Microzonation of Liquefaction Hazard using Liquefaction Index in Babol City

Transcription

1 Microzonation of iquefaction Hazar using iquefaction Inex in Babol City A Choobbasti, Mehran Naghizaehrokni, R Charaty To cite this version: A Choobbasti, Mehran Naghizaehrokni, R Charaty. Microzonation of iquefaction Hazar using iquefaction Inex in Babol City. Geotechnical Engineering Journal of the SEAGS AGSSEA, 217, 48. <insu > HA I: insu Submitte on 29 Sep 217 HA is a multi-isciplinary open access archive for the eposit an issemination of scientific research ocuments, whether they are publishe or not. The ocuments may come from teaching an research institutions in France or abroa, or from public or private research centers. archive ouverte pluriisciplinaire HA, est estinée au épôt et à la iffusion e ocuments scientifiques e niveau recherche, publiés ou non, émanant es établissements enseignement et e recherche français ou étrangers, es laboratoires publics ou privés.

2 Microzonation of iquefaction Hazar using iquefaction Inex in Babol City A. Janalizaeh choobbasti 1, M. Naghizaehrokni 2*, R. Charaty 3 1 Department of Civil Engineering, Babol University of technology, Babol, Iran 2 Department of Geotechnical Engineering, PhD Researcher, RWTH Aachen University, Aachen, Germany 3 Department of Civil Engineering, IAU Zanjan branch, Zanjan, Iran * Naghizaehrokni@geotechnik.rwth-aachen.e ABSTRACT: One of the evastating effects of the earthquake is on liquefaction phenomenon site, which is one of the most important an most complex topics in seismic geotechnical engineering. iquefaction is a phenomenon that occurs in loose, saturate seiments without stickiness in unraine conitions uner the influence of waves cause by earthquakes or heavy static loa. In orer to cope with evastating effects of this phenomenon, it is essential to ientify areas prone to liquefaction. This ientification can be conucte as microzoning, in which risk capacity is etermine in ifferent areas. Thus, in this paper, the zoning map of Babol liquefaction risk will be provie. In this regar, a stuy was conucte on the soils in Babol an after examining ifferent areas of the city, laboratory results an fiel stuies of more than 5 boreholes in ifferent areas with a epth of 2 m were analyze for fining liquefaction an non-liquefaction segments. In this stuy, ifferent approaches were use incluing See, Iwasaki, Haeri an Yasrebi, Chin & Zhang an Sewmez & Gocojlou proceures an finally, a computer program was written for examining an proviing microzoning map of Babol liquefaction risk. KEYWORDS: iquefaction, Microzonation, Babol, Inex, Seismic Geotechnic. 1. INTRODUCTION Since the awn of mankin an human settlement uner the roof, earthquake was always one of the risks that have kille the human from time to time. In recent years, iscussion about the effects of earthquakes on soil has attracte many soil engineers an researchers. Among the phenomena relate to seismic geotechnical risks, soil liquefaction is of great importance(gill an Berg 1967). In this phenomenon, the saturate soil will be influence by light stresses cause by earthquake an pore water pressure increases. Now if the spee of applying these loas is low so that the soil has an opportunity for rainage, pore water pressure will be amortize an liquefaction will occur. But if the spee of applying these loas is high, there is no opportunity for rainage, an the soil mass will ten to change volume an pore water pressure will increase so that it will be equal to the total stress applie to the soil mass(maurer, Green et al. 215). Therefore, the san particles will be floating in the water an effective stress will be equal to zero. In this case, soil bulk loses its shear strength an liquefaction occurs. iquefaction is the main reason for much of the estruction cause by the earthquake. arge an continuous eformations that occur in soil mass can lea to instability an ultimately great amage to these structures(maurer, Green et al. 214). This phenomenon can cause gable roofs instability, loss of bearing capacity of structures founation, an amage to the structures cause by non-uniform subsience. After the wie liquefaction that occurre in the evastating earthquake of Japan an Alaska in 1964, geotechnical engineers pai attention to this phenomenon. In the last 4 years, a significant progress has been one in terms of unerstaning liquefaction mechanism an the factors affecting it(rahman, Siiqua et al. 215). In the early years, more attention was focuse on investigating this phenomenon in clean sans so that it was thought that liquefaction is just relate to sans an coarse-graine soils are not capable to prouce an aitional pressure of pore water, which is the main reason of liquefaction (See an Iriss 1982). But as time passe an new earthquake occurre an following the observation of this phenomenon in coarse an fine-graine soils, many researchers aime to examine the factors affecting the liquefaction of the soil(iriss an Boulanger 26). Iran is locate on seismic Alpine-Himalayan region an this increase the occurrence of earthquakes as one of the most amaging natural isasters in the country. Major earthquakes such as Manjil earthquake (199), Arebil (1996), South Khorasan (1997), Bam (23) an Boroujer (26) confirms this issue; therefore, the nee is felt for a comprehensive review of earthquake phenomenon an its effects in the country. Therefore, in this stuy, Babol City (as shown in Figure 1) was evaluate in terms of geological an seismic features, using results of soil mechanic stuies an eventually liquefaction risk zoning map of the city was provie(choobbasti, Farrokhza et al. 215). Figure 1. Position of the Babol City in the Mazanaran Province 2. METHODS ess than one century has passe from the first use of the wor liquefaction by researchers. In fact, this is known as one of the most complex issues in geotechnical engineering. The Close connection of this phenomenon with earthquake engineering has attracte more attention from scientists. Hazen in 1918 use the wor liquefaction for the first time in orer to explain Calaveras am break. Stuies on liquefaction phenomenon were seriously

3 starte by researches after two earthquakes of Niigata in Japan an Alaska in America in 1964 (Ceyhun an Hilmi). Among the most important stuies in this fiel, I can refer to Casgrane, Castro, See an Iriss, You, Iwasaki et al. s research works. In this stuy, accoring to See et al. s metho, the safety factor is etermine against liquefaction in accorance with Eq. 1 (See, Tokimatsu et al. 1984). CRR R Cyclic Resistance Ratio F S CSR (1) Cyclic Stress Ratio Cyclic shear stress ratio is etermine by Eq. 2. av amax CSR / 65.. r (2) g Where av is the average equivalent uniform cyclic shear stress cause by the earthquake, which is assume to be.65 of the maximum inuce stress; a max is the peak horizontal acceleration at groun surface generate by the earthquake, g is the acceleration of gravity, an are the total an effective overloae stresses, respectively, an an Iriss 1971). r r is a stress reuction coefficient (See ha been suggeste by the national center for earthquake engineering research workshop (NCEER) in 1996 (You, Iriss et al. 21): r Z for Z 9.15m (3) r Z for 9.15m Z 23m (4) r.744.8z for 23m Z 3m (5) r.5 for Z 3m (6) The first step in etermining the cyclic shear resistance ratio (CRR) of the soil is the correcte number of SPT (N) to be achieve ( N ). 1 6 Pou an Iris suggeste that MSF coefficients are calculate accoring to Equation 9. FS ( CRR 7.5/ CSR ) MSF (9) Where MSF is the magnitue correction factor. 3. DIFFERENT PROCEDURES FOR EVAUATING FINE-GRAINED SOIS IQUEFACTION Natural san eposits may inclue some silt seam an bans which can play an important role on the excess pore pressures being evelope; therefore, this issue sometimes can be a critical factor in increasing the potential of liquefaction. Sites consists of silt an silty clays with low plasticity properties are wiely available aroun the worl, incluing Iran. Thus, it is very important to know the properties of silts encountere in fiel or use in laboratory testing. If the silt layer has a high plasticity, it can increase the resistance against liquefaction while low plasticity silts may alleviate the potential risk of liquefaction. Accoring to Chinese criteria, sany soils with low liquefaction properties have more tren to liquefaction at low shear strain an soils with high plastic properties ten to reuce the resistance an harness at the large strain. See et al. provie new criteria in 23 for fine-graine soil liquefaction assessment (See, Cetin et al. 23). These criteria consier all the properties of fine-graine soil an are wiely use in its engineering projects. This proceure is escribe in Figure 2. As it can be seen, if the soil is in A or B area, there is a nee for more investigations incluing laboratory tests or confience coefficient in SPT metho. In orer to calculate the liquefaction severity in this area, 3 methos of Haeri & Yasrebi, Iwasaki an Sunmez an Gukejlo were use. The proceure of Iwasaki inclues liquefaction severity from groun level to a epth of 2 meters. ( N ) N. C. C. C. C. C 1 6 m N E B R S (7) Where ( N 1) is the correcte number of SPT value, 6 stanar penetration resistance measure at the site, correction factor C E N m is hammer efficiency, N m is the C is the N is consiere as overhea effective stress, C B is the correction factor for borehole iameter, C is the correction factor for bar length an C R S is the correction factor for samples with or without cover. The NCEER workshop propose the Equation 8 for fine correction coefficients (You, Iriss et al. 21). N N (8) 1 6CS 1 6 Where α an β are coefficients that are obtaine base on the percentage of fines (F2). The cyclic shear resistance ratio (CRR) of soil is etermine to obtain the value of (N1) 6cs an using the See et al. s graphs with attention to the fine-graine soil (You, Iriss et al. 21). In orer to etermine the safety factor against liquefaction in earthquakes with ifferent magnitues, the scale magnification correction coefficient of the earthquake must be use. In this stuy, the suggeste coefficients of Pou & Iris are use. Figure 2. Recommenations Regaring of iquefiable Soil Type Assessment In this way, by calculating the liquefaction potential at any location using equation 1, the effects of liquefaction in the stuy can be conclue (Iwasaki, Tokia et al. 1982): I 2 FW. ( z ) z (1) 1FS FS 1 F FS 1 (11) W( z) 1. 5z (12)

4 Where I is the liquefaction potential inex, F is the function of the safety factor, FS is the safety factor against liquefaction at epth z an is the epth function. Iwasaki propose four categories W z for assessing the severity of liquefaction. iquefaction severity is very low for, low for, high for an very high for15i. I I Haeri an Yasrebi change the safety factor in Iwasaki metho, in orer to remove efects in this approach in orer to reuce the confience coefficient effect of ifferent layers against liquefaction in final potential function of surface occurrence. Also, the epth function was change so that if the liquefaction layer epth increase, the effect of liquefaction in that layer woul reuce nonlinearly on the surface. Following equation is suggeste to calculate the potential for liquefaction at surface(iwasaki, Tokia et al. 1982). 2 2 Z P (1 F ) z (13) 1.5 Z Where P the liquefaction potential inex at surface, Z is the epth in meters, F is the safety factor against liquefaction at epth Z. Analyzes have been conucte by Haeri an Yasrebi show that is the appropriate bounary for separating the P 1 two moes of occurrence an non-occurrence of liquefaction effects. Thus, the values inicate non-occurrence at P 1 surface an P 1 are inicative of the occurrence of the surface effects of liquefaction(haeri 1999). Chen an Zhang presente the possibility of soil liquefaction by P equation. This inex varies from zero to one which is associate with F (Chen an Juang 2). P 1 F I (14) Sunmez an Gukejlo esignate the S liquefaction severity inex instea of the liquefaction potential inex propose by Iwasaki. Sunmez an Gukejlo escribe the construction of liquefaction severity classifie accoring to the following formula: S (15) P Z z z The P (z) value is etermine for Eq.14 for each epth. z P ( z ) z S P( z )(1 z ) (1 z ) 4 z (16) Classification of liquefaction severity inex which was suggeste by Sunmez an Gukejlo is given in Table 1 with a escription of the liquefaction potential(sonmez an Gokceoglu 25). Table 1. Classification of the severity of liquefaction base on S (Sunmez an Gukejlo) Severity of liquefaction iquefaction Inex (s) Very high 85 s< 1 High 65 s < 85 Meium 35 s < 65 ow 15 s < 35 Very little s < 15 Non-liquefaction(F>1.411) s= 4. EVAUATION OF THE GEOOGICA, SEISMICITY AND GEOTECHNICA STUDIES AT BABO CITY Babol, a city of Mazanaran province in the northern part of Iran, is consiere as the stuy area in this research. The city is locate approximately 2 km south of the Caspian Sea on the west bank of the river Babolroo an receives abunant annual rainfall. Babol area is locate on alluvial eposits that belong to quaternary geology resulting from torrential rivers. The berock in the area is mae of Conglomerate, sanstone. In general, the soil texture in this area consists of san, clay an silt compouns. The percentage of these compouns epens on the istance from the sea. Thus, the closer to the sea, the higher percentage of san compouns an contrariwise: the more the istance from the sea, the higher percentage of silt compouns. A large number of faults have been ientifie along the North East - South West irection intersecting with faults along the North West - South East in Babol region, which leas to smashing berock in this area. The acceleration of plan in this project is consiere.35 g accoring to Babol location in a region with a relatively high risk. However, there is a consierable risk ue to the Micro-faults in Quaternary seiments an smashing berock. The fiel of stuy is consiere as a class (IV) accoring to the classification table of the new eition of the regulations [4]. Accoring to the seismic investigations that have previously been conucte in the area of the Mazanaran province, the assessment of seismic hazar in the Babol city on the analysis of earthquake magnitue (M) equals to 6.4 on the Richter scale. This is obtaine by the maximum horizontal acceleration (Amax) equal to.32g. This number roughly correspone with the number achieve by the ministry of Housing an Urban Development in a 5 year-return perio event for Babolsar area. The maximum horizontal acceleration for a return perio of 5 years is estimate to be between.2g to.3g in Babol area. In a stuy that was conucte by American researchers to emonstrate the effect of site, it was propose to the U.S. regulation raft, Martin an Dobry showe that for the accelerations less than.4g, acceleration over alluvial is more than the acceleration of the stone, an to obtain the acceleration over alluvial it shoul be 1.2 times the acceleration of the stone. From what has been iscusse above, which were obtaine from the latest stuies an research works, the acceleration number (Amax) is obtaine.35g in this research. Also, the earthquake magnitue has been consiere 7.5 on Richter scale for the calculations of liquefaction. aboratory an geological stuies imply the following results about Babol city soil: 1- Geological formations of plan scope generally belong to the Pleistocene (the present era). 2- Formations of the present era which has covere all over the stuie fiels have three origins of marshy fluvial, an the floo an most of the three categories of seiments surroun the seiments originating from the fenny an marshy areas. 3- The ominant soil type is clay an sany silt. 4- San particles with a iameter of up to.2 mm, are the iameter of the ominant particles in sany layers of the area. 5- Accoring to the USCS classification, the ominant soil type is the type of C an M (clay an silt with low pasty properties). 6- Dry specific weight of the soil for the soil's area is about 1.1 g/cm3 to 1.5 g/cm3. 7- Wet specific gravity of the soils for the propose area is locate in the range of 1.6 g/cm3 to 2.1 g/cm3. 8- Unergroun water epth varies from.2 to a maximum of 6.5 meters in height in the more southern areas. Due to the city map, accoring to Figure 3 an consiering the ispersion of boreholes location in the city, for appropriate conclusion an the best assessment of the area liquefaction, it was ivie into zones of 1 to 1, meters, in which 5 zones were

5 (N1)6c (N1)6 CN CSR Ϭ F2 Depth(m) Sunmez Inex Chen Inex Haeri Inex Iwasaki Inex Safety Factor CRR Geotechnical Engineering Journal of the SEAGS & AGSSEA Vol. 48 No.4 December 217 ISSN obtaine in the horizontal irection an 7 zones in the vertical irection. Overall, the city was ivie into 35 zones which can be seen in Figure 3. Overall, I will have 22 zones of important areas of the city for severity of liquefaction assessment that is usable for zoning map. Table 2. Physical characteristics an soil testing of Borehole number 33 Borehole No. 3 Depth of grounwater level: 1.5 m Date of test: 91/5/18 C(gr/cm2) Ǿ W (%) D 5 (mm) P2 Percent fine Γwet (g/cm3) γ(g/cm3) Nspt Soil Type (USCS) M M M SM SM M SM M SM SM 2 Depth(m) Figure 3. Zoning map of the Babol city for liquefaction assessment an the boreholes position 5. RESUTS AND DISCUSSION In the fourth an fifth columns of Table 2, the special weight of ry an wet soil is provie. The parameter of wet special weight is use in calculation of effective an total tension. P2 is the percentage of passing particles through the No. 2 sieve. This parameter is use in orer to consier the amenments relate to the assesse soil fine graine measure to etermine the cyclic resistance. D5 presents the particles iameter of soil that 5 percent of grains is small than it or in other wors D5 shows the average size of soil grain in millimeters. The physical properties an boreholes soil test were ajuste in the table for easy access to the boreholes ata. Table 2 also represents a sample of these tables from No. 33 boreholes ata. The results of liquefaction occurrence severity for each zone were calculate separately with three methos of Iwasaki, Haeri an Yasrebi an Sunmez an Gukejlo, which were ajuste in Table 3. Finally, by using a computer program written in this regar in Matlab Program, calculations were performe to evaluate the liquefaction hazar. Table 3 shows the sample output of written program for liquefaction potential assessment. This analysis was performe for all boreholes an overall results relate to the all boreholes are visible in Table 4. In this program, some soil parameters incluing special weight of soil an the percentage of fine-graine are known as a program input parameters. Table 3. Sample output from a program written for liquefaction assessment Nspt Ϭ r M M M SM SM M SM M SM SM 2 Soil Type (USCS) Depth(m)

6 Table 4. Summary of Results Inicators boreholes an liquefaction zone Zone Borehole Number Iwasaki Inex Haeri Inex Sunmez Inex A B Ave B Ave B B B C Ave C Ave D Ave D Ave D Ave D D6 C2 C3 C5 Ave Ave Ave Ave Ave C Ave C D D Ave E Information of all ata in Babol city can be seen in Table 4. Each borehole was analyze by three approaches an liquefaction inexe was obtaine for each borehole. To calculate the liquefaction inex of ifferent zones in this table, average of boreholes result was calculate in the last line of each zone where there was in that zone an finally three liquefaction inex has been obtaine for each zone base on Sonmez, Haeri an Iwasaki methos. In this map which obtaine from Iwasaki proceure which is showe in Figure 4, areas are categorize into three iverse parts as low liquefaction potential, high liquefaction potential an very high liquefaction potential that almost all zones in Babol city was consiere as a very high severity of liquefaction an just one zone was recognize as high liquefaction potential. Also there are four ifferent liquefaction severities in Iwasaki s approach; I can just two status of liquefaction as non-liquefaction an very high liquefaction potential. It seems that liquefaction will occur in almost all area of Babol city, base on obtaine map from Iwasaki metho Figure 4. Microzonation Map of liquefaction severity of Babol City accoring to Iwasaki In Haeri an Yasrebi s approach, there are just two conitions for occurring or non-occurring liquefaction an the map which has been obtaine from this approach are categorize into two sections as shown in Figure 5. In this metho, almost all areas are recognize as liquefiable areas. In fact, Haeri metho presents the presence or absence of liquefaction at surface, numbers of greater than 1 inicates presence of liquefaction in the surface an numbers of less than 1 inicates absence of liquefaction in the surface. This map provies information about liquefaction segments like Iwasaki proceure. In this map 22 zones have been evaluate in terms of etermining liquefaction an non-liquefaction areas. Overall, liquefaction will occur in 21 zones an this issue inicates that liquefaction inex is greater than 1 in these zones an one zone is recognize as non-liquefaction

7 segment that can represent that liquefaction inex is lower than 1. In Figure 6 which is obtaine by Sonmez & Gokceoglu proceure, almost all existing zones on the map have been ientifie as areas of liquefaction except for zone E2, E3 an A6. On this map, just one zone (C6) in the center of the map is known as liquefaction zone with high intensity. Other areas that were ientifie with highintensity liquefaction in previous proceures, in this metho have been etermine as liquefaction areas with high an meium intensity. Moreover, southern an central area of Babol are recognize as meium an high liquefaction potential whereas these segments were ientifie as very high liquefaction potential in Iwasaki approach. But non-liquefaction areas have almost been the same in all maps an almost all 3 zones map, A3 an E2, E3 are known as nonliquefaction. This issue inicates that to evaluate the nonliquefaction areas, all three methos have acte in the same way, an the non-liquefaction areas are the same for all three approaches. By comparing the obtaine map from the three propose methos, it can be conclue that Iwasaki an Haeri s metho have an acceptable consistency because there are many similarities in the obtaine maps from these two methos. On the other han, the obtaine liquefaction map from Sonmez s approach gives ifferent results. I can see similar results in Heiari et al(heiari, Amel-Sakhi et al.), Farokhza et al(farrokhza, Choobbasti et al. 212) an choobbasti et al(choobbasti, Farrokhza et al. 215) base on NCEER21 an artificial neural network but the number ata was not enough for receiving suitable results. In aition, for increasing the accuracy of results, the average of boreholes result was calculate for each zone. Finally, in this paper three maps were obtaine from ivers proceures were compare for enhancing valiation of results. With evaluation an comparison of obtaine maps with ifferent methos can be conclue that the central an southern parts of the Babol city are known as liquefaction areas in almost all three maps, but there are some ifferences about northern parts of Babol city. Evaluation of obtaine map from Haeri an Iwasaki metho shows that all northern parts of Babol city are known as liquefaction point with high intensity, while in the obtaine map from Sonmez proceure, northern parts of Babol city are known as liquefaction point with moerate intensity. However, about non-liquefaction areas, obtaine maps have a lot of consistency. 6. CONCUSIONS Figure 5. Microzonation map of occurrence or non-occurrence of liquefaction in Babol city accoring to Haeri an Yasrebi approach (1976) The results of 5 bore holes from fiel experiments were use for preparing microzonation map of the city of Babol. The city has been ivie to 35 separate zones for preparing microzonation map that 22 zones were use for zoning. The zoning maps were gaine from the ajuste results in table 4, in which the liquefaction intensity zoning map of Babol city is provie accoring to Iwasaki s proceure. Concerning the map was obtaine by this approach, 21 zones were evaluate with very high liquefaction intensity an 1 zone with high liquefaction severity from the set of 22 searchable zones. Obtaine map from Haeri & Yasrebi s approach inicates liquefie an non-liquefie segments in Babol. From a total of 22 evaluable zones, the results show the liquefaction incience at the surface for 21 zones an only one zone is etermine with the lack of liquefaction incience at the surface. The zoning map of liquefaction occurrence intensity in Babol city base on Sewmez an Gokojlou s metho illustrates that 2 zones with low liquefaction incience severity, 9 zones with moerate liquefaction incience severity, 1 zones with high liquefaction incience intensity an only 1 zone with very high liquefaction incience intensity were evaluate as shown in Figure 6. The zoning maps were obtaine from Iwasaki an Haeri s approach can confirm each other, so that 1 zone with low liquefaction intensity accoring to Iwasaki proceure is the same zone which is evaluate without liquefaction occurrence at surface in Haeri & Yasrebi s approach. Due to the ifferent ivisions of Sewmez & Gokojlou s metho or in the 2 previous proceures, I cannot have an appropriate analogy for results corresponence, hence; it is reasonable to conclue that the maps which obtaine from Iwasaki an Haeri s approaches give us more valuable results an I can trust on these maps. In aition, the main criteria of Iwasaki an Haeri s proceure are so similar an these methos have more compliance with soil in Iran. 7. ACKNOWEGDMENT Figure 6. Microzonation map of liquefaction severity of Babol city accoring to Sunmez an Gukejlo (25) I am using this opportunity to express my gratitue to everyone who supporte me to complete this paper. I am thankful for their aspiring guiance, invaluably constructive criticism an frienly avice uring the project work.

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