10 research outputs found
Large-strain finite element analyses of a retrogressive landslide triggered by pile driving in sensitive clays: The Case of the 1978 Rigaud landslide in Québec
No full textA retrogressive landslide triggered by pile driving in sensitive clays in Rigaud, Quebec, is analyzed. The article presents the landslide characteristics, post-failure assessments, and potential failure mechanisms. To gain deeper insights into the triggering and propagation of failure, large-strain finite element (FE) modelling was conducted using a Eulerian-based FE approach. The FE simulations reveal that pile installation can induce localized shear band formation, ultimately leading to a large-scale landslide without the need for additional external loading. Key factors influencing the failure pattern include soil stratification, sensitivity, and the rate of post-peak shear strength degradation. The numerical modelling effectively replicates the observed field behaviour of the landslide, capturing crucial aspects such as retrogression distance, failure pattern, and the downslope displacement of failed soil masses. Although the landslide involved complex three dimensional effects and triggering conditions, the current two-dimensional large-strain FE simulations under plane strain conditions provide valuable insights into the underlying progressive failure mechanisms—insights that cannot be obtained using traditional limit equilibrium and conventional FE analyses. These findings underscore the significant role of pile driving in initiating landslides in sensitive clays and highlight the necessity of advanced numerical approaches to accurately predict and mitigate such failures.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Centrifuge modelling of gas pipelines undergoing freeze–thaw cycles
No full textFrost heave and thaw settlement are two critical factors that need to be considered in the design of chilled gas pipelines in cold regions. Due to the variation in seasonal temperature and operating conditions (e.g., pressure and temperature at the compressor stations), the pipeline temperature in some segments might vary from subzero to above-zero during winter and summer. This study examines the freezing and thawing for cyclic and constant temperatures at the pipeline and ground surfaces based on the response of fourteen model pipes tested in a geotechnical centrifuge. The cyclic (temperature) operation reduces the frost heave rate per year and causes net settlement in some cases. When the thaw bulb resulting from an above-zero operating temperature is less than the previously developed frost bulb, upward water flow occurs through the thawed soil, which could alter the pipeline–soil interaction behaviour. Five types of freeze-thaw-induced vertical displacement of the pipe have been identified from the centrifuge test results.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Modeling of large deformation behaviour of marine sensitive clays and its application to submarine slope stability analysis
No full textPost-slide investigations suggest that many large scale submarine landslides occur through marine sensitive clay layers. A nonlinear mathematical model for post-peak degradation of undrained shear strength of sensitive clay is proposed based on experimental results. A method for estimation of model parameters is presented. Incorporating the model, an analytical solution is developed to examine possible mechanisms of large scale submarine landslides. Analyses are performed for mild infinite slopes where the failure initiates from a “fully weakened zone” of soil having undrained shear strength lower than the shear stress acting parallel to the slope. The driving force, in excess of resistance, generated from the fully weakened zone is then transferred to the surrounding soil elements resulting in shear band formation due to strain-softening behaviour of sensitive clays. When the length of the fully weakened zone is greater than a critical length, catastrophic shear band propagation (self-driven without any additional external force) occurs that could result in large-scale offshore landslides. A simple design chart is developed to calculate the critical length. Compared with a previous study based on a linear post-peak shear strength degradation model (Puzrin and Germanovich 2005), the present study gives a conservative estimation of critical length for catastrophic shear band propagation.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
One- and two-dimensional finite element modelling of thaw consolidation
No full textCoupled thermo-hydro-mechanical finite element (FE) modelling of thaw consolidation is presented. One-dimensional FE analyses are performed for thaw consolidation of a soil column due to self-weight and with a combination of self-weight and surcharge, with the linear and nonlinear void ratio–effective stress–hydraulic conductivity relationships of thawed soil. The nonlinear behaviour of thawed soil is modelled using a modified Drucker–Prager Cap model, while the hydraulic conductivity is varied with the void ratio. Finally, two-dimensional FE modelling of thaw consolidation around a warm pipeline buried in permafrost is performed. The rapid reduction of the void ratio with consolidation, especially at the low-stress level, results in a wide variation of hydraulic conductivity within the thawed zone. The significantly large hydraulic conductivity of soil elements along the curved thaw front, as compared to that of thaw consolidated soil, causes the flow of water along the thaw front, instead of a vertical flow, as assumed in previous 1-D thaw consolidation modelling of buried pipelines.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Numerical modelling of pile jacking in highly sensitive clays
No full textThis paper presents large deformation finite element (FE) modelling of penetration of solid cylindrical piles into highly sensitive soft clay. The simulations are performed using a Coupled Eulerian-Lagrangian (CEL) FE modeling technique. The pile is penetrated at a constant rate, and the analyses are performed for undrained conditions to simulate the response during penetration. The soil model considers the effects of strain softening and strain rate on the undrained shear strength. The FE calculated results are compared with available analytical and numerical solutions for idealized soil profiles. Simulations are also performed for two instrumented piles previously installed into highly sensitive clay at Saint-Alban in Québec, Canada. The installation-induced changes in stresses, degradation of undrained shear strength, and tip resistance obtained from FE analyses are consistent with the field test results. Large plastic shear strains develop near the pile, which can significantly remould the soil near the pile shaft. A parametric study shows that a quicker post-peak degradation of undrained shear strength of highly sensitive clay creates a smaller zone of high plastic shear strain near the pile, while the plastic zone is wider for low- to non-sensitive clays.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Centrifuge Modeling of Glide Block and Out-runner Block Impact on Submarine Pipelines
No full text
Abstract
This paper presents the results of a series of physical experiments to quantify the drag force on a submarine pipeline caused by a glide block or an out-runner block impact normal to the pipe axis. The experiments were carried out in a geotechnical centrifuge at C-CORE under submerged conditions at a centrifugal force of 30 times the Earth's gravity (i.e. N = 30) and simulated steady and uniform impact velocities ranging between 0.1 and 1.3 m/s with the soil blocks being approximately 5 m in height in prototype scale. The soil blocks were made of kaolin clay consolidated to have undrained shear strengths ranging between about 4 and 6 kPa. The diameter of the model pipes were 6.35 and 9.5 mm corresponding to about 0.19 and 0.29 m in prototype terms. The shear strain rates, defined as the ratio of impact velocity to pipe diameter, in the centrifuge model are N times higher than that in the prototype. The shear rates simulated ranged from about 10 to 136 reciprocal seconds. The paper presents a method for estimating block impact drag force on submarine pipelines based on the results of the centrifuge experiments.
Introduction
A submarine pipeline is a system of connected sections of pipe that usually transports crude oil or refined hydrocarbons. The pipe is laid on or buried in the seafloor. It typically ranges from 0.1 m to 1.0 m in diameter. The total length of a pipeline is dictated by the distances between the production platform(s) and the onshore or offshore destination(s) and by the route which poses the least risk in terms of offshore geohazards. Submarine landslides and the associated mass movement can potentially have devastating consequences on seafloor installations such as pipelines, flow lines, well systems, cables, etc. Submarine landslides occur frequently on both passive and active continental margins and slopes, releasing sediment volumes that may travel distances as long as hundreds of kilometres on gentle slopes (0.5 to 3°) over the course of less than an hour to several days [1]. The movement of landslide and the released sediment volumes in general terms are so called ‘density flows’. From the initiation to deposition, density flows undergo complex processes that depend on many factors such as the composition, strength characteristics and properties, terrain topography, etc.
Geohazards in an offshore oil and gas perspective can be due to local and/or regional site and soil conditions having the potential to develop into failure events causing loss of life and damage to the environment or field installations. Triggering of these events can be caused by natural geological processes or by man's activities, as outlined in a recent state of-the-art review [2]. Research on understanding the mechanisms behind and the risks posed by submarine slides has intensified in the past decade [e.g. 3, 4-10], mainly because of the increasing number of deep-water petroleum fields that have been discovered and in some cases developed. Production from offshore fields in areas with earlier sliding activity is ongoing in the Norwegian margin, Gulf of Mexico, offshore Brazil, the Caspian Sea and West Africa [11].
Estimating magnitude of the drag forces on pipelines caused by density flow impact is an important design consideration in offshore engineering. For buried pipelines in cohesive soils in slowly moving unstable slopes, the available methods seem to provide more or less similar estimates for the drag force normal to the pipe axis. However, this is not the case for estimates of the drag force parallel to the pipe axis [2]. In cohesive soils, the magnitude of the drag force is a function of the rate at which the soil is sheared during interaction with the pipe. Recent works by Zakeri et al. [1, 12-14] provide a method for estimating drag forces caused by clay-rich debris flow (fully remoulded and fluidized density flow) impacting a pipeline normal to its axis. Later, the work was extended to cover all angles of impact [15].
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Finite Element Modeling of Lateral Pipeline-Soil Interactions in Dense Sand
No full textFinite element (FE) analyses of pipeline-soil interaction for pipelines buried in dense sand subjected to lateral ground displacements are presented in this paper. Analysis is performed using the Arbitrary Lagrangian-Eulerian (ALE) method available in Abaqus/Explicit FE software. The pipeline-soil interaction analysis is performed in the plane strain condition using the Mohr-Coulomb (MC) and a modified Mohr-Coulomb (MMC) models. The MMC model considers a number of important features of stress-strain and volume change behaviour of dense sand including the nonlinear pre- and post-peak behaviour with a smooth transition and the variation of the angle of internal friction and dilation angle with plastic shear strain, loading conditions (triaxial or plane strain), density and mean effective stress. Comparing FE and experimental results, it is shown that the MMC model can better simulate the force-displacement response for a wide range of lateral displacements of the pipe for different burial depths, although the peak force on the pipe could be matched using the MC model. Examining the progressive development of zones of large inelastic shear deformation (shear bands), it is shown that the mobilized angle of internal friction and dilation angle vary along the length of the shear band, however constant values are used in the MC model. A comprehensive parametric study is also performed to investigate the effects of pipeline diameter, burial depth and soil properties. Many important aspects in the force-displacement curves and failure mechanisms are explained using the present FE analyses.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Probing compression versus stretch activated recruitment of cortical actin and apical junction proteins using mechanical stimulations of suspended doublets
No full textWe report an experimental approach to study the mechanosensitivity of cell-cell contact upon mechanical stimulation in suspended cell-doublets. The doublet is placed astride an hourglass aperture, and a hydrodynamic force is selectively exerted on only one of the cells. The geometry of the device concentrates the mechanical shear over the junction area. Together with mechanical shear, the system also allows confocal quantitative live imaging of the recruitment of junction proteins (e.g., E-cadherin, ZO-1, occludin, and actin). We observed the time sequence over which proteins were recruited to the stretched region of the contact. The compressed side of the contact showed no response. We demonstrated how this mechanism polarizes the stress-induced recruitment of junctional components within one single junction. Finally, we demonstrated that stabilizing the actin cortex dynamics abolishes the mechanosensitive response of the junction. Our experimental design provides an original approach to study the role of mechanical force at a cell-cell contact with unprecedented control over stress application and quantitative optical analysis. (C) 2018 Author(s)
Numerically efficient modeling of CNT transistors with ballistic and non-ballistic effects for circuit simulation
No full textThis paper presents an efficient carbon nanotube (CNT) transistor modeling technique which is based on cubic spline approximation of the non-equilibrium mobile charge density. The approximation facilitates the solution of the selfconsistent voltage equation in a carbon nanotube so that calculation of the CNT drain-source current is accelerated by at least two orders of magnitude. A salient feature of the proposed technique is its ability to incorporate both ballistic and nonballistic transport effects without a significant computational cost. The proposed models have been extensively validated against reported CNT ballistic and non-ballistic transport theories and experimental results
