Project Description

Lachel & Associates, Inc. performed an inspection and designed rehabilitation repairs for a short highway tunnel in 1999 and 2000.

The Little Switzerland Tunnel is a two-lane highway tunnel on the Blue Ridge Parkway in North Carolina. The tunnel is roughly semicircular in shape with a height of 20 feet, a width of 30 feet, and a length of 600-feet. The tunnel was constructed in the 1950's in metamorphic rock, mostly gneiss with some schistose zones, and for the majority of the length is unlined, supported only by rock bolts and chain link mesh. One section, about 100-ft-long, required initial support by means of steel ribs, and has an 18-inch-thick concrete liner for permanent support. Water seepage through the concrete lining created maintenance problems for the tunnel in winter.

Scope of Services

Lachel & Associates, Inc., working as subconsultants to HDR Engineering, Inc., conducted an inspection and damage survey of the tunnel. This included mapping all cracks and deterioration using the full perimeter mapping method and conducting a visual survey inside and outside the tunnel. Overall, the tunnel was found to be in relatively good condition. However, the concrete-lined section had experienced significant cracking in one location, and the cracks, as well as two construction joints, were the source of troublesome water inflows. The water, in conjunction with freeze-thaw action, had resulted in some concrete damage; and caused major icing problems in the winter, sometimes forcing closure of a section of the Parkway.

Lachel also developed rehabilitation recommendations for repair of the tunnel. A system of drainage chases was designed for the cracks and construction joints, aimed to intercept water inflow and convey it to the drain at the tunnel invert. Lachel produced detailed drawings and assisted in preparation of the specifications for the rehabilitation work.

Client

HDR Engineering, Inc.
FHWA - Eastern Federal Lands Highway Division