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APPENDIX E.

REPORT OF FEBRUARY 15 , 1887 .

New York, Feb. 15, 1887.

George H. Nettleton, Esq.,

Kansas City & Memphis JRailway and Bridge Co., Kansas City, Mo.

Dear Sir : At your request I went to Memphis on Nov. 23, 1886, accom-panied by my assistant, Mr. E. Duryea, Jr., and made arrangements for Mr.Duryea to begin work as early as possible in making borings on the locationof the proposed bridge across the Mississippi Eiver. I returned on theevening of the following day, leaving Mr. Duryea at Memphis, where he stillremains. I again went to Memphis on the 28th of December, reviewed theground and examined specimens obtained from the borings. The boringswere continued until stopped by the flood of the present month. While notas complete as I could wish to have them, they are enough to show in allessential features what the character of the bottom is.

The place selected for the crossing of the river is near the foot of Broad-way, the axis of the bridge to be at right angles to the current, and the ap-proach from the east being through Alabama Street (Virginia Avenue), theangle between the axis of the bridge and the street line being about 42°.

In our notes the point where the bridge line intersects the center line ofAlabama Street is called Station 100, the station numbering running westwardfrom there.

In this report I have assumed that the bridge would be so designed as togive a clear head room of 65 feet above high water, the bottom of tie on thebridge to be 70 feet above high water.

The ground on the Memphis side is a level bluff, the height of whichcorresponds almost exactly with this required elevation: the track can be laidon the surface of the ground almost as it now is.

The river at this place is practically 2000 feet wide, varying from 1900 feetat extreme low water, to 2100 feet when bank full.

The ground on the west side is a low bottom land, the average elevation ofwhich is about 5 feet below extreme high water.

In our levels we have called the low water of the United States Engineer’sgauge zero; high water is 35.15 feet above this gauge, and extreme low wateris 0.98 feet below this gauge. The elevation of tie on bridge would be 105.

The elevation of your tracks on the West side of the river is 37, so that theWest Approach must descend 68 feet. I should propose to make this descentwith a 1.25 grade (66 feet per mile), which will require a distance of 5440 feet,all of which would be on a straight line. Of this, I have estimated on building

the 3200 feet next to the bridge in the form of a permanent iron viaduct, andthe remainder as a timber trestle to be subsequently filled, unless availablematerial can be found for building an embankment at once.

Although the West Approach is long, its construction is very simple.

All the difficulties of building a bridge at Memphis are concentrated in thebridge itself, 2000 feet long.

The channel of the river is as well fixed here as it is ever found on theMississippi Eiver, and the work proposed by the Mississippi Eiver Commissionfor the preservation of the harbor of Memphis, much of which is already com-pleted, will secure the permanency of the channel where it now is.

The long continuance of the channel in one place has probably reducedthe width of the river here to that actually required for its discharge, as isalways the case when the channel of a silt-bearing river remains fixed for along period. The main discharge oi the river occupies the eastern two thirdsof its width, the current in the western one third being decidedly lighter andthe depth of water less. The water is deepest and the current strongestabout one third of the way over from the east shore.

The east bluff is the east boundary of the alluvial delta of the Missis-sippi. It is composed of clay and layers of sand and gravel, with a thinstratum of ferruginous sandstone, but practically is entirely without rock.The material below water is generally well adapted to bearing the weight of afoundation, but not wholly safe to resist the erosion of the river without arti-ficial protection. The location of the bridge, a few hundred feet below a pro-jecting point of the bluff, is one in which the necessary artificial protectionscan be made very cheaply.

The first boring made was on the west shore. This boring found sandto a depth of —52, when a hard blue clay was encountered. This claychanged to a very light-colored clay at a depth of — 72, which changed againto a brown clay at a depth of —98, which brown clay changed to a blue clay at—114.5, and this continued to —122, when the boring was abandoned. Thelower part of the cream-colored clay was sandier and softer than any of theothers. The second boring was made in the river 660 feet east of the firstboring, or about at the westerly limit of the strong current. At this boringthe upper clay was not found, the light-colored clay being found at —75.6and the brown clay at —101, the material being evidently identical with thatfound on the west side. The next boring was made 650 feet farther east, or a

little west of the strongest current. In this boring clay was struck at —84,and resembled in character the softer and sandier portion of the cream-coloredclay. The boring was discontinued at —104, being then apparently on thesurface of the brown clay, though we were driven out by the flood before thiscould be positively determined.

These clays are in all probability alluvial clays which have been de-posited by the river. The two lower clays are evidently continuous for a largedistance, and I believe are entirely safe for foundations. The upper clay(found only on the west side) is probably a later pocket much less in extent,but safe for a foundation at the location of the west shore pier. These allu-vial clays probably meet the older formation of the east bluff about 200 feetfrom the east shore, but I have as yet no facts to verify this probability. It ispossible that the lower clays are identical with strata which exist under thebluff.

I should propose to found the piers of a bridge at this place on caissonswhich should be sunk to the clay and a few feet into it, the caissons to be ofsuch size that the fatigue pressure on the base should not exceed tons persquare foot. I should also wish to place on the bottom of the river aroundeach pier a woven mat (such as is used by the Mississippi Eiver Commissionfor shore protection) about 300 feet square ; this woven mat to be sunk uponthe bottom of the river and to form the basis of a moderate riprap protection,the object being to prevent scour around the pier, and so give to the founda-tions the stability due to the lateral support of 40 or 50 feet of sand in addi-tion to that due to the bearing on the base.

The difficulties of building a bridge here would lie in the eastern two thirdsof the river. A pier could be built on the western edge of this two thirdswithout serious difficulty. If piers are to be built in the eastern two thirdsthere is not much choice of location. As a single pier in the middle of thistwo thirds would make two spans of about 660 feet, which is not more thanan economical length of span, the choice would seem to lie between crossingthis portion of the river with two spans or with one. In the former case thebridge would consist of three spans of about 660 feet each, spanning the whole2000 feet of the river. In the latter case the bridge would consist of one mainspan of 1300 feet (to be built on the cantilever principle) spanning the easterntwo thirds, with anchorage arms extending over the east shore and the westernpart of the river.

These two plans have been considered separately and estimates made.