Chapter 2
Macroscopic Characteristics
of Seismic Liquefaction
2.1
2.1.1
Characteristics of Seismic Liquefaction
Earthquakes Induced Widespread Liquefaction
since the Beginning of this Century
According to seismic data, seismic liquefaction and its damage to foundations and
upper structures since the beginning of this century were more frequent than before
in many places around the world. More liquefaction data have been acquired than
previously because of rapid development of science and technology, including
investigation methods and transportation facilities. To better understand macroscopic phenomena related to liquefaction, we examined several earthquakes in
the twenty-first century, considering the comprehensiveness and typicality of
earthquake liquefaction data acquired (Table 2.1).
2.1.2
Characteristics of Liquefaction Distribution
Liquefaction often occurs in areas with saturated and loose sandy soils, and is
distributed near the epicenter. In general, most liquefaction phenomena are
observed near rivers, lakes or coastal areas, owing to soil property and groundwater
level there.
For example, earthquake fountains were observed near the Gulf of Kachchh in
the 2001 Bhuj earthquake, and liquefaction phenomena were mainly reported along
the shore of Lake Pinios in the 2008 Greece earthquake (Margaris et al. 2010). In
the 2010 Chile earthquake, the northernmost liquefaction was in the tailings dam
Veta del Agua, while the southernmost liquefaction was in the Calafquén and
Panguipulli lakes (Verdugo 2011). According to observations of the 2010 Darfield
earthquake, the most serious liquefaction areas were near waterways such as rivers,
© Springer Nature Singapore Pte Ltd. 2017
Y. Huang and M. Yu, Hazard Analysis of Seismic Soil Liquefaction,
Springer Natural Hazards, DOI 10.1007/978-981-10-4379-6_2
11
12
2 Macroscopic Characteristics of Seismic Liquefaction
Table 2.1 General information on major earthquakes in the twenty-first century (reprinted from
Huang and Yu (2013) with permission of Springer)
Earthquake
Date (local
time)
Location
Magnitude
References
Bhuj
January
26, 2001
February
24, 2003
May 12,
2008
India
Mw = 7.6
Singh et al. (2005)
China
Ms = 6.8
Dong et al. (2010)
China
Ms = 8.0
Chen et al. (2009), Huang and Jiang
(2010), Hou et al. (2011), Yuan et al.
(2009)
Margaris et al. (2010)
Bachu
Wenchuan
June 8,
Greece
Mw = 6.4
2008
Chile
February
Chile
Mw = 8.8 Verdugo (2011), Villalobos et al. (2011)
27, 2010
Darfield
September New
Mw = 7.1 Wotherspoon et al. (2012)
4, 2010
Zealand
Yao et al. (2011)
Yingjiang
March 10, China
Ms = 5.8
2011
Tohoku
March 11, Japan
Mw = 9.0 Bhattacharya et al. (2011)
2011
Lushan
April 20,
China
Mw = 6.6 Liu and Huang (2013)
2013
Ms refers to surface wave magnitude, based on measurements of Rayleigh surface waves that
travel primarily along the uppermost layers of the earth; Mw refers to moment magnitude scale,
based on seismic moment of an earthquake (Huang and Yu 2013)
Greece
streams and swamps. In the 2011 Great East Japan Earthquake, Yamaguchi et al.
(2012) indicated that many liquefied sites were in old river beds and developed
areas near Tokyo Bay. In the 2008 Wenchuan earthquake, it was estimated that
70% of liquefied sites were on the Chengdu Plain, with 15% in the Mianyang area
(Cao et al. 2011). In the 2011 Yingjiang earthquake, liquefied areas were found on
both sides of the river, nearly parallel to the Dayingjiang fault. The liquefaction area
was about 2000 square km and was mainly in three areas—lowlands (even marsh
and desert), east of the earthquake region, and along rivers and to the northwest
along the tectonic line (Dong et al. 2010). Compared with the 2008 Wenchuan
earthquake, in the Lushan earthquake, liquefaction only occurred near river terraces
and alluvial flats along the Shuangshi-Dachuan fault, a sub-fault of the
Longmenshan fault (Shi et al. 2014).
2.1.3
Classification of Liquefaction Phenomena
Various liquefaction features have been observed, such as geometry, type, and
dimension. Wang et al. (1983) stated that for similar soil conditions, macro-features
2.1 Characteristics of Seismic Liquefaction
13
of liquefaction and damage on the ground depend on local geomorphic characteristics. Galli (2000) indicated that liquefaction features can be affected by many
factors, including amplification of seismic waves, anomalous propagation, and
geologic conditions (e.g., the grain distribution and density of soil, and groundwater
level). In spite of the various liquefaction features, Wang et al. (1983) pointed out
that macroscopic liquefaction topographic features that reveal various liquefaction
mechanisms can be divided into three categories, i.e., scattered stars, network and
tortile. In terms of liquefaction forms or phenomena, Fairless and Berrill (1984)
identified five types, namely, water ejection and sand boils, settlement, landslides
on moderate slopes, foundation failures, and flotation of light structures. Currently,
the latter three types are regarded as forms of liquefaction-induced damage.
Considering the above classification and data from recent field surveys or the
literature, macroscopic phenomena of liquefaction are classified into three types
here, i.e., sand boiling, ground cracking, and lateral spread based on seismic data
analysis.
2.1.3.1
Sand Boiling
Sand boiling, also called sand boils, sand blows or sand volcanoes, is regarded as
decisive evidence of liquefaction that occurs when void water pressure reaches a
certain value. The phenomenon is called sand boiling because water looks like it is
“boiling” up from the soil foundation. This boiling is actually a mixture of sand and
water that comes from shallow depths to form features of different shapes and sizes
on the ground surface during an earthquake. In general, it can be classified into two
categories based on its formation or the way that liquefied soils eject through the
weak upper soil layer. Both categories are described in the following.
The first formation category may be referred to as flat-cone sand volcanoes.
These volcanoes can be further divided into solitary and clustered cones, both of
which were observed in the 2005 Kashmir Earthquake (Sahoo et al. 2007). In the
2003 Bachu Earthquake, the typical sand boiling diameter was 1–2 m, with the
largest up to 3 m (Dong et al. 2010). Sand boiling was observed at many sites,
including farms where the water spouting was <1 m and the mixtures mainly
contained silty sand and water, according to field surveys. The shapes of sand
boiling holes can be separated into two types, circular and oval, with numerous
forms in the Bachu earthquake. In the 2011 Yingjiang earthquake, sand volcanoes
clustered with heights of no more than 30 cm, and diameters of 10–50 cm were
observed at some locales (Yao et al. 2011). In addition, various types of liquefied
materials that ejected in the shape of clustered cones were observed at certain spots
in the 2008 Greece earthquake (Margaris et al. 2010). In the 2013 Lushan earthquake, liquefaction in the form of sand boiling was observed and was mainly
distributed in a linear zone parallel to the Longmenshan front mountain fault zone.
The ejection holes were nearly 10 cm in diameter, and the ejection height
was *1.0 m (Zhang et al. 2013).
14
2 Macroscopic Characteristics of Seismic Liquefaction
Fig. 2.1 Sand boiling by
eruption on the surface
through existing cracks
(reprinted from Bhattacharya
et al. (2011) with permission
of Elsevier)
The second category refers to sands that erupt on the surface through cracks
while liquefied. Water and sediment mixtures eject immediately and violently to the
surface through preexisting cracks induced by seismic shaking, as seen in the 2005
Kashmir earthquake (Sahoo et al. 2007). This sand boiling category was also
observed in the 2011 Tohoku (Bhattacharya et al. 2011) and 2011 Yingjiang (Yao
et al. 2011) earthquakes. Figure 2.1 shows this type of sand boiling observed in the
Tohoku quake. In the 2001 Bhuj earthquake, a sand blow near Umedpur, 50 km
north of the epicenter, occurred with a crater *10 m long. In the Tohoku earthquake, liquefiable soil erupted from the bed of the Jukken-gawa River in Katori
City, and the riverbed floor was filled with erupted sand boils (Tsukamoto et al.
2012). This could be classified in the second category. In the 2008 Wenchuan
earthquake, sand boiling was accompanied by ground cracks, which caused secondary damage to structures (Huang and Jiang 2010).
2.1.3.2
Ground Cracks
Ground cracks, also called ground fissures, have been reported in almost every
earthquake because of highly uneven distributions of material in the soil layer.
According to field surveys, after the 2008 Wenchuan Earthquake, ground cracks
were reported at 70–80% of liquefaction sites, with elongation between tens and
thousands of meters (Chen et al. 2009). In the 2009 Olancha earthquake, the length
and width of fissures were reported at about 2–20 m and 1–4 cm, respectively
(Holzer et al. 2010). Similarly, the length, width, and depth of ground cracks were
30–50 m, 3–4.5 cm, and 60–130 cm, respectively, in the 2005 Kashmir earthquake
(Sahoo et al. 2007). Sometimes, ground cracks may occur with sand boiling, as
shown in Fig. 2.2. Ground cracks induced by the 2008 Greece earthquake may be
divided into two types, open or filled with sand, with widths of 2–8 cm (Margaris
2.1 Characteristics of Seismic Liquefaction
15
Fig. 2.2 Cracks observed with ejected sand (Pacific Earthquake Engineering Research Center
2001a)
et al. 2010). Cao et al. (2011) stated that in the 2008 Wenchuan earthquake, ground
fissures were found at many sites, and these damaged numerous buildings. In the
2011 Yingjiang earthquake, ground cracks were seen as the main cause of manufacturing damage. Ground cracking was seen everywhere in villages such as Heha
and Yunmao. Soil liquefaction also led to severe cracking of dykes. A crack in the
Yingjiang Dyke was *19 km in length, with average depth 1 m (Yao et al. 2011).
In the 2003 Bachu earthquake, fractures and cracks formed along the Bachu
Yarkand road slope direction, seriously damaging the highway (Dong et al. 2010).
2.1.3.3
Lateral Spread
Lateral spread refers to permanent horizontal displacement of the ground induced
by liquefaction. Bartlett and Youd (1992a, b) indicated that lateral spread produced
by liquefaction occurs mostly on mild slopes underlain by loose sand with a
shallow water table. Lateral spread may be classified into two types, lateral sliding
of mild sloping ground induced by liquefaction at relatively shallow depths, and
large horizontal movement associated with deep-seated liquefaction damage.
Generally, lateral spread has a fixed direction parallel to the course of rivers,
which then possibly generates tensile ground cracks in the same direction. In the
2005 Kashmir earthquake, there was lateral spread toward a bend in the Jhelum
River, 100 m in length, 50 m in width, and with a total displacement of 120–
160 cm. The direction of tensile cracks was parallel to the course of the river
(Aydan et al. 2009). Following the 2009 L’Aquila earthquake, liquefaction-induced
cracks extended toward the river embankment, with widths of 250–350 mm
(Kawashima et al. 2010). Lateral spread displacements generally increased toward
the sea in the 2008 Greece earthquake, with a maximum displacement of 60 cm
16
2 Macroscopic Characteristics of Seismic Liquefaction
Fig. 2.3 East–West view of lateral spread of embankment at Capitol Interpretive Center (Pacific
Earthquake Engineering Research Center, 2001b)
(Margaris et al. 2010). Figure 2.3 shows that lateral spread of an embankment at the
Capitol Interpretive Center occurred with damage length of *75 ft during the
Nisqually earthquake, and its direction was parallel to the river course (Pacific
Earthquake Engineering Research Center, 2001b). In addition, lateral spread is
frequent at relatively flat sites astride streams and other waterfronts, where saturated, recent sediments are common. In the 2001 Bhuj earthquake, lateral spreads
were observed over a wide area in Gujarat and on the border between India and
Pakistan (Tuttle and Hengesh 2002). Chatzipetros et al. (2008) reported that lateral
spread was observed in the 2008 Greece earthquake along the banks of Pinios
Reservoir, at the southern end of a fault. Papathanassiou et al. (2008) reported that
the banks of the Pinios River had a horizontal displacement of 1–2 cm toward the
river. Figure 2.4 shows the location of liquefaction along the Kaiapoi River and
lateral spread around the Kaiapoi Visitors Information Center and Coast Guard
building (identified by “1”), leading to the settlement and tilt of both structures in
the 2010 Darfield earthquake (Wotherspoon et al. 2012).
Fig. 2.4 Aerial photograph of central Kaiapoi River, indicating former river channel (reprinted
from Wotherspoon et al. (2012) with permission of Elsevier)
2.1 Characteristics of Seismic Liquefaction
2.1.4
17
Related Liquefaction Damage
Seismic liquefaction often causes great damage to houses, buildings, bridges,
routes, ports, railways, buried structures, and tailings dams. Such damage can be
distinguished as having three types, i.e., abject failure (including structure failure on
the ground), underground, and other facilities damage in ports or near rivers.
Regarding damage from liquefaction on the ground, damage to piles and bridges,
tilt or uneven settlement of buildings and wire poles, cracks in roads and high
buildings were generally observed. In the 2001 Bhuj earthquake, there were
widespread ground and structural failures at the port of Kandla, 50 km from the
earthquake epicenter, and more than 2300 piles in five berths were seriously
damaged (Hazarika and Boominathan 2009). Tile floors settled unevenly and there
were fine sand deposits around them, which may be seen as evidence of soil
liquefaction under the buildings during the earthquake (Hazarika and Boominathan
2009). In the 2010 Chile earthquake, some bridges suffered severe damage. For
example, noticeable pier settlements from liquefaction occurred at several locations
along Juan Pablo II Bridge, causing it to bend (Ledezma et al. 2012). According to
Yasuda et al. (2012), in the 2011 Tohoku earthquake, *27,000 houses were
damaged in the Tohoku and Kanto districts because of liquefaction, while 3680
houses were more than partially destroyed. Nakai and Sekiguchi (2011) indicated
that the type of surface soil and its amplification characteristics were the major
influences on the severity of liquefaction damage. Cao et al. (2011) stated that
fissures intersecting structures caused structural damage and sporadic collapse
during the 2008 Wenchuan earthquake. Serious damage to the Banqiao School
building was attributed to ground fissures generated by lateral spread toward a
nearby river and intersected building. In the 2011 Yingjiang earthquake, the
damage level of structures was strongly related to liquefied areas (Yao et al. 2011).
It was observed that ground cracking induced by soil liquefaction was the main
cause of building collapse. Damage to buildings, especially residential housing, was
caused by soil liquefaction and the seismic performance of those buildings (Zhang
et al. 2009). Most buildings in the Bachu-Jiashi area were constructed on soft soil,
where the water table was high. This unique geologic condition aggravated damage
from soil liquefaction. Liquefaction caused serious damage to highways. For example,
fractures and cracks formed along the Bachu Yarkand road slope direction in the 2003
Bachu earthquake (Dong et al. 2010). According to field investigations, damages to
structures and liquefaction-induced ground and building failures were widespread
throughout the town of Shuangshi. Damage from soil liquefaction accounted for a
certain proportion during the 2013 Lushan earthquake (Zhang et al. 2013).
Uplift is the main type of damage to underground structures from liquefaction. In
the 2010 Darfield earthquake, Orense (2011) indicated that liquefaction led to a
wide range of uplift of buried structures, including gasoline tanks, sewage tanks,
manholes, and buckled pipes. It is believed that damage from soil liquefaction there
may have been worsened by a high water table caused by a wet winter. In the 2003
Bachu earthquake, a pipeline was lifted *0.3 m in Qiongxiang, and the tilt of
18
2 Macroscopic Characteristics of Seismic Liquefaction
double utility poles led to uneven settlement of a foundation (Dong et al. 2010).
Damage to facilities in ports or near rivers was mainly in coastal areas. In the 2001
Bhuj earthquake, Mavroulis et al. (2010) reported that considerable coastal subsidence was generated by soil liquefaction, which induced secondary damage in
several coastal areas north of the epicentral area. Papathanassiou et al. (2008) stated
that there were small ground cracks in banks of the Pinios River, owing to the
ejection of coarse-grained material. Horizontal displacement of 1–2 cm toward the
river was observed. Structural damage from subsoil liquefaction was seen in the
waterfront area of Vrahneika village, at an epicentral distance of 25 km where the
pavement was cracked and lifelines were damaged.
2.2
2.2.1
Case Study: Field Investigation of Liquefaction
from the 2008 Wenchuan Earthquake
Introduction to Wenchuan Earthquake
The Wenchuan earthquake, also called the 2008 Sichuan or Great Sichuan
Earthquake, struck Sichuan Province in southwestern China on May 12, 2008. It
measured Ms 8.0 and Mw 7.9, with its epicenter in Wenchuan County, and resulted
in the deaths of more than 69,000 people. According to earthquake records, the
earthquake was the most destructive in China since the 1976 Tangshan earthquake.
The earthquake had widespread effects, and it was felt in most provinces of China
and even other countries in Asia.
2.2.2
Survey Area
The author did extensive site investigation of soil liquefaction and structural
damage, including residential buildings, libraries, dams, bridges, highways, tunnels,
underground structures, and other facilities. By combining information on earthquake geological conditions and forms of structural destruction, soil liquefaction
and related engineering damage were analyzed based on field investigation. The
survey area included six serious disaster zones—Wenchuan County, Beichuan
County, Mianzhu, Shifang, Qingchuan County, and Dujiangyan. This area is large
and the investigation scope was comprehensive. Table 2.2 shows investigation
subjects and Fig. 2.5 the distribution of survey sites.
2.2 Case Study: Field Investigation of Liquefaction from the 2008 …
19
Table 2.2 Earthquake damage survey list
Time
Investigation locations
Main investigation subjects
2008.6
Dujiangyan
2008.8
Dujiangyan, Wenchuan County,
Chengdu
2008.9–
11
Mianzhu, Shifang, Qingchuan County,
Beichuan County, Dujiangyan,
Wenchuan County
Mianzhu City, Shifang, Qingchuan
County, Beichuan County, Dujiangyan,
Wenchuan County, Deyang, Mianyang
Investigation of earthquake damage
phenomena
Earthquake damage phenomena of
Duwen Highway, Longxi Tunnel,
Chengdu metro line stations and
tunnels, railway station subway station
Investigation of geological condition
and phenomena of secondary disasters,
collapse, and slip flow
Investigation of foundation damage
phenomenon of housing construction,
reservoir dams, bridges, embankments
etc
Fig. 2.5 Map of investigation sites (modified from Jiang 2009)
2.2.3
Liquefaction Distribution and Characteristics
The earthquake liquefaction extent involves a region with area about 500 km long
and 200 km wide, including the areas of Suining, Meishan, Deyang, Chengdu,
Mianyang, Leshan, Ya’an and Guangyuan (Chen et al. 2009). The farthest district is
Suining in the east, about 210 km from the epicenter, and Hanyuan County in the
south, about 200 km away. Longnan in Gansu Province was the northernmost point
of liquefaction, about 280 km from the epicenter.
20
2 Macroscopic Characteristics of Seismic Liquefaction
Based on the field investigation of hydrology and geology after the Wenchuan
earthquake, the liquefaction distribution and characteristics were analyzed comprehensively as follows.
(1) As shown in Fig. 2.6, liquefaction sites were in a rectangular area about
160 km long and 60 km wide, with the long side in a northeast direction
(Yuan et al. 2009). Liquefied areas were mainly in the cities of Chengdu,
Deyang and Mianyang. The highest earthquake intensity areas (X, XI) were
mainly in the mountains, and a few liquefaction points were found there.
There were liquefaction points in areas of earthquake intensity VI, VII, VIII
and IX, but they were concentrated in area VIII. According to the survey, such
points concentrated in the Deyang area, Mianzhu, and Shifang, especially in
Mianzhu, which had serious damage. Liquefaction in the Chengdu area was
moderate, and was mainly in Dujiangyan. Liquefaction in Mianyang was slight,
mainly in Youxian and Jiangyou.
(2) Liquefaction points were mainly in rural areas, similar to the Tangshan earthquake. Unlike hydrologic conditions in rural areas, underground water depths
were 5–10 m in urban areas, such as southwest of Guanghan and west of
Deyang. Few liquefaction phenomena were observed there.
(3) Soil liquefaction was largely influenced by geologic conditions. By analyzing
the distribution of liquefaction points, it was seen that these points were
mainly in loose sediments of the Quaternary.
Fig. 2.6 Liquefaction points in the Wenchuan earthquake (modified from Yuan et al. 2009)
2.2 Case Study: Field Investigation of Liquefaction from the 2008 …
2.2.4
21
Foundation Damage Related to Liquefaction
in the Dujiangyan Area
To detail the soil liquefaction, a case study of that liquefaction and foundation
damage in the Dujiangyan area was undertaken, as follows. Dujiangyan County is
in a transition area between the south edge of the Longmenshan fault belt and the
Chengdu new-generation, depressed northwest edge of the Sichuan Basin.
2.2.4.1
Liquefaction and Related Damage
Huang and Jiang (2010) showed that sand boiling was observed at several sites in
Dujiangyan County, with maximum ejecta height >1.0 m. Sand boiling was generally accompanied by land subsidence, ground cracks, uneven settlement, and
ground collapse, which caused secondary damage to structures (Huang and Jiang
2010). Water ejection was reported at several sites, with heights from centimeters to
tens of meters. Cao et al. (2011) indicated that most investigated sites had ground
fissures, sand boil deposits, or wells clogged with intruded sand and gravel, which
evidence liquefaction.
At the locations of team numbers 17 and 18, i.e., Xingyi Village, Zhongxing
Town in Dujiangyan County, sand boiling appeared over a large area of cropland
and residences. Maximum ejecta height in these boils was >1.0 m. A large proportion of ejected material was made up of yellow and white sands and cobbles
(Fig. 2.7; Huang and Jiang 2010). Sand boiling was also observed in croplands at
the locality of Team No. 14—Huzhu Village, Puyang Town, Dujiangyan County.
Yellow sands and large cobbles were ejected from croplands and surrounding
roads, reaching a maximum height of *1.0 m. Localized sand deposits 10 cm in
depth were observed in fields after the earthquake (Fig. 2.8; Huang and Jiang
2010). Sand boiling was accompanied by land subsidence, uneven settlement,
ground cracks, and ground collapse. This damaged buildings, involving leaning,
cracking, and even collapse (Fig. 2.9; Huang and Jiang 2010). At the location of
team number 14, Huzhu Village in Puyang Town of Dujiangyan County, numerous
ground cracks were observed (Fig. 2.10; Huang and Jiang 2010), accompanied by
surface uplift. The broadest ground cracks were almost 30 cm wide, which were
partly hunched and shut in during aftershocks. In addition, surrounding buildings
suffered many cracks caused by leaning (Fig. 2.11; Huang and Jiang 2010).
In Dujiangyan Puyang Town, group 14, there was widespread ejected sand and
water, with a large number of ground fissures and ground swell. The earthquake
ground crack width was *30 cm. Some cracks were from uplift, and because of
aftershocks some cracks gradually closed. Figure 2.12 shows the uneven subsidence caused by liquefaction in Puyang Town. The uneven settlement cracked and
damaged foundations, causing some buildings to collapse. Figure 2.13 shows
bridge foundation displacement caused by liquefaction.
22
Fig. 2.7 Liquefaction of
fine-grained yellow sand
(ejection area *1094 m2)
(reprinted from Huang and
Jiang (2010) with permission
of Springer)
Fig. 2.8 Liquefaction of
white sand (ejection
area *294 m2) (reprinted
from Huang and Jiang (2010)
with permission of Springer)
Fig. 2.9 Subsidence caused
by liquefaction (length of
subsidence area *12 m,
mean width *3 cm)
(reprinted from Huang and
Jiang (2010) with permission
of Springer)
2 Macroscopic Characteristics of Seismic Liquefaction
2.2 Case Study: Field Investigation of Liquefaction from the 2008 …
23
Fig. 2.10 Cracks caused by
liquefaction (cracks
distributed over 8 5 m2
area) (reprinted from Huang
and Jiang (2010) with
permission of Springer)
Fig. 2.11 Building cracks
caused by liquefaction
(reprinted from Huang and
Jiang (2010) with permission
of Springer)
Quaternary sediments were widely distributed in the toes of dams and nearby
rivers, and mainly included fine-grained sand and silty clay. In such areas, pore
pressure can increase rapidly during an earthquake and the ground can become
liquefied because of a high groundwater level. Figure 2.14 shows buildings
downstream from the toe of the major dam of Boling Reservoir in the city of
Mianzhu (Huang and Jiang 2010). These buildings partially collapsed during the
earthquake, whereas those farther from the dam toe were only moderately or
slightly damaged. Figure 2.15 shows buildings near the Minjiang River at the
location of team number 10, Tongyi Village of Dujiangyan County (Huang and
Jiang 2010). These buildings were as close as 10 m to the levee, which was
severely damaged in the Wenchuan earthquake. As known from previous earthquakes, the major types of liquefiable soil are sandy silt and fine-grained sand
(Xenaki and Athanasopoulos 2003). However, in the Wenchuan earthquake,
24
2 Macroscopic Characteristics of Seismic Liquefaction
Fig. 2.12 Subsidence caused
by liquefaction
Fig. 2.13 Bridge foundation
displacement caused by
liquefaction
numerous larger-diameter cobbles were contained in the liquefaction ejecta. This
finding creates a new challenge to traditional liquefaction research, including criteria of liquefiable soil and liquefaction resistance measures.
2.2.4.2
Analysis of Liquefaction Mechanism
(1) Stratum distribution in Dujiangyan area
In the Dujiangyan area, the ground is flat and consists of Quaternary Holocene
artificial fill earth and Quaternary Holocene alluvium (Huang and Jiang 2010). This
strata is widely distributed in that area. From top to bottom are filled earth, silty
2.2 Case Study: Field Investigation of Liquefaction from the 2008 …
25
Fig. 2.14 Partially collapsed
buildings near dam (reprinted
from Huang and Jiang (2010)
with permission of Springer)
Fig. 2.15 Collapsed
buildings near Minjiang River
(reprinted from Huang and
Jiang (2010) with permission
of Springer)
clay, fine sand, loose cobble, slightly dense cobble, moderately dense cobble, and
dense cobble.
Dujiangyan is a geological transition area, located between the northwestern
edge of Chengdu Cenozoic in the Sichuan basin and Longmen Mountain tectonic
belt. The terrain is open, with few geologic disasters such as landslides or debris
flow. However, fine sand with medium liquefaction is widely distributed.
Quaternary Holocene artificial soil and Quaternary Holocene river alluvium
deposits are widespread in the area, and typical regional strata are as follows.
A. Fill soil: gray, grayish yellow, gray and black, mottled. Loose, slightly wet,
composed mainly of silt, gravel composite, with a thickness of 0.8–5.4 m.
B. Silt, silty clay: gray, brown gray. Slightly wet, loose, scattered distribution, with
a thickness of 0–3.0 m.
26
2 Macroscopic Characteristics of Seismic Liquefaction
C. Fine sand: gray, slightly wet, loose, lentoid distribution, with thickness 0.6–
1.9 m.
D. Loose gravel: yellow, pale yellow, slightly wet, gravel content 50–55%, with
diameters of 3–5 cm, with a maximum 15 cm, fine sand and silt filling a pebble
skeleton. Lentoid distribution with a thickness of 0–1.4 m.
E. Slightly dense gravel: yellow, pale yellow, close to saturation, gravel content
55–60%, diameters of about 3–18 cm, with some >30 cm; disarrayed, fine sand
and gravel fill between around 40 and 45% and a small amount of gravel, the
layer of which is continuously distributed over the dense gravel layer, with a
thickness of 0.8–4.1 m.
F. Dense gravel: yellow, pale yellow, saturation. Pebble content 60–70%, a
general diameter of 5–12 cm, a maximum diameter 40 cm, staggered
arrangement, most in contacts, pebble can form a skeleton, fine sand skeleton
filled between about 30 and 40% and a small amount of gravel, pebble content *30%, unknown hickness.
G. Compacted gravel: particle size of 8–20 cm, maximum size >40 cm, gravel
skeleton content about 70–85%, unknown thickness.
(2) Liquefaction factors (Huang and Jiang 2010)
In view of regional geological and ground conditions in Dujiangyan County, the
liquefaction of cobble layers was investigated by considering the following factors.
A. Seismic conditions
Dujiangyan is 16 km from the epicenter of the Wenchuan earthquake. The seismic
intensity at Dujiangyan during the earthquake was VIII, which means strong ground
motion and long seismic duration (China Earthquake Administration 2008). As is
commonly known, higher intensity and stronger peak ground acceleration is more
likely to result in soil liquefaction. In addition, longer duration means long cyclic
loading on soil, and therefore a greater risk of soil liquefaction.
B. Overlying earth pressure
In the Dujiangyan area, Quaternary Minjiang River alluvial deposits consist of
loose sand and cobbles distributed as lenses. Because the sediments have a top layer
of 0.5–5.0 m beneath the surface, overlying earth pressure is low. The ejection of
sands and cobbles from the ground occurred when pore pressure increased rapidly.
Investigations show that sand boiling occurred mostly in croplands and around
buildings, whereas it was seldom found inside buildings or in other locations with
additional load. This suggests that overlying pressure is one of the most crucial
factors in liquefaction.
As is well known, the stronger the overlying earth pressure, the greater the liquefaction resistance. This was verified by field investigation of macro phenomena.
Therefore, for low-rise buildings, if their site has liquefiable soil, it can be treated by
increasing overlying earth pressure by adding a certain thickness of earth fill. This
reduces the probability of liquefaction damage.
2.2 Case Study: Field Investigation of Liquefaction from the 2008 …
27
In the Dujiangyan area, the sand and silt are in a lentoid distribution, and are not
deep beneath the surface. Thus, in engineering design, removal of all liquefiable
soil is recommended.
C. Density
The top cobble layer in Dujiangyan County is generally loose and unconsolidated,
with an uneven thickness of 0–1.4 m over the entire area. Cobbles make up 50–
55% of the material in this soil layer by volume and have typical diameters of 3–
5 cm, with some as large as 15 cm. The cobbles are irregularly packed and most are
independent, not forming a skeleton. They are usually suspended with fine-grained
sands and silty soil.
Undrained cyclic triaxial tests showed that the liquefaction resistance of
sand-gravel composites increases with density. By increasing the amount of gravel
(Evans and Zhou 1995), the likelihood of liquefaction decreases with increasing
density of the sand-gravel composite. In contrast, the cobble layer has a lower
density, increasing the potential for liquefaction. Groundwater in Dujiangyan
County is found on the first terrace of the Minjiang River. This water is abundant
and the water table is shallow. Perched aquifers are common in silty soil and
fine-grained sand layers. The major regional aquifer has a shallow sand and gravel
layer. The groundwater is supplied by precipitation and underground transport, and
its distribution correlates well with the large number of liquefaction occurrences
along both sides of the Minjiang River.
For deep soil, methods like water-washed vibration and vibration-immersed
tubes can be used. Vibroflotation construction causes saturated loose sand particles
under forced vibration to have a high frequency; these particles rearrange and
became compact. This produces a strong horizontal vibration force in the surrounding soil, increasing relative density of the sand and reducing porosity. This
improves liquefaction resistance of the soil.
D. Fabric
The fabric of soils and buildings is also important in liquefaction. The cobble layer
in Dujiangyan County was loose and extremely porous. As a result, it had a lower
liquefaction resistance strength. Under these conditions, liquefaction takes place
much more easily through high-intensity shaking from an earthquake. Subsidence is
a common earthquake-induced phenomenon that results in the sinking of ground
and buildings. This is also known as permanent or residual deformation, and
accounts for some of the most substantial primary damage from earthquakes. The
extent of subsidence caused by past earthquakes has varied. Huang and Jiang
(2010) showed a building of brick column structure atop soft soil at Hanwang Town
in the city of Mianzhu, which did not have adequate bearing capacity. During the
earthquake, its columns sank by nearly 15 cm because of non-uniform ground
subsidence, which destroyed the structures supported by the columns. The steps of
a telecommunications building in Dujiangyan County show another example of the
effects of earthquake subsidence.
28
2 Macroscopic Characteristics of Seismic Liquefaction
Additionally, along the concreted edge of the building, nonuniform subsidence
occurred on the porch (Huang and Jiang 2010). Highways with soft roadbeds also
experienced non-uniform earthquake subsidence, which caused their substantial
damage.
2.3
New Liquefaction Phenomena During Recent
Earthquakes
In comparison to the conventional liquefaction characteristics mentioned above,
something different was found according to the 2008 Wenchuan earthquake survey
and other literature published in recent years. Yuan et al. (2009) listed three new
findings from analysis of liquefaction phenomena in that earthquake. Based on the
aforementioned survey, research findings, and the literature, the new characteristics
are summarized into four categories: Liquefaction occurred in areas of moderate
seismic intensity; liquefaction could occur in areas with gravelly soils; liquefaction
might also occur in deep-level sandy soils; re-liquefaction could occur during
aftershocks. These findings are explained as follows.
(1) Liquefaction in areas of moderate seismic intensity
In China, the Code for Seismic Design of Buildings (Ministry of Construction of
China 2001) stipulated that areas with seismic intensity VI or less could be treated
as free from liquefaction. However, liquefaction can occur in areas with moderate
seismic intensity. Chen et al. (2009) reported that although seismic intensity was
VI, liquefaction and serious related damage was observed at more than 10 sites.
Such a phenomenon was observed in mainland China for the first time, and reveals
that areas of moderate seismic intensity can liquefy because of relatively
high-amplitude ground motion and sufficient duration of shaking. Further, Shi et al.
(2014) discovered that in the Wenchuan earthquake, the threshold energy required
to induce liquefaction was just 5% that of the Lushan earthquake. This may be
related to two factors: (1) Liquefaction occurrence may be more sensitive to low
seismic frequencies; (2) the sensitivity of unconsolidated materials may have been
altered by the Wenchuan earthquake. Both of the above factors need further study.
(2) Liquefaction of gravelly soils
Liquefaction generally occurs in coarse silts and fine sands that are saturated. To
mitigate liquefaction potential in engineering practice, saturated coarse silts or fine
sands may be replaced by gravelly soil, which was once thought to be
non-liquefiable.
Until the 2008 Wenchuan earthquake, the aforementioned Code for Seismic
Design of Buildings held that gravels and gravelly soils may be treated as
non-liquefiable (Ministry of Construction of China 2001). However, Cao et al.
(2011) observed that gravelly soils with mean grain sizes from 1 to >30 mm were
2.3 New Liquefaction Phenomena During Recent Earthquakes
29
liquefied in the Wenchuan earthquake. In general, gravelly sand refers to cohesiveless, and individual gravel grains and cobbles suspended by fine-grained sand
and silty soil (Huang and Jiang 2010). The liquefied gravelly Holocene soils found
in the Wenchuan earthquake were shallow and loose, with low shear-wave
velocities. This may have increased the liquefaction potential (Hou et al. 2011).
Both sand boils and gravelly sand ejected from the surface were observed (Chen
et al. 2008), and gravelly soil liquefaction was also reported in Shuangshi Town
during the Lushan earthquake (Liu and Huang 2013). Owing to a lack of research
on liquefaction of gravels and gravelly soil, both the liquefaction mechanism or
conditions and method of evaluating liquefaction resistance of gravels and gravelly
soil require further study.
(3) Liquefaction of deep-level sandy soils
Sahoo et al. (2007) indicated that liquefaction occurs when a saturated sandy layer
is overlain by a certain thickness of confining medium, such as clay or silt. The
overlying medium reduces the overall hydraulic ability, preventing rapid drainage
and mitigating liquefaction potential. Moreover, according to the Code for Seismic
Design of Buildings (Ministry of Construction of China 2001), almost no liquefaction has been observed below a depth of 15 m.
In contrast with conventional experience, deep-level sandy soils were observed
to be liquefied in recent century earthquakes. For example, it was found in field
investigations that the depth of liquefaction reached *20 m in the large-magnitude
2008 Wenchuan earthquake (Ms = 8.0; Yuan et al. 2009), and 12–16 m in the 2011
Tohoku earthquake (Mw = 9.0) (Bhattacharya et al. 2011). There have been no
reports of soil liquefaction deeper than 30 m during recorded earthquakes (Youd
et al. 2001). However, it has been proven by centrifuge tests that medium-density
sand layers at depths >30 m can also fully liquefy under high confining stress.
Moreover, compared with surface soil, deposits at greater depths would require
more cycles of excitation to be liquefied (Gonzailez et al. 2005). Accordingly,
deep-level sandy soils may be liquefied under high-amplitude ground motion of
long duration.
(4) Re-liquefaction in aftershocks
In the 2008 Wenchuan Earthquake, an intensity-VII area liquefied following the
main shock on 12 May, and then re-liquefied during an aftershock of magnitude Ms
6.4 (Chen et al. 2009). By analyzing observational data of paleoseismic liquefaction, Ha et al. (2011) indicated that sand can liquefy again during aftershocks
following initial liquefaction during seismic shaking. Dong et al. (2010) held that
the most important feature of re-liquefaction is stacked sand volcanoes, with small
holes developing in larger holes. In the 2003 Bachu earthquake, diameters of large
and small holes were observed in ranges of 50–100 cm and 5–10 cm, respectively
(Dong et al. 2010). Following the 2010 Darfield Earthquake, liquefaction
30
2 Macroscopic Characteristics of Seismic Liquefaction
reoccurred in a Mw 6.3 aftershock on February 22, 2011, over a smaller part of the
region previously liquefied (Wotherspoon et al. 2012). Re-liquefaction during
aftershocks was also found following the 2011 Tohoku Earthquake (Onoue et al.
2012).
Research into the mechanism of re-liquefaction during aftershocks has received
much attention recently. After initial liquefaction, the soil fabric is destroyed and
becomes highly anisotropic and unstable (Ha et al. 2011). If excess pore water
pressure cannot be dissipated to a certain value before aftershocks, the liquefaction
assistance will reduce significantly. In such cases, soil may re-liquefy more readily
and lead to secondary damage (Oda et al. 2001).
2.4
Summary
Earthquakes occur in many locations worldwide every year, especially along plate
boundaries such as the one between the Pacific and North American plates.
Earthquakes can cause shaking and ground rupture, landslides, tsunamis, floods and
soil liquefaction, causing numerous injuries and loss of life. People have come to
recognize soil liquefaction over the past several centuries, from the discovery of its
related phenomena to its general characteristics.
This chapter examined several representative earthquakes around the world since
the beginning of this century and liquefaction phenomena in detail. These phenomena were classified into three types—sand boiling, ground cracks, and lateral
spread. Survey investigations of the 2008 Wenchuan earthquake were then
described in detail to determine seismic liquefaction. New liquefaction characteristics were discovered according to these surveys and other literature published in
recent years. Yuan et al. (2009) forwarded three new findings from analysis of
liquefaction phenomena in the Wenchuan earthquake. Based on the surveys
described above, research findings, and the literature, the new characteristics were
divided into one of four categories:
(1)
(2)
(3)
(4)
Liquefaction in areas of moderate seismic intensity
Liquefaction of gravelly soils
Liquefaction of deep-level sandy soils
Re-liquefaction during aftershocks
Most engineering design criteria in use are based on previous experience.
Because the new liquefaction characteristics were found in the recent field investigations, previous criteria of liquefaction and building design codes may not be
adequate and must be improved or revised. If this is not done, some areas may again
suffer serious loss of life and property. We should continually correct our understanding of nature through further surveys or study of new phenomena, and this is
precisely the intent of our work.
References
31
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