New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1915-10-02
IA the Editor Of The Tribune.

To the Editor Of The Tribune.
Sir: In the interest Of public safety,
would like to state my opinion that the re-
cent subway construction accidents on sew
emit. Avenue and Broadway were unquestion-
ably due TO insecure timbering of the ex-
cavations. / have noticed many explanations
ir the newspapers at variance with this. Inc
construction of these particular sections OF
subway | believe, can be safely carried on
t.:.dcr street decking, as can any other work
Of the same character at present in progress
or contemplated. feel qualified to express
an cpinion. owing 10 my experience in under
GROUND timbering, as mining engineer, op-
Grating in this country and in Canada. Also,
| have inspected much of the subway con-
struction in greater New York and designed
the timbering on a section Of the Brooklyn
subway now under construction.
Subway timbering, In the case Of main
tanning the street surface during construc-
lion. is combination OF ordinary trench
timbering 70 hold the sides Of the ex-
cavntion and trestle 70 support the street
decking, tracks and sub-surface pipes and
ducts. The design of the timbering varies
according as the excavation is In earth or
rock. but in either case most Of the heavy
timber members are compression mem
bers. and the security OF the whole
timber structure in most subway timber
ing methods depends largely on wedging
these members firmly into place. That is the
faulty feature of this kind Of timbering when
used under street decking, as traffic vibration
and blasting have a tendency TO loosen 1t
which explains the recent accidents. To
.naxe the structure safe it should be dag
|orsilv braced. both transversely and longi-
tudinally. and the timbers firmly tied togeth-
or rs in ordinary treste construction.
I The collapse of the structures on Seventh
Avenue and Broadway was undoubtedly
oaused not by breakage Of the timber but by
the falling apart Of the structure because
81 loosening of the wedging, due 70 trahic
vibration and blasting. The immediate cause
or trigger action that started the Seventh
Avenue collapse was probably the blasting
ont of some Of the posts or other timber,
which might be likened to the loosening OF
th,, keystone of an arch causing all the parts
10 collapse. In the Broadway accident slide
Of rock seems to have had the same effect
in loosening a prop and starting the failure
Of an insecure structure. In this particular
case. although the rock strata dip down
toward the excavation at the location OF the
stree, cave-in and would tend to slide into
tao cut il loosened the rock could have been
safely held by adequate timbering. How
ever. the point to emphasize in accounting
for the accidents is that the timber structures
ware not sufficiently self-contained, through
g .ure tying and diagonal bracing, TO stand
Ii7Jerendent of loosened wedging and small
local injury, caused by blasting or sliding
rock.
Subway timbering holds the sides Of the
excavation and supports a temporary street
surface. the tracks and sub-surface sewers,
pipes and electric ducts, both permanent and
temporary, until the permanent subway
structure IL completed The timber structure
n u.s. necessarily be placed so as not to in
lerfere with the subsequent construction of
the permanent steel and concrete subway.
Where the excavation is in earth the sides
are held By sheathing or plank. two to three
inches thick, placed vertically close together
along each side of the excavation. The
shcsthing is held in place by heavy continu-
OTIS timbers, called rangers. placed horizon
tally in rows inside the sheathing, like the
horizontal framing Of fence. The vertical
distance apart of the rows Of rangers is
usually five to six feet, depending on earth
rressures.
According to the depth OF the excavation,
additional courses Of sheathing are used,
each course being placed inside the course
above, to allow space to drive it. The rangers