A Modern Apartment House

Concrete-Lined Tunnel.

Plate 21 shows the style of forms and methods used in the construc tion of the 12 by 13-foot bore underneath the Chicago Postoffice from Adams street to Jackson boulevard. On account of the excessive weight overhead, this tunnel was built in small sections, which accounts for the small ribs inside of the larger ones. This construction consists of four small tunnels—namely, two side sections, one lower center section, and one upper center sec tion. This style of construction will appeal to engineers and contractors who may have large work of this kind, as a large tunnel can be built as easily as a smaller sized bore, through soft ground and where heavy weights are encoun tered overhead.

Reinforced Concrete Sewer.

Through the courtesy of Mr. C. W. Hendrick, Chief Engineer of the Sewerage Commission of Baltimore, Md., we are able to reproduce cuts showing details of a large outfall sewer recently constructed in that city. The frontispiece of this volume shows not only a section of the completed work, but also the forms and reinforcement for a section on which the concrete has not been placed. It is well to notice the care which is exerted to keep the network of twisted rods, which were used in this construction, rigid and in their proper places. Notice also the length of lap allowed at ends of bars where they join others.

Plate 22 shows an end section of the com pleted work. Notice the likeness to an arch in the top part of the section. The inside dimen sions were 11 feet by 12 feet 3 inches.

Regarding the great engineering problem which confronted the city of Baltimore in the development of a modern sewerage system, Mr. Hendrick, the chief engineer, writes as follows: "Baltimore, one of the oldest and most aristocratic cities in the country, has allowed itself to grow to a size of 700,000 people without a sewer system, depending on the old methods of disposing of sewage by means of cesspools and otherwise. The State of Maryland has recently passed laws forbidding the discharge of sewage into the Chesapeake Bay or its tributaries without first purifying it, bringing the city face to face with one of the most stupendous engineering projects of modern times—that is, the installation of a storm-water and a sanitary sewer age system throughout the streets and alleys of the entire city, carrying connections to each individual house.

"We expect to spend somewhere in the neighborhood of $20,000,000 to carry the sewage to great disposal plants, in which the sewage will be brought to a state of purifica tion equal to drinking water before discharging it into Chesapeake Bay. In carrying out this great project, some of the sewers are of such size as to remind you of the ones in Paris.

"In order not to have to purify the storm-water that falls, two systems—one for storm-water, and one for sani tary sewage—are being constructed. This, in some cases, causes two large sewers of the different systems to come together on the same level, necessitating the siphoning of one beneath the other. Plate 23 shows one of these

siphons—one of the largest in the world—constructed along such unique lines of engineering as to have caused wide comment in the engineering world.

"The great trouble with siphons is brought about by having to make the siphon large enough to take care of a heavy cloudburst, and still be operative during the sum mer flow, when there is a mere trickle, causing deposits to accumulate in the siphon. In this case a battery of pipes is used in connection with dams, the small pipe being for the summer flows, which keep it under pressure. Should a rain cause the flow to increase, it rises over a dam, dis charging into a larger pipe, with still another pipe in reserve, with a higher dam, to take care of a cloudburst; thereby putting all the pipes under pressure, scouring them out by the water pressure. As the storm recedes, each pipe is put out of commission in the reverse order, until the flow is back in the small pipe, which pipe is under constant pressure from the dry weather flow.

"Concrete is being used to a great extent, and won ders are being moulded under the city with this concrete construction. Our system will cover in the neighborhood of 1,100 miles." A recent example of the inherent strength and wonderful tenacity of reinforced concrete structures is found in the grain elevators erected at Tunis, in Northern Africa, shown in Plate 24. Owing to unequal settlement, the two outside buildings tipped as a whole away from the cen tral structure, until in one case an angle of 25 degrees from the vertical was reached. Both buildings were returned to a vertical position by loading the elevated sides with sand, and at the same time making excavations along the founda tions on the same side. Throughout this severe test the buildings remained whole and intact.

Plate 21 shows a cofferdam constructed of steel sheeting in the city of Chicago for the foundation of the Randolph Street bridge over the Chicago river. It was necessary to construct the cofferdam 85 feet long and 75 feet wide. The sheeting was driven alongside of the build ing known as the old Linn Block. About 1896 this building was considerably damaged by fire, but even in the face of this, the steel sheeting was driven alongside of the foundation to a depth of 31 feet below datum. The mill was in operation during this time, and the foundations were constructed without any damage whatso ever to the building. It is conceded by engineers and architects that the building is in better con dition now than it was before the foundations were constructed. This illustrates the use of steel sheeting, and also shows a right-angle cor ner of the cofferdam constructed with interlock ing steel sheeting; the I-beams being standard I-beams, 18 inches wide, weighing 55 pounds to the foot; the channels being 15-inch channels and weighing 33 pounds to the foot. The right-angle turn was made by riveting two I-beams together, forming an L.