Bob Ortblad says that unlike the proposed massive, fixed bridge, an immersed tunnel needs no drilled shafts costing hundreds of millions which is one reason it offers tremendous cost savings as compared to the IBR’s proposed mega-bridge
Editor’s note: Opinions expressed in this letter to the editor are those of the author alone and may not reflect the editorial position of ClarkCountyToday.com
The Columbia River Crossing (CRC) spent $200 million, and the Interstate Bridge Replacement Program (IBR) has spent an additional $250 million. However, the IBR is still researching the bottom of the Columbia River to see if drilled shafts are physically and economically feasible. At the December 15th Bi-state Legislative meeting the IBR said it plans to spend more millions to “assess soil conditions below the water and inform requirements for bridge construction”. (slide 37)
The CRC spent $12 million on geotechnical consultants and a drilled shaft test that failed on its first attempt when it encountered boulders. The IBR has spent an additional $3 million on geotechnical consultants.
The IBR has a high cost, high risk foundation design that requires about 100 drilled shafts in the Columbia River with 10-foot diameters and up to 250 feet long, plus over 2,000 temporary piles. Test drilling encountered boulders and cobbles. Portland’s Abernethy Bridge with only six similar in water drilled shafts has more than tripled in cost to $815 million. The SR 520 Portage Bay Bridge has a similar drilled shaft foundation design, and its low bid was 70% over the engineers’ estimate.
The IBR’s “Geotechnical Data Report -May 2024” prepared by Shannon & Wilson at a cost of one million dollars, was never released to the public. I obtained it with a Public Disclosure Request. Six holes were drilled on the Columbia River bottom and five of the holes inferred the existence of cobbles and boulders.
An immersed tube tunnel alternative was fraudulently disqualified by the IBR partly because of false claims about seismic vulnerability. An immersed tunnel is in fact extremely resilient to earthquakes because it displaces is weight and is supported by free buoyancy. Unlike the proposed massive, fixed bridge, an immersed tunnel needs no drilled shafts costing hundreds of millions which is one reason it offers tremendous cost savings as compared to the IBR’s proposed mega-bridge.
Bob Ortblad MSCE, MBA
Seattle
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