penetrations are often much greater than those required for fixity against lateral loading.
Although base resistance to axial loading can be achieved by grouting beneath the pile toe
as described in Section 3.3.9, the operations of cleaning-out the pile and grouting are slow
and relatively costly. An alternative method of developing base resistance of open-end piles
which has been used on a number of marine projects is to weld a steel plate diaphragm
across the interior of the pile. The minimum depth above the pile toe for locating the
diaphragm is the penetration below sea bed required for fixity against lateral loading.
However a further penetration is necessary to compact the soil within the plug and to
develop the necessary base resistance. It is not possible to achieve a resistance equivalent
to a solid-end pile but the penetration depths are much shorter than those required for an
open-end pile.
The diaphragm method was used for the piling at the Hadera coal unloading terminal near
Haifa(8.22). Open-end piles 1424 and 1524 mm ODwere proposed but initial trial driving
showed that very deep penetrations, as much as 70 m below sea bed in calcareous sands, would
be needed to develop the required axial resistance. The blow count diagram in Figure 8.17
422 Piling for marine structures
Figure 8.17The effects of different methods of plugging steel tubular piles driven with open
ends, Hadera coal unloading terminal.0 100 200 300 400 500510152025303540Diaphragm reaches sea bed for 1422 mm
pile and is driven down 21.5 mDiaphragm reaches sea bed for 1524 mm
pile and is driven down 19 mPILES DRIVEN BY MENCK
2 500 HAMMER1 524 mm OD pile (concrete plug placed at
32 m penetration)Diaphragm with 300 mm hole
(95% closure) in 1422 mm OD pileDiaphragm with 600 mm
OD pileNo diaphragm
in 1422 mm OD pileDriving resistance (blows/m)Penetration below sea bed (m)Driving with concrete
plugRedrive
hole (83% closure) in 1524 mm