New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1915-10-02
INSECURE TIMBERINC COLLAPSED
That Is What the Recent Broadway and Seventh Avenue
Subway Accidents
Subway Accidents.

are in turn held in place BY cross-braces,
tightly wedged in place across the excava-
ton, between corresponding rangers. They
sre usually 12xl2 inch timbers, generally in
several pieces to reach across the trench and
cheated at the joints. A better construction
for the cross brace is to build it OF SKIP inch
tinbers, 16 feet long, Tapped feet, and
boted together, forming continuous member
from ranger to ranger.
The cross-braces are spaced ten feet apart
longitudinally in the direction OF the street
and vertically under each other at each ten
foot spacing, from top to bottom of the ex-
cavation, between each pair of rangers on
either side of the excavation. The street
decking lies on heavy floor beams of wood
or steel, as does also the car tracks, placed
longitudinally across the top course of cross
braces. Posts are placed between each verti-
cal group of oss-braces 10 form continuous
members from the top cross-brace, carrying
tire street floor beams and decking. down 10
the bottom of the excavation. The posts in
conjunction with the cross-braceS, therefore,
form trestle bents spaced ten feet apart
along the excavation. They serve the double
purpose of carrying the street loads, sub
surface pipes and duets and structure loads
and Of stifenHg the cross-braces against
tarklng, owing to earth pressures against
the sheathng.
AS additional stiffening, longitudinal struts
or spacers are placed between the cross
braces or bents. Owing to the heavy earth
pressures on the sheathing, this system Of
timbering for subway construction in loose
ground is reasonably secure, especially when
the continuous bolted cross-brace is used and
a moderate amount of diagonal bracing, both
always be diagonal transverse brscing OF the
bents under the car tracks, to prevent side
vibration, and sufficient diagonal bracing al
all cross streets; also, all timber members
should be securely tied in place by cleats or
other means.
In excavating in rock under street decking
there are several notifications of the above
method of timberlng, the idea being TO truss
up the street structure and have as little
timber as is possible in the bottom of the
excavation to interfere with blasting opera
TORS The principal difference S the lack
o. sheathing, rangers and crossbraces. In
"ome cases the entire street structure, per-
ranent and temporary. and the pipes and
duets are supported and hung BY and from
ieavy long steel girders placed longtudnally
with the street. These girders are supported
by posts TO the bottom Of the excavation,
generally ten feet apart, but are strong
enough TO span twenty feet or more, in case
some of the posts are temporarily removed
by blasting.
The system Of timberng in the rock cut in
rros away and Seventh Avenue is surface
decking, with tracks resting on longitudinal
floor beams, which are, in turn, supported
by cross-beams The sub-surface pipes and
duets rest on other cross-beams lower down.
The cross-beams are supported by posts TO
tn bottom of the excavation, short temporary
posts being replaced with longer ones the
excavation proceeds in depth. The system at
the scenes of the recent accidents has proved
Inadequate. in the lack Of diagonal bracing
Of the posts, both transverse and diagonal,
particularly at street crossings, to make a
strong, scN-contained trestle 70 support the
street construction. As TO holding the sides
.. the excavation % prevent the breaking
loose of rock vertical posts should be placed
against the rock face. where the rock strata
dip down toward the excavation, and at other
places where the rock is of dangerous char
actGr. and these posts should be braced by
kca braces TO the floor OF the excavation or
by braces across the excavation to the other
vsll, as circumstances require. Between the
posts and rock face wedges should be in
serted to hold the rock fast.
The above explanation indicates, believe,
the essential facts in the subway construc-
ton accidents. The results have proved that
worG of this character should be carefully
inspected by men experienced in earth and
rock excavation and t;mbering methods, and
hey should have the authority 10 eliminate
RI ,thods that threaten the safety of the pub
lie. JOHN SEWARD.
West Nutley. N. j.. Sept. 20. 1915