Drilling samples taken from a mountainside in Provo Canyon show it is feasible to tunnel through the mountain to avoid encroaching on the Provo River in the Narrows section of the canyon.
Now, the Utah Department of Transportation must decide whether it can afford to build the tunnels.A supplemental environmental impact statement drafted for the Upper Falls-to-Wildwood section of the canyon identifies tunnels as one means of building a wider road without affecting the river. Another option identified in the document is stacking traffic lanes.
In the tunnel proposal, two tunnels would be built from just south of Wildwood near the Sundance turnoff to just north of the Riverbend Trailer Park. One tunnel would be 700 feet to 800 feet long while the other would be about half that length.
Boyles Brothers Drilling Co. of Salt Lake City finished the sample drilling project in the canyon on Jan. 21.
"Basically we found that the rock is sound," said Dean Smith, supervisory civil engineer with Parsons, Brinkerhoff, Quade and Douglas Inc. of Murray, the firm overseeing the project. "There are some traces of water in the tunnel and there are some inactive fault lines, which is to be expected in this kind of rock."
The drilling company did encounter talus slopes - loose piles of rock fragments - through the area, however.
"That . . . is one of the big problems we're trying to resolve right now," Smith said.
Parsons, Brinkerhoff, Quade and Douglas is preparing conceptual designs for UDOT that will show how tunnels could be constructed along that section of highway and how much the tunnels would cost. That report will be given to UDOT at the end of February, Smith said.
Tunnels constructed in other areas cost on average $10,000 a linear foot, according to Dan F. Nelson, director of UDOT District No. 6 in Orem. At that rate, Provo Canyon's tunnels could cost as much as $12 million, although Nelson has heard figures as high as $25 million.
Still, tunnels may be cheaper to build than a stacked-lane structure, he said.
Meanwhile, UDOT officials say work on the next section of highway - from the Murdock Diversion Dam to Upper Falls - should be under way by early summer. UDOT is approaching the final stages of reviewing road plans before letting the project out for bid.
Project engineer Larry Buss said the 5.4-mile section will take 18 months to finish, at a cost of $14 million.
A recreation path will be built along the old railroad grade from the mouth of the canyon to Bridal Veil Falls; work on the path will proceed simultaneously with construction of the highway.