Crossing the broad, deep Tunkhannock Creek valley in northeastern Pennsylvania required a half-mile-long viaduct 240 ft above the streambed. Although concrete cost more than steel, the railroad chose it for lower maintenance and overall appearance. The result was a 10-arch, reinforced-concrete bridge that is 2,375 ft long. Built using 167,000 cu yd of concrete, Tunkhannock Creek is the biggest and most impressive concrete bridge in the U. S.

Almost half of the bridge is underground and out of sight. All of the 13 piers were sunk to bedrock; two were excavated from open pits and the others through cofferdams. In some cases, this meant going 95 ft below ground level through loose, water-bearing alluvial sediments. Quicksand complicated work on two piers.

The main construction tool was a 3,028-ft, twin-line cableway that turned out to be a major project in itself. Timber towers at each end of the viaduct--one 150-ft high and the other 165-ft high--and a 240-ft-high center tower supported two tandem duplex cableways 20 ft apart that could each handle 10-ton loads. Each of the four cable spans was operated by a separate engine.

The viaduct is comprised of 10 concrete semicircular arches, each of which have two ribs and open spandrels, and spans of 180 ft. One 100-ft abutment arches at each end and is buried in fill.

The arches' formwork is made up of five sets of three-hinged steel arch trusses, each composed of four ribs that support concrete cast for one of the two ribs that compose each arch.

Made without hinges and reinforcement other than longitudinal and transverse bars near the extrados and intrados to provide for contraction and temperature stress, each arch was cast in 11 blocks in the form of huge masonry voussoirs (Engineering Record 5/3/13).

Flickwir and Bush, the contractors, began construction in 1912 and completed the viaduct in 1915. It is not used for regular rail traffic today.

NEWS IN BRIEF 1910

Edison Concrete Houses
Thomas Edison proposes to construct one-family houses of poured cement by erecting a mold for a house in four days and pouring the concrete in a six- hour period. Within a mere 14 days after pouring, the house is complete (Reported in Engineering Record 9/6/10 p. 52).

Raising the Maine
The U.S. Army Corps of Engineers announced its plan to raise the battleship Maine, which sank after an explosion in 38 ft of water in Cuba's Havana Bay in 1898. An interlocking sheet steel cofferdam will be built around the wreck and the interior will be pumped dry (Reported in Engineering Record 10/20/10 p. 92).

A New Insulator
"Bakelite" is a new substance whose properties are similar to--or in some cases--even more effective than those of hard rubber, Japanese lacquer and celluloid. Bakelite can resist temperatures of 572° F and higher. It is also insoluble in all solvents, able to withstand a variety of substances, including chemicals, oil, hot water and steam. These and other characteristics makes bakelite an excellent electrical insulator (Reported in Engineering News 12/29/10 p. 717).

Electrolysis of Pipes
The fact that electrolytic injury to buried gas and water pipes is a very common occurence is familiar to many engineers. The source of the injury in almost every instance stems from the currents that come from using the ground as the return by electric traction systems. But there has been as yet no definite agreement as to the proper remedial measures to be undertaken (Reported in Engineering Record 8/27/10 p. 225).

Inclined to Worry
The leaning tower of Pisa is worrying authorities in the Italian city. The tower at Pisa is 15.4 ft out of plumb in its 177-ft height, an inclination of about 1 in 12. The tower's plumb had increased since being measured in 1829 by several English engineers who found it then merely 14.4 ft out of plumb (Reported in Engineering News 9/1/10 p. 242).