14

THE MEMPHIS BRIDGE.

a height of 11.0 feet, and the upper 10.4 feet of the whole 39.6 feet werebuilt of solid timber.

Pier III contains 1085 M B.M. of timber and 367 000 pounds of iron.

Precisely the same machinery was used here as at Pier II. The cut-ting edge of the caisson was placed on the 30th of July on the samelaunching ways from which the caisson for Pier II had been launched,and this caisson was itself launched on the 26th of October.

The situation of Pier III had been considered less exposed than thatof Pier II, and one mat only was woven for this pier. The caisson wasbrought into position without serious trouble on the 28th of Octoberand the concrete filling begun on the 5 th of November. It was none tooearly ; the river had already begun to rise, and it continued to rise till the25th, when it attained a 23 feet stage. These three weeks formed perhapsthe most critical time of the entire work. During this rise the currentin this part of the river made an angle of about 10 degrees with the axisof the pier and tended to move the caisson towards the west; on the19th of November the caisson was 20 feet out of place; finally, by the aidof two tugs and of five lines leading to Pier II, the caisson was broughtback into position five feet east of where it belonged; four days later all thelines leading east and one of the northeastern lines parted, and the caissonwas carried 50 feet west of its true position. Five coils of wire rope wereordered and brought down on a passenger train from St. Louis (350miles) in one night. Additional anchors were put on until the caissonwas held by 18 wire ropes leading up stream and five leading eastward.The arrangement of the anchorage at this time is shown on Plate 23.With these lines the caisson was brought into practically correctposition and held there until it was finally landed on the 10th of Decem-ber, at elevation 157, in 44 feet of water; on the following day the caissonand upper works were completed. It had been necessary to build upthe sides of the caisson before putting in the solid timber and to carry itup four to six feet above the intended height by false sides. If the waterhad been five feet deeper it would have been impossible to land thiscaisson.

The caison had been saved and no loss experienced. Its safety maybe ascribed to two things : first, the mat, which alone prevented the deep-ening of the bottom; and second, the strength of the anchorages. Thecredit for the former is due to the Chief Engineer, that of the latter tothe Resident Engineer.

Air pressure was applied on the 16th of December, the first workdone being to cut through the mat, which occupied six days. Sinking

was conducted in the same manner as at Pier II, and the clay was reachedat elevation 109.0 on the 7th of February, 1890; one week later workwas suspended until the river should be at a more favorable stage.Before stopping work borings had been made below the edge of the cais-son and a well sunk into the clay. The character of the clay was lesssubstantial than had been expected, and it was evidently not prudent tostop at elevation 103 as originally intended.

During March and April the river attained a height exceeding any-thing before observed, the maximum height at the bridge site being 216.2feet on the 25th of March.

By the middle of June the water had fallen enough for it to be safeto resume work, which was done on the 18th of that month. The prog-ress of sinking through clay was slow, especially as three of the five clayhoists proved to be of inferior workmanship. On the 18th of Augustthe cutting edge reached its final position at elevation 85.39, eighteenfeet lower than had originally been intended. An experimental wellwas sunk to elevation 78.15 and a boring carried from the bottom of thiswell to elevation 72.15. On the 4th of September this foundation wascompleted.

Full detailed records of the cost and progress of sinking are given inAppendices I and J. The rate of progress of sinking is shown graphi-cally on Plate 28. For twenty-five days in August and September, 1890,the work was carried on in over 100 feet of water; the actual maximumdepth at which men worked was about 108 feet.

The detailed cost of the entire pier was as follows:

Material.

Labor.

Total.

Total.

$1 890.3032 780.14

7 170.56

6 373.14

$1 788.07

18 006.78

$3 678.3750 786.92

9 620.47

8 548.00

2 449.91

2 174.86

Cost, not including sinking, protection, etc.

$48 214.14

$24 419.62

$72 633.76

$72 633.76

f10 438.48

7 608.75

$6 698.43

3 778.95178.69

59 773.08826.86

$17 131.9111 387.70234.5076 615.89

6 273.58394.81

55 81

16 842 81

5 446 72

Riprap...

Insurance...

394.81

Sinking, protection to foundation, etc.

$40 782.38

$71 256.01

$112 038.39

112 038.39

Total Foundation.

Masonry (4870 cubic yards).

. $184 672.15. 124 679.77

Total cost of Piek

$309 361.92

The total volume of the foundation is 47 feet by 92 feet by 39.6feet, equal to 171 230 cubic feet; so that the cost of the foundation, notincluding sinking and placing, was $0,424 per cubic foot and the costincluding everything $1,078 per cubic foot.

The entire pier, including the masonry, was completed on the 23dof January, 1891. The pier had been sunk 18 feet deeper than originallyintended, this increase of height being made entirely in the masonryand the pier kept to its proper dimensions by a reduction of batter,which is shown on Plate 14.

Three samples of the same character as those taken from Pier IIwere taken from the clay on which Pier III rests and tested with thefollowing results:

First sample.Broke under 503 pounds

Second “ “ “ 503 “

Third “ “ “ 603 “

if-

The first and second samples had small cracks in them and the thirdsample appeared sound.

The weights and pressures for Pier III are as follows:

90 458 cu. ft. timber @ 50 lbs.

Ironwork.

2379 cu. yds. concrete @ 3780 lbs..

4870 cu. yds. masonry @ 4200 lbs.

Total weight of pier.

Superstructure.

Live load.

Total weight on foundation...

Deduct for buoyancy 212 700 cu. ft. belowelevation 182 @ 62.5 lbs.

Deduct for sand displaced as above.

Fatigue weight .

Deduct skin friction as above.

Actual probable fatigue pressure.

4 522 900366 9708 992 62020 454 000

34 336 4904 908 0003 164 000

42 408 490... .9 808 lbs. per sq. ft.13 293 750

29 114 740... .6 733 “ ‘

10 032 000

19 082 740... .4 413 “ “ “ “

4448 000

14 634 740... .3 385 “ “ “ “

The fatigue pressure, therefore, on this foundation is a little lessthan on Pier II. As already stated, it would have been wiser to makeboth caissons alike and both 50 feet high instead of 40 and 60 feet.

The foundation of Pier III is sunk 21 feet below the surface of theclay; but as the last nine feet of clay were of a sandy character, thisfoundation is, if anything, inferior to that of Pier II. The clay which itrests on, however, is entirely solid and free from sand.

In August, 1892 an additional mat was placed around this pier inthe same manner as was done at Pier II: 1550 cords of brush and 8tf9