Evening star. [volume] (Washington, D.C.) 1854-1972, 1886-04-24
THE WArKR WORKS GXTINsION.
Capt. Hoxie's Answer % The Appropri.
atfOns Comnittee's Request Ter In.
formation.

1ORmoe100s
The following IL COPY Of Capt. Hoxie's letts,
to the House appropriations COMMITTEES con
corning the water works extension OF the Dis
trict:
Hon. Samuel J. Randall, Chairman Hos.ss Obus
nasftee on Appropriations Washsaotor, DC:
Dear sIR-In compliance with your requss
the following with respect 70 the "Extension O
the Washington AQueduct'':
The plan and estimates originated in the
ONCE OF the Engineer Commissioner, ID. c., and
were presented to Congress in q report with my
signature, dated February IS, 1879. Pursuant
20 THESE estimates, as nodded subsequently
ies igggs for the work was made july
Pending the long consideration OF the matte,
line Of the work the method Indicated in the tn,
original estimates for CRUSHING Rock creek. az
tunnel through the compact rock which under
forced-conduit, under heavy internal pres
sure. which must have the properties
OF cast-iron water main. In designing
the driving OF tunnel In the compact sound
rock, which is exposed to view in numer
gus quarries near the line of the tunnel, and
Georgetown, whenever the decompes r SS
upon the surface has been penetrated to 8
suf1cent depth.
This as the first consideration. 1t entails no ad
oitional cost upon the United States on account
theoretical depth adopted a. basis Of compar
ct uniform rates, Of sinking the several shsis;
TO reoi tn Of SOUND rocs
the tunnel" Had this principal feature OF the
Snd sound rd Ran oun been kept in view
nifty feet lower than the present location OF the
tunnel, estimate that the deficiency would
n nave been less than now stated by S296, 1856
in demoralixed rock. The methods under
which II ~ prosecuted are at variance with
the original plan, and are. in my Judgment, con
ducive to failure through failure to observe the
essential requirements of such structure, and
are unnecessarily expensive, because OF toe
large an excavation for lining and timberine
the tunnel, and too costly . material for lining
1t. The internal pressure of water will be very
great and should be resisted, in the lined
medium ke tine rock by a wallis un lhs%
selves, else the lining will open in mum
berless cracks and seams, and permit the water
tract pIescribes concrete for this lining, which
can be remmed hard against the natural roch
surface, niiing every inequality, making a per
rock ITSELF Brick has been substituted, witt
dry stone packing, TO Ill the void spaces be
tween the brick and the irregular surface o
can give to this dry stone packing the resistina
properties of concrete to internal pressure. The
dimensions OF the rough rock tunnel were
veyance OF water equal to that Of q smooth
circular brick conduit Of nine feet diameter
The lined portion of the tunnel requires only &
suncient interior space to give With its smooth
surface capacity equal to that of the nine foo
conduit. To give greater capacity In the linec
portion OF the tunnel than in the unlined Dor
ton Ia like mending . small rope with chair
cable. Both tor lining and timbering the ex
cavation has been made unnecessarily large
greatly increasing tho cost; the cost OF THU
prick lining IL $14 per cubic yard, as agains
20 per cubic yard for the concrete prescribed
by the contract, and which the contractor Il
bound to put in. There is no analogy between
this work and that upon the aqueducts, whict
are not, like this, forced cOnduits; yet such 40 ue
ducts appear to have been studied as examples
with tie tunnel in demoralixed rock as a
present. were the normal capacity retained
upon which its delivery is com puted, a suitabl,
cross section adopted, and the concrete lining
which Is prescribed by the contract not re
placed by more costly and less efficient brici
with dry-stone backing, in my opinion ths
work could be SO done that the chances OF fail
ure would be greatly diminished and the def
clency less than now stated by S2O9. 342.35. A
part Of the work has already been done by thu
more expensive methods. Isend herewith de
tailed estimates which will, think, give thu
Information desired.
Very respectfully, your obedient servant,
r. Z. HoxIE,
Captain Engineers u. 8 A.