Fixation of Tops of Sheet Piling. (See Figure 25.) This scheme
reduces the moment in the sheet piling by fixing the upper end as well as the
lower end. In effect it creates a fixed-end beam.
Methods to Reduce Wave Action.
(See Figure 26.)
Types of Front Wall.
(See Figure 27.)
Selection Factors - Types of Front Wall
Sheet Piling. (See Figure 27, Examples A, B, and C.) This type of
construction is the usual selection and should be given primary consideration
even if the use of cover plates to strengthen available rolled sections is
required, the selection of steel, timber, or concrete (for low walls,
aluminum, fiberglass, and corrugated asbestos may be considered) is a matter
of relative cost. For concrete or timber sheet piling, which displace a large
volume of soil during installation, consideration must be given to achieving
the required toe penetration without excessive driving and damage to the
sheets. Jetting often is required.
Soldier Pile Wall (also called "King" Pile Wall). Where the
strength of available sections of sheet piling is insufficient for the
proposed height of wall and loading, consider a soldier pile wall (Figure 28,
type D). By using heavy soldier beams, large bending capacities can be
achieved. The sheeting between the soldier piles is draped to act as a
catenary (in tension). In the case of the PZ, PDA, and PMA sections, pure
catenary action is not achieved. The fill "arches" between the soldier beams
so that the sheeting gets little load. The sheeting is not "designed." For
normal spacing of the soldier piles (about 6 to 12 ft) (1.83 to 3.66 m), and
assuming the soil behind the wall does not consist of soft clay or silt,
minimum commercial sections of sheet piling are adequate.
Soldier Beams and Lagging. Sometimes a bulkhead can be constructed
in the dry. An example is when dredging is to be done after the wall has been
completed. In such a case, use of soldier beams and lagging often is a more
economical solution than the use of sheet piling. One of the reasons is that
the lagging can be virtually any material. Timber, concrete, aluminum,
galvanized steel, and corrugated fiberglass have all been used.
As with the soldier pile wall, arching between the soldier beams
reduces the pressures acting on the lagging so that the lightweight sections
can be employed. Theories as to pressure acting on lagging vary from an
assumption of full arching wherein pressures may be estimated by considering
the soldier beams as a series of silo walls (see Figure 29) to assumptions of
partial arching. In its simplest form, partial arching is estimated by
applying a reduction factor (often 13 to 12) to the basic trapezoidal pressure
diagram. For timber lagging, assuming the use of commercial lumber and not
stress graded lumber, the recommendations in Table 1 may be followed.