Figure 8-29.Rubble-mound breakwater or jetty.
Four crew members to place the piles in the leads.
One or two crew members to prepare the piles.
This is based on the further assumption that the
pile driver can pick up and place the piles in the
leads. If this cannot be done because of the
location of the undriven piles, you must allow for
an additional crane and increase the total
man-days required by 15 percent.
The time in man-days required to drive each pile
depends on the type of pile and its length. Precast
concrete bearing piles drive slower than wood or steel
ones; and logically, the use of a longer pile usually
means that you plan to drive it deeper, which will take
more time. Under average conditions, it takes 3.0
man-hours to drive a 25-foot wood pile, but for a steel
pile, it takes 4.0 man-hours, and for a precast concrete
pile, it takes 13.2 man-hours. These estimates take into
account pile preparation, placing it in the leads, driving,
and cutoff, if required.
When estimating the man-days required to
complete a pile-driving operation, you cannot forget to
include time for the assembly of the leads and hammer,
preparing the equipment for driving, cutting holes in
steel piling to facilitate handling, and disassembly of the
equipment upon completion, if required. You must also
allow time for pile extraction if it is a required part of
Waterfront structures may be broadly divided into
three types as follows: (1) harbor-shelter structures, (2)
stable-shoreline structures, and (3) wharfage structures.
Harbor-shelter structures are offshore structures
that are designed to create a sheltered harbor. Various
types of these structures are covered next.
A BREAKWATER is an offshore barrier, erected
to break the action of the waves and thereby maintain an
area of calm water inside the breakwater. A JETTY is a
similar structure, except its main purpose is to direct the
current or tidal flow along the line of a selected channel.
The simplest type of breakwater or jetty is the
rubble-mound (also called rock-mound) type shown in
figure 8-29. The width of its cap may vary from 15 to
Figure 8-30.Composite breakwater or jetty.