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Pipeline plough behaviour has been investigated by means of reduced scale physical model testing. A testing programme was devised to investigate the influence of permeability, relative density, and plough depth on the associated tow force measured during ploughing over a range of velocities in saturated granular material. An increase in tow force with velocity was found during all of the tests and the results have been compared to previously developed analytical models. A new empirical equation has been developed to describe the change in tow force with velocity for a variety of model siliceous sand conditions. Application of this new approach to full-scale ploughing requires consideration of scaling effects and the use of appropriate input parameters determined to replicate field conditions. Key words: pipeline ploughing, rate effects, dilation, low effective stress. Le comportement en labourage d'un pipeline a ete etudie a l'aide d'essais realises sur un modele physique a l'echelle reduite. Un programme d'essai a ete elabore dans le but d'etudier l'influence de la permeabilite, de la densite relative et de la profondeur du labourage sur la force de tire associee mesuree durant le labourage a differentes vitesses dans un materiel granulaire sature. Une augmentation de la force de tire avec la vitesse a ete observee durant tous les essais, et les resultats ont ete compares avec des modeles analytiques developpes precedemment. Une nouvelle equation empirique a ete developpee pour decrire les changements dans la force de tire selon la vitesse, et ce pour une variete de conditions de sable de silice modelise. L'application a l'echelle reelle de cette nouvelle approche necessite de considerer les effets d'echelle et d'utiliser les parametres d'entree appropries, qui sont determines dans le but de repliquer les conditions de terrain. Mots-cles: labourage de pipeline, effets de taux, dilatation, faible contrainte effective. [Traduit par la Redaction], Introduction The oil and gas industry often buries offshore pipelines under the sea bed (cover depths 1.5 m are common) as this provides protection against mechanical impact, shelter against hydrodynamic [...]

Offshore pipelines can be buried in the seabed by ploughing a trench, placing the pipe at its base, and then backfilling. The presence of sand waves or megaripples on the seabed surface can affect the progress of the plough and prevent the plough from generating a level trench with a uniform trench depth. A calculation method has been presented that makes assumptions about the motion of the plough to predict the kinematics of ploughs through regions of nonuniform seabeds. Results from the calculation methodology are compared with those from small-scale model tests with good agreement, and the detailed kinematics of ploughs are then examined. The calculation method suggests that as a plough moves through a sand-wave field, the oscillation of the plough about the skids results in the trench base being formed alternately by the share tip and heel. The new method allows prediction of likely offshore plough performance given known plough geometry, sand wavelength, and wave amplitude and may be used as a tool for assessing the feasibility of pipeline ploughing in zones of sand waves or megaripples. Key wards: pipeline plough kinematics, seabed, sand waves, trenching. Les pipelines en mer peuvent etre enfouis dans les fonds marins dans une tranchee labouree. Le tuyau est place a la base de la tranchee et ensuite est remblaye. La presence de vagues de sable ou de mega-ondulations sur la surface du fond marin peul affecter la progression de la charrue et empecher la charrue de creuser une tranchee au niveau el de profondeur uniforme. Une methode de calcul qui permet d'elablir des suppositions sur le mouvement de la charrue a ete presentee afin de predire la cinetique des charrues a travers les /ones ou le fond marin n'est pas uniforme. Les resultats de cette methode de calcul sont compares a des resultats obtenus lors d'essais a petite echelle. Comme les resultats concordent bien. la cinetique detaillee de la charrue est ensuite examinee. La methode de calcul suggere qu'a mesure que la charrue avance a travers un champ de vagues de sable, les oscillations de la charrue font en sorte que la tranchee est formee par la pointe et le talon du soc, en alternance. La nouvelle methode permet de predire la performance probable d'une charrue marine en connaissant la geometrie de la charrue, la longueur d'onde et l'amplitude des vagues de sable, et ainsi cette methode peut etre utilisee comme outil pour evaluer la faisabilite du labourage de pipelines dans des zones de vagues de sable et de mega-ondulations. Mots-cles : cinetique de labourage de pipeline, fond marin, vagues de sable, tranchee. [Traduit par la Redaction], Introduction Offshore pipelines are buried to protect them from thermal expansion and external loadings. Burial is often achieved by ploughing a trench in the seabed into which the pipeline is [...]

Offshore pipelines are often buried in the seabed by ploughing a trench, placing the pipe at the base, and then backfilling. The ploughing operation is critical in terms of cost and project lime, with increased risk due to uncertain soil conditions or geohazards. One problem that can be encountered is the presence of sand waves or megaripples on the seabed surface. This may affect the progress of the plough, prevent the plough from generating a level trench or modify the size of The spoil heaps for backfilling. These aspects have been investigated by conducting a series of small-scale model tests in the laboratory. These have revealed information about the plough kinematics and the resulting trench conditions when ploughing in sand waves with different wavelengths and amplitudes. It is shown that it may be possible to plough through regions of sand waves and estimate likely plough performance by knowing the sand wavelength and amplitude relative to the plough size. Key words: pipeline plough, seabed, megaripples, sand waves, trench depth, drag forces. Les pipelines en mer sont souvent enfouis dans les fonds marins dans une tranchee labouree, el le tuyau est place a la base et ensuite remblaye. L'operation de labourage est critique en termes de couts et de temps pour le projet, en plus des risques accrus causes par des conditions de sol incertaines ou geo-dangers. Un de ces problemes pouvant se produire est la presence de vagues de sable ou de mega-ondulations sur la surface du fond marin. Ces ondulations peuvent affecter la progression de la charrue, empecher la charrue de creuser une tranchee au niveau, ou bien modifier la dimension des empilements de rejets utilises par la suite pour le remblayage. Ces aspects ont ete evalues par une serie d'essais a l'echelle reduite au laboratoire. Ces essais out revele des informations sur la cinetique du labourage ainsi que sur les conditions de la tranchee produite lors du labourage dans des vagues de sables de differentes longueurs d'onde et d'amplitudes. Il a ete demontre qu'il est possible de labourer a travers des zones de vagues de sable et d'estimer les performances de labourage probables en connaissant la longueur d'onde et l'amplitude du sable par rapport a la dimension de la charrue. Mots-des : charrue a pipeline, fond marin, mega-ondulations, vagues de sable, profondeur de tranchee, force de trainee. [Traduit par la Redaction], Introduction Offshore pipelines are frequently buried beneath the seabed to provide protection from external loadings and prevent lateral or upward movements during thermal expansion (Nielsen et al. 1990; Cathie et [...]

A series of centrifuge model tests is reported that investigated the effects of foundation position on the interaction of reverse, dip-slip faults with shallow foundations resting on sand. The model tests have allowed careful examination of both the soil and foundation deformation as a shear localization (fault) propagates through a 15 m thick sand layer for fault throws up to 5 m. By comparing results of the tests with foundations present with those from a 'free-field' test, the effect of the foundation on the faulting pattern has been observed directly. The response of the foundation is very sensitive to the exact position of the fault and even when the fault emerged remotely from the foundation it sometimes caused significant foundation movements. Detailed results are presented for the tests and it is suggested that these results are used as: (1) indications of likely foundation--soil--fault interaction mechanisms; and (2) to allow future validation of numerical models for similar problems. Finally, foundation rotations measured during the fault-foundation interaction tests are compared to those predicted using a simple method based on free-field soil displacements. This simple method makes surprisingly good prediction of maximum fault rotations for different throws. DOI: 10.1061/(ASCE)GT.1943-5606.0000072 CE Database subject headings: Soil-structure interaction; Shallow foundations; Earthquake engineering; Geological faults; Sand.