Evening star., 1896-01-23

can be used for the rubble-masonry back
ing.
Our examination of those portions of the
tunnel already lined taken in connection
with the published testimony and supple
Eented by the statements of others whom
we have called before us, shows that there
Is great diversity in the character of the
lining. In some portions of the tunnel ver-
tical rubble sidewalks have been built.
Where these occur we have been unable to
find any void spaces of magnitude behind
the wallis. In other cases the sidewalks are
built of brick, generally filled on the out
side to the crown of the arch with loose
packing. Some portions contain brick in
vert. AS a general rule, empty spaces exist
over the crown of the arch. In the wester-
ly part of the tunnel these spaces are COM
paratively small, but in the easterly por-
ton they are much larger, in some cases
extending to more than ten feet in height.
These cavities must be filled with rubble
masonry lad solidly in cement mortar. In
some cases timbering exists in the spaces
over the arch. The timbering should be
taken out in sectiops and rubble masonry
substituted. Where the spaces will not al
low Of laying rubble masonry, provision
has been made for filling the spaces with
stone packed by hand, and then grouting
the whole mass with cement under pres
sure. In other words, it is intended to fill
every space or void now existing in these
portions of the tunnel. either with cement
grouted rubble, or with rubble masonry
lad in cement, thus securing a solid back
ing everywhere between the lining and the
rock.
Where no invert now exists. we recon-
mend slight excavation of the rock and
tie building of an invert of Portland ce-
ne mt concrete smoothly finished.
Reinforcement of the Rock Creek
Section.
Experiments made by Maj. Knight in
1895, and detailed in his report upon this
subject indicate that the covering of rock
over the tunnel in the Rock creek valley is
rot sufficient to provide the necessary re-
s1stances required, or to prevent serious
percolation These experiments confirm our
own opinion that for length of about
1,GOO feet under Rock creek it will be neces-
sary to provide some special form of con-
struction. We have considered various
plans, and have come to the conclusion
that either a Subtunnel built at a consider
able distance below the present tunnel
should be provided, or that the present tun-
mel should be liEed with cast iron surround
ed with concrete. majority of the COM
mission is inclined toward the metallic lin
ing. The cost of the two plans is practi-
c2lly the same.
Accessories.
In the course of our examination we nave
found that ii will be necessary TO provide
seN eral accessories in connection with the
tunnel for the purpose of making it avail
able, and for the purpose of maintaining
1T in a proper manner after construction
is completed. We will now allude to these
briefly in their order. beginning at the
westerly end.
A connection now exists with the seven
foot by-conduit around the distributing
reservoir. A direct connection should also
be made with the reservoir, near tie west
-erly shaft, to be controlled by a gate house,
provided with the necessary gates and ap-
plianceS to regulate the flow.
AS it is probable that there are voids
existing between the brick lining and the
rock surrounding the westerly shaft the
whole of this shaft should be thoroughly
grcUted.
The estimate has included gate house
covering the shaft, which will contain
for the raising of material from the bot
tom of the tunnel. The shaft is to be pro-
vided with a deep sump, protected by
heavy paving.
The profile of the tunnel shows a slight
summit near the westerly end, and
have provided a small brick structure
through this divide for the purpose of
draining the water in an easterly direc-
ton.
We have deemed it advisable to close
the Foundry branch shaft entirely. This
can only be accomplished by providing
drainage through the Fayette street sum
creek shaft. We recommend the con-
struction through this summit of a 24-inch
masonry pipe. properly protected with
concrete. Owing to slight percolation in
the immediate neighborhood of the Foun-
dry branch shaft the brick lining at this
point is to be reinforced, the shaft lined,
grouted and permanently sealed.
All three of the air shafts existing on
the llne of the tunnel are to be repaired,
sroUted and protected by suitable cover
ingS.
level in the tunnel and there is here but
a small amount of material over the arcf1,
TINS point has been selected for the con-
stTuction of a forty-eight-inch blow-off
with gates, to empty the tunnel CT all the
water which can be taken out, with the
exception of that which must be pumped
The shaft is to he provided with metal
lining six feet in diameter. backed with
brick and concrete. To this lining will
be attached a cover of sufficient strength
to resist the internal pressure. The shaft
will be protected by brick house pro-
vided with hoisting apparatus A short
distance from the shaft an excavation VIII
be made in the rock to receive a large
pump pit surrounded with a heavy wall
and containing the pumping machinery
the whole covered by a substantial SUPER
structure. boiler house will contain the
necessary boilers for supplying power to
the pumps, which will be of sufficient ca
pacity to raise 120O0,o00 gallons in twen-
ty-four hours from the level of the tunnel
to ROCK creek.
In the Champlain avenue shaft the pres
ent timbering is to he repaired and the
sHdll liileu with DFick ana concrete, con-
tainirg an opening not less than eight feet
in diameter A stand pipe twenty-five
feet in height should be built upon the
top of the shaft, and the whole covered
with brick house containing the pumping
and hosting machinery. A connection
with the local sewer should be made at
this point to avoid the discharge of water
on to the surface of the ground.
The Howard, or easterly shaft is to be
reinforced by a twelve-inch brick lining
inside the present shaft, and the backing
of the Shaft grouted throughout it's whole
height. There will be a paved sump at
the bottom.
\ liberal sum has been estimated for
the erection of a gate house over the east
erly shaft 1t is an important adjunct in
connection with the construction of the
tunnel The foundation of the gate house
Is 10 be Independent of the shaft and sunk
to considerable depth, not less than fifty
feet below high water in the reservoir
The gate house will be large enough to
control the flow of water to different parts
of the reservoir. and double sets of gates
will be provided for this purpose. 1t will
also receive the ef11uent water from the
reservoir and discharge it into the large
cast iron main already laid from the reser-
voir and connecting with the distribution
system.
Estimates.
The following table contains estimates for