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Transactions of the American Society of Civil Engineers (Volume 81) online

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building is of heavy construction, and was completed about 30 years
ago.

The subway, known as Route 5, was designed to run north on
Church Street as far as Fulton Street, then to curve eastward be-
neath the Vestry Building and the Churchyard to Vesey Street, and
then to curve again to the northward into Broadway. A special
agreement was entered into between the Vestry of Trinity Church
and the Public Service Commission, representing the City of New
York, whereby the Vestry gave the City, luider certain restrictions,
a right of way for the purpose of constructing tunnels for a rapid
transit railway beneath the Church property. The right of way was
deeded to the City, as the Vestry realized that this subway work was
part of a great municipal improvement.

The City was given possession of the basement for 18 months, so as
to facilitate the work of construction, and agreed to build new founda-
tions capable of carrying a new building of eight stories or one of
lighter construction not exceeding ten stories.

Fig. 3 is a plan of the building, and shows the positions of the east
and west tunnels beneath the building and the proportion of the
foundations cut away by them. The tops of these tiumels were just
beneath the level of the footing stones under the building walla, as
shown in Fig. 4.

An examination of the building was made before any work was
done; its condition was carefully noted, and all defects or cracks
were recorded. Survey marks were made at various places around the
exterior walls, and their elevations taken.




Fig. 1. — General, View of Trinity Vestry Building a>:d St. Paul's
Churchyard.




Fig. 2. — Longitudinal Lattice Girder Being Erected and Fastened in Place.



UNDERPINNING TRINITY VESTRY BUILDING 79

The following are the dimensions of the building:

Length on Church Street 164 ft. in.

Width on Fulton Street 35 ft. in.

Width on Vesey Street 48 ft. in.

Length of exterior walls 428 ft. in.

Area of ground plan 6 055 sq. ft.

Area of one floor (less walls) 5 340 sq. ft.

The following are the estimated weights:

Exterior walls 7 950 000 lb. = 3 975 tons.

Interior walls and partitions . . .

Floors

Plastering, ceilings and walls . . .

Roof construction

Equipment, trim, plumbing, etc.

Live load, maximum 1378 000 " =

Total weight on foundations, 12 786 000 lb. = 6 393 tons.
The area of the original foundations was :

Under exterior walls 2 140 sq. ft.

Under interior weight-bearing walls 400 " "



994 000


" = 497


773 000


" = 386.5


797 000


" = 398.5


393 000


" = 196.5


501 000


" = 250.5


1 378 000


'' = 689



Total area of foundations 2 540 sq. ft.

The unit loading on the original foundations, assuming the weight
to be distributed uniformly over the footings, therefore, was 2.51 tons
per sq, ft.

The soil was sand, varying in places from fine to moderately coarse.
Mean high water level was 23 ft. below the street, but the ground-water
was found about 4 ft. 6 in. above that level. Pumping in the adjacent
subway excavations reduced the ground-water to about high water.

After conferences, the City agreed that the new foundations should
be able to support the building if four new stories of similar con-
struction were added, or their equivalent in weight. These additional
floors were estimated at 3 907 tons.

Original weight of building 6 393 tons.

Additional weight, agreed upon 3 907 "

Estimated load for new foundations 10 300 tons.



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UNDEEPIXNIXG TRINITY VESTRY BUILDING



tion of these longitudinals was to strengthen and tie the brickwork
together, that is, to make it more monolithic in character. The brick
walls were thns enabled to distribute the loads from above over longer
lengths, and to span safely the openings which were to be dug subse-
quently for the concrete imderpinning piers.

At one place on the Church Street side, 24-in. longitudinal plate
girders, 20 ft. long, were used in place of the 24-in. lattice girders.
These are marked L 3, in Fig. 3. This change in design was made so
that the load of the side-wall could be carried over a space left between
)iests of cross-girders, which had to be placed diverging, so that their



GIRDERS UNDER FOOTING COURSE OF WALL.




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concrete piers could clear a foundation of an elevated railway column
in Church Street.

Projections on the sides of the footing walls were cut away, leaving
the vertical surfaces somewhat rough. This cutting was done by both
hand-drills and by power channel drills. Grooves were cut for the
angles of the top and bottom chords, in order that the girders could fit
snug against the walls.

The girders were then doweled to the walls at frequent intervals.
The dowels were square rods driven into the walls and bent over to
catch the framing of the girders. Ties also were inserted in holes
drilled through the wall at intervals. These bound the top chords of



UNDERPIXNING TEINITY YESTRY BUILDING 85

the inside and outside girders together. The arrangement is illustrated
in Figs. 7 and 8. After the girders were in place they were embedded
in concrete, a strong bond being secured by the friction of the roughed
surfaces of the sides of the walls aided by the dowels. To facilitate the
placing of these girders, they were built up in place and bolted. Splices
were staggered, both of the upper and lower chords and of parallel
girders. Fig. 2 shows a 24-in. longitudinal lattice girder in process of
erection. It is similar to those used under the Yestry Building.



60-INCH PLATE GIRDERS

AT FULTON STREET FACE

OF BUILDING.




[J 12-1-40-1 o. y



G4



i











Top of Tunnel

SECTIO^J



Fig. 8.



Across the Fulton Street face, two GO-in. plate girders were used
in the same manner as the side lattice girders. These 60-in. girders are
marked G^ 4, in Fig. 3, and were made in three parts for convenience in
placing, the sections being bolted together when in position. They were
tied together by 12-in. I-beams, 40 lb. per ft., as shown in Fig. 8,
and were encased in concrete. The weight of the wall was transmitted
to the girders by these needle I-beams, as it was not deemed wise to
rely on the bond of the concrete casings.



86 UNDEBPINNING TRINITY VESTRY BUILDING

After completing the work of fastening the longitudinal girders,
G 4i, L 1, L '2, and L 3, excavations for the underpinning piers were
conunenced. Excavations for adjacent piers were not made at the same
time. When one pit was started, the next would be 30 or 40 ft. away,
or as far as convenience would allow.

The pits were sunk by hand digging. As the excavations proceeded,
the sides were box-sheathed with 2-in. planks laid horizontally. These
planks were cut to fit, and when a set of four was in place the pieces
were toe-nailed at the corners. When an excavation had advanced
sufficiently, a 3 by 3-in. timber was put in each corner and spiked.
Occasionally, these corner timbers were cross-braced with waling pieces
which were wedged into place. No difficulty was experienced in this
work. The average time required for three men to sink one of these
pits varied from 3 to 6 days, including from 1 to 2 days in making the
access.

Each pit was filled with concrete as soon as excavated. For piers
directly imder the walls, the spaces between the concrete tops and the
footing course were packed with brick and cement, all tightly wedged,
so that such pits could receive their share of the building load. For
piers not under the walls, the plate girders, marked G^ 1, G2, G Z, and
G 5, in Figs. 3 and 6, were put into place and secured. The spaces be-
tween these girders and the footing course were then packed, and a
portion of the load was transferred to the concrete piers, as before.
These cross-girders were then encased in concrete, so as to protect the
steel and make the nests of girders into solid floor-slabs. This feature
is best understood by referring to Figs. 3 and 7.

As there were 115 of these concrete piers, each 5 ft. square, the
average load on each was, for the present building (6 393 tons divided
by 115 times 25) = 2.22 tons per sq. ft. ; or, for the assumed future
building, would be (10 300 tons divided by 115 times 25) = 3.58 tons
per sq. ft.

In the Churchyard, some of the graves and vaults were in the way
of the pit excavations. To avoid disturbing them, cross-tunnels were
routed in from convenient sides, at sufficient depths to clear the graves,
as shown in Fig. 5. When the correct locations were reached by the
cross-tunnels, the pit excavations were carried dovsTi vertically in the
usual manner.



UNDERPIKXING TRINITY VESTRY BUILDING 87

It was the original intention to excavate the pits for the concrete
piers to about ground-water level and then to drive concrete piles to
a depth below sub-grade. As the subway pumping reduced the ground-
water level, the plan was changed, the pits being carried down to about
1 ft. below sub-grade, and the piles omitted. However, at the Fulton
Street end, short concrete piles were used under the pits, as seen in
Fig. 4.

Elsewhere on this subway route some similar concrete piles were
tested by the contractors, under the supervision of the writer. As these
tests were interesting, the results are here given.

Two piles were tested under columns of the elevated railway in
Trinity Place, between Rector and Thames Streets, during January,
1913, and three piles were tested under the retaining wall of Trinity
Churchyard, just north of Rector Street, during February, 1913.

The piles were made by forcing into the sand a steel casing 14-in.
in diameter. No. 12 gauge (about i in. thick). The casing was made
in sections about 24 in. in length, each section having an inside sleeve
so as to permit one section to fit on top of the one just below, see Fig. 9.
The steel casing was sunk by a pile-driver until its upper edge was level
with the sand; then a new section was inserted, and the driving was
continued until the proposed depth of pile was reached. The sand
was removed by a small grab-bucket from the inside of the casing as
the sections were sunk. When the entire casing was in place and the
sand had been removed from the inside, the pile was formed by filling
the casing with 1:2:4 concrete. For filling below ground-water, the
concrete was put in paper bags and the bags were lowered into place
and tamped. After about 2 ft. had been filled in this way the con-
crete was placed by a bottom self-dumping bucket.

The piles were tested, after the concrete had set, by a hydraulic
jack, using the footing courses of the foundations as a base against
which the jack was blocked. Owing to the short stroke of the jack, the
pressure had to be relieved and the blocking readjusted as each pile
sunk under the test loads. Whenever the pressure was relieved, there
was a slight rebound of the pile. A graphic representation of Test IV
is shown in Fig. 9, which illustrates this rebound.

Test I. — Steel casing, 9 in. outside diameter, driven inside a 14-in.
casing which had buckled. The pile was 15 ft. long, and projected



UNDEEPIXNIKG TKTNITY VESTRY BUILDING




Penetration, in Inches.



'



53 -i




Tl O




1 -i-




o o


H


-r, O


m


is


(n


-i

O
-n



iUi ,J1



UNDEEPINNING TRINITY VESTEY BUILDING



89



about 2 ft. below the 14-in. casing. The 9-in. casing was filled with
concrete. The soil was fine, wet sand.



Time.


Test load,
in tons.


Penetration,
in inclies.


Total movement

from start of test,

in inches.


3:59
4;00
4;06
4:16
4:18
4:28
4:83
4:37
4:42


0.0
0.63
18.80
21.40
31.40
31.40
31.40
37.70
37.70


0.0

0.0

0.276

0.012

0.228

0.156

0.024

0.864

0.324


0.0

0.0

0.276

0.288

0.516

0.672

0.696

1.560

1.884


4:45


0.0


0.336*


1.548



Rebound when pressure was relieved.



Test II. — This test was made to measure the end resistance of a
9-in. outside diameter, pointed casing. A 14-in. steel casing, 12 ft.
long, was first sunk, and about 2 ft. of sand allowed to remain at the
bottom. Inside this casing a steel pile 9 in. in diameter, 14 ft. 6 in.
long, of ^-in. steel, with cast-iron point, was driven until the point
was below the outer casing. ^N^either casing was filled with concrete.
The soil was fine, wet sand.



Time.


Test load, in tons.


Penetratiou, in
inches


Total movement

from start of test,

in inches.


3:15


0.0


0.0


0.0


3:16


6.3


0.875


0.875


3:18


12.6


4.0


4.875


3:24


0.0*


0.125+


4.750


3:26


12.6


0.8125


5.5625


3:29


14.4


1.1875


6.75


3:31


18.8


2.125


8.875


3:34


0.0*


0.25+


8.625


3:38


23.2


7.625


14.25


3:44


0.0*


0.1875+


14.0625


3:46


25.1


1.1875


15.25


3:51


25.1


1.0


16.25


3:52


0.0*


0.1875+


16.0625


3:57


31.4


1.8125


17.875


4:02


31.4


0.6875


18.5625


4:03


34.6


1.375


19.9875


4:06


0.0*


0.3125+


19.625


4:08


31.4


0.5625


20.1875


4:09


34.6


1.125


21.3125


4:10


84.6


0.75


22.0625


4:11


34.6


0.625


22.6875


4:12


0.0*


0.3135+


22.375



* Pressure relieved, to reset blocking under jack.
t Rebound, when pressure was relieved.



90



UNDERPIXKIXG TRINITY VESTRY BUILDING



Test III. — Steel casing, 14 in. in diameter; length of pile, 18 ft.;
concrete, 1:2:4 mixture, allowed to set for 10 days. The soil was fine,
wet sand.



Time.


Test load, 1 Penetration,
in tons. in inches.


Total movement

from start of test,

in inches.


4:10
4:11
4:18

4:31


0.0 ' 0.0
1.9* 0.0

32.0 1 .

28.9 (^ 2.940

34.5 1 +

31.3 f^ 2.052t


0.0
: 0.0

2.940

4.992



* Pile started to move when a load of 23 tons was reached.
t Load slowly reducing by a leak in pump.
t Rebound was not recorded.

Test IV. — Steel casing, 14 in. in diameter; length of pile, 12 ft.
A concrete plug, 48 hours old, 13i in. in diameter and 18 in. long, was
first dropped into the casing. Concrete was poured into the casing
above the plug and allowed to set for 9. days. The soil was .fine, wet
sand. II ,.,j . f^c,t8 H ■:f\i. .p.



f*^- ' -

Time.


Test load,
in tons.


Penetration,
in inches.


Total movement

from start of test,

in inches.




0.0


0.0


0.0




23.2


5.0


5.0




0.0*


0.250t


4.750


2:48


25.8


1.635


6.375


2:47


24.5


0.250t


6.125


2:48


32.0


1.375


7.500


2:.53


30.2


0.0


7.500


2:54


36.5


0.875


8.375


3:04


38.3


0.062


8.437


3:05


0.0


0.125t


8.312



* Pressure relieved, to reset blocking under jack.
t Rebound, when pressure was relieved.



Test V. — Steel casing, 14 in. in diameter; length of pile, 16 ft. 6 in.;
concrete, 1 : 2^ : 4^ mixture, allowed to set 17 days.



Time.


Test load,
in tons.


Penetration, in
inches.


Total movement

from start of test,

in inches.


9:40
9:42

9:42:30


0.0
12.6
18.8


0.0

0.1250

0.3750

1.13.'i0

0.4375


0.0
0.1250
5000


9:43::W
9:53 :.30


25.1
25.1


1.6350
2.0625



UNDERPINNING TRINITY VESTRY BUILDING

Test V. — (Continued.) •■



91



Time.


Test load,
in tons.


Penetration, in
inches.


Total movement
from start of te&t,
in inches.


9:54:30


31.4


0.9375


3.0000


10:04:30


31.4


0.3500


3.2500


10:06:00


35.8


1.1250


4.3750


10:08:00


0.0*


0.3750t


4.0000


10:17:00


6.3


0.0


4.0000


10:17:20


12.6


0.5000


4.5000


10:17:30


18.8


0.0


4.5000


10:17:40


25.1


0.0


4.50OO


10:18:00


31.4


0.0625


4.5625


10:19:00


36.4


0.8135


5.3750


10:19:30


37.7


0.3750


5.7500


10:24:20


37.7


0.3750


6.1250


10:29:30


37.7


0.1350


6.2500


10:34:30


37.7


0.0


6.2500


10:49:30


37.7


0.0


6.2500


10:50:20


0.0


0.3125t


5.9375



* Pressure relieved, to reset blocking under jack.
t Rebound, when pressure was relieved.



Some conclusions, deduced from a study of the test loads and
penetrations, are:

(1) The initial loads, which the piles supported before sinking,
were variable.

(2) The sinking increases more rapidly than the load.

(3) When the pressure is relieved, the pile rebounds.

(4) When the same load is again put on the pile, the penetration
is greater than the original penetration, that is, the pile sinks more
than its reboiuid.

(5) The supporting power of one of these concrete piles depends
chiefly on the area of its base. The side friction in sand probably does
not exceed from 5 to 8% of the load.

(6) To secure the maximum supporting power without additional
settlement, a concrete pile should receive its permanent load while
under pressure, that is, the permanent underpinning load should be
transferred to it without relieving the test load.

(7) This latter condition can be accomplished by placing struts
between the footing to be underpinned and the pile top before the
pressure of the jack is relieved.

After the underpinning work had been completed, and the load of
the Vestry Building had been transferred to its new foundations, exca-
vation beneath the basement was commenced, and the tunnels were



92



UNDEKPIXXING TRINITY VESTRY BUILDIXG



allowed to advance toward the building. At the same time, excavation
under Church Street, which had been decked with wood, also was
being made.

The tunneling commenced from a shaft in Vesey Street, and the
east timnel was kept somewhat in advance of its westerly mate. Both
tunnels were worked forward from Vesey Street across the Churchyard
toward Eulton Street. They are 20 ft. in outside diameter, and are
lined with cast-iron plates covered with concrete inside.



HALF SECTION OF EEXH .- HAI-F SECTION OF HEADING

Blocliing - ^T^-i / WN.;.



METHOD OF
DRIVING THE TUNNELS



•Tin Frame




-V-



Rubble Packing,




Fig. 10.

^'' As the soil was sand, varying from fine to mediimi coarse, the
method of tunneling adopted by the contractors is shown in Fig. 10.
Jills, arranged side by side in the curve of the roof, and supported by
cap timbering, were driven forward by jacks. As the jills were pushed
ahead, the space behind them was sheeted and filled with blocking rest-
ing on the caps. The sides of the tvmnel were sheeted with 2-in. planks,
held in place by braces and struts. A steel pilot girder formed the base
from which the various braces and capping were supported. This pilot
girder also formed tlie truss for supporting the centering machine
which raised and put the cast-iron lining sections in place.



UNDEEPIXNING TRINITY VESTRY BUILDING 93

The excavation was carried forward by an advance drift close under
the roof, and benches formed by deeper excavations to sub-grade were
kept back at safe distances, depending on circumstances. Timbering
was placed as the section was enlarged, and the cast-iron lining plates
of the tunnel were erected as soon as the full section was cut. Fig. 11
shows one of the headings as it advanced under the Churchyard.

The Jills were made of timber, sheathed with steel plates bent over
the forward nose to form a cutting edge. These jills rested on, and
were bolted to, steel frames, built up as seen in Fig. 10, and were all
supported on timber capping braced radially from the tunnel center.
They were pushed ahead by hydraulic jacks, the center one being kept
slightly in advance of the others. The sand was removed in cars to
the Vesey Street shaft and hoisted to the street.

The tunneling was accomplished without serious accident, although
the method required great care and attention to prevent slips. There
was a noticeable loss of sand, that could not be avoided, and there was
a slide of sand at one place which caused a marked settlement of the
Churchyard. The engineers of the Public Service Commission ap-
proved the tunneling plans before work started, and the contractors are
entitled to credit for the manner in which the work was done. The
tunneling beneath the Churchyard was accurately carried forward, and
the headings entered the spaces between the concrete foundation piers
as planned.

When the drift reached the partial excavation beneath the building,
the advancing jills, as they emerged from the sand, are shown in
Fig. 12.

Fig. 13 shows the excavation beneath the building. The concrete
foundation piers are seen on both right and left, and the concreted
cross-girders are shown overhead. The cast-iron lining of the tunnel
can be seen in the background. As the lining plates were erected, the
spaces around them were back-filled.

Fig. 14 is another view of the excavation beneath the building.
The basement windows can be seen through an opening between the
concreted cross-girders.

Fig. 15 shows the east tunnel at Fulton Street, with the concreted
cross-girders, 5, overhead. At the top of the picture in the fore-
ground is seen the footing course of the Fulton Street wall of the



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