Missouri University of Science and Technology Scholars' Mine
International Conferences on Recent Advances 2001 - Fourth International Conference on in Geotechnical Earthquake Engineering and Recent Advances in Geotechnical Earthquake Soil Dynamics Engineering and Soil Dynamics
30 Mar 2001, 10:30 am - 12:30 pm
Water Films Involved in Post-Liquefaction Flow Failure in Niigata City During the 1964 Niigata Earthquake
Takeji Kokusho Chuo University, Japan
Katsuhisa Fujita Chuo University, Japan
Follow this and additional works at: https://scholarsmine.mst.edu/icrageesd
Part of the Geotechnical Engineering Commons
Recommended Citation Kokusho, Takeji and Fujita, Katsuhisa, "Water Films Involved in Post-Liquefaction Flow Failure in Niigata City During the 1964 Niigata Earthquake" (2001). International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. 25. https://scholarsmine.mst.edu/icrageesd/04icrageesd/session05/25
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. WATER FILMS INVOLVED IN POST-LIQUEFACTION FLOW FAILURE IN NIIGATA CITY DURING THE 1964 NIIGATA EARTHQUAKE
Takeji Kokusho Katsuhisa Fujita Professor, Chuo University Graduate Student 1-13-27 Kasuga Bunkyo-ku ditto Tokyo, Japan 112455 1
ABSTRACT
Natural sand deposits are in most cases heterogeneous and layered in the horizontal direction due to stratification. If such deposits are liquefied during earthquakes, water films are likely to develop beneath less permeable sublayers leading to destabilization of a sloping ground. In Niigata city, large lateral flow displacements were reported during the Niigata earthquake in almost flat areas. Possible involvement of the water films in lateral flow failure in liquefied ground during the earthquake is examined in this research based on various site investigation data of Niigata city. Soil profiles in the area estimated from many bore-hole logging data indicate that there exists a continuous sublayer of silt or clay capping liquefiable loose sand. The elevation contoursof O.lm pitch are drawn basedon insitu leveling survey and local maps. The flow displacements during the earthquake seem to head downward normal to the contours and showa clear correlationwith groundslope. This suggests that the large flow deformation in this area was driven by the slight ground surface inclination of less than 1% and that was made possible due to the formation of water films, which will considerably reduce the shear resistance of the soil against flow. lNTKODUCTfON but still much gentler than internal friction angle of sea-floor deposit. In Greece,at the occasion of 1995 Aegion earthquake, a In past earthquakes, lateral spreads in alluvial sand deposits took post-earthquake submarine slide involving coastal land with the place in coastal or river-side areas like Alaska and Niigata. slope of 12% occurred. The soil profile at the failure site was Submarine slides were also seismically triggered worldwide. characterized by a continuous interchange between silty sand and Normally the ground slope in those slides was not so steep but clay layers (Bouckovalas et al. 1999). much gentler than the internal iiiction angle of the soil. The lateral spreads or flows took place not only during but also after Sand deposits are thus often composed ofmany sublayers because the earthquake shaking. The distance of ilow sometimes reached of sedimentation processes. The present authors (Kokusho et al. several meters even with very gentle slope of less than a few 1998 and Kokusho 1999) already demonstrated by means of percent. 2-dimensional shake table tests and one-dimensional tube tests that such layered sand, if liquefied, will form a water film beneath In Niigata city, a famous lateral spread occurred in the Meikun a less pervious sublayer due to a local migration of pore-water, High School along the Shinano River where a rather large flat which serves as a sliding surface for post-liquefaction flow failure. area of 250m by 150m moving toward the river by maximum 7 The failure may occur not only during but also after shaking. ‘l‘he meters (Kawakami and Asada 1966). Soil profiles in this area soil mass above the water film can slide even along a very gentle consistednot only of sandbut also of sublayers of silts or clays slope and may also behave as a mud flow if the water ftlrn breaks according to a chart in a previous report (Kishida 1966). during sliding triggering re-liquefactionof the above soil mass. In contrast, the majority of previous researches concentrated On the other hand, during the 1999 Kocaeri earthquake in Turkey, themselves on the undrained behavior of liquefied uniform sand southern coastal areas along the Izmit bay suffered submarine and paid little attention to the layering efEect on the slide triggered by the quake, which deprived coastal land together post-liquefaction flow failure. with many human lives and properties. The average seabed slope in front was about 10% and rather steep compared to other areas In this research, in addition to the similar one by the same authors
Paper No. 5.38 1 (Kokusho, Fujita and Morishima 2000), case histories of flow bank, mostly in the south-east direction toward the Niigata station. failure in liquefied sandy deposits in Niigata city during the The magnitude of the lateral flow exceeded 4m in some of the Niigata earthquake will be reviewed from the viewpoint of a investigated points despite very gentle slope of less than 1%. potential involvement of water films. Bore-hole logging data provided by the Niigata Municipal Office and ground surface unevennessdata collected from local map and insitu measurement are compared with previously available data on lateral flow displacements in the liquefied area to investigate the possibility of water fiIm generation and its role in the flow failure.
SITE CONDIl‘lON
Fig.1 shows the major part of Niigata city along the Shinano river, where severe damages occurred due to soil liquefaction during the 1964 Niigata earthquake (M,=7..5). It is located at the mouth of Shinano river (one of the longest rivers in Japan) where the ground surface is essentially Hat. Fig.2 is a large scale map of the investigated area between the right bank of the Shinano river and the Niigata railway station. Hamada(1992) investigated the Fig.1. Major part of Niigata city with investigated lateral flow deformation in this area by comparing the area and long-term land subsidence measuring air-photographs taken before and after the earthquake, It revealed points.(4422,4423, n 16 and n 184) that despite the existence of the river channel in the north-west direction, the flow occurred, except in the vicinity of the river
Fig.2. Investigated area between right bank uf Shinano river and Niigata railway station (Horizontal displacements are after Hamada 1992)
Paper No. S.38 2 Ni gata GROUND SURFACE UNEVENNESS
Niigata city is located on a fan delta at the mouth of Shinano river and the ground surface is essentially flat. Nonetheless, a slight unevenness is focused in this research based on a hypothesis that it may serve as a sufficient driving force to induce a large magnitude flow displacement if water films with no shear resistance are formed in liquefied sand deposits (Kokusho et al. 1998, Kokusho 1999). For that purpose the ground elevation contours are drawn based on the information of l/2500 scale map issued in 1994 by the Geographical Survey Institute in Tsukuba and also on additional data measured with the leveling survey carried out in 1999 by the present authors in Niigata city. The elevation contours with a O.lm pitch, which are drawn by interpolating given elevations at nearby points, are superimposed However, the elevation contours in Fig.2 thus on Fig.2. 1965 1970 1975 1980 1985 1990 1995 2000 established for the present time may be different from those at the Year time of the earthquake in two reasons. Fiig.3. Long-term land subsidence records at One is a long term ground subsidence taking place along the coast fuur geodetic points in Niigata city of the Japan Sea in the Niigata Prefecture due to artificial dewatering. Fig. 3 depicts the ground subsidence records repair works to better fit to the original one. It is therefore between 1964 (at the time of the Niigata earthquake and 1998) at postulated in this research that the original features in the ground four geodetic points in Niigata city indicated in Fig. 1. Note that surface unevenness still remains after the quake and the the record at No.4422 includes some discontinuity due to a subsequent considerations based on the elevation contours at malfunction of the recording equipment. It may be justified from present is possible. the records that the ground settled about 40cm during these 35 years in the major part ofthe city. It may be judged, therefore, that By comparing the contours and the tlow displacement vectors in the long-term settlement did not greatly change the local elevation Fig.2, a fairly good coincidence can be identified in that the contours because it occurred quite uniformly in a wide area. -I- -- -__p- Another reason to be considered is the difference in the elevation before and after the quake. Because of extensive post-liquefaction lateral fiow and settlement, the elevation contours may have changed considerably afier the quake. +-I Geodetic data IO quantify the elevation difference were found in >” the Geographical survey Institute in Tsukuba, although they are a4 available only along the national road, Route 7, crossing the south -ii western part of the area as indicated in Figs.1 and 2. Fig.4 shows -0 the comparison in the elevation at three time periods (just before 5* and just after the quake as well as at present (1993)) along the 0 distance of the road passing through the investigated area. The & different symbols in the chart are the elevation measuring points 0 about one-hundred meters apart. Points A, B and C in Fig.4 correspond to the points with the same notations in Fig.2. It is obviously seen by comparing the two data in the section A-B-C, -2 -L!L- 0 500 l( included in the investigated area, just before and just after the quake that the ground elevation settled almost everywhere due to t Distance from No.4423 1 the earthquake. The maximum settlement was about O.Sm. In No.4423 to No. 4422 Cm) No.4422 some intervals the ground slope changed locally, although it still Fig.4. Comparison in elevation just before and just after maintained the original qualitative features in most cases. Even in the quake as well as at present along the road the interval where the slope became reverse very locally, the Rout 7 passing through the investigated area. present ground slope is modified presumably due to subsequent
Paper No. 5.38 3 vectors mostly direct downward normal to the contours. It seems Bore-hole 1.52, while other nearby bore-holes indicate the interesting that the soil behaved like a liquid, flowing on a very thickness of about lm or smaller. Thus the substructure of the gentle slope of less than 1% in the downward direction normal to soil in this area may still have some uncertainties presumably the contours. because of spatial variability of soil. However, it may be possible to assume a widespread existence of a continuous or semi-continuous horizontal fine soil sublayer near the surface in SOIL CONDITION this area as conceptually illustrated in Fig.5.
The bore-hole logging data in this area are systematically The liquefaction susceptibility of the sandy soil is evaluated along compiled along the solid bilinear line in Fig.2 to draw the the bilinear line according to a conventional method sometimes two-dimensional soil profile. The line is chosen so that it used in Japan (Road Bridge Design Code 1997). The maximum approximates the direction of flow displacement vectors surface acceleration used in the evaluation is 17Ocm/s* and the evaluated by Hamada (1992). These bore-hole data consist of fines content of the sand is assumed between 0 to 10 percent. The soil profiles, a water table depth and SPT blow-counts; N-value. values of FL (=R/L, where R=the stress ratio for a soil element to Fig5 depicts the two-dimensional soil profile based on 11 liquefy and L=the stress ratio exerted in soil during a given bore-hole data along the bilinear line. earthquake) are indicated along the depth of each bore-hole log in Fig.5. Liquefiable layers judged by FL<~ .O are evidently located The soil essentially consists of loose sandy soils down to 10 to 15 below the fine soil sublayer as shown in Fig.5. This indicates that m deep from the ground surface with N-value less than 10 with during the earthquake, a water film was possibly formed beneath the water table around GL2.0m. However one or more sublayers the sublayer almost continuously. If this is the case, the ground with fine soils of either silt or clay are sandwiched in the most of surface with a very small inclination may be able to flow because the bore-bole. The most conspicuous one is commonly found in of literally no shear resistance in the water Mm. the top part of each hole. Near Hotel Niigata indicated in Figs.2 and 5, the sublayer thickness exceeds 6m locally according to
lOOr On 3oorl EAST / WEST L -II SH I NANO HOTEL RIVER NIICATA WALL
bore-hole ‘I? 45 46 47 152 ,~OOl ,318 57 227 63 79 number Less pernreabl e Sand : .~ sublayer El
Liquefiable sand
Fig.5. l’wo dimensional soil profile based on bore-hole date alung the bilinear line in Fig.2 with SPT N-value and FL-value.
Paper No. 5.38 4 COORELATIONS WITH FLOW DISPLACEMENT
Some parameters, which may correlate with the flow displacement, are examined here; the thickness of a liquefiable soil (HL , in which FL<1 .O), its FL and ground surface inclination. Fig.6 shows the flow displacement (Dr) versus H,plots. Here, DI is taken as the length of a flow vector for which a comparable bore-hole data is available nearby. If the liquefied soil is thicker, the excess pore-water, which comes up to form a water ftim, may become greater resulting in a larger flow displacement. However, no clear correlation seems to be identified in Fig.6. In order to .- -0 improve the correlation by considering not only the liquefiable soil thickness but also the severity of liquefaction, a modified 4 0. thickness of the liquefiable soil tlL* is calculated by dividing HL I& by FL for individual sandy sublayers and summing them up. In Fig.7, Dr is plotted against ML’ , which indicates a little better correlation than Fig.6 but only a slight improvement. Modified thickness of I iquefiable soi I :H L*(m) One of the reasons that Figs.6 and 7 do not irldicate strong correlations may be explained by the absence of driving force Fig.7. Relationship between flow displacement(Dr) mechanism in flow displacement in the above consideration. By and thickness of liquefiable soil(HL) assuming that the slight surface unevenness serves as the driving force of the lateral flow, the flow displacement is plotted versus 0 5 surface inclination in Fig.8. Here, the flow displacement is taken Y- as a downward normal component of the displacement vector -- 64 with respect to the nearby elevation contours and denoted here as mLc 6 ‘The displacements thus defined are correlated with the Dm. 0Ln .' 3 maximum surface inclination normal to the contours, i,,,. c" Obviously, a clear correlation can be identified for the plots -0 =2 encircled by a solid curve in Fig.8 despite some scattered data for c- i,,>l.O% and Dr,,
inclination of less than 1% has a great influence on the post-liquefaction flow displacement and 0.5% slope may induce iz about 4m horizontal displacement along the slope. The water 0L- -L-i..,;1,.;... films beneath continuous line soil sublayers may exclusively be 0 2 8 10 able to explain this phenomenon, because no other mechanism is ThicLessG of likely to provide such a low shear resistance against flow. liquefiable soiI:Hdm) One of the uncertainties involved in this case study is the degree Fig.6. Relationship between flow displacement(l)r) and of uniformity or continuation in the fine soil sublayer in the thickness of liquefiable soil(HL) horizontal direction. Its thickness seems to greatly vary from
Paper No. 5.38 5 point to point and may possibly disconnect at some places. Even bore-hole data in the Niigata city were provided by the Niigata in such cases, however, the water film may develop with some Municipal Office. The elevation measuring data along the horizontal extent for some time duration enough to cause national road before and after the quake were provided by the post-liquefaction lateral flows. During that period, excess Geographical Survey tnstitute in Tsukuba. The long-term pore-water tends to rush to weaker points, breaking the fine soil subsidence data in Niigata city were provided by the Niigata sublayer and triggering boiling or re-liquefaction of the overlying Agricultural Office. The authors are grateful to those in the sandy layer as demonstrated in the model test carried out by the above organizations who kindly made efforts for the data present authors (Kokusho 2000). This re-liquefaction process dissemination. seems to be very significant to satisfy the compatibility in the lateral flow displacement in a surface soil, although it is just a speculation at this stage of the research. REFERENCES
Bouckovalas,G.D., Gazetas,G. and Papadimitriou,A.G. [ 19991. CONCLUSlONS Geotechnical Aspects of the 199.5 Aegion , Greece, earthquake” Proc. of 2”d International conference on Earthquake Geotechnical Based on experimental findings of previous researches; nalurti Engineering, Balkema, Rotterdam, The Netherhind, Vol. 2, sand deposits normally sandwich line soil sublayers and they 739-748. serve to form water films underneath during seismic liquefaction, which greatly influence the lateral flow mechanism in a sloping Hamada,M. [ 19921 Large ground deformations and theii eFects ground, a case history in Niigata city during the Niigata on lifelines:1964 Niigata earthquake, Case Studies of earthquake is reviewed here. The major findings are; Liquefaction and Lifeline Performance during Past Earthquakes, Vol.1, Japanese Case Studies, ~~3.1-3.123. I) The existence of a continuous sublayer of fine soils is suspected near the surface in the investigated area. Kawakami,F. and Asada A. [ 19661. “Damage to the ground and 2) Liquefiable loose sand is located beneath the f-me soil layer earthstructures by the Niigata earthquake of June 16, 1964”. Soils down to 10 to 15m deep, implying that water films may have and Foundations, Tokyo, VI(l), 14-30. developed continuously during the earthquake. 3) The elevation contours by O.lm pitch are drawn based on Kishida,H. [1966]. “Damage to reinforced concrete buildings in large scale map and insitu survey. This contours at present Niigata City with special reference to foundation engineering”. seem to reflect qualitative features of ground surface Soils and Foundations, Tokyo, VI (l), 71-88. unevenness at the moment of the earthquake. 4) By comparing the contours and the flow displacement Kokusho,T. , Watanabe,K and Sawano,T.[ 19981. “Etlect of vectors it is found that the soil behaved like a liquid, flowing water film on lateral flow failure of liquefied sand”. Proc. lllh on a very gentle slope in the downward direction normal to European Conference on Earthquake Engineering (Paris), Cl) the contours. publication, ECEE/T2kokeow,pdf. 5) The flow displacement components normal to the contours are correlated with the maximum surface inclination. A clear Kokusho,T.[ 19991. “Formation of water fdm in liquefied sand and correlation can be identilied, indicating that even a slight its effect on lateral spread”. Journal of Geotechnical and surface inclination of less than 1% has a great influence on Geoenvironmental Engineering Division, ASCE, 125(10), the post-liquefaction flow displacement. A slope with 0.5% 817-826. inclination induced about 4m horizontal displacement along the slope in average in this particular site. Kokusho,‘l:, Fujita,K and Morishima,S. [ZOOO]. Possibility of 6) The water film beneath the continuous fine soil sublayer may water fdm generation in liquefied sand during the Niigata exclusively be able to explain this phenomenon, because no Earthquake, Proc. Annual Conference, Japanese Geotechnical other mechanism is likely to provide such a low shear Society, pp.2249-2250 (in Japanese). resistanceagainst flow. Kokusho,T. [2000]. “Mechanism for water film generation and lateral flow in liquelied sand layer”. Soils and Foundations, Tokyo, ACKNOWLEDGMENTS in print.
Mr. Morishima, S. and Mr. Kurose, H., undergraduate students of Road Bridge Design Code [ 1997) Vol.11: Earthquake Resistant Civil Engineering Deparlment of Chuo University are Design, Japan Road Association (in Japanese). acknowledged for their great contribution in this research. All the
Paper No. 5.38 6