Evening star., 1936-08-23
Fifty Years Ago
In The Star

The Star Of August q. 1885, prints the
following synopsis Of the recommends
Army Engineers Engineers who in
Tunnel Report. accordance with an
act of Congress,
examined the Aqueduct tunnel so years
ago:
The report of the Board of Engineer
Off1cers upon the new Aqueduct tunnel
recommends the use of brick for the lin
ing Of the tunnel, as the exclusive use
of concrete is, in the opinion OF the
board, impracticable. The report was
approved by the chief of engineers and
the Acting Secretary of War and copy
was today sent to Maj. Lydecker for
his guidance in prosecuting the work.
The report states that the character OF
the rock encountered is unfavorable
TO endurance. from its tendency to de-
teriorate when exposed to the air. In
some places this change has already
occurred; at others rock which, when
blasted, is sound and hard, will some
times remain so, while that excavated
only a few feet away will in a few
months crumble almost into clay. The
headings were started in sound rock,
giving no indication of the probable
presence of this disintegrating rock on
the line of the tunnel, and there appears
to be no reason why better results should
have been anticipated by carrying the
shafts and tunnel any lower. If the
character of the rock had been antici-
pated the grade Of the tunnel would have
been fixed much higher. The work has
now advanced too far for any change in
grade to be practicable and 1t remains
only to make suitable provision to re-
sist the hydraulic pressure to be appre-
hended.
Where the rock Is solid and can
safely be trusted to resist diSintegration,
which the engineer in charge judges will
be the case for about four-tenths of the
length of the tunnel, no lining is neces-
sary and no change in the present cross
section is suggested. Where the rock,
although fairly good. is unsafe to trust
without lining the present plan Is to
line with a 13-foot (three-brick) arch
and fill in solidly with dry stone between
the bricks and the rock in place. The
board recommends that such places shall
be filled with rubble laid in cement
mortar or with fine concrete packed
solidly around larger stones. according to
convenience. No motion can be permit
ted among the stones which are to trans
nit the ultimate pressure to the rock
in place. and this can only be certainly
accomplished by filing up all the inter-
stices with a solid mass.
Where the rock is still worse, so that
timbering becomes necessary to the
safety of the miners, the present plan
Is to insert such beams as may be needed
and leave them in position. The board
advises the removal of all wood when
practicable, and when not to bed it in
solid mass Of concrete or rubble, filling
all voids.
I'm Rock Creek and Foundry Greek
Valleys, which have points where the
ground is 135 and so feet, respectively,
below the water surface in the reservoir
and where the unbalanced pressures will
probably reach So and 81 pounds per
square inch, all the lining and backing
wherever the rock is not unchanging and
impermeable should be done with the
greatest care in the most substantial
way and with mortar rich in cement.
THE inspection of the new reservoir
satisfied the board that the work is pro-
ceeding in an entirely satisfactory man
ner as proposed by the special board OF
1885, and no changes are recommended.
The total length Of the tunnel Will be
20.700 feet when completed and the
aggregate length then lined will be about
$4,000 feet. At the present time LAO feet
have been lined and Its feet timbereo.