Investigation of soil liquefaction and geotechnical properties in Kathmandu
Japan-Nepal Urgent Collaborative research/survey program (J-RAPID)
Final Workshop June 21-22 ,Kathmandu Nepal
Mitsu Okamura, Ehime University (Project Leader) Netra Prakash Bhandary, Ehime University. Narayan Prasad Marasini, Ehime University. Ikuo Towhata, Kanto Gakuin University.
Surya Narayan Shrestha, NSET (Nepal side leader) Indra P. Acharya, Tribhuvan University . Sujan Raj Adhikari, NSET Dinesh Pathak, Tribhuvan University
Abstract of the project • The peak accelerations of the 2015 Nepal earthquake observed at a few locations in
Kathmandu valley were approximately 180gals. Although this acceleration was much smaller than that expected (i.e. 300 gal), extensive soil liquefaction was observe at several locations in the vicinity of major rivers in Kathmandu city. This strongly indicate that soils in the city are quite prone to liquefaction and liquefaction assessment is of great importance to prepare for stronger earthquakes in the future.
• Because of the uniqueness of soils in Kathmandu, which are rich in Mica, liquefaction assessment methods established based on the experiences in Japan and the US have to be verified. In order to refine or reestablish liquefaction assessment methods, identification of field evidences of liquefaction including sand volcanos and lateral spreading are necessarily and the 2015 April earthquake provided us a valuable opportunity to do this. Our research team will conduct field survey, in-situ tests as well as laboratory test described below and establish a liquefaction assessment method which is suitable for Kathmandu.
• Extensive field survey to identify locations of soil liquefaction all over the valley and summarize in a map.
• In-situ tests at several liquefied sites including boring, standard penetration tests, undisturbed soil sampling and PS logging. Based on test results we will be able to prepare relationship between N value or S wave velocity and threshold acceleration which separates liquefied and non-liquefied sites.
• Laboratory tests on samples including physical test, cyclic triaxial test to measure liquefaction strength and X-ray deflection test. It is expected from these tests that liquefaction strength characteristics of Kathmandu soils, which may exhibit strong influences of Mica contents, are revealed.
• Extensive microtremor measurements will be conducted all over the valley which is expected to reveal local amplification characteristics.
Background • Peak accelerations of the 2015 Earthquake in Kathmandu was around
160gal (Dixit et al., 2015; Goda et al. 2015) • Observed Peak acceleration is less than that expected (i.e.<300gal) • Even in small acceleration, extensive soil liquefaction was observed at
several locations in Kathmandu city. • This strongly indicate that soils in the city are quite prone to liquefaction
and liquefaction assessment is of great importance to prepare for stronger earthquakes in the future.
Acc
eler
atio
n (c
m/s
/s)
40 60 80 100 120-300-200-1000100200300
Time (sec)
Max. acc. at the central area of KTM, Kanti path= 150-182 gal
• Kathmandu soil is unique and heterogeneously distributed. • Kathmandu soil are rich in Mica, liquefaction assessment methods
established based on the experiences in Japan and the US have to be verified.
• In order to refine or reestablish liquefaction assessment methods, identification of field evidences of liquefaction including sand volcanos and lateral spreading are necessary.
• and the 2015 April earthquake provided us a valuable opportunity to do this.
Background
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Diffr
action c
ounts
(cps)
Angle,2θ (°)
X-ray diffractometryQuartz
CalciteMica
feldspar
MicaMica(B)
Mica(W)
MicaQuartzfeldspar
X-ray diffractometric
Objectives To conduct extensive field survey, in-situ tests as well as laboratory tests described below and establish a liquefaction assessment method which is suitable for Kathmandu; • Extensive field survey to identify locations of soil liquefaction
all over the valley and summarize in a map. • In-situ tests at several liquefied sites including boring, SPT,
undisturbed soil sampling and PS logging to prepare the relationship between N value or S wave velocity and threshold acceleration which separates liquefied and non-liquefied sites.
• Laboratory tests on samples including physical test, cyclic triaxial test to measure liquefaction and reveal the liquefaction strength characteristics of Kathmandu soils, which may exhibit strong influences of Mica contents.
• Microtremor measurements to reveal the local amplification characteristics of Kathmandu valley.
: Liquefied by 2015 earthquake
: Liquefied by 1934 earthquake
Ramkot
Manamaiju
Guheswori
Syuchatar
Bungmati
NEC
Mulpani
Jharuwarashi
Hattiban
Imadol
Tundikhel
Nayabazar
Kamalvinayak
Identification of liquefaction An extensive field survey was conducted all over the valley and 11 liquefied locations were identified.
Observed liquefaction
Approx.. 150m Silty sand
At Jharuwarashi
Observed liquefaction Cont….
Approx.. 150m Silty sand
0.01 0.05 0.1 0.5 1 5 100
20
40
60
80
100
Grain size (mm)
Perc
ent f
iner
by
wei
ght
Jharuwarashi area (L1) Bungamati are (L2)
At Bungmati
At Nepal Engineering College (NEC) area
Observed liquefaction Cont….
At manamaiju area
Liquefaction of central KTM in 1934
Liquefaction in Tundhikhen and Nayabazar area by the 1934 earthquake (after Rana, 1935)
Nayabazar Tundikhel
: Liquefied by 2015 earthquake
: Do not liquefied by 2015 earthquake
Ramkot
ManamaijuNEC
Imadol
Manahara
• Manamaiju
• Imadol
• NEC
• Ramkot
• Manahara
In-situ tests Standard Penetration test (SPT)
Undisturbed soil sampling
PS-logging
Rotary wash boring Energy loss others
SPT
Problem on weight drop
SPT-N value based Liq. Assess. at 5 sites
dvo
vo
vo
av rg
aCSR
=
= '
max' 65.0
σσ
στ
Manamaiju
LegendBlack clay
Filled material
Sand
Silty sand
Silty clay
Sandy gravel
Silt
0
5
10
15
0 100 20SPT N Value
Manahara
0 100 20SPT N Value
Ramkot
0 100 20SPT N Value
0 100 20SPT N Value
NEC
0 100 20SPT N Value
Imadol
dv
v rg
L ** 'max
=
σσα
10 20 30 40
0.25
0.5
0Normalazied N value,�(N1)60cs
Cyc
lic st
ress
ratio
or r
esis
tanc
e,C
SR o
r CR
R
Seed et al. (1983)(M =7.5, Number of cycle=15)
Liquefied site Manamaiju, NEC, Imadol, Ramkot
Not Liquefied site (Manahara)
Ramkot (FC=35%)
Gorkha Earthquake 7.8 (Number of Cycle 5-6)
Liquefaction
No-Liquefaction
10 20 30 40
0.2
0.4
0.6
0.8
0Normalized N value,�(Na)
Cyc
lic st
ress
ratio
or r
esis
tanc
e ra
tio C
SR o
r CR
R
RL (Japan Road Association)(Converted to An-isotropic Condition)
Liquefaction
No-Liquefaction
Liquefied site (Manamaiju, NEC, Imadol & Ramkot)
Not-Liquefied site (Manahara)
Simplified Method
JRA method
Both the curve under estimate the Liquefaction Potential for Kathmandu soil
PS- logging
Time (msec)
Typical PS-Logging data Manamaiju Site
100 200 300
0.1
0.2
0.3
0.4
0.5
0.6
0Normalized shear wave velocity, Vs1 (m/s)
Cyc
lic st
ress
ratio
or r
esis
tanc
e ra
tioC
SR o
r CR
R
CRR (Mw=7.5)
Liquefacion
NoLiquefaction
Andrus and Stokoe (2000) Not-liquefied (JICA Study,2002)
Liquefied (Manamaiju, Imadol, NEC & Ramkot)
Not-liquefied (Manahara)
S-wave (Vs) based Liq. Assessment d
v
v rg
aCSR max
'65.0
σσ
=
25.0
1 '100
=
v
VsVsσ
This curve Over estimate the Liquefaction Potential in Kathmandu soil
00
0 100 200 300100
200
300
Vs1
(m/s
)
N1
ManamaijuRamkotNECImadol
Holocene clean sand(Andrus et al, 2004)
'70170
1v
NNσ+
=
Laboratory Experiment
0.0001 0.001 0.01 0.1 1 10 100
20
40
60
80
100
Perc
enta
ge fi
ner (
%)
Particle grain size (mm)
Manamaiju at 12mNEC at 7mManahara at 5mImadol at 2mRamkot at 5m
Tests Conditions
Cyclic triaxial setup
Triaxial specimen
Manamaiju (Dr=80%)
Typical undrained cyclic triaxial test results
0 5 10 15 20-0.2
-0.1
0
0.1
0.2
Cyc
lic st
ress
ratio
(σ
d/2σ'
c)
0 5 10 15 20-10
-5
0
5
10
Axi
al st
rain
ε a
(%)
Axi
al st
rain
ε a
(%)
0 5 10 15 200
0.5
1
Pore
pre
ssur
e ra
tio
(u/σ
' c)
Number of Cycless-N
DA=5%
0 20 40 60 80 100 12-40
-20
0
20
40
Dev
iato
r stre
ss
σ d(k
Pa)
Mean Effective Principle Stress -P'(kPa)
-10 -5 0 5 10-40
-20
0
20
40
Axial strain,εa(%)D
evia
tor s
tress
σ d
(kPa
)
0.04 0.06 0.08 0.1-2
-1
0
1
2
Shea
r stre
ss(τ=σ
d/2)
Shear strain -γ (%)
G0
1 10 100 1000
0.25
0.5
Number of Cycles -N
Cyc
lic st
ress
ratio
(CSR
)
Effective stress, σ'c = 100kPa
Relative Density, Dr=45%Relative Density, Dr=60%Relative Density, Dr=80%Relative Density, Dr=110%
Liquefaction strength curve
1 10 100 1000
0.1
0.2
Number of Cycles -N
Effective stress, σ'c = 100kPa
Relative Density, Dr = 45%Relative Density, Dr = 60%Relative Density, Dr =80%Relative Density, Dr =100%
1 10 100 1000
0.1
0.2
Number of Cycles -N
Cyc
lic st
ress
ratio
(CSR
)
Effective stress, σ'c = 100kPa
Relative Density, DR =45%Relative Density, DR =60%
Manamaiju NEC
Imadol
40 60 80 100 120
0.2
0.4
0.6
0.8
Relative Density, Dr (%)
Cyc
lic re
sist
ance
ratio
(CR
R(σ
d/(2σ
' c)
Tatsuoka et al. (1986) Toyoura sandManamaijuNEC
wet- tampedσ'c=100kPa
Deformation test results
0.00001 0.0001 0.001 0.010
0.4
0.8
1.2[×105]
Shear strain (γ)
Shea
r Mod
ulus
, G (k
Pa)
Kathmandu soil (Manamaiju)Toyoura sand (Kokusho ,1980)
Relative Density, Dr= 60%Confining pressure, σ'
c= 100 kPa
Ottawa sand (A.Gunzman A.,1989)
0.00001 0.0001 0.001 0.010
0.4
0.8
1.2
Shear strain (γ)Nor
mal
ized
shea
r mod
ulus
G/G
0
Confining pressure, σ'c = 100 kPa
Ottawa sand (A-Gunzman A., 1989)
Toyoura sand(Kokusho, 1980)
Kathamndu sand
ManamaijuKathmandu sand
NEC ImadolMore Elastic
4-5 times
• Kathmandu soil is soft & more compressible
• More elastic than Toyoura and Ottawa sand
• Stiffness is 4-5 times less than Toyoura and Ottawa sand
• Deformation characteristic is similar with the Toyoura sand
20 sVG ρ=
Shear wave velocity calculate by using this relation;
100 200 300
0.1
0.2
0.3
0.4
0.5
0.6
0Normalized shear wave velocity, Vs1 (m/s)
Cyc
lic st
ress
ratio
or r
esis
tanc
e ra
tio(C
SR/C
RR
)
CRR (Mw=7.5)
Liquefacion
NoLiquefaction
Andrus and Stokoe (2000)
Not-liquefied (JICA Study,2002)
Cyclic Triaxial test
Field data
NECImadol
Manamaiju
Liquefied (Manahara, Imadol, NEC & Ramkot)
Not-liquefied (Manahara)Proposed boundary curve for kathmandu soil
10 20 30 4
0.25
0.5
0Normalazied N value,�(N1)60cs
Cyc
lic st
ress
ratio
or r
esis
tanc
e,C
SR o
r CR
R
Seed et al. (1983)(M =7.5, Number of cycle=15)
Liquefied site Manamaiju, NEC, Imadol, Ramkot
Not Liquefied site (Manahara)
Gorkha Earthquake 7.8 (Number of Cycle 5-6)
Proposed boundary curve for Kathmandu soil
10 20 30 40
0.2
0.4
0.6
0.8
0Normalized N value,�(Na)
Cyc
lic st
ress
ratio
or r
esis
tanc
e ra
tio C
SR o
r CR
R
RL (Japan Road Association)(Converted to An-isotropic Condition)
Liquefaction
No-Liquefaction
Liquefied site (Manamaiju, NEC, Imadol & Ramkot)
Not-Liquefied site (Manahara)
Purposed Boundary curve for Kathamndu soil
Proposed boundary curve for Kathmandu soil • Field in-situ & laboratory test results are
combined and proposed the new boundary curve based on S-wave velocity
• For the time being until & unless the SPT test procedure improve, new boundary curve based on SPT N-value are proposed to assess the liquefaction in Kathmandu valley
Conclusions Extensive field survey was conducted and identified 11 liquefied locations
during the April 25 Earthquake.
X-ray diffraction analyses were conducted on sands erupted at liquefaction sites and found that quartz, feldspar, mica and calcite are the dominant minerals. The relative amount of minerals in the sands determined by the integrated intensity ratio were quartz 60-–80%, feldspar 10–20%, mica 10–20% and calcite 5–10%
SPT, PS logging and continuous soil sampling were conducted at 5 sites in which 4 are liquefied and 1 did not liquefied during April 25, earthquake.
Undisturbed samples were obtained and carried out the laboratory tests including undrained cyclic triaxail tests to measure the liquefaction strength and found very susceptible for liquefaction.
The detail investigations on in-situ field tests and laboratory experiments carried out in the cyclic triaxil suggested that the existing method either based on SPT-N value or S-wave velocity do not fully valid for Kathmandu soil.
Finally, new boundary curve to separate the liquefaction and non-liquefaction locations based on the relationship between N-value or S-wave velocity and threshold acceleration are proposed. The proposed curve based on N-value are for time being until and unless the field test procedure improve and maintain the standards.
Thank you !!
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Ambient Vibration Survey on Ground and Tall Buildings of Kathmandu Valley
Japan side Nepal sideMitsu Okamura Surya Narayan ShresthaNetra P. Bhandary Sujan Raj AdhikariNarayan Marasini Indra Prasad AcharyaIkuo Towhata Dinesh Pathak
Netra Prakash BhandaryEhime University
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Building Damage Pattern
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Other Low Natural Frequency Structures
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One cycle
Ground vibration
Structural vibration characteristics
Natural Period and Vibrational Resonance
Time
Amplitude
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Tall building
Short building
Medium-height building
Rotating handle
Small-scale Shake Table Demo (Resonance Effect)
Long period shaking
Short period shaking
Medium period shaking
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Mini shake-table video demonstration
(Refer to the video file if time allows!)
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Research FrameworkThis study is composed of two parts:Part I: Liquefaction Study
Part II: Ambient Vibration Study
Field Investigation(Site identification, SPT-N value, S-wave
velocity, Sand sampling) Laboratory Testing
(Physical tests, Cyclic triaxial test, X-Ray diffraction test)
Field Measurement(Predominant natural frequency of
ground and tall buildings)Comparative Analysis(with previous data and 2015
Gorkha Earthquake motion data)
Liquefaction Resistance of Kathmandu Soil
Ground-Building resonance characteristics
Natural Frequency-based earthquake intensity and PGA maps
Hazard Predication
PGA prediction for scenario earthquakes and more reliable/accurate liquefaction map for KTM valley
Future Work
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Total: 175 points~ 1
1 km.
~ 18 km.
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Microtremor (vibration) sources
Tidal currents
Industrial machines
Vehicles
RailwayStrong winds
Shock waves
Measu-rementPoints
Volcano
In Kathmandu:• Vehicle movement• Winds• Industrial machines• etc.
(From Tokyo Soil Research)
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SensorTransducer
Computer for data recordingThree components (EW, NS andUP) of ground motion (velocity)measured at single station
-0.004
-0.002
0
0.002
0.004
0.00 20.48 40.96 61.44 81.92 102.40 122.88 143.36 163.84 184.32 204.80 225.28 245.76 266.24 286.72 307.20
Time (T) Sec
Vel. (c
m/s)
16 7
89 10 11 12 13 14 152 543
Noise-0.004
-0.002
0
0.002
0.004
0.00 20.48 40.96 61.44 81.92 102.40 122.88 143.36 163.84 184.32 204.80 225.28 245.76 266.24 286.72 307.20
Time (T) Sec
Vel. (c
m/s)
16 7
89 10 11 12 13 14 152 543
Noise
-0.004
-0.002
0
0.002
0.004
0.00 20.48 40.96 61.44 81.92 102.40 122.88 143.36 163.84 184.32 204.80 225.28 245.76 266.24 286.72 307.20
Time (T) Sec
Vel. (c
m/s)
16 7 8 9 10 11 12 13 14 152 543
Noise
-0.004
-0.002
0
0.002
0.004
0.00 20.48 40.96 61.44 81.92 102.40 122.88 143.36 163.84 184.32 204.80 225.28 245.76 266.24 286.72 307.20
Time (T) Sec
Vel. (c
m/s)
16 7 8 9 10 11 12 13 14 152 543
NoiseNorth- South (NS) component data
East- West (EW) component data
Vertical (UP) component data
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MT Instrument
V T (sec)
T (sec)V
Horizontal (R or T) component
Vertical component
Incident wavefield
SedimentBedrock
Three components (EW, NS and UP) of ground motion (velocity)
measured at single station (Time domain)
Analysis process of microtremor data
Fourier amplitude spectra (Af)Horizontal component Vertical component
Fast Fourier Transform
Fourier amplitude versus frequency (Frequency domain)
Frequency correspondences to maximum value of H/V ratio gives the predominant frequency of the
site
Transfer Function or H/V Spectral Ratio
Amax
A(f) HorizontalA(f) VerticalH/V =
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Fourier Analysis
tPeriod Function
Fourier Analysis
Frequency analysis
Frequency (Hz.)
Amplit
ude Spe
ctra
-0.004
-0.002
0
0.002
0.004
0.00 20.48 40.96 61.44 81.92 102.40 122.88 143.36 163.84 184.32 204.80 225.28 245.76 266.24 286.72 307.20
Time (T) Sec
Vel. (c
m/s)
16 7 8 9 10 11 12 13 14 152 543
Noise
P 8
0.1
1
10
0.1 1 10Frequency (Hz.)Frequency (Hz.)
H/V spe
ctral ra
tio
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P 163
0.1
1
10
100
0.1 1 10
P 8
0.1
1
10
0.1 1 10
P 133
0.1
1
10
100
0.1 1 10 100
P 100
0.1
1
10
0.1 1 10Frequency
H/V sp
ectral
ratio
Frequency
H/V sp
ectral
ratio
Frequency
H/V sp
ectral
ratio
Frequency
H/V sp
ectral
ratio
Analysis and result (F – Predominant frequency of the sites)
F = 3.0 Hz
F = 8.9 Hz
F = 0.73 HzF = 0.95 Hz
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0.1
1
10
100
0.1 1 10
Period range D 1.01 s to 1.30 s
Period, s
H/V sp
ectral
ratio
0.1
1
10
100
0.1 1 10
Period range B 0.60 s to 0.80 s
Period, s
H/V sp
ectral
ratio
0.1
1
10
100
0.1 1 10
Period range C 0.80 s to 1.01 s
Period, s
H/V sp
ectral
ratio
0.1
1
10
100
0.1 1 10
Period range E 1.30 s to 2.05 s
Period, sH/V
spect
ral ra
tio
H/V spectral ratio of 5 zones
Predominant period range
Description of zone
A 0.11 s to 0.60 sB 0.60 s to 0.80 sC 0.80 s to 1.01 sD 1.01 s to 1.30 sE 1.30 s to 2.05 s
0.1
1
10
100
0.1 1 10
Period range A 0.11 s to 0.60 s
Period, s
H/V sp
ectral
ratio
Study area is divided into five different range of predominant period using natural break techniquewhich regroups similar values together and represents the distribution properly
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Ground Predominant Frequency of the Survey Area
Kathmandu valley center is a low frequency area
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Ground Predominant Period Map of the Survey Area
Period in the study area varies from 0.1-2.05 s Period in central part varies from 1-2 s, which covers about 30% of the urban area of the valley
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Predominant period contours for the Kathmandu Valley
Higher period range in the eastern and western part of the valley is separated by the long low period line extended from north-west to south-east in the valley
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The circle indicates the average value whereas the length of the line suggests deviation from the average
Average standard deviation = 7.44
050
100150200250300350400
0 20 40 60 80 100 120 140 160 180 200Microtremor observation points
Thick
ness (m
)
Microtremor observation points
Thick
ness (m
)
Comparison between depths calculated using Birgöen et al. (2009) and Özalaybey et al. (2011) relationships
Proposed frequency depth relationship for Kathmandu Valley D=146.01fr-1.2079
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Predominant Frequency-based Sediment Depth Distribution of the Survey Area (D=146.01fr-1.2079 )
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Contour lineMajor road
River and water bodies
Basement Contour map for the Kathmandu Basin based on the proposed relation, D=146.01fr-1.2079
AB
A number of depressions are seen which are connected/separated by the buried ridges
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0
200300400
100
W S
NE
Top
Base
I
II0
200300400
100
Thickness (m)
3D view of Basement opography of the Kathmandu Basin
Large deep depression in the center part of the valley represents the main ancient lake of the valley
Longest buried ridge which separated the central large depression from the eastern shallow depression is extended from northwest to southeast
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What We Did in This Particular WorkPart II-1: Ground-Tall Building Resonance EffectPart II-2: Estimation of Peak Ground Acceleration in
the Core Kathmandu Valley
Why? Equation-derived value of natural period for a building structure is too
theoretical and does not exactly match with the real measured value. Ground and structural vibrations must resonate for shaking, thereby leading
to damage Still today, we do not know in numerical value what part of Kathmandu was
shaken how severely because we do not have a good network of devices to measure the intensity.
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Predominant Period:T = 0.1n
(n: No. of story)e.g., n = 10 storyT = 1 s
Microtremor (Ambient Vibration) Survey Plan on Buildings
Sensor locations
Building structure
Roof floor
Middle floor
Ground
General Relation
Does it hold true for Kathmandu buildings?
What exactly happened to the tall buildings during the Gorkha Earthquake?
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KMC College Duwakot
UGC Sano Thimi (Only ground)
DMG Lainchsaur (Only ground)
CDG TU Kritipur (Only ground)
Municipality Kirtipur (Only ground)
NASA Building Gairigaun
Pashupati vision Gaushala
Sunrise apartment Dhobighat
Sunrise apartment Nakhkhu
suncity apartment Gothatar
cityscape apartment Hattiban
Cityview apartment Bakhundol
Downtown apartment Dhapakhel
Bagmati apartment Shankhamul
Gunacolony Gwarko
Kohinoor Hill Housing Sanepa Height
Metro apartment Kuleshwor
Ambe apartment Chabahil
Grand apartment Dhumbarahi
Super builders Sukerdhara
Grande apartment Tokha
Park view horizon Dhapasi
silver luxury apartment Kalikathan
Kings way (Only ground)
Pulchowk engineer college (Only ground)
signature1 Teku
Swoyambnath Temple (Only Ground)
New baneshwor building
Rio apartment Jwagal
Balkumari building
Ekantakuna building
Kumaripati building
LP apartment
Vibor apartment
Imperial apartment
LLP apartment
Mercury sterling Sanepa
Status enclave
The residency apartment Sanepa
Gunacolony Sinamangal
Sunrise city homes Bijulibazar
Kalash apartment Tahachal
Retreat apartment Bijeshwori
Sigunature apartment ⅡTeku
Oriental colony ⅠKuleshwor
Oriental colony ⅡKuleshwor
Sunrise homes Balkumari
Cresha plaza Newroad
Maroitt hotel Thamel
TCH 3 Panipokhari
Kathmandu residensy Baghdole
Tall Building Locations in Kathmandu Valley
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Tall Buildings in Kathmandu Valley
Number of story, n
Pre-do
mina
nt Na
tural P
eriod
, T (s
)
T = f (n)
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Intensity Map Interpretation
KirtipurMunicipalOffice
IoEPulchowk UGC
Predominant Period, T (s)PG
A, a pg
(gal)
apg = f (T)
DMGAmerican Center
Tribhuvan University
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Ambient Vibration Survey 44 building sites 51 ground sites
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Survey Glimpses
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Analysis Method Separate the data into segments.(2048 data for 1 segment) Remove the noise. Convert the data from time-domain to frequency-domain by
Fourier analysis Find the spectral ratio (H/H for building, H/V for ground)
-0.01
-0.005
0
0.005
0.01
0 20.48 40.96 61.44 81.92 102.4 122.88 143.36 163.84
velocity (cm
/s)
Noise
Fourier transform
Smoothing by Parzen window bandwidth 0.5 Hz
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Evaluation of Natural Frequency
ω : Natural frequency of groundω₀ : Natural frequency of building
0123456789
10
0 1 2 3 4
Dynam
ic magn
ifier
Frequency ratio
h=0.05h=0.1h=0.2ωg/ωb
Most of building are amplified by frequency of ground.
h (damping ratio) = 0.05
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Wave Forms (Takai et al. 2016)
KATN
PKT
PPT
NTH
MTV
U The only waveform of KTP is different from others.
The seismic motion was overlapped and amplified in basin.
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Earthquake Motion Characteristics
The seismic wave reflects and overlap by surrounding hard rock.
The seismic waves is getting the slow velocity and big amplitude from hard rock to sediment.
The long period shaking would occur in Kathmandu valley.
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Predominant Period of Earthquake
The predominant frequencyf = 3.33f = 1.43f = 0.66f = 0.33f = 0.20Plot the dynamic magnifier at these values
Multiple periods as observed in velocity response spectra (Takai et al. 2016)
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f=3.33 (T = 0.3 s)
f=0.33 (T = 3 s)
f=0.66 (T = 1.5 s)
f=0.20 (T = 5 s)
Fg/Fb
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f=1.43 (T = 0.7 s)
The amplitude is not high when T = 3~5 (s) (Long period)
Dynamic magnifiers are greater than 1 for most of the buildings at all case of T except for T = 0.3 (s)
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Damage extentPark View Horizon, Basundhara Cityscape Club House, Hattiban TCH Phase II, Thaiba
Oriental Apartment Phase II, Kuleshwor Cityscape Block B, Hattiban Southern Height Apartment, Thaiba
Prestige Apartment, Chandol Dhumbarahi Apartment, Dhumbarahi
Central Park Apartment, Bishal Nagar TCH Tower, Lazimpat
Grande Apartment, Dhumbarahi Bhat Bhateni Apartment, Bhat Bhateni
Grande Towers, Tokha Indreni Apartment, Bhat Bhateni
LP Apartment, Lazimpat Egrace Apartment, Naxal
KL Apartment, Sano Gaucharan
Binayak Apartment, Baluwatar
Sun Rise Apartment, Nakhkhu
Imperial Apartment, Sanepa
City View Apartment, Bakhudol
Mercury Sterling Apartment, Thado Dhunga
Sun Rise Apartment, Dhobighat
Kalash Apartment, Tahachal
Metro Apartment, Kuleshwor
Oriental Apartment Phase I, Kuleshwor
TCH Tower Phase IV, Sitapaila
TCH Tower Phase III, Pani Pokhari
Retreat Apartment, Bijeshwori
Sun City Apartment, Gothatar
Ambe Residence, Chabahil
Downtown Apartment, Dhapakhel
Silver City Apartment, Kalikasthan
Signature Apartment I, Teku
Signature Apartment II, Teku
Civil Apartment II, Dhapakhel
Guna Colony, Sina Mangal
LLP Apartment, Pani Pokhari
Vibor Apartment, Kamal Pokhari
Westar Apartment, Balkumari
DUDBC categorized the damage extent.Red:dangerous to useYellow:available after
repaired Green:safe to livePark view horizon has been damaged seriously.
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Damage extentPark View Horizon, Basundhara Cityscape Club House, Hattiban TCH Phase II, Thaiba
Oriental Apartment Phase II, Kuleshwor Cityscape Block B, Hattiban Southern Height Apartment, Thaiba
Prestige Apartment, Chandol Dhumbarahi Apartment, Dhumbarahi
Central Park Apartment, Bishal Nagar TCH Tower, Lazimpat
Grande Apartment, Dhumbarahi Bhat Bhateni Apartment, Bhat Bhateni
Grande Towers, Tokha Indreni Apartment, Bhat Bhateni
LP Apartment, Lazimpat Egrace Apartment, Naxal
KL Apartment, Sano Gaucharan
Binayak Apartment, Baluwatar
Sun Rise Apartment, Nakhkhu
Imperial Apartment, Sanepa
City View Apartment, Bakhudol
Mercury Sterling Apartment, Thado Dhunga
Sun Rise Apartment, Dhobighat
Kalash Apartment, Tahachal
Metro Apartment, Kuleshwor
Oriental Apartment Phase I, Kuleshwor
TCH Tower Phase IV, Sitapaila
TCH Tower Phase III, Pani Pokhari
Retreat Apartment, Bijeshwori
Sun City Apartment, Gothatar
Ambe Residence, Chabahil
Downtown Apartment, Dhapakhel
Silver City Apartment, Kalikasthan
Signature Apartment I, Teku
Signature Apartment II, Teku
Civil Apartment II, Dhapakhel
Guna Colony, Sina Mangal
LLP Apartment, Pani Pokhari
Vibor Apartment, Kamal Pokhari
Westar Apartment, Balkumari
DUDBC categorized the damage extent.Red:dangerous to useYellow:available after
repaired Green:safe to livePark view horizon has been damaged seriously.
Park view horizon
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T1: Natural period of vibration of the first mode of the structure (s)D’: Overall length of the building at the base in the direction under consideration (m)
What Nepal Building Code says (Period of Buildings)
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Simplified Dominant Period for Buildings Comparing the predominant period, height and width of the
buildings with previously proposed relation/s
Predominant period is influenced by the height and width. The shapes, structures and materials effects on predominant period
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Major Assumption (Concept)
Greater depth(i.e. low frequency or high period)
Shallower depth(i.e. high frequency or low period)
Basement Rock Line
Ground surfaceLow Peak Ground Acceleration (PGA)
High Peak Ground Acceleration (PGA)
Sediment Deposit
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Estimating Peak Ground Acceleration (2015 Gorkha Earthquake)Accelerometer Stations and MT Survey Points
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F = 0.73 Hz
PTN
F = 0.75 Hz
KATNP
F = 0.83 Hz
THM
F = 0.88 Hz
DMG
F = 1.37 Hz
TVU
F = 2.15 Hz
KTP
H/V Spectral Ratio for Accelerogram Stations
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S.No Station latitude longitude EW (m/s2) NS (m/s2) UD (m/s2) PGA (gal) Intensity (MMI) IJMA Frequeny (Hz) N. Period (s)1 KATNP 27.71 85.32 1.55 1.542 1.549 155 6.357 5.321 0.75 1.332 KTP 27.68 85.27 2.548 1.536 1.14 254.8 7.147 5.752 2.15 0.473 TVU 27.68 85.29 2.288 1.647 1.383 228.8 6.976 5.659 1.37 0.734 PTN 27.68 85.32 1.281 1.507 1.339 150.7 6.312 5.296 0.73 1.375 THM 27.68 85.38 1.505 1.338 1.837 150.5 6.31 5.65 0.83 1.206 DMG 27.72 85.32 1.268 1.771 2.055 177.1 6.568 4.934 0.88 1.14
(Data source: DMG, USGS, and Takai et al.)
Interpreting PGA on the basis of Natural Period(2015 Gorkha Earthquake)
Preliminary Relationship
apg = 102.8*ln(T) + 183.35
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Predominant Natural Frequency (Ground) Distribution
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Predominant Period (Ground) Distribution
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Estimated Peak Ground Acceleration (2015 Gorkha Earthquake)
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Paudyal et al. (2012) reveal that the central Kathmandu Valley is a long period ground composed of thick sediment deposit. This is in agreement with previous research work. During the 2015 Gorkha Earthquake, most tall buildings in the Kathmandu Valley were heavily shaken, which is supposed to be due to long-periodground shaking (i.e., 3-5 s). The ground shaking was long period in the central part while shorter in the peripheral part where the basement rock is close to surface. Post-earthquake evaluation of pre-dominant period of ground and buildings at tall building locations in the Kathmandu Valley reveals that most buildings might have been shaken during 0.5 – 1.5 s dominant period of the ground motion. A very rough relationship of peak ground acceleration (PGA) with the ground natural period was established: PGA (gal) = -102.8ln(T(s)) + 183.35 A very preliminary PGA map has been proposed (using the above relationship) for the core Kathmandu Valley during the 2015 GorkhaEarthquake.
Concluding Remarks
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The damage depends on the duration of resonance Possible change in predominant periods of the buildings after earthquake Preliminary micortremor measurement data might be erroneous, and they need precise check
Limitations:
Further Research Plan Precise estimation and verification of peak ground acceleration (PGA) through the use of massive aftershock data (possibly at all six accelerogramstations). Relational analysis for epicentral distance (main shock as well as aftershocks) and peak ground acceleration in the Kathmandu Valley. And finally, interpretation of liquefaction-susceptible areas (locations) on the basis of precisely estimated peak ground acceleration map.
Thank you very much!