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DETERMINATION OF SHEAR WAVE VELOCITY AND SHEAR MODULUS
ESTIMATION OF PEAT SOIL USING SEISMIC GEOPHYSICAL METHOD
MOHD JAZLAN BIN MAD SAID
A thesis submitted in partial
fulfillment of the requirement for the award of the
Degree of Master of Civil Engineering
Faculty of Civil and Environmental Engineering
Universiti Tun Hussein Onn Malaysia
APRIL, 2016
v
For my beloved father, mother, brothers and sisters
Thank you for your supports and always being there for me. Without you all, I can’t
have achieve successful life and become better person
vi
ACKNOWLEDGEMENT
In the name of Allah, to the Most Gracious and Most Merciful,
I wanted to express greatest gratitude and sincere appreciation to my main
supervisor, Assoc. Prof. Dr. Adnan Zainorabidin and my co-supervisor, Dr. Aziman
Madun for their guides and knowledge with their kindness and patience that they have
shared to me for this past two year of research. They have shown me the importance
of knowledge by doing this research and motivation to achieved success to finish this
thesis.
I also want to give thanks to my family who gives supports, encouragement
and sacrifice for my journey in finishing my master’s research.
An acknowledgement for all the people and friends that helped and
supported me to finish my thesis from the beginning until the end of this research
especially for my group member.
Finally, an appreciation is also extended to all academic and non-academic
members of the Faculty of Civil and Environmental Engineering and Research Centre
of Soft Soil (RECESS) for assisting me in my works.
vii
ABSTRACT
This research is about dynamic characterization of peat using field seismic geophysical
method. There are demands on dynamic characteristics in construction due to their
importance towards the society. The dynamic behaviours of peat are shear velocity
(Vs) and shear modulus (G). The scope of this research is meant for peat and soft clay
by using multi-channel analysis of surface wave (MASW) method and seismic
refraction method. The estimation of shear modulus is based on shear wave velocity
and soil bulk density using the sampler with 0.5 m depth each. Peat sampler was used
to verify the soil profiles at every location except for soft clay. The shear wave velocity
for peat is ranging from 26.02 – 95.89 m/s. Meanwhile, for soft clay, it has velocity
from 61.25 – 86.37 m/s. As for shear modulus of peats, the range is between 0.82 –
7.26 MPa while for soft clay, the range is between 7.29 MPa – 13.92 MPa. The
variations of shear wave velocity and shear modulus of peat are due to the differences
in peat soils properties in term of organic content, fibre content, void ratio and moisture
content for every research location. Furthermore, seismic attenuation in peat is also
affected the seismic wave velocity. The dynamic behaviour of peat and soft clay have
slight changes in shear wave velocity. However it has significant difference in shear
modulus due to the existence of organic content that contributes to their differences.
Shear wave velocity was obtained by applying seismic refraction method. The data
shows the increment of velocity with depth. The determination of dynamic behaviour
of peats was achieved by using seismic geophysical method have shown good findings.
viii
ABSTRAK
Kajian ini adalah mengenai pencirian dinamik tanah gambut menggunakan kerja
lapangan kaedah geofizik seismik. Terdapat permintaan kepada ciri-ciri dinamik
dalam pembinaan kerana kepentingan mereka terhadap masyarakat. Tingkah laku
dinamik gambut adalah halaju ricih (Vs) dan modulus ricih (G). Skop kajian ini adalah
untuk tanah gambut dan tanah liat lembut dengan menggunakan analisis pelbagai
saluran gelombang permukaan kaedah (MASW) dan kaedah pembiasan seismik.
Anggaran modulus ricih berdasarkan halaju gelombang ricih dan ketumpatan pukal
tanah menggunakan sampler pada kedalaman setiap 0.5 m. Peat sampler telah
digunakan untuk mengesahkan profil tanah di setiap lokasi kecuali untuk tanah liat
lembut. Halaju gelombang ricih untuk tanah gambut adalah antara 26.02 – 95.89 m/s.
Sementara itu, bagi tanah liat lembut, ia mempunyai halaju 61.25 – 86.37 m/s. Bagi
modulus ricih tanah gambut, adalah berjulat diantara 0.82 - 7.26 MPa manakala bagi
tanah liat lembut, berjulat antara 7.29 MPa - 13.92 MPa. Variasi halaju gelombang
ricih dan modulus ricih tanah gambut adalah berbeza disebabkan sifat dalam tanah
gambut dari segi kandungan bahan organik, kandungan serat, nisbah lompang dan
kandungan lembapan bagi setiap lokasi penyelidikan. Tambahan pula, pengecilan
seismik dalam gambut juga dipengaruhi halaju gelombang seismik. Kelakuan dinamik
tanah gambut dan tanah liat lembut mempunyai sedikit perubahan halaju gelombang
ricih. Walau bagaimanapun ia mempunyai perbezaan yang signifikan dalam modulus
ricih disebabkan oleh kewujudan kandungan organik yang menyumbang kepada
perbezaan mereka. halaju gelombang ricih telah diperolehi dengan menggunakan
kaedah pembiasan seismik. Semua data menunjukkan peningkatan halaju mengikut
kedalaman. Penentuan tingkah laku dinamik gabus telah dicapai dengan menggunakan
kaedah geofizik seismik telah menunjukkan penemuan yang baik.
ix
TABLE OF CONTENT
TITLE iii
DECLARATION iv
DEDICATION v
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENT ix
LIST OF TABLE xv
LIST OF FIGURE xvii
LIST OF SYMBOL AND ABBREVIATION xxii
LIST OF APPENDICES xxiv
CHAPTER 1 INTRODUCTION 1
1.1 Background of research 1
1.2 Problem statement 2
1.3 Aim of research 3
1.4 Objective of research 3
1.5 Research scope 3
1.6 Research significant 3
1.7 Thesis layout 4
CHAPTER 2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Peat soil 5
2.2.1 Properties of peats 7
2.3 Dynamic behaviour of soil 8
2.3.1 Previous researches of shear modulus (G)
on peat 10
x
2.3.2 Previous researches on shear wave velocity
(Vs) on peat 13
2.4 Determination of peat bulk density using peat
sampler 15
2.5 Seismic wave 16
2.5.1 Body wave 16
2.5.2 Surface wave 18
2.6 Seismic wave attenuation 19
2.7 Seismic geophysical method 20
2.7.1 Multi-channel analysis of surface wave
(MASW) 21
2.7.1.1 Past researches on multi-channel
analysis of surface wave 22
2.7.1.2 Phase velocity in frequency domain
(MASW) and dispersion curve 25
2.7.1.3 Fundamental mode of dispersion
curve in phase velocity image in
frequency domain 25
2.7.2 Seismic refraction 26
2.7.2.1 Past researches on seismic refraction 28
2.7.2.2 Snell’s law 30
2.7.2.3 Limitations and interferences 31
2.7.2.4 First arrival time of p-wave 33
2.8 Chapter summary 34
CHAPTER 3 METHODOLOGY 35
3.1 Introduction 35
3.2 Seismic challenges in data acquisition on peat 35
3.2.1 Attenuation of seismic wave 37
3.2.2 Poor signal to noise ratio (S/N) 38
3.2.3 Seismic source energy 38
3.3 Research location 42
3.3.1 Parit Nipah 43
3.3.2 Parit Sulong 43
xi
3.3.3 Malaysia Agricultural Research and
Development Institute (MARDI) station,
Pontian 44
3.3.4 Penor, Pekan 45
3.3.5 Research Centre for Soft Soil (RECESS) 46
3.4 Data acquisition (field work) 46
3.4.1 MK-8 ABEM seismograph configuration 46
3.4.1.1 Seismograph settings before start-up 47
3.4.1.2 Seismograph settings before data
acquisition 48
3.4.1.3 Seismograph setting during data
acquisition 52
3.5 1-D Multi-channel analysis of surface wave
(MASW) method 53
3.5.1 1-D MASW equipment arrangement 55
3.6 Seismic refraction method 56
3.6.1 Seismic refraction equipment arrangement 56
3.7 Data process and analysis 57
3.7.1 SeisImager/SW software 58
3.7.1.1 Pickwin module 58
3.7.1.2 WaveEq module 59
3.7.2 Optim software 60
3.7.2.1 SeisOptPicker software 60
3.7.2.2 SeisOpt @2D software 61
3.8 Determination of peat in-situ density using peat
sampler 62
3.8.1 Peat sampler equipment 62
3.8.2 Peat in-situ density acquisition 63
3.8.3 In-situ peat density calculation 64
3.9 Shear modulus estimation 65
3.10 Chapter summary 65
CHAPTER 4 RESULT AND DISCUSSION 66
4.1 Introduction 66
xii
4.2 Soil profile at research locations 66
4.2.1 Soil profile at Parit Nipah 67
4.2.2 Soil profile at Parit Sulong 67
4.2.3 Soil profile at Pontian 68
4.2.4 Soil profile at Penor 69
4.3 Soil density for all research locations 70
4.4 Dispersion curve on phase velocity image in
frequency domain 73
4.4.1 Dispersion curve at Parit Nipah 73
4.4.2 Dispersion curve at Parit Sulong 75
4.4.3 Dispersion curve at Pontian 77
4.4.4 Dispersion curve at Penor, Pekan 79
4.4.5 Dispersion curve at RECESS 81
4.5 Multi–channel analysis of surface wave results 83
4.5.1 Shear wave velocity profiles at Parit Nipah 83
4.5.1.1 Shear wave velocity comparison for
Parit Nipah 86
4.5.2 Shear wave velocity profiles at Parit Sulong 87
4.5.2.1 Shear wave velocity comparison at
Parit Sulong 90
4.5.3 Shear wave velocity profiles at Pontian 91
4.5.3.1 Shear wave velocity comparison at
Pontian 94
4.5.4 Shear wave velocity profiles at Penor 95
4.5.4.1 Shear wave velocity comparison at
Penor 98
4.5.5 Shear wave velocity profiles at RECESS 99
4.5.5.1 Shear wave velocity comparison at
RECESS 102
4.5.6 Shear wave velocity results discussion 103
4.6 Shear modulus estimation 106
4.6.1 Shear modulus at Parit Nipah 106
4.6.2 Shear modulus at Parit Sulong 107
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4.6.3 Shear modulus at Pontian 108
4.6.4 Shear modulus at Penor 110
4.6.5 Shear modulus at RECESS 111
4.6.6 Shear modulus results discussion 113
4.7 Seismic refraction results 116
4.7.1 Compressive wave velocity profile at Parit
Nipah 116
4.7.2 Compressive wave velocity profile at Parit
Sulong 117
4.7.3 Compressive wave velocity profile at
Pontian 118
4.7.4 Compressive wave velocity profile at Penor 119
4.7.5 Compressive wave velocity profile at
(RECESS), UTHM 119
4.7.6 Compressive wave soil velocity comparison
for all research locations 120
4.8 Comparison of shear wave velocity from MASW
method and seismic refraction method 122
4.9 Chapter summary 129
CHAPTER 5 CONCLUSION 130
5.1 Objective 1: To determine peat soil shear wave
velocity using multi-channel Analysis of surface
wave method (MASW) 130
5.2 Objective 2: To analyse the shear modulus (G) of
peat using empirical formula 131
5.3 Objective 3: To compare shear wave velocity
between multi-channel analysis of surface wave
method and seismic refraction method 132
5.4 Objective 4: To investigate and compare the
dynamic behaviour of peat with inorganic soil 133
5.5 Knowledge contribution 133
5.6 Recommendations for future research 134
xiv
REFERENCES 135
LIST OF APPENDICES 143
xv
LIST OF TABLE
2.1 Percentages of peat land area in Malaysia. (Kleine,
2010) 6
2.2 Properties of peat according to previous researchers 7
2.3 Field and laboratory test implemented for dynamic
measurement of soil. (Kumar et al., 2013) 9
2.4 Limitations and interferences for geophysical method
and seismic refraction method. (ASTM D - 5777, 2000) 31
3.1 Offset distance and geophone takeout spacing for Test
1, Test 2 and Test 3 39
3.2 Seismograph keyboard description used during data
acquisition 53
4.1 Soil profile at Parit Nipah (Hemic) 67
4.2 Soil profile at Parit Sulong (Sapric) 68
4.3 Soil profile at Pontian (Fibrous) 68
4.3 Soil profile at Pontian (Fibrous) (continued) 69
4.4 Soil profile at Penor (Sapric) 69
4.5 Average density of soils at Parit Nipah 71
4.6 Average density of soils at Parit Sulong 71
4.7 Average density of soils at Pontian 71
4.7 Average density of soils at Pontian (continued) 72
4.8 Average density of soils at Penor 72
4.9 Interpolated shear wave velocity for every 0.5 m
interval depth at Parit Nipah 86
4.10 Interpolated shear wave velocity for every 0.5 m
interval depth at Parit Sulong 90
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4.11 Interpolated shear wave velocity for every 0.5 m
interval depth at Pontian 94
4.12 Interpolated shear wave velocity for every 0.5 m
interval depth at Penor 98
4.13 Interpolated shear wave velocity for every 0.5 m
interval depth at RECESS 102
4.14 Average shear wave velocity for all research locations 105
4.15 Shear modulus of soils at Parit Nipah 106
4.16 Shear modulus of soils at Parit Sulong 108
4.17 Shear modulus of soils at Pontian 109
4.18 Shear modulus of soils at Penor 111
4.19 Shear modulus of soils at RECESS 112
4.20 Average shear modulus for all locations 115
4.21 Compressive wave velocity comparison of different
research location 121
4.22 Shear wave velocity from MASW and Seismic
Refraction (SR) at Parit Nipah 124
4.23 Shear wave velocity from MASW and Seismic
Refraction (SR) at Parit Sulong 125
4.24 Shear wave velocity from MASW and Seismic
Refraction (SR) at Pontian 125
4.25 Shear wave velocity from MASW and Seismic
Refraction (SR) at Penor 125
4.26 Shear wave velocity from MASW and Seismic
Refraction (SR) at RECESS 126
xvii
LIST OF FIGURE
2.1 Peat soils distribution in Malaysia (Kleine, 2010) 6
2.2 The relationship between Gmax, G, shear strain γ, and
shear stress τ in the hysteresis loop for one cycle of
loading (Zhang et al., 2005) 10
2.3 Typical results of peat shear modulus from levee bench,
levee midtoe and free field (Wehling et al., 2003) 11
2.4 Graph of shear modulus versus frequencies for all peat
samples (Zainorabidin and Wijeyesekera, 2009) 11
2.5 P1 and P2 with isotropic effective stress, σ’o, at 24 hour
confinement time (Kallioglou et al., 2007) 13
2.6 Peat profile at Mercer Slough (Kramer, 2000) 14
2.7 The location of downhole test at the levee crest and free
field (Wehling et al., 2003) 14
2.8 Propagation of (a) P-wave and (b) S-wave (astro.uwo.ca,
2003) 17
2.9 Propagation of Love wave and Rayleigh wave
(Reynolds, 2011) 19
2.10 The process of the MASW method to obtain a shear
wave velocity profile (Xia et al., 2000) 22
2.11 Illustration of MASW test spread (Neelima, 2010) 23
2.12 Vs profiles with (a) Vs max < 400 m/s (b) Vs profiles with
400 < Vs max < 600 and (c) Vs profiles with Vs max >
600 m/s (Wood et al., 2011) 24
2.13 Examples of the seismic waveform data in phase
velocity in frequency domain (Ivanov et al., 2001) 26
2.14 Seismic refraction technique (ASTM, 2007) 28
xviii
2.15 P-wave velocity soil profile for SL 1 (Zainal Abidin et
al., 2012) 29
2.16 Seismic refraction results of p-wave velocity profile
(Hamzah and Samsudin, 2006) 30
2.17 Snell’s law principle in seismic refraction (Redpath,
1973) 31
2.18 Arrival of seismic wave (Pavlovic and Velickovic,
1998) 34
3.1 Flow chart of seismic geophysical methodology 36
3.2 Flow chart for shear modulus estimation 37
3.3 Penetration of impact plate on peat soil during data
acquisition 39
3.4 Shot point location for point A, B and C 40
3.5 (a) Point A and (b) Shot C for offset distance 41
3.5 (c) Point C at centre of array line (continued) 41
3.6 Geological map at Parit Nipah (Jabatan Mineral dan
Geosains Malaysia, 1985) 42
3.7 Research location at Parit Nipah 43
3.8 Research location at Parit Sulong 44
3.9 Research location at MARDI station, Pontian 45
3.10 Research location at Penor 45
3.11 Research location at RECESS 46
3.12 External connection at the rear of seismograph 47
3.13 SeisTW Interface on seismograph 48
3.14 Acquisition setup interface 49
3.15 Setup for trigger sensitivity 49
3.16 Acquisition setup for noise monitor 50
3.17 Acquisition setup for filter 51
3.18 Interface for Layout Geometry Dialogue in seismograph 52
3.19 Equipment for MASW method 54
3.20 Spread line arrangement for five repeated tests 55
3.21 Location of shot point for the 1-D MASW method 55
3.22 Location of shot point for seismic refraction method 57
xix
3.23 Flowchart process of Pickwin module 59
3.24 Flowchart, process of WaveEq module 60
3.25 SeisOptPicker flow chart 61
3.26 SeisOpt@2D summary flow chart 62
3.27 Equipment of peat sampler 63
3.28 Measuring diameter of peat samples 64
3.29 Measuring length of peat samples 64
4.1 Comparison of peat density for every research location 72
4.2 Dispersion curve at Parit Nipah (a) Test 1 and (b) Test 2 73
4.2 Dispersion curve at Parit Nipah (c) Test 3 (d) Test 4 and
(e) Test 5 (continued) 74
4.3 Dispersion curve at Parit Sulong (a) Test 1 and (b) Test 2 75
4.3 Dispersion curve at Parit Sulong (c) Test 3, (d) Test 4
and (e) Test 5 (continued). 76
4.4 Dispersion curve at Pontian (a) Test 1 and (b) Test 2. 77
4.4 Dispersion curve at Pontian (c) Test 3, (d) Test 4 and (e)
Test 5 (continued) 78
4.5 Dispersion curve at Penor (a) Test 1 and (b) Test 2 79
4.5 Dispersion curve at Penor (c) Test 3, (d) Test 4 and (e)
Test 5 (continued) 80
4.6 Dispersion curve at RECESS (a) Test 1 and (b) Test 2 81
4.6 Dispersion curve at RECESS (c) Test 3, Test 4 (d) and
(e) Test 5 (continued) 82
4.7 Shear wave velocity profile at Parit Nipah (a) Test 1 and
(b) Test 2 84
4.7 Shear wave velocity profile at Parit Nipah (c) Test 3, (d)
Test 4. and (e) Test 5 (continue) 85
4.8 Shear wave velocity comparison at Parit Nipah 87
4.9 Shear wave velocity profile at Parit Sulong (a) Test 1
and (b) Test 2 88
4.9 Shear velocity profile at Parit Sulong (c) Test 3, (d) Test
4 and (e) Test 5 (continued) 89
4.10 Shear wave velocity comparison at Parit Sulong 91
xx
4.11 Shear wave velocity profile at Pontian (a) Test 1 and (b)
Test 2 92
4.11 Shear wave velocity profile at Pontian (c) Test 3, (d) Test
4 and (e) Test 5 (continued) 93
4.12 Shear wave velocity comparison at Pontian 95
4.13 Shear wave velocity profile at Penor (a) Test 1 and (b)
Test 2 96
4.13 Shear wave velocity profile at (c) Test 3, (d) Test 4 and
(e) Test 5 (continued) 97
4.14 Shear wave velocity comparison at Penor 99
4.15 Shear wave velocity profile at RECESS (a) Test 1 and
(b) Test 2 100
4.15 Shear wave velocity profile at RECESS (c) Test 3, (d)
Test 4 and (e) Test 5 (continued) 101
4.16 Shear wave velocity comparison at RECESS 103
4.17 Average shear wave velocity profile for all research
location 105
4.18 Shear modulus comparison for all tests at Parit Nipah 107
4.19 Shear modulus comparison for all tests at Parit Sulong 108
4.20 Shear modulus comparison for all tests at Pontian 110
4.21 Shear modulus comparison for all tests at Penor 111
4.22 Shear modulus comparison for all tests at RECESS 113
4.23 Shear modulus comparison from all research location 116
4.24 Compressive wave velocity profile at Parit Nipah 117
4.25 Compressive wave velocity soil profile at Parit Sulong 118
4.26 Compressive wave velocity soil profile at Pontian 118
4.27 Compressive wave velocity profile at Penor 119
4.28 Compressive wave velocity profile at RECESS 120
4.29 Compressive wave velocity graph of different research
location 121
4.30 Shear wave velocity from MASW and seismic refraction
(SR) at Parit Nipah 126
xxi
4.31 Shear wave velocity from MASW and seismic refraction
(SR) at Parit Sulong 127
4.32 Shear wave velocity from MASW and seismic refraction
(SR) at Pontian 127
4.33 Shear wave velocity from MASW and seismic refraction
(SR) at Penor 128
4.34 Shear wave velocity from MASW and seismic refraction
(SR) at RECESS 128
xxii
LIST OF SYMBOL AND ABBREVIATION
1D - One dimension
2D - Two dimension
cm - Centimetre
D - Damping ratio
dB - Desibel
e - Void ratio
g - Gram
G - Shear modulus
g/cm3 - Gram per centimetre cubic
Gmax - Maximum shear modulus
Hz - Hertz
kg - Kilogram
km - Kilometre
kPa - Kilo Pascal
m - Metre
m/s - Meter per second
mm - Millimetre
MPa - Mega Pascal
obs - Observed file
xxiii
OC - Organic content
rec - Received file
S/N - Signal to noise ratio
src - Source file
Tn - Natural period of vibration
Vs - Shear wave velocity
wo - Water content
γ - Shear strain
ν - Poisson’s ratio
ρ - Soil density
τ - Shear stress
K - Bulk modulus
π - 3.194
µs - micro second
CHS - Cross-hole seismic
DHS - Down-hole seismic
MASW - Multi-channel analysis of surface wave
P-wave - Primary wave or Compressional wave
RECESS - Research Centre of Soft Soil
SMS - Strong motion station
SR - Seismic refraction
S-wave - Secondary wave or Shear wave
UTHM - Universiti Tun Hussein Malaysia
xxiv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Calculation of peat bulk density for every location 143
B Apparent results at A, B and C point for every tests 149
C Shear wave velocity for all research location 152
D Shear modulus estimation of Peat soil 167
E Compressive wave first arrival for seismic refraction for
all research location 170
F Correlation from compressive wave velocity into shear
wave velocity 180
G Calculation used in research 182
H List of publication 184
1
CHAPTER 1
INTRODUCTION
1.1 Background of research
This research is about dynamic characterization of peat soil using field geophysical
method. There are demands on dynamic characteristics in construction especially in
planning and design stages. The critical and important structures to society such as
nuclear power plants, arch dams, hospitals and bridges demand for detailed dynamic
parameters to be used in investigating the dynamic soil–structure interaction (Francois
et al., 2007). In addition, dynamic characteristics of soil are considered as important
aspect in area prone to seismic activity (Kumar et al., 2013).
In dynamic characteristics, there are three main properties usually used in
geotechnical parameter such as shear modulus (G) and Damping ratio (D) and shear
wave velocity (Vs). These parameters are important for the design structures involving
dynamic load, such as building, bridge, roads and for site response analysis (Jafari et
al., 2002). In the conventional method, dynamic properties can be determined in the
laboratory using cyclic triaxial, torsional shear and resonant column test for
determining modulus of elasticity, shear modulus and damping ratio. In the field, these
parameters can be determined using plate loading test and geophysical seismic wave.
This research is focussed on the field test using geophysical seismic wave
methods and tested on the peat ground. Peat soil is very problematic soil for civil
engineers due to its unique characteristics. This soil has very high compressibility, low
bearing capacity, low shear strength and highly heterogeneous due to high moisture
content, organic content and fibre content, and thus cause the problem in design and
2
construction (Sing and Hashim, 2008). The peat soils is easily compressed and cause
high settlement when subjected to load. The settlement will continue in very long
period of time to reach maximum consolidation.
There are various geophysical seismic wave methods that have been used for
dynamic subsurface soil characterization such as refraction, reflection, multi-channel
analysis of surface wave (MASW), spectral analysis of surface wave (SASW) and
continuous surface wave (CSW). This research utilised two geophysical seismic
methods i.e. multi-channel analysis of surface wave (MASW) and refraction. Both of
these methods are commonly used for the determination of soil velocity profile for
geotechnical application. Multi-Channel Analysis of Surface Wave (MASW) has
provided 1-dimensional shear wave velocity profile. Meanwhile, seismic refraction
method is able to visualize in 2-dimensional of velocity compression wave or p-wave
profile. Both methods used an active source via hammering on the impact plate to
generate seismic wave. The seismic shear wave velocity and compression wave
velocity are used for computing the dynamic properties of soil.
1.2 Problem statement
Constructions on peat soils have experienced a lot of structural damage such as
buildings crack and roads embankment settlement (Duraisamy et al., 2007; Kazemian
et al., 2011). Peat soil can easily deformed due to the static and dynamic load such as
load from building, road, moving vehicles and vibrating heavy machineries. The
dynamic load from moving vehicles causes the peat ground vibrated, and thus
accelerates ground deformation (Mhanna et al., 2011; Ouyang, 2011). The
deformation of peat will damage the existing civil structures and cause major problems
to the society. Sarawak is the largest area covered by peat, and experiences problem to
infrastructure development. Similar problem also encountered in the area along the
coastal of Peninsular Malaysia. Therefore, it is important to determine the dynamic
properties peat. Via using the seismic geophysical method, it is the fastest and cost
effective way to determine the dynamic properties of soils which involving large
volume of measurement (Madun, 2012).
3
1.3 Aim of research
The purpose of this research is to determine the dynamic behaviour of peat soil such
as seismic wave velocity and shear modulus (G) at the field using geophysical seismic
wave techniques.
1.4 Objective of research
The objectives for this research are:
a) To determine peat soil wave velocity profiles using Multi-channel Analysis of
Surface Wave and seismic refraction methods.
b) To analyse the shear modulus (G) of peat using soil wave velocity.
c) To compare shear wave velocity between multi-channel analysis of surface
wave method and seismic refraction method.
d) To investigate and compare the dynamic behaviour of peat with inorganic soil.
1.5 Research scope
This research focuses on the characterization of the dynamic parameter of peat soil at
the field using geophysical seismic testing. There are two different types of soil that
have been investigated which are peat and soft clay. The research locations were at
Parit Nipah, Pontian, Parit Sulong, and Penor, Pekan for peat, and RECESS (soft clay).
Multi-channel Analysis of Surface Wave and seismic refraction methods were used to
determine seismic wave velocity and to compare between these methods. The peat
sampler was used for verifying the peat layers and determining peat density for
estimation of peat shear modulus.
1.6 Research significant
This research investigates the dynamic properties using geophysical seismic wave
velocity. The significances of this research are as follows:
a) Seismic velocity profile of peat soil can be used to determine the dynamic
characteristics of peat soil.
4
b) Preliminary site investigation using Multi-channel analysis of surface wave
(MASW) and seismic refraction able to obtain soil profile information.
c) Able to identify suitable geophysical seismic method for the peat ground
investigation.
1.7 Thesis layout
Thesis layout is as followings:
a) Chapter two: Literature review on characteristics of peat and its properties. The
dynamic behaviour of soil including past researches on shear wave velocity
and shear modulus has been explained in this chapter. Literature reviews on
seismic waves and seismic geophysical methods such as Multi-channel
Analysis of Surface Wave and Seismic Refraction have been explained.
b) Chapter three: This chapter explains on the challenges of the seismic
geophysical tests on peat and characteristics of all research locations. Field
configuration of seismograph and seismic geophysical methods data
acquisition on field also have been explained. For the determination of peat
density using peat sampler has been defined.
c) Chapter four: Since peat sampler has been used, thus soil profile for every
location has been shown to differentiate peat layer and soft clay or clay soil
layer. The results of peat densities were discussed. Furthermore, shear wave
velocity, compressive wave velocity and estimation of peat shear modulus also
have been shown in this chapter. Finally, results on correlated shear wave
velocity from compressive wave velocity of seismic refraction method were
compared with shear wave velocity of MASW method to differentiate their
suitability for seismic wave velocity soil profile for peat.
d) Chapter five: This chapter shows the summary and conclusion in achieving the
aim of this research. The research aim has been achieved by completing the
four objectives that can be concluded in this chapter.
5
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter discusses on the literature reviews involved in dynamic properties
characterization of peat soil. Properties of peat soil were reviewed in this chapter and
it is very important to understand the effect of geotechnical properties towards the
seismic wave propagation. Dynamic properties in soil are discussed since this research
involves the dynamic behaviour of the soil. Seismic geophysics technique is the main
technique that was used in this research. Therefore, the introduction of geophysics is
explained and theory about multi-channel analysis of surface wave (MASW) and
seismic refraction method were also described.
2.2 Peat soil
Peat is formed by the accumulation of organic material that undergoes partially
decomposition process with proper condition. Peat is a combination of fragmented
organic and animal matter and formed in wetland under appropriate anaerobic
conditions for long periods (Hashim and Islam, 2008) (Zainorabidin et. al., 2010). Peat
soil is an organic with content more than 75 % (Kolay et al., 2011) which caused a lot
of problems for construction due to unpredictable behaviour of its properties. Peat soil
is very unstable soil, which contains organic materials, has high water content (more
than 100%), high compressibility (0.9 to 1.5) and low strength (typically 5 to 20 kPa)
(Mohd Razali et al., 2013). It is in the category of problematic soil because of having
the low shear strength and high compressibility (Said and Taib, 2009). Due to various
6
organic content in peat soil, it has large air void thus, has a high void ratio. Peat has
very high in-situ void ratio because of the very compressible and bendable hollow
cellular fibres form an open entangled network of particles and the high initial water
content (Kazemian et al., 2011). Under loads, peat soil will tend to settle and cause
soil deformation, which is not suitable for constructions structural performance. Peat
poses serious problems in construction due to its long-term consolidation settlements
even when subjected to a moderate load (Youventharan et al., 2007)). It is generally
considered that peat soil is not suitable for supporting foundations or loadings in its
natural state (Kolay et al., 2011).
In Malaysia, there are about 2.7 million hectares of peat soils and organic soils
that covers 8% of land in this country (Said and Taib, 2009). Sarawak has the largest
area of peat soil in Malaysia followed by peninsular Malaysia and Sabah region. Table
2.1 shows the percentage of peat land in Malaysia (Kleine, 2010). Peat soils
distribution in Malaysia is highlighted with green as shown in Figure 2.1.
Table 2.1: Percentages of peat land area in Malaysia. (Kleine, 2010).
Region Area (Hectare) Percentage (%)
Sarawak 1,697,847 69.08
Peninsular Malaysia 642,918 26.16
Sabah 116,965 4.76
Figure 2.1: Peat soils distribution in Malaysia (Kleine, 2010).
7
2.2.1 Properties of peats
Peat is divided into three major types such as hemic, sapric and fibrous (Huat et al.,
2011) where each type has it is own characteristics such as degree of humification,
moisture content, fibre content, liquid limit and etc. Table 2.2 shows the properties of
peat according to the previous researchers. Based on American Society for Testing and
Materials, ASTM D 1997-91 (2001), the types of peat are characterized based on their
fibre contents where fibrous peat has fibre content greater than 67%, hemic is between
33% and 67 % while sapric is less than 33% of fibre content. The percentage of fibre
contents affected the shear strength, void ratio and water content of peats (Michael,
2005). High fibre content contributed to higher shear strength, void ratio and moisture
contents (Kazemian et al., 2011). Other properties of peats such as poisson’s ratio
ranges between 0.35 – 0.5 (Huat et al., 2011) (Timothy et al., 2003) and the average
is 0.43.
Table 2.2: Properties of peat according to previous researchers.
Properties Fibrous Hemic Sapric
Moisture Content, W (%) 350 – 598a,c 472 – 554 569 – 598e
Liquid Limit, LL (%) 200 – 550b,c 140 – 150 240 – 330d
Specific Gravity (Gs) 1.07 - 1.63b,c 1.14 – 1.40 1.49 – 1.56d
Organic Content (%) 50 – 95b 92 - 96 70 – 93d,e
Fibre Content (%) 77 – 84a 43 – 63 31 – 32d
pH 2 – 6b,c 3.75e
Void Ratio (e) 9 - 12.5a 4.13 – 5.77d,e
Von Post Classification H3b H5 – H6 H7 - H8d,e
Reference
Dehghanbanadaki et al., 2013a
Zainorabidin, and
Wijeyesekera, 2008b
Kolay et al., 2011c
Zainorabidin et al., 2010
Youventharan et al., 2007e
Aldin, 2014d
8
2.3 Dynamic behaviour of soil
The dynamic behaviour of soil involved the mechanical properties of soil, which
becomes an important aspect that needs to be considered for structures influences by
dynamic movement. The knowledge of the dynamic response of the soil- structure is
required for dynamic structural analysis of the superstructures (Luna and Hadi, 2000)
which, in turn relies on dynamic soil properties. Soils tend to behave differently and
in a high complexity under dynamic loading such as earthquake, moving traffic,
machineries and bomb blasting. The loadings will contribute to an accumulation of
shear strains, and when the threshold shear strain has been exceeded, the shear
modulus will be reduced (Schneider et al., 1999). Dynamic loading is distinguished
by the magnitude of the loading fluctuating with time and the deformations of the soil
which consists of both recoverable and permanent displacement (Bødker, 1998).
Dynamic properties of soil can be determined by field measurement and
laboratory measurement of low strain (<0.001%) and high strain (>0.01%)
respectively. Table 2.3 shows the field and laboratory tests implemented for dynamic
measurement of soil. There are several typical mechanical properties of soil associated
with dynamic behaviour of soils that are determined by field investigation and
laboratory test such as the shear modulus (G), shear velocity (Vs), damping ratio (D)
and poisson’s ratio (ν) (Luna and Hadi, 2000). According to Kumar et al., (2013),
dynamic properties of soils, particularly shear wave velocity, variation of stiffness or
modulus reduction and material damping with strain levels, and liquefaction
susceptible parameters are the primary input parameters for various dynamic studies
and investigations. In dynamic soils research, various parameters influence soil
dynamic behaviour such as relative density, confining pressure, soil plasticity, strain
amplitude, frequency and magnitude of cyclic loading (Kumar et al., 2013).
In many researches of peat soil, there are three typical dynamic properties of
field test and laboratory test which are shear modulus, shear wave velocity and
damping ratio. Shafiee et al., (2013) also claimed that the dynamic properties of peat
that typically investigated in prior work with cyclic shear strain are the differences
between shear modulus and damping ratio.
9
Table 2.3: Field and laboratory test implemented for dynamic measurement of soil. (Kumar et al., 2013)
Field test Laboratory test
Low strain (< 0.001%)
High strain (> 0.01%)
Low strain (< 0.001%)
High strain (> 0.01%)
Seismic reflection and refraction Steady-state Vibration Spectral and Multi-channel analysis of surface waves (SASW and MASW) Seismic borehole survey (Cross-hole, Down-hole and Up-hole) Seismic cone tests
Standard penetration test (SPT) Cone penetration test (CPT) Dilatometer test (DMT) Pressuremeter test (PMT)
Resonant column test Ultrasonic pulse test Piezoelectric bender element test
Cyclic triaxial test Cyclic direct shear Test Cyclic torsional shear test
Shear modulus is a resistance to deformation when subjected to shear stress
and directly related with shear strength properties when soil is subjected to loads. Shear
modulus of the soil also represents the soil stiffness (Zhang et al., 2005). Figure 2.2
shows the relationship of between Gmax, G, shear strain γ, and shear stress τ in the
hysteresis loop for one cycle of loading (Zhang et al., 2005). In geophysical theory,
shear modulus related to shear velocity is shown in formula 2.1 (Aboye et al., 2011).
Increment in shear velocities indicates the increasing value in shear modulus.
10
Figure 2.2: The relationship between Gmax, G, shear strain γ, and shear stress τ in the hysteresis loop for one cycle of loading (Zhang et al., 2005).
Gmax = ρVs2 (2.1)
Where Gmax is small-strain shear modulus and ρ is density of soil
2.3.1 Previous researches of shear modulus (G) on peat
Wehling et al. (2003) performed triaxial test on peat to determine shear modulus at
Sacramento–San Joaquin Delta in California. Samples were obtained by using thin-
walled tubes from three locations between the levee crest and the free field with in situ
vertical effective stresses were ranged from about 12 kPa in the free field to about 135
kPa beneath the levee crest. Wehling et al. (2003) have shown typical results of peat
shear modulus from levee bench, levee midtoe and free field that have been
consolidated to their estimated in-situ vertical stresses as shown in Figure 2.3. The
shear modulus from beneath levee bench was 4.8 MPa which greater than beneath the
midtoe, 3.0 MPa which were also greater than samples from the free field with 0.9
MPa at 0.0001% strain. Wehling et al. (2003) claimed that the difference of shear
modulus may due to the effect of sample bedding plane rather due to the effect of
different consolidation stress.
11
Shea
r mod
ulus
(MPa
)
Figure 2.3: Typical results of peat shear modulus from levee bench, levee midtoe and
free field (Wehling et al., 2003).
Zainorabidin and Wijeyesekera (2009) attempted using the undrained cyclic tests on
different peats. Their samples were gathered from Holme Fen Post, Cambridgeshire
and Solway Post, Carlisle. After performing the cyclic tests, the peat type,
microstructure, loading frequency, confining pressure and index properties have been
discussed for different peats. From the cyclic tests, there were various results obtained,
such as axial deformation response to cyclic deviator stress, pore water response to
cyclic deviator, displacement response to a number of cycles of different frequencies,
damping ratio, (%) for different frequencies (Hz) and dynamic shear modulus (MPa)
at different frequencies (Hz). Figure 2.4 shows plotted graph of shear modulus versus
frequencies for all peat samples.
Figure 2.4: Graph of shear modulus versus frequencies for all peat samples (Zainorabidin and Wijeyesekera, 2009).
12
Zainorabidin and Wijeyesekera (2009) have determined that shear modulus of peats
were ranged between 0.5 MPa and 1.7 MPa at a frequency between 0.5 Hz and 2 Hz.
The test results indicated that the dynamic shear modulus of peats increased with the
increment of frequencies. They stated that the shear modulus and the damping ratio
increased with the increment of frequency caused by the soil viscous component of
resistance. They claimed that scattered results due to the influence of changes in
effective confining pressure made these parameters slightly inconsistent. These results
indicated the complex nature of the behaviour of these peat materials, and they
suggested in considering a wide range of frequencies to characterize the effects of rate
dependence on peats response.
Kishida et al., (2009) has conducted nonlinear dynamic properties tests of
highly organic soils from Montezuma Slough and Clifton Court in the Sacramento-
San Joaquin Delta in California. They have performed cyclic triaxial, resonant column
and torsional shear tests with in situ vertical effective stresses ranged between 16 and
67 kPa. Kishida et al., (2009) used cyclic triaxial test to determine shear modulus. At
Montezuma Slough, the peat with highly organic soils has considerably different
organic characteristics where organic components that ranged from highly fibrous to
highly decomposed and amorphous. Shear modulus for the peaty organic samples have
a modulus of about 1.0 MPa. Meanwhile, at Clifton Court, the peat sample is highly
fibrous with individual fibres ranged from hair like threads less than 1 mm thick, to
tubular plant stems up to 3 mm in diameter and have peat shear modulus about 8 MPa.
Referring to Kishida et al., (2009), the difference in the cyclic triaxial test was mainly
caused by the organic content. The organics at Montezuma Slough were generally
highly decomposed and often amorphous, whereas the organics at Clifton Court were
highly fibrous and only mildly decomposed.
A research had been conducted by Kallioglou et al. (2007) to determine shear
modulus and damping ratio of organic soils using resonant-column test. They showed
the variation of small-strain shear modulus, Gmax, of two peats assigned as P1 and P2
with isotropic effective stress, σ’o, at 24 hour confinement time for the tested peats in
Figure 2.5. They have obtained maximum shear modulus for P1 that ranged between
15.9 and 27.8 MPa with effective stress ranged between 39 and 374 kPa. Meanwhile,
shear modulus for P2 ranged from 60.7 until 73.1 MPa with effective stress from 111
until 396 kPa where the effective stress was approximately equal to the in-situ effective
13
stress. They stated that high shear modulus was might due to strong similarity to very
plastic clays.
Figure 2.5: P1 and P2 with isotropic effective stress, σ’o, at 24 hour confinement
time (Kallioglou et al., 2007).
2.3.2 Previous researches on shear wave velocity (Vs) on peat
There were various determinations of peat soils shear velocity that have been done by
researchers in order to characterize its dynamic properties. Ross et al. (1998) have
conducted dynamic properties of Sherman Island to determine the shear wave velocity
of peat using bender element tests, and seismic downhole OYO Suspension P-S
logging system. They compared the laboratory and in-situ and they found out that
shear wave velocity from laboratory test that values from 81 until 87 m/s was slightly
lower with in situ test values from 83 – 90 m/s at depth 12.8 until 13.7 m but still
showed good agreement for both testing.
Kramer (2000) had determined peat shear wave velocities at Mercer Slough in
Bellevue, Washington. The site condition on surface was flat and heavily overgrown
with horsetails,grasses, and small trees. The thickness of peat was varied across the
slough with maximum thickness approximately at 18 m. Figure 2.6 shows the peat
profile at Mercer Sloughusing seismic cone profiling. He performed seismic cone
profiling near to the three boring locations. From the results of seismic cone testing,
the shear wave velocities of peat were as low as 12 until 30 m/s. Kramer (2000) found
14
that the propagation of shear waves through the peat was difficult in the extremely soft
unfilled areas.
Figure 2.6: Peat profile at Mercer Slough (Kramer, 2000).
Wehling et al. (2003) performed nonlinear dynamic properties of a fibrous
organic soil at Sherman Island and determined the shear wave velocity using seismic
downhole OYO Suspension P-S logging system. They presented the shear wave result
of peat on levee crest and free field as shown in Figure 2.7. The data obtained from the
levee crest were ranging between 88 and 129 m/s, while free field showed very low
shear wave velocity which ranging between 22 and 27 m/s. The differences of shear
wave peat beneath the crest were due to sandy silt interlayers. Figure 2.4 shows the
location of downhole test at the levee crest and free field.
Figure 2.7: The location of downhole test at the levee crest and free field (Wehling et al., 2003).
Other researchers like Rafiu and Ganiyu (2013) have attempted estimation of shear
wave velocity for near surface characterization at Ifako/Gbagada Area of Lagos State,
15
Nigeria. They used Multi-channel Analysis of Surface Wave (MASW) technique to
determine the shear wave velocity towards the public safety and mitigation of property
damage by delineating the existing or potential hazards related to subsidence,
distressing and weakening of structures. There were four tests where MASW technique
had been conducted. The results showed average shear wave velocity, 80 – 110 m/s
approximately at 4 until 12 meter depth of peat. The low shear wave velocity was
considered as very loose sediment that affected the structures safety.
2.4 Determination of peat bulk density using peat sampler
In-situ bulk density of peat has been determined for quantifying stock carbon by
several researchers. Most often method used to determine peat bulk densities was by
using peat sampler or also known as Russian sampler. This peat sampler penetrated
through peat layer from surface until 10 meter depth. The equipment of peat sampler
will be explained in subtopic 3.8 in Chapter 3. According to Agus et al. (2011), peat
auger is recommended since it can be used to sample almost undisturbed soil from the
top to bottom layers under inundated conditions. For stock carbon quantification, most
researchers extracted samples in bulk samples and then dried until reached a constant
dry weight.
Farmer et al. (2014) had determined that peat dry density for quantifying
carbon (C) stocks in five tropical peat sites in Sumatra, Indonesia where two in an
intact peat swamp forest, one in a logged forest and two in an oil palm plantation. They
extracted peat samples by using an Eijkelkamp peat auger and each core was sampled
in 50 cm increments depth. From the peat samples, they obtained 0.12 g/cm3 for dry
density in swamp forest and from oil palm plantation, the reading was 0.15 g/cm3.
Another research oncarbon stocks in the peatlands in Great Lake region was conducted
by Ott (2013). He determined the peat bulk density by using Russian corer (Aquatic
Research Instruments) that used the same technique as Eijkelkamp peat auger for every
50 cm increments. From his research results, he obtained average dry density of peat
which was 0.16 g/cm3 where the lowest bulk density was 0.13 g/cm3 and then increased
to 0.17 g/cm3. Wellock et al. (2011) performed Soil organic carbon stocks of afforested
peatlands in Ireland. They had determined that peat density varied and did not increase
with depth. Wellock et al. (2011) used peat sampler Eijkenkamp Agrisearch
16
Equipment at four different points with increment of 0.5 m depth. There were three
different sites where dry density ranged between 0.118 – 0.133 g/cm3.
2.5 Seismic wave
Seismic waves propagate through earth whenever there are events of seismic activities
such as earthquake, moving traffic, vibrating machine, explosion or any movement
that impacts ground and creates seismic waves. Seismic waves are divided into two
general waves such as body wave and surface wave. Body wave is faster and non-
destructive while surface wave is much slower but very destructive. Body wave
contains only about 6% of the generated energy while the surface wave contains almost
2/3 of the energy when reflected or refracted back to surface (Karlsson, 2011).
2.5.1 Body wave
There are two body elastic body waves, such as compressive wave (p-wave) and shear
wave (s-wave) as shown in Figure 2.7. These waves travel in a medium (soils/rocks)
will be subjected to the elastic characteristics and can move in all directions through
the means of direct, reflected and refracted wave. The p-wave velocity is double the s-
wave velocity and when the poisson’s ratio equals to 0.33 (Reynolds, 2011). The
maximum poisson’s ratio is 0.5, for hard rock approximately 0.05. For loose,
unconsolidated sediment is 0.45 and the average poisson’s ratio is 0.25 (Reynolds,
2011).
17
Figure 2.8: Propagation of (a) P-wave and (b) S-wave (astro.uwo.ca, 2003).
P-wave is also known as compressional wave or longitudinal wave and it is the fastest
wave travels in the earth. P-wave is a type of elastic wave that can travel through gases
(as sound waves), solids and liquids including the earth. (Bery and Saad, 2012). The
propagation of compressive wave is always in longitudinal directions where the
particles are vibrated, move parallel with the direction of wave energy in isotropic and
homogeneous condition (Bery and Saad, 2012). The bulk modulus, shear modulus and
density are factors affecting the determination of p-wave velocity as shown in Equation
2.1 (ASTM D5777, 2000).
Vp = ���K + 43G� ρ� � (2.2)
Where: Vp = Compressive wave or P-wave velocity
K = Bulk modulus
G = Shear modulus
ρ = density
S-wave is also known as transverse wave or shear wave due to wave motion, move in
sideways at right angle to the direction of propagation. S-wave can only determine the
shear modulus of solid material but cannot propagate liquid and gases since its shear
modulus is zero (Lowrie, 2007). Thus s-wave cannot travel through water. Shear wave
18
velocity is affected by the shear modulus and density of soil as shown in equation
(Bernard et al., 2012).
Vs = �Gmax
ρ (2.3)
Where:
Vs = Shear wave velocity
Gmax = Maximum shear modulus
ρ = Soil density
2.5.2 Surface wave
Surface wave is the slowest seismic wave travels on the surface of the earth but it is
more destructive than body waves. These waves can be generated from various sources
such as moving traffic, vibrating machineries, running people and commonly most
destructive surface wave is generated by seismic earthquake. Adel et al. (2013)
mentioned that surface wave has the strongest wave energy with the highest signal-to-
noise ratio which is an effective source for the near-surface characterization. Surface
wave characteristics are low velocity, low frequency and high amplitude where the
wave consists propagation vertical and radial component (Eker, 2012).
Surface wave is divided into two typical waves, such as Rayleigh wave and
Love wave. For researchers, Rayleigh wave is always utilized in the exploration of
shallow subsurface and soil characteristics. The seismic energy from surface wave is
dispersed in the form of Rayleigh wave and the velocity depends on the elastic
constants near the surface (Mathews et al., 2000). Figure 2.9 shows the propagation
of Love wave and Rayleigh wave.
19
Figure 2.9: Propagation of Love wave and Rayleigh wave (Reynolds, 2011).
Surface wave has a phase velocity that sensitive to the shear wave velocity as surface
wave is 0.9 to 0.95 times of shear wave with poisson’s ratio is 0.25 (Mathews et al.,
2000) (Reynolds, 2011). The velocity of surface waves is near to. The velocity of shear
waves (Abbiss and Viggiani, 1994). This wave disperses as travel in the soil and
provides the difference of wavelength and cause the difference of survey depth. When
the active source induces into the ground, the source efficiency of surface wave greater
than body wave such as surface wave has 67%, while s-wave and p-wave gives 26%
and 7% respectively. Surface wave also capable to survey low velocity, soil layer (soft
soil) that position under high velocity soil layer (hard soil) (Reynolds, 2011).
2.6 Seismic wave attenuation
Seismic wave attenuation is very important factor in seismic research for good quality
data of seismic. The attenuation is caused by geometric, intrinsic or scattering effects.
The geometric effect occurs as an elastic wave front expands when energy density
decreases (Harsh and Vernon, 2014). Intrinsic effect involved with energy lost to heat
an internal friction during the propagation of an elastic wave (Harsh and Vernon,
20
2014). Meanwhile, scattering effects involved elastic energy that is scattered and
redistributed into directions away by reflection, refraction, and diffraction from the
geophones or into waves arriving slow at the geophone (Harsh and Vernon, 2014)
(Reynolds, 2011).
As seismic wave travels in the ground, the energy or amplitude of the wave
will be dissipated through distance from the seismic source. This dissipation is the
consequence of wave energy losses in the subsoil and it is named as “attenuation”
(Dikmen, 2005). This attenuation is a complex phenomenon involving several
mechanisms and interactions that cause to seismic energy dissipation (Dikmen, 2005).
In seismic velocity profile, the velocity itself will be changed, not showing the accurate
velocity. Almost all seismic energies are in a layer about one wavelength deep. Thus,
when material properties change with depth, the velocity of surface waves changes
with the frequency of the energy excitation because the different wavelengths sample
materials with different average properties (Abbiss and Viggiani, 1994).
Some portion of the velocity will show incorrectly to the stiffness of the soils
(Paul, 1998). Attenuation effect is different between body wave and surface wave. In
body wave, the energy of seismic wave will be dissipated by depth as travel interior of
earth while surface wave energy dissipates with distance as wave travel parallels with
the ground surface. The main consideration of attenuation or damping in geotechnical
parameter is a void percentage (e), and organic density. According to Beamish (2014),
higher porosity materials indicate high void ratio and low density organic soils would
affect greater attenuation towards higher saturation levels.
2.7 Seismic geophysical method
Most seismic geophysics methods involve in-situ test to evaluate soil properties of
undisturbed condition and less material disturbance. Direct measurement of soil or
rock stiffness in the field has the advantage of the minimal material disturbance
(Boominathan. 2004). Luna and Jadi (2000) stated that the geophysical field tests have
the advantage to test undisturbed soil in the actual field condition with the actual
effective stress and drainage conditions. In-situ test is divided into two methods such
as invasive and non-invasive techniques. The invasive techniques are like downhole,
uphole, and crosshole. Meanwhile, non-invasive methods are like spectral analysis of
surface wave (SASW) method, multichannel analysis of surface wave (MASW)
21
method and seismic refraction method. For accuracy in determining dynamic soil
properties, many researchers preferred invasive method since it can directly measure
wave in the ground without major interferences from surface activities such as traffics,
vibrating machine or anything creates vibration. Soupios et al. (2005) also said that
most scientists preferred to apply Crosshole and Downhole Seismic (CHS and DHS)
tests, since they are highly accurate methods for determining material properties of
rock and soil sites. Non-invasive method is a technique using geophone sensor and is
placed on the ground surface to capture seismic wave velocity without doing any major
damage to the ground surface. Recently, Multi-channel Analysis Surface Wave
(MASW) is the most popular method for non-invasive method because it can obtain
large volume information on soil formation. MASW method was developed to
estimate shear wave velocity profile from surface wave energy and it is powerful, rapid
and cost effective tool for constraining shallow wave velocity structures (Park et al.,
1999)
2.7.1 Multi-channel analysis of surface wave (MASW)
Multi-channel analysis of surface wave is well-known by the researchers to determine
shear wave velocities on the field for subsurface characterization. This method uses an
active source which means seismic energy with intention generated to create seismic
waves at specified location along linear direction with spread length (Eker, 2012). The
recorded propagation of surface wave was processed through Fourier transform and
inversion dispersion curve of phase velocities in the frequency domain of surface
waves. An iterative inversion process that requires the dispersion data and estimations
of Poisson’s ratio and density then used least-squares approach to allow automation
for calculation of shear wave velocity profile (Park et al., 1999). The shear velocity
and soil profile can be determined when measuring the phase velocity of Rayleigh
waves at different frequencies (Neelima, 2010). The MASW method commonly used
4.5 Hz geophones to record the propagation of surface waves. Park et al., (1999)
suggested on using twelve recording channels connected to single low-frequency
geophones (<10 Hz).
This method is ideal for effective identification and isolation of seismic noise
such as body waves, scattered, and non – source generated surface waves and higher
mode of surface waves according to distinctive trace to trace comparison of coherency
22
in arrival time and amplitude (Xia et al., 2000). The MASW method can take out
accurate phase velocities of Rayleigh wave ground roll (Xia et al., 2000). Figure 2.10
shows the process of MASW method in obtaining shear wave velocity profile. In
general, the propagation velocities of shear waves and Rayleigh waves provide the
most valuable data for stiffness measurements in near-surface deposit is (Mathew et
al., 2000).
Figure 2.10: The process of the MASW method to obtain a shear wave velocity profile (Xia et al., 2000).
2.7.1.1 Past researches on multi-channel analysis of surface wave
Neelima (2010) is one of the researchers that used MASW for characterization in Delhi
region. According Neelima (2010), there was borehole data and based on the data, the
soil profiles were covering almost the entire region to study the sub soil heterogeneity.
Multi-channel analysis of surface wave was conducted in Delhi at various locations
for estimation of 2-D velocity profile. MASW field setup is shown in Figure 2.11.
Neelima (2010) used 48 channel signal enhancement seismographs and geophones of
4.5 Hz. All the geophones connected to seismograph by the connecting cable. She used
11 kg of wooden hammer and then impacted on 165cm2 aluminium plate to generate
surface wave source. For each test site, there were 13 shots created to increase noise-
signal ratio. All the data were analysed using SeisImager/SW software which consists
of three parts (Pickwin95, WaveEq, and GeoPlot).
23
Figure 2.11: Illustration of MASW test spread (Neelima, 2010).
Wood et al., (2011) had also conducted dynamic characterization of Christchurch
strong motion stations at three different sites in New Zealand. He has tried to
characterize the small-strain dynamic properties at 13 out of the 19 strong motion
stations in Christchurch, Lyttelton, and Kaiapoi. Wood et al., (2011) used active and
passive source of surface wave testing to determine shear wave velocity (Vs) profiles
at the indicated strong motion stations. Wood et al., (2011) used a combination of the
spectral analysis of surface waves (SASW) and multi-channel analysis of surface wave
(MASW) for active source method, whereas passive source method used the
combination of linear and 2-D microtremor array method (MAM). Vs profiles derived
from surface wave testing were used to calculate the average Vs over the top 30m of
the subsurface and to estimate the natural period of vibration (Tn) at each strong motion
station (SMS).
Wood et al., (2011) performed surface wave testing at 13 SMS close to the
station, but some testing was conducted approximate 300m from SMS because of the
test area limitation. He used a combination of active source (SASW and MASW) and
passive source (1-D and 2-D MAM) to determine the shear stiffness and layering
underneath each station. Wood et al., (2011) selected a receiver array composed of 24
unit geophones (4.5 Hz) with spacing between geophone approximately 1.5m with
total spreadline length is 35m for linear array (1-D) surface wave testing. Then he
analysed MASW data with frequency domain beamformer methods. A dispersion
curve from each source offset was created by picking the maximum spectral peak in
24
the frequency/wavenumber domain. Wood et al., (2011) analysed passive data using
two-dimensional slowness-frequency (p-f) transform in SeisOpt ReMi software.
Wood et al., (2011) plotted shear wave velocity profiles for each strong motion
station and all the profiles achieved depth at least 30m below the surface, while other
profile extends depth to 60m deep. He grouped the Vs profiles according to the
maximum velocity encountered (Vs max) in Figure 2.12 (a) is for profiles with Vsmax
< 400 m/s, Figure 2.12 (b) is for profiles with 400 m/s < Vs max < 600 m/s, and Figure
2.12 (c) is for profiles with Vs max > 600 m/s. Wood et al., (2011) stated that from
these figures, greater profiling depths were possible at stiffer sites (i.e., Sites with
greater Vs max values). He had expected that most of the profiles have a soft soil layer
(Vs < 200 m/s) ranging from 6 to 20 m thick near the surface. Only three sites have the
thickest and/or softest soil layers, which are in excess of 10-m thick with Vs of 160
m/s or less.
Figure 2.12: Vs profiles with (a) Vs max < 400 m/s; (b) Vs profiles with 400 < Vs max < 600 and (c) Vs profiles with Vs max > 600 m/s (Wood et al., 2011).
135
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