15 August 2002
cutting off the large volume of seepage flow which would otherwise reach the drydock.
For an example of this type, see (e) of Figure 3-3.
Granular Material Filter. Granular materials generally found at these
drydock sites must be excluded from the relief system flow. This requires the use of
carefully designed filter courses and a system of drainage pipes adjacent to the walls
and under the floor. The amount of pumping for this type will depend on the efficiency
of the cutoff and the permeability of the soil.
Partially Relieved. A partially relieved drydock has relief provided for the
floor only. Its use reduces the amount of floor concrete and minimizes difficulty in
construction of the cofferdam. Provide the following:
Cutoff Wall. Generally, a cutoff wall to surround the floor area only.
Filter Course. A filter course under the floor. A system of collector pipes
in the filter course may be used to carry the seepage water into the drydock collecting
Alternate. As an alternative to a collector system, provide holes through
the floor for the seepage water to flow into the drydock chamber then through trenches
and scuppers to the collecting tunnel. See (c) of Figure 3-3.
Miscellaneous Types. For drydocks of temporary or semi-permanent
nature, a great variety of types may be used. These types are so much different in
general character from the conventional naval drydock that classification in accordance
with the method of solving the water pressure problem is not entirely definitive. These
drydocks are generally for shipbuilding or for building other types of floating structures,
and take a great variety of shapes and forms (see Figure 4-1). For these drydocks,
provide the simplest drainage systems. Either the floor or walls, or both, may not be
watertight, and the water may seep through them into the dock chamber and run off the
floor into trenches or pump sumps for disposal by pumping.