*
eme jction
H
in a trench below water-level, is great. The sides of the
trench must be timbered, and it is difficult to ensure the
withdrawal of all of the struts or shores. If any of these
be left in, then a direct channel, through the puddl s-wall,
may be formed; through which leakage may take place, which may result in erosion, endangering the stability of the
whole structure. If good concrete be substituted for clay-
puddle, then the only evil of a leak, is a loss of water.
There is no danger to the dam.
4.
149
The use of concrete in the trench below ground
presents a further advantage.
To cut and puddle clay properly,
the trench must be kept dry.
Rich cement concrete may be put
in, by means of buckets or skeps, below water. Probably this
will be the best procedura. Any struts may be removed by
divers, as the concrete rises to their level.
5. It is practicable to drive the sheet-piling in
horizontal lengths of about three feat. Each compound pile
is composed of three 12* x 12" baulks, bolted and dowelled
together, united at the bottom by a long shoe, and at top by
A monkey,
a hoop, embracing the heads of the three baulks.
with a wide head is used, striking all three piles simultaneous
ly. The wide compound piles are less easily deflected by
boulders, than aingle piles.
6.
No.
It is proposed to draw off the water for use, by
means of a tunnel, with its invert at the levels 14.00 and
12.00 respectively, at inlet and outlet. This tunnel is
also intended to carry off flood-water, during construction,
and in it are to be laid the permanent suction-pipes,
taking the water to the pumping-station. A Valve-tower is to
be provided; but no mention is made of its position.
opinion, it should be placed, in solid ground, and the
In my
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