The 1995 South Hyogo Earthquake took several thousand of lives and destroyed momentarily infrastructures which were designed to perform for a long time. Particularly damages of harbor facilities including Kobe Port were almost completely destroyed. Geological hazards occurred on a large scale at many areas too. This paper describes results of field surveys about damages of harbor facilities and liquefactions mainly in Kobe City, and discusses some about the mechanism and the countermersure

Gotoh Keinosuke

Yamanaka Minoru

Nagasaki University's Academic Output SITE: NAOSITE

Reports of the Faculty of Engineering, Nagasaki University, Vol. 26, No. 46, January 1996 43Liquefaction Damage of Harbor Facilitiesduring the 1995 South Hyogo EarthquakebyMinoru YAMANAKA* and Keinosuke GOTOH*The 1995 South Hyogo Earthquake took several thousand of lives and destroyed momentarilyinfrastructures which were designed to perform for a long time. Particularly damages of harborfacilities including Kobe Port were almost completely destroyed. Geological hazards occurred on alarge scale at many areas too.This paper describes results of field surveys about damages of harbor facilities and liquefactionsmainly in Kobe City, and discusses some about the mechanism and the countermersure.1. IntroductionThe South Hyogo Earthquake with a magnitudeof 7.2 on the Richter scale occurred on January 17,1995. This strong quake had caused severe dam-ages to all infrastructures in a wide area of Kansairegion.The important point to note is that this earth-quake was a direct-type occurred at very nearlocation to a city. Therefore the earthquake accel-eration was very large both in horizontal andvertical directions, and collapse of buildings andN+----_..-,,.--highways. And more its structure were greatlyaffected.As a result of this earthquake a lot of geotech-nical problems have appeared such as the liquefac-tion occurred widespreadly in the seaside area ofOsaka Bay mainly around Hanshin district. Andmany harbor facilities were destroyed by this lique-faction.In this paper we describe mostly about liquefac"tion problems. At first characteristics of damageare shown in field survey. Secondly the relation-Osaka Bay,--',.,'; Location of field surveyFig. 1 Location map of field survey.Received on October 27, 1995* Department of Civil Engineering44 M. Yamanaka, K. Gotohship between liquefaction and topography and geo-logical structure, are shown. Further more mecha-nism of liquefaction is explained. Finally Theeffect of liquefaction countermeasure methods isdescribed.2. Damage SurveyFor the survey purposes, a total of six fieldsurveys were carried out in Kobe City.Figure 1 shows locations of the field survey ofharbor facilities. It's clear that these locations arewidely distributed throughout Hanshin region.The major damaged spots are presented in thefollowing.2. 1 Rokko IslandPhoto 1 shows damage of the north caisson qua-ywall in Rokko Island. At the ground on the rightside some cracks run on the surface. A lateralflow of ground is occurred due to liquefaction.Photo 2 shows a slide of caisson quaywall to thePhoto 1 Lateral flow (taken on Feb. 4).Photo 3 Moving of caisson quaywall (taken onFeb. 12).sea side and a scene of destruction of quay surfacedue to liquefaction. Under pavement a decom-posed weathered granite, called "Masado", is ac-cumlated. This soil is colored light brown colorand has a large cohesion. Inside, much sand boil-ing is spread over the surface.2. 2 Port IslandThe moving to the sea side of the east caissonquaywall in Port Island is shown in Photo. 3. Thefront line of quaywall had moved all alike. Fromthis moving style point of view one may say thatthe quaywall had been moved by the main shock ofthis earthquake.It can be seen in Photo. 4 that the leg of gantrycrane is dropped from the driving rail.2. 3 Meriken ParkPhoto 5 shows the destruction of bulkhead on thesouth side in Meriken Park. This place is consid-ered as a recreation spot for citizens particulary forPhoto 2 Destruction of quay surface (taken onFeb. 4).Photo 4 Damage of gantry crane (taken on Feb.12).Liquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake 45Photo 5 Destruction of bulkhead (taken on Feb. 3). Photo 6 Settlement and rised pile (taken on Feb.3).Table 1 Topographical classification of Kobe Cityl).direction districts geologyvisitors. The symbol of a sightseeing in Kobe hadcompletely damaged too. The ground under con-crete pavement slab has undergone a surface soilStabilization, because the upper layer under cru-shed stones is white and is self-supported. it canbe regarded that the lower layer had been.Photo 6 shows a condition on which liquefied thestep of pedestrian bridge rised due to settlement.This location is about 200m from one of Photo. 5,and the ground have subsided about 20cm. Fromthis view point one may say that the whole areahave subsided.The fourth survey was carried out on May. 12four months after the earthquake. On this time areconstruction work is not done yet.northtJsouth§ clayF:::.:;J si ItE3J sand~ gravelmountainous granite, Kobe group, Palaeozoichilly and heights Osaka group, terrace gravelcoastal plains Alluivialreclaimed lands reclaimed soil, AlluivialFig. 2 Geological structure l ).3. Relationship among damaged area, topogra-phy and geologyIt was the first time that the intensity 7 on theJapanese intensity scale of 7 was applied on theSouth Hyogo Earthquake. Area of intensity 7 onthe Japanese intensity scale of 7 which released bythe Meteoroligical Agency is distributed as a beltwhich lies between the Rokko mountains in thenorth side and the Osaka Bay in the south side.Because of this reason it has been said that thecharacteristics of topography and geology isemphatically related to the transmission mecha-nism of earthquake waves.Therefore we can describe the characteristics oftopography and geology in the following.The topographical classification l ) of Kobe City isshown in Table 1. For a ground which lookedfrom the direction for south-north, in the north sidethe steep Rokko Mountains which formed by gran-ite or by Kobe layer group rises high in the sky, inthe south side on the foot of the mountains a gentlealluvial cone is distributed continuously. Thisalluvial cone is topographic features shaped byweathering colluvium deposits run off as a debrisflow from the Rokko Mountains, have accumlatedcomparatively as large particle deposits as a cobblestone or a gravel. And also a coastal plain formedby the Jomon transgression is spread in the sea side,artificial reclaimed lands are spread along thecoast line.Figure 2 shows the geological structure!) near thecoast line. Between the Jomon transgression costline, located at 4m above the sea level about tenthousand years ago, and the coast line, it can beregarded that the alluvial low plane is mainly46 M. Yamanaka, K. Gotohcomposed of sand and clay layers.Figure 3 shows the relationship between the oldmap and the area of 7 on the Japanese intensityscale. The old map presents natural topographicalfeatures, in other words, it presents actions oferosion and deposition due to the natural forces.Regarding this matter one can get many infor-matins from the old map. As Fig. 3 indicates, thedistributed area of 7 on the Japanese intensity scaleis within 20m above the sea in Hyogo Ward, iswithin 40m in Tyuo Ward, Nada Ward and Higa-shinada Ward, and is within about 20m in AshiyaCity and Nishinomiya City. Besides it can beregarded that the 7 area is distributed within 5mabove the sea, namely anywhere, is distribute inhilly districts or tablelands above the Jomon trans-gression level. It follows that there is a relationbetween the damaged area and the thickness of thelayer.N ow we look at the damaged area from a differ-ent angle in Fig. 3. If one look at a location of acolony early in the Meiji era, a large colony indicat-ed by dots had been developed along waterfront fora reflection of a fishery life in that days, a smallcolony had been dotted in a little-rise land like anatural levee. And generally, these colonies hadbeen distributed in away from the damaged area.For the reasons mentioned above, it seems that theyhad chosen a safe area for the purpose of disasterprevention.Figure 4 shows the result of the piled up the areasof intensity 7 on the Japanese intensity scale on thepresent topographical map2l. First, as comparedwith Fig. 3 from a topographical change point ofview, we can see that topographic features of thepresent map, namely in Fig. 4, is quite differentfrom Fig. 3 regarding the shape of contour lineswhich, is formed like a rised river bed by theaggradation along Sumiyoshi river, Ashiya riverand Shuku river.Concerning the relation of the area of intensity 7on the Japanese intensity scale, areas between theHankyu Railway and Hanshin Railway are includ-ed in damaged area. Judging from the above, itcan be regarded that the great damage is affectedwith the spread to the mountain direction alongwith urbanized areas.Figure 5 shows the points where liquefactionswere occured. the area of intensity 7 on theJapanese intensity scale and the J omon transgres-sion line are presented together. These liquefac-tion points are not included within the area ofintensity 7 on the Japanese intensity scale, they arelocated below the Jomon transgression line, theyare distributed in the alluival plain or the reclaimedland. Because these areas are considered as youngsedimented areas, the loose grounds are spread.As shown in Fig. 5, we can verify the topographi-cal factor that make liquefaction easy to happen, 1)a loose ground, 2) a high water table.4. Judgement of liquefaction for Grain sizedistributionResults of grain size analysis of sand boilingsample obtained from in situ are shown in Fig. 6.Because sand boiling is a soil which spouted andaccumulated above the ground with waters, wemust be care that the grain size distribution forlaboratory test is different from which in the field.The No.2 sand boiling that picked up at theschool ground in Port Island includes some biggravels with the biggest diameter of 19mm of theparticle size. This fact indicates that a very largewater pressure has occurred when the earthquakewas started.The grain size accumulation curve shown inFig. 7 includes all curves shown in Fig. 6 can beused as a judgement criterion of liquefaction3l asestablished by the Harbor Office, the Ministry ofTransport. If a curve is included within the rangeA, the soil is judged as a soil with a big possibilityof liquefaction occurence. If a curve is includedwithin the range Bf or Be, the soil is judged as a soilwith possibility of liquefaction occurence.As a result of laboratory test for the sand boiling,it can be regarded that all soils are included withinthe range A.In Fig. 7, the No.6 soil at the north quaywall inRokko Island is not a sand boiling. The grain sizeaccumulation curve is distributed in wide range.So far as the grain size distribution is concerned, itcan be used in judging weather liquefaction mayLiquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake.: Area of 7 on the Japanese intensity scale of 7Fig. 3 Damaged area on the old map.• : Area of 7 on the Japaneseintensity scale of 7Fig. 4 Damaged area on the presel).t map.47//-<""'PO' <~1'¥.:; liq uefaction pointsFig. 5 Relationship the liquefaction area and the Jomon transgression line.Fig. 6 Grain size distribution of a sand boilings at any point.,j:>.00~~PlSPl~Pl;:.;-'Jlrc;Jori-op-''00100100101/,.II /II II I I __I II I" 'Uozaki minami" machi 1tyome./ ~ I I0.1 1Particle size (mm)0.01 0.1 IParticle size (mm)I @, "-,~~II I!iI I ' II'1 1II II I I II I I II I I II I I II I,/F!OkkO Li ~er II~100(IIIIII [ !The south quawallin Rokko Islandf - I0.01 0:1 1 10Particle size (mm)@C/) 100~ 9'E~a,Q) e! 70C) C) 60~.= 50~ . . . .:"j~~./' 1'/ :uc.20I ;;;; '" jJ ~ s ll. 10I I 00.001\'\" f' 11\100C/)'0090 C/) 90 @~ ~ ~~I Q)~I Cl Cl 60I CtS c: 50I c'c;; 40I~ [~~, !,The ground (1) Q) 10ll.00,01 0.'1 1 10 100 0.001 01 1 10 100Particle size (mm) Particle size (mm)Liquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake 49Fig. 7 Grain size distribution of a sand boiling.0.01 0.1 1Particle size (mm)10 lDDdegree; m1n=i==::'1l~==l railclay layerUX±IIsandy layerFig. 8 Grain size distribution of a reclimed mate-rial (comparing our data with the data of K.Ishihara & S. Yasuda4»).Fig. 9 A sectional diagram of the caisson qu~­ywa1l5).works to be impossible for a long time.The destructive mechanism of the damaged qua-ywall can be explained by looking at Fig. 9 whichshows the cross sectional diagram5) of the caissonquaywall at the Port Island container berth. Thepart under the caisson was substituted by adecomposed weathered granite in stead of the weakmarine clay similar to the reclaimed soH, and thepart behind the caisson was back-filled by rubbles.Under the rail at seaside, steel pipe piles wereplaced.An estimated diagram for the damaged conditonis shown in Fig. 10. As a result of our field sur-veys, we noticed that most of the caissons werebent forward the sea side, and uniformly movedforward. Because of the moving of the caissons,the behind ground had sunk about 1.......,2m. Andsand boilings were accumulated on the subsidencedground and the behind area from the ground.For the reasons mentioned above, conditions anda scale of the earthquake, and the destructivemechanism of the caisson quaywall can be judgedas follows,• At first the caisson is lifted by the seismic. acceleration which was beyond the expectations,which is in the vertical direction in this case, thefriction force between the base of the caisson andthe foundation riprap is lost, and the caisson ismoved in forward direction due to a active earthpressure of the behind reclimed soils.• Because of the moving of the caisson andoccurrence of the liquefaction, the behind ground(A)//~ 100 .,,----.----:-----r-/...,.------r---:,-----::----r--.,.,e------,~ 90 /' /g> 80 / /'jg 70 I~ 60 III) IlQ 50 I~ 40 /g' 30 0 :Rokko Island5l 20 (Goloh&Yamanaka)- : Port Island~ 10 (lshihara&Yasuda)0. 0-t--J:2;::::;~4~~"":"...J--~;""""'~::-"::;:;:;:;:;~::;::;:;:~0.001 0.01 O. 1 1 10 100Particle size (m m)5. Destructive mechanism of the caisson qua-ywallMany harbor facilities have got grave damagesby this earthquake. Because Kobe City is a harbortown in particular, this earthquake caused manyinfluences on a social and a economical activity.The gantry crane on caisson quaywall was almostcompletely destroyed as shown in Photo. 4, and thisdamage have made almost loading and unloadingoccur or not. But some sand boiling have beenspreaded on the surrounding area, and there weresome traces of liquefaction too.A decomposed weathered granite origined atRokko Mountains have been used in reclaimingartificial islands like Rokko Island and Port Island.As Fig. 8 indicates, this soil has a good grain sizedistribution and has a cohesion to some degree, andit has been said as a suitable soil for reclimationpurposes material because it has a good resistanceagainst liquefaction. Eventhough liquefactionhave been occured widespreadly in these artificialislands. We can say that some analysis are left forfuture.50 M.· Yamanaka, K. Gotohsand boilingcrackincreasing·pressure due toliquefaction and lateral flowtvertical accelationFig. 10 Estimated diagram for the damaged con-dition.flows in lateral direction and some cracks occur inthe ground.On the other hand, it may be that the caisson wasmoved by the increasing pressure due to the lique"faction and the lateral flow. But the seismic accel-eration of this earthquake is very large, and is adirect type earthquake which occurs in a shortperiod of time. By considering the a appearanceprocess of liquefaction, it is difficult to think thatthe pore pressure rises at a short time like thisshake and the liquefaction occurs later. Thereforeit seems reasonable to suppose that the most impor-tant external force, which moved the caisson, is theinertia force due to the seismic acceleration.6. Effect of liquefaction countermeasureConsidering the effect of liquefaction counterm-easure in Port Island, some liquefaction counter-measure methods or some accelerated consolida-tion methods were carried out mainly at the resi-dential section in the Island.Figure 11 shows the relationship between thearea of these countermeasure methods6) and theliquefaction distribution area7) based on the surveyof the Geographical Survey Institute, Ministry ofConstruction. In areas which constructed by therod compaction method as a liquefaction counter-measure, there is few area of liquefaction, thiseffect is obviously. And in the area which done bythe sand- drain method as an accelerated consolida-tion method, it is noticed that there is some effectof liquefaction countermeasure. On the otherhand, in area of no liquefaction countermeasureliquefactions widely occured, from here we canobserve the effect of these soil improvement.. Liquefactionrn Sand-drain_ Rod-compactionNtFig. 11 Distribution of liquefaction in Port Island.methods and techniques and their importance inliquefaction reduction.7. ConclusionsIn this papar we have described the damageconditions and the destructive mechanisms of theharbor facilities only. The cause of the damge isnow under investigation, enough data to concludethe cause have not been published yet. Thereforein a condition like this, we could write only anoutline and a qualitative explanation on the SouthHyogo Earthquake. But we should notice that thegrain size distribution method to make a judgmentof liquefaction must be reconsider once more. Andit must be realized that the liquefaction have beenreduced by using some soil improvement methodand techniques.References1) The Ground of Kobe: Kobe City (in Japanese),1980.2) Kobe town maps at the former Meiji era andthe former Showa era (in Japanese): Kashiwa-Shobo, 1995. 4.3) The Japan Harbor Institute: The standardand its explanation for engineering of harborfacilities (in Japanese), 1989. 6.4) K. Ishihara & S. Yasuda: The geological haz-ard near a coastal region (in Japanese), Thegreat Hanshin earthquake disaster survey-TheLiquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake 51emergency briefing session materials, TheJapan Society of Civil Engineers, pp. 13-18,1995. 3.5) The 100th Kobe Port anniversary editorialcommittee: The Kobe open port 100 yearshistory·the Construction volume (in Japanese),Kobe City, p. 615, 1970. 4.6) M. Matsuo et al.: The geological hazard (inJapanese), The great Hanshin earthquakedisaster survey"-"the second briefing sessionmaterials, The Japan Society of Civil Engi-neers, pp. 37-44, 1995. 3.7) The 1995 South Hyogo Earthquake disastermaps (the second edition) (in Japanese), theGeographical Survey Institite, Ministry of Con-.struction. 1995. 4.

Liquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake

Yamanaka, Minoru

Gotoh, Keinosuke

Nagasaki university's Academic Output SITE

https://nagasaki-u.repo.nii.ac.jp/?action=repository_action_common_download&item_id=21036&item_no=1&attribute_id=18&file_no=1

Liquefaction Damage of Harbor Facilities during the 1995 South Hyogo Earthquake

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