47
11. END-OF-DRIVING TABLES
11.1 General
The end-of-driving tables and graphs have been prepared on
the basis of analyses made using the GRLWEAP program built
on the one-dimensional wave theory according to the main
principles of Ch. 1, App. 2 of PO-2016.
The end-of-driving tables present five different ultimate
geotechnical resistance values (
R
c
) for each pile size,
pile length and driving equipment. In addition to the
R
c, max
values corresponding to piling classes PTL1 to PTL3,
the tables also present the smaller than maximum values
corresponding to PTL2 and PTL3. The reduced value of
PTL2 is about 88 to 90 % of its maximum value, and the
reduced value of PTL3 is the average of the maximum
values of PTL2 and PTL3 corresponding to 80 % of the
yield strength of steel. The reduced values are presented
to facilitate setting appropriate end-of-driving criteria
in situations where the goal is not to attain the maximum
values of the piling class in question. End-of-driving curves
have also been drawn for hydraulic rams and pneumatic
hammers as function of geotechnical resistance and end-
of-driving settlement. The end-of-driving tables and graphs
are suitable for steel piles serving as end-bearing piles.
The end-of-driving tables present the design geotechnical
resistance values (
R
d
) of piles. The
R
d
values apply in the
case of so-called non-rigid structures. In PTL3,
R
d
values
are calculated using a correlation coefficient
ξ
5
of 1.47.
End-of-driving criteria have been calculated for three pile
lengths: 10, 20 and 30 m.
11.2 Drop and hydraulic hammers
11.2.1 Basics of modelling
In connection with the building of the soil model, the
number of final blows imparted with drop and hydraulic
hammers was determined using a shaft resistance of
10% of the total ultimate geotechnical resistance of a
pile and shaft resistance distributed evenly in the form
of a downward expanding triangle. The used Smith
damping factor (
J
s
) is 0.23 s/m, which corresponds to the
typical piling conditions for the above-mentioned shaft
resistance distribution where about half of the pile lies in
cohesion soil and the rest in friction soil. Otherwise, the
dynamic soil parameters of App. 2 of PO-2016 are used in
creating the soil model.
•
elastic compression of soil under the tip before quake
q
t
=
d
/120 [mm]
•
elastic compression of soil around pile before quake
q
s
= 2.5 mm
•
Smith’s damping factor at pile tip,
J
t
= 0.5*(25/
σ
t
) [s/m],
(
σ
t
[MPa] = soil failure stress under pile tip)
Drop and hydraulic hammers up to 2000 kg have been
analyzed using the SELF PJ hammer model created for
GRLWEAP using typical moving part dimensions based on
hammer weight. Drop and hydraulic hammers have been
calculated with the same driving equipment model using
80 % as the efficiency of the drop hammer and 90 % for
the hydraulic hammer.
In the modelling of 3000 to 9000 kg drop and hydraulic
hammers, the Junttan HHK hammer models have been
used as follows:
•
the efficiency assigned to drop hammers was 80 %
•
the efficiency assigned to hydraulic hammers was 95 %
Pile cushion values of Junttan have been used in modeling
3000 and 4000 kg hammers up to pile size RR170/12.5.
With other driving equipment/pile combinations
calculations have been made ignoring pile cushions.
11.2.2 Instructions for use of end-of-driving tables
The end-of-driving settlement of piles driven by hammers
is always 10 mm/10 blows in PTL1 and PTL2, while in PLT3
it is 7 mm/10 blows.
The tables present with an accuracy of 0.05 m the
required drop height for the combination of hammer
weight, pile size and length, and intended geotechnical
ultimate resistance and design value of resistance of
each pile. The maximum allowed drop height used is the
highest value suggested for each combination. When a
value is given in parentheses in connection with maximum
drop height, it refers to the fact that when maximum drop
height is used, the maximum stress on the pile is 90%
according to modelling, and that using the drop height
in calculation will produce the ultimate geotechnical
resistance indicated in parentheses. Drop heights can be
interpolated on the basis of pile length.
The drop heights of the end-of-driving tables of piling
class PTL3 are tentative. Mobilising geotechnical
resistance and stresses on the pile during driving must be
determined on the basis of PDA measurements.
In case the driving equipment includes an impact energy
tester found reliable, the required impact energy can be
determined as follows: required impact energy [kNm] =
hammer weight of table [kg] x drop height [m] x efficiency
given in table [-] x 0.00981. If the efficiency of the driving
equipment is known from measurements to be something
other than the 80 % or 95 % of the tables, drop height can
be changed to correspond to actual efficiency.