6-inch sewer would actually cause less stranding and less deposition, but it is also true that such things as combs and brushes, which might accidentally enter the sewer, would tend to choke a 6-inch sewer more often than they would tend to choke an 8-inch one. Consideration of such small details and apparently minor matters must be given to a well considered and well balanced system, and it is the speaker's opinion that the sewers as designed will provide for the prompt and satisfactory removal of all sewage and drainage in an economical way. A cheaper system could have been, no doubt, designed, but the maintenance of a system in which deposition and possible stoppages would occur would have proven costly and unsanitary and unsatisfactory. The system designed and now being constructed will have a life, it is confidently believed, that will carry it through many generations and will suffice even when Coney Island becomes a city by the sea, with an all-year-round population of a million people. Mr. Conlon is to be congratulated upon his paper and upon having had so large and important a part in the development of the Mecca of metropolitan New York-Coney Island. MR. WM. C. ORMOND: What percentage of the sewers have been completed? MR. CONLON: When the contracts now under way are completed, almost the entire sewerage system from West 15th to Sea Gate will have been constructed. This is nearly 50% of the entire Coney Island system. MR. ORMOND: It looks as though it would cost a few dollars. I have been down to the work myself, and I realize the conditions are difficult, and that it is no easy matter to provide sewerage facilities for such a place as Coney Island. Can you give any idea of the cost? MR. CONLON: There is no doubt that the system will be expensive, but that must be expected in such construction. In view of the benefits derived and the permanent nature of the work done the expense is fully warranted. The value of the contracts completed and those now under way is about $800,000. MR. Cuozzo: Is the system to be taxed on the people? I, naturally, am interested in this part of it. MR. CONLON: The entire cost is assessed on the property benefited. MR. ORMOND: We have had fewer complaints about assessments in Brooklyn than anywhere else. No matter how expensive this work should be, it is worthy of the cost. BROOKLYN ENGINEERS' CLUB No. 124 EXPLOSIVES ON THE CATSKILL AQUEDUCT. BY J. S. LANGTHORN, MEM. B. E. C. Presented April 9, 1914. April 9, 1914. It has been suggested that a description of the methods employed on the Catskill Aqueduct for handling explosives might be of interest and profit on account of the large amount used and the variety of conditions encountered. The total amount of rock excavation from the Ashokan dam to Silver lake reservoir in grade and pressure tunnels alone was about 2,769,000 cubic yards, and over 12,000,000 pounds of dynamite were used. Of the total length of 126 miles of aqueduct, 65 miles were tunnels. Beside the tunnels, rock was excavated from dam sites, quarries, cut-and-cover aqueduct and highway locations, and in the relocation of the Ulster & Delaware Railroad. Large quantities of material were also loosened by dynamite in advance of the steam shovel. The work was carried on in places varying from the busy and crowded portions of New York City, such as Broadway and 25th street, to the almost inaccessible Breakneck location. From the beginning of construction it was realized that the utmost care was necessary in the handling and use of explosives, and to this end the co-operation of the contractors and the Municipal Explosives Commission was obtained. As the City tunnel, comprising 18 of the 65 miles of tunnel on the entire work, was the last to be undertaken and inherited the experience of previous work, and as its location through the most densely populated part of New York City required the utmost care and precautions, this paper will deal chiefly with the methods followed on that part of the work. TRANSPORTATION Before taking this up, however, we will follow the travels of a stick of dynamite from the mill to the drill hole, every step of which is strictly regulated. At the mill it is wrapped in paraffin paper, packed with sawdust, to absorb any leaking nitroglycerin, and placed in 25 or 50-pound boxes, made and labelled in a definitely prescribed way. The boxes are packed in a specially inspected car that is placed in the middle of the train and separated from cars containing inflammable articles, charcoal, cotton, acid, lumber, iron, pipe, or other articles liable to break through the end of the car in case of accident. Time permits only the briefest mention of the precautions laid down through the regulations of the Interstate Commerce Commission and the rules of the American Railway Association for the transportation of explosives and other dangerous articles. The railroads, keenly alive to the dangers, maintain through the American Railway Association a Bureau of Explosives, the chief inspector of which has an office at 24 Park place, New York City. Dynamite for New York City is taken from the cars in New Jersey and stored on barges in the harbor. From these a small power boat carries it to designated piers, whence it is delivered through the city by special wagons. Once it reaches the city it is under the control of the Municipal Explosives Commission, whose regulations are enforced by the Fire Department through its Bureau of Combustibles. The wagon, horse drawn or electric storage battery propelled, must be of a certain type with the word "EXPLOSIVES" in letters 12 inches high on its sides and back, and a red flag marked "DANGER" always flying. Two persons with certificates of fitness issued by the Fire Commissioner, after examination by the Municipal Explosives Commission, must be with the wagon, which is required to avoid streets with elevated railroads, subways or crowds, except for one city block. Exploders are transported separately. The wagon load is limited to 1,000 pounds and its use restricted to between sunrise and sunset. Upon arriving at the work, one man remains with the wagon while the other makes the delivery. The boxes are at once taken to the magazine and unpacked. In opening the boxes no metal is used, only wooden mallets and wedges. On leaving the magazine the dynamite is placed in charge of a licensed blaster, who carries the dynamite to the heading in substantially covered wooden boxes, prepares the primers, loads the holes and fires them. LOADING For those not familiar with rock tunnel excavation, a short explanation may be permitted. The City Aqueduct tunnels were generally excavated by the top heading method. This consists of two operations: the so-called heading taken out first with the bench following. The heading consists of the upper semi-circle and is excavated as shown on Figure 124 - 1. The cut holes consist of the six inner holes; they are not driven perpendicular to the face but are inclined towards the vertical diameter so as to come almost to a meeting on the vertical diameter at a point about seven feet from the face. Next to them and parallel with the upper circumference, another set of holes are drilled perpenIdicular to the face of the tunnel. These are called the relief holes or relievers. Beside them at practically the circumferential breaking line of the tunnel another set of holes are drilled, called the line or rim holes. The spacing and arrangement of these holes are shown on Figure 124-1. In shooting the heading, the cut holes are fired first. If the shot is successful, the wedge of rock bounded by the inclined cut holes is thrown out. If the entire depth of rock is not thrown out by the first shot the holes have to be re-loaded and re-fired. Following this, the relief holes are loaded and fired and then the line holes. The bench is then removed in the manner shown in the diagram. In general tunnel practice, it has been customary to load all the holes in the heading at once. The advantage of this is that the work can be done while the tunnel heading is free from smoke, and the men are not hurried. If each of the shots, the cut, the relief holes and the line holes are loaded separately, it necessitates the shooting squads staying at the tunnel face a longer time to load the round to be fired than would be required to connect up the firing wires. The number of trips through the smoke is the same, however, in each case. The air at the face is comparatively clear, as the compressed air is turned on after the cut is fired. Combined loading, while having certain merits, has also its dangers in that where all the holes were loaded at once the collars of the holes adjacent to the cut might be blown off when the cut was fired, the dynamite shot out into the muck, or a shifting of ground made in such a way that the hole would be cut off and dynamite remain in the bottom of the hole concealed from view by the rock that had slipped over it. Where such a condition occurs, there is the utmost danger of the next drilling shift drilling into this undischarged dynamite which was entirely concealed from view. For these reasons, the Board's engineers |