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October, 1921 MARINE REVIEW ti \e# Square Miles of Anchorage=————>. Me - « . r “9 ? . is > hs M ’ aes hes ot eS GN Dea 2d5 YES iy ere JS. ~s a SUN ae ry = st = ta " ae ‘ae Le. rigieyd Jubes *.'f \e/-<0Ff Vehicu/ar7ube ‘ating Plant s gebind tighiouse \ ‘ sed ~*~ eda Fro, Ala \\Wava/ Base +o ADS SH Go Awe 7 ; ae Oy ASEAN See ge ERE ALI eng 1/500 Ft. of Bridge \ = ee Saree ¥ a} ory) the - FED FL! (= 5 5600 FtOf Pr/e Trestle. so OVE PLAN CALLS FOR $40,000,000 COMBINATION TUBE, BRIDGE, TRESTLE AND MOLE ACROSS SAN FRANCISCO BAY tube, dipping under the deeper part of the bay, and leaving the waterfront of San Francisco as clear for all shipping as it now is. On the report of these engineers it has been decided to con- struct the passage in the form of a combined tunnel, bridge, trestle and causeway or mole, running from a point near the Union Iron Works, in South San Francisco, 5.8 miles, al- most due east, to a projecting point of land in the city of Alameda. Starting 800 feet. back from _ the pier-base line in San Francisco, the tube will dip downward until, when it strikes the pierhead line, where there is at mean low tide a depth of 40 feet, it will be 50 feet beneath the surface—40 feet of water, and 10 feet of mud and silt, the bay bottom. The tube maintains this depth for 2300 feet due east, leaving a deep-water channel of this depth and width, ample for all the traffic of San Francisco. for years to come, as compared with the channel entrances of other large and important harbors, both in America and in Europe. At the eastern side of this 2300 feet of channel, the tube begins to rise, maintaining an _ easter- ly course, and, after 400 feet, comes to the surface on an artificial island. This contains a lighthouse, to mark the outer edge of the channel, and a pumping plant to force air through the tube back toward the San Francisco terminal, where it is to be sucked out by pumps synchronized with those on the island. The tube is to be either cylindrical, of concrete, lined with steel, and driven with driving heads and shields, or will be a square, reinforced con- crete box, dropped into a trench pre- viously dug in the bottom of the bay. Phe: exact, type: of tube isi: leit“ te the engineers who do the actual con- struction. Within the tube will be two passageways, one containing a 20- foot roadway for automotive and other vehicles, and a 5-foot sidewalk, while the other will contain two railroad lines, over which will pass the city and interurban and suburban cars, and such freight and passenger cars from the steam railroads as can be handled by electric engines. Naturally, no steam engines will be allowed in the tube. At the artificial island above men- tioned,. starts the bridge proper, which will be of steel, 11,500 feet in length, probably 40 spans of 300 feet each, resting on unusually large and heavy reinforced concrete piers, due to the heavy and’ constantly changing cur- rents to be found in this part of San Francisco bay. The number and character of these piers, and the meth- od of construction of the island, how- ever, will depend entirely on the re- sults of a survey of the bottom of the bay, .and of the ‘currents ‘and the tides, which is now being made. The bridge will clear about 40 feet above the water, possibly more than this, to give ample room for. -the movement of power-boats, small tugs, power-freight and passenger carriers and other craft engaged in inland waterways traffic up and down the bay, between the Sacramento and San Joaquin rivers. and towns around the southern section of San _ Francisco bay. There will be no openings in the floor of the bridge, either lifts, draws or rollers, and larger water traffic will be confined to the 2300 foot channel, 40 feet deep, on the west- ern side of the bay. The bridge-floor, however, will be wider than the floor of the tube, allowing for 40 feet of roadway, instead of 20, as in the tube, and four lines of railway, instead of two. This greater width will persist from the artificial island to the east- ern terminus of the passage-way. After the 11,500 feet of steel bridge, will come 3600 feet of trestle, made of cement and steel piers, floored with concrete slabs. This trestle will carry traffic across the shallow waters of the eastern side of the bay, but will be high enough for the passage of small boats, such as power freight and passenger carriers and power tugs which may wish to use the eastern waters of the bay. There will be no openings in the floor of this trestle, and it will be as wide as. the bridge proper. _ At the eastern end, the trestle runs on to a fill, causeway or mole, 12,000 . feet in length, which will carry traffic into the heart of the city of Alameda, and deliver it to the wide paved thoroughfares which run northward to Oakland, Emeryville, Berkeley, Rich- mond and on into the interior of northern California, and southward to San Jose, and on to all the towns of the state lying to the south of the ‘bay. The fill is to be made of rip- rap rock work, filled with material dredged from the bottom of the bay, and floored with gravel and _ shells. It will be considerably wider than either bridge or trestle, and will be ornamented with flowers, and probably have pleasure piers running out from it into the deeper water created by the dredging necessary to make the mole. This fill also will afford pro- tection from the south to the proposed naval base at Alameda, which lies just to the north of the causeway. we?