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1 INTRODUCTION
In remote times the South-eastern Sicily were
shaken from strong earthquake that destroyed Au-
gusta, Noto and Syracuse, blooming and rich of his-
torical and artistic evidence cities. Altogether, the
seismic history of this area is yet signed from few
earthquake of high energy, divided from long peri-
ods characterised from moderate activity, both for
number and for low relaxed energy.
Over the last 9 centuries the strongest earthquake,
with epicentral intensity falling within the interval
VIII and XI MCS, are only 8, and the last of these
with epicentral intensity of VIII MCS, dates back to
11 January 1946 (Boschi et al. 1997, Camassi &
Stucchi, 1998). Afterwards, the strongest earthquake,
about 140 years later, is the 13 December 1990 one
with epicentre close to Augusta and epicentral inten-
sity of VII - VIII MCS.
The old city of Noto, few kilometers in the upper
part of the city of Noto, was destroyed from the 11
January 1693 earthquake and both the build-up areas
had heavy damages in occasion of the 7 January
1727 earthquake. The recent 13 December 1990
earthquake damaged several eighteenth century con-
structions in Noto and called the attention on need of
safeguarding the artistic monumental patrimony of
this city, maximum expression of Sicilian baroque
(Maugeri et al. 2000).
In order to study the dynamic characteristics of
soils in the Noto municipal area, laboratory and in
situ investigations have been carried out to obtain
soil profiles with special attention being paid to the
variation of the Young Modulus (E) shear modulus
(G) and damping ratio (D) with depth. Moreover the
effect of the freezing method on the preparation of
the specimen was also evaluated. This paper tries to
summarise this information in a comprehensive way
in order to provide a representative model of ground
condition for realistic seismic scenarios response
analysis.
Figure 1. Location of Noto (Sicily).
2 GEOLOGICAL AND STRUCTURAL
CHARACTERISTICS OF THE AREA
The prevailing interest area falls within in the
eastern sector of the foreland that is one of the most
important structural elements of the Eastern Sicily. It
represents the emerged part of northern margin of
the African plate, steady zone towards which the
Neogenic nappes of the Apennine-Maghrebide Ore-
gone converge (Finetti et al. 1996). The Apennine-
Maghrebide Oregone consists of a complex system
of thrust nappes with African vergence that over-
thrust on the Iblean foreland that is lending to sub-
Small strain stiffness from in situ and laboratory tests for the city of
Noto soil
A. Cavallaro
CNR - IBAM, Catania, Italy
M. Maugeri & A. Ragusa
Department of Civil and Environmental Engineering, Catania, Italy
ABSTRACT: The city of Noto is locat
ed on the east coast of Sicily, which is one of the most seismically a
c-
tive areas of Italy. The paper shows the results of in situ and laboratory investigations to provide a representa-
tive model of ground condition of the city for realistic seismic scenarios response analysis. Moreover normal-
ised laws are proposed to consider shear modulus decay and damping ratio increase with strain level. Special
attention is paid to the variation of shear modulus and damping ratio with strain level and depth. The effect of
the freezing of the specimen, soil degradation and pore pressure build up were also investigated.
side through a series of normal faults arranged as
steps. Off Ionic coast, the foreland is interrupted
from Iblean-maltese escarpment that separates the
continental platform and the Malta channel from the
Ionic coastal plain.
Figure 2. Sud-Eastern Sicily: geological sketch (Nicoletti et al.
2000).
The stratigraphyc succession that surface in the
Iblean area is characterised from prevalently carbon-
ate sediments aged between the Cretaceous and the
Quaternary, separated, at different levels, from layers
of basic vulcanites. The deepest element reached by
petroleous drilling carried out for petroleous re-
search, is represented from limestone of the upper
Trias over 4800 meters thick (Patacca et al., 1979).
The Iblean-Maltese escarpment was originated from
a system of step faults that delimited from East the
Ionic coastal Plain; it was active during the last 5
million of years, as shown from the geodynamic evo-
lution of Western Iblean border (Carbone et al.
1982), and would be related with the progressive
collapse of the Western border of Ionic Basin. This
system of faults, with direction NNW - SSE, would
be placed on a old crustal weakness zone, already
present in the upper Cretaceous, as shown from great
thickness of vulcanites present from the Iblean zone
to the Maltese one.
The tectonic framework, that characterises the Iblean
foreland, was already loomed from the upper Mio-
cene in the western sector and in successive epoch in
the eastern one. The northern border of plateau is
furrowed from graben delimited from faults, with
NE - SW direction, that are the border structures of
Plateau before the deflection and the underthrust be-
low the Gela nappe (Carbone et al. 1982). From
Maddalena peninsula to Agnone the faults have a
trend subparallel to contiguous Iblean-Maltese es-
carpment; the structures delimited from them are,
generally, rhombic graben elongated towards NE -
SW, medially, divided from horst with subparallel
trend. The filling of these tectonic lows, that begun
to form between the Pliocene and the Pleistocene, is
given from infrapleistocenic biocalcarenites that
reached an one hundred meters thickness. The faults
system that delimit grabens are to be related to the
recent tectonic evolution of the Iblean-Maltese es-
carpment and to its progressive recession; following
lower Miocene deformations along ionic coast are
represented from faults with E-W trend that cross the
infrapleistocenic biocalcarenitcs.
Another important faults system is the Scicli line,
NNW - SSE oriented, with activity evidence up to
medium Pleistocene, that is a first order transcurrent
zone (Azzaro & Barbano, 2000).
3 INVESTIGATION PROGRAM AND BASIC
SOIL PROPERTIES
The site investigation was performed within the
municipal area of Noto with a territory of about 6
square Km and reached a maximum depth of 51 m.
Laboratory tests have been performed on undis-
turbed samples retrieved by means of an 86 mm
Shelby tube sampler. The Pliocene Noto deposits
mainly consist of a medium stiff, overconsolidated
lightly cemented silty-clayey-sand.
The preconsolidation pressure σ'
p
and the over-
consolidation ratio OCR = σ'
p
/ σ'
vo
were evaluated
from the 24
h
compression curves of incremental
loading (IL) oedometer tests. Moreover, 9
Marchetti's flat dilatometer tests (DMT) were used
to assess OCR and the coefficient of earth pressure
at rest K
o
following the procedure suggested by
Marchetti (1980).
For depths of about 15 m, DMT results show an
OCR from 1 to 4.5 (K
o
= 0.5 ÷ 1.0).
The OCR values inferred from oedometer tests
(OCR from 1 to 3) are lower than those obtained
from in situ tests. One possible explanation of these
differences could be that lower values of the pre-
consolidation pressure σ'
p
are obtained in the labo-
ratory because of sample disturbance.
Figure 3. Index properties of Noto soil.
The general characteristics and index properties
of the Noto soil are shown, as a function of depth, in
Figure 3. The value of the natural moisture content
w
n
prevalently range from between 12 - 37 %. Char-
acteristic values for the Atterberg limits are: w
l
= 37
- 69 % and w
p
= 17 - 22 %, with a plasticity index of
PI = 15 - 47 %. The data shown in Figure 3 indicate
a low degree of homogeneity with depth of the de-
posits.
Figure 4. Standard penetration test results.
This dishomogeneity with depth is also confirmed
by analysing the number of blows NSPT from me-
chanical standard penetration test (SPT) performed
over the investigated area (borehole S7) (Figure 4).
The soil deposits can be classified as inorganic soil
of low to medium plasticity.
As regard strength parameters of the deposits mainly
encountered in this area c' ranged between 0 kPa for
brown silty sand with traces of minute calcareus
elements and 85 kPa for brown clay in an abundant
minute elements of stone while φ' ranged between
16° for brown clayey silt and 33° for brown silty
sand with traces of minute calcareus elements. The
values of c' and φ' were calculated from Direct Shear
Test.
The cone penetration tests, Menard pressuremeter
tests, piezometer tests, dilatometric tests, down-hole
and cross-hole tests, seismic tomography tests,
ground penetrating radar tests and surface seismic
tests have also been performed.
4 STIFFNESS AND DAMPING RATIO
4.1 General
Young modulus, shear modulus G and damping
ratio D of Noto soil were obtained in the laboratory
from cyclic triaxial tests (CLTxT), resonant column
tests (RCT) and cyclic loading torsional shear tests
(CLTST). These tests were performed on Shelby
tube specimens retrieved from Noto site. The cyclic
triaxial apparatus (Cavallaro 1997, Cavallaro et al.
1998) and Resonant Column/Torsional shear appara-
tus (Lo Presti et al. 1993) were used for this purpose.
E and G are the unload-reload shear modulus
evaluated from CLTxT, CLTST and RCT respec-
tively, while E
o
and G
o
are the maximum value or
also "plateau" value as observed in the E-log(ε) or
G-log(γ) plot. Generally E and G is constant until a
certain strain limit is exceeded. This limit is called
elastic threshold shear strain ( )γ
t
e
and it is believed
that soils behave elastically at strains smaller than
γ
t
e
. The elastic stiffness at γ<γ
t
e
is thus the already
defined G
o
. Monotonic loading torsional triaxial test
(MLTxT) was also performed on Shelby tube speci-
mens using the same triaxial apparatus, obtaining the
measurement of the secant Young modulus E
s
.
For CLTxT and CLTSTs the damping ratio was
carried out using the definition of hysteretic damping
ratio (D) by:
D
W
4
W
=
∆
π
(1)
0
2
4
6
8
10
12
14
0 10 20 30
40
N
SPT
H [m]
NOTO
SPT - S7
0
4
8
12
16
20
24
28
32
36
40
44
17 18 19 20 21
γ
γγ
γ
(KN /mc)
0
4
8
12
16
20
24
28
32
36
40
44
0.5 0.6 0.7 0.8
0.9
e
0
4
8
12
16
20
24
28
32
36
40
44
10 30 50 70 90
W
p
- W
n
- W
l
(%)
Wp
Wn
Wl
0
4
8
12
16
20
24
28
32
36
40
44
0.75 0.90 1.05 1.20
IC
0
4
8
12
16
20
24
28
32
36
40
44
0 25 50 75 100
CF (% )
depth (m)
in which ∆W is the area enclosed by the unload-
ing-reloading loop and represents the total energy
loss during the cycle and W is the elastic stored en-
ergy. For RCTs the damping ratio was determined
using two different procedures: following the steady-
state method, the damping ratio was obtained during
the resonance condition of the sample; following the
amplitude decay method it was obtained during the
decrement of free vibration.
4.2 Young and shear modulus and damping ratio
from laboratory tests
Five Resonant Column (RCT) and Cyclic Load-
ing Torsional Shear (CLTST) tests have been per-
formed by using the same apparatus (Lo Presti et al.
1993) to evaluate the shear modulus G and damping
ratio D of the municipal area of Noto soil.
The laboratory test conditions and the obtained
small strain shear modulus G
o
are listed in Table 1
and 2.
Because generally the soil investigated in this
study was characterised by low or no values of plas-
ticity index, after the sampling the tube sampler were
preventively frozen at a temperature of – 20 ° C.
Table 1. Test condition for Noto soil specimens.
Test
No.
H
[m] σ'
vc
[kPa]
σ'
hc
[kPa]
γ
[kN/m
3
]
e PI
RCT
CLTST
CLTxT
1 4.50 144 144 15.97 1.236 - U - S
2 7.60 145 145 18.81 0.777 - U - S
3 10.00
190 163 19.69 0.740 41
U - H
4 17.50
336 336 19.13 0.747 - U - S
5 17.50
380 380 16.40 1.238 - U - S
6 10.00
225 195 19.47 0.817 41
U - S
where: U = Undrained. S = Solid cylindrical specimen. H =
Hollow cylindrical specimen.
Table 2. Test results for Noto soil specimens.
Test
No.
G
o
[MPa]
(1)
G
o
[MPa]
(2)
G
o
[MPa]
(3)
G
o
[MPa]
(4)
∆u
[kPa]
γ
max
[%] E
o
[MPa]
(5)
1 122 25 - 86 70 0.074
-
2 185 80 165 153 12 0.033
-
3 49 46 52 40 2 0.325
-
4 465 35 - 337 303 0.210
-
5 244 150 - 207 122 0.029
-
6 - - - - 80 0.265
195
where: U = Undrained. Go (1) before RCT, Go (2) after RCT,
Go (3) 24 hrs after RCT, Go (4) from CLTST, Eo (5) from
CLTxT.
Then the samples were extruded from the tube
sampler and the specimens were cored. Generally
this method was used immediately after the extru-
sion of sample (Test No. 1, 2, 3, 4). Only in one case
the specimen (Test No. 5) was prepared after the de-
freezing of sample.
The specimens were isotropically reconsolidated
to the best estimate of the in situ effective stress.
The same specimens were first subjected to RCT
(Resonant Column Test), then to CLTST (Cyclic
Loading Torsional Shear Test) after a rest period of
24 hrs with opened drainage. CLTST were per-
formed under stress control condition by applying a
torque with triangular time history at a frequency of
0.1 Hz. The size of solid cylindrical specimens are
Radius = 25 mm and Height = 100 mm while the
size of hollow cylindrical specimens are External
Radius = 25 mm, Internal Radius = 25 mm and
Height = 100 mm.
Figure 5. G/G
o
- γ curves from CLTST, RCT and CLTxT.
One specimen was tested in the triaxial apparatus
(Cavallaro, 1997; Cavallaro et al., 1998). The size of
solid cylindrical specimens are Radius = 35 mm and
Height = 140 mm. This specimen was reconsolidated
to the in situ geostatic stresses (K
o
condition). After
the consolidation stage, the specimen was subjected
to cyclic loading triaxial test (CLTxT), at constant
strain rate. Six different strain levels of progressive
amplitude were imposed to the specimen. For each
strain level about 30 cycles were applied. The
maximum applied axial strain (single amplitude)
was about 0.3 %. The same specimen was subjected,
after a rest period of 24 hrs with open drainage, to
monotonic loading triaxial test (MLTxT). The ob-
tained small strain Young modulus E
o
is reported in
Table 2.
The G
o
values [G
o
(1) and G
o
(4)], reported in Ta-
ble 2, indicate moderate influence of strain rate even
at very small strain where the soil behaviour is sup-
posed to be elastic. Normalized shear modulus G/G
o
obtained from RCT and CLTST are shown in Figure
5. The same shear modulus decay is obtained from
both type of tests.
In Table 2 the shear modulus values at small
strain obtained by CLTST [G
o
(4)] are comparable to
those obtained by RCT [G
o
(3)]. The differences gen-
erally ranged between 8 and 30 %.
0
0.2
0.4
0.6
0.8
1
1.2
0.0001 0.001 0.01 0.1 1
γ
γγ
γ [%]
G/Go
CLTST
RCT
CLTxT
NOTO
Test N°. 3 - 6
σ'
v
= 190 - 225 kPa
σ'
h
= 163 -195 kPa
The initial shear modulus values, reported in Ta-
ble 2, at the end of RCT [G
o
(2)] are always lower
than those obtained at the beginning of test [G
o
(1)].
This modulus reduction was probably caused by
these factors:
- pore pressure build up with a reduction of effec-
tive stress;
- soil degradation caused by the maximum shear
strain level investigated during the test.
Moreover, considering that after a period of 24
hrs with opened drainage, the shear modulus values
at small strain [G
o
(3)] are comparable to those ob-
tained at the beginning of the test [G
o
(1)], it is possi-
ble to assume the reduction of shear modulus as the
consequence of effective stress reduction for the
pore pressure build up. So it is possible to consider
that the elastic energy loosed was recovered in a pe-
riod of 24 hrs with the dissipation of pore pressure.
Figure 6. G - γ curves from RCT.
In Figure 6 a comparison of RCT results by Test
No. 4 and Test No. 5 are reported. The tests were
performed on the same specimen reconsolidated at
the same condition but with a different method of
the sample preparation. For Test No. 4 the specimen
was cored immediately after the extrusion of speci-
men. While for Test No. 5 the specimen was cored
after the defrost of the sample. The specimen used
during Test No. 5 showed (Table 2) a void ratio in-
dex higher than that used during Test No. 4 while
the G
o
(1) value obtained is almost the half.
This result showed the validity of the freezing
method to maintain the structural and mechanics
characteristics of soil. Moreover it is possible to
consider that the disturbance effects are more evi-
dent at small strain rather than large strain.
Typical G/F(e)-γ curves obtained from undrained
CLTST, TCT and CLTxT on Noto soil specimens
are shown in Figure 7.
The shear moduli plotted in Figure 7 are normal-
ised by means of a void ratio function F(e) = e
-1.3
(Lo
Presti 1989, Jamiolkowski et al. 1994) in order to
take even very small variations of the void ratio into
account.
Figure 7. G/F(e)-γ curves from CLTST, RCT and CLTxT.
Figure 8 shows the results of RCTs normalised by
dividing the shear modulus G(γ) for the initial value
G
o
at very low strain.
The experimental results of specimens were used
to determine the empirical parameters of the equa-
tion proposed by Yokota et al. (1981) to describe the
shear modulus decay with shear strain level:
β
o(%)αγ11
G)γG( +
= (2)
The expression (2) allows the complete shear
modulus degradation to be considered with strain
level. The values of α = 115 and β = 1.206 were ob-
tained for the city of Noto.
Figure 8. G/G
o
- γ curves from RCT.
The damping values obtained from RCT and
CLTST are compared in Figure 9. The damping ratio
values obtained from RCT using two different pro-
cedures are similar even if higher values of D have
been obtained from steady-state method. Consider-
ing that the influence of number of cycles N on D
has been found to be negligible, in the case of clayey
soils for strain levels of less than 0.1 % (Cavallaro
1997, Cavallaro et al. 1999, Cavallaro et al. 2001, Lo
Presti et al. 1997a, Lo Presti et al. 1997b, Lo Presti
et al. 1998), it is possible to see that, at very small
strains, the damping ratio obtained from CLTST is
0
10
20
30
40
50
60
0.0001 0.001 0.01 0.1 1
γ
γγ
γ [%]
G/F(e)
CLTST
RCT
CLTxT
NOTO
Test N°. 3 - 6
σ'
v
= 190 - 225 kPa
σ'
h
= 163 - 195 kPa
0
0.2
0.4
0.6
0.8
1
1.2
0.0001 0.001 0.01 0.1 1
γ
γγ
γ [%]
G/Go
Test N°. 1
Test N°. 2
Test N°. 4
Test N°. 5
Yokota et al. (1981)
NOTO
RCT
0
50
100
150
200
250
300
350
400
450
500
0.0001 0.001 0.01 0.1 1
γ
γγ
γ [%]
G [MPa]
Test N°. 4
Test N°. 5
RCT
equal to about 2 %, whilst that from RCT is about 5
% from Steady State Method and about 6 % from
Amplitude Decay Method. Moreover greater values
of D are obtained from RCT for the whole investi-
gated strain interval.
Figure 9. Damping ratio curves from CLTST, RCT and
CLTxT.
The results from CLTxT are also compared in
Figures 5 and 9. It is possible to notice that CLTxT
results in Figure 5 show a greater non-linearity while
in Figure 9 the damping ratio values from CLTxT
and those from CLTST are comparable for stress
level less than 0.01 %. Greater values of D are ob-
tained from CLTST for strain level higher of 0.01 %.
It should be remembered that CLTxT have been per-
formed at constant strain rate equal to 0.01 %/min.
Yet the different deformation mechanism (differ-
ent stress-path) could be responsible for the observed
differences.
Figure 10. D-G/G
o
curves from RCT.
As suggested by Yokota et al. (1981), the inverse
variation of damping ratio in respect to the normal-
ised shear modulus has an exponential form, like
that reported in Figure 10:
(
)
⋅−⋅=
o
G
γG
λexpη)(%)γD(
(3)
in which: D(γ) = strain dependent damping ratio; γ =
shear strain and η, λ = soil constants. The values of
η = 20 and λ = 1.941 were obtained for the city of
Noto. For the city of Noto equation (3) assumes the
maximum value D
max
= 20 % for G(γ)/G
o
= 0 and a
minimum value D
min
= 2.87 % for G(γ)/G
o
= 1 .
Therefore, equation (3) can be re-written in the
following normalised form:
(
)
⋅−=
omax
G
γG
λexp
)γD( )γD(
(4)
4.3 Shear modulus from in situ tests
Dynamic in situ tests were performed on Noto
area. In Figure 11 the Poisson ratio variation with
depth, obtained from a Down Hole (DH) test, is plot-
ted to show site characteristics. It is seen that from
the top 16 m, the values oscillates around 0.36.
It was also possible to evaluate the small strain
shear modulus in the Noto area by means of the fol-
lowing empirical correlations based on standard
penetration tests results or laboratory test results
available in literature.
Figure 11. Poisson ratio from in situ tests.
a) Ohta & Goto (1978)
V N Z F F
s
A
G
= ⋅ ⋅ ⋅ ⋅69
60
0 17 0 2. .
(5)
where: V
s
= shear wave velocity (m/s), N
60
=
number of blow/feet from SPT with an Energy Ratio
of 60 %, Z = depth (m), F
G
= geological factor (clays
= 1.000, sands = 1.086), F
A
= age factor (Holocene =
1.000, Pleistocene = 1.303);
b) Yoshida & Motonori (1988)
(
)
0.14
v0
0.25
SPTS
'NV σ⋅⋅β= (6)
0
5
10
15
20
25
30
0.0001 0.001 0.01 0.1 1
γ
γγ
γ [%]
D [%]
CLTST
RCT - Steady-State Method
RCT - Amplitude Decay Method
CLTxT
NOTO
Test N°. 3 - 6
σ'
v
= 190 - 225 kPa
σ'
h
= 163 - 195 kPa
0
5
10
15
20
25
30
35
0.30 0.33 0.35 0.38 0.40 0.43 0.45 0.48
0.50
Poisson Ratio
H [m]
NOTO
DOWN - HOLE
1
10
100
0 0.2 0.4 0.6 0.8 1
G/Go
D [%]
Test N°. 1
Test N°. 2
Test N°. 4
Test N°. 5
Yokota et al. (1981)
NOTO
RCT
where: V
S
= shear wave velocity (m/s), N
SPT
=
number of blows from SPT, σ'
vo
= vertical pressure,
β = geological factor (any soil = 55, fine sand = 49);
G V
o
s
= ⋅ρ
2
(7)
where ρ = mass density
c) Hryciw (1990)
0.5
a
'v
0.25
o
wD
wD
0.25
a
'v
o
)p(K
/2.7
1/
)/p(
530
G⋅
⋅⋅
⋅⋅
⋅⋅
⋅
−
−−
−
−
−−
−
=
==
= σ
γγ
γ
γ
σ (8)
where: G
o
, σ'
v
and p
a
are expressed in the same unit;
p
a
= 1 bar is a reference pressure; γ
D
and K
o
are re-
spectively the unit weight and the coefficient of
earth pressure at rest, as inferred from DMT results
according to Marchetti (1980).
d) Jamiolkowski et. al. (1995)
Gp
e
om a
=⋅600
0 5 0 5
13
σ
' . .
.
(9)
where: σ'
m
= (σ'
v
+ 2 · σ'
h
)/3; p
a
= 1 bar is a refer-
ence pressure; G
o
, σ'
m
and p
a
are expressed in the
same unit. The values for parameters which appear
in equation (9) are equal to the average values that
result from laboratory tests performed on quaternary
Italian clays and reconstituted sands. A similar
equation was proposed by Shibuya and Tanaka
(1996) for Holocene clay deposits.
Equations (8) and (9) incorporate a term which
expresses the void ratio; the coefficient of earth
pressure at rest also appears in equations (8) and (9).
However only equation (8) tries to obtain all the in-
put data from the DMT results.
The G
o
values obtained with the methods above
indicated are plotted against depth in Figure 12. The
method by Jamiolkowski et al. (1995) was applied
considering a given profile of void ratio and
K
o
.
The coefficient of earth pressure at rest was in-
ferred from DMT.
Figure 12 clearly shows that laboratory test re-
sults provide relatively similar values of G
o
. Labora-
tory test results are in good agreement with those in-
ferred from the method by Hryciw (1990). On the
whole, the considered empirical correlations based
on SPT results provide values of G
o
that are in good
agreement with those inferred from the method by
Jamiolkowski et al. (1995) and Hryciw (1990).
Figure 12. Go from different empirical correlations.
5 CONCLUSIONS
In this paper some information concerning geo-
logical and geotechnical conditions, shear modulus
and damping ratio of historical area of Noto has
been presented for seismic response analysis.
Available data enabled one to define the small
strain shear modulus profile for the city of Noto and
empirical equations to describe the G and D varia-
tion with strain level.
On the basis of the experimental results obtained,
it is possible to draw the following conclusions:
- the freezing of the sample is a good method to
maintain the structural and mechanics characteris-
tics of soil;
- the shear modulus obtained from CLTxT results
show a greater non-linearity;
- damping ratio values determined from RCT are
greater than those obtained from CLTST while the
damping ratio values from CLTxT and those from
CLTST are comparable for stress level less than 0.01
%. The observed differences between RCT, CLTST
and CLTxT results are probably due to rate and/or
frequency effects and different deformation mecha-
nism (different stress-paths).
Moreover empirical correlations between the
small strain shear modulus and penetration test re-
sults were used to infer G
o
from SPT and DMT. The
values of G
o
were compared to those measured in
the laboratory tests. This comparison clearly indi-
cates that a good agreement exists between G
o
and
the penetration test results, which would encourage
one to establish empirical correlations for a specific
site. This approach makes it possible to consider the
spatial variability of soil properties in a very cost ef-
fective way:
- relationships like those proposed by Jami-
olkowski et al. (1995) or Shibuya and Tanaka
(1996) seems to be capable of predicting G
o
profile
with depth.
0
5
10
15
20
25
30
0 50 100 150 200 250
G
o
[MPa]
H [m]
Ohta and Goto (1978)
Yoshida and Motonori (1988), fine sand
Yoshida and Motonori (1988), any soil
Jamiolkowski et al. (1995)
Hryciw (1990)
CLTST
RCT
CLTxT
Noto - S15
The accuracy of these relationships could obvi-
ously be improved if the parameters which appear in
the equations were experimentally determined in the
laboratory for a specific site.
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