The results of field testing and of simplified liquefaction analyses of the Enmedio Island soil deposits are presented and discussed in this paper. It is found that for this case history simple criteria for assessing liquefaction potential yield results in accord with field behavior

Jaime, A.

Montañez, L.

Romo, M. P.

English

Missouri University of Science and Technology (Missouri S&T): Scholars' Mine

Missouri University of Science and Technology Scholars' Mine International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics 1981 - First International Conference on Recent Advances in Geotechnical Earthquake Engineering & Soil Dynamics 01 May 1981, 9:00 am - 12:00 pm Liquefaction of the Enmedio Island Soil Deposits A. Jaime lnstituto de lngeniería, Universidad Nacional de México L. Montañez lnstituto de lngeniería, Universidad Nacional de México M. P. Romo lnstituto de lngeniería, Universidad Nacional de México Follow this and additional works at: https://scholarsmine.mst.edu/icrageesd  Part of the Geotechnical Engineering Commons Recommended Citation Jaime, A.; Montañez, L.; and Romo, M. P., "Liquefaction of the Enmedio Island Soil Deposits" (1981). International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics. 7. https://scholarsmine.mst.edu/icrageesd/01icrageesd/session08/7 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 scholarsmine@mst.edu. Liquefaction of the Enmedio Island Soil Deposits A. Jaime, L. Montanez, M.P. Romo lnstituto de lngenierla, Universidad Nacional de Mexico SYNOPSIS. The results of field testing and of simplified liquefaction analyses of the Enmedio Island soil deposits are presented and discussed in this paper. It is found that for this case history simple criteria for assessing liquefaction potential yield results in accord with field behavior. INTRODUCTION On March 14, 1979, a 7.6 Richter magnitude earthquake with epicenter located in the Pacific Ocean, about 50 km ofi the coast ofthe state of Guerrero, Mexico, caused damage ran£ ing from severe to light at distances over 350 km (i.e. Mexico City). During the earthquake, the Enmedio Island soil deposits liquefied. The phenomenon was observed only at the South and Southwest zones of the island (zone 2, fig 1), which is located at the mouth of the Balsas River; its strati-graphy is composed of typical deltaic deposits, mainly, sand, gravelly sand, silt and mixtures of them. Prior to the earthquake ocurrence, geotechnical studies were performed at the North and North-east of the site (zone 1, fig 1); with this information a liquefiable sand stratum was identified, and it was suspected that this layer could extend into the zone which actually liquefied. A second site boring exploration program carried out after the seismic event at zone 2 showed that the sand stratum was also present in this zone. A description of the earthquake effects, soil deposit characteristics and field detection of the liquefied sand layer is presented in this paper. SITE CHARACTERISTICS Geology The Enmedio Island is located between the state of Guerrero and Michoacan, Mex. at the mouth of the Balsas River in the physiographic province of Sierra Madre del Sur. According to Gutierrez (1971), the main fea-tures of the Balsas River delta are: irregular boundary between pre-deltaic rocks and the delta sediments; alluvial fans; ancient wander ing of the River bed; wide flood plains; and -marginal lagoons. 529 The deltaic sediments in the Enmedio Island are composed of sandy and silty soils down to 40 to 50 m deep, which are the product of eroded igneous, sedimentary and metamorphic pre-deltaic rocks. Mineralogical studies revealed that the upper ten meters of sandy soils consist of: quartz (50%), rock frag-ments (7%); dark minerals (10%), feldspar (25%), mica (0-3%), seashells and fragments (0-6%). Seismicity The Enmedio Island is located in a highly seismic zone associated with the subduction of the Pacific Ocean plate under the American Continent. According to the results of a seismic risk study carried out by Esteva et al (1973), a seismic event of magnitude 8 can occur near DY the site producing accelerations of 0.27 g and 0.35 g for recurrence periods of 100 and 500 years, respectively. The earthquake of March 14, 1979 had a 7.6 rna£ nitude and its epicenter was located in the Pacific Ocean some 50 km from the site, and its depth fixed at 59 km. The maximum ground acceleration recorded at SICARTSA steel mill, which is across the Balsas River, was about 309 cm/s 2 • The duration of the event was 35 s, of which, the strongest part lasted 15 s. The recording accelerometer is founded on an alluvial deposit 40 m deep, having similar characteristics to those encountered in the site. Stratigraphy at the North Part of the Island Several years before the March 14, 1979 earth-quake occurred, the Balsas River was dredged and the waste product dumped at the North part of the Island. This resulted in a hydraulic fill with irregular thickness (2m at most). Cobbles, gravels and coarse sand deposited at the North of zone 1 whereas finer products settled towards the center of the Island. 530 1400 9 •1o .,er I \~ 1200 r' I .28 \ ,---J •a \ \ 1000 / / •n 800 .16 600 0 0 200 400 600 800 • Bore holes 0 Sand Fig 1. Plan view of the site. Boring and sand boils A compacted fill was placed on these deposits; the elevation reached to the northern side of the access road (fig 1) was 3.60 m, and an elevation of 1.2 m to the southern side. These elevations corresponded to the actual ground level during the seismic event. Prior to the earthquake occurrence an explor-ation program, which included standard pene-tration tests (SPT) and sampling with Shelby tubes, was carried out (fig 1). The stratigraphic profile along axis 2 (fig 1) is presented in fig 2. A stratum of dark gray fi.ne sand ranging from loose to medium dense, with less than 15% of fines, is found throughout the profile. The thickness of this layer ranges from 1 to 6 m and is underlain by a series of strata composed of gravelly sand, sand and gravels, silty sand, silty clay and silty sands. The number of SPT blows on this strata sequence was greater than 40. The ground water was at elevation 0.0 m when the earthquake occurred. Soil Behavior During the seismic event cracks (5 to 10 em wide) and sand boils (0.3 to 1.5 min diameter) developed at zone 2, fig 1. Many of the cracks .18 .27 .4 .23 ·11 •6 .26 .12 .22 .2 1 ZONE I 1000 1200 1400 1600 1800 -..::C Meters bolls Cracks location and observed damage cracks were observed along the access road in the section NW-SE. Perpendicular to these cracks a different cracking pattern developed as shown in fig 1. Due to the cracking two columns of a building under construction tilted. On the other hand, most of the sand boils occurred at the Southern part of the Island. It was also observed that some boils were associated with cracks. According to an eyewitness, the sand volcanoes appeared just before the shaking ended, and the jets of the sand-water mixture expelled reached a height of about 2 m. Few minutes later the flow and height of the jets were negligible, although water kept flowing for approximately 1 1h hours after the end of the earthquake. The material expelled throughout the sand boils and some of the cracks was the dark gray, fine sand found at elevations 0.0 to -6.0 m. Potentially Liquefiable Sand Stratum From the stratigraphic information of the Northern part of the site (zone 1) together with the characteristics of the soil ejected from the volcanoes and cracks, it was concluded that the layer of dark gray fine sand was also present in the southern part of the Island where liquefaction occurred. PM-7 0 Ci) ~ > ~ ,:· ~ -5 -~ ... ~ . ~ ·. ~! c -· ~ .a.r•· ~--· Qj -10 '. ·, > 0 ., .. ..0 2 ..... c -15 .2 0 > Qj w-20 -25 -30 100 ~ + Fill 0' c <f) <f) c Q. ~ 0 100 80 60 PM -13 .. . ... ~ .... · .- ... ... -... .. ::,: :·-· ·.· .. :· 200 1---j Silt PM-25 ..-... -~ .P .... 300 ~Clay 531 PM-3 :::· . .• -..;:;,.-~: .f:·.~­..:..f .:-: ~--·. ~-...... ··.":"":-~ -~.--400 J:l .. • ;/J Gravel PM-21 500 ··-·; ... ·,· ... ····· ~: ··-~-l .> ) Fine sand PM -13 ·.• .. ·, ·_, 600 700 Meters l',r,rj Organic soil Fig 2. Stratigraphic profile along axis Fines 10 0.1 0.01 Grain diameter (mm l Fig 3. Grain size distribution curves. Liquefiable sand Analyzing the grain distribution curves of the dark gray sand (fig 3) in zone 1 the following features are observed: a) 0 . 0 7 4 mm < D 50 < 2 mm b) Cu < 10 (Uniformity coefficient) c) Fines content 5 to 15% On the other hand, the geometric characteristics of the soil deposit and the SPT results can be summarized as follows: a) The layer thickness (h) of the soil over lying the sand stratum varies between -3.5 and 6.5 m. b) The ratio of thickness h to sand layer thickness (H) is in average less than 1. c) Taking into account the mean value of the minimum and maximum SPT results of each boring in the sand layer, the following values were obtained: N . = 9 and N = 28, with variation m~n max coefficients CV . 0.53 and cv max m~n = 0.39. These values correspond to a loose to medium dense sand. d) Nmin is less than the product 2 h = 10m. 532 From the results described, according to Kinshida's and Ohsaki's criteria (cited by Shanon & Wilson and Agbabian-Jacobsen Associates, 1971) it was concluded that the dark gray layer of sand, found in the North of the site was liquefiable. On the basis of the above mentioned results, a second exploratory boring program was carried out in the zone which exhibited liquefaction (zone 2), with the purpose of having a more detailed stratigraphic information of the area. ADDITIONAL SITE EXPLORATION The location of the borings for the field exploration which is shown esquematically in fig 4 consisted of: standard penetration tests (14), boring combining SPT and Shelby tubes to elevation -21 m (12), pressuremeter tests (4), Lefranc permeability tests (2); and two open pits. Stratigraphy At the Southwest of the site the ground level was at elevation +1.2 m; from this level down to 0.0 m the soil consisted of a yellowish silty sand medium to fine. Close to elevation 0.0 there was a silty clay layer 40 em thick. 1400 r--------------------------------------------------------------------------------, ---- Soft layer 1200 Liquefiable sand layer 1000 BOO 600 400 200 400 1600 1800 Meters Fig 4. Additional site exploration The boring studies carried out revealed that stratigraphy at zone 2 was very similar to that found in the Northern part of the Island (fig 2). The layer of dark gray fine sand was also found at elevations 0.0 to -1.80 m with thickness varying from 1.5 to 5 m, and fines content less than 15%, it exhibits a minimum SPT mean value N . = 10 blows and a maximum N = 22 with mln max cvmin = 0.37 and cvmax = 0.19. As before fro~ elevation -7.5 m below the soil is dense with SPT values greater than 40 blows. Pressuremeter Tests Nine tests were performed in 4 boreholes located close to the borings shown in fig 4. Four tests were made in the dark gray sand stratum obtain-ing a limit pressure p£ between 1.9 and 3.95 kg/cm 2 and M~nard modulus of deformability E = 15- 20.5 kg/cm 2 • According to Centre s D'Etudes Geotechniques de Paris (1972), these values correspond to a rneoium to loose sa.nc .. Lefranc Permeability Tests The Lefranc permeability tests gave the follow-ing data: k = 6.4 x 10- 3 em/sec for the gray sand layer; k = 8.11 x 10- 2 em/sec for the gravelly sand stratum underlying the sand; k = 1.8 x 10- 4 em/sec for the silty clay layer overlying the dark gr&y sand. LIQUEFACTION EVALUATION Characteristics of the Sand Layer In table I are presented the main characteris tics of the dark gray sand encountered through out the Enmedio Island. These results include both site exploration programs. TABLE I. Description of the Dark Gray Sand Particle size Gral.n shape M1nerals Bounding 0.1 < D~c < 0.50 mrn 2,43 < cu < 3,92 angular Quartz (SOi.), feldspar (25%} ferromagnesians (10%), roc}!; fragments (7%), m1ca (0-3 ll seashells (0-6!) There l.S no trace of bounding neither by carbonation by oxidation On the basis of grain distribution curves, stra tigraphic profiles and SPT results, the spatial distribution of the liquefiable sand layer was determined (fig 4). The upper part of the layer is found at elevations 0.0 and -2.0 m, with a mean elevation of -0.25 m. Its thick-ness varies between 1 and 6 m, having an average of 3.40 m. Overlying the sand layer there is an impervious stratum having an average thickness of 0.70 m and composed of clay (CH) with lenses of silt (ML). Its spatial distribution is also shown in fig 4. Below the sand stratum there is a layer of gravelly sand and sandy gravel. 533 The statistical SPT results obtained in zones 1 and 2, for the sand layer "!re shown in table II. TABLE II. SPT. Pesults in zones 1 and 2 Statistical Sand layer Sand layer value zone 1 zone 2 N min 12 10 0 min 5. 58 3 .92 cv min 0. 45 a .3B N 27 21 max 0 max 8. 29 4. 98 cv max 0. )0 0. 24 N 20 16 av 0 5. 16 3. 95 av cv 0. 26 0. 25 av The average mean values (Navl were obtained taking into account all SPT test results, obtained in each boring within the correspon~ ing zone. Eventhough there is a small difference jn SPT values between zones 1 and 2, it can be observed a consistent trend showing higher values in zone 1. This is due to the fact that the over burden pressure in the sand layer of zone 2 is lower than that of the zone 1, because of the differences existing in ground level elevations. The stress profiles for both zones are shown in fig 5. Liquefaction Susceptibility Analysis Using the SPT results shown in table II, the stress profiles of fig 5, the maximum ground acceleration estimated from the records at SICARTSA steel mill (0.3 g) and the simplified criterion proposed by Seed et al (1975), the liquefaction susceptibility analysis was carried out. The results obtained are sum-marized in table III and plotted in fig 6. TABLE III. Susceptibility to liquefaction of the Dark Gray Layer of Sand Parameter Zone 1 Zone 2 Total stress oo {kg/cm 2 ) 1.0 a .ss Effective stress if 0 (:W.g/cm 2 ) N•. m1n N' max N' av 1/00 In this 0. 8 13 30 22 0. 23 table N• = eN N eN = 1 - 1.25 log ~ 01 a 1 = 1 kg/cm2 a 0.65~ g 0. 4 15 31 24 0. 26 . max max1mum acceleration on the ground surface Fig 'E Zone 1 (8orinQ, PM-15) 12. 4. 0 • .._!... ··;..,. ( Ysat)sand"' 19 ~~~ ( Ysat)Qra~el"' 17 f~~ Zone 2 (Boring,SE-5) Fig 5. Soil stress distribution in zones 1 and 2 0,,_--------------------------. I • Lower bound for sites where I ltquefoction occurred---... / '-t / + . / I I I I I / •••• 0 0 ~ ··~ ;;; 0 ••• )( Zone 1 + Zone 2 I I 0 o~~--~,Lo--~--,~o---L--~,o~~--~.o Blows per foot N' • Liquefaction, stress ratio based on estimated acceleration e LiQuefaction, stress ratio based on Qood acceleration data 0 No liquefaction, stress ratio based on estimated acceleration 0 Na liQuefaction, stress ratio based on Qood acceleration data 6. Correlation between stress ratio causing liquefaction in the field and penetration resistance of sand (Seed, 1979) From this figure it is seen that the points corresponding to N' . of both zones lie in nun the liquefiable part, the N' values fall on av the borderline and the N' values fall on the max non-liquefiable part. According to these results it is concluded th~t the dark gray layer of sand in both zones is liquefiable or at least it is in the borderline. Since the sand layer actually liquefied in zone 2; there remains to be answered why zone 1 did not show signals of liquefaction. This is the main subject of a companion paper to this 534 conference, in which the results of cyclic triaxial tests and of analyses of pore pressure generation and dissipation during the earthquake are presented, .Ti1irne, ?orm and rbntanez (1931) FINAL COMMENTS On the basis of the results of this investiga-tion several conclusions can be drawn: a) Empirical criteria (such as Ohsaki's and Kishida's) based on geometric characteristics of the soil deposit, SPT results and grain distribution of the material, can be very useful to detect liquefiable soils on preliminary basis. b) Seed's empirical correlation gives a good estimate of the susceptibility to liquefaction. Eventhough, it seems that the borderline of fig 6 could be drawn a little further to the right. c) There remains to be answered why zone 2 liquefied and why zone 1 did not. ACKNOWLEDGMENTS Financial support for this study was proviGed by FERTIMEX, S. ~-REFERENCES Centre D'Etudes Geotechniques de Paris (1972), "Regles D'Utilisation des Techniques pres-siometriques et D'Eploitation des Resultants obtenus pour le calcul des fondations", B.P. No 2 bulletin D660/67, march, France Esteva, L., J. L. Trigos and R. Guerra (1973), "Riesgo Sismica en Las Truchas, Michoac~n", Internal report, Institute de Ingenier1a, UNAM, M~xico Guti€rrez, E. M. (1971), "Fisiografia y Sedi-mentaci6n del Delta del Rio Balsas, Mich., M~xico", Boletfn 93, Institute de Geolonfa, Ulll'-'1, M~xico -Jaime, A., 1-l.P. R::JITD and L.I-bntanez (1)31), "Observed an.l PreJictErl .wiquefaction of a Sand Stratl.nn", Proc. Int. Conf. on Recent 1\dvan:::es in Geothecnical Earthquake Eng. and Soil D'jl1al11ics, St. lDuis ilisscuri, April 2G, USZ\ Seed, H. B., I. Arango and C. Chan (1975), "Evaluation of Soil Liquefaction Potential during Earthquakes", Report No EERC 75-27, University of California, Berkeley, USA Shanon & Wilson, Inc., and Agbabian-Jacobsen Associates (1971), "Soil Behavior under Earthquakes Loading Conditions", Report prepared for U8lFC, Contract W-7405-eng 26, UP~ 

Liquefaction of the Enmedio Island Soil Deposits

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=2595&amp;context=icrageesd

Liquefaction of the Enmedio Island Soil Deposits

Abstract

Similar works

Full text

Available Versions

Missouri University of Science and Technology (Missouri S&T): Scholars' Mine