Hard rock near base delays Swinging Bridge project in Craig
June 8, 2010
Completion of the Swinging Bridge rehabilitation project has been delayed by about a month due to hard rock buried near the bridge's anchor blocks.
Bill Mack, Moffat County road and bridge department director, said crews worked for about a month trying to break up the rock in order to pour cement for the new blocks.
"It went pretty slow," he said. "We ran into some unknowns as far as the rock there."
The project was originally slated to be completed sometime in June, but Mack said he now expects the project to be completed in late July.
Crews tried to bust up the rock with a breaking hammer, but the rock was too hard.
The crews then resorted to drilling holes into the rock, filling them with explosives and blasting it apart, Mack said. The rock was removed last week and Mack said concrete and rebar work on the anchor blocks will start this week.
The new anchor blocks will sit on top and behind the old anchor blocks and are about three times as large.
The old anchors are designed so the cable is cemented in the 9-feet-long, 3-feet-wide block and buried underground. The design prohibits the cable from being changed if damage, such as rust or breaking strands, weakens the cable.
Mack said more than 60 holes were drilled into the rock surrounding the four anchor blocks. The holes ranged from 16 inches to 3 feet deep, he said.
Drilling into the hard rock, however, wore down the drill bits of the jackhammer drill used and forced the department to buy several replacement drill bits, Moffat County commissioner Tom Gray said.
"The rock was so hard it would eat up the drill bits so it took more drill bits than we figured on … a couple thousand (dollars) worth of drill bits," he said.
But, the blasting and drilling work did not severely affect the project's budget, Gray said.
"There are going to be some incidental costs, like the drill bits, but I think we have a little bit of room there so I think we are OK," he said.
Original estimations placed the project at about $460,000, but the county was able to cut the cost by choosing cost saving measures, and saved about $100,000 in labor costs by doing the project in-house.
The cost of the project was further offset by a Department of Local Affairs grant for $65,000.
The county will spend about $35,000 on the project, Gray said.
The Swinging Bridge was built in 1954 in Browns Park. It provides access to public lands, but has been closed since November 2009.
The bridge was closed after officials noticed several broken cable strands incurred by the design and gradual bending of the bridge.
The improvement project will outfit the bridge with new cables, anchor blocks and saddle design.
New cables for the bridge were ordered in March and will arrive within the next few weeks, Mack said.
The new saddles, which will hold the cables above the bridge, are being built in-house, and should be completed shortly, Mack said.