International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
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Mechanical Parameters and Bearing Capacity of Soils Predicted from
Geophysical Data of Shear Wave Velocity
Qassun S. Mohammed Shafiqu a, Erol Güler b and Ayşe Edinçliler c
aAssistant Professor, Dr., Civil Engineering Department, Al-Nahrain University, College of Engineering, Baghdad, Iraq. Professor, Dr, Civil Engineering Department, Bogazici University, College of Engineering, Istanbul, Turkey.
Professor, Dr, Earthquake Engineering Department, Bogazici University, College of Engineering, Istanbul, Turkey.
aORCID: 0000-0002-0389-6872
Abstract
The analysis of foundation vibrations and earthquake problems
in geotechnical engineering demands characterization of
dynamic soil properties by geophysical techniques. Also the
dynamic structural analysis of the superstructures needs
knowledge of the dynamic response of the soil-structure,
which, in turn depends on dynamics properties of soil. The
estimation of seismic velocities, modulus of elasticity and
structural properties of soils is not enough in the design of
engineering projects. Therefore, an ultimate bearing capacity
has been predicted using the seismic shear wave velocity. It is
indicated that the allowable bearing pressure and the coefficient
of subgrade reaction together with many other elasticity
parameters may be obtained rapidly and reliably once the
seismic wave velocities are determined in situ by convenient
geophysical survey. In this study, S-wave and P-wave
velocities data were obtained from seismic borehole survey in
the foundation layers of Iraq. Use was made of the existing
mathematical relations between various parameters and seismic
wave velocities for the study of foundation layers in the study
areas. Based on the results, the elastic constants, allowable
bearing capacity, and other parameters were determined and
evaluated. It was indicated that for cohesive and cohesionless
soils, up to a shear wave velocity of 300 m/s and 400 m/s
respectively, the shear wave velocity may predicts the bearing
capacity relatively well.
Keywords: Bearing capacity, soil parameters, shear wave
velocity, seismic technique, shear modulus.
INTRODUCTION
A footing is the supporting base of a building which forms the
interface across which the loads are transmitted to the
sublayers. If the structural loads are transmitted to the near-
surface soil, then it is referred to as shallow foundation.
Earthquakes may cause a reduction in bearing capacity and
increase in settlement and tilt of shallow foundations due to
seismic loading. The foundation must be safe both for the static
as well for the dynamic loads imposed by the earthquakes. Soil-
foundation-structure system should work together in a coherent
manner. In particular, if the site is exposed to high seismic
loadings it is highly desirable that the soil-foundation part of
the system should play an appropriate role in delivering the
required overall performance.
In the design of shallow foundation one of the main factors
related to soil is bearing capacity and the other is settlement or
in other words the subgrade reaction. The seismic S-wave
velocity is an effective parameter for estimating the bearing
capacity of soils [1]. Elastic parameters such as Young’s
modulus, Bulk modulus, shear modulus, Poisson’s ratio,
Oedometric modulus and others are related to shear wave
velocity leading to the determination of allowable bearing
capacity for shallow foundations [2].
For the calculation of allowable bearing capacity, the
geophysical methods, utilising seismic wave velocity
measuring techniques with absolutely no disturbance of natural
site conditions, may yield relatively more realistic results than
those of the geotechnical methods, which are based primarily
on bore hole data and laboratory testing of so-called
undisturbed soil samples [3].
Many researchers have extensively studied to obtain a relation
between the various parameters of soil mechanics and the
seismic wave velocities. Hardin and Black [4], and Hardin and
Drnevich [5] established indispensable relations between the
shear wave velocity, void ratio, and shear rigidity of soils based
on extensive experimental data. Also, Ohkuba and Terasaki [6]
supplied different expressions relating the seismic wave
velocities to density, permeability, water content, unconfined
compressive strength and modulus of elasticity. Also the use of
geophysical methods in foundation engineering has been
extensively investigated [7, 8, 9, 10, 11 and 12].
Keçeli [10 and 13] indicated that the determination of the
allowable bearing capacity could be obtained by means of the
seismic technique. Tezcan et al. [2]; Kaptan et al. [14] has
defined an allowable bearing capacity and a settlement as
depending on the layer thickness. But, it is well known that the
soil bearing capacity, settlement and modulus of elasticity
cannot be dependent on the layer thickness. Nevertheless, they
obtained also an allowable bearing capacity by changing the
notation of the relations in the article of Keçeli [13].
GEOLOGY AND SEISMISITY OF THE STUDY AREA
Iraq lies at the north east comer of the Arabian Peninsula. It is
a land of contrasting geography with an arid desert in the west
and the rugged mountains of the Taurus and Zagros in the north
east, separated by the central fertile depression of
Mesopotamia: long known as the cradle of civilization. This
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
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morphology facilitated early human migration and dispersion
of knowledge between the East and West. Sumerian cities as
old as 6000 years are a witness not only to a thriving early
civilisation but also to the early industrial use of raw-materials.
With respect to geological terms Iraq lies at the transition
between the Arabian Shelf in the west and the intensely
deformed Taurus and Zagros Suture Zones in the north and
north east. The evolution of the Arabian Shelf has been effected
by the mobility of the Precambrian basement and by tectonism
along the Neo-Tethyan margin. The tectonic framework of Iraq
has been affected by intracratonictranspressional and
transextensional movements controlled by the interactions of
stress along the plate margin with the Precambrian basement
fabric and structural grain.
After 1900, earthquakes in Iraq were better known in amounts
ranging from (M=2.7 to 7.2) within the geographical
boundaries of Iraq's earthquake map, with the majority of
shocks deep in the Earth's crust. The earthquakes in Iraq have
a general and distinct increase from the west to the east and
from the south to the north. The eastern side of the study area
is a relatively wide zone of compressional deformation along
the Zagros – Taurus active mountain belt, which is entrapped
between two plates, the Arabian in the southwest and the
Iranian plate in the northeast [15], although the territory of Iraq
not directly located on a dense cluster of recent earthquake
epicenters; But geodynamic formations for high seismic risks
show medium. This will be coupled with the increasing
vulnerability of the major highly populated cities. Over the past
two decades, the state of seismological research, seismic
monitoring and earthquake risk education has seen better times
[16].
Tectonically the study area is in a relatively active seismic zone
at the northeastern boundaries of the Arabian Plate. The
corresponding Zagros - Tauros Belts manifest the subduction
of the Arabian plate into the Iranian and Anatolian Plates .The
seismic history reveals annual seismic activity of various
strength. The north and northeastern zones shows the largest
seismic activity with strong diminution in the south and
southwestern parts of the country.
The geodynamic configurations of Iraq show a medium to high
seismic risk, although the territory of Iraq not directly located
on a dense cluster of recent earthquake epicenters. This will be
coupled with the increasing vulnerability of the major highly
populated cities. The state of seismological research, seismic
monitoring, and seismic hazard awareness have seen better
times during the last two decades.
THEORY
The response of soils to dynamic loading is controlled mostly
by the mechanical properties of the soil. Many types of
geotechnical engineering problems are associated with
dynamic loading, such as: machine vibrations, seismic loading,
liquefaction and cyclic transient loading, etc. The dynamic soil
parameters related with dynamic loading are shear wave
velocity (Vs), damping ratio (D), shear modulus (G), and
Poisson’s ratio (ν), which are also used in many non-dynamic
type problems. The problem of predicting the bearing capacity
of soils from wave propagation properties is that the soil
undergoes only very low strain during the wave propogation.
However when soils are subjected to earthquake loads or static
loads upto failure, they undergo large strains.
The P and S-wave velocities are usually denoted by Vp and Vs respectively. Once the seismic wave velocities are measured,
shear modulus (G), Bulk modulus (K), Young’s modulus or
modulus of elasticity (E), Poisson’s ratio (ν), Oedometric
modulus (Ec) and other elastic parameters may be obtained
from the Equations (1) to (8) below. These expressions make
the determination of the allowable bearing capacity possible.
1) Shear modulus (G) relates with shear wave velocity as
expressed in Equation (1):
G = ρ Vs2 (1)
Where ρ is the mass density equal to ρ = γ/g , γ is the unit weight
of the soil and gis the acceleration due to gravity which isgiven
as 9.8g m.s2.
The unit mass density relates with P-wave velocity Vpas shown
in Equation (2)
γ = γ0+ 0.002 Vp (2)
Tezcan et al., [2] defines γo as the reference unit weight value
in kN/m3.γo= 16 for loose, sandy and clayey soil. According to
[17], some elastic parameters were defined in Equations (3) to
(9):
2) Young’s modulus/modulus of elasticity (Ed)
E = ρ Vp2 (3)
3) Oedometric modulus (Ec) given by Equation (4)
Ec = E (1-v)/(1+v)(1-2v) (4)
4) Bulk modulus (K) is expressed in Equation (5) as
K =2(1+v)G / 3(1-2v) (5)
5) Poisson’s ratio (ν) is given as in Equation (6) as
ν=(α -2) / 2(α-1) (6)
where α= Ec / G= (Vp / Vs)2 (7)
6) Subgrade Coefficient ks, ultimate bearing capacity qult and
allowable bearing capacity qall are given by Equations (8) to
(10) according to [18] and [19] as,
ks = 4 γ Vs = 40 qult (8)
7) Ultimate Bearing Capacity (qult)
qult=ks/40= 4 γ Vs/40=0.1 γ Vs (9)
for shallow foundation [18]
8) Allowable Bearing Capacity (qall)
qall=qult / n =0.1 γVs / n (10)
Where n is the factor of safety (n = 4.0 for soils)
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© Research India Publications. http://www.ripublication.com
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Low compressibility and compliance and high bearing capacity
are required in construction or foundation sites which can be
determined from the reciprocal values of bulk modulus (K) and
Young’s modulus (E) respectively. Shear modulus and shear
wave velocity of the soil layer is reduced with increasing shear
strain [20].
MATERIALS AND METHODS OF DATA ANALYSIS
Resources of Geophysical and Geotechnical Data
For many projects in Iraq the engineering parameters of the
different strata from many geophysical and geotechnical
investigation reports are collected [21], and a data base is
prepared for static, shear and compression wave velocities
parameters of different soils for most zones in Iraq. The
available geotechnical and geophysical reports were collected
from different forty nine projects like gas power station, cement
plant, multi-story buildings, thermal Power plant, water
sewerage system, oil refinery and other projects from different
locations of Iraq and the data has been grouped into nine
regions, based on the governorates, namely (North, Eastern
North, Western North, Middle, East, West, Western South,
Eastern South and South) as shown in Table (1) and Figures
(1 and 2), where the zones borders are according to the
governorate boundaries. These parameters are evaluated from
field and laboratory tests results of the available geotechnical
and geophysical investigation reports collected from different
resource such National Center of Construction Laboratories
and Research (NCCLR), engineering consulting bureaus of
Baghdad and Al-Nahrain universities together with some
private companies and laboratories such as Andrea Engineering
Test labs, AL-Ahmed Engineering Test lab and others.
When the seismic wave velocities, Vs and Vp, are obtained,
several parameters of elasticity, like shear modulus G,
oedometric modulus of elasticity Ec , modulus of elasticity E
(Young’s modulus), bulk modulus K, and Poisson’s ratio ν may
be obtained from the Equations (1) to (7). Also the subgrade
modulus ks, ultimate and allowable bearing capacities are
onbtained depending on the Equations (8), (9) and (10)
respectively and as will be presented in Table (2).
Figure 1. Map study of seismic zones in Iraq [21 Figure 2. Map study of projects locations in Iraq [21]
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
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Table 1: Iraq seismic zones and sites symbols according to [21]
NO. Zone Governorate Site
symbol
Map
symbol
NO. Zone Governorate Site
symbol
Map
symbol
1
North
Dohuk N1 1 26 Middle Babylon M10 26
2 Dohuk N2 2 27 East
Diyala E1 27
3 Irbil N3 3 28 Diyala E2 28
4 Irbil N4 4 29 West Anbar W2 30
5
Eastern
North
Sulaymaniyah EN1 5 30
Western
south
Karbala WS1 31
6 Sulaymaniyah EN2 6 31 Karbala WS2 32
7 Kirkuk EN3 7 32 Karbala WS3 33
8 Kirkuk EN4 8 33 Karbala WS4 34
9 Kirkuk EN5 9 34 Najaf WS5 35
10 Kirkuk EN6 10 35 Najaf WS6 36
11 Kirkuk EN7 11 36
Eastern
South
Missan ES1 37
12
Western
North
Mosul WN1 12 37 Missan ES2 38
13 Mosul WN2 13 38 Missan ES3 39
14 Mosul WN3 14 39 Missan ES4 40
15 Salah Al-den WN4 15 40
South
Al Dewaniya S1 41
16 Salah Al-den WN5 16 41 Al Dewaniya S2 42
17 Baghdad M1 17 42 Al Nasiriya S3 43
18
Middle
Baghdad M2 18 43 Al Nasiriya S4 44
19 Baghdad M3 19 44 Al Nasiriya S5 45
20 Baghdad M4 20 45 Al Basrah S6 46
21 Baghdad M5 21 46 Al Basrah S7 47
22 Baghdad M6 22 47 Al Basrah S8 48
23 Baghdad M7 23 48 Al Basrah S9 49
24 Baghdad M8 24 49 Al Basrah S10 50
25 Babylon M9 25
Investigated Soil Parameters
The data for soil parameters investigated were taken from
geotechnical and geophysical investigation reports for most
Iraqi soil. Soil parameters such as; γwet ,γdry, c and ϕ which are
given in the geotechnical reports had evaluated by the field or
laboratory tests, also the depth of the water table and
description of the soil types according to borehole logs were
presented in these reports. While the seismic wave velocities
Vs, Vp values are listed in the geophysical reports that been
evaluated from the cross hole and down hole tests. The
geotechnical bore hole should be the same for the geophysical
bore hole or might be different bore hole but they should be
near to each other or collected either from the same borehole or
two adjacent ones which have the same soil layers profile.
The soil strength parameters (c or ϕ ) were evaluated by the
correlations from N value (SPT) according to the type of soil
when their values are not mentioned or evaluated in some of
the soil investigation reports.
Soil Parameters Evaluation
As mentioned earlier the soil parameters γwet ,γdry , c, ϕ
determined from field and laboratory tests results are presented
in the geotechnical investigation reports, and the dynamic
parameters Vs and Vp are prepared from geophysical
investigations reports. Once seismic wave velocities, Vp and Vs
, together with the density are measured, many parameters of
elasticity, such as shear modulus G, oedometric modulus of
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© Research India Publications. http://www.ripublication.com
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elasticity Ec , modulus of elasticity E (Young’s modulus), bulk
modulus K, and Poisson’s ratio ν may be obtained from the
Equations (1) to (7). Also the subgrade modulus ks, ultimate
and allowable bearing capacities are obtained depending on the
Equations (8), (9) and (10) respectively.
able (2) presents the geotechnical and geophysical parameters
collected and evaluated together with the values of ks, qult and
qall estimated.
Table 2: Soil properties and bearing capacity in different locations and zones of Iraq.
No. Site
Depth Soil Type WT γwet γdry c ϕ Vp Vs E×103 G×103 ν K×106 Ks×108 qult
1×102 qall
1×102 qult
2×102 qall
2×102 qall
2×102
m m kN/m3 kN/m3 kN/m2 (o) m/s m/s kN/m2 kN/m2 kN/m2 N/m2.s kN/m2 kN/m2 kN/m2 n=4 n=3
1 N1 0-3 Brown silty clay
with little fragment
NO
W.T
18.4 15.3 32 17 992 302 501.95 171.55 0.463 6.62 0.2223 5.56 1.39 4.87 1.22 1.62
3-10 Dense grey gravel with sand to gravel
with silt and sand
(GP,GP-GM)
19 14.9 0 42 1445 468 1233.6 422.46 0.46 5.14 0.3557 8.89 2.22 16.34 4.08 5.45
2 N2 0-7.5 Reddish brown rock
fragment of
limestone with silty
sand
>25 19.6 16.8 0 39 1623 832 3642.64 1354.1 0.345 39.17 0.6523 16.31 4.08 9.31 2.33 3.1
3 N3 4-10 Brown silt/clay with few sand & trace of
gravel,(CL-ML)
No W.T
21.3 18.1 49 28 807 354 706.4 248.56 0.421 1.5 0.3016 7.54 1.89 16.95 4.24 5.65
4. N4 0-6 Brown silt/clay with
few sand,(CL)
21.4 18.1 43 21 988 296 517.13 178.32 0.45 1.72 0.2534 6.33 1.58 8.6 2.15 2.87
6-10 Brown silt/clay with little sand& few
gravel,(CL-ML)
21.2 17.8 35 34 1460 462 1204.83 413.75 0.456 4.56 0.3918 9.79 2.45 22.45 5.61 7.48
5. EN1 0-4 Unknown 19.9 16.6 94 0 1745 262 419.05 144 0.486 5.13 0.2086 5.21 1.30 5.36 1.34 1.79
4-15 Unknown 20.9 18.4 0 44 2606 576 1963.11 670.6 0.463 8.84 0.4815 12.04 3.01 27.33 6.83 9.11
6 EN2 0-5 Unknown 19.4 17.6 81 3 1485 233 336.53 113.62 0.481 2.95 0.1808 4.52 1.13 4.62 1.16 1.54
5-10 Unknown 21.6 18.1 4 42 2313 384 932.18 283.48 0.467 4.2 0.3318 8.29 2.07 18.57 4.64 6.19
7 EN3 0-4 Stiff brown lean to
fat clay (CL, CH)
3.9 19.7 16.8 55 0 535 219 253.86 90.6 0.401 0.43 0.1726 4.31 1.08 3.14 0.79 1.05
4-6 Medium brown silty
Sand (SM)
19.6 17.2 21 33 679 301 477.75 172.47 0.385 0.69 0.2359 5.9 1.48 3.13 0.78 1.04
6-12 Dense grey gravel with sand to gravel
with silt and
sand(GP, ,GP-GM)
19.5 16.8 0 42 1384 733 2760.89 991.7 0.392 4.26 0.5717 14.29 3.57 16.77 4.19 5.59
8
EN4
0-2 Brown silt with
(ML)
2.9 19.4 17.7 5 37 360 145 124.2 44.25 0.403 0.21 0.1125 2.81 0.7 6.33 1.58 2.11
2-6 Stiff brown lean clay
(CL)
17.3 15.8 80 0 514 212 284.06 98.44 0.392 0.42 0.1467 3.67 0.92 4.56 1.14 1.52
6-15 Stiff brown to grey lean clay (CL)
19.4 17.5 21 39 1065 323 663.2 229.3 0.424 1.43 0.2506 6.27 1.57 9.22 2.3 3.07
9
EN5 0-2.5 Stiff brown sandy silt (ML)
>25 19 16.8 0 32 1125 225 290.15 98.09 0.479 2.3 0.1710 4.28 1.07 2.55 0.63 0.85
2.5-15 Very stiff to hard
brown lean to fat
CLAY (CL,CH)
20.6 18.2 227 0 1250 321 634.86 216.38 0.467 3.21 0.2645 6.61 1.65 12.94 3.24 4.31
15-20 Very dense silty
gravel with sand (GM)
20.6 18.2 0 42 2500 476 1409.8 475.9 0.481 12.37 0.3922 9.81 2.45 17.71 4.43 5.9
1seismic method [17]
2conventional method [18]
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1080
Table (2): Continue
No. Site
Depth Soil Type WT γwet γdry c ϕ Vp Vs E×103 G×103 ν K×106 Ks×108 qult1×102
qall1×102
qult2×102
qall2×102
qall2×102
m m kN/m3 kN/m3 kN/m2 (o) m/s m/s kN/m2 kN/m2 kN/m2 N/m2.s kN/m2 kN/m2 kN/m2 n=4 n=3
10 EN6 0-10 Stiff to very stiff
brown lean or fat clay (CL,CH)
2.6 21.0 18.1 120 0 1541 304 585.82 197.91 0.48 4.88 0.2554 6.39 1.6 6.84 1.71 2.28
11 EN7 0-10 Very stiff to hard brown lean clay
(CL)
3.8 20.1 17 130 0 1250 312 585.43 199.53 0.467 2.96 0.2508 6.27 1.57 7.41 1.85 2.47
12 WN1 0-15 Very Stiff to hard
moderately
gypseous, brown lean to fat clay
(CL,CH)
2.8 19 17.3 65 0 1330 459 1069.8 378.56 0.413 2.05 0.3488 8.72 2.18 3.71 0.93 1.24
13 WN2 0-7.5 Dark brown sand silt
with rock fragments
>25 18.3 16 0 37 773 319 542.6 189.3 0.432 1.33 0.2335 5.84 1.46 5.97 1.49 1.99
7.5-20 Brown sand gravel 17.8 15.3 0 42 1113 348 600.3 202.5 0.416 1.14 0.2478 6.2 1.55 15.3 3.83 5.1
14 WN3 4-15 Medium dense to
very dense grey silty
gravel with sand (GM,GP)
2.3 19.4 16.3 0 38 1057 362 584.6 217.2 0.424 1.36 0.2809 7.02 1.76 7.63 1.91 2.54
15 WN4 0-2 Grey gravel with silt sometimes with
sand(GM)
No W.t
18.3 16.8 0 36 714 292 445.39 160.21 0.39 0.67 0.2137 5.34 1.34 4.57 1.14 1.52
2-5 Medium stiff to hard
brown lean clay
sometimes with sand and gravel to
silt(CL,ML)
20.1 15.3 46 34 1055 346 676.62 238.08 0.421 1.43
0.2782
6.96
1.74
28.03 7.0 9.34
5-10 Dense to very dense
grey gravel with silt and sand to gravel
17.8 16.1 0 43 1335 606 2009.1 714.45 0.406 3.56 0.4315 10.79 2.7 18.83 4.71 6.28
16 WN5 0-4 Highly gypseoussilty sand to sandy silt
with little gravel
16 18.4 15.9 0 37 942 451 1030.4 374.97 0.374 1.36 0.3319 8.3 2.07 6 1.5 2
4-20 Silty sand with
gravel to sand with
gravel
19 14.8 0 41 1373 701 2559.4 916.7 0.396 4.1 0.5328 13.32 3.33 13.35 3.34 4.45
17 M1 0-10 Stiff to very stiff brown to green
slightly
gypseousmarly lean to fat clay and silt
clay (CL,CH,CL-
ML)
2.1 18.7 14.8 76 12 544 186 187.1 64.84 0.446 0.578 0.1391 3.48 0.87 4.33 1.08 1.44
10-16 Loose to medium
grey to green silty sand (SM)
20 16.3 0 36 736 258 381.9 140.42 0.433 1.0 0.2064 5.16 1.29 5.44 1.36 1.81
18
M2 0-8 Medium to stiff to very stiff brown lean
clay (CL)
2.65 20.1 17 125 0 820 265 414.42 144.1 0.438 1.11 0.2131 5.33 1.33 6.42 1.61 2.14
8-15 Loose to dense grey
silty sand to clayey
silty sand
19.1 15.5 0 36 1150 395 815.79 283.26 0.44 2.27 0.3018 7.55 1.89 5.19 1.3 1.73
19 M3 0-10 Soft to stiff brown
lean or fat clay or silt sometimes lean clay
with sand to sandy
silt (CL,CH,ML)
0.8 18.7 14.9 52 12 443 153 146.53 45.52 0.43 0.31
0.1144 2.86 0.72 2.67 0.67 0.89
10-18 Medium to very dense grey silt sand
or clayey sand
(SM,SC)
19 14 0 39 769 215 263.34 91.12 0.445 0.8 0.1634 4.1 1.02 9.03 2.26 3
20
M4
0-10 Stiff to very stiff
brown lean clay
1.55 19.78 17.43 180 0 761 298 538.8 191.5 0.408 0.98 0.2358 5.9 1.47 9.25 2.31 3.08
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10-15 Stiff to very stiff grey to brown to
black lean clay
sometimes with sand (CL)
1.55 20.2 17.1 68 16 1113 428 995.34 373.2 0.415 2.1 0.3458 8.65 2.16 9.48 2.37 3.16
15-20 Medium grey silty
sand (SM)
20.89 17.02 0 34 1351 507 1388.6 511.6 0.417 2.9 0.4236 10.59 2.65 3.97 0.99 1.32
21 M5 10-15 Loose to medium
grey silty sand (SM)
3.1 18.4 15.6 0 38 1191 430 977.68 336.2 0.454 3.5 0.3165 7.91 1.98 7.23 1.81 2.41
22 M6 0-1 Brown clayey silt to
sandy silt with filling materials, organic to
salts (ML)
1.3 19.00 15.8 28.7 0 322 140 251.99 91.1 0.383 0.36 0.1064 2.66 0.67 1.48
0.37 0.49
1-15 Brown to grey silty
clay to clayey silt (ML,CL,CH)
18.88 14.7 31.5 0 776 219 403.34 138.51 0.456 1.53 0.1654 4.14 1.03 1.62 0.41 0.54
15-20 Grey sand to silty or
clayey sand to
gravilly sand
(SM,GP)
22.31 17.04 0 38 1504 408 941.3 321.92 0.462 4.13 0.3641 9.10 2.28 8.77 2.19 2.92
23 M7 0-6 Medium stiff to stiff brown fat clay (CH)
0.6 19.8 15.8 50 0 641 189 209.16 72.13 0.45 0.7 0.1497 3.74 0.94 2.57 0.64 0.86
6-12 Very stiff brown lean clay (CL)
19.0 14.5 100 0 675 248 338.44 119.17 0.42 0.71 0.1885 4.71 1.18 5.14 1.29 1.71
12-15 Medium dense to
dense silty sand to
silty sand with gravel
19.0 15.0 0 37 750 225 284.46 98.09 0.45 0.95 0.1710 4.28 1.07 6.2 1.55 2.07
24 M8 Stiff to very stiff brown lean to fat
CLAY(CH)
19.8 17.1 65 10 841 165 162.7 54.97 0.48 1.36 0.1307 3.27 0.82 6.3 2.1
0-7.5 1.58
7.5-12 Medium to very
dense grey silty sand
(SM)
2.2 19.0 16.5 0 38 1025 279 440.3 150.8 0.46 1.83 0.2120 5.3 1.33 7.47 1.87 2.49
25 M9 0-5 Very soft to stiff brown lean to fat
clay sometimes with sand (CL,CH)
1.41 21.26 17.85 90 0 735 260 406.11 145.35 0.397 0.66 0.2211 5.53 1.38 4.63 1.16 1.54
5-15 Losse to dense grey
silty SAND(SM)
18.6 15.4 0 38 1503 369 682.46 242.5 0.403 1.17 0.2745 6.86 1.72 7.31 1.83 2.44
26 M10 0-2.4 Grayish sandy silty
clay soil, medium
consistency
1.5 16.18 14.5 144 0 306 111 57.9 20.33 0.424 0.13 0.0718 1.8 0.45 7.4 1.85 2.47
2.4-15 Grayish silty sand
soil, medium dense
18.44 16.5 0 38 450 183 176.33 62.98 0.4 0.29 0.1350 3.38 0.84 7.25 1.81 2.42
27 E1 0-10 Very stiff to hard
brown to grisg
brown marl lean clay (CL)
1.72 21.1 18.3 83 0 976 372 835.49 298.82 0.398 1.37 0.3140 7.85 1.96 4.27 1.07 1.42
28 E2 0-15 Stiff brown clay (CL)
1.46 20.3 17.1 76 0 1076 398 945.39 331.95 0.424 2.07 0.3232 8.08 2.02 3.9 0.98 1.3
29 W2 0-5 Stiff to very stiff brown lean clay(CL)
1.75 20.4 17.07 120 0 730 257 386.09 135.85 0.421 0.81 0.2097 5.24 1.31 6.17 1.54 2.06
5-10 Loose to dense grey to dark grey silty
sand and clayey silty
sand sometimes with gravel (SM,SC-SM)
18.2 15.2 0 33 1513 379 809.19 282.34 0.433 2.01 0.2759 6.9 1.72 2.91 0.73 0.97
30 WS1 0-5 Stiff brown to green 1.2 19.5 15.6 77 0 688 198 223.14 72.87 0.458 0.84 0.1544 3.86 0.97 3.96 0.99 1.32
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
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lean clay
5-9 Loose to medium
brown to grey silty sand (SW-SM)
18.4 14.8 0 33 948 265 401.85 137.62 0.46 1.67 0.1950 4.88 1.22 2.94 0.73 0.98
9-15 Very dense grey silty
sand
19.1 15.3 0 36 1370 497 1329.6 463.92 0.433 2.29 0.3797 9.49 2.37 5.19 1.3 1.73
31 WS2 0-18 Loose to very dense off white yellow,
light brown to grey
sometimes moderately
gypseoussilty sand
or sand with silt or sand (SM,SP-
SM,SP)
NO W.T
19.6 17.93 0 38 986 417 958.17 340.98 0.405 1.68 0.3270 8.18 2.04 7.7
1.93 2.57
32 WS3 0-10.5 Stiff brown silty to
moderately gypseous fat clay (CH)
1.5 18.5 14.7 100 0 1416 312 541.76 183.65 0.475 3.61 0.2309 5.77 1.44 5.14 1.29 1.71
33 WS4 0-4.5 Dense white to yellow slightly to
moderately gypseous
sand with silt to silty sand with gravel
(SP,SM)
0.8 18.8 18 0 37 1433 284 457.0 154.6 0.478 3.46 0.2136 5.34 1.34 6.14 1.53 2.05
4.5-12 Dense to very dense
white to yellow sand with silt (SP,SM)
19.4 18 0 35 1733 550 1727.2 598.46 0.443 5.05 0.4268 10.67 2.67 4.4 1.1 1.47
12-22 Very dense white to
yellow sand with silt
to silty sand (SP,SM)
19.4 18 0 35 1650 563 1801 627.1 0.436 3.71 0.4369 10.92 2.73 4.4 1.1 1.47
34 WS5 0-10 Very loose grading to very dense
slightly to
moderately gypseous sand (sm) or sand
with silt (SP-SM)
2.1 17.5 14.9 0 41 1613 618 1975.9 696.75 0.4185 4.04 0.4326 10.82 2.70 12.29 3.07 4.1
35 WS6 0-1.2 Medium- dense light
brown slightly
gypseoussilty sand (SM)
0.9 19.1 17 0 43 805 268 412.33 143.37 0.438 1.11 0.2048 5.12 1.28 20.15 5.03 6.71
1.2-7 Medium- dense to
very dense light
brown sand (SP)
19.5 18 0 40 1450 557 1743.5 616.95 0.413 3.34 0.4345 10.86 2.72 11.24 2.81 3.75
7-10 Very dense light
brown silty sand (SM)
19.6 18 0 39 1812 659 2472.2 868.03 0.424 5.42 0.5167 12.92 3.23 9.31 2.33 3.1
36 ES1 0-6 Stiff to very stiff brown to green
sandy lean to fat
CLAY (CL,CH)
0.41 19.2 14.8 53 4 451 111 69.32 23.67 0.464 0.32 0.08525 2.13 0.53 3.7 0.93 1.23
6-14 Loose grey silty sand (SM)
20.45 17.8 0 36 605 152 167.53 57.49 0.457 0.65 0.1243 3.11 0.78 5.56 1.39 1.85
14-20 Stiff to very stiff
brown to green fat
clay (CH)
19.9 15.6 63 0 690 211 254.57 89.07 0.429 0.61 0.1680 4.2 1.05 3.24 0.81 1.08
37
ES2 0-5 Medium stiff to stiff
brown lean to fat clay (CL,CH)
0.6 18.0 14.6 65 0 377 131 90.15 31.5 0.431 0.22 0.0943 2.36 0.59 3.34 0.84 1.11
5-8
Stiff brown lean to fat clay (CL,CH)
19.5 15.8 60 0 604 250 347.98 124.28 0.4 0.58 0.1950 4.88 1.22 3.08 0.77 1.03
8-17 Stiff brown lean clay (CL)
20.8 15.9 60 8 1362 420 1082.8 374.17 0.447 3.41 0.3494 8.74 2.18 5.2 1.3 1.73
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38 ES3 0-9 Medium stiff to stiff brown lean to fat
clay (CL,CH)
0.6 19.7 15.7 80 0 696 179 188.5 64.37 0.464 0.87 0.1411 3.53 0.88 4.11 1.03 1.37
9-18 Stiff brown lean
CLAY (CL)
20.9 16.1 60 0 1167 380 886.78 307.76 0.44 2.46 0.3177 7.94 1.99 3.08 0.77 1.03
39 ES4 0-7.5 Medium stiff to stiff
brown lean to fat clay (CL,CH)
0.6 19.5 15.1 80 0 500 176 175.96 61.57 0.429 0.41 0.1373 3.43 0.86 4.11 1.03 1.37
7.5-9 Loose grey silty sand 19.5 15.7 0 29 600 200 228.51 79.51 0.437 0.6 0.1560 3.9 0.98 1.58 0.39 0.53
9-10 Stiff brown lean clay (CL)
19.5 15.7 60 8 600 250 346.6 124.23 0.395 0.55 0.1950 4.88 1.22 5.2 1.3 1.73
40 S1 0-5 Stiff to very stiff brown to green
sandy lean to fat clay
(CL,CH)
0.3 19.6 15 42 8 685 225 281.99 99.02 0.424 0.62 0.1764 4.41 1.10 3.64 0.91 1.21
5-6.5 Loose grey silty sand (SM)
20.7 17.2 0 33 814 243 340.53 117.34 0.451 1.16 0.2012 5.03 1.26 3.31 0.83 1.1
6.5-10 Stiff to very stiff brown to green fat
clay (CH)
19.3 14.9 65 0 1224 333 645.63 220.2 0.466 3.16 0.2571 6.43 1.61 3.34 0.84 1.11
41 S2 0-1.5 Brown lean clay(CL) 0.3 18.5 14.4 94 0 625 188 193.28 66.65 0.450 0.64 0.1391 3.48 0.87 4.83 1.21 1.61
1.5-2 loose grey silty sand
layer (SM)
20.0 15.0 0 30 909 185 213.45 72.21 0.478 1.62 0.1480 3.7 0.93 1.91 0.48 0.64
2-10 Medium stiff to very
stiff brown to green
lean to fat clay (CL,CH)
19.3 14.7 60 5 909 200 232.17 78.73 0.475 1.55 0.1544 3.86 0.97 4.41 1.1 1.47
42 S3 0-8 Medium stiff to hard brown or grey or
dark grey lean to fat
clay sometimes with sand to sandy lean
clay or silt or sandy
silt(CL,CH,ML)
1.2 19.1 15.8 78 0 646 185 198.82 68.72 0.458 0.79 0.1413 3.53 0.88 4.0 1.0 1.33
8-15 Dense to very dense grey or dark grey or
brown silty sand
otsilty clayey sand or
sand with silt
(SM,SC-SM,SP-SM)
17.7 14.6 0 40 1094 321 562.51 198.94 0.464 2.7 0.2273 5.68 1.42 10.2 2.55 3.4
43 S4 0-12 Soft to medium
black, brown, green light, green lean to
fat clay (CL,CH)
1.7 19.5 15.2 90 3 434 110 70.54 24.06 0.466 0.35 0.0858 2.15 0.54 5.96 1.49 1.99
12-14 Loose grey silty sand
(SM)
20.8 18 0 41 500 145 129.7 44.6 0.454 0.47 0.1206 3.02 0.75 14.61 3.65 4.87
14-15 Very stiff brown,
green lean clay(CL)
20.8 17 191 0 600 166 170.56 58.45 0.459 0.69 0.1381 3.45 0.86 9.82 2.46 3.27
44 S5 0-4 Very stiff brown
lean clay (CL)
4 19.07 15.1 34 0 600 200 223.45 77.75 0.437 1.7 0.1526 3.82 0.95 1.75 0.44 0.58
4-10 Stiff to hard brown
lean to fat clay (CL,CH)
19.93 15 112 0 750 240 337.6 117.1 0.442 0.97 0.1913 4.78 1.2 5.76 1.44 1.92
45 S6 0-3 Medium light brown
gypseous soil
1.6 20.3 16.8 0 35 803 329 780.35 258.63 0.397 1.17 0.2671 6.68 1.67 4.61 1.15 1.54
3-10 Medium to very
dense light brown to
grey slightly to highly gypseoussilty
sand or sand with silt or sand (SM,SP)
18.9 16.01 0 34 1811 627 1797.46 737.98 0.446 6.59 0.4740 11.85 2.96 3.59 0.89 1.19
46 S7 0-3.7 Grey gypseous 1.8 18.18 16.1 5.33 39 566 230 269.05 96.012 0.401 0.45 0.1673 4.18 1.05 8.63 2.16 2.88
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1084
sand (SM)
3.7-15 Grey gypseous silty sand (SM)
19.16 15.3 8.4 40 1404 365 750.38 256.45 0.463 3.38 0.2797 6.99 1.75 11.04 2.76 3.68
47 S8 0-6 Very soft to stiff brown lean clay
(CL)
5 21.1 16.4 60 0 434 166 168.06 59.47 0.412 0.32 0.1401 3.50 0.88 3.08 0.77 1.03
6-15 Very loose grey
clayey silty sand
(SC-SM)
19 15.3 0 37 510 194 250.53 88.4 0.417 0.50 0.1474 3.69 0.92 6.2 1.55 2.07
48 S9 0-6 Medium to stiff
brown lean to fat clay (CL,CH)
1.1 19.7 15.7 80 0 294 117 82.58 29.47 0.401 0.14 0.0922 2.31 0.58 4.11 1.03 1.37
6-12 Stiff brown lean clay
(CL)
20.9 16.1 60 0 381 198 239.08 83.77 0.427 0.55 0.1655 4.14 1.03 3.08 0.77 1.03
49 S10 0-10 Very soft to stiff
brown lean or fat
clay(CL,CH)
1.0 18.37 13.92 40 0 550 138 104.6 35.7 0.466 0.51 0.1014 2.54 0.63 2.06 0.52 0.69
10-13 Grey silty sand (SM) 19.63 15.54 0 37 334 103 61.8 21.23 0.455 0.23 0.0801 2 0.5 6.4 1.6 2.13
13-15 Very soft to stiff lean
clay (CL)
20.02 16.03 48 0 450 102 62.57 21.24 0.473 0.39 0.0817 2.04 0.51 2.47 0.62 0.82
RESULTS AND DISCUSSION
Evaluation of the Allowable Bearing Capacity
In this research, geotechnical parameters, i.e. Young modulus,
bulk modulus, shear modulus, subgrade modulus were obtained
from the result of the secondary wave velocities for each layer
of the areas of study using Equations (1) to (8). These
relationships also led to the determination of the ultimate
bearing capacity and the allowable bearing capacity according
to the Equations (9) and (10) respectively. The results obtained
are presented in Table (2). Also, following the classical
procedure of [18], the ultimate and allowable bearing capacities
were determined, by assuming the factor of safety equal to n=3
and 4 and as given in Table (2) for the purpose of comparison.
The numerical values of the ultimate and allowable bearing
capacities determined in accordance with the conventional
Terzaghi theory and seismic technique (Tezcan et al., 2006) for
cohesive soils are plotted in Figures (3 and 4 respectively). And
the results of ultimate and allowable bearing capacities
estimated from both methods for cohesionless soils are plotted
in Figures (5 and 6 respectively).
Two separate linear regression lines were also shown in the
Figures (3 and 5), for the purpose of indicating the average
values of ultimate bearing pressure determined by ‘seismic’
and ‘conventional’ methods. For cohesive and cohesionless
soils it can be indicated that up to a shear wave velocity of 300
m/s and 400 m/s respectively, the shear wave velocity predicts
the bearing capacity relatively well. Above 300 m/s and 400
m/s the scatter is large and it looks like there are quite many
points that are falling below the bearing capacity estimated by
the shear wave velocity. The linear regression line indicates for
Vs values smaller than 300 m/s and 400 m/s a narrow band,
which should be regarded as quite acceptable. The ‘seismic’
method proposed herein yields allowable bearing cabacities (on
the order of 10 to 20%) greater than those of the ‘conventional’
method for Vs values smaller than 400 m/s. In fact, the
‘conventional’ method fails to produce reliable and consistent
results for relatively strong soils, because it is difficult to
determine the appropriate soil parameters c and ϕ for use in the
‘conventional’ method [22]. Therefore, from the results the use
of ‘seismic’ method can give an order of magnitude for such
strong soils with Vs > 300 m/s for cohesive soils and >400 m/s
for cohesionless soils.
The allowable bearing capacity has been obtained at different
sites in various regions of Iraq as shown in Table (2) and
Figures (4 and 6) for cohesive and cohesionless soils
respectively. Factor of safety used for allowable bearing
capacity estimated from shear wave velocity is 4 (Tezcan,
2006), and allowable bearing capacity is estimated from
Terzaghi equation using factor of safety, n=3 and 4, it can be
indicated that values from shear wave velocity are close to that
from conventional method till Vs=300 m/s for cohesive soils
and 400 m/s for cohesionless soils and above these velocities
the scatter is large. It can be concluded from these graphs that
allowable bearing capacity estimated from shear wave velocity
may be obtained for n less than 4 for soils that have Vs less and
equal than 400 m/s. Table (3) shows the range of values for
seismic wave velocities and allowable bearing capacity for
different types of soil with various description. In order to
demonstrate that the technique used covers all soils types, the
values of seismic velocities and allowable bearing capacity
given in Table (3) are compared with the values for foundation
materials given in building codes with entire seismic velocities
covering all soils and rocks types and with the values calculated
by using seismic velocities of soils and rocks [23] which has
been obtained at thousands of construction sites in various
regions of Turkey since 1990. The comparison shows that the
allowable bearing capacity values obtained from hard through
loose soils were in agreement with the building codes and
Keçeli [23] values. Thus, allowable bearing capacity values
obtained by the technique proposed here are evaluated for
accuracy. Table (3) also demonstrated awide range for soil
types description.
Allowable bearing capacity for cohesive and cohesionless soils
is plotted in each case against the shear wave velocity for each
of the layers as given in Figures (4 and 6 respectively) which
shows linear empirical relationships between the allowable
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1085
bearing capacity and the shear wave velocity. This is
demonstrated in Equations (11 and 12):
For Cohesive Soils qall (kN/m2) =(0.0053Vs - 0.073)×102
(11)
For Cohesionless Soils qall(kN/m2)=(0.0048Vs + 4.0E-6)×102
(12)
The slopes in the equations are dimensionless constant which
gives the coefficient of elastic deformability of shallow
foundation geomaterial caused by the load applied on the
considered shallow foundations. The slopes of qa and Vs plots
reflecting the impulse/driving force producing the
deformability of a layers per cubic meter of the foundation
layers is about 0.5 kNs·m−3. From Equations (11 and 12), layers
near surface are more relatively susceptible to deformation than
sublayers based on the magnitudes of qall and shear modulus
G which is plotted against Vs for cohesive and cohesionless
soils as shown in Figures (7 and 8 respectively). As it increases,
the degree of elastic deformation decreases. Although
consolidation of subsurface increases with depth due to
compaction, other tectonically induced secondary structures
like divide, fault lineament and fold within the sedimentary
facies could cause voids in the subsurface thereby leading to
elastic deformation of subsurface.
The layers also show polynomial relationships between qa and
G as shown in Figures (7 and 8) for cohesive and cohesioless
soils respectively. The unit weight of the soil layer also
determines the shear modulus and S-wave velocity in Equation
(1) constitutes the significant variation noticed in layers in the
relation between allowable bearing capacity qa and shear
modulus G which is given by Equations (13 and 14):
For Cohesive Soils qall (kN/m2) =(-4E-06G2 + 0.0061G + 0.4843)×102
(13)
For Cohesionless Soils qall (kN/m2) = (-1E-06G2 + 0.0043G + 0.6675)×102
(14)
The highest value of qall for sublayers is seen on north zone and
reduces through middle and south of Iraq. This trend shows that
low allowable bearing capacity is associated with zones that are
highly undrained with water while the high bearing capacity is
associated with zones that are unsaturated with water. The
appeared transition in magnitude of allowable bearing capacity
toward high value with depth is due to cementation/compaction
which increases with depth.
The results show that the higher value of allowable bearing
capacity in the study areas is obtained in North of Iraq (i.e., N1)
with a value of about 408 kN/m2 and the lowest is at Middle
and South regions (i.e., M10 and S10 respectively) with avalue
of about 50 kN/m2. According to the depths of investigation and
soil descriptions shown in Table (2), three layers with
approximate depths can be considered for investigation, layer
one extends to about 6m from the ground surface, while layer
two extends for a depth 6m to 10m and third one for depth
between 10m to 15m. qall value has an average value of about
142 kN/m2 for layer one, while the average bearing capacity for
layer two is about 176 kN/m2and about 162 kN/m2 for layer
three. With respect to cohesive and non-cohesive soils, the
results of the minimum, maximum and average values of shear
modulus, G, and allowable bearing capacity, qall appears for the
layers to a depth of about 15m from ground surface in the study
areas are as shown in Table (4).
Table 3: Allowable bearing capacity for different soil descriptions.
Soil type Vp -range (m/s) Vs -range
(m/s)
qall ×102
(kN/ m2)
Rock Fragment of Limestone with Silty Sand to Gravel with
Sand or Gravel with Silt and Sand
Silty Sand (Loose)
Silty Sand (Medium)
Silty Sand (Dense)
Gypseous Sand to Silty Sand
Clay (Very Soft to Soft)
Clay (Medium)
Clay (Stiff)
Clay (Very Stiff to Hard)
714-2500
334-909
450-1191
1025-1733
803-1811
294-550
377-820
381-1076
675-1541
292-733
103-243
183-507
279-659
268-627
102-153
131-265
198-398
248-459
1.34-4.08
0.5-1.26
0.84-2.65
1.33-3.23
1.28-2.96
0.5-0.88
0.59-1.33
0.97-2.02
1.18-2.18
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1086
Table 4: Shear modulus and allowable bearing capacity for different depths in cohesive and cohesionless soils.
Soil type
Depth
Approx.
(m)
G×103 –value
(kN/m2)
qall×102-value
(kN/m2)
Min. Avg. Max. Min. Avg. Max.
Cohesive
soil
0-6 21.24 105.5 374.17 0.45 1.06 1.96
6-10 83.77 206 413.75 1.03 1.54 2.45
10-15 21.24 207.6 374.17 0.51 1.47 2.18
Cohesionless soil 0-6 44.25 387.76 1354.1 0.7 1.78 4.08
6-10 57.49 693.8 4142.8 0.78 1.97 3.57
10-15 21.23 464.1 3370 0.5 1.76 3.33
Figure 3: Ultimate bearing capacity against shear wave velocity for cohesive soils.
0
5
10
15
20
25
30
0 50 100 150 200 250 300 350 400 450 500
qult(×
10
2 kP
a)
Vs(m/sec)
conventional method [18]
seismic method [17]
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1087
Figure 4: Allowable bearing capacity against shear wave velocity for cohesive soils.
Figure 5: Ultimate bearing capacity against shear wave velocity for cohesionless soils.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 50 100 150 200 250 300 350 400 450 500
qal
l(×
10
2kP
a)
Vs (m/sec)
seismic method-n=4 [17]
conventional method-n=3 [18]
conventional method-n=4 [18]
0
10
20
30
40
50
60
70
0 100 200 300 400 500 600 700 800 900
Vs (m/sec)
seismic method [17]
conventional method [18]
qal
l(×
10
2kP
a)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1088
Figure 6: Allowable bearing capacity against shear wave velocity for cohesionless soils.
Figure 7: Allowable bearing capacity against shear modulus for cohesive soils.
0
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300 350 400 450
qal
l(×
10
2kN
/m2)
G(×103 kPa)
0
5
10
15
20
25
30
0 100 200 300 400 500 600 700 800 900
qall
(×10
2kP
a)
Vs (m/sec)
2 .2 2
4 .0 8
5 .4 5
seismic method-n=4 [17]
conventional method-n=3 [18]
conventional method-n=4 [18]
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1089
Figure 8: Allowable bearing capacity against shear modulus for cohesionless soils.
Evaluation of the Soil Parameters
This study aimed also at obtaining model equations from the
correlations of the shear wave velocities and the different
geotechnical parameters studied. This was to obtain direct
relationships between the S-wave velocity and the geotechnical
parameters. These equations can be used for a quick evaluation
and inexpensive estimation of the various soil parameters.
The graphs of the parameters were plotted against the shear
wave velocities. Also, the relations and correlations have been
investigated between seismic velocities and geotechnical
parameters using the best fit curve. The relations give obvious
variations in the geotechnical properties affecting the velocities
differently in different parts of the velocity ranges.
The graphs of modulus of elasticity, E, bulk modulus, K, and
subgrade modulus, ks, against the S-wave velocity (Figures 9,
11 and 13 respectively) gave the empirical equations defined in
Equations (15, 16 and 17) for cohesive soils. And the plots of
modulus of elasticity, E, bulk modulus, K, and subgrade
modulus, ks, against the S-wave velocity (Figures 10, 12 and
14 respectively) gave the empirical equations defined in
Equations (18, 19 and 20) for cohesionless soils. The equations
shows polynomial relationships between E with Vs and
exponential relationship between K and Vs and linear
relationship between ks with Vs. The minimum, maximum, and
average values of modulus of elasticity, E, bulk modulus, K,
and subgrade modulus, ks for the cohesive and cohesionless
soils estimated to a depth of about 15m from ground surface in
the study areas are given in Table (4).
This result shows that the lower layers are more compressed
than the first layer. This may be as a result of the geologic
formation of these layers, their level of saturation and the level
of cementation of the geomaterial. It was also indicated that the
Young modulus of the subsurface increased in direct proportion
with the seismic wave velocity and the two parameters
generally increased with depth. This also shows that the second
layer has more strength than the other layers. The results also
shows that the first layer would deform more easily under shear
stress than the lower layers. The bulk modulus results further
confirmed that the second geologic layer to be more competent
than the first layer. The subgrade modulus ranges also reveals
that the second geologic layer is more competent than the first
layer.
For Cohesive Soils
E (kN/m2) = (0.0047Vs2 + 0.5284Vs-47.13) ×103 (15)
K (kN/m2) = (0.1566e0.0074Vs) ×106 (16)
ks (N/m2.s)= (0.0008Vs - 0.0119) ×108 (17)
For Cohesionless Soils
E (kN/m2) = (0.0047 Vs2 – 0.4619Vs
-50.866) ×103 (18)
K (kN/m2) = (0.2789e0.005Vs) ×106 (19)
ks (N/m2.s) = (0.0008Vs - 0.0002) ×108 (20)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 200 400 600 800 1000 1200 1400 1600
qal
l(×
10
2kN
/m2 )
G(×103 kPa)
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Table 4: Soil parameters for different depths in cohesive and cohesionless soils in the study areas.
Soil type
Depth
Approx.
(m)
E×103 -value
(kN/m2)
K×106-value
(kN/m2)
ks ×108-value
(N/m2.s)
Min. Avg. Max. Min. Avg. Max. Min. Avg. Max.
Cohesive
soil
0-6 57.9 304.14 835.5 0.13 1.34 6.62 0.072 0.169 0.314
6-10 239.1 592.7 1204.8 0.55 1.88 4.56 0.165 0.247 0.392
10-15 62.57 588 1082.8 1.58 1.58 3.41 0.082 0.236 0.35
Cohesionless
soil
0-6 124.2 1057.6 3642.6 0.21 2.28 5.14 0.113 0.303 0.65
6-10 167.5 1926.5 11343 0.29 3.64 14.43 0.124 0.39 1.191
10-15 61.8 1313 9397 0.23 3.43 14.62 0.08 0.316 0.953
Figure 9: Young’s modulus against shear wave velocity for cohesive soils.
0
200
400
600
800
1000
1200
1400
0 50 100 150 200 250 300 350 400 450 500
E(×
10
3kP
a)
Vs(m/sec)
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© Research India Publications. http://www.ripublication.com
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Figure 10: Young’s modulus against shear wave velocity for cohesionless soils.
Figure 11: Bulk modulus against shear wave velocity for cohesive soils.
0
500
1000
1500
2000
2500
3000
3500
4000
0 100 200 300 400 500 600 700 800 900
E(×
10
3kP
a)
Vs(m/sec)
0
1
2
3
4
5
6
7
8
9
10
0 50 100 150 200 250 300 350 400 450 500
K(×
10
6kP
a)
Vs(m/sec)
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Figure 12: Bulk modulus against shear wave velocity for cohesionless soils.
Figure 13: Subgrade modulus against shear wave velocity for cohesive soils.
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500 600 700 800 900
K(×
10
6kP
a)
Vs(m/sec)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 50 100 150 200 250 300 350 400 450 500
k s(×
10
8N
/m2.s
ec)
Vs(m/sec)
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Figure 14: Subgrade modulus against shear wave velocity for cohesionless soils.
CONCLUSION
The conclusions that can be drawn from this study can be
summarized as follows:
1. Ranges for values of seismic wave velocities and
allowable bearing capacity for different types of soil
with various description are presented, extending the
knowledge for the limit of theses values. Also the
allowable bearing capacity values obtained from hard
through loose soils were in agreement with the
building codes and references values.
2. Correlations between seismic velocity Vs and
allowable bearing capacity has been obtained. This
relationship show direct proportionalities between Vs
with qall. The results show that the range of bearing
capacity for the study area was between 50 and 408
kN/m2, being highest at north regions and reduces
through middle and south regions of Iraq.
3. The cross and down hole tests results revealed three
geologic layers with the second layer being more
competent. qall value has an average value of about
142 kN/m2 for layer one, while the average bearing
capacity for layer two is about 176 kN/m2and about
162 kN/m2 for layer three.
4. As the bearing capacity is a mechanism where large
shear strains develop and the measured shear wave
velocity is based on very small strains, thus the
bearing capacity estimated from the shear wave
velocity may be used to check the values calculated by
other means.
5. The empirical equations obtained can be used to
evaluate and predict the geotechnical parameters of
the study area studied.
6. Empirical expressions estimated for the allowable
bearing capacity using shear wave velocities
measured at low shear strains, is appropriate to
produce reliable results for a wide range of soil
conditions.
7. Allowable bearing capacity increases with increase in
shear modulus enhanced by high shear wave velocity.
For cohesive and cohesionless soils it was indicated
that up to a shear wave velocity of 300 m/s and 400
m/s respectively, the shear wave velocity may predicts
the bearing capacity relatively well.
8. Using the empirical formulations generated from the
sites data, surface layer has been found to show lower
bearing capacity than layers two and three based on
the coefficients of elastic deformability of shallow
foundation realized from the plots of qall against G.
The layers also show relationships of seconed order
between qa and G.
9. Correlations between seismic velocity Vs and
geotechnical properties have been derived. These
relations show polynomial relationships between E
with Vs and exponential relationship between K and
Vs and linear relationship between ks with Vs.
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0.1
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0.4
0.5
0.6
0.7
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k s(×
10
8N
/m2.s
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Vs(m/sec)
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1075-1094
© Research India Publications. http://www.ripublication.com
1094
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