Proceedings of the Eighteenth (2008) International Offshore and Polar Engineering Conference
Vancouver, BC, Canada, July 6-11, 2008
Copyright © 2008 by The International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-70-8 (Set); ISBN 1-880653-68-0 (Set)

Damage of Houses and Residential Areas by Niigata Prefecture Earthquakes (Part 1)
Katsuya Matsushita
Misawa Homes Institute of Research and Development Co., Ltd.
Tokyo, Japan

Mamoru Fujii
Tokai University
Kanagawa, Japan

Toru Takata
Soil Design Inc
Tokyo,Japanby settlement problems that make daily life difficult, implementing
countermeasures against earthquakes that might occur without warningat any time is quite difficult. This is thought to become especially moredifficult as the time passed since a major earthquake increases, or as therequired countermeasure expense grows.

ABSTRACTThe earthquakes of Chuetsu (2004) and Chuetsu offshore (2007) in
Niigata Prefecture caused frequent slope failures, landslides and groundliquefaction, and numerous instances of ground-induced damage tohouses and residential areas were noted. In many cases, damage fromliquefaction occurred not only on reclaimed land in coastal areas but
also on residential areas where river channels had been filled.

Although the fact ground hazards can occur more easily on new graded
land and sloped land compared with existing residential land is widely
recognized, and measures such as soil improvement or pile foundations
are adopted in some cases in consideration of site safety when
executing house designs, such hazards become more difficult to take
into account for normal housing construction when, for example, thestability of surrounding sites including adjacent ground is considered.

This research investigates the characteristics and propensities ofliquefaction damage to houses and residential areas. Case histories ofdamage are analyzed, and the current state of aseismic capacity
evaluations of residential areas in Japan and future issues are reported.

Given such conditions, slope failures and liquefaction occurred innumerous instances on graded land during the earthquakes of Chuetsu(2004) and Chuetsu offshore (2007) in Niigata Prefecture, causing
damage to residential areas and houses. In this report, case histories ofdamage are introduced, and the current state of aseismic capacity
evaluations of residential areas in Japan and future issues are reported.

KEY WORDS: Earthquake; damage; wooden building; foundation;
ground; liquefaction; landslide
INTRODUCTION
Houses in Japan are typically made of wood, with the form of woodenbuilding foundations being either continuous footing or raft foundation.
The Swedish weight sounding test is employed widely for housing
ground surveys. The allowable stress of ground is determined from thetest results, and the form of the foundation decided.

Niigata Prefecture-Chuetsu
Offshore Earthquake M6.8

Normally the bearing capacity is investigated, and buildings aredesigned with piles if the capacity is insufficient. For detached houses,
however, cases where the bearing capacity is insufficient are extremely
limited. When ground contact pressure is 20 to 30kN/m2, a spreadfoundation can be used in the foundation design, with the foundation
specifications determined approximately based on settlement.

Niigata Prefecture-Chuetsu
Earthquake M6.8

Fig.1 Epicenters of the two earthquakes

While steps can be taken easily to address building inclination caused743

DAMAGETOHOUSINGRESIDENTIAL LANDFOUNDATIONS

including houses adjacent to the outer perimeter road on the graded
land and houses located outside the perimeter road, were declaredunsafe houses.

ANDGeneral

Before being graded this residential area was a range of steep hills.
Because most of the area is now flat terrain, it is known that the higher
portions of the hilly land were cut and used as fill and earthfill in thesurrounding area to create level terrain. Consequently, the land inside
the residential area can roughly be assumed to be cut land, while theouter perimeter area assumed to be earthfill.

Table 1 summarizes the scale of the earthquake damage resulting fromthe collapse or damage of houses since the 1995 Hyogo PrefectureNanbu Earthquake. According to the reports of housing firms that
conducted disaster studies, of the damage caused by earthquakes that
occurred during the ten years from 1995 to the Niigata Prefecture
Chuetsu Earthquake in 2004, the frequency of housing damage inconnection with ground settlement in residential areas was about 0.07%
of the total number of homes constructed during this period. This result
was approximately 40% of the frequency of occurrence of normal
settlement damage. (Sato, et al, 2005)

Many of the damaged houses were homes where the house bearing
ground was lost as a result of slope collapse or landslide of the earthfill
in the buried ravines, which resulted in damage such as building
inclination and cracks in structure foundations.

Table 1. Recent earthquakes that caused houses to collapse
Structures Number
Maximum damagedof deadMagnitude seismicor
intensity Destroyed
missinghouses

DateEarthquake name

1995/01/17

Hyogo Prefecture-Nanbu
Earthquake

7.37104,906

6,436

2000/07/01

Niijima-Kozushima Near
Shore Earthquake

6.5

Under 6151

2000/10/06

Tottori Prefecture-SeibuEarthquake

7.3

Over 64350

2001/03/24

Geiyo Earthquake

6.7

Under 6702

2003/05/26

Miyagi PrefectureOffshore Earthquake

7.1

Under 620

2003/07/26

Miyagi Prefecture-Hokubu
Earthquake

6.4

Over 6

1,27602003/09/26

Tokachi Offshore
Earthquake

8

Under 61162

2004/10/23

Niigata PrefectureChuetsu Earthquake

6.8

73,18549

2005/03/20

Fukuoka Prefecture-Seiho
Offshore Earthquake

7Under 61331

2005/08/16

Miyagi PrefectureOffshore Earthquake

7.2

Under 611

2007/03/25

Noto Hanto Earthquake

6.9

Over 64031

2007/07/16

Niigata PrefectureChuetsu OffshoreEarthquake

6.8

Over 6

1,244

11Fig.2 Collapse of buried ravine earthfill

Fig.3 Collapsed residential land
As shown in Fig.4(a)(b), such damage was not limited just to theperimeter areas and fractures and faulting of residential land and streets
inside the perimeter road occurred in a number of locations. These
areas are conjectured to be near the boundary between the cuts andearthfill. Houses where ground fissures opened directly beneath thehouse suffered damage such as foundation cracking, but on residential
land where ground fissures veered away from houses, homes frequently
escaped damage.

DAMAGE CAUSED BY SLOPE FAILURE OF GRADES
LAND

Tsurugaoka-danchi, a residential zone more than 30 years old, wasgraded beginning in 1965.

This section reports on the case history of damage to the Takamachidanchi and Tsurugaoka-danchi residential areas, which suffered thegreatest damage from the 2004 earthquake.

This zone is divided into a residential area composed mainly of ravinesburied with earthfill in the vicinity of a storage reservoir, and aresidential area located to the south where a range of steep hills was

At Takamachi-danchi, over 20 years had passed since the area wasdeveloped after 1975. About 70 homes among the total of 522 houses,744leveled. Damage in the residential area in the vicinity of the storage
reservoir where the land is mainly ravines buried with earthfill was
remarkable, with roads collapsed and houses destroyed or inclined as
the result of slope collapse and landslides.

Fig.4 (a) Fractures and faulting near perimeter edge (b) Fractures andfaulting of residential land

Fig.8 Upper side of slide

DAMAGE CAUSED BY LIQUEFACTION

Fig.5 shows the damaged condition of a flank road on this residential
land, where a landslide occurred in the direction of the storage reservoir.

In the 2004 earthquake, liquefaction occurred in the vicinity of theKariyata River, a branch of the Shinano River. Roads in the area
affected by liquefaction were covered with sand boils and muddy water(Fig.9).

Fig.6 shows an example of a retaining wall made a reinforced concrete,
on a residential lot located on sloped land upstream of the storage
reservoir, which was slid more than 1m. Although soil improvement
was performed as a normal countermeasure to prevent settlement, thehouse was inclined toward the direction in which the retaining wall hadslid.

Fig.5 Road collapse causedby landslide

Fig.6 Slide and settlement ofresidential land retaining wallFig.9 Road buried under sand boil
In this area an urban district has formed centered on the natural leveealong the Kariyata River, although it also contains a number of houses
built on reclaimed land. From the topographical map shown in Fig.10,(Geographical Survey Institute) the peripheral reclaimed land can beseen to meander, following the former river channel of the Kariyata
River. Liquefaction generally occurred in places located along thisformer river channel.

In the 2007 earthquake, residential land made with earthfill on sloped
land on sandhills suffered a circular arc landslide over an area 30m
wide and 60m long( Fig.7 and 8). There were six homes located within
this range. The houses in the vicinity of the top part of the slide weremoved 1m horizontally and subsided by more than 50cm. The houses in
the center of the slide area suffered broken foundations and the houses
were completely destroyed. The first floor area of the houses at theedge of the slide was completely destroyed by earth surge.

Former River Channel

Fig.7 Lower side of slide

Fig.10 Topographical map745

Damage to houses caused by liquefaction resulted from inclination that
accompanied house settlement. Among houses where a spreadfoundation or friction type soil improvement had been adopted, there
also were cases of differential settlement of more than 10cm. The
extent of the inclination caused by settlement showed a propensity toincrease at shallower ground water levels. The heavy rains fromTyphoon No. 23 immediately before the earthquake are also believed tohave had an affect, with the rise in the water level being one factor thatcaused differential settlement damage. The site investigation conducted
after the earthquake occurred confirmed that the water level was only
50cm from the ground surface.

Percentage passing by mass(%)

graded land in hilly areas.

Figure 11 (Wakame, et al, 2005) shows the results of the standard
penetration test and Swedish weight sounding tests conducted at thesites where liquefaction occurred, and Fig.12 (Wakame, et al,2005)shows the grain size distribution of the soil samples collectedduring the standard penetration tests. In Fig. 11, the N-values for thestandard penetration test are extremely small, ranging between GL-3.04.0m, in contrast to the results of the SWS tests, which exhibit adifferent trend.

Sand boil No.1
Sand boil No.2
Depth 1.15m
Depth 2.15m
Depth 3.15m
Depth 4.15m
Depth 5.15m
Depth 6.15m

Furthermore, according to the results of the grain size analysis, thenature of the soil of each depth is classified as sandy soil, but at depths
greater than GL-4.0m the figures shows Fc(Fine fraction content)>30%
and Pc(Clay content)≥10%, and the percentage of fine grained soil
content has increased.

ClayGrain size (mm)Fine Medium Coarse Fine Medium Coarse
Silt sandsandsand grave gravel gravel

Fig.12 Results of grain size analysis
Nagaoka New Town is a large-scale residential area whose
development began in 1975. Because the area was created out rolling
hills, damage in Nagaoka New Town was confined to a very limited
narrow range, in contrast to the extensive liquefaction that occurred
near the coast in past earthquakes.
Figure 14 (Matsushita and Tamura, 2005) shows the results of the SWS
test conducted at the site where liquefaction damage occurred. A
stratum with a low resistance value, from the ground surface to a depthof approximately 6m, was confirmed. Because the houses that suffereddamage settled by sinking into the ground surface, the liquefaction isconjectured to have occurred in a comparatively shallow stratum.
Moreover, the site has a 1.5m high retaining wall, and it is thought thewater level behind the wall had risen, thus causing the damage to be
more extensive (Fig.13). In addition to house settlement, upheavals ofearth floors and streets caused by sand boils also occurred.

Fig.11 Results of SPT test and SWS test
The reclaimed land located along the periphery of the former river
channel is conjectured to have similar ground conditions. For newhouses in this vicinity, soil improvement or pile foundations weregenerally adopted as settlement countermeasures, and there was nosettlement damage to houses where the ground had been improved to
the load bearing stratum.

Fig.13 House settlement
and upheaval of earth floor
Fig.14 Results of SWS test

Although damage such as structural damage to buildings andoverturned furniture also occurs frequently in houses in strong
earthquake regions, such damage seldom occurred in the liquefaction
zones. Liquefaction damage also occurred on low ground and on

Figure 15 shows the areas where liquefaction caused by the 2007
earthquake occurred. Damage caused by liquefaction was concentrated

746

around the bases of sandhills and in the vicinity of the Sabaishi River.

Fig.20 shows the results of the standard penetration test on theresidential area ground where damage caused by liquefaction occurred,and Fig.21 shows the results of the liquefaction layer grain size analysis.

This region lies in the vicinity of the boundary where the alluvial
deposits rapidly become very deep, as shown in Fig.16 and Fig.17. The
thickness of the alluvial deposit layer ranges between 50 to 70m.
Alluvial sand strata or reclaimed land were distributed in the areas
where liquefaction occurred.

Reclaimed land
Low ground and valley plain
Natural levee
Former river channel andformer water areas
Sandhills
Alluvial fanTerraces
Other topographic feature(slope,etc.)

Fig.18 Sand boil caused by liquefaction

Water areas

Fig.15 Geomorphological land classification map (GeographicalSurvey Institute)

Fig.19 Deformed house
Fig.16 Geologic cross section position map
Matsunami

Altitude(m)Distance (m)Fig.17 Geologic cross section (Niigata Prefecture GeotechnicalConsultants Association)
At Site A, houses that suffered structural damage caused byliquefaction were dwellings located near the boundary of the sandhills
and low-lying alluvial ground or houses on residential land that had
been filled prior to house construction.

Fig.20 Results of standard penetration test
Sand strata composed mainly of medium sand are distributed from GL3m to about GL-11m, showing an N-value of roughly 10-20 and747

comparatively high “median” relative density at depths of GL-4m andlower. At GL-3m, the ground water level is high. Maximum groundlevel acceleration is estimated to have been about 400gal, andliquefaction is thought to have occurred in ground where large
acceleration had a comparatively high N-value.

CONCLUSIONS
When areas such as newly graded land are used as building sites,
differential settlement of houses or other problems will occur as a resultof ground consolidation settlement caused by earthfill load. Moreover,in addition to such normally occurring settlement, slope failures andlandslides, as well as numerous instances of house foundation orresidential land ground damage originating in ground, are also
recognized to occur frequently in a major earthquake.
Unfortunately, studies that give consideration to the seismic hazards ofresidential land are seldom performed today when constructing
residential housing. Reasons cited include the fact ground disasterprevention is impractical in view of the cost-effectiveness, and thedifficulty of obtaining ground improvement information. Consequently
it is not easy to consider residential land seismic hazards as an elementof design.
One necessary point for detached housing foundation design in thefuture will be the upgrade of ground surveys. Although the SWS test is
the main test for house ground surveys, soil typing or water level
confirmation is difficult simply because of the test’s simplicity. In casesof topographic features whose topographical classification can beconfirmed by means such as a topographical map, and where there is
the possibility of liquefaction, considerations such as conducting
additional studies are critical. Moreover, because soil improvement
design is thought to not be adopted to improve aseismic capacity as apractical matter, there is a danger of settlement damage occurring if thesurrounding surface frictional force on piles is lost as a result ofliquefaction, or if liquefaction occurs beneath the surface layer
improvement load bearing stratum. This is a matter of clarifying thenecessity of soil improvement, and seeking the rationalization orupgrade of the soil improvement designing methods.

Fig.21 Results of liquefaction layer grain size analysis(GL-7~9m)
At Site B, liquefaction occurred in the vicinity of the former river
channel and houses suffered settlement damage. Liquefaction occurredin this area in both the earthquakes of Chuetsu (2004) and Chuetsu
offshore (2007) in Niigata Prefecture. Numerous houses located on theformer river channel suffered from settlement or inclination, withground fissures opening in the residential land straddling the former
river channel and its bank that that damaged houses or their foundations.
Houses where soil improvement to the load bearing stratum had been
undertaken as a normal measure against settlement were also confirmed
to be effective against liquefaction (Fig.22).

REFERENCES
Sato S, Tamura M, Matsushita K and Wakai A, “Development ofHousing Foundation Ground Performance Assessment Technology(1. Basic Approach),” Japanese Geotechnical Society, July 2005.
Geographical Survey Institute, Land Condition Map (Sanjo)
Wakame Y, Tamura M, Matsushita K and Sasaki T, “Damage to Smallscale Building Residential Land and Foundations Caused by the2004 Niigata Prefecture-Chuetsu Earthquake (4. LiquefactionEvaluations),” Architectural Institute of Japan,August 2005.
Matsushita K and Tamura M, “Detached Housing Foundation andGround Settlement Damage and Ground Damage”, Proceedings ofthe Symposium on Evaluation of Safety and Performance ofResidential Ground, Japanese Geotechnical Society, July 2005.
Niigata Prefecture Geotechnical Consultants Association, Niigata
Prefecture Ground Map Editing Committee, ed., Niigata Prefecture
Ground Map Guide, 2002.

Fig.22 Result of soil improvement, heave748