There’s a “light in the tunnel” for the Truckee-Tahoe area’s numerous bicyclists and hikers, who have long had to negotiate Truckee’s 25-foot-wide, 1928 Mousehole tunnel on Highway 89.
A smaller tunnel just for them was punched through east of the Mousehole last week, and a paved pedestrian/bike trail through it, connecting West River Street and Deerfield Drive, is expected to be finished early next summer.
Although the tunnel phase is now completed, Truckee and state Department of Transportation officials advise that much work still needs to be done before it will be safe for public travel.
Dubbed the “mini-Mousehole,” the new tunnel also will allow safer passage for parents pushing baby carriages from a nearby mobile home park, students attending a close-by college, and shoppers and employees at a shopping center on the other side of the highway.
On the busy traffic route between Truckee and Tahoe City, the two-lane Mousehole, which cuts through Union Pacific Railroad’s overhead crossing, has no shoulders, not to mention bike lanes.
A safety project to remedy the situation has been long in the planning.
Although its humorous nickname may make the smaller tunnel sound somewhat easy to drill, officials said it was quite an operation.
First, during the warm month of August, the ground above the tunnel-to-be had to be frozen to support the train tracks, as well as to retain soil as the tunnel was dug.
Project manager Becky Bucar described the unusual process followed by the town’s contractors to insert the tunnel into the embankment.
“In order to not disrupt train traffic above, the contractor inserted 22 freeze pipes through the embankment,” Bucar said. “A calcium chloride freezing solution was then circulated through the pipes to create a frozen arch over the area under which the tunnel would later be jacked.”
In about four weeks, monitoring devices in some of the pipes determined the ground was solid enough to start removing soil from the unfrozen portion and jacking the tunnel into the embankment.
As soil was removed by a road-header machine – a grinder on the end of an excavator – the tunnel, which had been constructed in one piece on the south side of the embankment, was pushed forward along a concrete slab using hydraulic jacks.
“Little by little – a few feet at a time – the area in front of the tunnel was excavated and then the tunnel would be jacked forward,” said Bucar, who is also the town’s engineering manager.
On Sept. 14, she said, the tunnel was pushed through the north side of the embankment, about a week after the jacking operation began and a little more than five months after the project’s April 2 groundbreaking.
The $14 million joint Caltrans-Truckee Mousehole Pedestrian/Bicycle Improvement Project is being built with federal, state and town funding.
To view its daily progress (although, depending on weather, construction will possibly be halted October through May), visit the town’s website, townoftruckee.com, and click on the “SR 89 Mousehole Construction Camera.”