Landslide studies along
National Highway (NH 39) in Manipur
Arun Kumar and Manichandra Sanoujam
Department of Earth Sciences
Manipur University
Imphal: 795003 India
Presenter: Arun Kumar
The present study deals with the landslide investigations along
with the National Highway (NH 39).
The kinematics and slope stability analyses are used to
understand the causes of slope failure in the terrain inspite of
material of a high safety factor.
The study area falls under high seismic zone where a
Churachandpur-Mao- Thrust (CMT) of regional extent situated
west of the Indo Myanmar subduction boundary.
By quantifying the landslide incidences, creeping, seismicity and
creeping rates, it is observed that CMT is a creeping regional
fault, runs closely parallel to the subduction boundary.
The results indicates the causes of landslide hazards are due to
the presence of the creeping segment of CMT and further
requirement of long term measurement of seismicity and
creeping.
1
LITHO-SECTIONS OF VARIOUS LANDSLIDES
Geological Cross Section (Mt. Iso-Sedzu River) Through Mao Area
2
Kinematics of Minor Structures
The word kinematics refers to the study of movement
without reference to the forces that produce it.
The methodology is followed and attributes of the joint
sets and wedges are estimated.
For the Landslide-1, attitudes of 40 joints, Landslide-2,
attitudes of 27 joints for Landslide-3 attitudes 29 joint
are taken and plotted in the stereo net using GEOrient
software.
JOINT ANALYSIS OF LANDSLIDE 1 (PHIKOMEI)
W2
slope
W1
Joint
Dip
amount/angle
Dip
Direction/aspect
Joint set 1
53°
53°
089°
089°N
Joint set 2
51°
51°
221°
221°N
Joint set 3
83°
83°
200°
200°N
Joint set 4
88°
88°
024°
024°N
Slope
45°
45°
135°
135°N
Wedge
Dip amount
Dip Direction
W1
34°
34°
151°
151°N
W2
50°
50°
118°
118°N
W3
51°
51°
110°
110°N
W4
26°
26°
113°
113°N
W1 causes wedge Failure
3
JOINT ANALYSIS OF LANDSLIDE 2
W1
Slope
W
4
W2
W3
Joint
Dip amount
Dip
Direction
Wedge
Dip amount
Dip direction
W1
48°
48°
99°
99°N
Joint 1
53°
53°
133°
133°N
W2
52°
52°
141°
141°N
Joint 2
83°
83°
223°
223°N
W3
16°
16°
220°
220°N
Joint 3
87°
87°
306°
306°N
W4
18°
18°
89°
89°N
Joint 4
78°
78°
176°
176°N
Slope
40°
40° in lower slope
70°
70° in upper slope
160°
160°N
W2 causes in toppling of various sliding
blocks
JOINT ANALYSIS OF LANDSLIDE 3 (MOUZHU)
Slope2 W2
Slope1
W2
Wedge
W1
Dip amount
39°
39°
Joint
Dip amount
Dip Direction
Joint 1
56°
56°
191°
191°N
Dip direction
Joint 2
63°
63°
314°
314°N
21°
21°N
Joint 3
64°
64°
10°
10°N
Joint 4
67°
67°
92°
92°N
W2
59°
59°
46°
46°N
Slope
45°
45° in upper scarp
73°
73° in lower scarp
52°
52°N
W2 causes wedge failure in slope 1 and
Causes toppling of blocks in slope 2
4
Slope Stability
Galena (http://www.scisoftware.com
unit weight, cohesion and angle of internal
friction of the unstable slope ground water
conditions and failure surface
Slope stability analysis of Landslide-2
: Slope stability analysis of Landslide-1
Slope stability analysis of Landslide-3
Stability factors are analysed and interpreted below :
Landslide 1 – Factor of safety is 1.81 - 1.82
Landslide 2 – Factor of safety is 1.66
Landslide 3 – Factor of safety is calculated for soil material
only since uniaxial strength and triaxial strength could not be
detected as the rock sample is highly jointed. From the
strength parameters of soil the factor of safety is 0.67- 0.69
5
For the stable slopes of the terrain, the factor of
safety is <1, whereas in the present studies the
factors of study is 0.670.67-1.82 for these landslide
sites.
The factor of safety ranging from 1.25 – 1.4 is
considered satisfactory for routine and fills.
Even with the factor of safety 1.82, the landslide
has still occurred in the study area, calls for
other triggering factors.
Rainfall and Water-table fluctuations
1680.8
45
1680.7
9
1680.7
40
1680.6
8
35
1680.5
7
30
1680.4
6
1680.3
5
1680.2
4
1680.1
3
1680
2
1680.6
1680.5
25
1680.4
20
15
1680.3
10
1680.2
5
1680.1
0
1
31
61
91
121
151
Days
181
1679.9
1
1679.8
0
1
31
61
91
121
151
181
Days
Rainfall (mm)
Pizometric level (above MSL)
a
Piezometer level (meter above MSL)
Rainfal (mm)
b
Rainfall and water-table fluctuation, a. during monsoon season (Apr.-Sep. 203) and b. during lean
season (Oct 2003-Mar.2004)
There is a good correlations of the water table and rainfall
patterns.
The possible reason for the landslide triggering in September is
not the rainfall as there is a gradual decrease the water table in
the same month.
6
Creep Displacement:
Extensiometer data showing creep movement
Creep displacement is 1.76 mm and 3.25 mm in 2003 and 2004
sudden creep displacment records are June –July, August-September
The relationship of the creep displacement can be
explained as the possible landslide triggering mechanism
during the months of September-October.
There is hardly any creep displacement in May but in June
it begins and continues till October first week.
The creep displacement becomes rapid when the pore
water pressure induces the displacement or may be due
to the shallow earthquake activity in the vicinity of the
terrain.
As the study area is effected by the seismo-tectonically
active CMT, there may be a possibility of earthquake
induced phenomenon.
7
The creep observations for Slumgullion landslide’
landslide’s south
boundary strike slip fault show seasonal variations around a
steady state rate of -1.5 cm/month and similar observations of
creeping section of San Andreas fault also exhibit season
variations. The change in slope in both cases correspond to
increase climatic moisture.
The creep rates from the present study and else parts of the
world have been compared and reveals the similar causes for
the landslides such as heavy rainfall, active strike slip faults
and high moisture conditions.
Microseismicity and Creeping along CMT
Creeping segment of the strike slip fault are often
characterized by the high rates of microseismicity on or near
the fault.
This micro-seismicity releases only a small fraction of slip
occurring on the fault and majority of the accumulating
elastic strain is released while high aseismic creep or near
large events
The creeping faults are first identified along the San Andreas
fault in central California, where cultural features were
progressively off set.
8
The landslides may provide useful analog for the study of
process involved in crustal scale tectonics.
The Churachandpur-Mao-Thrust (CMT) has a regional
extent of 300 km. from the Kohima (Nagaland) to
northern Mizoram, which displays creeping as well as the
microseismicity.
Digital Elevation
Model of the terrain
displays the CMT
and detailed view of
the study area
shows the scarps
and geomorphic
expression of the
CMT
9
Map showing
the epicenters,
fault plane
solutions along
the CMT in the
study area
26.0
Mao
25.5
Latitude
25.0
Imphal
24.5
Churachandpur
24.0
23.5
0.0
10.0
20.0
30.0
40.0
Depth (Km )
Focal depth section along the CMT
10
The geodetic observations have been undertaken along two sites
of CMT shows that the slip rates in its southern part are 0.5 mm/yr
whereas on the northern part is 3.9 mm/yr, monitored during
2004-05.
There is large number of shallow focal depth micro-earthquake of
which in the month of July 2004 most of the events with magnitude
less than 1.5 are less than 7 km.
The frequency of the microearthquake in the area is maximum in the
month of July and continues up to September 2004.
The mircoearthquake of shallow depth and near distance from CMT
might be influenced by creep displacement.
The fault plane solutions are from the existing database and indicate
the ongoing rupturing style.
Results indicate that probable micro earthquake can be recorded
which are being triggered by the creeping.
It is quite similar from the observations from San Andreas Fault zone
because it is the only fault in which creep and microseismicity is well
documented.
11
CONCLUSIONS
The kinematics studies revealed that the landslide is caused by
the wedge failure for the slope instability
Landslides are frequently triggered in a terrain comprising of
soil and rocks of high factor of safety (0.66-1.82).
The monitoring of the rainfall and water table fluctuations
indicates that the high rainfall in the study area is during the
months of June and July and the rising of the water table also
follows the same trend and it makes over saturated soil which
serves as attendant factors for landslides.
The creeping, landslides incidences, geodetic and microseismicity
aspects are the monitored in the present study along the CMT and
results have been compared with well established San Andreas
faults (crustal fault with creeping), where the creeping and
seismicity is well documented.
The CMT is recognized as strike-slip fault, situated west of the Indo
Myanmar subduction, which is a northern segment of IndoAustralian and Southeast Eurasian plate boundary
The accessibility in three dimensions such as creep, seismicity and
landslides incidences make it a natural laboratory for the study of
active faults/thrust.
The manner in which the rate of distribution of seismicity and creep
correlate with fault slip remains to be determined by the future
experiments.
12
13