The significance of Surface Logging For The Formation Evaluation Advance Surf...
Oslo_present_2008
1. Generation of Geological Database for
Liquefaction hazard assessment in
Kathmandu valley
By
BIRENDRA KUMAR PIYA
Department of Mines and Geology
Kathmandu, Nepal
and
Dr. C. J. van Westen
ITC, Enschede,
The Netherlands
August, 2008
3. Introduction Contd.Introduction Contd.
Kathmandu is the capital city of Nepal.
KV is an intramontane tectonic basin filled up by
fluvio- lacustrine sediments >550m in thickness.
KV lies in Seismically active zone and some
major earthquakes have rocked the Valley in the
past causing huge damages.
Liquefaction has been reported in some parts of
KV in 1934 earthquake (M= 8.4R).
Kathmandu valley is a rapidly growing city with
population of nearly 3 million.
4. Evidence of liquefaction in KTM valleyEvidence of liquefaction in KTM valley
in1934 earthquakes ???in1934 earthquakes ???
Fissures due to earthquake of
1934 along the way to Balaju
Fissures due to earthquake of 1934 in
Tundikhel, the main city centre.
Wide fissures
Ref: Nepalko Mahabhukampa (1935)
Bramha Shamsher J.B.R
5. Some glimpses of 1934 earthquakesSome glimpses of 1934 earthquakes
After 1934 earthquakeBefore 1934 earthquake
6. Some glimpse of 1934 earthquakesSome glimpse of 1934 earthquakes
Clock Tower
Before
Clock Tower
AfterBhairabnath Temple
Before
Bhairabnath Temple
After
7. Generation of layer models
Generation of lithological
cross sections
Generation of fence diagrams
Generation of stratigraphic
projections
Generation of
Geological database
and Liquefaction
hazard analysis
Soil
Response
Modelling
Infrastructure
vulnerability
Building
Vulnerability
Population
vulnerbility
INPUT
INPUTINPUT
INPUT
Objective
9. DATADATA
185 boreholes data for layer models and 328
borehole data for Liquefaction susceptibility
analysis, were collected.
Out of them 36 reached up to the bedrock
level.
Based on these borehole data, the required
analysis was carried out.
12. Subsurface geology in the central part of the valley
Lithologs in the central part of the valley and the formation names
Bagmati Formation (Pre Lake
deposit)
Kalimati Formation
Lake deposit
Patan Formation (Post
lake deposit)
Basal lignite
member
P 14b
B20 Paleo1
Bal2
Bedrock
Bedrock
13. Lukundol Formation
Lake deposit
Itaiti Formation
Post_Lake deposit
Tarebhir Formation
Pre-Lake depsoit
Legend
Subsurface geology in the southern part of the valley
15. • A layer model for 3 different type of deposits has
been prepared for the entire valley sediments
using 185 number of deep and shallow boreholes
including 37 boreholes that have touched the
bedrock.
16. In this study the Kathmandu valley sediment is
divided into 3 major units:
Post Lake deposit
Lake deposit
Pre-lake deposit
28. What are the conditions for Liquefaction to occur?
The soil must be susceptible to liquefaction (i.e.
The soil should be loose, water-saturated, sandy
soil typically between 0 and 10 meters below the
ground surface).
Ground shaking must be strong enough to cause
susceptible soils to liquefy.
Ground water should lie within 15 meter deep
inside the surface.
29. Age of the deposit,
Depth to water table
Geologic history
Grain size distribution
Depth of burial
Capping Layer
Density state
Proximity to a free face and
Ground slope
(Youd and Perkins, 1978).
What factors affect the liquefaction susceptibility?What factors affect the liquefaction susceptibility?
30. Methodology
Borehole data
Quantitative
analysis
Qualitative
analysis
Spreadsheet
Seed and Idris
method 1971
Iwasaki et al.
method 1984
etc. Juang and
Elton method
Others
Grain size
Age of deposit
Water table
Capping layer
Liquefiable
thickness
Depth of overburden
Factors
Considered
Weighting and
scoring of the
factors
Summation
of the score
value
transferring
the score
value in Ilwis
table
Ilwis
Operation
Liquefaction
Susceptibility
map
Classifying the score
value as High,
moderate, low and
very low
35. Analysis of Liquefaction PotentialAnalysis of Liquefaction Potential
• Qualitative Analysis,
• A. Tsuchida:
– Based on SPT-values and sieve curves
– Adequate as a first appraisal test
– If this method shows any risk of
liquefaction, quantitative studies have to be
performed
36. Tshuchida method for the evaluation ofTshuchida method for the evaluation of
Liquefaction potential mapLiquefaction potential map
Analysis
37. Qualitative Analysis,Qualitative Analysis,
A. Juang and Elton (1991):A. Juang and Elton (1991):
• Based on Geological factors
• - Depth to Water table
• - Grain Size distribution
• - Depth of burial
• - Capping Layer
• - Age of the formation
38. Factor Weig
h
Very Very
ting High Score High Score Medium Scor
e
Low Scor
e
Low Score
Depth to water
table
x 2 <1.5 m 5 1.5-3
m
4 3 - 6 m 3 6-10
m
2 >10 m 1
Grain Size x 4 fine- 5 med- 4 coarse 3 silt 2
medium coars
e
Depth of burial x 1 1.5-3m 5 3-6 m 4 6-10 m 3 <1.5m 2 >10 m 1
Capping layer
(low k)
x 2 good 3 fair 2 no 1
capping cappi
ng
cappi
n
g
Age of deposit x 1 <500
yr
5 late 4 Holocen
e
3 Pleis
to
ce
ne
2 pre- 1
Holoc Pleis
t
Liquefaction SusceptibilityAnalysis
39. water
table
Grainsi
ze
depth
of
burial
Cappin
g layer
Age of
deposit
Liquefa
ction
layer
thick Total
Borehol
e_ID
Score
value
weighti
ng*2
Score
value
weighti
ng*4
Score
value
weighti
ng*1
Score
value
weighti
ng*2
Score
value
weighti
ng*1
Score
value
weighti
ng*1 score
Cl
as
s
286 2 4 4 16 5 5 1 2 2 2 5 5 34 M
287 2 4 4 16 2 2 1 2 2 2 5 5 31 M
288 3 6 3 12 2 2 1 2 2 2 5 5 29 M
289 3 6 4 16 2 2 1 2 2 2 5 5 33 M
290 3 6 3 12 3 3 2 4 2 2 5 5 32 M
291 5 10 2 8 5 5 2 4 2 2 5 5 34 M
292 5 10 2 8 5 5 2 4 2 2 5 5 34 M
293 5 10 2 8 5 5 2 4 2 2 5 5 34 M
294 5 10 2 8 5 5 2 4 2 2 5 5 34 M
295 5 10 2 8 2 2 2 4 2 2 5 5 31 M
296 4 8 3 12 2 2 1 2 2 2 2 2 28 M
297 4 8 2 8 1 1 2 2 2 2 1 1 22 L
298 4 8 3 12 5 5 1 2 5 5 5 5 37 H
299 4 8 4 16 5 5 1 2 5 5 5 5 41 H
302 5 10 3 12 2 2 2 4 2 2 5 5 35 M
C - 300 4 8 4 16 5 5 1 2 5 5 5 5 41 H
Analysis Contd.
40. Assigned level of Liquefaction susceptibility
High (score>36):- Significant areas may liquefy
under moderate to high seismic loading.
Moderate (score between 26 and 36):- Some
areas may liquefy under high seismic loading.
Low (score between 20 and 26):- Localized
areas (such as ribbon sands) may liquefy under
high seismic loading.
Very low (score <20):- Negligible liquefaction
expected even under high seismic loading)
41. Classification Means
The bed rock pga value calculated by NSC
(DMG) in Kathmandu Valley area is 0.1g.
Therefore High liquefaction Susceptibility
means that The liquefaction is likely to
occur at 0.1g pga value.
Moderate Liquefaction susceptible class
means that the liquefaction is likely to occur
at the shaking of 0.1g to 0.2g.
and
Low liquefaction susceptible is likely to
occur at the shaking pga value of >0.2g.
42.
43. Graph showing liquefaction susceptibility behavior for different PGA values using
the method of Iwasaki et al. (1984).
PGA value Yes No Total % Yes %No
0.1g 37 50 87 43 57
0.2g 69 18 87 79 21
0.3g 80 7 87 92 8
50. ConclusionConclusion
Kathmandu valley is underlained by thick
lacustrine sediments mainly composed of black
clay.
Some parts of Kathmandu valley is potential to
liquefaction hazard in case of strong
earthquake motion.
The borehole database is an important source
for earthquake hazard and risk assessment and
for disaster mitigation, as well as for engineering
work designs, such as buildings, bridges and
other infrastructure development.
51. Conclusion Contd.Conclusion Contd.
The borehole database is an important source for
earthquake hazard and risk assessment and for disaster
mitigation, as well as for engineering work designs, such as
buildings, bridges and other infrastructure development.
In the lack of geotechnical data, qualitative method is also
very much applicable for liquefaction hazard mapping.
The qualitatively analysed liquefaction map can be used
as a basis for planning purpose in the urban development
activities but not for a site specific purpose.
A detailed study with comprehensive merging of geologic,
geotechnical and seismological data is required for specific site
investigation.
52. • More borehole data with bedrock information
is required to prepare a precise layer model.
• More deep boreholes are recommended to be
made especially in the Eastern and Western
side of the Manahara well field, and in the
South of the study area where gaps in
borehole information are noticeable.
• The borehole database prepared in this study
should be updated to include new borehole
data each time when new boreholes will
become available.
Recommendations
