Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanTHE DAMAGE TO ABANDONED MINES AND
QUARRIES BY THE GREAT EAST JAPAN
EARTHQUAKE ON MARCH 11, 2011Ömer AYDAN1 and Hisataka TANO2
1Professor, Ocean Research Institute, Tokai University,Shizuoka, Japan, aydan@scc.u-tokai.ac.jp
2
Professor, Department of Civil Engineering, Nihon University,Koriyama, Japan, tano@civil.ce.nihon-u.ac.jp

ABSTRACT: The East Japan Mega Earthquake with a moment magnitude 9.0 occurredon March 11, 2011 and shook almost the entire Japan. There are many abandoned lignite
mines in the close vicinity of the epicentral area such as Miyagi and Iwate
Prefectures.and many sinkholes occurred following the earthquake. There are also reportson the delayed occurrence of numerous sinkholes in the same areas. In addition, somecollapses and settlement occurred in abandoned underground quarries in Oya town of
Utsunomiya City. The authors investigated damaged areas soon after the earthquake andthey present their investigations results. They also discuss their implications in short andlong-term performance of abandoned mines and quarries in this article.
Key Words: Great East Japan earthquake, abandoned mines, underground quarries,
sinkholes, settlement,

INTRODUCTION
The East Japan Mega Earthquake with a moment magnitude 9.0 took place at 14:46 (JST) on March
11, 2011 (JMA, 2011). The earthquake was a subduction plate-boundary earthquake and the rupturearea was 450 km long and 200 km wide. This earthquake caused gigantic tsunami waves, which
destroyed many cities and towns along the shores of Tohoku and Kanto Regions of Japan. The
casualties caused by this tsunami exceed 20,000 people. The tsunami destroyed and heavily damagedbuildings of various type, transportation facilities and infrastructures. The authors visited Oya(Tochigi) in Kanto region and Iwaki (Fukushima), Wakayanagi, Ohira (Miyagi) and Ichinoseki (Iwate)in Tohoku region and made observations on the collapsed abandoned lignite and coal mines andunderground stone quarries and associated damage to super structures (Figure 1).
The earthquake occurred along the subduction zone between North American plate (NAM) andPacific plate (PAC) and the inclination of the rupture plane was estimated to be 14-16 degrees. Thefaulting was due to thrust faulting with an estimated offset of 25-30 m. The seabed was uplifted by 5m while the land sank-down by about 0.8 m with a horizontal movement of 4.6 m. The rupture
initiated in the area where an earthquake with a magnitude of 7.5 was anticipated and it propagatedbi-laterally.

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Figure 2 shows the maximum ground acceleration contours, which are obtained using the data ofKNET(2011) and KiKNET(2011) (Iwatate and Aydan, 2011). The highest ground acceleration
reaching to the level of 3g was recorded at the Tsukidate strong motion station of KNET. Although theground conditions are very good at this station, it is still difficult to understand the cause of highground motions recorded at the Tsukidate station.
In this article, the authors present the outcomes of their investigations in areas Oya (Tochigi) inKanto region and Iwaki (Fukushima), Wakayanagi, Ohira (Miyagi) and Ichinoseki (Iwate).
Furthermore, they discuss their implications of the observations in relation to the in short andlong-term performance of abandoned mines and quarries, which are widely distributed allover Japan.

Fig. 1 Investigation locations

Fig. 2 Maximum acceleration contours

ABANDONED COAL AND LIGNITE MINES
Figure 3 shows the distributions of coal and lignite (brown coal) fields in Tohoku Region and thelocations and number of sinkhole damage at each locality. The number of sinkhole formation orrelated events are from the news release of the Ministry of Economy, Trade and Industry (METI) on
July 25, 2011. The number of sinkholes and related event were 5 locations in Iwaki City in Fukushima
Prefecture, 11 locations in Kurihara City, 7 locations in Osaki, 11 locations in Higashi Matsushima and3 locations in Kurogawa in Miyagi Prefecture 11 locations in Ichinoseki City and 10 locations in Oshu
City in Iwate Prefecture in the News Release of the METI on March 30, 2011 and the number has
become more than 10 times in the News Release of the METI on July 25, 2011. It is also reported thatthe number of abandoned lignite mine damage events become 20 times that every year in the southernpart of Iwate Prefecture.
The shallow lignite seams are commonly exploited using the room and pillar technique connectedto ground through inclined shafts and vertical shafts. The long-wall technique was employed for
exploiting the coal seams. The coal fields are Jobando coal field and Shirakawa coal field. The authors
explain the observations of damage to abandoned mines investigated by the authors in this section.

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Fig 3 Locations of sinkhole damage (number in parenthesis is the number of damage event)
The numbers are quoted from the New Release of METI on July 25, 2011

Fig. 4 Acceleration records at Iwaki station

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Figure 4 shows the acceleration record at Iwaki strong motion station of KIKNET. The maximum
ground acceleration at Iwaki strong motions station of KIKNET was 481 gals at the ground surface.
There were 5 sinkholes at the abandoned Yoshima mine of Jobando coal field as shown in Figure 5.
The collapses were associated with inclined shafts. The sloshing of the underground water in inclined
shafts caused the failure of roof rock resulting in sinkholes as seen in Figures 6 and 7.

Fig. 5 Locations of sinkholes at the abandoned Yoshima Coal mineFig. 6 Views of sinkholes locations L1-L3984

Fig. 7 Views of sinkholes locations L4-L5
The Ministry of Economy, Trade and Industry of Japan (2011) reported that collapses occurred at
32 locations in Miyagi Prefecture and 21 locations in Iwate Prefecture in the News Release of March30, 2011. The section responsible with abandoned mines incidents in Miyagi Prefecture did notreleased the locations of sinkholes to the authors and the sites were located by the own efforts of theauthors together with the generous help of the local people suffered from this earthquake.
The ground motions records differ from place to place. The largest ground motions were recordedat the Tsukidate strong motion station of KNET. Except top 1 m thick clay layer, this station is basedon sedimentary rocks, which are commonly observed in lignite mine areas. Figure 8 shows theacceleration record at the Tsukidate strong motion station of KNET. The maximum groundacceleration at Tsukidate strong motion station of KIKNET was 2933 gals at the ground surface.
In Wakayanagi town of Kurihara City, 5 sinkholes occurred in residential area as seen in Figure 9.
Luckily , these sinkholes did not cause the collapse of the residential houses on the ground surface.
However, the fracturing of the base concrete occurred and one corner of the building was overhanging
with a slight tilting. The overburden of the sinkholes ranged between 1 m to 3 m at this locality.

Fig. 8 Acceleration records at Tsukidate station

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Fig. 9 Views of sinkholes and related damage in Wakayanagi town
In a large rice field near Ohira Village of Kurihara City, more than 10 sinkholes with a diameter
ranging from 1 m to 5 m were observed as seen in Figure 10. Besides ground shaking, the sloshingphenomenon of ground water in the underground openings abandoned lignite mine areas contributed
to the collapse of the roof layers. As a result of this phenomenon, sandy material together withfragments of rocks and lignite appeared on the ground surface and this ejected sandy material issometimes misinterpreted as ground liquefaction by soil-mechanics researchers and engineers. The
overburden of the sinkholes ranged between 2 to 4 m at this locality.
Besides sinkholes in the rice field, some sinkholes were observed along the roadway and in theparking lot next to residential buildings as seen in Figure 11. The overburden of the sinkholes with adiameter of 2-3 m ranged between 1 to 2 m at this locality. The ground shaking caused the collapse.
Two sinkholes in residential areas and one sinkhole in rice field occurred in the Tsukidate town ofKurihara City. Although there was no casualty in these events, it causes some anxiety in the people
living in such areas.

Fig. 10 Views of sinkholes in a rice field near Ohira Village986

Fig. 11 Views of sinkholes along a roadway and parking lot near Ohira Village
The 2011 East Japan Mega Earthquake caused a number of sinkholes in both residential areas andfields caused in Ichinoseki. The sinkholes were enlarged in size after each large aftershock. Figure 12and 13 shows the sinkholes beneath or close vicinity of houses in Ichinoseki City. Figure 14 shows asinkhole along a roadway in Ichinoseki City. In addtion to these there were sinkholes in rice fields.

Fig. 12 A sinkhole beneath a house in Ichinoseki. (L1). The size of the sinkhole enlarged after theApril 7, 2011 aftershock
In addition to the sinkholes explained in this article, there were also some sinkholes formations inabandoned lignite mine areas in Oshu City (Iwate Prefecture) and Matsushima City (MiyagiPrefecture) . Sinkholes were observed in both residential areas and fields. However, there was no
casualty in any incident.

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Fig. 13. A sinkhole beneath a house in Ichinoseki. (L2)

Fig. 14 Sinkhole beneath the roadway in Ichinoseki (L3)ABANDONED QUARRIES
Damage to abandoned underground quarries occurred in Oya Town (Tochigi Prefecture). Oya tuff orOya stone, has been quarried in the Oya region, Utsunomiya, Japan. Over 200 underground quarries
have been exploited for more than 100 years and some of those are below residential areas. Oya town
is about 295 km away from the earthquake epicenter.
Although ground motions recorded in the vicinity of abandoned underground quaries in Oya, theinstruments are mainly velocity based and they do not measure three components of the groundmotions. Figure 15 shows the acceleration record at Utsunomiya strong motion station of KiKNET
near the Oya town. The maximum ground acceleration at Utsunomiya strong motions station ofKiKNET was 358 gals at the gound surface.
Total or partial collapse of semi-underground quarries occurred as seen in Figures 16 and 17. The
toppling of pillar (P1) caused the collapse of thin roof of the abandoned quarry as seen in Figure 16. Insome cases, partial collapses of the overhanging parts occurred as seen in Figure 17.

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Fig. 15 Acceleration records at UtsunomiyaFig. 16 Totally collapsed semi-underground openingFig. 17 Partially collapsed semi-underground opening

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The settlement of back-filling material of three shafts of abandoned quarries occurred. In theexample shown in Figure 18, the settlement of back-filling material was more than 5 m and thediameter of the shaft was about 7 m. The back-filling material was non-cohesive.
The back-filling material of the abandoned shaft settled more than 3 m as seen in Figure 19.
There was a hut on top of this shaft. The hut and the car parked next to the hut was fallen into thesettled shaft. These observations are very similar to those observed in Yamoto town (re-named asHigashi-Matsushima) during the 2003 Miyagi-Hokubu earthquake.

Fig. 18 The settlement of back-filling material of the shaft

Fig. 19 The settlement of back-filling material of the shaft and the fall of the hut and car into the shaft

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IMPLICATIONS
The 2011 Great East Japan earthquake caused damage to structures and collapses of abandoned mines in
Iwate and Miyagi prefectures where the mining activity was intense about 40 years ago. There are several
locations with similar characteristics in Japan. The observations in this earthquake may have important
implications on areas with abandoned lignite and coal mines where extraction was done by room and pillar
method. Besides the possibility of caving of abandoned mines during earthquakes due to either pillar failure
and/or roof failure, the ground water may present additional effects on the submerged abandoned mines.
These effects may be observed as sloshing, which may weaken the rockmass and cause additional
collapses.
The sand ejection or sand boiling from the abandoned mines are mistakenly mis-interpretted as theground liquefaction by people having soil mechanics background. Although there is no doubt that the sandhaving similar characteristics to liquefied soil is ejected, it is the sand which accumulated at the bottom ofmine adits and were ejected to ground surface through vertical and inclines shafts or collapsed openings
connected to ground surface.
When shafts of abandoned mines and quarries are not deep, they may be filled up using gang material
or debris, the behaviour of which may be similar to that of a non-cohesive granular material. When groundmotions are sufficient enough to cause the yielding of filling material, the filling material would flow into
the adjacent openings and result in the settlement of filling material in the shafts as observed in th shafts ofabandoned quarries of Oya during the 2011 Great East Japan earthquake and in abandoned lignite mines of
Yamoto area (presently Higashi-Matsuhima City) during the 2003 Miyagi Hokubu earthquake.
The fallen material from the roof or collapse of sidewalls may block adits and inclined shafts inabandoned mines and quarries. When these underground openings are fully or partially submergedwith ground water, earthquakes may cause the relative movement of ground water similar to thesloshing phenomenon. When ground motions are strong enough, the ground water may cause thebreach of blocked sections and the collapse of the roof and subsequent ejection of accumulatedmaterial in underground openings (Aydan and Kawamoto, 2004). This behavior was observed inabandoned coal mines of Yoshima in Fukushima Prefecture, Ohira and Wakayanagi in Miyagi
Prefecture during the 2011 Great East Japan Earthquake.
Besides the problems mentioned in this article, the stability of spoils from mining works andtailing dams, the outflow of acidic underground water in mines and outburst of explosive gases due toearthquakes may cause some problems to the environment. Undoubtedly, the 2011 Great East Japan
earthquake caused such problems to some extent and such cases histories should be also well
documented and potential problems should be addressed.

CONCLUSIONS
The following conclusions can be drawn from the observations reported in this study as follow:
1) Strong ground shaking induced the collapses of semi-underground openings in the abandoned Oyaquarries, which are relatively high and having overhanging configurations.
2) Besides the possibility of caving of abandoned mines during earthquakes due to either pillar failure
and/or roof failure, the ground water may present additional effects on the submerged abandoned
mines. These effects may be observed as sloshing, which may weaken the rockmass and cause
additional collapses. Sinkholes are thought to be due to the rupture of ground by the sloshing ofground water in inclined shafts. This phenomenon is the same as that observed in the abandoned
lignite mines of Yamoto Town (presently Higashi-Matsushima City) during the 2003 Miyagi Hokubu
earthquake (Aydan and Kawamoto, 2004; Aydan et al. 2006).
3) When the filling material of shafts of abandoned mines is non-cohesive, the filling material would
settle in the shafts due to its flow into adjacent openings when ground shaking is strong enough to
induce the flow of filling material particles.
4) This earthquake clearly showed that the abandoned mines and underground stone quarries exploitedusing the room and pillar technique are very vulnerable to cause sinkholes and associated collateral
damage to super structures on the ground surface.

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ACKNOWLEDGMENTS
The authors sincerely acknowledge Mr. K. Sugiura and A. Sakamoto of Tobishima Corporation andMiss T. Ono from Iwaki City Council and Mr. K. Sugawara from Wakayanagi town for joining theauthors in some of field investigations reported in this article when it was still difficult to access somesites following the earthquake.

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