Abstract Flowlines and pipelines installed in deep-sea waters are submitted to axial and lateral loads due to the effects of flow stoppages and starts, thermal influences and internal pressure. To study the phenomenon of soilpipeline interaction, a physical model was used and special emphasis was given to the application of large horizontal loads coupled with vertical loads. This paper focuses on the experimental results of two sideswipetype tests with a pipeline model in a very soft soil with undrained shear strength of ~3kPa. Experimental yield envelopes are also included. The experimental tests revealed that for very shallow pipe embedments the maximum horizontal load is obtained for a value of V/Vmax = 0.5, and that for larger embedments this value is in the order of 0.2. 1. Introduction The design of pipelines installed in deep-sea waters is still a challenge for offshore geotechnical engineering. Flowlines and pipelines can be submitted to combined vertical and horizontal loads, thermal expansion and internal pressure, among other loadings. The pipeline laying installation is not a guarantee of their penetration embedment and, consequently, their stability. The problem of untrenched pipelines has been studied and reported in literature (Murf et al., 1989; Brennodden and Stokkeland, 1992; Cassidy, 2004; Fontaine et al., 2004; Cathie et al., 2005; Zhang and Erbrich, 2005; Cheuk and Bolton, 2006; Dendani and Jaeck, 2007; Bruton et al., 2008; Tian and Cassidy, 2008; among others). A physical model was used to understand the mechanisms of interaction between pipe and soil through a lateral visualisation, and then to simulate the pipe response under combined vertical and horizontal loads. This paper concentrates on the results obtained using sideswipe tests with large and short horizontal displacements, in order to obtain an experimental yielding envelope of the pipe.

Abstract A study of the break-out factor ( Nc ) for plate anchors is presented in this paper. Comparisons among finite element method (FEM) analysis and laboratory results were performed. A soil corresponding to a soft normally consolidated clay was considered. Numerical FEM analyses were performed with the Plaxis® code, using an elasto-plastic model with a Mohr-Coulomb criterion. Undrained soil parameters and an adhesion factor α = 1 were used. Values of Nc factor for axisymmetric and 2D FEM were obtained. Two geometries considering a perpendicular load applied in the anchor area and horizontal anchor position to different depths were studied. In the same way, anchor plates to a reduced scale were tested in a tank containing a soft soil. It was verified that the factors Nc reach constant values beyond a determined depth of the soil. Finally, the experimental and numerical values were compared with suggested methods reported in the literature. 1. Introduction Plate anchors are frequently used as foundation solutions for offshore structures to transmit forces to surrounding soils at various depths. The capacity estimation of the anchor is nevertheless uncertain insofar as there are factors that have a large influence in its behaviour. Examples of such factors include the installation process, soil characteristics, geometry of plates and large numbers of methods used to calculate the holding capacity of the anchors. In this context, this paper presents a study of Nc values, obtained from axisymmetric and plane strain finite element model (FEM) simulations done in Plaxis® code. In addition, it outlines the results of scaled-down plate anchors tested in the laboratory. In both cases, the soil considered was soft clay with deepwater sediment characteristics. The description of specific FEM analyses and laboratory test characteristics taken into account are described. Comparisons with expressions found in literature were made.

Introduction The evaluation of burial conditions for pipelines or telecommunication cables in the seabed requires essentially two demands to be fulfilled as regards the terrain survey. Firstly, a large distance must be covered (from a few kilometres to several hundreds of kilometres) and, secondly, the survey must provide a precise identfication of the subsoil stratigraphy and a preliminary evaluation of the mechanical characteristics in the 3 to 5 metres below the seabed. In order to achieve this, two techniques are generally employed : In situ geotechnical techniques such as the Cone Penetration Test (CPT) that provide detailed but punctual information concerning the zone in the immediate neighbourhood of the borehole and geophysical techniques such as seismic reflaction, whereby a quasi-continuous picture of the survey route can be built up from the measurement of seismic propagation velocities (e.g. Puech and Tuenter, 2002). The harmonising of these two techniques and the research into correlations between the two sets of data are therefore of great Importance. Numerous laboratory studies using the Cone Penetration Test (CPT) have already been carried out on soils in calibration chambers and there exists a large amount of CPT data, obtained from both research conducted in calibration chambers and m-situ surveys. Seismic measurements can also be performed on soils confined in calibration chambers m parallel with the CPT, enabling one to examine the relationship between seismic velocities and CPT data, as well as their correlation with the mechanical properties of the soil. Such correlations have been investigated by a number of researchers and have lead to publications by Stokoe et al (1991), Baldi et al. (1986) and Rix & Stokoe (1991) amongst others. However, these studies have mainly concentrated on depths and confining pressures in excess of 50kPa, which is greater than the low confining pressure (typically < 30kPa) found close to the surface of the seabed. In sands, a simple extrapolation of these results to shallow depths is not justified due to the specific transitory response of the cone resistance along the first one or two metres of penetration. Furthermore, most of the studies concerned shear wave velocity measurements and correlations between small strain shear moduli and cone resistances. Burial assessment techniques, such as the Gambas]> <![CDATA[system developed by Fugro, require a correlation with compressive waves. The purpose of the laboratory study presented in this paper was to accumulate a database of both CPT and seismic measurements in well controlled conditions at very shallow depths in sands. The aim was firstly to compare the results with existing data from studies conducted at greater depths and coding pressures and, secondly, to establish a correlation between the resistance at the tip of the penetrometer and the compressive wave velocity. The laboratory study The research program undertaken consisted of a series of tests earned out in the calibration chamber of the Laboratory 3s (Fig.1) This calibration chamber is a right, circular cylinder of depth 1.5m and of diameter 1.2m. Above the chamber a rigid frame holds in place the penetrometer, which is driven into the soil at a standard, constant rate of 20mm/s by a hydraulic system.