Shear-Wave-Velocity Measurements at Seismic Recording Stations.
Empirical correlations between shear wave velocity and
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Transcript of Empirical correlations between shear wave velocity and
Abstract Prediction of the ground shaking response
at soil sites requires knowledge of the soil, expressed in
terms of shear wave velocity. Although it is preferable
to measure this dynamic soil parameter in situ, this is
often not economic at all locations. Existing correla-
tions between shear wave velocity and penetration
resistance have been assessed in this study and com-
pared with correlations with SPT values obtained
based on geotechnical and geoseismic data collected
from a first-degree earthquake zone in Turkey. The
results obtained support the findings of earlier studies
that blow-count is a significant parameter in these
correlations while type of soil has no important influ-
ence. The regression equations developed in this study
compare well with most of the previous equations and
exhibit good prediction performance. It is noted that
better correlations are obtained when uncorrected
blow-counts are used.
Keywords Correlation equation Æ Geotechnical
borehole Æ Seismic refraction Æ Shear wave velocity ÆStandard penetration test Æ Turkey
Resume La prevision de la reponse d’un site a une
sollicitation sismique necessite des connaissances sur le
sol, relatives en particulier a la vitesse de propagation
des ondes de cisaillement. Il est preferable de mesurer
ce parametre de dynamique des sols in situ. Cependant
ceci n’est pas toujours possible en raison de la config-
uration du site et de contraintes economiques. Des
correlations entre la vitesse de propagation des ondes
de cisaillement et des donnees penetrometriques ont
ete evaluees et comparees avec des correlations entre
la vitesse de propagation des ondes de cisaillement et
des donnees SPT, ces dernieres obtenues a partir de
donnees geotechniques et sismiques issues d’une zone
de forte sismicite en Turquie. Les resultats obtenus
confortent de precedentes etudes montrant que les
donnees SPT apportent un parametre significatif, tan-
dis que le type de sol ne joue pas un role important
pour les correlations etablies. Des equations de
regression ont ete etablies et permettent de prevoir la
reponse d’un site a une sollicitation sismique.
Mots cles Equation de regression Æ Sondage
geotechnique Æ Refraction sismique Æ Vitesse de
propagation des ondes de cisaillement Æ Essai SPT ÆTurquie
Introduction
It has been recognized for a very long time that
earthquake damage is generally larger over soft sedi-
ments than on firm bedrock outcrops. This is particu-
larly important because most urban settlements have
occurred along river valleys over such young and soft
surface deposits. For this reason, particular consider-
ation is paid to the effect of local site conditions when
assessing ground motion characteristics for the seismic
design of buildings and other structures. Shear modu-
lus, damping ratio and shear wave velocity profiles are
important input parameters in site response analysis.
Prediction of the ground shaking response at soil sites
N. Hasancebi Æ R. Ulusay (&)Department of Geological Engineering,Hacettepe University, Beytepe, Ankara 06800, Turkeye-mail: [email protected]
Bull Eng Geol Environ (2007) 66:203–213
DOI 10.1007/s10064-006-0063-0
123
ORIGINAL PAPER
Empirical correlations between shear wave velocity andpenetration resistance for ground shaking assessments
Nilsun Hasancebi Æ Resat Ulusay
Received: 30 March 2006 / Accepted: 7 July 2006 / Published online: 29 August 2006� Springer-Verlag 2006
requires a knowledge of the stiffness of the soil, ex-
pressed in terms of shear wave velocity (Vs), which is
measured at small strain levels by in situ seismic
methods. While it is preferable to determine Vs directly
from field tests, it is often not economically feasible at
all locations. For this reason, a reliable correlation
between Vs and penetration resistance would be a
considerable advantage, reducing the number of field
verifications required.
In this study, which is an integral part of a research
study on soil amplification (Hasancebi 2005), the var-
iation of shear wave velocity measured by seismic
refraction and SPT blow-count (SPT-N) was investi-
gated and new correlations have been developed for
estimating the shear wave velocity. For this purpose, a
site with recorded high seismicity at Yenisehir, foun-
ded on an alluvial plain located in the Marmara Region
of Turkey (Fig. 1), was selected. The investiga-
tion programme included SPT borings at different
locations, seismic refraction studies, laboratory soil
classification tests, the use of borehole data from the
previous work in the study site and statistical assess-
ments. Based on the statistical assessments and taking
into account the type of soil, a series of empirical
equations for the prediction of Vs from SPT-N
were developed and compared with those suggested in
previous studies in order to evaluate the prediction
capability of the equations.
General setting of the study site
Geology and seismotectonics
Yenisehir town is located within an alluvial basin which
is surrounded by ridges both to the north and south
(Fig. 2). The study site is geologically represented by
the basement rocks of pre-Neogene age and Neogene
and Quaternary deposits. The basement rocks seen in
the southern part of the site consist of schists and
Fig. 1 Location map of thestudy site
204 N. Hasancebi and R. Ulusay
123
marbles. The Neogene deposits which appear on the
gentle slopes at the north and south consist predomi-
nantly of loosely cemented conglomerate, sandstone,
claystone and marl and unconformably overlie the
basement rocks (Genc 1992). The Quaternary deposits
are represented by alluvial soils and detritus and are
observed in the middle of the basin. Based on the data
from the records of the boreholes drilled by the State
Hydraulic Works (DSI), the thickness of the alluvial
sequence in the basin ranges between 25 and 115 m.
Yenisehir is located within a first-degree earthquake
zone of Turkey (GDDA 1996). The study site is sur-
rounded by a number of active faults as shown in
Fig. 3. The southern strand of the North Anatolian
Fault Zone (NAFZ) and the Bursa and Inonu–
Eskisehir faults are the most important earthquake
sources in the study site. The 1999 Kocaeli earthquake,
which resulted in extensive loss of life and damage to
structures particularly in the Marmara Region, was
also felt in Yenisehir and its vicinity.
SPT soundings, geoseismic investigations
and laboratory testing
In the present and future settlement areas of Yenisehir,
geotechnical studies for the assessment of foundation
conditions and a railway route were conducted by
Doyuran et al. (2000) and the State Port and Airport
Directory (DLH 2002). These previous studies in-
cluded a total of 37 boreholes and associated SPTs.
Twelve of these boreholes are relevant to the present
study. It is well known that the average shear wave
velocity in the upper 30 m of the ground is an impor-
tant factor for ground characterization (Borcherdt
1994; Dobry et al. 2000). Therefore, for the present
study, the boreholes were planned to penetrate to a
depth of 30 m if possible. In fact, 9 extended to 30.45 m
while the others ranged between 4.5 and 17 m. SPT
tests were conducted at 1 m intervals and the samples
from SPT tubes were used for laboratory testing. The
groundwater table in each hole was also measured.
Locations of the previous and recent boreholes and the
geoseismic investigations are shown in Fig. 2.
The most commonly used seismic methods for
velocity logging are the cross-hole and down-hole
techniques. Seismic refraction is largely used in deter-
mining the dynamic properties of the underlying layers.
In this study, shear wave velocities were measured
using seismic refraction with the assistance of the
General Directorate of Disaster Affairs (Dikmen et al.
2004) and Geophysical Engineering Department of
Ankara University. These measurements were taken at
the locations of nine boreholes drilled during the study.
Due to some restrictions at the locations of boreholes
H6 and H7 and the very shallow depth of borehole
H12, seismic studies were not undertaken at these
locations.
A total of 149 specimens extracted from SPT tubes
were tested in the laboratory to determine their grain
size distribution and Atterberg limits. The tests were
conducted in accordance with the methods given by
Fig. 2 Geological map of the study site, and locations ofgeotechnical and geoseismic investigations (modified fromDoyuran et al. 2000)
Fig. 3 Siesmotectonic map of the Eastern Marmara Region(after Doyuran et al. 2000)
Connection of shear wave velocity with SPT 205
123
ASTM (1994). Based on these results, the specimens
were classified according to the Unified Soil Classifi-
cation System.
Subsurface conditions
The data from the previous and recent boreholes and
the resistivity study (Dikmen et al. 2004) suggest that
the alluvial sequence generally starts with silty clay.
This clay, with high SPT-N values, is a stiff soil. Below
this, there exists medium dense to loose silty sand.
However, at some localities the silty clay may also ap-
pear below the sandy zone. Occasionally, gravel layers
of variable thickness can be observed in the Quaternary
deposits at shallow depths. A typical cross-section
through the Yenisehir settlement area, some selected
geotechnical logs and two typical seismic refraction
profiles showing the variation of Vs at the locations of
boreholes H3 and H8 are depicted in Fig. 5, respec-
tively. As can be seen from the Vs–SPT(N) versus depth
plots for some selected borehole locations in Fig. 6, Vs
increases with increasing SPT values.
Statistical evaluations of the data from grain size
analyses are given in Table 1. Sand sized material in
the Quaternary deposits is dominant at the southern
part of the site and these soils are represented by SP
and SW, and SC and SM soil classes. Towards the
north, grain size decreases and clays and silty clays with
high plasticity dominate. Most of the tested soils from
the north of the site fall into the CH and CL soil
classes.
The groundwater table in the study site is shallow,
generally ranging between 3 and 8 m. However, based
on the data from Doyuran et al. (2000), it is deeper
(‡14 m) at the north and shallower in the south.
Fig. 4 Geological cross sections (a) and some typical engineer-ing logs (b) illustrating the subsurface ground conditions atYenisehir settlement and its vicinity
Fig. 5 Seismic refractionprofiles at the locations ofboreholes H3 and H8
206 N. Hasancebi and R. Ulusay
123
Proposed empirical correlations for Vs–SPT(N)
While it is preferable to determine Vs directly from
field tests, it is often not economically feasible to make
Vs measurements at all locations. Many correlations
between Vs and penetration resistance have been
proposed; 17 are quoted in Table 2, the majority based
on uncorrected SPT-N values. Sykora and Stokoe
(1983) suggest that geological age and soil type are not
Fig. 6 Variation of Vs and SPT-N with depth at some boreholelocations
Table 1 Statistical evaluation of grain size distribution of soilsamples
Grain size Max Min Mean Standarderror
Standarddeviation
Gravel (%) 0 49 11 12.47 0.084Sand (%) 4 100 49 27.74 0.186Silt (%) 0 76 30 23.91 0.160Clay (%) 0 34 10 9.3 0.066
Fig. 7 Correlations between Vs and SPT-N for all soils (a), sandysoils (b) and clayey soils (c)
Connection of shear wave velocity with SPT 207
123
important parameters in determining Vs, while the
SPT-N value is of prime importance. However, as can
be seen from Table 2, some investigators have also
proposed correlations between Vs and SPT-N for dif-
ferent soils, such as clays, silts and sands. In addition,
the soil properties considered in the regression analy-
ses for some correlations included stress-corrected Vs,
energy-corrected SPT-N, energy- and stress-corrected
SPT-N, depth (D) and fines content (FC).
In this study, 97 data pairs (Vs and SPT-N) were
employed in the assessments. The correlations were
developed using a simple regression analysis for the
existing database. In the first series of analyses, new
relationships were proposed between uncorrected Vs
(m/s) and corresponding SPT-N values in three cate-
gories, i.e. for all soils, sandy soils and clayey soils
(Fig. 7). Because few data from the silty layers were
available, this category was not included in the evalu-
ations. The following relationships with their correla-
tion coefficients (r) are proposed between Vs (m/s) and
SPT-N values for the three different soil categories.
Vs¼ 90N0:309 ðr ¼ 0:73Þ; All soils ð1Þ
Vs ¼ 90:8N0:319 ðr ¼ 0:65Þ; Sandy soils ð2Þ
Vs ¼ 97:9N0:269 ðr ¼ 0:75Þ; Clayey soils ð3Þ
Comparisons between the measured Vs and Vs pre-
dicted from Eqs 1–3 are presented in Fig. 8. The
plotted data are scattered between the lines with 1:0.5
and 1:2 slopes, with smaller Vs values (Vs < 250 m/s)
falling close to the line 1:1.
The correlations from the present study are plotted
in Fig. 9 to assess the effect of soil type. Figure 9
suggests that the correlations for different soil catego-
ries yield similar values of Vs indicating that soil type
has little effect on these correlations. This is consistent
with the findings of Iyisan (1996). However, Iyisan
(1996), who also studied gravely soils in Turkey, indi-
cated that the situation for gravels is different because
the correlation for gravels estimates higher Vs values
when compared to those from other soils, due to the
effect of grain size and cementation.
Equations 1–3 are plotted in Fig. 10a, c together
with several of the earlier regression equations given in
Table 2. Except the relationships of Ohsaki and Iwa-
saki (1973), Seed and Idriss (1981), Sisman (1995),
Iyisan (1996), Jafari et al. (1997) and Kiku et al. (2001)
in Fig. 10a (which were recommended for all soils), all
the equations including the equation of the present
study (Eq. 1) yield similar Vs values. There is only a
slight difference between Eq. 1 and those developed by
Ohba and Toriumi (1970) and Imai and Yoshimura
(1970); Eq. 1 proposed in this study estimates Vs values
considerably closer to those derived from most of the
existing equations.
Similar comparisons made for sands (Fig. 10b)
indicated that except the equation developed by Lee
(1990), the proposed equation (Eq. 2) compares well
with the other equations for the prediction of the Vs of
sands. Based on the distribution of the plotted data, the
equation of Lee (1990) generally over-predicts Vs for
N > 20 and under-predicts Vs for N £ 20.
Table 2 Some existing correlations between Vs and SPT-N
Author(s) Vs (m/s)
All soils Sands Clays
Ohba and Toriumi (1970) Vs = 84N0.31 – –Imai and Yoshimura (1970) Vs = 76N0.33 – –Fujiwara (1972) Vs = 92.1N0.337 – –Ohsaki and Iwasaki (1973) Vs = 82N0.39 – –Imai (1977) Vs = 91N0.337 Vs = 80.6N0.331 Vs = 80.2N0.292
Ohta and Goto (1978) Vs = 85.35N0.348 – –Seed and Idriss (1981) Vs = 61N0.5 – –Imai and Tonouchi (1982) Vs = 97N0.314 – –Sykora and Stokoe (1983) – Vs = 100.5N0.29 –Jinan (1987) Vs = 116.1(N + 0.3185)0.202 – –Lee (1990) – Vs = 57.4N0.49 Vs = 114.43N0.31
Sisman (1995) Vs = 32.8N0.51 – –Iyisan (1996) Vs = 51.5N0.516 – –Jafari et al. (1997) Vs = 22N0.85 – –Pitilakis et al. (1999) – Vs = 145(N60)0.178 Vs = 132(N60)0.271
Kiku et al. (2001) Vs = 68.3N0.292 – –Jafari et al. (2002) – – Vs = 27N0.73
208 N. Hasancebi and R. Ulusay
123
The comparison for clays given in Fig. 10c suggests
that the equations developed by Imai (1977) and Lee
(1990) predict higher Vs values when compared to
those from Eq. 3 of the present study. The equation of
Jafari et al. (2002) differs from the other three equa-
tions and yields under-predicted and over-predicted Vs
values for SPT-N £ 20 and SPT > 20 conditions,
respectively. The specific geotechnical conditions of
the studied area are probably the main cause of this
while the quantity of the processed data, the SPT
procedure and the different methods of shear wave
velocity measurements employed in various studies
may be other causes of difference.
In addition to the comparisons shown in Fig. 10, the
scaled percent error (Eq. 4) versus cumulative fre-
quency graphs have also been drawn in Fig. 11.
Scaled percent error ¼ ½ðVsc � VsmÞ=Vsm� � 100 ð4Þ
where Vsc and Vsm are the predicted and measured
shear wave velocities, respectively.
Fig. 8 Measured versus predicted shear wave velocities for allsoils (a), sandy soils (b) and clayey soils (c)
Fig. 9 Effect of soil type on Vs–SPT(N) relationship
Fig. 10 Comparisons between proposed and previous correla-tions for Vs and SPT-N for all soils (a), sandy soils (b) and clayeysoils (c)
Connection of shear wave velocity with SPT 209
123
As seen in Fig. 11a, c, about 85% of the Vs values
predicted from Eqs. 1 to 3 for all soils, sands and clays
respectively, are within 20% of the scaled percent er-
ror, indicating a better estimate than those from the
existing equations.
The relationship between Vs and energy-corrected
SPT-N(N60) was also investigated and equations for all
soils, sands and clays were established. These were
compared to those suggested by Pitilakis et al. (1999)
who previously investigated N60–Vs relationships for
clays and sands. The SPT blow-counts were corrected
for striking energy during the test employed in this
study (donut-type hammer raised and dropped by two
turns of rope). The developed relationships for differ-
ent soils are given in Fig. 12a, c. When the correlation
coefficients obtained from Vs to N60 relationships are
compared to those obtained from Eqs. 1 to 3, the
equations based on uncorrected SPT-N values provide
a somewhat better fit than the equations based on
energy-corrected measurements. This situation is also
seen from Fig. 12d, f. The equations given in Fig. 12b, c
are plotted in Fig. 13a, b respectively, together with the
Fig. 11 Scaled percent errorof Vs predicted for all soils(a), sandy soils (b) and clayeysoils (c)
210 N. Hasancebi and R. Ulusay
123
regression equations developed by Pitilakis et al.
(1999) for sands and clays. As shown in Fig. 13a, the
equation in Fig. 12b compares well with the regression
equation of Pitilakis et al. (1999) for sands. However,
the equation of Pitilakis et al. (1999) for clays yields
considerably higher Vs estimations when compared to
those from the equation developed in this study
(Fig. 13b). It appears from these assessments that the
equations based on uncorrected SPT-N values are
preferable for indirect estimations of Vs.
Conclusions
In this study, based on the geotechnical and geoseismic
data from the Yenisehir settlement situated in the
Marmara Region of Turkey, an attempt was made to
develop new relationships between SPT-N and Vs to
indirectly estimate the Vs to be used for practical
purposes. The results obtained from the study support
the findings of earlier work suggesting that blow-count
is a significant parameter in Vs–SPT(N) correlations,
while the type of soil has little influence.
The regression equations developed in this study
compare well with most of the previous equations and
exhibit a good prediction performance. The equations
based on uncorrected SPT-N values provide a some-
what better fit than the equations based on energy-
corrected SPT-N values. Therefore, the use of an
equation developed for all soils based on uncorrected
blow-counts is recommended for practical purposes.
The regression equations developed provide a viable
way of estimating Vs from SPT blow-count for pre-
liminary regional ground shaking mapping and site-
specific response analysis. The differences between
existing and proposed equations are mainly due to the
specific geotechnical conditions of the studied sites, the
quantity of processed data and the procedures used in
Fig. 12 Vs–N60 relationshipsfor all soils (a), sandy soils (b)and clayey soils (c), andmeasured versus predictedshear wave velocities for allsoils (d), sandy soils (e) andclayey soils (f)
Connection of shear wave velocity with SPT 211
123
undertaking the SPTs and geoseismic surveys. In view
of this, these empirical equations should be carefully
used and wherever possible checked against measured
Vs values.
Acknowledgments This study was supported by Project No.0302602008 of the Research Projects, Division of HacettepeUniversity. The authors would like to thank the GeneralDirectorate of Disaster Affairs and the geophysical team of thisorganization for their cooperation and the geophysical surveys;the Municipality of Yenisehir for providing the logistic support;the Geophysical Engineering Department of Ankara Universityfor seismic refraction equipment and interpretation of the mea-sured data; and the General Directorate of State HydraulicWorks (DSI) for permission to use the borehole logs.
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