.THE.MEMPHIS BRIDGE.

27

The track is laid throughout with 80 poflnd steel rails of what is ukuowu as the Michigan Central pattern* or Pattern 8001 of the Illinois u.Steel Company by which they were rolled. i

The Highway uses the same floor as the railroad from the EastAbutment to Pier V. At the east end of the. bridge the Highway Ap.proach is a solid earth embankment, finished with a granite pavementlaid on Portland cement concrete foundation and 30 feet wide betweencurbs; this paved approach is on the line of Virginia Avenue, and itdescends with a 13 per cent, grade from the abutment, reaching the streetgrade near the east line of Delaware Avenue. At the west end the High-way Approach makes two rectangular turns. A 60 feet plate girderspan, supported at the south end on the first viaduct span and at thenorth end on an iron bent, connects the bridge floor with a woodentrestle; this wooden trestle, which is parallel to the viaduct and 80 feetfrom it between centers, is a simple cheap structure 20 feet wide on top,descending towards the west with an eight per cent grade.

The quantities of the principal materials in the approaches are asfollows:

EAST RAILROAD APPROACH.

Earthwork... cu bi c yards 15 076

Delaware Avenue Bridge, Concrete..... “ “ 216

“ “ “ Masonry. “ “ 408

“ “ “ Iron in Superstructure.. .pounds 87130

“ “ “ Brick paving under.square yards 209

EAST HIGHWAY APPROACH.

Earthwork.cubic yards 1 140

Granite paving.square “ 363

WEST RAILROAD APPROACH.

Earthwork.cubic yards 69 525

Piles in work. lineal feet 27 267

Timber in work. feet B.M. 976 092

Iron, bolts, etc.pounds 69 344

WEST HIGHWAY APPROACH.

Iron in girders and support for same.pounds 60 430

Timber in trestle.feet B.M. 238 000

Piles “ “ lineal feet 3123

Iron “ “ .pounds 14 513

Earthw ork.cubic yards 876

! - VII.

shore: protection.

While comparatively little shore protection was done at Memphis,that little was very important. It was put in with reference to twothings; to hold the bluff which forms the east shore both from abrasionby the river and from surface-wash, and to restore the west shore tosomething like its position in 1886.

The east shore protection consisted; first, of a mat, the upper edgeof which was near the high water mark; and second, of grading thebank to a uniform slope from the east abutment to Pier I and pavingthis slope.

The mat was of the character used by the Mississippi River Com-mission in its shore protection Work. It is 365 feet wide and 1320 feetlong, extending from 240 feet below the axis of the bridge to 1080 feetabove it. This mat was put in in September to December 1890. Itconsists of brush and poles and is heavily covered with riprap. Theportion below low water is secure. The portion above low water mayrequire repairs and will at all events require watching, or it will bedestroyed by the negroes who would steal the poles for fuel.

There were used in this mat 6520 cords of brush and poles and 9304tons of stone.

The sloping of the bluff was done with special reference to prevent-ing surface water cutting in around the edge of the small piers and soundermining the foundations. This work was postponed till after thecompletion of the bridge. The ground was graded to a uniform slope ofone vertical to four horizontal; and this inclined surface was not made atrue plane, but sloped slightly from the center and each edge so as toform two parallel valleys 120 feet apart, the total width of the aboveslope being 180 feet. This slope was then paved with limestone blockslaid rather roughly and bedded in sand. This pavement will requiresome little repairs from year to year, and these should be made immedi-ately whenever it shows sign of settlement. They should be made by

removing the stones which have settled, filling the cavity underneathwith well packed gravel, and replacing the original stones.

The protection of the west shore was of an entirely different char-acter and consisted principally of a screen dike which was intended toform a deposit behind Pier IV; the general location of this screen dikeis shown on Plate 2. It is 1155 feet long, of which 1080 feet are abovethe axis of the bridge and 75 feet below. It was constructed by firstplacing a mat 150 feet wide* 50 feet inside and 100 feet outside of thecenter line, on the bottom of the river; this mat extended below thelower end of the screen dike 155 feet and 370 feet above the upper endof the screen dike; for a length of 550 feet from the upper end, the matwas made 250 feet wide extending from the bank of the river outward.Two lines of piles, 14 feet apart and 15 feet between centres in each line,were driven through the mat, waling pieces were bolted to the piles, andthe bents were braced. A second mat, 76 feet wide, was woven, theupper edge of which was attached to the top of the piles and the loweredge allowed to fall on the foundation mat; this was held in position byputting riprap on the lower edge. The upper end of the screen dike wasconnected with the shore line by a short dike- built of brush and stone,the top being at the same elevation as the top of the screen dike itself.This structure forms a current deadener, and with each successive flood anadditional deposit is made behind it, so that in due time the whole spaceshould be filled to the level of the bottom land. When this has occurredthe new shore line should be heavily riprapped.

Some trouble was experienced by the river cutting behind the upperend of the screen mat, and to meet this condition the short brush andstone dike was raised to the level of extreme high water and extendedinland about 200 feet to a point where the natural surface of the groundis within a few inches of high-water level. This dike may require re-pairs from time to time. Two other dikes of a more or less temporarynature were put in to hasten the silting action back of the screen.

There were usnd in the screen mat and the auxiliary work 14 476lineal feet of piles, 67 M. ft. B.M. of timber, 23 500 pounds of bolts andwashers, 5040 cords of brush and poles, 19 900 pounds of wire and 6466tons of rock.