284 



ENGINEERING. (TUNNEL AND ELECTRIC RAILWAY.) 



great engineering works of the year. The 

 special construction of the hydraulic shields 

 need not here be described in detail, as the prm- 



MAP SHOWING LOCATION OF TUNNEL. 



ciple has long been known to the engineering 

 profession. Substantially it is a section of large 

 pipe surrounded by another movable section of 

 pipe, the latter having a cutting edge and being 

 capable of movement through the action of 

 powerful hydraulic rams. The cutting edge is 

 thus pressed through the soil, and a compart- 

 ment between the movable section and the fixed 

 section gives working room for several men who 

 throw the material excavated back into the fixed 

 tunnel whence it is transported to the heading 

 on small cars. Two shields of this description 

 were used, one at each end of the tunnel, and 

 the two met, their circular edges coinciding al- 

 most exactly, under the middle of the river. 

 The very difficult soil mentioned in connection 

 with the experimental shafts extended all the 

 way under the bed of the river, and was at 

 times so nearly fluid as greatly to delay the 

 progress of the work. Experience taught the en- 

 gineers how to deal with it, and no serious acci- 

 dent occurred during the period of construction. 

 The chief obstacles encountered were due to 

 the occurrences of large bowlders imbedded in 

 the clay, against which the advancing shields 

 occasionally struck. Blasting was impossible 

 under the existing conditions, and accordingly 

 they had to be split by hand drilling and 

 wedge work or other primitive devices. Mason- 

 ry is not employed in the tunnel proper, the 

 entire excavation being lined by flanged, seg- 

 mental cast-iron plates (see figure). The flanges 

 rest against one anoth- 

 er, and bolts are passed 

 through the holes of 

 each two contiguous seg- 

 ments. Thirteen of these 

 cast-iron segments com- 

 plete the circle of the 

 tunnel, with a small key 

 segment at the crown 

 of the arch. Each seg- 

 ment is 4 feet 10 inches 

 long, 18 inches wide, 

 and 2 inches thick; the flanges are 6 inches 

 deep inside, and If inch thick; the segments 

 are cast with 32 bolt holes in each, the bolts be- 

 ing | inch in diameter. This makes an exceed- 

 ingly strong structure, and with proper precau- 

 tions against oxidation should be practically 

 indestructible. The total length of the tunnel 

 is 2,267 yards, of which 777 yards is under the 

 American side of the river, and 770 yards under 

 the Canadian side. The central section of the 



SEdJTENT OF CAST IRON OF 

 WHICH TUNNEL IS COM- 

 POSED. 



tunnel under the river is nearly level for about 

 500 yards, but at either end there is a gradient 

 of about 1 in 50 until the approaches are 

 reached. The length of the grade on the Ameri- 

 can side is 1,683 yards, and on the Canadian side 

 1,657 yards. The minimum thickness of the 

 river bed above the tunnel is 15 feet, and the 

 maximum below the surface of the water 66| 

 feet. The cross section of the tunnel is circular, 

 with an interior diameter of 20 feet, admitting 

 but a single line of rails. The total cost at the 

 beginning was estimated at about $2,500,000, of 

 which the Dominion Government granted the 

 company a subsidy of 77,625. The latest at- 

 tainable figures show that about 200,000 cars 

 were transferred by ferriage across St. Glair 

 river in the year, an average of over 500 a day. 

 It is evident that the tunnel will largely facili- 

 tate the regularity desirable for this enormous 

 traffic. It is extremely probable that increasing 

 business will necessitate the duplication of this 

 tunnel before many years. The work of con- 

 struction has been under the charge of Joseph 

 flobson as chief engineer. 



In this connection it may not be amiss to call 

 attention to the different interstate relations of 

 the United States and Canada, and of Great 

 Britain and France. In one case a tunnel is 

 built with hardly a word of protest ; in the 

 other Parliament can not be induced to grant a 

 permit for construction. 



Tunnel and Electric Railway. One of the 

 great tunnels of the year passes under some of 

 the most densely populated portions of London, 

 from King William Street, in the " City," under 

 the Thames, to Stockwell, about three miles, with 

 intermediate stations. The company has the 

 chartered right of way to Clapham Common, one 

 mile farther. The line is tunnel work through- 

 out. It was opened to the public on Oct. 28. 

 The work of excavation was done by a movable 

 shield of the Beach pattern, similar to that used 

 in the St. Glair River Tunnel, an American inven- 

 tion long familiar to our engineers. Most of the 

 line passed through stiff clay, such as underlies 

 a large portion of the city. Owing to the im- 

 portance of preventing any subsidence at the 

 surface of the earth, it was necessary to force 

 grouting cement into the space surrounding the 

 cylinder. This was accomplished by an opening 

 in the segmental iron plates lining the tunnel, 

 through which the cement was forced at a high 

 pressure. The end of the line near King Will- 

 iam Street station is peculiarly arranged, owing 

 to the value of horizontal space. Two tunnels 

 are made, one for public traffic and the other for 

 railway traffic. At the start these are placed 

 one over the other, but the relative position 

 changes while passing under the river, and they 

 are side by side before reaching East London. 

 The tunnels are 10 feet and 6 inches in diameter. 

 Electricity is used throughout as a motive pow- 

 er. There are three large generating dynamos 

 of the Edison-Hopkinson type, each worked in- 

 dependently by an engine of 375 horse-power. 

 The efficiency of the dynamos is 95 per cent., 

 and the measured applied efficiency of engine 

 and dynamo is 75 per cent. There are fourteen 

 electrical locomotives for the traction work, each 

 intended to develop 100 horse-power arid a speed 

 of 25 miles an hour. The armatures of the loco- 



