Strength Tests on Grounded Rubble

Bailey, Eleanor (C-CORE’s Centre for Arctic Resource Development) | Croasdale, Ken (K. R. Croasdale and Associates Ltd.) | Taylor, Rocky (C-CORE’s Centre for Arctic Resource Development)

OnePetro 

Abstract

Punch tests were carried out on manufactured freshwater ice rubble keels during the Pipeline Ice Risk and Mitigation (PIRAM) and Development of Ice Ridge Keel Strength (DIRKS) projects. The majority of the tests were carried out while the keel was still in contact with the soil tray, as would be the condition for a grounded sea ice ridge or stamukha. Results showed that peak ice pressures on the platen ranged from 61 kPa to 427 kPa, with an average value of 192 kPa and a standard deviation of 131 kPa. A conservative value for the bearing capacity of grounded freshwater ice rubble can be approximated to be 550 kPa (calculated by taking the mean plus three standard deviations).

INTRODUCTION

The continuously increasing demand for energy has pushed hydrocarbon exploration into arctic and northern environments. While industry is evolving in this relatively new area of expertise, knowledge gaps remain in the engineering of both pipelines and structures to withstand ice loading. Subsea pipelines are often at risk of being damaged by gouging ice features, such as icebergs or sea-ice ridges. This occurs when an ice feature drifts into shallow waters and contacts the seabed, producing long narrow gouges or scours that can be meters deep, tens of meters wide and hundreds of meters long.

Ice gouging mechanisms are very different, depending on the ice type. Icebergs are solid bodies that do not experience significant failure while gouging the seabed. Ice ridges consist of an assembly of ice pieces (ice rubble) that are typically bonded together to form a competent matrix and, as such, can deform though shear, tension and compression. To date much of the research on ice gouging has focused on icebergs. This is not only because icebergs produce the deepest gouges but also due to the complexities involved with modelling both the ice rubble and soil deformation, and the interaction between both materials. Understanding these processes is, however, vital for development of subsea infrastructure in regions where sea ice ridges are the dominant ice hazard (e.g. Beaufort Sea, North Caspian Sea and Offshore Sakhalin).