Page:Popular Science Monthly Volume 88.djvu/359

 Popular Science Monthly

��rial is quicksand. William Street is a narrow winding lane of old downtown New York. It is barely forty feet in width between building fronts, and in the half-mile section where the subway is being dug (from Beekman Street to Pearl) it bears twenty buildings of from seven to twelve stories in height, and ten of from thirteen to twenty stories. When the digging was first proposed, owners of abutting property assessed at forty million dollars protested and carried the case into court. The Public Service Commissioners had so much confidence that the work could be done safely that they assumed responsi- bility for any damages that might result.

BuUdiug on IVafer

"The conditions encoun- tered are unique," writes John H. Aladden, Asst. Di- v^ision Engineer, "in the num- ber of large and heavy build- ings, few of which have foundations to rock or hard- pan, and with these excep- tions all other foundations are abo\-e the subway sub- grade and uniformly above water level as well." The sub- way's floor is, in general, three to five feet below mean low water ; and below ground water level the material is swimming sand. ''To guard against any possible flow of material into the subway trench, continuous bulkheads, either in the form of rigidly held, tight sheeting or con- crete cut-off walls, will be in- troduced between the under- pinning piers so as to form an integral portion of the latter and will be carried to such depth below the subgrade of the subway as to eliminate any tendency of the quick- sand to flow under the toe and be released into the ex- cavation," The total esti- mated ccst of the section is two million, two hundred fifty- four thousand, six hun-

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dred and seventy dollars, of which six hundred and four thousand, five hundred dollars is for underpinning.

William Street is not the only place where the subway diggers have to be particular about building stanch floors and sidewalls. At Broadway and Canal Street an underground watercourse was encountered and a very heavy floor had to be built to resist the water's upward pressure. Pumps with a capacity of twenty million gallons a day were kept

���One of the serious difficulties often met by the engineers. Underground water is seeping into the tunnel near the corner of Broadway and Canal Street so fast that a set of pumps removes twenty million gallons a day from this one spot. The flooring here is reiinforced to resist the upward pressure of the water and quicksand

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