By September 1, all the fender piles, except one, were in place, including the two isolated clusters of piles, of 9 piles each, at the outer corners of the pier. The last fender-pile was subsequently settled with the force-pump-the proximity of the freight house, built across the shoulder of the pier, preventing the use of the pile-driver. The number of piles driven during the fiscal year was 107, making a total in place of 185. During the months of September and October the fender-piles and the intervening wale and chock pieces were connected to the pier, the heads of the piles were cut down to a uniform height, the two clusters at the end of the pier were securely bolted and chained, and the machinery was dismantled. The partial reconstruction of the superstructure of the pier-head was then proceeded with. The 4 by 9 inch floor-joists of the seventeen bays, between the fifty-fifth and seventy-second rows of piles, were taken up and carried ashore, to be replaced at the proper time by pieces of larger dimensions. The 12 by 12 inch stringers of this section of the pier becoming thus more exposed, close inspection revealed the fact that a greater number of them than had been anticipated were in a more or less advanced state of decay. The 9 by 9 inch cross-beams were in no better condition. Seventeen of the former and twelve of the latter were subsequently taken out and replaced by new pieces. The remainder of the decaying pieces cannot be removed until new lumber has been contracted for. All the lumber that could be profitably used at the time having been put in place, the work of replacement was discontinued. During the rest of the season heavy chock-pieces of yellow pine were fastened to the wale-pieces with long drive-bolts and between the heads of the fender-piles, to brace the piles laterally. This was accomplished by the 15th of February, when work closed for the season. It was expected that $13,000, the amount asked for in the last annual report for the completion of the pier, would be sufficient for that purpose. A recent examination and an estimate based thereon show, however, that this amount must be increased to $19,000. This increase of the estimate is solely due to the rapid deterioration of the lumber already laid in the pier and of that originally purchased and piled upon the beach. Attention has been repeatedly called to this matter, which has now assumed such proportions that a practical rebuilding of the superstructure, from the shore to the seventy-second row of piles, will be necessary. Many of the pieces marked to be removed are but slightly affected by decay; it is certain, however, that they cannot last much longer, and their removal can more advantageously take place now while the general overhauling is progressing. Thus 70 per cent. of the stringers and 51 per cent. of the cross-beams will have to be removed in the pier-head. In the narrow part of the pier several stringers, 49 per cent. of the cross-beams, and all of the floor-joists must be removed and replaced. Instead of using the old planks as decking for the pier-heads, new planking has been estimated for, as the former will be nearly worthless when the time arrives to lay them. The cost of removing so much finished work, in order to reach the pieces that are to be replaced, adds materially to the increase of the estimate. The state of the pier at the end of the fiscal year is as follows: The substructure is finished. The superstructure of the narrow part of the pier is laid as originally planned, but must be rebuilt; that of the pier-head is in great part removed, awaiting reconstruction. All the fender-piles are in place and connected to the pier. If sufficient appropriation be made, it is proposed during the coming season to continue the renovation of the older portions of the superstructure. During the fiscal year ending June 30, 1884, it is proposed to finish the pier according to the original plan, if the necessary amount shall be appropriated as a whole. This work is in the collection district of Delaware, the nearest port of entry being Wilmington, Del. Fort Delaware is the nearest fort, and the breakwater light is the nearest light-house. The original estimated cost of the pier was. Which was reduced previous to 1878 by various revisions to.. Total amount required July 1, 1882, for completion of pier according to Respectfully submitted. $387,419 67 360,000 00 374,500 00 355,500 00 19,000 00 A. STIERLE, Assistant Engineer. Col. WILLIAM LUDLOW, Captain, Corps of Engineers, U. S. A. F 20. ICE-HARBOR AT THE HEAD OF DELAWARE BAY. The original preliminary report upon this harbor, given on pages 612 and 613 of the annual report of the Chief of Engineers for 1880, suggested that if it should be finally determined to build the harbor, detached from the shore in the bay between Liston's and Reedy Island, a structure consisting of lines of piers with a decking above high-water, resting upon iron piles, promised certain advantages over the solid detached stone piers, of which the other ice-harbors in the Delaware are built. These advantages may be summarized as follows: The work once begun may proceed in almost any weather; the harbor is capable of indefinite extension as may be found desirable; the open character of the substructure, while the flow of ice is prevented, offers no obstruction to the free passage of the tidal currents, and the harbor will therefore require no dredging to maintain its depth. It affords continuous passage for sailers from end to end, and as many points of mooring as may be required. The cost of an iron and timber structure of this character will not exceed that of the stone piers, and will probably be less. The stone piers are necessarily somewhat widely separated and present comparatively few points for mooring; they interfere with the flow of water and create powerful eddies; they are reached only by boat, and access to them is frequently difficult or even impossible at the very time when, from the pressure of running ice, their shelter and support are most needed. The construction of the timber foundations to low-water and the laying of the stone work above is tide work, and therefore tedious and uncertain. Operations can only proceed during favorable weather, and the pier, until completed well above high-water, is a danger to shipping. It might furthermore be stated that the lines of pier, having a continuous deck, afford opportunities for the placing of lights accessible one from the other, and of storing temporarily, wholly or in part, the cargo of a vessel, if necessary. Other conveniences, such as supplies of coal and provisions, suggest themselves.. The preliminary estimate of cost at prices then ruling was $250,000. The greater present cost of labor and material add to this. The last annual report of the Chief of Engineers, for 1881, page 847, states as follows: Consultation with those interested in the navigation of the Delaware discloses predominating weight of opinion in favor of the vicinity of Liston's over Reedy Island as the proper location for the harbor. The construction will depend partly upon the location, but it may be said that subsequent investigation tends to confirm the conclusion suggested in Colonel Ludlow's report of January 24, 1880, namely, that the structure should be entirely detached from the shore, and be built of iron piles rather than stone piers. The most advantageous position indicated by the chart seems to be in the vicinity of the intersection of the Finn's Point Ranges with the Port Penn Ranges. These ranges make such an angle with each other as to compel vessels to haul nearly five points to eastward to pass from one course to the other. Sailing vessels in winter consequently get as far as Liston's, even with a northeast wind, and are frequently unable to get further, both by reason of the change of course and the masses of drifting ice encountered near the head of the bay. Placing the ice-harbor outside and to the westward of the ranges avoids any possible interference with vessels pursuing their voyages, while it would be perfectly accessible to such as require its protection, whether on the outward or inward passage. After further consultation with the maritime interests, studies have been made during the past year in the direction above indicated of the most suitable plan and details of construction. The simplest form of harbor protected against both flood and ebb tides would be one inclosed between two straight parallel lines of pier, which, with a length each of 1,008 feet and a distance apart of 600 feet, would define a harbor space of about 13.8 acres. Each line of pier would stand upon sixty-four trestles, about 16 feet apart, composed each of four iron or steel piles, with a timber deck, fender piles, and mooring facilities. Red harbor lights at the four ends of the piers would mark the entrance. Further consideration leads to the belief that it would be better to build the two lines of pier, so that each should consist of two lines, making with each other angles looking respectively up and down stream. This form, with the same width of opening at the east and west ends of the harbor, gives more harbor space or conversely allows of the partial closing of these openings without loss of area. Moreover, the angle made by the lines of pier with the currents admits of the more ready flow of ice past the harbor on the exterior without admitting it. The addition to the cost of the works in consequence of this change is about 8 per cent. In considering what should be the dimensions of parts and other details of the proposed structure, it became necessary to inquire as to the strains to which it might be subjected. Aside from the chance of collisions, against which it is impossible to fully protect a structure of any character, the most dangerous pressures to which the harbor would be exposed are those due to the ice moving in the bay at certain seasons under the influences of wind and tide. An attempt to compute the total possible thrust of a field would be useless, since practically no limits could be set to its area and weight. Considering, however, the comparatively open character of the structure, it becomes evident that the greatest resistance to be required of the piles would only be that sufficient to crush the ice in motion against them; in other words, that the ultimate pressure would be limited by the crushing strength of the ice, and that if the piles were able to withstand this the structure would be reliably stable. As a matter of fact, this degree of resistance, if computed from the pressure of a field of solid, clear ice, would never be demanded of the piers, for the reason that the ice, in floating about, is broken into blocks of various sizes, and, from the softening action of the air and sun and the saltness of the water in which it is immersed becomes rotted and disintegrated. After diligent search for data as to the crushing strength of ice through all the engineering records available, it became evident that no information of practical value could be found. Numerous examples are recorded of the destructive effects of ice, but little or no attempt had apparently been made to analyze and classify the forces in action. The only discussions found are as follows: In 1845 a Board of Engineers (report on file in office of Chief of Engineers, U. S. A.), considered the effect of an acre of ice, 12 to 15 inches thick, in motion, with a velocity of 3 feet per second, impinging against a breakwater, and estimated that every foot front of the field would exert a pressure of 27.11 tons against each foot front of the structure. After careful reading of the report, and of the comments thereon by Col. T. J. Cram (page 231, Report Chief of Engineers, 1868), I am unable to determine what pressure per square inch of surface against the breakwater these figures are intended to represent. The annual report of the Illinois and Saint Louis Bridge Company for 1868, contains a discussion of the probable pressure of ice against the piers of the bridge. Under the assumption that the crushing strength of ice is 600 pounds per square inch, it is deduced that the pressure of an impinging floe 500,000 square feet in area and 1.2 feet in thickness against the pier will be about 43.2 tons per square foot, which, at 2,000 pounds to the ton, exactly equals the 600 pounds per square inch originally assumed as the crushing strength of ice. In the absence of reliable data, I made some experiments, the results of which are tabulated in the accompanying exhibit. The blocks used were prepared in different forms of prism, and the ice of which they were composed varied from "snow ice" to the clearest and hardest from the Kennebec River. As was to be anticipated, the figures showing pressures of yielding and crushing vary in consequence between considerable limits, viz: for yielding, from 23 to 300 pounds, and for crushing, from 94 to 1,000 pounds. The blocks were compressed as rapidly as possible. The separation into vertical columus, whether the pressure was applied horizontally or vertically, was a constant characteristic. The conditions of original formation, of internal and external temperature, and in especial of the greater or less accuracy of form, evidently affected greatly the resistances. Great difficulty was found in cutting the blocks to plane surfaces, the saw, even when carefully guided, almost invariably leaving warped surfaces. It was my intention to continue these experiments by freezing the ice in iron molds previously prepared and in such form as should appear most advisable. It may be inferred, however, from the data at hand, that ice in the condition in which it is ordinarily found in the Delaware will begin to yield to a pressure of from 100 to 200 pounds, and will disintegrate under pressure of from 400 to 600 pounds to the square inch; these limits being assumed for the condition of the press in which it would be firmly confined. When floating loosely and in contact with rounded bodies these pressures will be reduced more or less, but in what ratio it would be difficult to estimate. The structure for the proposed ice harbor at the head of Delaware Bay has been devised in accordance with these data. The general plan and details of construction are shown on the accompanying drawing. Each trestle is composed of two vertical and two inclined screw piles 7 inches in diameter, preferably of steel. Each inclined pile is firmly connected to the head of a vertical pile, and all points of crossing are secured by bolted clamps. The form of screw shown is that considered best for the raking piles. For the vertical ones, if found desirable, less development of thread is required. Accompanying this report is also a summary of the detailed estimate of cost of one bay of 16-foot span. The total cost of the harbor as proposed will be $300,000, for which, if it is to be constructed, the whole amount should be available at one time in order to provide for the making of favorable contracts. The actual expenditure per annum should not be less than $100,00J. I desire to record my obligation to Lieutenant Black, of the Corps of Engineers, for his valuable assistance in searching for data regarding the pressure of ice, as well as in the work of the office generally. Money statement. Amount appropriated by act passed August 2, 1882.... $25,000 00 275,000 00 Amount (estimated) required for completion of existing project.. ESTIMATE FOR ONE BAY (16 FEET) FOR ICE HARBOR AT HEAD OF DELAWARE BAY. Cost of material for one trestle: 4 steel piles, 7 inches by 52 feet, wt. 27,000 pounds, at $5 per 1,000. $1,350 00 Cast iron (3 clamps, 4 screws, 2 caps), 24,000 pounds, at 4 cents per pound Bolts and nuts, 200 pounds, at 6 cents. 960 00 $2,322 00 Decking and fender piles: 6 piles, 15 to 17 inch butts, 9 to 10 inch points by 52 feet, at $5.25. 31 50 |