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.

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.

Numerical Analysis of Passive Pile due to Excavation

2012 ◽  
Vol 594-597 ◽  
pp. 198-201
Author(s):  
Yue Sun ◽  
Zhi Yun Wang ◽  
Yue Nan Chen ◽  
Yun Shen Jiang
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Dimensional Space ◽  
Undrained Shear Strength ◽  
General Purpose ◽  
Soil Movement ◽  
Finite Element Software ◽  
Passive Pile ◽  
Pile Response ◽  
Undrained Shear

An elasto-plastic total stress finite-element computational model is established in two dimensional space to study pile response due to excavation-induced soil movement on the basis of the general-purpose finite element software ABAQUS. And the soil is assumed to be a uniform normally consolidated clay layer. Influences of various parameters including undrained shear strength of soil, excavation depth, strut stiffness and distance from excavation on pile response are investigated. The results indicate that the excavation-induced soil movement is critical for adjacent piles and increasing the undrained shear strength of soil and distance from excavation face would be helpful to control passive pile responses.

Investigating performance of micropiled raft in foundation of power transmission line towers in cohesive soil: experimental and numerical study

2018 ◽  
Vol 55 (3) ◽  
pp. 312-328 ◽  
Author(s):  
Ali-Asghar Zekavati ◽  
Alireza Khodaverdian ◽  
Mohammad-Ali Jafari ◽  
Ahmad Hosseini
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Transmission Line ◽  
Power Transmission ◽  
Cohesive Soil ◽  
Undrained Shear Strength ◽  
Sensitivity Analyses ◽  
Power Transmission Line ◽  
Efficiency Coefficient ◽  
Undrained Shear

This paper captures the behavior of micropiled rafts in power transmission line tower foundations in cohesive soil, concentrating on their uplift performance whether due to the tower position along the line or under wind loading conditions. In this regard, first a number of micropiles were driven into the ground of a project site at the ParehSar power plant, Gilan, Iran. Compression and uplift loading tests were conducted according to relevant standards. On the basis of the field data, a three-dimensional finite element model was developed and subsequently calibrated and verified. The behavior of micropiled rafts subjected to uplift, which is a typical type of loading in foundations of 230 kV four-circuit lattice towers, was then studied by means of this model in terms of a wide-ranging parametric study. In the sensitivity analyses, the impacts of various parameters, such as micropile spacing-to-diameter (s/d) and length-to-diameter (l/d) ratios along with undrained shear strength of the soil, on the uplift capacity of an individual micropile within and out of the group were investigated. Furthermore, interaction factors were computed based on diverse values for undrained shear strength of the soil, s/d ratio, l/d ratio, and grout–soil adhesion. From design and analysis perspectives, the finite element method (FEM) outputs revealed that the efficiency coefficient of micropiled rafts during uplift can be considered equal to one. Moreover, it was found that not only does the behavior of micropiles affect the neighboring micropiles immediately adjacent to the loaded one, but it also influences those in further rows, the result of which would be considering their significance as well.

scholarly journals Rate effects on the undrained shear strength of compacted clay

2016 ◽  
Vol 56 (4) ◽  
pp. 719-731 ◽  
Author(s):  
W. Mun ◽  
T. Teixeira ◽  
M.C. Balci ◽  
J. Svoboda ◽  
J.S. McCartney
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Compacted Clay ◽  
Rate Effects ◽  
Undrained Shear

A New Procedure for Simulating Active Lateral Force in Spatially Variable Clay Modeled by Anisotropic Random Field

2015 ◽  
Vol 31 (4) ◽  
pp. 381-390
Author(s):  
Y.-G. Hu ◽  
J. Ching
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Shear Strength ◽  
Random Field ◽  
Retaining Wall ◽  
Lateral Force ◽  
Undrained Shear Strength ◽  
Undrained Shear ◽  
Element Method

AbstractA new procedure for simulating the active lateral force (Pa) is proposed for clays with anisotropic spatially variable undrained shear strength (su). With the proposed procedure, the Pa samples can be simulated without the use of the random field finite element method (RFEM). It requires only simple algebraic calculations and chart checking. Two retaining wall examples with isotropic or anisotropic random field are used to demonstrate the effectiveness of the proposed procedure.

Numerical solutions for strain-softening surrounding rock under three-dimensional principal stress condition

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sheng Yu-ming ◽  
Li Chao ◽  
Xia Ming-yao ◽  
Zou Jin-feng
Keyword(s):  
Finite Element ◽  
Principal Stress ◽  
Stress Condition ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Strength Criterion ◽  
Surrounding Rock ◽  
Flow Rule ◽  
Finite Element Software

Abstract In this study, elastoplastic model for the surrounding rock of axisymmetric circular tunnel is investigated under three-dimensional (3D) principal stress states. Novel numerical solutions for strain-softening surrounding rock were first proposed based on the modified 3D Hoek–Brown criterion and the associated flow rule. Under a 3D axisymmetric coordinate system, the distributions for stresses and displacement can be effectively determined on the basis of the redeveloped stress increment approach. The modified 3D Hoek–Brown strength criterion is also embedded into finite element software to characterize the yielding state of surrounding rock based on the modified yield surface and stress renewal algorithm. The Euler implicit constitutive integral algorithm and the consistent tangent stiffness matrix are reconstructed in terms of the 3D Hoek–Brown strength criterion. Therefore, the numerical solutions and finite element method (FEM) models for the deep buried tunnel under 3D principal stress condition are presented, so that the stability analysis of surrounding rock can be conducted in a direct and convenient way. The reliability of the proposed solutions was verified by comparison of the principal stresses obtained by the developed numerical approach and FEM model. From a practical point of view, the proposed approach can also be applied for the determination of ground response curve of the tunnel, which shows a satisfying accuracy compared with the measuring data.

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