34
APPENDIX E.—CONTINUED.
THREE SPAN BRIDGE.
The four piers of the Three Span Bridge would be numbered from east towest. Pier I would be located on the bench at the foot of the bluff where theelevation of the ground is about 8 and at station 104; Pier II would be atstation 110 -|- 60, in the deepest water of the river ; Pier III would be at station117 -(- 25, or at the west edge of the strong current; Pier IV would be atstation 123 -j- 85, close to the west bank and about at the low water shore line..
' I have estimated on sinking the foundation of Pier IV to —55, or aboutthree feet into the blue clay ; on sinking the foundation of Pier III to —79, orabout three feet into the light-colored clay ; and" on sinking the foundation ofPier II to —105, or through the light clay to the brown clay. The borings atthe base of the bluff are not yet complete, but I have estimated on sinking thisfoundation to the same depth as that of Pier IV.
The foundation of Pier IV offers no special difficulties, it being in veryshallow water and the depth being materially less than foundations I havelately put in on the Missouri River. The same may be said of the foundationof Pier I. The depth to which the foundation of Pier III must be sunk is nogreater than that of our deep foundations at Omaha, but the foundation and thepier would be very large. At Pier II tfie difficulties are undoubtedly great,especially if it is found necessary to go as deep as I have estimated, namely,to —105, which is deeper than any foundation I know of which has been car-ried to any hard material, though by carefully choosing the time of year itmight not be necessary to work in any deeper water than was done at the eastabutment of the St. Louis Bridge.
For the present I have thought it best to estimate on putting in all fourfoundations by the pneumatic process, as I feel certain that this can be done.It is possible, however, that after we have put in the foundations of Piers IIIand IV and thereby learned more than we now know of the character of theclays, a better and cheaper method of handling Pier II may be devised.
The great length of span which it is proposed to use will require largemasonry piers, and these piers will require foundations of correspondinglylarge size, especially as they are to rest on clay and not rock. I have esti-mated on making Piers II and III 14 feet thick and Piers I and IV 12 feetthick under the coping; the piers to be of limestone and of the form whichexperience has shown presents the least obstruction to the current and catchesthe least amount of driftwood, the caissons for Piers I and IV to be of rectangularform 36 feet by 82 feet; the caissons for Piers II and III to be octagonal, thearea of base being 3936 feet in Pier II and 3357 feet in Pier III. In pneu-matic foundations of ordinary size it is usually desirable to get all the weightpossible to facilitate sinking. In foundations of the size we are now consider-ing the reverse will be the case, and it will be desirable to reduce the weightas much as possible. I should propose to build the caisson entirely of oak, tosurmount this caisson with a cribwork structure which should terminate at
—31, on which the masonry should rest. The cribwork would be built oftimber and concrete, with three large wells, which wells would extend up intothe masonry ; these wells to be 'filled with concrete after the foundation iscompleted. In this way the weight on the roof of the caisson and the weightto be handled while sinking would be reduced to very comfortable limits.
Both Piers II and III should have protection mats around them, whichmats should be subsequently riprapped. The only protection required atPiers I and IV would be the protection which must at any rate be given to theshores. In my estimates I have provided for all these protections in one itemand at a liberal figure. ».
The superstructure of this bridge would consist of three spans of 656 feeteach (200 metres) between end pins, the trusses to be 77 feet deep and 33 feetbetween centers, and to be built entirely of steel. While these dimensions aregreater than those of any trusses yet built, they are entirely within practicablelimits and not so great an:undertaking now as 400 feet spans were twentyyears ago. I have estimated on simple trusses with straight chords, though itis probable it would be expedient to use a curved upper chord. The details ofone of these spans have been studied r and a careful estimate made of theweights, showing that the weight of such a span will not exceed 3 600 000pounds, or a little more than 5000 pounds per foot.
To connect the east end of the bridge with the top of the bluff will requirea short iron viaduct 240 feet long, the details of which will be similar to thatof the longer viaduct on the west side.
The estimated cost of this bridge complete will be as follows:
Pier I.
3 000 c. y. Masonry at $20...70 000 c. ft. Cribwork “ 40 cts60 000 “ “ Caisson “ 80 cts
Sinking.
Pier II.
4 200 c. y. Masonry at $20..;163 000 c. ft. Cribwork “ 40 cts
70 000 “, “ Caisson “ 80 ctsSinking.
Pier in.
4 200 c. y. Masonry at $20...80 000 c. ft. Cribwork “ 40 cts67 000 “ “ Caisson “ 80 ctsSinking..
Pier IV.
3 000 c. y. Masonry at $20...70 000 c. ft. Cribwork • ‘ 40 cts60 000 “ “ Caisson “ 80 ctsSinking... ..
Outfit for Foundation Work.....
Protection Work, including Mats and Band III, and Shore Protection at PieiTotal Substructure.
Three 656 ft. Spans, 10 800 000 lbs. at 6 cts.
$648 000
Floor and Painting.
15 000
663 000
Total Bridge Proper.
$1 546 800
East Approach.
240 ft. Iron Viaduct.
$12 000
West Approach.
2 400 000 lbs. Iron at 5 cts.
$120 000
3 000 c. y. Masonry at $10.
30 000
Floor and Painting.
20 000
3 200 ft. Iron Viaduct.
170 000
Wooden Trestle.
25 000
195 000
207 000
Total Bridge and Approaches..
$1 753 800
Add 10# for Contingencies......
175 380
: i:: . ■ •:; • r
$1 929 180sn non
jf u
f ■!
$1 979 180
This is the entire estimated cost of the bridge ready for rails from theedge of the bluff at Memphis to the foot of the grade on the west side of theriver. It includes nothing for real estate damages, and I do not think theseought to amount to anything. It is perhaps entitled to a credit for tracks, asthe amount of track which will be required is very much less than that nowused in the connections with the transfer landings.
The prices used for caissons and cribwork are those for which experiencehas shown me this work can be done on the Missouri River. I think thereshould be a large reduction in these prices at Memphis. The same may besaid of the cost of the masonry, but I have not yet examined any stone quarries.
The price for the superstructure (six cents per pound erected) is at least20 per cent higher than this work could have been contracted for a year ago.
I should hope that the item of contingencies could be saved, and the actualcash cost of the bridge could be kept within $1 800 000.
If your company should decide to build on this plan the matter of time isan important one. The foundations for Piers III and IV should be put in dur-ing the low water season of the present year. These piers should be finishedduring the Spring of 1888.
The foundation for Pier II should be put in in the Fall, during the lowwater season of 1888. Pier I can be put in at almost any time. The masonryof Piers I and II should be finished in the Spring of 1889.
The west long span should be raised in the Fall of 1888 and the other twospans in the Fall of 1889.
The approaches should be built in the Spring of 1889.
The bridge could be opened for traffic before the end of 1889.
It might be possible to save one season in the construction of this bridge,but in view of the time required to make preparations for a work of this mag
.iprap of Piers II 1rs I and IV.
$60
000
28
000
48
000
15
000
CO
000
65
200
56
000
40
000
4*
00
000
32
000
45
600
35
000
$60
000
28
000
48
000
15
000
$151 000
245 200
186 600
151 00050 000
100 000
4rrs son