SEWER UNDER THE SUDBURY TUNNEL.
A difficult, costly, and dangerous piece of engineering was recently successfully concluded at Newton Highlands, Mass., where a tunnel was built under the Sudbury aqueduct to contain a sewer. The method pursued was novel. On each side of the aqueduct excavations were made to the desired depth, after which steel cylinders, six feet, six inches long were forced by a jackscrew through the soil, and the material dug out from in front of them. These cylinders were telescopic in form—the largest being ten feet, five inches in diameter, and the smallest live feet inside measurement. The material of which they were composed was boiler steel three-eighthinch thick, in one sheet lapped and fastened with one row of rivets. When placed in position in the tunnel, each cylinder lapped six inches over the adjoining one. Between the plank bulkheads at each end the whule length of the tunnel was thirty-five feet, with seven feet, six inches of roof between the under side of the bottom of the aqueduct and the steel cylinders. From the top of the embankment to the bottom grade ot excavation was twenly-seven feet. Coarse, loose gravel, containing stones of all sizes up to two cubic feet, formed the material through which the tunnel was driven, and all the work was done by one jackscrew properly applied—that method being very successful and avoiding any settlement of the material unde: the cylinder, which, while the excavating was being done, was pressed hard against the gravel round the edge of the cylinder. After this had first been scraped away with trowels and a sharp-pointed hammer, the centre portion fell of itself. Whatever large stones the workmen came across partially outside the line of the cylinders were carefully removed and the cavities filled up with stiff cement. The tunneling was all done from one end,and only four men were needed for the work—two at the jackscrew outside and two in the cylinders. The alignment was kept true by having each cylinder two inches smaller than that which went before it. The average time of driving each cylinder, excavating and removing the gravel was twelve hours and two-thirds ot an hour. On the completion of the tunnel, the sewer and underdrain were built inside of it, and all the spaces were filled up with masonry. The same method was afterwards tried on Cochituate aqueduct when the sewer was taken under it in the presence of water. The water was first lowered by pumping, so that the excavation was comparatively dry.
Another sewer was laid across the Cochituate aqueduct on the Newton boulevard, opposite Irving street, Newton Centre. In thtsca.se, to render the sewer perfectly watertight, it consisted of a ten-inch iron pipe, forty-three feet long, with lead joints. The sewer and the six-inch earthen subdrain are surrounded by from six inches to ten inches of American cement. A private sewer, eight inches in diameter, crossing the aqueduct about 1,200 feet west of the Chestnut Hill reservoir grounds, has been made secure ia the same way as the preceding.