LAYING SHEET WATERPROOFING IN BOTTOM
SPECIAL BRICK AND ASPHALT WATERPROOFING
Methods of Construction Typical Subway
The construction of the typical subway has been carried on by a great variety of methods, partly adopted on account of the conditions under which the work had to be prosecuted and partly due to the personal views of the different sub-contractors. The work was all done by open excavation, the so-called "cut and cover" system, but the conditions varied widely along different parts of the line, and different means were adopted to overcome local difficulties. The distance of the rock surface below the street level had a marked influence on the manner in which the excavation of the open trenches could be made. In some places this rock rose nearly to the pavement, as between 14th and 18th Streets. At other places the subway is located in water-bearing loam and sand, as in the stretch between Pearl and Grand Streets, where it was necessary to employ a special design for the bottom, which is illustrated by drawing on [page 42].
This part of the route includes the former site of the ancient Collect Pond, familiar in the early history of New York, and the excavation was through made ground, the pond having been filled in for building purposes after it was abandoned for supplying water to the city. The excavations through Canal Street, adjacent, were also through made ground, that street having been at one time, as its name implies, a canal.
From the City Hall to 9th Street was sand, presenting no particular difficulties except through the territory just described.
At Union Square rock was encountered on the west side of Fourth Avenue from the surface down. On the east side of the street, however, at the surface was sand, which extended 15 feet down to a sloping rock surface. The tendency of the sand to a slide off into the rock excavation required great care. The work was done, however, without interference with the street traffic, which is particularly heavy at that point.