Numerical Investigations of the Extraction of Submerged Foundations by Coupled CFD-DEM

2017 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe ◽  
Alice Hager ◽  
Christoph Goniva ◽  
Christoph Kloss
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Solid Phase ◽  
Water Pressure ◽  
Discrete Element ◽  
Offshore Structures ◽  
Spherical Particles ◽  
Embedment Depth ◽  
Sea Bed ◽  
Element Method

Offshore structures are founded on submerged foundations. The excavation of submerged foundations in the sea bed is a difficult task to accomplish when it comes to the decommissioning of these offshore structures. The extraction resistance is a lot higher than the pressure acting on the structure due to hydrostatic pressure, earth pressure and its self-weight. Once the extraction begins, a negative pore water pressure is created until inflowing pore water compensates this negative pore water pressure. This depression is hindering the extraction of the submerged foundation. Additionally, the resistance is dependent on the embedment depth of the structure, the soil properties as well as the extraction velocity, which influences the dimension of the negative pore water pressure. The numerical investigation of this dynamic problem is a limitation for continuum based approaches like the Finite Element Method (FEM) due to the occurring large deformations. These results from the soil bed failing under the movement of the structure and hence starting to flow. Additionally, in order to estimate the created depression, the investigation of the water-soil-interaction is crucial, as the change of the pore water pressure plays a significant role. Therefore, it is necessary to analyze the behavior of the soil particles and the pore water pressure. In order to do this, a coupled Euler-Lagrange approach, namely the combination of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), is used. In these simulations on one hand, the liquid phase, e.g. the water, is considered as a continuum, while on the other hand, for the solid phase, e.g. the soil, a particle representation is chosen. Hence, it is possible to compute the particle-particle — as well as the fluid-particle-interactions. The calculations are carried out with the open source software package CFDEMcoupling®, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. This paper introduces the coupled CFD-DEM approach to simulate the extraction of a submerged plate in the soil bed. In this work, the soil grains are idealized by spherical particles of different diameters. In order to consider effects of dilatancy and contractancy in the soil bed, different relative densities are investigated. Additionally, a variation of the extraction velocity of the plate is carried out to examine the dependence on the creation of negative pore water pressure. For each case, the extraction resistance is calculated. The flow velocity and the pressure distribution in the vicinity of the structure are analyzed.

Experimental Study of the Influence of the Pore Water Pressure Evolution and the Shear Band Formation on the Extraction Resistance of Submerged Anchor Plates

2018 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe
Keyword(s):  
Experimental Study ◽  
Shear Band ◽  
Pore Water ◽  
High Speed ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Offshore Structures ◽  
Shear Band Formation ◽  
Band Formation ◽  
Anchor Plates

Floating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.

Softening of the Clayey Seabed Foundation due to Earthquakes

1988 ◽  
Vol 110 (1) ◽  
pp. 17-23 ◽  
Author(s):  
N. Mori ◽  
Y. Ishikawa ◽  
A. Hirayama ◽  
K. Tamaoki ◽  
H. Kobayashi
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Offshore Structures ◽  
Model Tests ◽  
Shaking Table ◽  
Earthquake Response ◽  
Response Analysis ◽  
Earthquake Response Analysis

Offshore structures are subjected to repeated loads from earthquakes and waves which may cause softening of the clayey seabed foundation. Carrying out a series of model tests on a shaking table, the following results are obtained. Settlement and inclination of a model of the base-part of the structure occur when the excess pore water pressure beneath the model rises to about 5 percent of the initial confining pressure. The earthquake response analysis even taking the nonlinearity of the soil into account cannot predict the results of the model test when the pore water pressure does generate and accumulate. Model tests show that the values of the pore water pressure are about twice as large as those predicted by calculation. From these results, rough evaluation of earthquake stability of the clayey seabed under offshore structures are obtained.

Effect of Pore Water Pressure on Response of Asphalt Concrete

2017 ◽  
Vol 2631 (1) ◽  
pp. 114-122 ◽  
Author(s):  
Maryam Shakiba ◽  
Masoud K. Darabi ◽  
Dallas N. Little
Keyword(s):  
Pore Water ◽  
Asphalt Concrete ◽  
Pore Water Pressure ◽  
Solid Phase ◽  
Water Pressure ◽  
Moisture Diffusion ◽  
Traffic Loading ◽  
Constitutive Relationships ◽  
Nonlinear Viscoelastic ◽  
Asphalt Concrete Pavement

Rapid traffic loading induces pore water pressure inside partially or fully saturated interconnected cracks and voids of asphalt concrete. The induced pore pressure contributes extra stresses within the pavement and accelerates crack evolution and propagation. Crack propagation facilitates diffusion of moisture through the solid phase and accelerates the degradation of the time-dependent stiffness and strength of asphalt concrete. Therefore, it is imperative to consider the coupled effects of pore water pressure, moisture diffusion, and mechanical loading on asphalt concrete pavement. The effect of pore water pressure was considered by using the effective stress concept inside deformable media. Biot’s approach was used and coupled to the nonlinear viscoelastic and viscodamage (moisture and mechanical) constitutive relationships for asphalt concrete. The models were implemented in PANDA, a finite element code developed at Texas A&M University. Capabilities of the proposed framework and constitutive relationships were demonstrated through the simulation of several realistic microstructural representations of asphalt concrete. The results of numerical simulations demonstrated how the effect of pore water pressure can intensify damage within asphalt concrete and reduce its strength. Therefore, this outcome emphasizes the importance of incorporating the effect of pore water pressure in investigating the response of asphalt concrete.

Consolidation modelling of soils under the test embankment at Chek Lap Kok International Airport in Hong Kong using a simplified finite element method

2001 ◽  
Vol 38 (2) ◽  
pp. 349-363 ◽  
Author(s):  
Guofu Zhu ◽  
Jian-Hua Yin ◽  
James Graham
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hong Kong ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
International Airport ◽  
Geological Conditions ◽  
Test Embankment ◽  
Element Method

This paper models consolidation of the foundation soils under a test embankment at the new Chek Lap Kok International Airport in Hong Kong. The modelling used a simplified finite element method and material parameters derived from results in the original site investigation report. Various features that need to be considered in applying the simplified method are illustrated through this case study. Good predictions of settlement results are obtained. Relatively large discrepancies in pore-water pressure predictions suggest that the nonlinear nature of hydraulic conductivity needs to be taken into account when large compressions are likely to occur. Geological conditions are shown to be a key factor in successful modelling of consolidation behaviour.Key words: consolidation, pore-water pressure, case modelling, finite element method, vertical drains, settlement.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

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