They were allowed to do this, however, in only a few cases as
experiments. After the holes were drilled, the bottom 4 in. next the
flange was filled with soft neat cement mortar. Immediately on top of
this was placed two plugs of neat cement about 2-1/2 in. long, which
were 5 or 6 hours old and rather hard. Each was tamped in with a round
caulking tool of the size of the hole driven with a sledge hammer. On
top of this were driven in the same way two more plugs of neat cement of
the same size, which were hard set. These broke up under the blows of
the hammer, and caulked the hole tight. When finished, the tamping tool
would ring as though it was in solid rock. Great pressure was exerted on
the plastic mortar in the bottom of the hole, which resulted in the
re-caulking of the joint of the iron. No further measurable leakage
developed in the repaired cracks, during a period of four months, and
the total leakage has been reduced to about 0.002 cu. ft. per sec. in
each tunnel, an average of 0.00000051 cu. ft. per sec. per lin. ft.


SUMP AND PUMP CHAMBERS.

To take care of the drainage of the tunnels, a sump with a pump chamber
above it was provided for each pair of tunnels. The sumps were really
short tunnels underneath the main ones and extending approximately
between the center lines of the latter. They were 10 ft. 9-1/2 in. in
outside diameter and 44 ft. long. The water drops directly from the
drains in the center lines of the tunnels into the sumps. Above the
sumps and between the tunnels, a pump chamber 19 ft. 5 in. long was
built. Above the end of the latter, opposite the sump, a cross-passage
was constructed between the bench walls of the two tunnels. This passage
gives access from either tunnel through an opening in the floor to the
pump chamber and through the latter to the sump.