Results From Model Testing of Ice Protection Piles in Shallow Water

Abstract

The development of oil and gas fields in shallow icy waters, for instance in the Northern Caspian Sea, have increased the awareness of protecting offshore structures by means of ice barriers from the impacts of drifting ice. Protection could be provided by Ice Protection Piles (IPPs), installed in close vicinity to the offshore structure to be protected. Piles then take the main loads from the drifting ice by pre-fracturing the advancing ice sheet. Hence, the partly shielded offshore structure could be designed according to significant lower global design ice loads. In this regard, various configurations of pile arrangements have been model tested during the MATRA-OSE research project in the Ice Model Test Basin of the Hamburg Sip Model Basin (HSVA). The main objective was to analyse the behaviour of ice interactions with the protection piles together with the establishment of design ice loads on an individual pile within the pile arrangement. The pile to pile distances within each arrangement were varied from 2 to 8 times the pile diameter for both, vertical and inclined (30° to the horizontal) pile arrangements. Two test runs with 0.1 m and 0.5 m thick ice (full scale values) were conducted respectively. The full scale water depth was 4 m. Based on the model test observations, it was found that the rubble generation increases with decreasing pile to pile distances. Inclined piles were capable to produce more rubble than vertical piles and considerable lower ice loads were measured on inclined arrangements compared to vertical arrangements. As initial rubble has formed in front of the arrangements, the rubble effect accelerated considerable. Subsequent to the build-up of rubble accumulations, no effect of the pile inclination on the exerted ice loads could be observed. If piles are used as ice barriers, the distance between the piles should be less than 4D for inclined piles and 6D for vertical piles to allow sufficient rubble generation. Larger distances only generated significant ice rubble after initial grounding of the ice had occurred.