88 Civil .Engineering.

JEngineer's O.~ice, .Bergen Tunnel, 1st DeeemSer, 1860 . JOSEPtI BE]NNETT, :ESQ.

D e a r S i r : - - B e r g e n T u n n e l was c o m m e n c e d in 1855, and p r o s e c u t e d for some e i g h t e e n mon ths , w h e n the w o r k was suspended on accoun t o f f inanc ia l difficulties, and was n o t r e s u m e d un t i l F e b r u a r y , 1859, a t ~vhich t ime :[ f irst b e c a m e e n g a g e d on it . B e f o r e t he w o r k suspended , al l t he s h a h s ( e igh t in n u m b e r ) had ,been sunk , t he h e a d i n g , wi th the e x c e p t i o n o f 168 fee t , h a d been d r iven , and abou t 900 f ee t of t h e bot- t om t a k e n out.

T h e t u n n e l is 4 2 0 0 fee t long , and has a sec t iona l a r e a of 580 feet , or abou t 21½ cubic y a r d s p e r l inea l foot . T h e e x t r e m e h e i g h t is 23 fee t , e x t r e m e wid th 28 fee t . A s t h e r e was such a sma l l a m o u n t of b e a d i n g to dr ive a f t e r I b e c a m e c o n n e c t e d w i t h t h e work , and as t h a t ~vas in d e t a c h e d p ieces , I had n o t much o p p o r t u n i t y to find out t he a c c u r a t e c o s t ; b u t the f o l l o w i n g f igures m a y be r e l i ed on as n e a r l y co r rec t . T h e a m o u n t t a k e n out as h e a d i n g was four cubic y a r d s per l i nea l foot , a n d our g a n g s d rove abou t one foot p e r d a y o f ,04 hours . T h e e x p e n s e in t h e 24 hours was as fol lows :

24 miners at $1.37,~, . ----- $33.00 2 foremen at $2.00, ° = 4.00 4 laborers at $1"12½, ~ 4.50 2 tool°boys at 75 cents, ° ~ 1"50 ½ keg powder at $3"75, ~ 1'87.~

50 feet fuse at $4 per M, ~ .20 Lights, . = .50 Steel, say 5 ibs. at 15c. = .75

Expenses per day, . . $46.32½ 4 cubic yards at $11'58, . . = $46.32

Cost of heading per cubic yard, $11.58

T h e b o t t o m or b r e a s t - w o r k in t he shaf ts , wh ich , w e r e w o r k e d to the b e s t ~dvan t age , cos t as fo l lows :

Expenses under ground on one breast, each 24 hours. 30 miners at $1.25, . . ~ $37.50 14 laborers at t~1.12~, . ~ 15"75 2 foremen at $2"00, .~ . ~ 4-00 2 blacksmiths at ~1"37~, . . ~ 2"75 2 helpers at $1"00, . ~ 2.00 2 tool-boys at 75c., ~ 1,50 2 kegs powder at $375, • ~ 7"00

100 feet fuse at $4"00 per M, ~ .40 25 lbs. steel at 15c., . ~ 3.75 1½ gallons oil for light at 60e, , ---- .90

$75.55 Expenses on top for 24 hours.

4 top-men at $1.00, = $4.00 2 engineers at $l"50, . ~ 3"00 2 f i r e m e n a t $ 1 " 0 0 , . = 2-00 Oil . . . . . . "20 Coal for engine and blacksmiths, nearly 2 tons at $5, say, 9.00

$18 20

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Observations on the 1Viagara JBrldge. 89

Amount brought forward, . . $75'55 Add one-half of this expense (,$18"20) to the u n d e r - g r o u n d

e x p e n s e s o n o n e breast, . 9.20

Total expenses for one breast in 24 hours, $84"75 Average number of days worked per month, 23. 23 days at $84.75, ~ $1949.25 per month.

The amount taken out as bottom was 17'5 cubic yards per lineal foot, and the average number of feet worked per month was 27 on one breast, making 472"5 cubic yards per month.

472'5 cubic yards at $4.12½ = $1949"06 Expense per month, as above, ~ ~;1949.25 Cost per cubic yard, $4'12,~

To this cost it would be safe to add 12½ cents per yard, for tools, &c., and for trimming the sides and bottom before laying the perma- nent tracks.

With regard to the expense of sinking the shafts, I can say nothing further than that from all I can learn, those of the Bergen._Tunnel being large (16 X 20) and generally dry, did not differ much per yard from the cost of the heading. They are from 80 to 90 feet deep.

The rock through which the tunnel is bored is basaltic trap, and said by miners to be a good rock to work, blasting well, though hard to drill.

Observations on the Niagara Bridge.* By PETER W. BARLOW, Esq., C.E., F. R. S., F. G. S., &e., &c.

(Continued from page 22.)

Ou the Yleehanism of Bridge Construction. In the following table is given the weight of metal, deflection, and

ratio of ultimate strength to strain by weight of bridge, in the :Niagara Bridge, and in those of the longest girders

/ Name of Bridge. IDepth"

/ | ft.

Niagara, .

Britannia , Conway, . *Saltash,

59

• 30 24 54

Span. Weight .

ft. tons.

820 l cables, 400 l wood, 600

460 1550 tons. 400 1150 " 450 1100 "

Deflection.

tons

0"82 ft. with 326

2 in. with 248 0"69 in, with 100 1'17 in, with 384

Ratio of Strength to

Strain by Weight of

Bridge.

6.5 to I

3.4 to 1 3.9 to 1 5.0 to 1

* See Report of Col. Yolland, in the Appendix.

My object is now to endeavor to explain why these differences are consistent with understood mechanical laws/and the peculiar proper- ties of the material employed.

FlO. I .

V / Let A B O, Fig. 1, represent an arch supported on ~butments, Aand

* From the London Engineer~ No. 253. 8"