1. Engineering Geological Mapping and
Liquefaction susceptibility analysis
Of
Birendranagar Municipality and the
surrounding areas Surkhet District
By
Birendra Piya (Sr. Div.Geologist)
G. R. Chitrakar (Sr.Div.Geologist)
2009
3. • Coordinates between 556000 to 3156000Coordinates between 556000 to 3156000
meters Northing and 566000 to 3166000meters Northing and 566000 to 3166000
meters Easting.meters Easting.
• Area covers 100 Sq. Km.Area covers 100 Sq. Km.
Introduction
Location
Surkhet
4. • Geologically the study area lies in the DunGeologically the study area lies in the Dun
valley in the mid-western developmentvalley in the mid-western development
region of Nepal.region of Nepal.
• The altitude of the study area varies fromThe altitude of the study area varies from
632m in the valley up to more than 1000m632m in the valley up to more than 1000m
msl in the surrounding hills.msl in the surrounding hills.
• It lies in the subtropical humid type ofIt lies in the subtropical humid type of
climateclimate
• The main rivers in the Valley are ItramThe main rivers in the Valley are Itram
Khola, Neware Khola, Jhupra Khola etcKhola, Neware Khola, Jhupra Khola etc
flowing from North to South.flowing from North to South.
Introduction
5.
6. Objectives
• To prepare an Engineering Geological map of
the study area to assist to prepare the
Engineering and Environmental Geological
Map as per the Departmental objective.
• To determine N-value of various layers of
the soil to estimate bearing capacity of the
land surface using SPT test.
• To delineate the area susceptible to
liquefaction hazard.
• To delineate the area susceptible to
settlement due to heavy loads on it.
7. 1. Desk Study:
Aerial Photographs, Satellite imageries, Topo maps
were studied to obtain the overall view and plan of
the study area.
2. Field study:
Auger hole drilling and Standard Penetration Test
(SPT), were carried out in the field to obtain
necessary data.
3. Field outputs:
–75 auger holes and 40 SPT tests were
performed during the field.
–Some soil samples were collected for the
laboratory tests.
Methodology
8. Methodology Contd.
Tools used to carry out analysis
–Winsieve 5, Ilwis 3.2, Rockworks
2002, Spreadsheet
Laboratory tests.
– Liquid limit, plastic limit, Sieve
analysis, Moisture content.
19. ResultGrainsizeanalysis
The soil sediments are well graded to uniformly
graded.
Very Low Permeability value ranging from 2.7 X 10-5
to 3.8 X 10-5
m/s.
Sediment classes are:-
Silty sand, Sandy silt and fine to medium sand
Limitation: Hydrometer test is not performed.
20. Representative Soil Sample Analysis Report
S
P
T
N
o Depth M- %
Fi
% fs
m
s cs
f
g
m
g
c
g D10
D30
D50
D60
D60
/D10
=U
D30
2
/D10
xD60
=C k m/s Symbol Permeability
1
a
1.0-
1.45
39.9
3
9
2 2 1 1 2 1
0.048
7
0.052
2
0.055
7
0.057
4 1.178 0.974 2.8x10-5
Uu Very low
1
b
2.0-
2.45
14.9
5
5
3
2
1
1
1
1
0 5 0.05 0.056 0.062
0.095
8 1.917 0.654 2.9x10-5
Us Very low
2
a
1.0-
1.45
12.4
3
2
7
3
4
2
7 4 2 5
0.052
8
0.076
7
0.166
3
0.204
1 3.862 0.546 3.2x10-5
Schwa
ch
kiesig Very low
2
b
2.0-
2.45
18.6
7
6
7
2
4 4 1 2 2
0.049
4
0.054
1
0.058
9
0.061
3 1.241 0.969 2.8x10-5
Us Very low
2
c
3.0-
3.45
19.4
1
6
6
2
6 7 1 1
0.049
4
0.054
3
0.059
2
0.061
7 1.247 0.968 2.8x10-5
Us Very low
2
d
4.0-
4.45
16.3
4
6
7
2
5 7 1
0.049
4
0.054
2 0.059
0.061
4 1.243 0.969 2.8x10-5
Us Very low
3
a
1.0-
1.45
16.1
1
6
0
2
8
1
1 1
0.049
7
0.055
1
0.060
4
0.064
6 1.3 0.944 2.9x10-5
Us Very low
3
b
2.0-
2.45 23.4
9
9 1 1 2 3
0.048
7
0.052
2
0.055
7
0.057
4 1.178 0.974 2.8x10-5
Uu Very low
3
c
3.0-
3.45
22.6
2
9
6 1 1 1 1
0.048
7 0.052
0.055
3 0.057 1.171 0.975 2.7x10-5
Uu Very low
4
a
1.0-
1.45
15.2
8
7
0
2
3 5 2
0.049
3
0.053
8
0.058
4
0.060
6 1.231 0.969 2.8x10-5
Us Very low
4
b
2.0-
2.45
14.3
2
7
3
2
3 4
0.049
2
0.053
6 0.058
0.060
2 0.97 0.97 2.8x10-5
Us Very low
5
a
1.0-
1.45
11.9
8
8
7 6 4 2 1
0.048
8
0.052
5
0.056
1 0.058 1.187 0.973 2.8x10-5
Uu Very low
6 1.0- 16.9 7 1 1 0.049 0.053 0.057 0.060
-5
21. Results
Based on laboratory analysis of soil samples,
lithological observation in the field and SPT
data, 7 different lithological units are identified
in the study area.
1. Itram deposit
2. Belghari Deposit
3. Purano Ghushra Deposit
4. Sano Surkhet Deposit
5. Floodplain deposit
6. Residual Soil deposit
7. Colluvial deposit
22. Itram Deposit
Boulder, Pebbles and Gravel dominant areas. N values very
high >50. High bearing capacity, No liquefaction potential,
Permeability is high
Belghari deposit
It consists of silty clay to clayey silt alternated with sandy
gravel. N-value low to medium (1 to 12). Low to very low
bearing capacity. Low to Moderate liquefaction areas. High
at some places.
Purano Ghushra Deposit
Clay dominant areas. N value very low. Black clay observed
at many places. Indicates Low bearing cacpaity. Moderate to
high liquefaction area.
Result:
23. • Sano Surkhet Deposit : Topographically separated area,
consisting of light to brownish yellow silty clay to clayey silt. this
unit is of low plasticity and firm to stiff consistency. Groundwater
table is more than 6m deep. This soil has moderate bearing
capacity and has moderate to low liquefaction potential zone.
• Flood plain deposit: Along the river bed and flood plain
areas.Consist of medium to coarse grained sand, gravel,
pebbles and boulders. Moderate to high bearing capacity and
moderate to high liquefaction potential area.
• Residual Soil Deposit:
• Colluvial Soil Deposit
31. The bearing capacity is defined as a
load carrying capacity of foundation
soil or rock, which enables it to bear
and transmit loads from a structure.
Bearing Capacity
32. Conditio
n
N-
value
Bearing
Capacity (Kpa)
Quality
Very
soft
<2 <25 Extremly Low
(EL)
Soft 2 – 4 25 – 50 Very Low (VL)
Medium 4 – 8 51 – 100 Low (L)
Stiff 8 – 15 101 – 200 Medium (M)
Very
stiff
15 – 30 201 – 400 High (H)
Hard >30 >400 Very High (VH)
Peck et al (1974)
Bearing Capacity Classification
35. What is Liquefaction ??
It is the process by which sediments below
the water table temporarily Lose strength
and behave as a viscous liquid rather than
solid, mainly caused by the seismic waves.
Type of Liquefaction
Flow, slumping
Lateral spreading
Ground oscillation
Loss of bearing strength
Sand boils
36. • Depth to Water table
• Grain Size
• Depth of burial
• Capping Layer
• Age of the formation
• Liquefaction Layer thickness
Geological Factors considered for
Liquefaction hazard analysis
37. Factor Wei
g
h
Very Very
ting High Scor
e
High Scor
e
Medium Scor
e
Low Scor
e
Low Scor
e
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
mediu
m
coar
s
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
cappin
g
cappi
n
g
capp
i
n
g
Liquefaction Susceptibility
Analysis
42. • High (score>36) :
Significant areas may liquefy under
moderate to high seismic loading.
• Moderate (score betn
26 and 36):
Some areas may liquefy under high
seismic loading.
• Low (score betn
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.
Assigned level of Liquefaction Susceptibility
43. • The scoring and weighting value used in
the preparation of liquefaction Potential
map is based on the UNDP/UNCHS habitat
Project – 1994, that used the value for the
preparation of Liquefaction Potential map
of the Kathmandu valley. It is completely a
qualitative analysis. The map is not
applicable for site specific development
purpose.
• The bearing capacity map is based on SPT
value and is prepared according to Peck et
al. (1974) classification. The map is not
applicable for site specific development
purpose.
Limitation
44. SPT no. From To
N-
value
2*dept
h
Resu
lt SPT no. From To N-value 2*depth Result
1 1 1.45 10 2.9 L 8 1 1.45 7 2.9 L
2 2.45 12 4.9 L 2 2.45 5 4.9 L
2.45 2.9 45 5.8 L 3 3.45 11 6.9 L
2 1 1.45 1 2.9 H 9 1 1.45 2 2.9 H
2 2.45 3 4.9 H 2 2.45 3 4.9 H
3 3.45 3 6.9 H 3 3.45 5 6.9 H
4 4.45 2 8.9 H 3.5 2.95 15 5.9 L
5 5.45 7 10.9 H 10 0
5.45 5.9 14 11.8 L 11 1 1.45 2 2.9 H
3 1 1.45 8 2.9 L 2 2.45 1 4.9 H
2 2.45 8 4.9 L 3 3.45 2 6.9 H
3 3.45 7 6.9 L 4 4.45 4 8.9 H
3.7 4.15 8 8.3 H 12 1 1.45 5 2.9 L
4.15 4.6 5 9.2 H 2 2.45 2 4.9 H
4 1 1.45 8 2.9 L 2.45 2.9 7 5.8 L
2 2.45 6 4.9 L 13 0
3 3.45 8 6.9 L 14 1 1.45 2 2.9 H
3.45 3.9 18 7.8 L 2 2.45 7 4.9 L
5 1 1.45 8 2.9 L 3 3.45 18 6.9 L
2 2.45 50 4.9 L 4 4.45 13 8.9 L
6 1 1.45 5 2.9 L 15 1 1.45 7 2.9 L
2 2.45 6 4.9 L 2 2.45 13 4.9 L
3 3.45 6 6.9 H 3 3.45 19 6.9 L
4 4.45 7 8.9 H 4 4.45 6 8.9 H
5 5.45 11 10.9 L 16 1 1.45 7 2.9 L
OhsakiMethod
45. • According to Ohsaki no Liquefaction
takes place in SPT no. 1,3,4, 8,9 and
14
• The Liquefaction potential map is
compared with the result of Ohsaki
method and other reported data. It
was found correlated.
46. SPT
no. Juang Ohsaki
SPT
no Juang Ohsaki
1 Very low Low 11 High High
2 High High 12 Moderate High
3 Low Low 13 Verylow Low
4 Moderate Low 14 High Low
5 Very low Low 15 High Low
6 High High 16 Low High
7 High Low 17 Very low Low
8 Moderate Low 18 Low High
9 High High 19 Low Low
10 Very Low Low 20 Moderate High
Comparison of the result between Juang and Ohsaki Method
47. Liquefaction Potential Map
Area covered
High 07 %.
Moderate 18 %
Low 24 %
Very low 51 %
Results
Liquefaction Susceptibility
0
10
20
30
40
50
60
High Moderate Low Verylow
Category
Percent
Bearing capacity Map
Area covered
Very low 1.14 %
Low to Vlow 5.00 %
Midim 2.66 %
Medium to high 16.0 %
High 11.0 %
Very High 48.0 %
Bearing Capacity
0.00
10.00
20.00
30.00
40.00
50.00
60.00
VL LVL L LM M MH H VH
Category
Percentage
48. Conclusion
The sub surface geology of the study area is
classified into 7 different deposit types.
The soil sediments of the study area is not
uniformly distributed rather it is heterogeneously
distributed.
The bearing capacity calculated in the study area
varies from Very low to very high types.
The study area lies in moderate to high
Liquefaction potential zone in the southern part
and very low in the northern part.
49. Conclusion Contd.
The soil condition in the study area according to
Peck et al. varies from very soft to stiff with SPT
value ranging from 0 to >30 at different depths,
Water table in the area varies from place to
place. In the northern part it is very low and in the
middle and the southern part it is very high. At
some places the water is emerged in the form of
springs.
50. Recommendations
• The results obtained in this work is not
intended to be used as a precise tool for
site specific construction. A more detail
investigation with comprehensive
merging of geologic, geotechnical and
seismological data will be required to
carry out precise liquefaction
susceptibility mapping as well as
bearing capacity for each major
development activities.
51. • The present settlement area in Birendranagar Municipality
lies in very low liquefaction and high bearing capacity zone,
where as the middle and the southern part of the valley lies in
moderate to high liquefaction potential zone and moderate to
low bearing capacity area. Hence for the future it is
recommended to expand settlement in the northern part of
the present Jumla highway only. Where as the southern part
should be developed as an agricultural land.
• The archaeologically and historically important places such
as Kakre Bihar, Utarganga and Deuti Bajai should be well
preserved.
• The wet lands and the natural springs which are important
from touristic point of view should be preserved and
developed.
Contd. Recommendation
