(5) Use Equation (1) to determine the stability against overturning
about Point B. If the factor of safety is less than 1.50,
increase the depth D'. The stability safety factor can be also
increased by increasing the new sheetpile distance d.
(6) Use the same type of sheetpile and the same size of anchor-rod
for the new structures.
(7) Connect the top of the existing sheetpile to the new concrete
The following steps are recommended to assure a proper design.
(1) Take enough soil borings to accurately estimate the subsoil
conditions. Preferably, the spacing of the soil borings along the
bulkhead line should nut exceed 50ft.
(2) Perform soil laboratory tests on undisturbed soil samples to determine
shear strength parameters accurately, as they are essential to the
bulkhead design. Consolidated undrained triaxial shear tests are
recommended, if there is no dredging.
(3) Inspect the existing structures, i. e. sheetpiles, wales, tie-rods,
and anchorage system by diver and by excavation of test pits to verify
that the supporting capacity of the existing structures can be
included in the design. The validity of this depends on an accurate
assessment in this regard.
(4) Check earthquake loading requirements. If the bulkhead is an
important structure and the earthquake induced loading is critical to
the bulkhead, the earthquake load should be included. One approach
for this case is to use the total stresses, in lieu of the effective
stresses, to compute the active earth pressure against the sheetpile.
In this dynamic loading case, the anchor-rod working stress may be
increased to 75% of the yield strength and the required safety factor
against overturning may be assumed somewhere between 1.3 and 1.2.
If an anchored bulkhead has corroded after many years of service, but is
structurally stable and field inspection revealed that the anchorage system is
in good condition, then a cost effective replacement method may be adopted
using the above method. The new sheetpile need not be installed deeper than
the existing sheetpile unless dredging in front of the new wall is needed.