6th International Conference on Earthquake Geotechnical Engineering
1-4 November 2015
Christchurch, New Zealand
Study of the Mechanism of Liquefaction-induced Damage to Water
Pipes during the Great East Japan Earthquake in Urayasu City
K. Ishikawa 1, S. Yasuda 2, S. Ikarashi3
ABSTRACT
Approximately 85% of Urayasu City was liquefied during the Great East Japan Earthquake,
causing serious damage to water pipes. This shaking of liquefied ground (a type of sloshing)
produced large cyclic compressive and tensile strains in water pipes in the horizontal plane near
certain boundaries, resulting in the disconnection of water pipe joints. Two-dimensional seismic
response analyses were conducted to demonstrate the concentration of horizontal tensile strain in
five areas of Urayasu City under four levels of shear modulus by considering the effect of
liquefaction. Analyzed results showed large tensile strain was induced on the ground surface
where the bottom of the liquefaction layer was inclined. Large tensile strain was also induced on
ground where shear modulus was low. These locations, where large tensile strain was induced,
largely coincided with the sites where water pipes were damaged.
Introduction
The 2011 Great East Japan Earthquake, with a magnitude of Mw = 9.0, occurred in the Pacific
Ocean about 130 km off the northeast coast of Japan’s main island on March 11, 2011. The
epicentral distance was very long, about 380 to 400 km, and liquefaction occurred over a wide
area of reclaimed land along Tokyo Bay. Large amounts of boiled sand, a large degree of settling,
and a type of sloshing of the liquefied ground were observed in the Tokyo Bay area. According
to Yasuda and Ishikawa (2012) and Towhata et al. (2012), many houses, roads, utilities, and river
dikes were severely damaged by soil liquefaction. The most seriously damaged area was Urayasu
City, where about 85% of the area was liquefied. Seismic intensities in the liquefied zones were
not high, although the liquefied grounds were covered with boiled sand. Most likely, the very
long duration of the main shock along with the large aftershock that hit 29 min later induced the
severe liquefaction. Sidewalks and alleys buckled at several sites, probably due to the
aforementioned sloshing of the liquefied ground. Water pipes were seriously damaged by the
liquefaction. Disconnection of water pipe joints was found at many sites caused by the shaking
of liquefied ground, i.e., a type of sloshing. The shaking produced large cyclic compressive and
tensile strains in water pipes along the horizontal plane near some boundaries, resulting in the
disconnection of pipe joints. The water pipe damage was a characteristic event not confirmed in
previous earthquakes.
The authors recorded buckling damage on a flat road via field investigation after the earthquake.
The buckling damage at the site in Maihama 3-chome is shown in Figure 1. The damage to the
flat road is classified into two damage modes, as shown in Figure 2. In the first damage mode,
some thrust might have occurred at the boundaries due to the sloshing of liquefied ground. In the
1
Keisuke Ishikawa, Tokyo Denki University, Assistant Professor, Saitama, Japan, [email protected]
Susumu Yasuda, Tokyo Denki University, Professor, Saitama, Japan, [email protected]
3
Shota Ikarashi, Graduate School of Tokyo Denki University, Saitama, Japan
2
Horizontal
buckling
A type of sloshing
Horizontal
buckling
Nonliquefied Layer
Liquefied Layer
Slope bottom
a) Horizontal buckling on a sloped bottom of liquefied layer
Structure
Horizontal
buckling
Photo by Mr. Ogawa
A type of sloshing
Liquefied Layer
b) Horizontal buckling at a boundary
Fig. 1 Buckling damage to a flat road
at the Maihama 3-chome study site
Fig. 2 Two possible mechanisms of heaving
Moto-machi
Irihune E’
Maihama
2-Chome A’
A
B’
Sandbar
CTomioka D
C’
ImagawaD’
E
B Maihama
3-Chome
Fig. 3 Water pipe damage and study site
in Urayasu
Fig. 4 Aerial photograph of the study
second mode, horizontal buckling of the surface layer might have occurred due to the
concentration of horizontal compressive stress. In this study, two-dimensional seismic response
analyses were conducted to analyze the concentration of horizontal tensile strain at five areas in
Urayasu City under four levels of shear modulus by considering the effect of liquefaction.
Investigation of the Ground Status in the Study Area
The study area is shown in Figure 3, and it includes the Urayasu City region. Urayasu consists of
three areas: the Moto-machi area is the natural deposition ground and Naka-machi and Shinmachi are the reclaimed lands. Development of the area started in 1965. After the 2011 Great
East Japan Earthquake, liquefaction was confirmed throughout the reclaimed lands but was not
confirmed in Moto-machi. The present study considers five cross-sections with confirmed
damage in the form of water leakage from affected water pipes following the earthquake. Ground
Moto-machi
Natural deposit
ground
E’
Sandbar
Maihama
2-Chome
C
Mud flat
C’
A’
Sandbar A’
A
A
B’
E
D
D’
B’
B
Sandbar
Study section
Damage of Water pipe
B
Maihama
3-Chome
Fig. 5 Sandbar and water route of Old Edo
River and water pipe damage locations
Arakawa Peil (m)
+1.8～+1.9
+1.2～+1.3
+0.6～+0.7
+0.0～+0.1
-0.6～-0.5
-1.3～-1.1
-2.4～-2.3
+1.6～+1.7
+1.0～+1.1
+0.4～+0.5
-0.2～-0.1
-0.8～-0.7
+1.4～+1.5
+0.8～+0.9
+0.2～+0.3
-0.4～-0.3
-1.0～-0.9
-1.6～-1.4
-2.2～-1.7
-2.8～-2.6
-3.0～-2.9
Fig. 6 Bathymetry before the reclamation
structure made the model using the surface wave exploration results, aerial photographs, and
bathymetry results before reclamation.
Urayasu is located at the mouth of the Old Edo River. Therefore, the topography before
reclamation was formed in the tidal flat, the old river channel, the sandbar, and the water route.
The aerial photograph shown in Figure 4 was taken in 1961 (before reclamation) and shows
these features. On the A-A′ line (Maihama 2-chome) shown in Figure 6, the sandbar in the river
mouth of Old Edo River is confirmed; moreover, it is confirmed that there is a river channel near
A′. On the B-B′ line (Maihama 3-chome), the Old Edo River channel is confirmed, and the
sandbar (though not as clear as on the A-A′ line) is also confirmed. From this, the A-A′ line and
B-B′ line show the topographical characteristics that cross the sandbar and the old river channel.
However, the sandbar and water route of the river mouth on the C-C′ line (Tomioka), D-D′ line
(Imagawa), and E-E′ line (Irifune) could not be confirmed. Figure 5 shows the present sandbar
location and water route of the Old Edo River; the locations of water pipe damage in the
Maihama area are also shown. Water pipe damage was concentrated near the boundary of the
river channel and the sandbar. Moreover, it is considered that the damage was concentrated near
the point where the undersurface layer of the reclaimed land inclines.
The elevation of the ground before reclamation was confirmed with bathymetry, and the results
are shown in Figure 6. On the A-A′ line, the elevation of the sandbar is high, and the elevation of
the Old Edo River channel is about 2 to 3 m lower than the sandbar. Similarly, the B-B′ line
confirms a difference of about 2 to 3 m in elevation between the river channel section and the
sandbar section. The change in topography shown by aerial photography agreed with the change
tendencies shown by numerical topography. In addition, the elevation of the C-C′, D-D′, and EE′ lines, where the sandbar was not confirmed, was consistent. This suggests that there is almost
no tilt in the undersurface of the reclaimed land in these cross-sections.
The objective of surface wave exploration is to understand the toughness of a ground surface
(Ishikawa et al. 2014). These results are used to estimate the difference in the toughness of the
A
A’
B
-5
-10
-15
0
B’
0
Depth (m)
Depth (m)
0
10
20
30
40
50
60
70
80
90
-5
-10
-15
0
100 110 120 130
20
40
60
80
100
120
140
160
Distance (m)
A-A’ line : Maihama 2-Chome
C
D
D’
0
Depth (m)
Depth (m)
200
B-B’ line : Maihama 3-Chome
C’
0
-5
-10
-15
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
-5
-10
-15
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Distance (m)
Distance (m)
C-C’ line : Tomioka
E
D-D’ line : Imagawa
E’
0
Depth (m)
180
Distance (m)
-5
-10
-15
0
20
40
60
80
100 120 140 160 180 200 220 240 260
Distance (m)
E-E’ line : Irihune
S-Wave propagation
Velocity VS
Fig. 7 Surface wave exploration result
ground from the construction boundaries of the ground surface. In this study, the exploration was
conducted at a depth of 15 m and evaluated the distribution of the S-wave propagation velocity
(V S ) of the surface lines. The surface wave exploration results of each of the lines are shown in
Figure 7. The results confirm that the loose ground has deposited on the A-A′ line at 60—100 m;
this layer is the ground that was reclaimed from the old river channel. The B-B′ line has
comparatively tough ground at 30—70 m and comparatively loose ground at 0—30 m and 100—150
m. Thus, the topographical characteristics of the sandbar and the river channel are
distinguishable from the exploration results. The C-C′ line has comparatively tough ground at 0—
10 m. A metropolitan expressway and a trunk road pass along this line near 0 m, and so, the
ground toughness is affected by the consequent improvement in surface ground soil compaction.
In a residential street, i.e., after a distance of 20 m on the C-C′ line, loose ground has deposited
thickly; V S is about 100 m/s. The D-D′ line has comparatively tough ground at 0—20 m. Here, the
toughness of the ground may be influenced by the construction of a medium-rise structure and its
pile foundation. After a distance of 20 m, a low-speed degree band was confirmed in the
residential street, i.e., as observed on the C-C′ line. Compared with the other results, the E-E′ line
does not have a characteristic layer structure. However, it was confirmed that both loose and
tough ground were distributed sparsely.
Ground modeling of a verification section
To reproduce the ground structure in detail, a ground model was constructed according to the
following procedures:
A’
Fill
Depth (m)
-5
Slope bottom
Reclaimed layer
-10
-15
0
B
Alluvial sand
10
20
30
40
50
60
70
80
90
B’
0
Depth (m)
A
0
100 110 120 130
Fill
-5
Reclaimed layer
Slope bottom
-10
-15
0
Alluvial sand
20
40
A-A’ line : Maihama 2-Chome
C Expressway
Reclaimed layer
-10
Alluvial sand
-15
-20 -10 0
10 20 30 40 50 60 70 80 90 100 110 120 130
140
160
180
200
Fill
-5
D’
Reclaimed layer
-10
Alluvial sand
-15
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
D-D’ line : Imagawa
E’
E
Fill
0
Depth (m)
120
D
C-C’ line : Tomioka
-5
Reclaimed layer
-10
Alluvial sand
-15
0
100
0
Depth (m)
Depth (m)
C’
Fill
-5
80
B-B’ line : Maihama 3-Chome
Residential section
0
60
20
40
60
80
100 120 140 160 180 200 220 240 260
E-E’ line : Irihune
Blue line : Ground water level
Red line : Water pipes,
Construction depth
Hatching : Liquefied layer
S-Wave propagation
Velocity VS
 The liquefaction layer
assumed that it was a
reclaimed-land layer.
Fig. 8 Created analysis model
1) The basic analysis model is the layer structure in each 250 × 250 m mesh created in the
representative soil profile model (RSPM). The details of the method for constructing the RSPM
are given in JGS (2014).
2) As for the A-A′ and B-B′ lines, the sandbar and the old river channel were confirmed; this
model corrects the basic analysis model in terms of the inclination of the undersurface of the
reclamation layer based on the bathymetry.
3) The analysis area is the reclaimed land of the Tokyo Bay coast. Consolidation of the alluvial
clay layer was confirmed by the overburden load of banking and the reclamation ground (Chiba
Prefecture, 2014). The depth of the layer at the lower end of the reclaimed ground was corrected
by evaluating the amount of consolidation of the alluvial clay layer according to the layer
thickness of the banking and reclaimed ground.
4) The surface of the analysis model evaluated was based on the V S value from surface wave
exploration. After considering the measurement accuracy of the exploration results, the depth
direction was assumed at 15 m. The V S values were categorized into four groups: very loose
layer, 60 m/s; loose layer, 100 m/s; slightly loose layer, 140 m/s; and middle rank layer, 200 m/s.
The analysis model is shown in Figure 8. Hatching shows the reclaimed land that is considered
to have liquefied. In the ground model of the A-A′ line, the undersurface of the reclamation layer
inclines, and the boundary of this topography is near 70 m. In the ground model of the B-B′ line,
the loose layer that buried the old river channel is confirmed at 0—30 m, and the undersurface of
the reclamation layer gently rises. A loose layer with a slow S-wave propagation velocity occurs
near the model center. In the ground model of the C-C′ and D-D′ lines, the area with high V S
values near 0 m is influenced by the boundary of a structure. The residential street after 20 m has
small V S values and is a loose layer. In the ground model of the E-E′ line, the reclamation layer
with a rapid band is sparsely distributed.
Seismic Response Analysis Considering the Effect of Liquefaction
Various Conditions of Seismic Response Analysis
This analysis assumed the existence or nonexistence of liquefaction of a reclaimed land layer.
The analysis method used in this study is “FLUSH,” a two-dimensional FEM seismic response
analysis. Evaluation of the shear modulus affected by the liquefaction was accomplished using
two methods. The first method assumed that the reclaimed land layer did not liquefy, and the
shear modulus was calculated using the equivalent liner method. The second method assumed
that the reclaimed land layer did liquefy. On the ground that liquefied, a very large shear strain
occurs in response to the action of a small shear stress. According to Yasuda et al. (2004), the
shear modulus of the liquefaction ground becomes a very small value, and so, the following rates
were used to evaluate the coefficient of the shear modulus of an infinitesimal strain. The rates
were set to 1/50, 1/100, and 1/200, and the model is linear. In the animation of this earthquake, it
was confirmed that the ground liquefied by a cycle of about 4 s was shaking. The S-wave
propagation velocity of the liquefied ground is set to 6 m/s when the layer thickness of the
liquefaction layer is 8 m. The shear modulus V S value is approximately 100 kPa, and examined
this value. The shear modulus of the liquefaction layer was analyzed for its accordance with five
potential patterns.
Acceleration　(m/s 2)
The setup of the shear modulus for a layer shallower than the alluvial sand layer was established
from the V S value acquired by surface wave exploration. The layer deeper than the alluvial clay
layer was set up using an average of the N value from the RSPM ground model. The dynamic
deformation properties follow Yasuda and Yamaguchi (1985). The unit weight of each layer is a
general value. As a boundary condition, a lateral boundary is taken as an energy transfer
boundary, and the bottom as a rigid basement. The groundwater level is a water level established
by the RSPM. Input earthquake motion is based on observation records from the Yumenoshima
Observatory of the Bureau of Port and Harbor, Tokyo Metropolitan Government. The seismic
waves are shown in earthquake engineering observation records of seismic bedrock. The time
history of input earthquake motion is shown in Figure 9.
1
0.5
0
-0.5
-1
0
Maximum acceleration
-0.6147　m/s2（22.03s）
50
100
150
200
250
300
350
400
450
Time　(s)
Fig. 9 Time history of input earthquake motion
Results of Seismic Response Analysis
As an example of an analysis result, the maximum acceleration contour figure and deformation
figure of line A-A′ are shown in Figure 10. To represent the most extreme condition, the shear
modulus of the liquefaction layer is reduced to 1/200 of the initial shear modulus. The maximum
input earthquake motion is approximately 0.6 m/s2. Maximum acceleration is a response of about
2 m/s2 near the ground surface. It was confirmed that maximum acceleration is amplified close to
where the liquefaction layer inclines. The acceleration response of other sections showed the
same tendency. Deformation occurs after maximum acceleration. It was confirmed that relative
displacement of the ground occurred close to where the undersurface of the liquefaction layer
inclines. The horizontal relative displacement by sloshing of a liquefaction layer is 0.1–0.2 m.
The surface wave exploration and analysis results for each section are shown in Figure 11. The
analysis results show the maximum tensile strain at 1.5 m, i.e., the construction depth of water
pipes. On the A-A′ line, the largest tensile strain occurred near 60 m where the undersurface of
the reclamation layer inclines. At the location of large tensile strain, V S values are low compared
with those of the surrounding ground. Therefore, a decline in the shear modulus of a liquefaction
layer becomes a factor that increases tensile strain. When the shear modulus of a liquefaction
layer was set to 100 kPa, it was confirmed that tensile strain increase by about 1.5%. Water pipe
damage was confirmed where tensile strain is amplified. On the B-B′ line near the old channel of
the Old Edo river at 0 m, the topography changes to a sandbar from 30 m. Therefore, the
undersurface of the reclaimed layer gently rises from 30 m. Large tensile strain is generated
where the V S value is small compared with that of the surrounding ground. Tougher ground is
located near 50 m, and it is considered that the tensile strain was concentrated on the loose
ground because the tougher ground and loose ground collide. On the C-C′ line, water pipe
damage was concentrated around 70—80 m, and the tensile strain in this region is about 1.0%. A
trunk road and the boundary of a residential street are found at around 20 m, and tensile strain
from this boundary is confirmed. Due to the shaking, the residential section that liquefied is
considered to have repeatedly collided with the trunk road of the nonliquefied ground. This is a
structural boundary (as shown by the differing shear modulus of the ground), and this
constrained the damage caused by the shaking of the liquefied ground.
From the above findings, the strain in the ground where the entire region liquefied can be
considered to have been caused by one of the two factors. The first factor, i.e., the liquefaction of
the ground, confirms that strain is concentrated near topographical or structural boundaries. The
second factor, i.e., the reclamation layer and heterogeneous ground, confirms that strain occurs in
the case of an earthquake where there are differences in the shear modulus of the ground.
a) Maximum acceleration contour
b) Deformation mesh
Fig. 10 An example analysis results: A-A’ line (Maihama 2-Chome)
Surface of the Analysis Model : WL－3.0 m
Surface of the Analysis Model : WL－1.2 m
-5
Reclaimed layer
Slope bottom
-10
Alluvial sand
-15
0
10
20
30
40
50
60
70
80
90
-15
0
100 110 120 130
-0.5
-1
-1.5
-2
20
30
40
50
60
70
80
90
100 110 120 130
Distance(m)
20
40
60
80
100
120
140
160
180
200
B
Maximum tensile
strain (%)
0
10
Slope bottom
-10
A’
-2.5
0
Fill
Reclaimed layer
-5
Alluvial sand
A
Maximum tensile
strain (%)
0
Fill
Depth (m)
Depth (m)
0
B’
0
-2
-4
-6
-8
0
50
100
150
200
Distance (m)
B-B’ line : Maihama 3-Chome
A-A’ line : Maihama 2-Chome
Surface of the Analysis Model : WL－1.5 m
Depth (m)
Expressway
Residential section
0
Fill
-5
Reclaimed layer
-10
Alluvial sand
-15
-20 -10 0
10 20 30 40 50 60 70 80 90 100 110 120 130
Maximum tensile
strain (%)
C
C’
0
-2
-4
-6
-8
-10
-20 -10 0
Shear modulus affected
by Liquefaction
1st : Equivalent liner method
( Green )
2nd : Decline of shear modulus
Severe condition by liquefaction
1/50*G0 ( Blue )
1/100*G0 ( Red )
1/200*G0 ( Purple )
G0=100kPa ( Magenta )
2nd method all Linear model
10 20 30 40 50 60 70 80 90 100 110 120 130 140
Distance(m)
S-wave
propagation
velocity VS
(m/sec)
60
100
140
200
: Damage point of water pipe
C-C’ line : Tomioka
Fig. 11 An example surface wave exploration result and analysis results
Moreover, when the groundwater level is deep, the tensile strain generated at the construction
depth of water pipes is small.
Conclusions
The following knowledge was acquired from the two-dimensional seismic response analysis of
water pipe damage due to liquefaction in the study area in Urayasu City.
1) When the ground liquefied across the entire region, the strain caused by earthquake-induced
shaking occurred near topographical and structural boundaries where the undersurface of the
liquefaction layer inclined.
2) A reclamation layer of heterogeneous ground will experience increased strain and shaking
after the liquefaction of areas that have shear differences in the inclined liquefaction layer.
3) Water pipe damage occurred where tensile strain was generated in connection with the
shaking of liquefied ground. Moreover, it appears that ground shaking is related to the
disconnection of water pipe joints.
Acknowledgments
The surface wave exploration was conducted as joint research of the Chiba Waterworks Bureau
and Kurimoto, Ltd. The authors would like to thank Messrs. M. Urano and F. Kondo, former
students at the Tokyo Denki University, for their cooperation.
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