Typical rock berms used to protect submarine pipelines may be damaged under shear by a first year grounded ice rubble keel. Physical model tests in a centrifuge have indicated that such damage occurs under loads less than those typical of actual design conditions. These novel tests have reproduced both failures of the rock berm and identified failure criteria for the ice rubble. The tests are of a preliminary nature given the discrete, rather than continuum, nature of the interaction event. The model freshwater ice rubble behaved as a frictional granular material under the shear test conditions with a peak friction angle of 38 degrees. Measured ice rubble shear strengths exceeded 65 kPa.
First year freshwater ice rubble large scale tests were conducted as part of the Pipeline Ice Risk Assessment and Mitigation (PIRAM) and Development of Ice Ridge Keel Strength (DIRKS) Joint Industry Projects. New finite element analyses of the PIRAM test set up indicate the boundary constraints on the test results. The measured PIRAM ice rubble shear strengths exceeded 35 kPa.
The first two test series indicate that ice rubble shear strength may exceed currently accepted design limits.
The Development of Ice Ridge Keel Strengths is a four-year collaborative venture between the C–CORE Centre for Arctic Resource Development (CARD) and the National Research Council – Ocean, Coastal & River Engineering (NRC-OCRE). The main focus of the project is to investigate the failure mechanisms associated with gouging ice ridge keels and the conditions under which these keels will continue to gouge without failure. This is important for the design of subsea structures in shallow waters, where ice keels have been observed to scour the sea floor, posing a threat to pipelines and subsea infrastructure. A series of near full-scale keel-gouge tests were carried out to investigate the strength characteristics of a first-year ice keel and its subsequent failure as it was pushed into an artificial seabed. The ice keels were constructed using freshwater ice blocks with a nominal thickness of 10 cm, produced in a cold storage facility prior to the start of the test program. The ice keels were constructed with the aid of a keel former that produced idealized keel geometries of 1.7 m depth, 4 m length and 3.5 m width. Once constructed, the keels were lowered into the water and left overnight to consolidate with air temperatures held at -20°C. The keel samples were tested using a custom-built frame that was designed and used in the Pipeline Ice Risk Assessment and Mitigation (PIRAM) Joint Industry Project. The frame applied a vertical surcharge load to the top of the keel whilst a soil tray was displaced horizontally, causing the bottom of the ice keel to interact with an artificial seabed. A total of ten keel tests were conducted in this test program. The parameters varied were the initial temperature of the ice (-3° and -18°C), the initial surcharge pressure (5-60 kPa), the soil tray velocity (1-20 mm s-1) and the consolidation time (19-48 hrs). An overview of the test program and preliminary results are discussed.
Lai, Rixin (GE Global Research) | Chi, Song (GE Global Research) | Garces, Luis (GE Global Research) | Elgsaas, Kristin Moe (GE Oil & Gas) | Alford, Mike (Chevron Technology Co) | Dong, Dong (GE Global Research) | Zhang, Di (GE Global Research) | Masoud, Haji (Chevron Technology Co) | Gunturi, Satish (GE Transportation) | Harfman Todorovic, Maja (GE Global Research) | Sihler, Christof (GE Global Research) | Song-Manguelle, Joseph (ExxonMobil) | Datta, Rajib (Arizona State University) | Pappas, James Marcus (RPSEA) | Gupta, Rajan (GE Global Research) | Rocke, Svend Erik (GE Oil & Gas)
The offshore oil and gas industry is developing subsea processing systems far away from the shore and in ultra-deepwater. These subsea systems are usually power intensive, and thus a reliable electrical transmission and distribution (T&D) system is desired. In this paper, the modular stacked direct current (MSDC) architecture is presented to meet the technical challenges of the ultra-deepwater subsea systems. Instead of using a bulky centralized high voltage direct current (HVDC) converter station, the high dc voltage is achieved by stacking a number of power converter building blocks in series on both the on-shore station and the seabed stations. The dc-link current is controlled to be constant, and the dc-link voltage will vary according to the loading condition. This architecture renders fault-tolerant capability and feasibility for field extension. The details for the system architecture, the control algorithm, the simulation and experimental results will be described. The test results and the studies show that the MSDC system is a very attractive solution for subsea applications.
Martin, L. Blanco (Department of Geosciences, MINES-ParisTech) | Hadj-Hassen, F. (Department of Geosciences, MINES-ParisTech) | Tijani, M. (Department of Geosciences, MINES-ParisTech) | Noiret, A. (ANDRA-Laboratoire de Recherche Souterrain de Meuse/Haute-Marne)
This paper deals with fully grouted rockbolts, both for mining and civil engineering applications. Their mechanical behavior under tensile loads is reviewed theoretically and experimentally. As for the theoretical part, a new solution able to predict the full range behavior of a grouted bolt subjected to a pull-out test is explained. The originality of the new approach lies in the fact that the boundary conditions only concern the free end of the bolt. The experimental part consists of a wide pull-out test campaign performed in laboratory on deformed steel bars and on FRP rockbolts. These tests have been carried out using a new experimental bench, whose main assets will be described. The influence of several parameters such as the confining pressure, the bolt profile and the quality of the grouting material has been considered. The results of these tests will help in the derivation of a constitutive law for the rockbolt-grout interface. In situ pull-out tests conducted in ANDRA’s URL in North-Eastern France to examine the performance of different bars have also been analyzed and compared to the laboratory-scale results.
Rockbolts have been extensively used for the past 30 years as reinforcement elements. A rockbolt reinforcement system has four principal components : the rock or soil, the reinforcing bar, the internal fixture to the borehole wall and the external fixture to the excavation surface (a plate and a nut in most cases). Such system is very efficient if used in one or several of the following applications [2, 3]; · Stabilization of blocky rock masses, provided the far end of the bolt is anchored to a stable zone; · Rock confinement, contributing to the use of the broken rock belt to confine the stable rock mass; · Improvement of the mechanical properties of the rock mass. In addition, the easy installation and low cost of rockbolts compared to those of other reinforcement elements have contributed to their worldwide success . Fully grouted rockbolts are able to support tensile, compressive, shear and bending loads. The current study focuses on their tensile behavior because it is very often encountered and furthermore it allows studying the load transfer mechanism between the rock mass and the reinforcement element. Experience throughout the world has shown that under tensile solicitations failure often takes place by debonding at either the bolt-grout interface or at the grout-rock interface, depending on which one is weaker: in fact, if a bolted rock mass tries to move, a load will be progressively transferred to the rod and a shear stress will develop consequently along the embedded length (see figure 1). As the shear strength of the interface is progressively reached, debonding will occur. Since Freeman  monitored for the first time in the 1970s the loading process and the stress distribution along the embedded length of a fully grouted rockbolt, numerous studies aiming at a better understanding of the load transfer mechanism between the surrounding ground and the bar have been conducted.
Rock-socketed piles are a common foundation solution to transfer heavy loads from structures to the underlying rock mass. Their total capacity is largely governed by a skin friction mechanism (shaft resistance) developed at the rock-pile interface. The prediction of shaft resistance is a complex engineering problem and a traditional method to experimentally evaluate it is by in-situ load tests. Rock mass quality has a great influence on the shaft resistance, however the mechanisms and details of such influence are poorly understood since the rock mass quality is usually not defined during these load test programs. This paper presents a laboratory attempt to study the influence of two significant rock mass characteristics (joint orientation and infilling material) on the shaft resistance by a series of large-scale two-dimensional load tests. The tests were performed in four differently configured synthetic rock masses composed of concrete. The test results revealed that diagonal orientation of joint sets caused an approximately 150% reduction in shaft resistance when compared to what was measured in horizontal-vertical joint oriented rock masses. The soft and weak infilling material caused a dramatic reduction in shaft resistance, by an order of magnitude, when compared with clean and tight joints. Finally, the test results were evaluated using the micromechanical approach developed by researchers at Monash University.
Rock-socketed piles are a common foundation solution to transfer high and concentrated loads from heavy structures to underlying rock mass. Their total axial capacity consists of two major components: end bearing load (base resistance) and side friction load (shaft resistance) in the rock. Although the base resistance component may significantly contribute to a total pile capacity, it is usually not taken into account in design calculations mainly because of two reasons. The inclusion of base resistance component requires the pier bottom to be clean of debris and this technically may be difficult and expensive to achieve. In addition, the shaft resistance is normally mobilized much earlier and at considerably smaller pile movements than that of the base. As a result, the shaft resistance at the rock-pile interface is usually considered as the major or the only component in total capacity estimation process. For this case, an estimate of the ultimate socket-shaft resistance (fsu) is required in order to evaluate the total capacity of the rock-socketed pile. In the absence of analytical solutions, most of the methods used to estimate shaft resistance in rocks are largely based on empirical rules, which usually relate to uniaxial compressive strength (qu) of the weakest component in the pile-rock interface. These rules are historically derived from pile design in clays, and for the rock masses are generally expressed as:
Recent studies have shown that shaft resistance is influenced not only by the intact strength of the weakest component along the interface, but also by borehole roughness, characteristics of the rock-mass (i.e. deformation modulus, Poisson’s ratio, structure and shear strength of discontinuities), pile diameter, initial normal stress on the interface prior to loading, and construction practice.
Brosset, L. (GTT (Gaztransport & Technigaz), Saint-Rémy-lès-Chevreuse) | Marhem, M. (GTT (Gaztransport & Technigaz), Saint-Rémy-lès-Chevreuse) | Lafeber, W. (MARIN, Hydro Structural Services) | Bogaert, H. (MARIN, Hydro Structural Services) | Carden, P. (Lloyd's Register EME) | Maguire, J. (Lloyd's Register EME)
Chen, J.-W. (Department of Civil Engineering, National Cheng Kung University) | Kuo, Y.-S. (Department of Hydraulic and Ocean Engineering, National Cheng Kung University) | Tseng, W.C. (Department of Civil Engineering, National Cheng Kung University)
Chun, S.E. (Samsung Heavy Industries Co. Ltd) | Hwang, J.O. (Samsung Heavy Industries Co. Ltd) | Chun, M.S. (Samsung Heavy Industries Co. Ltd) | Suh, Y.S. (Samsung Heavy Industries Co. Ltd) | Hwangbo, S.M. (Samsung Heavy Industries Co. Ltd) | Lee, J.M. (NAOE, Pusan National University) | White, Nigel (Lloyd’s Register) | Wang, Z.H. (Lloyd’s Register)