File:First-Nineteenth annual report of the Metropolitan water and sewerage board 1901-1919 (1902) (14778723774).jpg

Identifier: firstnineteentha01mass (find matches)
Title: First-Nineteenth annual report of the Metropolitan water and sewerage board ... 1901-1919
Year: 1902 (1900s)
Authors: Massachusetts. Metropolitan Water and Sewerage Board Sprague, Henry Harrison Walcott, Henry Pickering, b. 1838
Subjects: Water-supply Sewerage
Publisher: Boston : Wright & Potter printing co., state printers
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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tream face of themasonry, and generally 15 feet from the down-stream face. Themaximum width of the excavation at the top of the pit was 376 feet,and at the surface of the ledge 211 feet. The maximum amount ofwater pumped was about 4,000,000 gallons per day. There wassome caving of the up-stream slope, which was composed largely ofsand; but this was treated when it occurred, so that the slopes weremaintained without much difficulty, and the whole excavation wascompleted without accident or serious delay. As the earth excavation progressed, the granite clifi about 40 feethigh on the westerly side of the gorge was uncovered and found tobe overhanging, as indicated by the preliminary borings. The over-hanging part and some additional rock were removed by blasting.At one point it was necessary to blast to a distance of 30 feet backfrom the face of the cliff. The ledge rock in the bottom and on the easterly side of the gorgeis schist, sometimes gray and quite hard, and at other places black
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WACHUSETT DAM-Filling above Dam in Winter by CABLEWAY. No. 57.) AND SEWERAGE BOARD. 89 and rather soft, but impervious to water. The schist at the contactwith the granite, for a varjdng width, ranged from about 4 feet atthe cut-off, where it is quite soft, to a maximum of about 20 feet,where it is somewhat harder; but the junction with the graniteseemed to be a perfect one in nearly all cases, and the schist iswater-tight and sufficiently strong to resist any pressures which maycome upon it. After reaching the rock, the excavation was continued as far asnecessary to obtain solid rock nearly free from seams. The averagedepth of excavation in the rock has been about 13 feet, and the cut-off trench, 20 feet in width, has been excavated to an additionaldepth of about 14 feet. In order not to disturb the walls of thecut-off trench, lines of 3-inch holes, 6 inches apart on centres, weredrilled to the bottom of the trench; the rock in the centre of thecut-off was then removedby careful blast

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