Widening of Eastbound I-70 Tunnel – Idaho Springs, Colorado

Eastbound I-70 Tunnel Project

Enlargement and widening of the eastbound tunnel of the I-70 Twin Tunnels in Idaho Springs Colorado was the selected by Colorado Department of Transportation as the best way to improve traffic flow and reduce congestion of this heavily travelled roadway that leads to ski resort and recreational areas. The enlargement of this 800ft long horseshoe shaped tunnel began in March 2013 and upon completion allowed the construction of a third travel lane. Constructability reviews, independent cost estimates, as well as a construction scheduling, and resident construction management services were all provided by Brierley.

The tunnel widening work began after construction of an eastbound detour. After the detour was established the first step of demolition was to cut the reinforced concrete liner into sections with a diamond saw followed by use of a hydraulically powered breaker to remove the scored segments. Once removed the underlying gneiss with occasional pegmatite veins was excavated by drill and blast methods. Given the construction schedule, liner demolition and rock excavation were performed simultaneously from both the east portal and west portal using two complete and independent sets of construction equipment.

The 800ft long tunnel excavated cross section was approximately 56ft wide and 32ft high.  The new reinforced concrete tunnel lining, which was designed to vary from 18 inches to 24 inches thick, was placed using two independent sets of rebar gantries and tunnel formwork. The first concrete pour was made approximately in the center of the tunnel with subsequent work advancing eastward and westward from the center towards the portals. Contact grouting was completed after the concrete liner was in place.

In late December 2013 the eastbound tunnel was re-opened to traffic.

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