The Role of the Thermodynamic Consolidation of Ice Ridge Keels in the Seabed Gouging Process

Abstract

Many engineering challenges are currently posed by the Arctic and the sea ice found there. Ice ridge keels have attracted significant attention because of the potential damage they can inflict on subsea installations. The formation of seabed gouges in the winter has been documented. It has been hypothesised that moving ice ridge keels can gouge seabeds. Pipelines, power and communication cables and other subsea structures can also be affected by ridge keels.

In industry, the aforementioned structures are typically protected from the effects of ridge keels by burial into the seabed soil. This method is enormously expensive for linear structures such as pipelines and cables. The deeper the burial into the soil, the higher is the cost. Thus, the salient issue in industry is to strike a balance between safety and profit. This issue is obviously very complicated and has been the subject of interdisciplinary research by the international community, which has resulted in the formulation of international standards.

In this thesis, we focused on the physical and mechanical properties of ridge keels and the processes which can provide sufficient strength for keels to interact with the seabed and potential structures. Keels can be considerably strengthened through consolidation. Atmospheric cooling during the winter season causes a consolidated layer to form in the keel. In this work, we concluded that there are different physical processes for the thermodynamic consolidation of keels in the spring and summer seasons. The thermodynamic consolidation of ice ridge keels in water at varying freezing points is a significant research topic in this thesis.

This research is classified into four main areas, as given below.

RT1: The dynamics and thermodynamics of the seabed gouging process by ice formations

RT2: The hydrology regime for ice covered fiords with semidiurnal tides

RT3: The physical properties of old sea ice ridges that have survived at least one summer

RT4: The thermodynamic consolidation of ice ridge keels in water at varying freezing points

The main contributions of the thesis are summarised below.

C1: A mathematical model was developed for the ice ridge dynamics associated with the seabed gouging process and the ice-seabed interaction. The model was used to create a geographic information systems module to predict the trajectory and depth of the gouge in monitoring Baydaratskaya Bay.

C2: The physical properties of old ice ridges in the Fram Strait and the dynamic characteristics of fast ice in the Van Mijen Fiord were determined.

C3: A physical mechanism was developed for the thermodynamic consolidation of the ice ridge keels below the consolidated layer formed by atmospheric cooling; this mechanism was studied by laboratory experiments, analytically, and numerically.