Pile Design and Construction Practice, Fifth edition

the pile can be predicted accurately. If the upper part of the pile has to be cut away, they no
longer have any useful function, but they can serve as a means of lengthening a pile should
this be necessary.
Proprietary hydraulic pile croppers, suspended from the dipper arm of an excavator, can
either break off the excess length of a concrete pile at the required level or nibble the con-
crete leaving the reinforcement exposed.
Steel box, tubular, or H-section piles carrying only compressive loads can be terminated
at about 100 to 150 mm into the pile cap without requiring any special modifications to
the pile to provide for bonding (Figure 7.7a). There must, however, be a sufficient thick-
ness of concrete in the pile cap over the head of the pile to prevent failure in punching
shear. Research by the Ohio Department of Highways(7.7)has shown that if the concrete
forming the pile cap is of adequate thickness and if the reinforcement is correctly
disposed to withstand shearing and bending forces there is no need to provide a bearing
plate or other device for transferring load at the head of an H-pile. However, where steel
piles are carrying the maximum working load permitted by the material in cross-section,
the thickness of concrete in the pile cap to resist punching shear may be uneconomically
large. In such cases the head of the pile should be enlarged by welding on a capping plate
(Figure 7.7b) or by threading steel bars through close-fitting holes drilled in the pile
(Figure 7.7c). The capping arrangements shown in the latter two figures can be used to
bond the pile to the cap when uplift loads or bending moments are carried by the pile, or
alternatively bonding bars can be welded to the pile. Load transfer from large diameter
tubular piles to pile caps can be achieved by welding rectangular plates around the
periphery of the pile at its head.

Structural design of piles and pile groups 387

M.S.capping plate

M.S.plate

cover

M.S.plate

stiffeners

M.S.bars

Closely

fitting

drilled

holes

(a) (b) (c)

75 to 100 mm

Figure 7.7Bonding steel piles into pile caps (a) Compressive loads only on steel tubular piles
(b) Hexagonal box pile carrying heavy compressive loads or uplift loads (c) H-pile carrying
uplift loading or bending moments.