation design.

scholarly journals Effects of Parameter Uncertainties on Interaction between Submarine Telecommunication Cables and Lateral Seabed Movements

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Cuiwei Fu ◽  
Xiaogang Qin ◽  
Yu Wang
Keyword(s):  
Finite Element ◽  
Spatial Variability ◽  
Fe Analysis ◽  
Unit Weight ◽  
Soil Parameters ◽  
Environment Interaction ◽  
Parameter Uncertainties ◽  
Long Distance ◽  
Damage Probability ◽  
Cable Damage

Submarine telecommunication cables are the physical backbone of the Internet. They are often buried shallowly beneath seabed and affected by seabed movements. Due to the long distance of cables and the complexity of submarine environment, interaction between cables and seabed movements inevitably involves various parameter uncertainties. However, effects of parameter uncertainties on submarine cable responses to seabed movements have not been fully investigated. This paper aims to address this problem using random finite element method (RFEM) that integrates finite element (FE) analysis with Monte Carlo simulation (MCS). First, deterministic FE analysis is performed to investigate cable responses to lateral seabed movements. Then MCS is implemented to study the effects of parameter uncertainties on cable responses. Statistical analysis of the MCS results is performed to prioritize the effects of parameter uncertainties on cable damage probability. Random field is also used to model spatial variability of soil parameters. Effect of the correlation length on cable damage probability is investigated. The results show that uncertainty of the anchored cable length La has the most significant effect on cable damage probability, while the effects of uncertainties in soil friction angle ϕ and effective unit weight γ′ are minor. Ignoring spatial variability of soil parameters may lead to significant misjudgment of cable damage risk.

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