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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris2013
piles during pile installation with prediction or calculation of
PPV of ground vibrations generated by pile driving, Robertson
(2006) and Massarsch & Fellenius (2008).
The first such an attempt was made by Svinkin (1996) in
favor of the Impulse Response Function Prediction (IRFP)
method for prediction of ground and structure vibrations from
pile driving; the method was developed toward prediction of
complete time-domain vibration records on existing soils,
buildings, and equipment prior to installation of impact
machine foundations, Svinkin (2002). In the application of this
method to pile driving, wave equation analysis was used to
assign a movement of the pile top, but it’s necessary to
underline that the top pile movement can be assigned
arbitrarily, for example as a damped sinusoid, because ground
vibrations at some distance from a dynamic source depend only
on the dynamic force transmitted on the machine support and
soil properties, Svinkin (2002).
It is necessary to point out that a connection of the stress-
wave theory with ground vibrations from pile driving has few
problems. First, there are several different programs for signal
matching techniques which produce diverse results for the
same piles and their outcomes depend on variety of soil
conditions and pile types, Svinkin (2012). It is not clear what
software should be used. Second, stress waves in piles
obviously generate internal forces in driven piles. Third,
according to Saint Venant’s principle, wave propagation in piles
does not affect dynamic field at some distance from a driven
pile.
It is known that impact hammers for pile driving and forge
hammers released comparable amounts of the energy and they
generate similar vibration records of ground vibrations
(Steffens 1974). Therefore, it is reasonable to compare both
dynamic sources and their effects on ground vibrations.
A forge hammer foundation is considered as a rigid body
which transfers impacts loads from a hammer onto the ground.
Dynamic forces in the machine foundation itself are internal
forces generated by stress-waves propagated in the machine
foundation under forge hammer impact. The duration of internal
forces is substantially smaller than the duration of dynamic
forces transferred from a machine foundation onto the ground,
and these two kinds of dynamic forces work in different time
frames. Consequently, internal dynamic forces in hammer
foundations are not taken into account in determination of
dynamic loads transferred from a hammer foundation on the
ground and consideration of ground vibrations generated by
oscillations of forge hammer foundations (Barkan 1962 and
Richart et al. 1970).
In prediction of ground vibrations from operating forge
hammers, ground vibrations depend on the impulse dynamic load
applied to a hammer foundation, the damping coefficient and the
natural frequency of vertical foundation oscillations, and also the
impulse response functions of the considered dynamic systems.
The latter represent the soil medium where wave propagate from
the hammer foundations to destination locations. The
experimental studies showed that at some distances from the
source, ground vibrations become dependent only on the impulse
load transmitted to a hammer foundation and the soil medium
where waves disseminate from the source (Svinkin 2002). These
results are in agreement with a dynamic version of Saint
Venant’s principle (Timoshenko & Goodier 1951and Karp &
Durban 1997).
A similar picture of a dynamic load transfer from a forge
hammer on its foundation and the ground can be represented for
pile installation. Piles also can be considered as rigid bodies in
which stress-waves propagate from hammer ram impacts and
generate internal forced in piles which are the causes of pile
movement and vibrations
.
Besides, a pile-soil load transfer is
released by means of both concentrated loads from the pile toe
and distributed loads generated along pile shaft. Similarly to
hammer foundations, at some distances from a pile, as the
dynamic source, ground vibrations become dependent only on the
dynamic load applied to a pile and the soil medium where waves
propagate from the source. It is known that velocities of wave
propagation in piles are about 4000 m/s in concrete piles and
about 5100 m/s in steel ones (PDA 1991). Velocities of shear
wave propagation in the ground are shown in Table 1.
Velocities of surface waves are equal about 0.92-0.96 of the
velocities of shear waves, Barkan (1962).
Table 1. Velocity of shear waves in soils, Savinov (1979)
Soil
Velocity
m/s
Sand
120 – 150
Sand with gravel
150 – 250
Loess with natural
moisture
130 – 160
Plastic clay
150 - 400
It can be seen that that wave propagation in piles under
impact load is much faster process in comparison to wave
propagation in the ground. Therefore, dynamic loads
transferred from driven piles onto the ground for practical
purposes can be considered as the point impulse load at some
distance from the source, Svinkin (2000).
It can be expected that this conception is correct at distance
derived from an assumption that the time of surface wave
propagation with velocity, c
s
, in the ground at distance, D, from a
driven pile is 5-10 times larger than the time of stress wave
propagation with velocity, c, in the pile with length, L (Svinkin
2000).
c/ Lc)10 5(D
s
(
1
)
Minimum distances from a driven concrete pile as the point
vibration source are shown in Table 2 (coefficient 10 was used).
Table 2. Minimum distance from pile as point vibration source
c
s
/c
150/4000
300/4000
Pile
Length
m
Lc
s
/c
m
10Lc
s
/c
m
Lc
s
/c
m
10Lc
s
/c
m
10
0.375
3.75
0.75
7.5
15
0.5625
5.63
1.125
11.25
20
0.8438
8.44
1.5
15.0
30
1.125
11.25
2.25
22.5
40
1.6875
16.88
3.0
30.0
It can be expected at distances determined by equation (1),
that only dynamic forces transferred to piles during pile driving
and soil medium where waves propagate from driven piles will
affect ground vibrations generated by pile driving.
It is important to point out that calculation of expected
ground vibrations during the time of pile installation is irrelevant.
For example, Massarsch & Fellenius (2008) tried to connect
stress-wave propagation in piles under the hammer ram impact
with ground vibrations, but they eventually suggested the old
empirical equation to calculate attenuation of PPV of ground
vibrations generated by surface waves, which contain more
than 2/3 of the total vibration energy, from pile installation
without any connection with the stress-wave theory. Ground
vibrations have to be measured during pile driving operations.
