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6. DESIGN OF PILE FOUNDATIONS
6.1 Attachment of piles to superstructure
The joint between a pile and the superstructure can be
dimensioned as a hinge. The piles are cut so that the upper end
of pile pipe is embedded at least 50 mm inside the pile footing
or concrete superstructure unless otherwise required by the
structural design or attachment of piles. When joining a pile to
the above concrete structure as mentioned, it is not necessary
to fasten the bearing plate by welding to the pile pipe.
Short, under 3-metre long driven piles should always
be attached rigidly to the superstructure. Depending on
structure, longer piles may also be attached rigidly to the
superstructure. RR75...RR/RD220 piles are attached rigidly
to the superstructure when the upper end is embedded in
the concrete at a depth of at least 2·
d
, but not less than 200
mm. When empedding upper end of pile to concrete like
descriped above, it's not necessary to connect bearing plate
to pile by welding. When the upper end is attached directly to
a steel superstructure, a rigid joint can be created by welding.
Reinforced piles are usually attached to the superstructure
by extending the internal reinforcements of the piles into the
concrete structures. In rigid connection, the moment capacity
of the upper end of pile must be verified.
The bearing plates presented in Table 16 can be used for
axially compressed RR and RD piles.
6.2 Centre-to-centre distances between steel piles
The distances between piles are defined in design documents.
Recommended minimum centre-to-centre distances for
different pile diameters are presented in Table 24.
Table 24. Recommended minimum centre-to-centre spacing
of SSAB’s steel piles [
mm
] according to PO-2016 [
mm
].
Pile
min c/c [mm]
RR75
800
RR/RD90
800
RRs/RDs100
800
RR/RD115
800
RRs/RDs125
800
RR/RD140
800
RR/RD170
800
RR/RD220
800
RR/RD270
800*
RR/RD320
850**
RR/RD400
1000
RR/RD500
1200
RR/RD600
1350
RR/RD700
1550
RR/RD800
1700
RR/RD900
1850
RR/RD1000
2050
RR/RD1200
2400
* According to PO-2016, the recommended minimum centre-to-centre distance 800 mm
between RR/RD270 piles is valid up to a pile length of about 15 m. Thereafter, the mini-
mum distance must be increased to 950 mm as pile length increases to 25 metres.
** correspondingly, the minimum centre-to-centre distance 850 mm between RR/RD320
piles is valid up to a pile length of about 10 m, after which the minimum centre-to-centre
distance increases linearly to 1150 mm at a pile length of 25 m.
Smaller centre-to-centre distances than those presented
in Table 24 may be used with caution with RD piles, if they
can be installed straight or at the designed inclination
and the piles bear securely on bedrock. When designing
downward spreading pile groups, the upper ends of piles
can be spaced closer than in the table.
In the case of intersecting end-bearing piles in a fine-
grained soil layer close to ground level, a clearance
equal to pile diameter can be considered sufficient, if
the pile can be directed during installation so that it
does not touch adjacent piles. In coarse-grained soil
layers, especially with driven piles, the clearance must be
considerably larger. Pile intersections should be located
as close to ground level as possible. With large diameter
RR piles the minimum distance between intersecting piles
is determined by the equation:
e
r
= 50
l
r
≥
e
i
(3)
where
e
r
minimum distance between intersecting piles [mm]
l
r
depth of intersection [m]
e
i
shortest distance between parallel shaft surfaces =
300 + 0.7·
d
[mm]
6.3 Distance between side of pile footing and piles
The pile footing must be able to withstand the stresses
from pile forces and there must be no risk of the side of
the pile footing breaking off. Normally, the distance from
the edge of the pile footing to the outer surface of the
closest pile or the edge of the bearing plate must be at
least half of the pile diameter or the length of the side of
the bearing plate. The positional tolerances of a pile must
be taken into account at the design stage.
6.4 Distances between piles and other structures
The minimum distances between piles and other
structures are designed separately in each case
considering the piling equipment, pile type, vibration
caused by piling, compaction of soil, loosening or
displacement of soil, and special requirements and
restrictions posed by soil conditions and ambient
structures.
If the only restricting factors are the piling equipment
and available space, the minimum distance must be
determined on the basis of the properties of used piling
equipment and the site. Small diameter RR and RD piles
can be installed quite close to an existing wall or footing
line, etc. owing to the small-size installation equipment.
However, without a closer analysis, it is not advisable to
design piles in sizes RR/RD220 to RR/RD270 or smaller
so that the distance between the pile edge and the
structure is less than 200 to 300 mm (if there are no
structures restricting piling, such as eaves, etc., above the
piling level).