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Assessment of soil liquefaction incorporating earthquake characteristics D.S. Liyanapathirana a, * , H.G. Poulos b a Department of Civil, Mining and Environmental Engineering, University of Wollongong, Wollongong, NSW 2522, Australia b Coffey Geosciences Pty Ltd, Department of Civil Engineering, University of Sydney, Sydney, NSW 2006, Australia Accepted 18 November 2003 Abstract This paper investigates the effect of nature of the earthquake on the assessment of liquefaction potential of a soil deposit during earthquake loading. Here, the nature of the earthquake is included via the parameter V ; the ‘pseudo-velocity’, that is the gross area under the acceleration record of the earthquake at any depth below the ground surface. By analysing a number of earthquake records from different parts of the world, a simple method has been outlined to assess the liquefaction potential of a soil deposit based on the pseudo-velocity. For many earthquakes occurred in the past, acceleration records are available or can be computed at the ground level or some other depth below the ground surface. Therefore, this method is a useful tool at the preliminary design stage to determine the liquefaction potential before going into a detailed analysis. Validation of the method is carried out using a database of case histories consisting of standard penetration test values, acceleration records at the ground surface and field observations of liquefaction/non-liquefaction. It can be seen that the proposed method has the ability to predict soil liquefaction potential accurately, despite its simplicity. q 2004 Elsevier Ltd. All rights reserved. Keywords: Soil liquefaction; Nature of the earthquake; Pore pressure generation; Cyclic shear stress; Pore pressure dissipation; Liquefaction potential index 1. Introduction When saturated sand deposits are subjected to earth- quake-induced shaking, pore water pressures are built-up leading to liquefaction or loss of soil strength. Major earthquakes that have occurred during past years, such as the 1964 Alaska, 1964 Niigata, 1989 Loma – Prieta and the 1995 Hyogoken – Nambu have demonstrated the damaging effects of soil liquefaction. Therefore, it is necessary to obtain a proper understanding of the effect of parameters such as soil properties and the nature of the earthquake on the severity of the soil liquefaction. Most major earthquakes occur around the boundaries of the tectonic plates such as those that exist in California, USA. The Australian continent is in the middle of one of the world’s largest tectonic plates, and therefore, Australia is subjected to relatively low earthquake activity. However, the 1989 Newcastle earthquake, which caused 13 deaths, increased the awareness of the need to properly assess the possible consequences of earthquakes in areas subjected to intraplate events. Although Australian earthquakes can have acceleration levels as high as those in Californian earthquakes, evidence of liquefaction has not been reported. The major difference between Californian and Australian earthquakes is that, in Australian earthquakes, the predominant frequency is high and any large acceleration levels last for a very brief duration, while in Californian earthquakes, the predominant frequency is lower and high acceleration levels exist during a significant proportion of the longer duration of the earth- quake. Hence this gives a clear indication about the significance of the nature of the earthquake on the liquefaction. Although ground response analyses based on the finite element method provide a better assessment of liquefaction of a soil deposit by taking into account the nature of the earthquake and the pore pressure dissipation [13,16,17,21, 27,29,30,40,42], they are often costly and time-consuming. In addition, constitutive models used in those programs need large number of parameters to determine the pore pressure generation in soil due to earthquake loading. Therefore, simplified methods in assessing soil liquefaction are popular among practicing engineers. These procedures are very useful at the preliminary design stages to assess 0267-7261/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.soildyn.2003.11.010 Soil Dynamics and Earthquake Engineering 24 (2004) 867–875 www.elsevier.com/locate/soildyn * Corresponding author. E-mail address: [email protected] (D.S. Liyanapathirana).

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  • Assessment of soil liquefaction incorporating earthquake characteristics

    D.S. Liyanapathiranaa,*, H.G. Poulosb

    aDepartment of Civil, Mining and Environmental Engineering, University of Wollongong, Wollongong, NSW 2522, AustraliabCoffey Geosciences Pty Ltd, Department of Civil Engineering, University of Sydney, Sydney, NSW 2006, Australia

    Accepted 18 November 2003

    Abstract

    This paper investigates the effect of nature of the earthquake on the assessment of liquefaction potential of a soil deposit during earthquake

    loading. Here, the nature of the earthquake is included via the parameter V ; the pseudo-velocity, that is the gross area under the acceleration

    record of the earthquake at any depth below the ground surface. By analysing a number of earthquake records from different parts of the

    world, a simple method has been outlined to assess the liquefaction potential of a soil deposit based on the pseudo-velocity. For many

    earthquakes occurred in the past, acceleration records are available or can be computed at the ground level or some other depth below the

    ground surface. Therefore, this method is a useful tool at the preliminary design stage to determine the liquefaction potential before going

    into a detailed analysis. Validation of the method is carried out using a database of case histories consisting of standard penetration test

    values, acceleration records at the ground surface and field observations of liquefaction/non-liquefaction. It can be seen that the proposed

    method has the ability to predict soil liquefaction potential accurately, despite its simplicity.

    q 2004 Elsevier Ltd. All rights reserved.

    Keywords: Soil liquefaction; Nature of the earthquake; Pore pressure generation; Cyclic shear stress; Pore pressure dissipation; Liquefaction potential index

    1. Introduction

    When saturated sand deposits are subjected to earth-

    quake-induced shaking, pore water pressures are built-up

    leading to liquefaction or loss of soil strength. Major

    earthquakes that have occurred during past years, such as

    the 1964 Alaska, 1964 Niigata, 1989 LomaPrieta and the

    1995 HyogokenNambu have demonstrated the damaging

    effects of soil liquefaction. Therefore, it is necessary to

    obtain a proper understanding of the effect of parameters

    such as soil properties and the nature of the earthquake on

    the severity of the soil liquefaction.

    Most major earthquakes occur around the boundaries of

    the tectonic plates such as those that exist in California,

    USA. The Australian continent is in the middle of one of the

    worlds largest tectonic plates, and therefore, Australia is

    subjected to relatively low earthquake activity. However,

    the 1989 Newcastle earthquake, which caused 13 deaths,

    increased the awareness of the need to properly assess the

    possible consequences of earthquakes in areas subjected to

    intraplate events.

    Although Australian earthquakes can have acceleration

    levels as high as those in Californian earthquakes, evidence

    of liquefaction has not been reported. The major difference

    between Californian and Australian earthquakes is that, in

    Australian earthquakes, the predominant frequency is high

    and any large acceleration levels last for a very brief

    duration, while in Californian earthquakes, the predominant

    frequency is lower and high acceleration levels exist during a

    significant proportion of the longer duration of the earth-

    quake. Hence this gives a clear indication about the

    significance of the nature of the earthquake on the

    liquefaction.

    Although ground response analyses based on the finite

    element method provide a better assessment of liquefaction

    of a soil deposit by taking into account the nature of the

    earthquake and the pore pressure dissipation [13,16,17,21,

    27,29,30,40,42], they are often costly and time-consuming.

    In addition, constitutive models used in those programs

    need large number of parameters to determine the pore

    pressure generation in soil due to earthquake loading.

    Therefore, simplified methods in assessing soil liquefaction

    are popular among practicing engineers. These procedures

    are very useful at the preliminary design stages to assess

    0267-7261/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.soildyn.2003.11.010

    Soil Dynamics and Earthquake Engineering 24 (2004) 867875

    www.elsevier.com/locate/soildyn

    * Corresponding author.

    E-mail address: [email protected] (D.S. Liyanapathirana).

    http://www.elsevier.com/locate/soildyn
  • the liquefaction risk. If the liquefaction risk is high, then a

    detailed finite element analysis can be carried out to obtain

    the pore pressure distribution and ground displacement

    along the depth of the soil deposit, which is necessary in

    subsequent design of deep foundations.

    In simplified methods, the earthquake loading parameter

    is generally represented either by the cyclic shear stress

    generated due to the earthquake or by the amount of

    energy released due to the earthquake. The presently

    available simplified methods can be divided into three

    main categories: (1) methods based on the cyclic shear

    stress generated in the soil, (2) energy based methods and

    (3) probabilistic methods.

    In the cyclic shear stress approach, the cyclic stress ratio

    (CSR) generated at any depth of the soil deposit due to the

    earthquake loading can be obtained using the simplified

    equations [19,33,37,48] and CSR depends on the maximum

    acceleration at the ground surface. If CSR exceeds the

    cyclic resistance ratio (CRR) at any depth of the soil deposit,

    soil liquefaction occurs at that depth.

    Over the past 25 years, numerous studies have been

    carried out to correlate the CRR to the standard penetration

    test (SPT) data [34,37,38,41], cone penetration test (CPT)

    data [31,33,35,43], electrical probe measurements [3] and

    shear wave velocity measurements [1,8,9,20,32,38,44,46].

    In energy based methods, pore water pressure increment is

    related to the energy dissipated during the earthquake loading

    [5,7,12,23,24,28,45,47]. In contrast, energy based methods

    proposed by Egan and Rosidi [10] and Kayan and Mitchell

    [22] used the Arias intensity [2] to represent the energy

    content of the earthquake. Based on case studies of field

    behaviour during earthquakes, Arias intensity at any depth

    below the ground surface is associated with the liquefaction

    resistance at that depth, as measured by the SPT or CPT.

    Although probabilistic methods [6,11,14,20,25] have

    been developed to obtain the probability of occurrence of

    liquefaction as a function of earthquake load and soil

    parameters, the usefulness of these methods depends on the

    soundness of the assumed mechanistic models and on the

    feasibility of quantifying uncertainty of model parameters.

    Therefore, these methods are not very popular among

    practicing geotechnical engineers.

    Although a large number of simplified methods in

    assessing soil liquefaction are available, the cyclic shear

    stress method is the standard practice in most parts of the

    world. However, this method does not take into account the

    effect of the nature of the earthquake on the degree of soil

    liquefaction. The degree of liquefaction is assessed based on

    the maximum shear stress generated at any depth below the

    ground surface, which is calculated based on the maximum

    acceleration of the earthquake at the ground surface.

    This paper investigates the significance of the nature of

    the earthquake on the liquefaction potential of a soil deposit,

    and a simplified procedure is outlined to incorporate the

    nature of the earthquake into the assessment of liquefaction

    potential of a soil deposit.

    2. Liquefaction potential

    Here the liquefaction potential is assessed using the

    liquefaction potential index IL defined by Iwasaki et al. [18])

    based on the cyclic stress method proposed by Seed and

    Idris [37]. This term gives an indication of the degree of

    severity of an earthquake. Although, the factor of safety

    against liquefaction is a widely used term in assessing the

    degree of liquefaction, it gives an indication about the

    liquefaction potential only at a particular depth. When

    comparing liquefaction potential of different soil deposits,

    the factor of safety at various depths within the deposit

    should be compared, and this can be facilitated by using IL;

    as it is the integrated value of several factor of safety values

    along the soil deposit as shown below

    IL 20

    0FWzdz 1

    where F 1 2 FL for FL # 1:0 and F 0 for FL .1:0:Wz 10 2 0:5z and z is the depth in meters.

    FL is the factor of safety against liquefaction and

    defined as

    FL CRR

    CSR2

    where CRR is the in situ cyclic undrained shear strength of

    the soil mobilised for the equivalent number of stress cycles

    developed due to the earthquake, and CSR is the average

    shear stress level developed in the ground due to earthquake

    loading at the depth under consideration. According to the

    simplified method, the average shear stress developed at a

    depth z below the ground surface is given by

    CSR 0:65 amaxg

    rdgsz 3

    where gs is the unit weight of soil, amax is the peakhorizontal acceleration at the ground surface, rd is the stress

    reduction coefficient, z is the depth below ground surface in

    meters and g is the acceleration due to gravity. The

    coefficient rd is less than unity and Seed and Idriss [37],

    Iwasaki et al. [19] Liao and Whitman [48], T.F. Blake [48],

    and I.M. Idriss [1] have suggested values for rd:

    By analysing liquefied and non-liquefied sites during

    earthquakes Iwasaki et al. [18] proposed a simplified

    classification system as shown in Table 1, to assess soil

    liquefaction at a particular site based on the liquefaction

    potential index given by Eq. (1).

    Table 1

    Liquefaction risk assessment [18]

    Liquefaction risk

    IL 0 Very low0 , IL # 5 Low

    5 , IL # 15 High

    15 , IL Very high

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875868

  • 3. Ground response analysis

    When using the simplified method of calculating shear

    stresses induced in ground due to earthquake loading, CSR

    at any depth below the ground surface is calculated based on

    the maximum ground acceleration, neglecting the nature of

    the earthquake. In this present study, CSR is calculated

    using a one-dimensional finite element model based on the

    effective stress approach, which effectively captures the

    nature of the earthquake.

    The equations of the motion are integrated directly using

    the constant average acceleration method [4]. Soil beha-

    viour has been modeled using a hyperbolic stressstrain

    relationship, which reflects hysteretic behaviour of sands. In

    addition to the hysteretic damping, viscous damping is

    also included. According to Seed and Idriss [36], viscous

    damping should be on the order of 20% of the critical

    damping under the amplitude of motions likely to develop

    during earthquakes. This term takes into account the energy

    dissipation due to visco-elastic properties of the soil. Here,

    critical damping is calculated based on the initial maximum

    values of shear modulus G0 and shear strength t0 of the soil,and is kept constant throughout the analysis.

    The initial maximum values for shear modulus G0 and

    shear strength t0 of the soil are estimated using therelationships given by Hardin and Drnevich [15] as shown

    below

    G0 14:762:973 2 e2

    1 e

    ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi47 900

    1 2K03

    s0v0

    skPa

    4

    t0 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

    1 K02

    sinf0 2

    21 2 K0

    2

    2ss0v0 kPa 5

    where e is the void ratio of the soil, K0 is the coefficient of

    earth pressure at rest, f0 is the effective angle of shearingresistance and s0v0 is the initial effective overburden pressurein kPa.

    With the generation of pore water pressure due to an

    earthquake, the effective vertical stress of the soil is reduced

    during and after the seismic event. Consequently, the loss of

    soil strength and stiffness can be incorporated into the

    analysis through substituting the current value of effective

    stress in Eqs. (4) and (5).

    Generation of pore water pressure during earth-

    quake shaking has been calculated using the equivalent

    cycle method proposed by Seed et al. [40] and Martin

    and Seed [26]. Pore pressure dissipation due to consolida-

    tion of the soil has also been incorporated into the analysis.

    The earthquake motion induces periods of high stress

    intensity followed by periods of little activity. Therefore,

    the number of equivalent cycles of the earthquake, Neq [39],

    is calculated by dividing the total duration of the earthquake

    into number of periods for which, the rate of application of

    stress cycles are calculated separately.

    4. Calculation of liquefaction potential index

    The steps involved in computing the liquefaction

    potential index of a soil deposit can be summarised as

    follows:

    1. Using the finite element model stresses developed in the

    soil, and hence Ss at each depth, which is 65% of

    maximum shear stress, can be computed.

    2. Before calculating IL in Eq. (1), FL within the first 20 m

    of the soil deposit should be calculated. Now Ss is known.

    Since Neq is known, R in Eq. (2) can be obtained from the

    cyclic liquefaction strength curve of the particular soil

    considered.

    3. Once FL is known, F can be obtained based on the value

    of FL as described in Section 2. By integrating FWzalong the upper 20 m of the soil deposit, the liquefaction

    potential index, IL; of the soil deposit can be obtained

    from Eq. (1).

    5. Effect of nature of the earthquake on liquefaction

    potential

    To study the effect of the nature of the earthquake on the

    liquefaction potential, acceleration records of 15 earthquakes

    scaled to different acceleration levels of 0.1, 0.15, and 0.2 g,

    that have occurred during the past 60 years in different parts

    of the world have been analysed. Here, a parameter, the

    pseudo-velocity V ; is introduced, which takes into account

    the nature of the earthquake, where V is given by

    V td

    0laccl dt 6

    where td is the duration of the earthquake and acc is the

    acceleration at time t:

    Table 2 summarises the V values obtained for earth-

    quakes used for this study, scaled to a maximum accelera-

    tion of 0.1g. All Australian earthquakes have lower V values

    compared to inter-plate earthquakes such as San Fernando,

    Northridge, Taft, Pasadena and El-Centro. According to the

    V values recorded in Table 3, all Australian earthquakes

    except the two Newcastle earthquakes, scaled to 0.1g, have

    values of V less than 0.7.

    Table 2

    Values of parameters used for the analysis

    Input parameters

    Density rS 1900 kg/m3Coefficient of earth pressure at rest K0 0.6Poissons ratio e 0.6Pore pressure parameter a 1.3Friction angle f0 408Relative density (Dr %) 55

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875 869

  • The liquefaction potential index IL has been computed

    for the soil deposit with properties as given in Table 3, when

    subjected to the earthquakes listed in Table 2, scaled to

    acceleration levels 0.1, 0.15 and 0.2g. Pore pressure

    dissipation is found to be significant only for clean sands

    and sand mixed with gravels with permeability greater than

    1024 m/s. Therefore, the soil is assumed to be undrained. G0and t0 are modelled using Eqs. (4) and (5). Pore pressuregeneration is calculated based on the liquefaction strength

    curves given by Seed et al. [40].

    Pseudo velocity is a parameter, which varies along

    the depth of soil deposit for a particular earthquake.

    Therefore, when relating IL with V ; a reference depth

    should be selected. Here, 15 m below the ground surface has

    been taken as the reference depth and V at 15 m depth is

    referred as Vref :

    Fig. 1 shows the variation in IL with Vref ; when relative

    density is 55%. It can be seen that although all earthquake

    records are scaled to the same acceleration level, the

    calculated liquefaction potential index increases with

    increasing Vref : Therefore, it can be concluded that the

    nature of the earthquake has a significant influence on the

    liquefaction potential and it is not the maximum acceleration

    level at the ground surface that controls the soil liquefaction.

    According to Fig. 1, there is a critical value for Vref ;

    beyond which, IL starts to increase with Vref : If the

    variation in maximum excess pore pressure generated in

    the soil deposit is studied, it can be seen that beyond the

    critical Vref ; the maximum pore pressure ratio is 1.0, and

    when Vref is less than the critical Vref ; the maximum pore

    pressure ratio generated in the deposit has a linear variation

    with Vref : This is illustrated in Fig. 2 for the sand at relative

    density of 55%.

    If the analysis is repeated for several relative densities,

    it can be seen that each relative density has a different

    critical Vref : Fig. 3 shows the IL corresponding to different

    Vref ; when Dr varies from 45 to 90%. A chart such as this is

    very useful in assessing IL for a soil deposit if the

    acceleration record at z 15 m and relative density of thesoil are known.

    According to Figs. 1 and 2, it is clear that the liquefaction

    potential is very low when Vref is relatively low. Australian

    earthquakes have relatively low Vref values, and conse-

    quently, it can be concluded that the risk of liquefaction of

    sand deposits in Australia may be significantly lower than

    the same deposit in the USA, Japan and other areas

    subjected to inter-plate seismic events.

    For many earthquakes, acceleration records are available

    at the ground surface. Therefore, to relate the Vref to Vsurfaceat the ground surface, the ratio of Vz=Vsurface; along the depth

    for a 30 m soil deposit are given in Fig. 4, for the earthquake

    records given in Table 2. The average line given for

    Vz=Vsurface can be used to relate Vsurface to V at any depth

    below the ground surface. The analysis is repeated by

    varying the profile of shear modulus along depth, density of

    the soil and the relative density of the soil. It can be seen that

    the distribution of Vz=Vsurface with depth does not change

    significantly with those parameters.

    Fig. 1. Variation in liquefaction potential index with Vref :

    Table 3

    V values for the earthquakes used for the study

    Name of earthquake V (max. acc. 0.1g)

    New Zealand-1973 2.36

    New Zealand-1991 1.07

    San Fernando 3.05

    Northridge 2.89

    Oolong 0.44

    Taft 3.95

    Gunjung 1.53

    Tenant Creek 0.32

    Meckering 0.66

    Cadoux 0.19

    Newcastle-1989 2.29

    Newcastle-1994 2.13

    Pasadena 7.33

    Melendy Ranche 0.51

    El-Centro 4.11

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875870

  • 5.1. Maximum pore pressure ratio based on ILfor non-liquefying soil

    Fig. 5 shows the variation in IL with maximum pore

    pressure ratio, rp; generated in the soil deposit for several

    relative densities. It can be seen that there is a reasonably

    unique relationship between IL and the maximum pore

    pressure ratio, irrespective of the relative density of the soil.

    This chart shows three regions. If rp , 0:65; IL is zero andhence the liquefaction risk is very low. If rp 1:0; IL . 5and the liquefaction risk is high. If 0:65 # rp , 1:0; 0 ,IL # 5 and the liquefaction risk is low. In this region, IL andrp are linearly related as follows:

    IL 14rp 2 9 0:65 # rp , 1:0 7

    Fig. 2. Variation in max. pore pressure developed in the deposit with Vref :

    Fig. 3. Variation in liqueaction potential with critical Vref : and relative density (Dr%).

    Fig. 4. Variation of V along depth/V at the ground surface.

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875 871

  • When the liquefaction risk is low, the above equation can

    be used to estimate the maximum pore pressure ratio

    generated in the soil deposit. Charts like this are very useful

    for preliminary design when there is a lack of detailed site

    information.

    5.2. Depth of liquefied zone based on IL

    Fig. 6 shows the variation of depth of liquefied region/

    depth of soil deposit HL=H for different IL: These resultswere obtained using the earthquake records given in Table 2

    and by varying the relative density of the soil from 45 to 90%.

    It can be seen that irrespective of the relative density, HL=H

    has a reasonably unique relationship with IL: According to

    Fig. 6, with the increase in IL; HL=H increases. There is

    a rapid increase in liquefied depth when the 5 , IL , 15:When IL reaches 15, according to Table 1, the liquefaction

    risk is very high and the depth of liquefied region is about

    45% of the total depth of the soil deposit.

    6. Summary of practical procedure

    The proposed practical procedure for assessing the

    liquefaction potential of a soil deposit can be summarized

    as follows:

    1. First calculate Vsurface for the soil deposit Eq. (3), based

    on the acceleration record at the ground level.

    2. According to Fig. 4, on average, Vref < 0:5 Vsurface at15 m.

    Fig. 5. Variation of IL with maximum pore pressure rario, rp:

    Fig. 6. Variation of depth of liquefaied zone with the IL:

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875872

  • 3. Based on the relative density of the soil and the Vref ; ILfor the deposit can be obtained from Fig. 3.

    4. If IL is less than 5, soil liquefaction risk is low or very

    low. If required, the maximum pore pressure generated in

    the soil deposit can be assessed using Fig. 5.

    5. If IL is greater than 5, soil liquefaction risk is assumed to

    be high and it may be necessary to develop mitigation

    measures.

    7. Application of the method to case histories

    The method presented in the paper has been applied to 23

    liquefied and non-liquefied sites due to 1964 Niigata, 1971

    San Fernando, 1976 Tangshan, 1978 Miyagi-Oki, 1979

    Imperial Valley, 1981 Westmoreland, 1987 Elmore Ranch,

    1987 Superstition Hills and 1989 Loma Prieta earthquakes

    as shown in Table 4. The SPT values for these sites have

    been obtained from the data given by Berrill and Davis [5]

    and Egan and Rosidi [10].

    The approximate values of relative densities for these

    sites were calculated based on the SPT data. For these

    earthquakes, acceleration records are available at the

    surface level and thus, to relate the Vref at 15 m below the

    surface to Vsurface; Fig. 4 has been used.

    According to Fig. 5, when IL is 5, the maximum pore

    pressure ratio in the soil deposit becomes one. That means

    the boundary between the liquefied and non-liquefied sites

    should be represented by the IL 5 line shown in Fig. 3.Fig. 7 shows the Vref vs. Dr for the data given in Table 4.

    Also the IL 5 line given in Fig. 3 is plotted. It can be seenthat this line quite satisfactorily separates the liquefied and

    non-liquefied sites.

    Table 4

    Summary of earthquake characteristics

    Earthquake Site PGA (g) SPT Dr % Vz0 Vz15m Liquefaction? Reference

    Loma Prieta 1989 Mission Pointe (Sunnyvale) 0.22 16 63 4.04 1.5 No [10]

    Port of Oakland (Fill) 0.29 12 54 7.0 2.7 Yes [10]

    Port of Oakland (Native A) 0.29 14 58 7.0 2.7 Yes [10]

    Port of Oakland (Native B) 0.29 30 80 7.0 2.7 Yes [10]

    Coyote Creek (Milpitas) 0.17 10 50 5.3 1.8 No [10]

    Coyote Creek (Agnew) 0.14 10 50 4.9 1.6 No [10]

    Treasure Island 0.16 6 37 5.44 1.9 Yes [10]

    Superstition Hills 1987 Imperial Wildlife (surface) 0.21 8 43 7.96 3.25 Yes [10]

    Imperial Valley 1979 McKim Ranch (El Centro #4) 0.49 10 50 6.02 2.25 Yes [10]

    McKim Ranch (El Centro #4) 0.49 21 70 6.02 2.25 No [10]

    Radio Tower (Brawley) 0.22 7 40 4.9 1.7 Yes [10]

    Radio Tower (Brawley) 0.22 14 58 4.9 1.7 No [10]

    River Park 0.17 4.7 34 8.23 3.5 Yes [5]

    River Park 0.17 8.8 47 8.23 3.5 Yes [5]

    San Fernando 1971 Juvenile Hall 0.26 2.1 16 5.09 1.7 Yes [5]

    Westmoreland 1981 Radio Tower (Brawley) 0.16 7.0 40 2.75 1.3 Yes [10]

    Radio Tower (Brawley) 0.16 14.0 58 2.75 1.3 No [10]

    Elmore Ranch 1987 Imperial Wildlife (surface) 0.13 8.0 43 3.71 1.5 No [10]

    Miyagi-Oki 1978 Ishinomaki 0.32 5.5 35 13.83 6.5 Yes [10]

    Niigata 1964 Niigata 0.13 6.9 40 6.0 2.3 Yes [10]

    Niigata 0.13 13.8 58 6.0 2.3 No [10]

    Tangshan 1976 Weigezhuang 0.14 15.2 60 10.0 4.5 Yes [5]

    Lujiatuo 0.14 4.4 33 10.0 4.5 Yes [5]

    Fig. 7. Validation of the method using case history data.

    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875 873

  • 8. Conclusions

    A simple method is presented for the preliminary

    assessment of liquefaction potential incorporating the

    effects of pore pressure dissipation and the nature of the

    earthquake. The pseudo-velocity Vref ; which is the gross

    area under the input acceleration record at 15 m below the

    ground surface, is introduced to represent the nature of the

    earthquake. By analysing 15 earthquake records at different

    maximum acceleration levels, it has been shown that

    although the maximum acceleration levels of the earth-

    quakes are the same, the liquefaction risk is low when Vref is

    relatively low.

    Using data collected at liquefied and non-liquefied sites

    during past earthquakes, it has been shown that the IL 5line plotted in the Vref vs. Dr space separates the liquefied

    and non-liquefied sites. This indicates that the pseudo

    velocity can be a useful and reliable measure of earthquake

    severity in the field.

    Acknowledgements

    This work is part of a project on Pile Design for

    Seismically Active Areas funded by the Australian

    Research Council, and it has been carried out within the

    Centre for Geotechnical Research, The University of

    Sydney. This support is gratefully acknowledged.

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    D.S. Liyanapathirana, H.G. Poulos / Soil Dynamics and Earthquake Engineering 24 (2004) 867875 875

    Assessment of soil liquefaction incorporating earthquake characteristicsIntroductionLiquefaction potentialGround response analysisCalculation of liquefaction potential indexEffect of nature of the earthquake on liquefaction potentialMaximum pore pressure ratio based on &f;I&m.inf;&rm;L&/rm;&/m.inf;&/f; &?show $262#;for non&hyphen;liquefying soilDepth of liquefied zone based on &f;I&m.inf;&rm;L&/rm;&/m.inf;&/f;Summary of practical procedureApplication of the method to case historiesConclusionsAcknowledgementsReferences