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The accompanying commercial statistics for the fiscal year ending June 30, 1892, have been furnished by Mr. Charles S. Rogers, Rockport, Mass.

The dates and amounts of appropriations for this work are as follows:

Act of July 5, 1884

August 5, 1886.
August 11, 1888
September 19, 1890

$100,000 100,000 100,000 150,000

Total

$450,000

Money statement.

July 1, 1891, balance unexpended

$127, 678, 63 June 30, 1892, amount expended during fiscal year.

77, 020.52 July 1, 1892, balance unexpended.. July 1, 1892, outstanding liabilities

50, 658.11

$19, 627. 18 July 1, 1892, amount covered by uncompleted contracts 16, 351.53

35, 978. 71 July 1, 1892, balance available

14, 679. 40 Amount appropriated by act approved July 13, 1892.

150,000.00 Amount available for fiscal year ending June 30, 1893...

164, 679. 40 Amount (estimated) required for completion of existing project.... Amount that can be profitably expended in fiscal year ending June 30,

4,400,000.00 1894 Submitted in compliance with requirements of sections 2 of river and

250,000.00 harbor acts of 1866 and 1867.

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REPORT OF BOARD OF ENGINEERS ON LOCATION, PLAN, AND ESTI

MATES FOR HARBOR OF REFUGE AT SANDY BAY, CAPE ANN, MASSACHUSETTS.

UNITED STATES ENGINEER OFFICE,

Boston, Mass., March 2, 1892. GENERAL: The Board of Engineers, constituted by Special Orders No. 91, Headquarters, Corps of Engineers, July 26, 1884, “ to consider and report upon the location, plan, and estimates for a national harbor. of refuge at Sandy Bay, Cape Ann, Massachusetts,” ordered to reassemble at the call of the senior member 6 to consider and report upon plan for superstructure of the breakwater at that place,” by Special Orders No. 3, Headquarters, Corps of Engineers, January 12, 189%, and

to “report a plan for substructure as well as superstructure for the entire breakwater proposed for that locality,” by Department letter dated February 1, 1892, has the honor to submit the following report:

Sandy Bay is situated at the northeastern extremity of the promon. tory of Cape Ann, which forms the north limit of Massachusetts Bay. Its shore lines form a little less than a right angle, and their directions are nearly north and souti and east and west. The rocky island of Straitsinouth forms the eastern extremity of one shore line, and the steep headland of Andrews Point the northern end of the other.

Following the adopted line of the breakwater, the bay is 23 miles wide and has a depth of about 2 miles.

On the land side the bay is perfectly protected by steep, high hills, but it is open to the full force of the violent easterly and northeasterly gales of this coast.

At the mouth of the bay sunken rocky ledges exist, viz: Avery Ledge, the Dry and Little Salvages, the Flat Ground, and Abner Ledge. Inside these ledges the bay is entirely unobstructed, and has an average depth of 50 feet at mean low water over an area of about 1,300 acres.

The river and harbor act of August 2, 1882, provided for an examination or survey of this bay with a view to the construction of a harbor of refuge.

Maj. C. W. Raymond, Corps of Engineers, the local engineer, on November 28, 1883, submitted a survey, project, and estimate for a breakwater to form the proposed harbor. His report, which will be found in the Annual Report of the Chief of Engineers for 1884, page 565, states that the project is preliminary and that detailed plans can only be determined after a protracted study of the forces in operation.

This Board, which then consisted of Col. Charles E. Blunt and Lieut. Cols. Wm. P. Craighill and Walter McFarland, Corps of Engineers, in its reports of August 22 and November 20, 1884, stated that the lines selected for the breakwater by the local engineer were the best that could be adopted for the formation of “ a national harbor of refuge of the first class” in this locality, if it be decided that such a harbor is necessary. The Board expressed no opinion as to the character and - details of the structure proposed, it being understood that these would depend upon investigations to be made before the commencement of the work, or during the earlier progress of operations on the substructure. The reports of the Board above referred to are published in the Annual Report of the Chief of Engineers for 1885, pages 523 and 528.

No detailed plan for this breakwater has yet been adopted by the Department, but the work in progress upon its construction since November, 1885, has been carried on in conformity with the preliminary project, modified from time to time by the approval of propositions for the expenditure of successive appropriations. A brief statement of the main features of the preliminary project, and of the modifications already adopted, with the reasons leading thereto, seems necessary to show the present condition of the improvement, and to explain the recommendations made by this Board, which are based upon the later experiences here and elsewhere in this and other countries.

The breakwater, as proposed by the local engineer and approved by the Board of 1881, consisted, essentially, of two branches, one starting from Avery Ledge and extending north by west to Abner Leilge, a distance of about 3,600 feet; the other starting from Abner Ledge and extending west-northwest for a distance of about 5,400 feet. Along the southern branch, between Avery and Abner ledges, the average mean

ENG. 92 -36

low-water depth is only about 45 feet, while along the western branch the average mean low-water depth is about 65 feet. The essential features of the structure adopted for estimate in the preliminary project of 1884 are as follows:

1. A solid conical pier of masonry on Avery Ledge, the diameter at top being 30 feet and at bottom 45 feet, and a similar but smaller pier at the western end of the breakwater.

2. A substructure consisting of an enrockment formed by dumping granite grout from barges, the smallest rubble placed in the core, the medium-sized in the inner layer and the largest in the outer covering. This arrangement was intended to increase the volume of the voids, and thus diminish the amount of stone required for the enrockment, and was based upon the experience at Bastia. The upper surface of the substructure was to be 15 feet below extreme low water. This depth was at that time considered to be the limit of the effective action of the sea, the adopted project for the Delaware Breakwater placing the base of the superstructure only 12 feet below mean low water.

3. A superstructure consisting of a masonry wall formed of very large stones laid up dry below water, and above low water a masonry wall laid in cement. The dry wall below water was provisionally adopted, pending further investigation, because of the great facilities for obtaining very large stones in the immediate vicinity, and because of the experience of the local quarrymen in laying large stones under water.

Assuming an annual appropriation of $100,000, and the employment of the best plant and the Bastia method, with rubble at 70 cents per ton, this breakwater was estimated by the Board of 1884 to cost $5,000,000.

It was proposed to commence the construction of the breakwater by building the pier on Avery Ledge, and to continue the work by extend ing the substructure and superstructure from that point along the southern branch toward Abner Ledge. This course was adopted because the southern branch of the breakwater is situated in the least depth of water, where beneficial results could soonest be obtained, and because it shelters the anchorage from the most violent northeast storms. The western branch covers the anchorage from the less vio. lent northerly storms, and would be of little or no value until after the construction of the southern branch. Avery Ledge is the most exposed portion of the whole line, and it was considered desirable to determine by actual construction the feasibility of building this most exposed part before committing the Government to heavy expenditures on the rest of the work. Avery Ledge is a great danger to navigation, many vessels having been wrecked thereon. It was considered that a pier constructed upon it would, therefore, be of some immediate value to commerce, would form a base for experiments to determine the character and details of the superstructure, and, finally, would serve to hold in position a spindle necessary as a range in forming the substructure. It was believed that it would be otherwise impossible to maintain such a spindle permanently in this locality.

On May 20, 1885, under the orders of the Department, the local engineer submitted a detailed project for the construction of a stone and concrete pier on Avery Lodge, and reported that he had considered a project for a pier consisting of a heavy cylinder of cast iron filled with concrete, which he rejected tor reasons stated. On June 25, 1885, the Board of Engineers for Fortifications and River and Harbor Improvements, etc., to whom this project was referred for consideration,

reported in favor of the building of the pier “of concrete in situ inside of a cast-iron casing, following the method used in the foundations of the light-house at Duxbury Pier, Massachusetts." The Chief of Engi . neers, in his indorsement upon this project, dated July 2, 1885, remarked that it would be less costly to cover Avery Ledge with masses of stone or concrete blocks, forming thus the termination of the breakwater after the portion contiguous to the ledge should have been built.”

On September 10, 1885, under the orders of the Department, the local engineer submitted a project for the expenditure of the available funds. In conformity with the orders, the project provided for “ a structure upon the summit of the ledge,” and for the distribution of broken stone upon the bottom along the line of breakwater.” By investigations in the locality, and by the study of more recent experience in foreign barbors, it had become apparent that the limit of wave action heretofore adopted—15 feet below extreme low water-was altogether too small, and that it would not be safe to establish the foundation of the superstructure at a higher level than 22 feet below mean low water. Under these circumstances it was considered that the plan for a dry masonry wall must be rejected, and that if any wall was to be built below low water it must be of concrete deposited either in place, as at Quebec and Wicklow, in bags, as at Aberdeen and New Haven, or in sloping blocks, as at Colombo, Réunion and elsewhere. The project repeats the opinion that the establishment upon Avery Ledge of a cast-iron cylinder, to be filled with concrete, is practically impossible; provides for the construction of a portion of the rubble base of the breakwater, the upper surface to be 40 feet in width and 22 feet below mean low water; states that it will probably be found most economical to construct the superstructure of concrete, and finally recommends the placing of two large concrete blocks upon the ledge. The advantages of the proposed structure on the ledge are stated in the project as follows:

1. It will test the durability of concrete exposed to ice and heavy seas in this locality. No wear from floating ice is anticipated, but it is possible that on the occasional quiet days of winter the water in contact with the concrete surface may freeze, and thus that surface may be gradually disintegrated.

2. It forms a convenient central core from which to construct in the future the pier of the breakwater, and it will be useful for this purpose withont reference to the method of construction adopted. Thus the final project for the pier is left to be decided upon after the durability of concrete in this locality has been determined by actual experiment.

3. Its spindle forms a permanent range mark for the construction of the rubblo base of the breakwater.

This project having been approved by the Department, work upon the rubble substructure was commenced under contract in November, 1885. The method of arranging the rubble suggested in the preliminary project was abandoned, the funds available not being sufficient to justify the establishment of the necessary plant for this purpose. Preparations were in progress for the formation of the concrete blocks when Maj. Raymond was relieved from charge of the work on February 4, 1886.

On May 14, 1886, the Department modified the plan of construction for the pier at Avery Ledge, authorizing a construction of 6 concrete in situ inside of a cast iron shell, as suggested by the Board of Engineers for Fortifications and for River and llarbor Improvements, etc., June 25, 1885.” This cast-iron and concrete structure was completel in July, 1886; the iron shell was destroyed in less than a month, and

finally the concrete and spindle were swept away. Since that timo operations on Avery Ledge lave been contined to the erection of spindles and their replacement when swept away by collision or storms. (The last spindle, 8 inches in diameter, sunk into the rock 34 inches, has been standing uninjureel since January 1, 1889.)

Under various appropriations and contracts, work upon the base of the southern branch of the breakwater has been in progress since November, 1885. The Board is informed that at the close of the existing contract the substructure between Avery and Abner ledges, and beyond, a distance of about 5,000 feet, will liave been essentially completed, with its upper swface 40 feet wide and 22 feet below mean low water, in accordance with the project. About 538,000 tons of unarranged rubble, at an average price of 67 cents per ton, will have been deposited to form this structure. The Board finds no evidence that any of this rubble has been moved by the action of the sea.

The original project of a random stone substructure, carrying a ma-. sonry wall, was proposed in order to save the great expense of carrying the rubble mass above high water, which involves the deposit of an enormous amount of material below the limit of the effective action of stornis. The execution of such a project is only possible with very large appropriations and the best appliances. If this method of construction is to be followed, the Board is of the opinion that the top width of the substructure should be 40 feet, and it should be 22 feet below mean low water, as now provided for.' The Board is further of the opinion that the employment of concrete in place or in bags of large size in the construction of the superstructure is not advisable, and the only method of wall-building which gives reasonable promise of success is the method of sloping concrete blocks adopted at Colombo and Réunion.

The Board, however, is not prepared to recommend such a construction at the present time. As stated in the revised project for the Delaware Breakwater (vide Annual Report of the Chief of Engineers for 1891, page 1079), there is no precedent for the construction of an offshore breakwater on the sloping block system. All the breakwaters built on this plan have started from the shore, and this fact has determined the character of the plant employed. Thus at Colombo, Madras, Mormugoa, Manora, Kustendjie, and Réunion, the blocks were placed in position by large and costly overhanging balance cranes, which trayeled on railways along the breakwaters, and could be run on shore duing seasons of exposure. The peculiar advantages of such machines would be entirely lost in an offshore construction. The exposure of the site to the violent action of waves and currents, and the necessity of accurate adjustment imposed by the sloping block system, render the use of floating appliances entirely out of the question. A special plant would have to be devised, which would be experimental in character and doubtless very expensive. The leveling of the upper surface of the substructure for the foundation of the wall would have to be done by divers and would be slow, difficult, and costly. The construction of a pier on Avery Leilge, as an abutment for the end of the wall, would be troublesome and expensive, as shown by previous experience. Finally, no experiments have yet been made to determine the durability of concrete in this locality, and the Board is far from satisfierd that this material would bear without rapid disintegration the exposure to which it would be subjected.

Under existing circumstances the Board is of the opinion that the best method of construction for the southern branch of the breakwater

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