Soil and permafrost conditions in the Federal/State Beaufort Sea Lease Sale Area were investigated by drilling, sampling and testing. Twenty holes were drilled to depths ranging from 82 to 300 feet below mud 1ine in an area extending from Long Island to Flaxman Island and as much as 12 miles offshore. Engineering properties of both frozen and unfrozen sediments were determined by laboratory testing. Stabilized thermal profiles were obtained in 14 of the holes.
The results of the investigation have been correlated with previous studies. Accessible and abundant gravel deposits appear to be restricted to the area north and west of Prudhoe Bay. To the east and farther offshore, the gravel is covered by overconso1idated clay and silt or is ice-bonded. The hole north of Flaxman Island encountered very little sand and gravel for its entire depth of 300 feet. Soft organic silt was encountered as deep as 33 feet below mud 1ine in Stefansson Sound and Mikkelsen Bay.
Ice-bonded sediments were encountered in 15 of the holes. Lenses of ice, up to 0.25 inch thick which varied in orientation from horizontal to vertical, were found to depths of 300 feet below mud 1ine. The surface of ice-bonded permafrost varied from 21 feet to 190 feet below mud line. Thaw consolidation characteristics of the ice-bonded sediments were evaluated.
The discovery of oil at Prudhoe Bay in 1968 aroused interest in the geotechnical problems of petroleum development in the Alaskan Beaufort Sea - interest that has increased dramatically in the past few years. Initial interest was directed towards the technical problems of ocean transport of the Prudhoe Bay crude oil and included studies for deepwater port and pipeline facilities. Some of the early offshore studies included the Humble Oil Company's boring on Reindeer Island in 1969 and the 1970 Hamilton Brothers Oil Company's borings west of Prudhoe Bay. Nearshore investigations initiated by the develop men t of the Prudhoe Bay un ita1so provided information about the offshore soils and permafrost.
Industry's interest in offshore oil and gas exploration led to an acceleration of government-sponsored studies in the area. In the early 1970's the USGS marine geology group began intensive exploration of the soil conditions and the ice-related geologic processes that affect the area. l-11/ Investigators at the University of Alaska used drilling, probing and seismic refraction techniques to evaluate the suspected bonded permafrost condition near Prudhoe Bay.12-15/ During the spring of 1976 and 1977acrril1ing and samp1ing program was undertaken in the Prudhoe Bay area by the USGS marine geology group and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL).16-22/ The 1ocations of the USGS/ CRREL borings are show n i n Fig. 1.
The results of these studies led to a comprehensive description of subsea soil and permafrost conditions in the vicinity Prudhoe Bay.
