Project Description

In 1995-1996, LACHEL & Associates, Inc. (LFA) was retained for a preliminary study of the feasibility of constructing a highway from Bear Cove off Silver Bay, southeast of Sitka, across Baranof Island to the vicinity of Baranof Warm Springs. An integral part of the project was an approximately 10,000-ft-long tunnel connecting the valleys of Medvede Lake and the Baranof River.

Scope of Services

Based on the available information, which included published geotechnical geologic data, as well as a geotechnical and environmental airphoto analysis, and helicopter fly-over examinations of the route, LACHEL & Associates developed the basic engineering assumptions and costs for three potential tunnel alternatives, varying in size, grade, and ventilation and lighting requirements. Three basic configurations were considered: a single-lane tunnel excavated by either drill-and-blast (D&B) or by tunnel boring machine (TBM); and a D&B excavated dual-lane tunnel. A significant portion of the cost of each alternative was comprised of the excavation and stabilization of the deep talus existing at the western tunnel portal.

LFA identified three critical factors which greatly impacted the viability and cost of the project and made specific recommendations to DOT&PF to minimize the potential costs related to mitigating these critical factors.

Client

Alaska Department of Transportation & Public Facilities (DOT&PF)