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Fig. 29. — Blaw Forms Used in Concreting Express Tunnels.



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SUBWAY TUNNEL WOKK 385

on the plans was put in, and a continuous concrete wall, 3 ft. thick,
was built over the center wall, solid between the roof and the overlying
rock. The space between the top of the side-wall and the center wall
was then filled with hand-packing. In the tunnel, with iour tracks
on the same level, where the steel-bent construction was used, the
structure was treated in the same manner, there being a longitudinal
wall over each partition wall (Fig. 28).

Where the rock was xinsound, and timbering had to be used for
support while making the excavation, the structure was generally con-
creted solid to rock. To strengthen the timbering, the space between
and back of the timber sets was first packed with concrete and grouted
(Fig. 6), and, later, when the concrete lining was put in, it was
placed solid against this concrete and the timber sets and the space
between the timbers and the lining grouted. The grout used was
generally a 1 : 1 mixture.

Mixing and Placing Concrete. — Central mixing plants were used
on all the four sections. On Sections 8, 10, and 11, the concrete was
mixed dry at the mixer, and water was added on the work; on Section 9,
just enough water was used to wet the mass, and more was added on
the work when considered necessary. The concrete was generally
dumped on the roadway decking or on special platforms, and then
transferred to the express tunnel below through iron chutes.

Several different methods of handling the concrete in the express
tunnels were adopted on different parts of the work. The concrete
cars were loaded directly from the chutes from the street surface. At
first, the cars were dumped on a platform, and the concrete, after
being passed by hand to several working platforms, was deposited in
place. This crude method of handling concrete was soon abandoned,
and various devices were used so that the concrete could be deposited
directly on a working platform from which it could be shoveled into
the forms.

On Section 8 (two-track tunnel), the common practice was to use
a ramp leading from the floor of the express tunnel to a working
platform. The cars were hauled to the platform, and the concrete
was dumped and placed in the form by hand. Though this was an
advance over the previous method, it was open to the serious objec-
tion that the ramps blocked the mucking tracks so that it was im-
possible to remove any muck while the concreting was being done.



386



SUBWAY TUNNEL WORK




T

\J Depressed Track/



SUBWAY TUNNEL WORK



389




390



SUBWAY TUNXEL WOEK



Where this objectionable feature became so serious as to interfere
materially with the progress of the work, a continuous working i^lat-
form was built from the chute to that part of the tunnel which was
being lined, so that there were separate tracks on different levels for
both the mucking and the concrete cars.

To dispense with the necessity of a long working platform and
double tracks, the contractor on Section 9 used a lift to raise the
concrete cars to the level of the working platform (Fig. 30). The
latter was provided with transfer tracks, so that only one lift was
necessary to raise the concrete for either arch. This method of

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DETAIL OF COTTER

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f|~% Tie-rods pgy^lL Qp WASHER



FORM USED FOR

CONCRETING

TIMBERED TUNNEL

ON

SECTION 9



handling the concrete eliminated all the objectionable features previ-
ously mentioned.

Toward the close of the work, another satisfactory method of han-
dling the concrete in the express levels was introduced on Section 11
(Fig. 31). The concrete car was mounted on a timber framework
built on a flatcar, so that the concrete could be dumped directly on
the working platform.

A continuous traveler or bucket elevator (Fig. 32) was tried for
a short time, but was soon abandoned, as it did not prove very suc-
cessful. The main objection was that the quantity of concrete that
could be handled in this way was too small. The concrete for the



SUBWAY TUNiSTEL WORK 39l

roof was deposited on the platform and then shoveled into the forms;
the concrete for the side-walls was dumped in a sloping trough, leading
into the forms.

Forms for Concreting. — Figs. 29 to 34 illustrate the principal types
of forms used in concreting the express tunnels. Where the excavation
was through sound rock which did not require any timbering, the
general practice was to use the Blaw movable forms (Figs. 29 and
33). Where the tunnel excavation had to be timbered, the posts
prevented the satisfactory use of the Blaw forms, it being impossible
to move them. In these cases, forms of wood or those having steel
ribs with longitudinal lagging were used (Fig. 34).

The tunnel work was started in April, 1912, and completed in
December, 1914. The work was done under the supervision of the
Public Service Commission for the First District, Alfred Craven, M.
Am. Soc. C. E., Chief Engineer. John H. Madden, Assoc. M. Am. Soc.
C. E., was in charge of the construction, as Assistant Division Engi-
neer, until the end of March, 1914, at which time he was assigned to
other work. The writer, who had acted as Section Engineer, succeeded
Mr. Madden, and continued in charge until the work was completed.



392 DISCUSSION ON SUBWAY TUNNEL WORK

DISCUSSION



Mr. Maurice Griest,* Esq. (by letter). — This paper describes the con-

Griest. g^r^ction of the rock tunnels in Lexington Avenue from 57th Street
to 102d Street. It has been prepared, however, from the point of view
of the construction engineer, rather than that of the designer, there-
fore some special features of the design will be presented, particularly
of that portion from 97th Street to 102d Street, where the structure
changes from a double-deck tunnel to a four-track tunnel on one level.

Two features seem worthy of brief mention: First, the flat-roof
construction with transverse beams and concrete jack-arches and the
reasons for its use; and second, the method of reinforcing the structure
after the steel therefor was delivered, in order to provide for materially
heavier loads than were contemplated originally.

The original design for this portion contemplated the use of con-
crete arches — twin tubes between 97th and 100th Streets as the local
tracks spread out, and four single-track tubes from 100th to 102d
Street as the grades approach. In the former case, the clear span
varied from 14 to 30 ft.; in the latter case, the spans were uniformly
14 ft. The principal reason for adopting the arch form of construc-
tion in preference to the ordinary subway construction, was the greater
ease in placing the concrete in the arch form than in the flat roof with
smaller clearance above.

It was soon apparent that it would be desirable, on account of the
condition of the rock, to construct one track at a time. To do so with
the original construction, it woiJd have been necessary to leave the
centers in place in one arch until the adjacent arch was poured and
packed to rock. Therefore, the ordinary flat roof construction with
transverse beams, 5-ft. centers, was substituted, the steelwork being
arranged to permit the construction of the center express tracks in
advance of the excavation for or construction of the local tracks.

Between 100th and 102d Streets, the roof in general for the ordinary
14-ft. width consisted of a 20-in., 80-lb. beam supported between the
tracks by 6-in. plate and angle columns, and at the sides by 12-in.,
31i-lb. wall beams, designed for both roof load and side-wall pressure.
This roof could carry safely the weight of 12 ft. of rock above it.
It was expected that the rock would be sound enough to arch over,
so that in no case would there be a weight greater than the foregoing
carried by the roof. It was necessary, later, to increase the strength
of the roof, for two reasons: first, at 102d Street, on account of the
poor rock, open-cut excavation was extended beyond the original portal
location, so that the maximimi depth of fill over the roof was increased
to depths varying from 28 to 38 ft. The roof, therefore, designed to
carry 12 ft. of rock, was now to support from 28 to 38 ft. of back-fill.

♦ Asst. Designing Engr., Public Service Comm., First Dist., New York City.



DISCUSSION ON SUBWAY TUNNEL WORK 393

As described in the paper, the rock in some cases broke out 12 ft. Mr.
beyond the neat line of excavation, the excess excavation being refilled
with hand-packed stone or concrete. In other cases, the rock was poor
and seamy, so that the weight to be supported on the roof was prob-
lematic. It was necessary, therefore, to make provision for the support
of more than 12 ft. of rock for a considerable part of the tunnel.

To meet these conditions, it was necessary to add from 50 to 100%
to the strength of the roof. The steel roof-beams were already
delivered. Several months would have been required to obtain addi-
tional structural steel. The conditions of the rock made it desirable,
even imperative, that the permanent construction be placed without
delay. The contractor had on hand a supply of rods ordered for other
parts of the section. Furthermore, the rock had broken out, as
described in the paper, above the neat line of excavation, so that the
thickness of the roof could be increased without additional excavation.
It was decided, therefore, to omit the jack-arches and increase the
thickness of the concrete of the roof, so as to develop in effect a rein-
forced concrete slab.

The original plans showed an average thickness of concrete 3 in.
above the top of the beams. This was increased to 12, 14, and 20 in.
in various cases (making the depth of concrete 32, 34, and 40 in.,
respectively). Four 1-in. tension rods were added in each 5-ft. bay
between adjacent bents. Assuming the roof to be a reinforced con-
crete slab, the reinforcing consisting of the rods and beams, the
neutral axis is found to be above the top of the beam. The web of the
beam, therefore, assisted in resisting the vertical shear, but did not
resist any part of the horizontal shear at the neutral axis. Six |-in.
inclined shear rods were added, therefore, in each 5-ft. bay over each
supi)ort. By this method of reinforcing, the supporting power of the
roof was increased 50% for 32 in. thickness, 70% for 34 in. thickness,
and 110% for 40 in. thickness of concrete.

It was also necessary to reinforce the center walls to carry a load
even greater than the supporting power of the roof. (The rock being
caught up near or over the center walls and the space filled later with
hand-packed stone and rubble, made it probable that a greater loading
would be carried on the walls than on the intervening roof beams.)
The columns, therefore, were embedded in 12-in. and, in some cases, in
16-in. concrete walls, with eight 1-in. vertical rods in each 5-ft. bay.
The load was then assumed to be distributed as in a reinforced concrete
wall, over the steel and concrete.

John H. Madden,* Assoc. M. Am. Soc. C. E. — This work was of Mr.
such magnitude, and the problems presented were so numerous, that
the details would readily afford a field for several papers of the extent

• New York City.



394 DISCUSSION ON SUBWAY TUNNEL AVORK

Mr. of that offered. Under such circumstances, the wisdom of illustrating
^ *""' the text profusely is apparent. The speaker believes that it may be of
interest to review the development of the methods adopted for the tun-
neling operations and the experience during their execution, and, to
that end, will devote his remarks in general to the work in progress for
the first two years of these contracts, when he was in direct charge of
the tunnel construction for the Public Service Commission. The
author succeeded to that capacity in April, 1914.

Design. — For subways to carry intraurban traffic it is essential to
provide ready access to stations, so as to offer the greatest convenience
to the traveling public, and, where the stations occur at frequent inter-
vals, as is necessary in I^ew York City, this demands the minimum
depth below the street surface consistent with a feasible re-adjustment
of the existing sub-surface structures which will be interfered with.
In the work under discussion, this was complicated further by the loca-
tion of the express stations of the lower level, at which points a prac-
tical connection had to be provided with the local or high-level service.

With these considerations in mind, the small rock cover in places,
with its incidental construction difficulties in the tunneling, can be
readily understood. Future building operations or other sub-surface
reconstruction involving a disturbance of existing conditions, was an
added factor in the problem of the design of the structure.

Excavation. — The general character of the material encountered
in the excavation has been sufficiently described, except that in many
places a considerable stratum of destroyed rock, overlying the ledge
rock, was penetrated^ These deposits had been deprived of their
cementing properties, and could usually be removed with a pick and
shovel, though, when exposed in the face, they presented every appear-
ance of ledge rock.

On starting the work, there was discussion as to adopting a bottom
heading, but, in view of the many faults and seams common to rock
of the character of Manhattan schist, it was feared that the use of this
method might loosen the overlying material and complicate the sub-
sequent removal of the upper section of the tunnel. With the top
heading, support could be provided with the advance, before the ground
had an opportunity to work and become heavy.

As shown in the paper, the finished two-track section was about
32 ft. wide, and the roof of the excavation was very flat. To permit
the structure to be completed piecemeal, steel columns and longi-
tudinal girders were substituted in the center wall for the original rein-
forced concrete design. By this means half of the structure could be
built and blocked against lateral movement, and thereby avoid expos-
ing the rock for the full section at one time.

Reference is made by the author to the completion of the upper
level in advance of the work for the lower tunnels. It must be borne



DISCUSSION OX SUBWAY TUNNEL WORK 395

in mind that it is necessary to maintain progress in work of this char- Mr.
acter, and that the contractor must base his methods on the preliminary
information as to the character of the material which will be
encountered. Except where it is known that the tunnel roof will pro-
ject above the rock outcrop into a sandy soil continuing to the upper
level, and thereby induce a bleeding off below that level, with the
probable disturbance of the intervening material, extending to either
side and entailing settlement outside of the normal limits of the work,
it would seem that some advantage can be claimed for this procedure.
The completion of the upper level excavation removes the overhead
load if poor ground is developed in the tunnel, or if the rock cover
above the roof of the tunnel is very thin. The timbering of the upper
level excavation may also act to localize any disturbance caused by
the tunnel excavation, by retaining the side banks above and diminish-
ing the possibility of an extensive outside settlement.

Where apprehension is felt as to settlement from this sequence of
operations, it is not believed that underpinning abutting buildings is
as effective for their protection against injury as supporting their
foundations on cribwork, as the latter admits of correction for settle-
ment and, on the completion of the subway structure, such foundations
can be extended to stable ground.

It is not intended, however, to question the wisdom of deferring
the construction of the structure at the upper level in advance of the
completion of the lower tunnel excavation where the latter is to be
conducted through poor material. As stated by the author, where this
course was followed, voids were caused under the upper structure, and,
in some instances, a cavity was developed between the two levels. An
attempt was made to close the neck of this crater with small timber,
sealing above it with concrete and packing the sides of the cavity with
sand bags to prevent sloughing off. Grout was introduced under pres-
sure from below, in order to consolidate the disturbed ground, but, as
no great success was attained in preventing further development of
the settlement, it was necessary ultimately to reconstruct the footings
and track floor. Indifferent results were likewise obtained from efforts
to compact the soft -ground underlying the upper level so as to retain
it in place during the subsequent excavation from the lower tunnel.

Blasting. — The diagrams and data in the paper supply full details
of the blasting operations. Where buildings abut on tunnel work and
are founded on the same rock strata to be excavated, some concussion
is unavoidable, but the damage from this source was remarkably slight,
under the circumstances.

In the vicinity of some of the portals the breakage of windows was
quite extensive, because of the air vibrations following the blasting,
and though several expedients were tried to break up the velocity of
the discharge at the portals, they met with no great success. The



396 DISCUSSION ON SUBWAY TUNNEL WOKK

Mr. increase in the number of holes or the reduction in the charge of
Madden, (jyjjamite had no material effect in reducing the damage to the
windows. The plate-glass store-fronts were protected with small
wooden blocks placed on each side of the glass over which wires were
carried to a frame at the top and bottom of the window. This oi>erated
to confine the oscillations induced by the vibration, and proved very
efficacious in preventing the breaking or cracking of the glass. It was
not practical, however, to place this device on each of the great number
of small house windows, and, when broken, these were promptly
replaced.

Emphasis might well be laid on the use of the powerful searchlight
which was mounted on a car in the tunnel and used for periodic
inspection of all exposed rock. This readily disclosed any indications
of the rock working, or spalls loosening, and suitable precautions could
be taken as required. In some instances where the groiind was
treacherous, the searchlight was used to examine the face of the head-
ing following the blasting and before any men were permitted to
enter. Its use was an insurance factor that is worthy of adoption on
work of this character.

Timbering. — Where timbering was necessary, the usual segmental
type was used, and the design contemplated either the support of the
overhead load where the ground was heavy, or protection against
injury through the dropping out of spalls or fragments where the rock
was firm but blocky. When the soft water-bearing material was
encountered at 74th Street, the contractor adopted the expedient (as
mentioned by the author) of driving long spikes in the sides of the
caps, and these projected from their face and formed a bond; the space
between the timber sets was then packed solid with concrete through
which the grout pipes extended. This method proved so advantageous
that it was used subsequently in other parts of the work to which it
would apply.

By this method the timbering was not only greatly reinforced, but
a very efficient and uniform support was provided for the roof between
the sets. A seal was also obtained for the water draining from
above, and, where desirable, this could be collected and removed under
control through grout pipes kept open for that purpose. In rock which
is seamed and faulted, to the extent of that encountered in many
places in this locality, it is important to minimize the time of the
exposure of the face in the excavation, so as to reduce the tendency to
work; and it is believed that concreting between sets as soon as prac-
tical after their erection offers an excellent solution of that problem.
This is particularly applicable when the permanent lining cannot be
completed coincident with the advance of the tunnel excavation.

As described in the paper, the work presented miusual problems in
tunnel construction, and required from the contractors a severe tax on



DISCUSSION ON SUBWAY TUNNEL WOKK 397

their experience and resourcefulness. Acknowledgment is due to The Mr.
Bradley Contracting Company and P. McGovern and Company for ^^^*^^°-
the successful completion of their respective sections.

Egbert H. Jacobs,* Assoc. M. Am. Soc. C. E. — This paper brings Mr.
forcibly to the mind of the engineer the hazards necessarily incident to
execution of work of this character. To those acquainted with such
work, it is unnecessary to emphasize the fact that the process of driv-
ing tunnels, of the dimensions required for subway operation, in rock
such as exists throughout Manhattan, within the limits of city streets,
is somewhat hazardous, even when carried on under the strictest and
most competent supervision. This applies not only to the force
employed, but also to some extent to the public. It is felt, therefore,
that it is a matter for congratulation that in the total of 9 700 lin. ft.
of tunnel work, including 3 100 lin. ft. of four-track tunnel, covered by
this paper, there were no accidents affecting the public, the only injuries
suffered being slight damages to buildings due to vibration and con-
cussion, and, in the case of soft ground tunnels, a iK)ssible slight settle-
ment in a few buildings.

Considering the close proximity of buildings (Lexington Avenue
being only 75 ft. wide), the character of the material excavated, and
the millions of people passing daily over the temporary supports in
the case of the cut-and-cover work, the record of casualties for the
whole subway work is an enviable one. It may be stated, however,
that the various processes of construction cannot be carried on with
the same degree of safety as may be obtained in the operation of com-
pleted machines or structures. For example, if the same safeguards
were thrown aro\m.d the structural ironworker engaged on the erection
of a skyscraper as are thrown around the passenger in the elevator of
a completed building, the speaker is sure we would have no skyscrapers..
In the same way, if the same safeguards were to be thrown around a
tunnel excavator as around a subway passenger, there would be no
subways.

It has seemed to the speaker that in undertaking this great work
at the behest of our masters, the people, that the latter should be
allowed to know in advance that there are certain necessary hazards
incidental to such work, no matter how conscientiously and ably
planned and executed. He is quite sure that such knowledge would in
no wise deter them from their purpose to have these very necessary
facilities provided. When, however, the public, through a lack of
knowledge of the conditions under which work of this character is
carried on, believes that it can and should be carried forward with
absolute safety by the exercise of even ordinary care and skill, those
in responsible relation to the work are subjected to the most severe
criticism or worse, in the case of casualties.

* New York City.



398 DISCUSSION ox SUBWAY TUNNEL WORK

Mr. This is being brought very forcibly to mind at this time by the

recent failure of a portion of the erecting appliance of the Quebec
Bridge. The general public is quite aware of the fact that the doctor
is dealing with certain unkno\vn elements in his work, and therefore
does not hold him to strict accountability for the success of his treat-
ment. It does not realize, however, that (although to a very much
less extent) there are certain imknown elements which confront the
engineer in the prosecution of work, which make it impossible for
him to insure that it will be conducted with absolute safety, notwith-
standing the fact that he is willing to accept full responsibility for the
finished product. The lack of realization of this results in the engi-
neer being held to an accountability which is unfair to the Profession.
Here is an opportunity for educational work which can be accomplished
by the engineer alone.

Mr. T. Kennaiid Thomson,* M. Am. Soc. C. E. — Mr. Werbin is entitled

■ to hearty thanks for his excellent presentation of a very interesting
subject.

The speaker cannot help contrasting the difference, in many ways,



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