Evening star. [volume] (Washington, D.C.) 1854-1972, 1886-08-27
THE WATER WORKS TUNNEL.
The Report Of the Board Of EngineeF
OmcerS.
WHAT IS NECESSARY, IN THEIR OPINION, 10
MAKE THE TUNNEL HOLD WATER.

WHAT IS NECESSARY, IN THEIR OPINION, 10
MAKE THE TUNNEL HOLD WATER
The report of the board of engineer officers
upon the new aqueduct tunnel recommends, as
announced in yesterdays STAR, the use OF brick
In the lining of the tunnel, as the exclusive use
OF concrete is, in the opinion OF the board, i'm
practicable. The report was approved by the
chief or engineers and the acting Secretary Of
war, and copy was to-day sent to Major Ly.
decker for ihis guidance In prosecuting the
work. The report states that the character Of
the rock encountered Is unfavorable to endur.
ance. from its tendency to deteriorate when ex-
posed to the air. In some places this change
has already occurred; at others, rock which,
when blasted is sound and hard, will sometimes
remain SO, while that excavated only q few feet
away Will, In q few months, crumble almost
rock, giving no indication Of the probable pres
ence OF this disfntegrating rock on the line of
the tunnel. and there appears to be no reason
pated by carrying the shafts and tunnel any
lower. If the character of the rock had been an
hfic,pafea happ the ezra grade Of the tTnne. would have
advanced too far for any change In grade to be
practicable, and it only remains to make suita-
BILE provision
TO RESIST THE HYDRAULIC PRESSURE
10 be apprehended. Where the rock is solid
and can safely be trusted to resist disintegra-
tion, which the engineer in charge judges will
be the case for about four-tenths OF the length
OF the tunnel, no lining is necessary and no
Where the rock, although fairly good, is un-
safe to trust without lining, the present plan is
to line with thirteen foot q brick) arch and
I'LL 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 round larger stones, according to con-
venience. No motion can be permitted among
the stones which are to transmit the ultimate
be certainly accomplished by flling up ali
tnterstices with a solid mass.
THE USE OF WOOD.
Where the rock is still worse, so that timber
ing becomes necessary to the safety of the
miners the present plan is to insert such beams
as as may be needed, and leave them in position:
The board advises the removal of all wood
when practicable; and when not, to bed 1t in q
solid mass of concrete or rubble, filling all
voids. Finally, the case of over head falls of
rock producing extensive dome-like cavities is
presented. Fortunately these are not common,
only two of very large size being reported.
THE WORST CAVE IN.
The board visited the site of the worst one. 1t
extended thirty-one feet along the axis of the
tunnel and the fall had crushed the timbering
The cavity had been 1t once filled with about
forty cords of wood laid up as well as possible
for a length OF fifty-two feet with brick The
space between the brick arch and the work in
place on the sides had been filled in with dry
stone packed as closely as possible. While 1t IS
probable that wood in such positions will be
covered ultimately by water, this will not be
true until the tunnel is filled, and in the mean
time dry rot may be at work among this wood,
as was seen to be the case with the beams In
several localities. Besides, the wood cannot
be trusted to resist the pressure tending
70 rupture the brick when the tunnel is filed.
The board therefore considers that before
the work Is completed all wooden backing
should be replaced by solid masonry by means
of auxiliary drifts run over the tunnel and
filled solid w tn masonry; or by q new tunnel
around the site of the cave, filling up the pres
ent tunnel with masonry, or by q shaft sunk at
the locality % may prove to be most econoIni-
CAL -.zf.s..-.s@ tyr
TIE POINTS OF eREATEsr PRESSURE.
In Rock creek and Foundry creek valleys
which have points where the ground is 135
and 50 feet respectively below the water sur
face In the reservoir, and where the unbal-
anced pressures will probably reach So and 21
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 NEW RESERVOIR.
The inspection Of the new reservoir satisfied
the board that the work is proceeding in an
entirely satisfactory manner as proposed by
the special board of 1885, and no changes are
recommended. The total length of the tunnel
will be 2O,7OO feet when completed. and the
1000 feet At the present time /, ,74O feet
hav vp heon lined and I 1TE fpaf m mhared