One of the peculiarities of ice regime of freezing seas is the availability of grounded ice hummocks, enormous hummock features, greatly affecting the sea floor. The depth of introduction of grounded ice hummock into the sea floor determines the technological solutions on the depths of underwater oil and gas pipelines in a certain soil to ensure their safety and reliability. To determine the conditions of formation and characteristics of grounded ice hummock, complex investigations of ice regime elements have been carried out recently in the area of perspective oil and gas deposits of the Okhotsk Sea. The results of investigations showed that the North Sakhalin region is characterizes by ice conditions unfamiliar for any other region of Arctic where oil prospecting and operation works are being carried out. Dynamic characteristics of ice cover are by one order of magnitude greater here than analogous parameters for the Beaufort Sea. In the region of constant drift shed characterized by intensive compression the hummock of more than 30 metres high are formed. While drifting into the shallow shelf regions they turn into grounded ice hummocks. Grounded ice hummocks may form on hummocked rim of fast ice too during prolonged compression together with intensive formation of packed ice up to the bottom under the fast ice. The grounded ice hummocks are most likely at the depth of 5… 20 m, but some were met at the depths up to 26 m. The results of investigations of maximum introduction grounded ice hummocks into the bottom ground as obtained during water sampling surveys and thermodrillings showed that the parameters off sea bottom disturbances correspond to analogous values of rare cases for the Beaufort Sea. The investigations carried out enabled to recommend the ways of determining the optimal value of pipeline depth in the bottom ground.

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