Chapter 08. Excavation

The New York Rapid Transit Railway Extensions · Engineering News, 1914

The general specifications provide for the classification of excavation as earth and rock, rock being led rock in place and boulders over 1/2 yd. Earth excavation is classified as above or below mean high water, and the prices "include the cost of the disposal of the materials excavated, of backfilling, of all decking and bridging for support of street travel, of all sheeting and bracing, and of maintenance and supporting of trenches during and after excavation, of all pumping or bailing, and of the maintenance and support, with all incidental work, labor and material of any kind, of all surface, subsurface and overhead structures and surfaces." (Support of street-railway tracks and elevated railroads is paid for separately as noted below. Underpinning of buildings when required is also paid for separately.)

Rock excavation is paid for, for 6 in. outside the neat line at the sides but no allowance is made on the bottom. It is required that all excavation in rock beyond the side neat lines of the structures shall be refilled solid with concrete which, except for the first 6 in., is at the expense of the contractor, so there is every incentive to avoid excessive excavation and for the use of care in drilling and blasting at the sides.

When pipes, sewers, electric-wire conduits, etc., have to be removed and rebuilt elsewhere, the work is paid for separately. All structures of this kind, however, which do not require change have to be supported and maintained by the contractor, the cost being included in the price paid for excavation. All gas pipes are removed and placed above ground during construction, and replaced afterwards, the necessary house connections, of course, having to be changed each time. This work is paid for at a price bid per lineal foot for each size of pipe which has to be taken care of. The ordinary 4- and 6-in. pipes from which the house supplies are taken are usually relaid along the edge of the sidewalk, on top of the timber decking. The large 10- and 12-in. mains are usually supported overhead.

In planning the excavation it has generally been found advisable to so arrange the work that if the material is suitable, there will be sufficient left till the end to complete or nearly complete the backfill, which the specifications require shall be made with "sand, gravel or other good, clean earth, free from perishable material, or stones exceeding 6 in. in diameter, and not containing in any place a proportion of stone of or below that size exceeding one part of stone to five parts of earth."

Usually there is no opportunity to store material for this purpose, but on some sections, where there is earth, a certain portion at the ends of the section is left to be excavated after most of the structure is completed. Where this is not possible, or where there is little or no earth, dependence is usually placed on material excavated elsewhere, mostly from cellars, etc., of which there is usually sufficient available at all times and in nearly all sections of New York. In one case the contractor was able to get a vacant lot for disposal of his earth excavation, conveniently located so that it will be practical to remove the material (by steam shovel and train) when required and use it for backfill. The following table will give a general idea of the range of prices bid for excavation under the many varying conditions.

The cost of supporting the tracks of the street or elevated railways is not included in the excavation price, but is paid for separately. The prices bid on the contracts thus far awarded range approximately as follows:

For the support of elevated-railway columns, from $300 to $500 each, though in one case where there were only two, the bid price was $1000 each.

For the support of main electric-railway tracks with underground trolley conduits from $5 to $20 per lin.ft. of single track. A fair average seems to be about $10.

For horse-railway tracks about $5 per lin.ft.

The excavation price does not include the relaying of the sidewalks or curb or repaving the streets, within the neat lines of the excavation; this is paid for at prices bid per square yard, for the various types of pavement. All street surfaces are first repaved with Belgian blocks and maintained by the contractor for six months, after which the final form of new pavement is laid.

The eight-hour labor law is strictly applied to all this work, no blasting is allowed between 11 p.m. and 7 a.m., and of course, all charges of explosives have to be quite light on account of danger to the timbering or adjacent buildings. On most of the work two shifts are employed, the men generally working from 6 a.m. to 2:30 p.m. and from 3 p.m. to 11:30 p.m. with half an hour for a meal.

All, or nearly all the material taken from the excavation in Manhattan has to be disposed of, usually by haulage to the water front, where it is loaded on scows and towed to the point of disposal. This involves the renting of pier or dock facilities by contractors, and a haul varying from 1/2 to 1 or 2 miles in wagons or auto-trucks. These latter, holding from 3 to 4 cu.yd., are being quite commonly used, and are generally said to be more satisfactory and cheaper than horse-drawn wagons. It is necessary that they be fully utilized-that is, that there be the least possible delay at loading and unloading points; otherwise the overhead charges, chauffeur's wages, and interest on investment, amount to too large a proportion of the unit cost.

Where auto-trucks are used for disposal of excavation, a storage hopper is usually provided at the head of the shaft, which will hold at least one load (or more, depending on the number of trucks in use, and the kind of material), so that there is no more delay in loading than that necessary to open the mouth of the hopper and fill the truck. The general practice seems to be to use hoppers and chutes when the excavated material is earth or a mixture of earth and boulders and to use some form of skip or bucket for rock.

On the Broadway line below 23rd St. the excavation is nearly all in earth. A small amount of rock is found in places but not enough to influence the methods. On account of the timbering and the necessary supports of the street decking, it has apparently been found most convenient and practical to handle all the material by hand. It is shoveled into buckets of about 1 yard capacity, hauled to shafts, hoisted and dumped into storage hoppers holding 25 to 50 yards, from whence it is discharged into wagons. Haulage to the water front is done almost wholly by teams, but auto-trucks are used on Section 1.

A very efficient and convenient arrangement of hoist and storage hoppers, Fig. 46, was installed at Broadway and Waverly Pl., on Section 4, by the Dock Contractor Co. A vacant lot permitted the construction of a long narrow head-house parallel to the street and over the sidewalk. A telpher was arranged over the shaft and hoppers, which allowed a much more rapid, because better controlled, handling of the buckets than is possible with a derrick boom. A structure of this type would not have been permitted in front of an occupied building.

Fig. 46. Headhouse over shaft at Waverly pl. and Broadway.

On one section on Broadway, where the excavation was mostly sand, a belt conveyor was used in the bottom which dumped the material into a hopper, from whence it was elevated to the bin above the street by an endless chain of buckets.

On these downtown sections, fewer shafts are permitted and they are usually from 1200 to 1500 ft. apart, making the necessary maximum haul on the bottom about half that. Track of 24-in. gage is generally used, two or sometimes three lines, with mules for haulage. In many places on the upper levels between timbers, small 34-yd. cars are used, which are pushed by hand short distances to where they can be dumped to the lower level. A typical bridge, over the street for handling materials is shown in Fig, 47.

Fig. 47. Bridge and derricks at Grand St. and Broadway.

Where the line crosses Union Square, most of the work was done in open cut, an electrically operated shovel being used. Shovels and trains were used on the open-cut work of the Sea Beach line in Brooklyn, and part of the Varick St. line is in open cut.

The rock excavated from the subways is of little general use for structural purposes. A certain amount of the best of it is permitted to be used in any walls or masses of concrete over 30 in. in thickness and some of it is used for rubble for blocking up the yokes of the street-railway tracks in Manhattan.

Buckets and Skips. On many parts of the work, 0.75- to 1-yd. buckets as shown at (A) and (B), Fig. 48, are used. These are handled in the excavation on small flat-cars on 24-in. gage track, hauled by mules to the shafts, hoisted by derricks to the surface and dumped into trucks or hoppers. At the face of the cut the buckets are loaded by hand, the simplest form of block and tackle being used to haul out and lift the boulders or pieces of rock too large to be conveniently handled by one or two men.

Fig. 48. Dump buckets for handling material. (Click image to enlarge.)

In one case where turntables were tried opposite the shaft, the tracks being arranged as shown at (A), Fig. 49, it was found that they frequently got out of order and caused considerable delay so they were taken out and the tracks arranged as shown at (B), the shaft being enlarged to permit of this being done. On Sections 8 to 11 on Lexington Ave., transfer tables were used at the shafts as shown in Fig. 52.

Fig. 49. Sketch of track arrangements at shafts. (Click image to enlarge.)

On certain sections 3- to 4-yd. skips of the type shown in Fig. 44 (C) are used. They are hoisted to the surface, and either dumped into a wagon or auto-truck or placed on the wagon bed, and hauled to the place of disposal where it is again lifted and then dumped. The skips are handled underground on small cars drawn by mules, or in one case where the timbering was very close and the headroom low, pushed by hand, the work being arranged so that there was a down grade to the shaft.

Fig. 51. A rock slide, Lexington Ave. Fig. 52. a transfer platform, Lexington Ave. subway.

The advantage of these large skips over the smaller buckets is greater facility in loading. They are taken off the cars and placed on the ground at the working face, a hoisting engine with a fall suspended from the timbering of the street decking being used for the purpose. There is no lift for the shovelers and, of course, very much larger pieces of rock can be handled without block-holing and handled more easily.

On Sections 8, 9, 10 and 11, on Lexington Ave., a type of bucket known on the work as a "battleship" (Fig. 43) is used. These buckets hold from 1.5 to 2 yards; they are handled in the excavation and tunnels of these sections on small cars 3-ft. gage) with cradles shaped to fit. The cars coast down grade either to or from the working face as the case may be, and are hauled up grade by small stationary hoisting engines. The line from the hoisting engine is usually carried out by hand and this method of haulage does not seem very efficient.

Fig. 43. Derrick for hoisting skips at 77th St. and Lexington Ave.

The buckets are hoisted to the surface by derricks, Fig. 43, or telpher, Fig. 45, placed on wagon beds and hauled to the dock by horses. This type of bucket with the top some 3.5 or 4 ft. above the ground (as they remain on the cars while being loaded) involves a fairly high lift for the shovelers, and the necessity of keeping the tracks up close to the face does not permit the flexibility which is possible with the skips, which are taken off the cars and placed in the most convenient position for loading. Many of these small tunnel cars consist merely of a rectangular frame of 6-in. I-beams to which the axle boxes for two axles are fastened. Those for use with the "battleships" have two or three wooden cross-pieces or cradles cut to fit.

The Contracts for Sections 8, 10 and 11, Lexington Ave., are being executed by the Bradley Contracting Co., that for Section 9 by Patrick McGovern & Co. Nearly the whole length of the lower level tracks is in tunnel, the excavation of which is described separately, but the upper-level double track has generally been built as cut and cover. An arrangement has heen made whereby the Bradley Company takes care of the disposal of all the material, that from the upper section being hauled to the dock at 96th St. and the East River, and from the lower sections to 76th and 68th Sts.

The use of these skips or the "battleships" is probably of greater advantage in rock excavation than in earth, as some kind of mechanical apparatus for handling the rock is generally necessary at the face and is therefore available to handle the skips on and off the cars and to load large pieces of rock. Small power shovels, operated by electricity or air, are often used for loading the spoil on underground work, but on most of the subway work, the extensive and close system of timbering hardly admits of their use.

Fig. 44. Gantry hoist for skips at 121st St. and Lexington Ave.

The system used for the rock excavation on Section 13 (McMullen, Snare & Triest) seems to be quite effective. Here the rock face is 25 to 35 ft. high, and 40 to 50 ft. wide. After the street decking was put in, a top lift, from 12 to 15 ft. high and mostly earth was taken off the whole length of the section, this permitting working access to the whole job, for underpinning, support of pipes, conduits, etc. A shaft was sunk to subgrade at every other cross street, about every 450 ft., and outside the main excavation. The location of the shafts in the cross streets is shown clearly in the photographs, Figs. 44 and 45. From this shaft a cut was drifted across the full width of the work and the excavation carried forward in both directions from it. About 120 skips were used on this section, and about 400 yd. of rock (place measurment) was handled each 24 hours from the two working faces with the two gantries.

Fig. 45. Telpher hoist at 74th St. and Lexington Ave.

The tower form of timbering (as described under timbering) was used, the working space being spanned by continuous I-beams reaching from the last towers to blocking on the floor of the first lift, as shown in the sketch, Fig. 50. Two side cuts, each about one-third the width of the excavation, were driven ahead 35 to 40 ft., then the center was blasted sideways into these cuts. This, as will be seen, protected the timbering, at least to a considerable extent, from direct blasting against it. When the face at the center was advanced 40 ft., another tower was erected, the girders moved ahead, the process repeated, etc.

Fig. 50. Sketch illustrating progress of excavaction in deep rock tunnel on section 13, Lexington Ave. (Click image to enlarge.)

Two double-drum air hoisting engines were located back from the face on top, with single fall lines leading over sheaves suspended from the timbers of the street decking above the working space. These two lines (two on each side) handled the larger pieces of rock and the skips on and off the cars, and were also used in handling timbers, etc.

Derricks and Gantries. On Section 13, Lexington Ave. (McMullen, Snare & Triest), gantries, as shown in Fig. 44, have been installed at the shafts, instead of derricks for hoisting material out of the excavation, and for lowering the structural material. The advantages of these gantries are said to be, greater safety to the public in the streets, greater rigidity, and therefore more security; better speed in hoisting, easier spotting of the skips over the wagon bed, less power required for hoisting, and the elimination of booming up and down with loads. It is said that the saving of power (in regard to which no definite data are available) is due largely to the elimination of the swinging engines which are necessary with derricks. It is also stated that there is a considerable saving in the wire hoisting ropes, which lasted only two to four weeks on the derricks, but which last from three to four times as long on the gantries.

These gantries will also handle heavy loads with much greater security; those now in use have handled loads up to 25 tons. This is of considerable advantage in the rock excavation, as it permits the handling of large rocks without breaking them up. They are so arranged that from 20 to 25 loaded skips can be stored at them (see Fig. 44), thus permitting night work when the teams are not available to haul this material and also permitting considerable flexibility. This latter is a great advantage, owing to the difficulties of disposal, which is dependent on the availability of the scows, a somewhat uncertain item in some of the severe winter weather, the difficulties of haulage in bad weather, and many other factors, as already noted. The teams which haul the spoil to the dock work only eight hours, and by storing the material under the gantries, delays are avoided and the work is accomplished in this length of time. On this work, the big stone is generally loaded into the skips during the day and the finer material, which must be shoveled, is handled by the night shift.

The first of these gantries was made about 40 ft. long and 22 ft. high, but those built afterwards were made 60 ft. long and 27 ft. high, thus giving more storage room, and the extra height greater facility in handling some of the structural steel. There are altogether seven of these in use on Section 13 and one shaft with a derrick. Their use on Section 13 has been apparently very successful, but it is to be noted that they are peculiarly well adapted to the conditions there, and it cannot be assumed that they would replace derricks to so great advantage under other conditions.

Miscellaneous Excavation Methods. On the first section north of the Harlem River (Section 15, Route 5, Rodgers and Hagerty, contractors), where more latitude was allowed in the matter of opening up the streets, only part of the excavation being decked over, the excavated material was handled in 4-yd. Western dump cars hauled by dinkeys (3-ft. gage) to the disposal grounds 1/2 to 3/4 mile distant.

On the next section to the north at the junction of the Southern Boulevard and 138th St., a model 49 Marion shovel is just being installed for loading the cars and a model 60 Marion was used in the deep rock cut through Franz Sigel Park, on the northwest end of Section 15. On the steep hill on Lexington Ave, between 102nd and 103rd St. where the traffic is light (on account of the steepness of the hill) and where the tunnel with all four tracks at the same level changes to a cut-and-cover section, one side of the street was left open and a cableway was installed for handling the material.

Varick St. is being widened from its original width of about 60 ft. to 100 ft. and the excavation in this widened portion is being made in open cut, the original width of the street being decked over and the material under it taken out at the open sides. The first lift of 10 to 12 ft. is loaded directly into wagons by shoveling, inclines being built from the surface down to this depth. Much of the excavation is sand, and below the first lift this is loaded into 1-yd. V-shaped Koppel cars which are dumped sideways into a hopper, under which runs a short belt conveyor, which in turn carries the material to a bucket elevator which raises it into a storage hopper above the street level.

Steam shovels were quite generally used on the construction of the 4th Ave., Brooklyn, lines in 1909-10 and are being used now on the open-cut work of the Sea Beach line, but generally speaking, very little use is made of mechanical apparatus of any kind on the subway excavation, most of the excavated material being shoveled by hand.

Drilling. On Section 13, the drillers work in two 8-hr. shifts, from 6 a.m. to 11 p.m.. and the muckers in two shifts, from 8 p.m. to 1 a.m. One feature of considerable interest, is the quite extensive use of the so called Jap or hand hammer drill with hollow drill steel. The New York rock, a soft to medium hard gneiss or mica schist, seems to lend itself particularly well to the operation of this kind of drill in excavations where most of the holes are down holes. The type which is in most general use, is the Ingersoll-Rand B.C.R. 33, which weighs about 90 lb., using air at 80 to 90 lb. pressure. The hollow drill steel is usually about 1 1/8 in. octagon, the holes are drilled dry, the air through the steel blowing out most of the dust, therefore keeping the holes clean and consequently increasing the effectiveness of the machines. These drills are used for drilling holes to depths up to 12 and 14 ft.; it is stated that they require from 50 to 75% less air at the same pressure than the usual tripod drill does, and only one man is required to operate each of them. The general opinion seems to be that unskilled laborers with very little instruction could use these drills, though of course, in New York the labor unions compel the employment of regular union drill runners.

On Section 14 (McMullen & Hoff) four men with as many drills were averaging from 80 to 90 ft. of hole per man per day of eight hours. There was one record of 113 ft. for one man in eight hours. It was considered advisable to keep a number of spare drills on hand, so that in case anything went wrong, there was no delay, and any damaged drill could be taken to the shops, where it could he carefully repaired by a competent machinist, even though the trouble was very slight. This was considered to be better than to have an ordinary drill runner try to fix it with the spanner or sledge hammer, the tools usually used by them when anything is wrong with a drill. These drills were also used on the heavy rock excavation of Section 13, a cut 30 to 50 ft. wide and as many feet deep, with excellent results.

On some sections a lighter type of drill weighing about 40 lb. and using about 50 ft. of air per min. is heing used; this is the Ingersoll-Rand B.R.C. No. 430 or so called Jackhammer type, used for holes up to 6 and 8 ft. in depth using 7/8-in. hollow steel.

Another point of interest is the almost universal use of machine drill sharpeners, nearly all of which are of the Leyner type. This use of machine sharpeners is possible due, to some extent, to the use of the hollow steel and the rose-shape form of bit generally used with these hand drills, though of course, it has been shown even with the old type of cross bit, that where the number of drills warranted, the installation of a drill sharpener was an economy.

It was noted that in many cases the heads of the steel drills had sheared square off just back of the head. This type of failure has not previously come to the writer's notice, and no adequate explanation was offered by the men on the work, but it would seem that it might be due to the severe internal stresses set up by the much greater force used in the machine sharpeners in forming the heads, and the fact that possibly in these machine sharpeners, the steel can be, and is, worked at a lower temperature than by hand.

It is stated by the contractors on See. 13 and 14 that the general breakage and wastage of steel used is rather greater than with the ordinary steel, and, of course, the hollow steel is more expensive, but it is thought this is much more than compensated by the greater amount of work done. The Leyner drill sharpeners are used to make all the bolts for the timbering on one section, where it was stated that 400 bolts were headed per hour.

Electric current is used for power at most of the compressor plants, and air is usually piped to all points of the work for use in drills, pneumatic riveters, etc. In some cases the air is used for operating hoists and derricks, in other eases electric power is used directly for this purpose; this apparently is governed most generally by the plant the contractor may have had on hand, but the use of air for hoists and derricks, so long as it has to be installed in any event, seems to be the most satisfactory and most generally used.

Various schemes for heating the air during cold weather were noted, some of the apparatus home-made and other manufactured especially for the purpose. On one section (McMullen, Snare & Triest) an upright coil of about 6 to 8 rings, 15 to 18 inches in diameter, was made in the air line near the point where it was to be used, and a fire built and maintained inside the coil. In another case a piece of 6- or 8-in. pipe about 3 ft. long was capped at the ends to take the regular air line (about 2 in.) and a fire built under the larger section. These home-made schemes are probably somewhat wasteful of fuel, but this amounts to very little and they probably stand up better under the rough usage they get on this kind of work than the manufactured heaters.