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タイトル Dynamic Characteristics of Volcanic Soil and Its relation to Landslide Mechanism in Gentle Slope
著者 Sumartini Wa Ode・Hazarika Hemanta・Kokusho Takaji・Kochi Yoshifumi・Ishibashi Shinichiro
出版 第61回地盤工学シンポジウム
ページ 59〜64 発行 2018/12/14 文書ID fs201812000010
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  • タイトル
  • Dynamic Characteristics of Volcanic Soil and Its relation to Landslide Mechanism in Gentle Slope
  • 著者
  • Sumartini Wa Ode・Hazarika Hemanta・Kokusho Takaji・Kochi Yoshifumi・Ishibashi Shinichiro
  • 出版
  • 第61回地盤工学シンポジウム
  • ページ
  • 59〜64
  • 発行
  • 2018/12/14
  • 文書ID
  • fs201812000010
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  • Dynamic Characteristics of Volcanic Soil and Its relation to Landslide Mechanism in Gentle SlopeWa Ode Sumartini 1, Hemanta Hazarika 1, Takaji Kokusho 2, Yoshifumi Kochi 3, and Shinichiro Ishibashi 41KyushuUniversity, JapanUniversity, Japan3Kslab Inc., Japan4Nihon Chiken Co. Ltd., Japan2ChuoKEY WORDS: Landslide, Triaxial, Liquefaction, Volcanic Soil, Resistivity1. INTRODUCTIONVolcanic soil is known for being hazardous due to its peculiarbehavior. The soil has a vesicular skeleton and brittle mineralwhich influences its deformation behavior and failurecharacteristics (aSumartini et al., 2018). Japan is a countrywith many volcanoes. Thus, volcanic soil mostly formed theground in Japan. Several researchers reported damages due tolandslide induced by earthquakes in those volcanic soilground (aSumartini et al., 2018; Sassa, 2005; Kazama et al.,2012; Miyagi et al., 2011; Hazarika et al., 2017; Song et al.,2017; Dang et al., 2016).The 2016 Kumamoto Earthquake struck Kyushu islandfrom 14 to 16 April 2016. The earthquake triggeredwidespread landslides in Kumamoto prefecture. Thelandslides occurred on steep slopes and gentle slopes, eventhough landslides on gentle slopes rarely occurred. One of thelandslides areas is near Aso Volcanological Laboratory ofKyoto University as shown in Fig. 1. The landslide happenedon gentle slopes (Song et al., 2017; Dang et al., 2016; Kochi etal., 2018). It left damage to public space, roads, houses (Fig.2), nature space, and even loss of lives. At the landslide site,all the layers above Takanoobane lava deposit were failed andscattered on the landslide site in small and big lump beside theorange colored pumice deposit which crumbled as shown inFig. 3. Thus, the authors deduced that the orange coloredpumice deposit (namely Orange soil in this paper) whichlocated right above Takanoobane lava layer is liquefyingduring the earthquake and results in the landslide.Accordingly, it is essential to understand the geological profileof the slope and the Orange soil characteristics with itsbehavior under cyclic loading to reveal their effect on thelandslide occurrence triggered by the earthquake.Many researchers are conducting a cyclic triaxial test toobserved the deformation behavior of volcanic soil due to thevarious disaster on volcanic soil area (aSumartini et al., 2018;Hatanaka et al., 1985; Suzuki and Yamamoto, 2004; IshikawaFigure 2.Figure 3.Swept away housesOrange soil deposit crumbled after landslide.and Miura, 2011; Sumartini et al., 2017). In previous research onthe Orange soil deposit, deformation behavior under staticloading of disturbed and undisturbed samples (aSumartini et al.,2018), and under cyclic loading of an undisturbed sample(aSumartini et al., 2018; Sumartini et al., 2017), have beenconducted and reported. However, under cyclic loading ofdisturbed samples have not undertaken yet. Following thismatter, a series of cyclic triaxial test on disturbed samples wereperformed and compared with the previous research. Also, theresistivity imaging test has been conducted to understand thegeological profile of the slope. This paper reported acomprehensive understanding relating to the liquefactionsusceptibility and deformation behavior of the Orange soil.2. GEOLOGICAL CHARACTERISTICSThe landslide site near the Aso Volcanological Laboratory ofKyoto University is a slope which forms by volcaniclasticsequence. Kochi et al. (2018) stated that the volcaniclasticdeposits are originated from various places as listed in Table 1.Several researchers are reporting the average slope gradient ofthe landslide. Kochi et al. (2016) said that the slope gradient is10-15 degrees, while Dang et al. (2016) and Song et al. (2017)Figure 1. Landside near Aso volcanological Laboratory ofKyoto University, sampling point, and arrangement oftraverses.59 are 11.3 and 12 degrees respectively. The schematic profile ofthe slope is shown in Fig. 4 (Sumartini et al., 2017). The profilereveals that numerous deposits of volcanic soil which havedifferent colors and characteristics formed the slope. Thedeposits with similar physical appearance had similar chemical,mineralogical and microstructural characteristics and defined asbeing composed of a brittle material in a vesicular structure(bSumartini et al., 2018).3. EVALUATION PROCESS3.1 Resistivity TestA resistivity measurement device manufactured by AGI(Advanced Geosciences Inc.) was used in the investigation. Thedipole-dipole method was employed for observation. In theanalysis, profiles were drawn up using RE2DINV, resistivitytwo-dimensional investigation software (Loke,1996). Fig. 1shows two traverse lines were arranged in the north-south andeast-west directions in the area free from landslides on the westslope of the Takanoobane lava dome. At survey stations, aTrimble R4 GNSS GPS surveying instrument was used formeasurement. The errors of accuracy are kinematic errors and10 mm horizontally and 20 mm vertically.Table. 1 Origin of volcanic soil in Aso caldera (Kochi et al.,2018).DepositOriginCal kaBlack soilOrganic (OL)10-presentBrown soilAso Central ConePumice (AC)7.3-10Dark brown soilKikai Akahoya Ash(K-Ah)7.3Light brown andgrayish soil withsandOtogase Lava Pumice(Otp)29-7.3Light brown soilAira Tn (Atn)29Orange soilKusasenrigahamaPumice (Kpfa)31Blackish soilTakanoobane LavaPumice (Tp)51±53.2 Triaxial Test3.2.1 MaterialsThe samples were collected at a depth of 5 m from the scarp atthe landslide site (Fig. 1). The samples were reconstituted fromundisturbed samples which were subjected to cyclic loading(aSumartini et al., 2018).The physical properties of Orange soil collected from thesite were measured in the laboratory which is listed in Table 2(aSumartini et al., 2018). The orange soil has low specificgravity which was varying from 2.24 to 2.38, water contentfrom 54.62 to 58.36% and plasticity index 25.15 which isconsidered high. It also contains more than 60 % of fines asshown in Fig. 5. Combining it with information from Table 2,using JGS 005-2009 the Orange soil is classified as volcanicsoil type II.The Orange soil has a vesicular structure which composedof crystal flakes (Sumartini et al., 2017) as shown in Fig. 6. Itsstructure indicates that the soil contains a high concentration ofalumina. Even though much of Al is a residual concentration, itis conveyed in the weathered deposits by groundwater whichindicates the occurrence of nodules (Patterson, 1971).The chemical content is listed in Table 3 (aSumartini et al.,2018). The Orange soil contains high alumina and containsminor alkaline metal and alkaline metal earth. Concerning thealkaline concentration, alumina is typically high from Alreplacing SiO2 during the weathering (Patterson, 1971).The mineralogical content of Orange soil was conductedusing X-ray diffraction analyses (XRD) by Sumartini et al.(a2018). The samples using in the analyses were powder and hasbeen air-dried to prevent the change of the mineralogy due tohigh temperature. The results are listed in Table 4 (aSumartini etal., 2018). The Orange soil contains dominantly of Albite andBytownite. These two minerals are a member of Plagioclasefeldspar group (Galleries, 2018). It is the principalaluminum-bearing mineral in the parent rocks whichdecomposed during weathering (Patterson, 1971).Table 2. Physical properties of Orange soil (aSumartini et al.,2018)Physical PropertiesFigure 4. Schematic profile of slope with volcanic soildeposits of Aso caldera (Sumartini et al., 2017).60Orange SoilSpecific Gravity2.24-2.38Dry Density, g/cm30.51-0.58Wet Density, g/cm31.23-1.30Water Content, %54.62-58.36Liquid Limit, %113.40Plastic Limit, %88.25Plasticity Index25.15 Table 4. Mineral properties of Orange soil (aSumartini et al.,2018)ContentsOrange soil (wt %)Albite57Bytownite40Sodium hydrogen sulfideCalcium copper germaniumoxide2.01.43.2.2 Testing procedureThe strength characteristics of Orange soil are evaluated oncyclic triaxial tests in undrained condition. To have the samedensity as the undisturbed sample, the tested sample from theundisturbed sample was reused and reconstituted. The sampleswere 50 mm in diameter and 100 mm in height. Double negativepressure and appropriate back pressure were applied to thesamples and isotropically consolidated at the target effectivepressure. B-values > 0.95 was ensured for all samples beforeshearing. The frequency of the cyclic axial load was 0.1 Hz forthe undrained triaxial cyclic tests. To decide whether liquefactionoccurred in this study, the pore water pressure ratio (ru), define asthe ratio of the pore water pressure to the normal stress, wasused. when ru ≥ 0.95, the specimen was considered to haveliquefied.Figure 5. Grain size distribution of Orange Soil (aSumartini etal., 2018).4. RESULTS AND DISCUSSION4.1 Resistivity ProfilesFig. 7 shows the resistivity profile along the A-B (north-south)and C (east-west) lines. Given below are an outline of resistivitydistributions and the results of estimation for geologicalinterpretation. Layers with a resistivity of 160 to 320 m wereobserved above the Kusasenrigahama pumice fall deposit to theground surface. They are assumed to be new tephra layer (Aira,Kikai-Akahoya and Aso central cone volcanic ashes, etc.) Thinlayers with resistivity 500 to 600 m are continuouslydistributed nearly at a depth of 1.0 m. It is unknown to whichhorizon the thin layers correspond.It was found that areas with resistivity 100 m or lower aredistributed in layers along both the A-B and C lines. The profilesshow a thickness of 1 m or larger. Electrodes are placed atspacings of 2.0 m. Accuracy is basically considered lower wherethe thickness is smaller than the spacing between electrodes. Theresistivity indicates clay layers or saturated sand and gravellayers. They are considered to be the Kusasenrigahama pumicefall deposit based on the geological conditions on the slope. Thelayer is distributed at an extremely small depth of approximately3 m at the starting point to measurement point 100 m along theA-B line, and a maximum depth of 10 m at the measurementpoint 100 m to the ending point as the above surface of theTakanoobane lava is structured as a valley. In the direction ofslope, the layer is distributed extremely low at a depth of 3 m atmeasurement point 75 m to the ending point along the C line,and relatively high at a depth of 7 m at measurement point 30 to65 m. The layers are generally distributed horizontally governedby the fact that the Takanoobane lava is distributed at shallowdepths near measurement point 30 m. The layer is distributeddeeper at the ending point along the C line. Certainty is, however,reduced because resistivity imaging involves a risk of ghostimages at outer edges. Areas with a resistivity of 160 to 640 mare observed above the area where high-resistivity zones aredistributed in the Takanoobane lava. This is considered to berelatively consolidated pumice fall deposit and volcanic ash layerthat serve as a base of slip surface.Figure 6. A vesicular structure of Orange Soil fabric(Sumartini et al., 2017)Figure 5. .Table 3. Chemical properties of Orange soil (aSumartini et al.,2018)ContentsOrange soil (wt %)SiO248.832Al2O335.959Fe2O38.910CaO3.300TiO21.843P2O50.489K2O0.259MnO0.172SrO0.069ZrO20.065SO30.060Ag2O0.018Y2O30.008ZnO0.008Ga2O30.007NbO0.00361 Figure 7.Profile of the resistivity of the Takanoobane lava domeLayers with resistivity exceeding 1,000 m were observedat the measurement point 100 m to the ending point along theA-B line and at measurement points 25 through 75 m along the Cline. They are assumed to be the Takanoobane lava proper. In theexploratory boring done on a plateau, the Takanoobane lavaproper appeared at depths below elevations 520 to 530 m(Miyoshi et al., 2007). Then, the layers with high resistivity wereassumed to be the Takanoobane lava proper. It was assumed thatthe Takanoobane lava proper existed continuously in areas with aresistivity of 600 or higher between measurement points 15 and100 m along the A-B line and between measurement point 75 mand the ending point along the C line. Resistivity was, however,slightly low in these areas probably because of weathering.pore water pressure for each cyclic load application is muchfaster for the disturbed samples compared to undisturbedsamples. This indicates that the deformation of the soil structuredue to the reconstituting process has a significant effect on theexcess pore water pressure development. Based on its effectivestress at liquefaction, it can be deduced that the liquefactionoccurs when the effective stress decreasing more than 78 % forlow CSR and more than 86 % for high CSR.Fig. 12 shows the liquefaction susceptibility of the4.2 Soil Behavior under Cyclic LoadingFigs. 8, 9, 10, and 11 show the response of undisturbed Orangesoil in the undrained cyclic triaxial test. The figures show thatregardless of its cyclic stress ratio (CSR), all the investigatedsamples exhibit cyclic mobility behavior. Also, stress path ofboth samples shares a similar trend. Under low CSR, theundisturbed sample starts liquefying at 172.5 cycles, thedoubled amplitude (DA) strain at 6.5 % and the effective stressdecreasing at 87.28 %. In another hand the disturbed sampleliquefying at 18 cycles, The DA strain at 7.25 %, and theeffective stress decreasing at 85.63 %. Under high CSR, theundisturbed sample starts liquefying at 8 cycles, the doubledamplitude (DA) strain at 2.5 % and the effective stressdecreasing at 77.88 %. In another hand the disturbed sampleliquefying at 4.1 cycles, The DA strain at 8.75 %, and theeffective stress decreasing at 77.38 %. Although the cyclicstress ratio of disturbed samples is lower than undisturbedsamples, the strain development of disturbed samples is fasterthan the undisturbed sample. The stress path trend of disturbedsamples is similar to the undisturbed sample although thedisturbed sample appears faster in liquefying. The effectivestress path of both samples indicates that the effective stress inundisturbed samples tends to decrease at a lower rate than indisturbed samples. Accordingly, the undisturbed samples appearto be more resistant to liquefaction. The generation of excessFigure 8. Response of the undisturbed Orange soil samplesin undrained cyclic triaxial test (CSR = 0.274, σc' = 60 kPa):(a) effective stress path, (b) shear stress versus shear strain,(c) shear strain versus number of cycles, and (d) pore waterpressure ratio versus number of cycles (aSumartini et al.,2018).62 Figure 9. Response of the disturbed Orange soil samples inundrained cyclic triaxial test (CSR = 0.268, σc' = 60 kPa): (a)effective stress path, (b) shear stress versus shear strain, (c)shear strain versus number of cycles, and (d) pore waterpressure ratio versus number of cycles.Figure 11. Response of the disturbed Orange soil samplesin undrained cyclic triaxial test (CSR = 0.402, σc' = 60kPa): (a) effective stress path, (b) shear stress versus shearstrain, (c) shear strain versus number of cycles, and (d)pore water pressure ratio versus number of cycles.Figure 12. Liquefaction susceptibility of Orange soil: (a)undisturbed samples and (b) disturbed samples.Figure 10. Response of the undisturbed Orange soil samplesin undrained cyclic triaxial test (CSR = 0.502, σc' = 60 kPa):(a) effective stress path, (b) shear stress versus shear strain,(c) shear strain versus number of cycles, and (d) pore waterpressure ratio versus number of cycles (aSumartini et al.,2018).undisturbed sample compared to disturbed sample at theeffective stress 60 kPa. It shows that a 5% double amplitudeaxial strain in 20 cycles of undisturbed samples occurred in 0.5of CSR respectively. In another hand, the disturbed samplerequires CSR = 0.310. Accordingly, it can be deduced that thedisturbed samples liquefaction resistance is less by about 0.2 ofCSR of undisturbed samples.Figure 13. The fabric of Orange Soil before cyclic loading(aSumartini et al., 2018).Figs. 13 and 14 show SEM analysis results of the Orangesoil structure before and after the liquefaction tests, respectively(aSumartini et al., 2018). Fig. 13 shows that the soil structure is63 Ishikawa, T. and Miura, S., 2011. Influence of freeze-thawaction on deformation-strength characteristics and particlecrushability of volcanic coarse-grained soils. Soils andFoundations, Vol. 51, pp. 785 -799.Kazama. M, Kataoka. S, and Uzuoka. R., 2012. VolcanicMountain Area Disaster Caused by the Iwate-Miyagi NairikuEarthquake of 2008,” Japan. Soil and Foundations, Vol. 52, pp.168-184.Kochi. Y, Kariya. T, Matsumoto. D, Hirose. T, andHazarika. H., 2018. Investigation of Slopes on TheTakanoobane Lava Dome Using Resistivity Imaging Method,Lowland Technology International, Special Issue on KumamotoEarthquake and Disasters, Vol. 19, pp 261-266.Loke, M.H., 1996. RES2DINV ver.2.0, Rapid 2D resistivityinversionusing the least-squares method, M.H.Loke,Advanced Geosciences Inc.Miyagi. T, Higaki. D, Yagi. H, Yoshida. S, Chiba. N,Umemura. J, and Satoh. G., 2011. Reconnaissance Report onLandslide Disaster in Northeast following the M 9 TohokuEarthquake,” Landslides, Vol 8, pp. 339-342.Miyoshi, M., Hasenaka, T., Mori, Y. and Yamashita, S.,2007. Materials of inhomogeneous composition in Tochinokilava distributed in the west of the Aso caldera and their formingfactors. Japanese magazine of mineralogical and petrologicalsciences, Vol. 36, pp. 15-29.Patterson, S. H., 1971. Investigations of Ferruginous Bauxiteand Other Mineral Resources on Kauai and a Reconnaissanceof Ferruginous Bauxite Deposits on Maui, Hawaii. U.S. Geol.Survey Professional Paper 656, 74p.Sassa. K, 2005. Landslide disasters triggered by the 2004Mid-Niigata Prefecture earthquake in Japan,” Landslides, vol.4, pp. 113-122.Song K, Wang F, Dai Z, Iio A, Osaka O, Sakata S., 2017.Geological Characteristics of Landslides Triggered by the 2016Kumamoto Earthquake in Mt. Aso Volcano, Japan, Bulletin ofEngineering Geology and the Environment, Springer-Verlag,pp. 1-10.Sumartini, W. O., Hazarika, H., Kokusho, T., Ishibashi, S.,Matsumoto, D. and Chaudhary, B., 2017. LiquefactionSusceptibility of Volcanic Soil in Aso Caldera due to the 2016Kumamoto Earthquake. Proc. of the 19th International SummerSymposium, pp. 13-14.aSumartini. W O, Hazarika. H, Kokusho. T, Ishibashi. S,Matsumoto. D, and Chaudhary. B., 2018. Deformation andFailure Characteristics of Volcanic Soil at Landslide Sites dueto the 2016 Kumamoto Earthquake, Lowland TechnologyInternational, Special Issue on Kumamoto Earthquake andDisasters, Vol. 19, pp. 237-244.bSumartini, W. O., Hazarika, H., Kokusho, T., Ishibashi, S.,Matsumoto, D., and Chaudhary, B., 2018. MicrostructuralCharacteristics of Volcanic Soil in Aso Caldera related to theLandslide Triggered by the 2016 Kumamoto Earthquake,Proceedings of 16th European Conference on EarthquakeEngineering, Thessaloniki.Suzuki. M, and Yamamoto. T, 2004. LiquefactionCharacteristic of Undisturbed Volcanic Soil in Cyclic TriaxialTest, Proc. World Conference on Earthquake Engineering.(13WCEE), Paper No. 465.Figure 14. The fabric of Orange Soil after cyclic loading(aSumartini et al., 2018).composed of a stack of the crystal flakes and is highly porous.In comparison, Fig. 14 shows that the soil structure is visiblybroken, and the crystal flake size has been reduced.5. CONCLUSIONSFrom the comprehensive investigation, it was observed that theslip surface occurred on the saturated deposit (Orange soillayer) which has low resistivity. Under cyclic loading, bothsamples show cyclic mobility behavior under the CSRinvestigated. Although the CSR applied to disturbed samplesquite lower than undisturbed samples, the disturbed samplesappear significantly more susceptible to liquefaction comparedto undisturbed samples. The results successfully describe thebehavior of the Orange soil under cyclic loading. Also, thepaper explains that the landslide occurred due to the liquefyingof the Orange soil deposit triggered by the 2016 Kumamotoearthquake.ACKNOWLEDGMENTThe financial grant for this research under the J-RAPID program(Principal Investigator: Hemanta Hazarika) of the Japan Scienceand Technology Agency (JST) is gratefully acknowledged. Thefirst author is grateful to the Indonesia Endowment Fund forEducation (LPDP) for financially supporting her study.REFERENCESDang. K, Sassa. K, Fukuoka. H, Sakai. N, Sato. Y, Takara.K, Quang L H, Loi. D H, Tien P V, and Ha. ND, 2016.Mechanism of Two Rapid and Long-Runout Landslides in the16 April 2016 Kumamoto Earthquake using a Ring ShearApparatus and Computer Simulation (LS-RAPID), Landslides,Vol. 13, pp. 1525-1534.Galleries. The Feldspar Group. Amethyst Galleries, Inc.http://www.galleries.com/Feldspar_Group, 2018.Hatanaka. M, Sugimoto. M, and Suzuki. Y, 1985.Liquefaction Resistance of Two Alluvial Volcanic Soils Sampledby in Situ Freezing, Soils and Foundations, Vol. 25, pp. 49-63.Hazarika, H., Kokusho, T., Kayen, R.E., Dashti, S.,Fukuoka, H., Ishizawa, T., Kochi, Y., Matsumoto, D., Hirose,T., Furuichi, H., Fujishiro, T., Okamoto, K., Tajiri, M. andFukuda, M., 2017. Geotechnical Damage due to the 2016Kumamoto Earthquake and Future Challenges. LowlandTechnology International, Special Issue on KumamotoEarthquake and Disasters, Vol. 19, pp. 189-204.64
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