A NEW PROPOSAL FOR LIQUEFACTION POTENTIAL BASED ON ENERGY BALANCE METHOD

Transcription

1 3 th orld Conference on Earthquake Engneerng Vancouver, B.C., Canada August 6, 4 Paper No. A NE PROPOSAL FOR LIQUEFACTION POTENTIAL BASED ON ENERGY BALANCE METHOD Shuch SHIMOMURA, Norak SAKO, Tosho ADACHI 3 SUMMARY In ths study, a new method for the evaluaton of lquefacton potental based on energy balance s proposed usng pseudodynamc tests. Ths method has been developed to evaluate the lquefacton potental and dynamc property of surface layers by usng commonly used parameters such as ntal shear modulus, reference stran and lquefacton resstance. In order to verfy the proposed method, a smulaton analyss was conducted on the sol of two dfferent artfcal slands, Kobe Port Island and Rokko Island, where the lquefacton damages were observed n the 99 Hyogoken Nambu Earthquake. Though the two slands are closely located, sgnfcant dfferent lquefacton damages were observed. Although t s dffcult to represent such dfferent damage patterns by the present smple method used n Japan, however, the proposed method can effectvely evaluate the actual damage by n consderaton of the dfference of the stffness of clay layer underlyng the reclamed ground. INTRODUCTION As a smplfed procedure for evaluatng lquefacton potental, the F l method [] s often used n Japan. Ths method compares lquefacton resstance rato τ l /σ wth shear stress rato τ d / σ that mght have developed n the feld durng the earthquake, and lquefacton potental s evaluated (τ l /σ τ d / σ : It s evaluated that the lquefacton potental s hgh). th ths method the shear stress rato τ d / σ s defned by Eq.(). τ d α σ g max σ γ d γ n σ () where, α max : the maxmum acceleraton at ground surface, g: the gravty acceleraton, σ : the ntal effectve vertcal stress, σ : the total vertcal stress. The parameters γ d and γ n are correcton factors n terms of depth, z n meters, and earthquake magntude, M, respectvely, as follows Research Engneer, Techncal Research Insttute, Kajma Co., Japan Graduate Student, Dept. of Archtecture, College of Scence & Technology, Nhon Unv., Japan 3 Professor, Dept. of Archtecture, College of Scence & Technology, Nhon Unv., Japan

2 γ d. z () γ. ( M ) (3) n The reducton coeffcent γ d s strongly dependent on the predomnant perod of the nput earthquake moton and the natural perod of the ground [], however the shear stress rato does not take nto account the effect of the predomnant perod of the nput earthquake moton and the natural perod of the ground. In partcular, Kazama [3] showed that t s dffcult to explan the level of damage from the shear stress when the frequency characterstcs of the nput earthquake moton s gnored. Moreover, the nfluence of layer consttuton s not consdered n ths method because the lquefacton potental of each layer s evaluated ndependently. Yamaguch [4] reported that the dfferent degrees of damage between two artfcal slands, Kobe Port Island and Rokko Island, was due to the dfferent stffnesses due to the degree of consoldaton of the clay layer underlyng the reclamed ground. Some studes on lquefacton potental based on an energy concept have been reported. Igarash [] proposed a method based on the concept of dslocaton energy. Kazama [6] proposed an evaluaton procedure based on the relatonshp between cumulatve dsspaton energy, modulus reducton rate and pore water pressure. However, these methods requre many parameters assocated wth analytcal procedures, whch makes them dffcult to apply n practce. Ths paper proposes a new method for determnng lquefacton potental based on energy balance derved from pseudodynamc tests. Ths method has been developed to evaluate the lquefacton potental and dynamc propertes of surface layers by usng commonly used parameters such as ntal shear modulus, reference stran and lquefacton resstance. In addton, the method consders the nfluence of the predomnant perod of the nput earthquake moton, the natural perod of the ground and the layer consttuton. OUTLINE OF PROPOSED EVALUATION PROCEDURE FOR LIQUEFACTION An energy balance formula s obtaned from the equaton of moton where each term s multpled by velocty vector and ntegrates to an arbtrary tme. T t T t T t T {}[ x M ]{} && x dt {}[ x& C]{} x& dt + {}{ x& R} dt && y{}[ x M ]{}dt t + & & (4) where, [M]: mass matrx, [C]: dampng matrx, {R}: restorng force vector, {& x& }: relatve acceleraton vector, { x& }: relatve velocty vector, & y& : nput acceleraton and {}: unt vector. Eq. (4) can be expressed as + + E () e h p where, e : elastc vbraton energy (the sum of elastc stran energy and knetc energy), h : dsspaton energy by vscous dampng, p : cumulatve plastc stran energy, and E: nput energy. Eq. (4) s an energy balance formula per unt cross sectonal area.

3 Akyama [7] developed the concept of energy nput and proposed sesmc desgn methods based on energy balance. The concept s appled to the lquefacton potental of the ground n ths study. Lquefacton potental based on the energy balance method s based on the followng three tems: ) The total nput energy n the surface layers above the engneerng bedrock. ) The energy dstrbuton rato of each layer. 3) The energy absorpton potental (cumulatve plastc stran energy). PSEUDODYNAMIC TESTING METHOD Pseudodynamc tests were conducted to smulate nonlnear behavor of saturated sand, and to verfy the valdty of the proposed method. The pseudodynamc testng method for a geotechncal system comprses a hybrd experment combnng earthquake response analyss wth laboratory dynamc sol tests usng a computer onlne data processng system. Ths method can represent the stressstran relatonshp wthout usng a mathematcal model. One layer or two layers were modeled as a lumped mass model wth a one or two degrees of freedom, as llustrated n Fg.. The tests of onelayer model were conducted to examne nput energy, and the tests of twolayer model were conducted to examne the energy dstrbuton rato of each layer and the energy absorpton potental. The test method was descrbed n detal n Kusakabe et al. [8] and Adach et al. [9]. The test condtons are shown n Table and Table. The apparatuses for the pseudodynamc test were hollow torsonal shear test equpment. A twntype apparatus was used n the test of twolayer model. The test samples were Toyoura sand whch s clean fne sand wth a mean gran sze between. to.mm. The ntal confnng stress was equvalent to an ntal effectve vertcal stress of an ntermedate pont n each layer. In the onelayer model, relatve densty was around at 6%, and four knds of actual earthquake waves wth dfferent predomnant perods were used for the nput moton. In the twolayer model, the relatve densty of the upper layer was fxed around at 6% and three combnatons of relatve densty (%, 6% and 8%) were fxed n the lower layer, and sx knds of actual earthquake waves wth dfferent predomnant perods were used for the nput moton. In addton cyclc undraned shear tests were conducted to examne nfluence of stress hstory for cumulatve stran energy. The test condton s shown n Table 3. The test samples were Toyoura sand, the apparatus s hollow torsonal shear test equpment and relatve densty was around at % and 8%. It was necessary to contnuously measure from small to large stran levels n Pseudodynamc test, but we could not measure over.% shear stran of double ampltude. Therefore, n ths study, ntal lquefacton was defned as that when the pore water pressure rato ncreased to.. H ρ m 4Hρ m π sand layer R : obtaned by G, ρ H Experment sand layer Hρ + H ρ G, ρ bedrock H bedrock R: obtaned by experment sand layer G, ρ bedrock m && x c c x& R m && y m & x + cx& + R my & + + m && x c c + c x& R R m && y c: dampng coeffcent, m: mass, R: restorng force (the vscous dampng s neglgble, snce the predomnance dampng s hysteretc n sand) Fg. Lumped mass model H bedrock m R : obtaned by experment

4 Case No. Relatve densty Intal confnng press ure Table. Test condton on one degree of freedom Ground model Input moton Intal shear modulus Thckness et densty Intal natural perod Name Maxmum Predomnant nput perod acceleraton (%) (kpa) (MPa) (m) (kn/m 3 ) (sec) (cm/s ) (sec) case case ElCentro_94.68 case (NS) case case Taft (E).44 case case Hachnohe (E) 7. case Kobe (NS).7 Case No. Layer Relatve densty Intal confnng pres sure Table. Test condton on two degree of freedom Ground model Intal shear modulus Thckness et densty Intal natural perod Name Input moton Maxmum nput acceleraton Predomnant perod (%) (kpa) (MPa) (m) (kn/m 3 ) (sec) (cm/s ) (sec) case Lower case case case Lower Lower Kushro Lower (E) 3.8 case3 case4 case Lower Lower Lower Taft (E ) case6 case Lower Kobe Port Lower Island (NS) Case No. Table.3 Cyclc undraned shear test condton Relatve densty Intal confnng pressure Intal shear modulus et densty Cyclc stress rato (%) (kpa) (MPa) (kn/m 3 ) case case9 8.3 case case case case

5 ENERGY CHARACTERISTICS OF GROUND DUE TO EARTHQUAKE MOTION Energy absorpton potental hen tme hstores of shear stress and shear stran are gven, the cumulatve plastc stran energy p s calculated as follows p t τ ( γ ) dγ τ ( γ ) & γ ( t) dt (6) An example of the relatonshp between pore water pressure rato u/ σ c and cumulatve plastc stran energy normalzed by ntal effectve confnng stress p /σ c was shown n Fg.. Crcles n Fg. show the ponts where shear stress τ was zero after the buldup of pore water pressure. From Fg., we pcked up the several crcles wth each specmen from the test results of the twolayer model and plotted those n Fg.3. There s a strong correlaton between the pore water pressure and the cumulatve stran energy for each relatve densty. But ths relatonshp s not nfluenced by the stress hstory. The upper lmtaton of cumulatve plastc stran energy s as hgh as relatve densty when the pore water pressure s bult up to.. In other words, the upper lmtaton of the plastc stran energy that can accumulate n sand s unquely determned from both the sol materal and ntal effectve confnng stress, and s regarded as energy absorpton potental at the ntal lquefacton..8.8 u/σc.6.4. case ( Layer) p /σ c u/σc.6.4. Dr% (Earthquake nput) Dr% (Snusodal wave) Dr6% (Earthquake nput) Dr8% (Earthquake nput) Dr8% (Snusodal wave).... p /σ c Fg. An example of relatonshp between pore water pressure rato and cumulatve plastc energy Fg.3 Relatonshp between pore water pressure rato and cumulatve plastc energy Estmaton of nput energy () Energy spectrum In the earthquakeresstant desgn for buldngs, the energy spectrum s used to evaluate the nput energy to a buldng. The energy spectrum s gven as the relatonshp between the velocty V E converted from the total nput energy E and natural perod of the buldng T. The total energy s calculated from the one degree of freedom system. V E ( T ) E / M (7) where E: nput energy, M: mass of the buldng.

6 Independent of the earthquake wave type, the energy ncreases as the natural perod of the equvalent elastc model system lengthens, ndcatng a peak at a certan perod, and descends gradually above the long perod area. Akyama [7] proposed an energy spectrum form as a general elastc system, as shown n Fg.4. As the ground moton above the engneerng bedrock s usually affected by the prmary mode durng an earthquake, the nput energy was estmated from the prmary natural perod. Because the dampng rato of the sol s generally hgher than that of the superstructure, the energy spectra of whch the dampng rato h equals. were adopted for the energy nput. () Effectve perod The ground lquefacton under cyclc shear loadng causes shear modulus reducton and extends the effectve natural perod of the ground. Therefore the nput energy may be underestmated f the energy s evaluated from the ntal natural perod. A concept of effectve perod T was thus ntroduced to estmate the energy spectrum of an elastoplastc system from that of elastc system. T ( κ + T (8) ) The parameter κ was estmated from Eqs.(9)(), focusng on the ntensty of nput earthquake moton and the shear strength of the ground, because t was necessary to take the modulus reducton nto consderaton. κ c (9) /τ max τ max G γ (). MVE () H where, τ max : the shear strength, G : the ntal shear modulus, γ. : the reference stran, : the ntensty of the nput earthquake moton, V : mean of the converted velocty, H: thckness of the surface layer above E the engneerng bedrock, and c: the constant ndcated n Fg.. The parameter V E was the mean value of the nput energy between the ntal natural perod to. sec referrng to spectrum ntensty defned by Housner. The effectve perod was calculated from the relatonshp between the energy spectrum obtaned from the test results and the energy spectrum of the nput earthquake motons for the test. The correlaton of T /T and τ s summarzed n Fg.. max (3) Estmaton of nput energy The nput energy calculated usng κ n Fg. was compared wth that drectly obtaned from the test results. Ths comparson s shown n Fg.6. Fg.6 also dsplays the results from the twolayer model test (the shear strength was calculated by consderng the thckness of each layer). If the calculated T s over T G n Fg.4, the nput energy s evaluated as the peak value V E (max). It s found n Fg.6 that the nput energy s estmated accurately when consderng the effectve perod, although the nput earthquake moton and the natural perod of the ground are dfferent.

7 V E V E (max) V E (T ) V E (T ) T T TG Fg.4 A general form of energy spectrum Energy dstrbuton to each layer () Relatonshp between cumulatve plastc stran energy and nput energy Fg.7(a)(d) represents an example of the tme hstores of elastc vbraton energy, cumulatve plastc stran energy, nput energy, and the rato of cumulatve plastc stran energy to the nput energy, respectvely. From Fg.7(a), t s found that the elastc vbraton energy s vared and radated hour by hour, and the amount of that s only a few percent of the whole nput energy. Therefore, t s approxmately recognzed that the cumulatve plastc stran energy s equal to the nput energy. The rato p /E showed. because the vscous dampng was assumed to be zero, so t wll be necessary to examne the energy absorpton by vscous dampng. The evaluaton method for lquefacton potental developed n ths study assumes that all of the nput energy s consumed by plastc deformaton of the ground (ths assumpton s on the safe sde for lquefacton potental). () Dstrbuton rato of nput energy An example of the tme hstory of the dstrbuton rato of nput energy s shown n Fg.8. The energy dstrbuton rato can be recognzed to be almost constant after fve seconds, where t begns to buld up pore water pressure. Fg.9 shows the energy dstrbuton rato for the lower layer (relatve densty of the upper layer s approxmately 6%). Thus, the characterstcs of nput earthquake moton may affect the energy dstrbuton. (3) Estmaton of energy dstrbuton rato From the above mentoned () and (), t can be consdered that the energy dstrbuton to each layer s represented by the rato of cumulatve plastc stran energy at the stran order where pore water pressure begns to ncrease (stran order s 3 ths order has the lmtaton that t s relable for the test results of deformaton propertes under cyclc load). Thus, n the proposed method, the energy dstrbuton s estmated accordng to the followng procedure (refer to Fg.). A) Calculate prmary mode of surface layer above the engneerng bedrock. B) Determne the free surface dsplacement usng acceleraton response spectrum and calculate shear stran γ of each layer. C) Determne shear modulus and hysteress dampng of each layer from γ based on strandependent curves (G/G γ, hγ) and update prmary natural perod. D) Iteratve calculaton of the above procedure A)C) untl relatve errors of both G and γ are become fve percent or less or γ of one of layers reached to 3 order. A hysteress dampng rato was determned as follows T T /T (κ+) 3 κ 3 τ max.. τ max VE of estmatons (kne) V E of experments (kne) Fg. Estmaton of effectve perod Fg.6 Comparson of V E between estmatons and experments

8 h 4π () further, γ / (3) G L H π h G γ H (4) The energy dstrbuton of each layer s estmated from D L () L where D s the energy dstrbuton rato of th layer. Fg. shows the estmaton results of the dstrbuton rato of the nput energy calculated from Eq.(). It s found that the dstrbuton rato was accurately estmated consderng the modulus reducton by the teratve calculaton. FACTOR OF SAFETY AGAINST LIQUEFACTION OF PROPOSED METHOD The factor of safety aganst lquefacton of the proposed method of th layer s evaluated as follows F ( E) / (6) L L R L F ( E) >. : Lquefacton potental s low, F ( E). : Lquefacton potental s hgh, L where, F L (E) : the factor of safety aganst lquefacton based on energy balance of th layer, R : the energy absorpton potental of th layer (cumulatve plastc stran energy when the pore water pressure rato ncreases to. or the ampltude of the shear stran generates several per cent) and L : the nput energy dstrbuted to th layer. Then L s calculated as follows L D σ (7) c M VE (8) H where, L : the dstrbuted energy of th layer, σ c : the ntal confnng stress of th layer, D : the dstrbuton rato of th layer, M: the total mass of the surface layer above the engneerng bedrock, V E : the converted velocty gven by the energy spectrum and the effectve perod, H: the thckness of the surface layer above the engneerng bedrock.

9 . e (kj/m ). p (kj/m ).. E (kj/m ).. p/e. Allocaton rato Tme (sec) Tme (sec) Tme (sec) Tme (sec) (a) Elastc vbraton energy (b) Cumulatve plastc stran energy (c) Input energy (d) The rato of p /E. layer Lower layer Tme (sec) Fg.8 Tme hstores of dstrbuton rato of energy nput (case) Fg.7 Tme hstores of energy balance (case) Dstrbuton rato Kushro Taft Kobe Port Island Relatve densty of lower layer (%) Fg.9 Effect of earthquake wave on dstrbuton rato Estmatons. Kushro Taft Kobe Port Island. Experments Fg. Comparson of dstrbuton Rato between estmatons and experments β u H H β u Acc. SA (gal) 3 h. 4 6 Perod (sec) Acceleraton response spectrum Shear modulus G G.... Shear stran γ h Hysteress dampng rato h S A γ.6 Fh ω β ( u, u H +, ). F h after [] + h β{u}: Partcpaton vector ω: Natural crcle frquency h Σh G γ ΣG γ H H Fg. A procedure of teratve calculaton APPLICATION IN ACTUAL SOIL To demonstrate the proposed factor F L (E), a smulaton analyss was conducted on actual sol condton of two dfferent artfcal slands, Kobe Port Island and Rokko Island, where lquefacton damage was observed n the 99 Hyogoken Nambu Earthquake. Although the two slands are closely located, sgnfcantly dfferent lquefacton damage was observed. Some studes (Tanaka et al. []; Yamaguch [4]) ndcated that the dfferent stffnesses due to the degree of consoldaton of the underlyng clay layer

10 affected the sesmc behavor of the reclamed ground. In addton, a smulaton analyss by the present smplfed method F l was conducted for comparson wth the analyss results by the proposed method. th the present smplfed method, lquefacton resstance rato τ l /σ was referred to study [4]. Parameters for analyss () Sol borng log: Sol profle, shear wave velocty, reference stran and densty were decded on the bass of the Kobe Cty Report [] and Yamaguch [4]. The shear wave velocty and reference stran of the alluval clay layer underlyng Rokko Island were assumed to be those for unconsoldated clay, and these were dfferent from those of the alluval clay layer underlyng Kobe Port Island where consoldaton had been completed. () Energy absorpton potental: The energy absorpton potental was examned from the test results of cyclc undraned traxal tests on the undsturbed weathered grante fll (locally called Masado) and alluval clay provded by Akhko Uchda [3]. Fg. shows an example of the stressstran relatonshp of the Masado and alluval clay. It s found that the axal stran of Masado reaches approxmately 8% at thrtyfourth cycle as shown n Fg.. On the other hand, the axal stran of the alluval clay s stll % at th cycle despte the same condton of the cyclc stress rato for Masado. The relatonshp between the normalzed cumulatve plastc stran energy and axal stran s shown n Fg.3. hen the pore water pressure rato ncreased to over.9, the normalzed cumulatve plastc stran energy of Masado was about.. Ths value was equvalent to that of relatve densty 6%8% of Toyoura sand, and ths tendency corresponds to the study by Hatanaka et al. [3] whch showed that the lquefacton resstance of Masado was nearly equal to that of relatve densty 7% of Toyoura sand. It s remarkable that the axal stran of the alluval clay was only.%, although the clay absorbed ten tmes amount of energy of Masado. Furthermore, even f more energy s absorbed, large deformaton may not occur. That s, clay s a materal of whch energy absorpton potental s very hgh compared wth the sand or gravel. (3) Input earthquake moton: An array record observed at Kobe Port Island (GL3m) was used for the nput moton of the smulaton analyss by the F L (E) method. Energy spectrum s shown n Fg.4. hen the effectve perod T was beyond T G (the perod at the peak value of energy spectrum) at both Kobe Port Island and Rokko Island, the peak value of the nput energy was used for the calculaton. Ths nput energy was 7.kJ/m. The maxmum acceleraton at the ground surface used for the F l method was set at 34 gal consderng the maxmum acceleraton of the vertcal array record at the free surface. The ground model used and the smulaton analyss results for the lquefacton potental are summarzed n Table 4. As the lquefacton potental of each layer s evaluated ndependently by the F l method, the results of both ground model were the same as when the lquefacton potental s hgh. However, the results of both ground model by the proposed method F L (E) were dfferent from those consderng the effect of layer consttuton. Ths makes t dffcult to represent the actual lquefacton damage at Rokko Island by the present smplfed method. However, the proposed method can effectvely evaluate the actual damage by ntroducng the dfference n the stffness of the clay layer underlyng the reclamed ground.

11 Cyclc stress amltude rato d / c ' Axalstran (%). 34th Cycles σ c '7kPa Cyclc stress amltude rato d / c '... Axal stran (%) Axal stran (%) (a) Masado (b) Alluval clay Fg. Stressstran relatonshp.9< u/σ c ' th Cycles σ c '6kPa N c N c p/σ c ' p/σ c ' (a) Masado (b) Alluval clay Fg.3 Relatonshp between axal stran and energy absorpton potental Axal stran (%) 3 V E (max) VE (kne) 3 4 Perod (sec) Fg.4 Energy spectrum Table.4 Ground model and results of lquefacton potental Kobe Port Island Rokko Island Sol profle H ρ R Vs γ. T E D Actual damage F l F L (E) Vs γ. T E D Actual damage F l F L (E) (m) (t/m 3 ) (m/s) ( 3 ) (s) (kj/m ) (m/s) ( 3 ) (s) (kj/m ) Reclamed Layer (Masado) Alluval clay Dluval gravel engneerng bedrock. 3 3 H: Thckness, ρ: Densty, R: Lquefacton resstance, V S : Shear wave velocty, γ. : Reference stran, T : Intal natural perod, E: Input energy, D: Dstrbuton rato : non lquefacton, : lquefacton

12 CONCLUSIONS A new method for evaluatng lquefacton potental based on energy balance s proposed. Ths method has the followng sgnfcant features. ) It has been developed to evaluate the lquefacton potental usng commonly used parameters such as the ntal shear modulus, the reference stran and the lquefacton resstance for the dynamc propertes of surface layers. ) The nfluence of the predomnant perod of the nput earthquake moton, the natural perod of the ground and the layer consttuton are taken nto consderaton, and t s possble to calculate the value usng a spreadsheet software. In applcaton to actual sol where lquefacton damage was observed, the proposed method can represent actual damage, whch cannot be represented by the present smplfed method F l. ACKNOLEDGEMENTS The test results of the cyclc undraned traxal test on undsturbed weathered grante fll (locally called Masado) and alluval clay were provded by Mr. Akhko Uchda, Takenaka Corporaton. The authors express ther grattude to hm. REFERENCES. Archtectural Insttute of Japan Recommendatons for desgn of buldng foundatons. (n Japanese).. Iwasak, T., Tatsuoka, F., Tokda, K. and Yasuda, S. A practcal method for assessng sol lquefacton potental based on case studes at varous stes n Japan. Proceedngs nd Internatonal Conference on Mcrozonaton, San Francsco, Vol., pp , Kazama, M. Reconsderaton of the shear stress rato generated by earthquakes. TsuchtoKso, JSSMFE, Vo.47, No.8, Ser.No.499, pp. 36, 999 (n Japanese). 4. Yamaguch, A. Sesmc behavor of Kobe's artfcal slands durng the 99 Hyogoken Nambu Earthquake. Doctor Thess at Tohoku Unversty, (n Japanese).. Igarash, S. Energybased factor of safety aganst lquefacton. Proceedngs of JSCE No.4/I, pp. 3 4, Kazama, M. A new dea for evaluatng lquefacton strength based on accumulatve hysteretc energy. Proceedngs of the 3nd. Japan Natonal Conference on JSSMFE., pp. 7374, 997 (n Japanese). 7. Akyama, H. Earthquakeresstant desgn method for buldngs based on energy balance. Ghodo Press, 999 (n Japanese). 8. Kusakabe, S. and Moro, S. The develop of a substructure onlne testng system for sesmc response analyss of geotechncal system. Sols and Foundatons, Vol. 3, No., pp.7, Adach, T., Yamada, M., Sekhara, H. and Enam, A. Pseudodynamc test on ntensty of earthquake ground motons at occurrence of lquefacton of subsurface layers. Journal of Structural and Constructon Engneerng, Trnsactons of Archtectural Insttute of Japan, No., pp. 89, 998 (n Japanese).. Inoue, Y., Osawa, Y., Matsushma, Y., Ktagawa, Y., Yamazak, Y., and Kawamura, S. A Proposal for sesmc desgn procedure of apartment houses ncludng Solstructure nteracton effect. Proceedngs of 9th orld Conference on Earthquake Engneerng, Vol.VIII, TokyoKyoto, pp. 3637,998.. Tanaka, Y., Kanatan, M., Hataya, R., Sato, K., Kawa, T. and Kudo, K. Evaluaton of lquefacton potental of gravelly sol layer based on feld performance data. Proceedngs of JSCE No.666/III3, pp. 7, (n Japanese).. Kobe Cty Report Investgaton of ground deformaton of reclamed ground due to Hyogoken Nanbu earthquake. Port Island, Rokko Island, pp. 9, 99 (n Japanese). 3. Hatanaka, M., Uchda, A. and Ohara, J. Lquefacton characterstcs of a gravelly fll lquefed durng the 99 Hyogoken Nanbu earthquake. Edton of Sols and Foundatons, Vol.37, No.3, pp. 7, 997.