Page:Popular Science Monthly Volume 88.djvu/560

 Amputating Pittsburgh's "Hump"

��THE "Hump" in Pittsburgh was a hilly prominence upon which stood the County Courthouse. Ad- joining it were the Frick, Carnegie, and other large sky-scrapers. It impeded travel. Hence it was decided to remove the "Hump." This involved the cutting down of fifteen thousand feet of city street, and affecting twenty-two im- portant city blocks.

In this district thirteen public service corporations had underground conduits,

cables, pipes,

etc.

In the busi- ness section of most large American cities the overhead wires and ca- bles have been so ef- f e c t u al 1 y placed under- ground that nothing re- minds us of the mechan- ism whereby water, gas and electrici- ty are sup- plied a few feet beneath the surface of the street.

Particular- ly difficult was the task of maintain- ing in opera- tive condi- tion seven thousand, two hundred paper-insulated cable wires contained in lead cable-sheaths. These cables, twenty-one in number, were originally drawn into vitrified clay con- duits and spliced in manholes located at the street intersections. When the cut- ting of the "Hump" proceeded and the street was down to the level of the con- duits, it was found that the drilling and

���How the cables carrying most of Pittsburgh's telephone

conversations were taken care of until the new conduits

were ready for use

��blasting in the immediate vicinity shat- tered the conduits, so that further exca- vating would cause the conduit line to collapse. The clay conduits were broken off the cables and the cables were planked up in a box or trough. Alongside the plank box was the trench, twenty-two feet deep, in which a conduit line was to be constructed by what is known as the "split duct" method. These special conduits are scored lengthwise inside and outside before being vitrified

or baked and can be easily split in two. After a layer of half-ducts is laid in ce- ment, it is possible to place the ca- bles in posi- tion and re- place the top halves of the ducts.

This pro- cedure of low- ering the tel- ephone cables into split ducts saved about $40,- 000 which would have been expenrl- ed in purchas- ing new un- derground cable to be pulled, splic- ed and cut into service, to say noth- ing of the oc- service and the working

��casional interruptions of confusion in transferring lines from the old cables to the new ones The cables thus lowered below the new grade of the "Hump" cut contained three thousand, four hundred and eighty- one miles of copper wire, paper-insulated, twisted into pairs and enclosed in a lead sheath. The time required to accomplish

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