North Slope-Construction Criteria for Roads and Facilities
Authors: Stokes William P. 
Published: December 2007

If you're planning to operate in the bitter north, put your house on stilts. For building your road, until something better comes along get yourself some gravel, and plenty of it. And forget all you ever knew about ditching for drainage.

Roads on the North Slope

The discovery of the Prudhoe Bay field on the North Slope of Alaska in early 1968 made it necessary to start planning immediately for the construction of permanent roads, airstrips, and other facilities. permanent roads, airstrips, and other facilities. Until that time all drilling operations had taken place in the winter months when the surface of the place in the winter months when the surface of the ground and lakes was frozen and therefore capable of supporting vehicles, planes, and other equipment required for construction and drilling. Temporary winter roads were constructed of snow. With the greater need for year-round operation, however, more stable roads were required.

The North Slope is located in a continuous permafrost zone where the subsurface soils are permafrost zone where the subsurface soils are permanently frozen to depths as great as 2,000 ft. permanently frozen to depths as great as 2,000 ft. The top foot or so of soil - called the active layer -thaws in the summer and refreezes every winter. In the summer, moderate temperature and long hours of daylight combine to promote the rapid growth of vegetation on the active layer. In fact, nearly all of the dry land areas of the North Slope (except tops of gravel bars in river bottoms) are covered with a thick, organic insulating sod, or tundra. Typical thaw depths of the active layer range from 12 to 18 in. for tundra sod to 4 or 5 ft for gravel.

Permanent road construction over permafrost requires special consideration not necessary in more temperate zones. Destruction or removal of the tundra cover will promote rapid and disastrous melting of the permafrost in the summer months. It is necessary therefore, to build the roads in such a manner that the insulating tundra cover is preserved intact and undamaged. Conventional road-building operations such as surface grading and side ditching would result in rapid deterioration of the road bed and right-of-way. Therefore, roads are built directly on the tundra surface with as little disturbance to existing conditions as possible.

Materials

Gravel. Adequate supplies of road-building gravel have been found in the North Slope rivers. Because the Dept. of Fish and Game has requested that no gravel be removed from the currently active channels, removal must be limited to overflow channels or other places where fish migration, spawning, etc., will, not be affected. It has been found that road-building gravel taken from silt-free areas on tops of gravel bars where the permafrost level is not very close to the surface of the ground is the best; and taking it this way does not interfere with active channels and has no detrimental effect on aquatic life.

Development of roads, drillsites, airstrips, production and personnel facilities, etc., at the Prudhoe production and personnel facilities, etc., at the Prudhoe Bay oil field will require several million cubic yards of gravel. However, the North Slope rivers can provide quantities of gravel far in excess of the presently known requirements.

P. 1209