National Republican. (Washington City (D.C.)) 1872-1888, 1886-04-17

have upon II, that tho decision to line con-
siderable portions With masonry was made.
IL was clear from the chemical constituent
cies OF the rock analysed by Prof. Merrill,
that evenin many portions where the rock
appeared sound at first contact, the pres
ence of the water in the tunnel would pre-
cipltate the processes OF the dislntegrating
elements, which would soon cause slips, or
"slumps,n OF masses OF rock from the
roof aud sides, derauging the flow and in
time damming the tunnel entirely, to say
nothing OF the enormous leakage which
must be consequent upon the application
Of pressure due to the great head OF water
which the structure would have to carry.
Under these circumstances lining with
masonry was the only alternative. In his
original estimate Capt. Hoxle had pro-
vlded for q contingency Of lining, and TO
meet IL he had proposed concrete arch,
estimates for which were included In the
proposals under which bids were received.
This, TO say the least, was an innovation.
At all events there was no instance known
to the practice Of mining engineering in
which concrete lining had been successfully
used. In fact the mechanical conditions
required for the proper 'settingn OF con-
crete In arch forms, render its use In sub
terranean work where the contact with
moisture is necessarily constant, quite i'm
practicable. On this subject the great
autnOrlby on Iunuelbi IIOl' henIy o.
Drinker, is very explicit. He insists
upon the most compact and i'm
pervious kind of stone or hard brick
masonry, laid In the best hydraulic cement.
Capt. Hoxie, however, proposed TO line the
Washington aqueduot tunnel with concrete,
wherever lining might be required. But
his successor, Capt. Thomas w. Symons,
was not inclined to make experiments
| So when confronted with the practical ne
cessity Of lining the tunnel Capt. Hoxie's
| proposed concrete arch was abandoned and
| the customary brick arch substituted. The
| following is an extract from the report Of
George II. Coryell, esq.,, ON this subject.
| [Mr. Coryell is an experienced mining en-
gineer, and is now the civil engineer OF the
Of the tunnel.1 He says:
| deprecate the use OF concrete in arch
| form in the tunnel. As generally made, con-
| crete Is nothing more than weak, artificial
stone. possessing little strength when exposed
TO transverse strain even whenthe ccmenting
| material Is thoroughly hard, which 1t may DO
fairly presumed In most cases. does not take
! place for many months and IL Is well
| known to those who have used II, that II
hardly arrives at Its initial strength for long
| time.
Ii is evident that itshould not be used whore
| II is subject to cross strain as in the tunnel.
| In foundation work the use of concrete Is in
valuable when applied in proper manner
| and confined on all sides, and Is consequently
subjected TO little cross strain, but II Is not III
to be used as substitute for brick masonry.
We have pursued this branch of the sub
iect at some length and In considerable de
| tail In order to make perfectly clear the
points Of difference between the present
officers in charge Of the tunnel--Maj. Ly-
decker and Capt. Symons-on the one hand
and Capt. Hoxie ON the other.
The latter in his communication to the
chairman Of the appropriations committee
appears to stake his professional reputation
upon two points: 1. The assertion that Maj.
| Lydecker proposes to line greater portion
OF the tunnel than is necessary. 2. The
theory that concrete is practicable mater
ial for such lining. We do not assume tc
decide the points in controversy. But IL Il
proper to remark that, as to the first point
namely, the extent OF lining required-Capt
Hoxie appears to stake his theory, ela6o
rated at the distance Of Montgomery, Ala,
against the practical experience Of equally
competent engineers who have inspected the
rock Of the tunnel in place through ever,
yard Of its excavation.
While as to the second point-namely
the practicability OF concrete as a materia
for lining-he stakes his untested theory
against not only the universal experience o.
hydraulic engineers everywhere, but agalns
the leading and generally recognized pro
fessional authority on tunnel work OF every
descrlptlon-Prof. Drinker. This certainly
has the merit Of being a bold stand. But
in view Of the fact that the permanency and
security of the water supply OF the capital
Of the nation are involved, and In further
view Of the fact that Capt. Hoxie's theories
In regard TO the character of the rock he hat
to deal with were shown by the experlenc,
OF the actual drift to be Numerically fal
lacious, IL would seem that there ought I,
be at least reasonable doubt as to his in
fallibility.
In the New York and Boston tunnels
brick lining has been introduced through
out, irrespective Of the character of tn,
rock to be dealt with. But In those case
the responsible engineers are civilians
Benjamin f. Church In one case and JOSEPH
z. Davis In the other-whose livelihood de-
ponds upon their efficiency, and who there
fore cannot Afford to commit blunders o.
indulge in empirical theories. An army
engineer has greater latitude; his pay ant
promotion 90 on just the same whether he
succeeds or fails, whether his calculations
and estimates are right or wrong.
We have been In no sense a partisan Of
Maj. Lydecker On the contrary, oul
columns have frequently been opened Il
severe criticisms upon his work, PARTICULAR.
In the management Of the construction of tht
new reservoir. But In this issue with Capt
Hoxie 1t is clear that Maj. Lydecker is mo-
only on the safe side, but he is also sus
tanned by the universal experience OF the
engineering profession, and to that exten
the public interests seem to require that h
be Endorsed and supported. The publ
has no concern with the personal squabble
Of the army engineers. But II has dec
and vital interest in the proper construc
ton of cost must be held wholly subordi
nate. And there is no room for hazardou
experiment or untried theory.
|