PRACTICAL DETERMINATION METHOD FOR SOIL PARAMETERS …

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i) Leader, Soil Mechanics and Geo-environment Research Group, Port and Airport Research Institute, Japan (watabe＠ipc.pari.go.jp).ii) Senior Researcher, Soil Mechanics and Geo-environment Research Group, Port and Airport Research Institute, Japan.iii) Director, Geotechnical and Structural Engineering Division, Port and Airport Research Institute, Japan.

The manuscript for this paper was received for review on January 10, 2008; approved on May 28, 2008.Written discussions on this paper should be submitted before July 1, 2010 to the Japanese Geotechnical Society, 4-38-2, Sengoku, Bunkyo-ku,Tokyo 112-0011, Japan. Upon request the closing date may be extended one month.

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SOILS AND FOUNDATIONS Vol. 49, No. 6, 827–839, Dec. 2009Japanese Geotechnical Society

PRACTICAL DETERMINATION METHOD FOR SOILPARAMETERS ADOPTED IN THE NEW PERFORMANCEBASED DESIGN CODE FOR PORT FACILITIES IN JAPAN

YOICHI WATABEi), MASANORI TANAKAii) and YOSHIAKI KIKUCHIiii)

ABSTRACT

The Japanese design code for port facilities was revised in April 2007, and a performance-based reliability designmethod was introduced. This report introduces a new practical method, which has been adopted in the annex of the de-sign code, to evaluate soil parameters. The new method uses a correction factor corresponding to the coe‹cient of datavariation. In this method, the characteristic value automatically re‰ects the variation of the derived values in associa-tion with the testing method and the reliability of the data interpretation. Compared to the lower limit of 95z conˆ-dence interval, which is widely adopted in general design codes such as Eurocode 7 and JGS4001, the characteristicvalue determined by this method is conservative when the number of data entries is larger than 10. This tendency iscaused by the concept, in which characteristic values always re‰ect the data variation, even though the number of dataentries are signiˆcantly large. Generally, data variation in the depth proˆle can be reduced when the depth distributionis appropriately modeled. Also, data variation can be reduced by adopting a more reliable soil test. Accordingly, anyeŠorts to reduce the variation are awarded in this new design code.

Key words: characteristic value, design code, performance based design, soil parameters (IGC: H7)

INTRODUCTION

This report introduces a new practical method, whichhas been adopted in the design code for port facilities inJapan (The Japan Port and Harbour Association, 2007),to evaluate soil parameters. The determination methoddescribed in the new design code for port facilities inJapan is called ``new port-design code'' hereafter. Theperformance-based reliability design method is expectedto be widely adopted in design codes for various facilities.Determination methods for soil parameters for reliabilitydesign method are introduced in Eurocode 7 (EN 1997–1,2004) and JGS4001 (JGS, 2004). The determinationmethod in these general-design codes is called ``generaldesign code'' hereafter.

In Japan, soil parameters for performance-based relia-bility design should be determined according to JGS4001:Principles for foundation design grounded on perfor-mance-based design concept. The characteristic value( see Fig. 1) is generally the expected value of the derivedparameters; however, it is not merely an average. Thevalue should be considered as the statistical estimation er-ror. In JGS4001, the characteristic value correspondingto a certain conˆdence level is determined followingeither the normal distribution when the standard devia-

tion of the population is known or the t-distributionwhen that is unknown. The soil parameters of the groundand the quality parameters of the industrial products aretotally diŠerent in their treatments. The statistical treat-ment as mentioned above is strongly required in consider-ation of the non-uniform sedimentary structure, the in-vestigation errors, the testing errors, the limited numberof data entries, etc. In the new port-design code, a simpli-êd and reasonable method, which pursues the practicalusability by simplifying the statistical treatment, to deter-mine the soil characteristic values was introduced.

It is well known that the undrained shear strength ob-tained by the unconˆned compression test is more varia-ble than that done by the triaxial tests, indicating that thereliability of the former is much smaller than that of thelatter (Tsuchida, 2000; Watabe and Tsuchida, 2001b). Ineach design procedure, however, it is di‹cult to take ac-count of the data variation depending on the testingmethods. Consequently, the method in the new port-de-sign code adopted the concept, in which the characteristicvalue is corrected corresponding to the reliability of thetesting method. This concept aims to use the partial safe-ty factor, which is independent of the testing methods.Therefore, the concept in the case of large number ofdata entries is a little bit diŠerent from that of the gener-

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Fig. 1. Flowchart in determination for soil parameters in design codefor port facilities in Japan

828 WATABE ET AL.

al-design code, in which the characteristic value is gener-ally to be the expected value of the derived values. Thisfact will be discussed later.

The applicability of the introduced method is studiedusing data set of unconˆned compression tests and in-cremental loading oedometer tests for samples retrievedfrom Kobe Port. The applicability of parameters inter-related between shear and consolidation is also studied.In addition, the new port-design code is applied to boththe unconˆned compression test results and recompres-sion triaxial test results in order to evaluate the undrainedshear strengths of the Osaka Bay clay to emphasize thatthe latter test has many advantages in design over theformer test.

PRINCIPLE OF THE SOIL PARAMETERDETERMINATION

In Japan, the design values of the soil parameters forthe performance veriˆcation are determined followingJGS4001 as shown in Fig. 1. This ‰owchart is modiêdfor the new port-design code, but re‰ecting the purportof JGS4001.

The measured value is the value directly recorded in theêld test or the laboratory test. The derived value is thevalue obtained by using the relationship between themeasured value and the soil parameter.

The characteristic value is the representative one ob-tained by modeling the depth proˆle of the data takingaccount of the variation of the estimated values. Thevalue must correspond to the critical state for the perfor-mance considered in the design. Taking into account theapplication range of either the veriˆcation equation orprediction equation, the characteristic value is convertedinto the design value by multiplying an appropriate par-tial safety factor. The partial safety factors for each facil-ity are listed in the design code corresponding to both thevariation and sensitivity of the soil parameter in the de-sign veriˆcation.

The characteristic value in Eurocode 7 is also deˆnedfollowing the same concept of JGS4001. In a case for in-dustry products, the characteristic value is generally de-ˆned as 5z fractile corresponding to Eq. (1), e.g., inEurocode 0 (EN 1990, 2002).

xk＝m(x)－1.645 s(x) (1)

where, m(x) is the average of x, and s(x) is the standarddeviation of parameter x. This kind of characteristicvalue is applicable for structural materials; however, it isnot applicable for soil parameters because they are sig-niˆcantly variable. If we consider ground failure, for ex-ample, we have to treat the whole ground failure, not thefailure in each element. From this background, Eurocode7 adopted the value corresponding to the 95z conˆdencelevel instead of the 5z fractile (Orr, 2006). In JGS4001,the characteristic value is described in the same manner asEurocode 7, but the conˆdence level is not ˆxed to 95z.

Ovesen (1995) proposed a simple equation expressed asEq. (2) to obtain the lower limit of 95z conˆdence level.

xk＝m(x)－1.645 s(x)/ n (2)

where n is the number of data entries. Schneider (1997)proposed a more simpliêd equation for n＝11.

xk＝m(x)－0.5 s(x) (3)

When n is larger than 12, Schneider's equation gives amore conservative value than Ovesen's equation.

The new port-design code adopted a more practicalmethod to determine the characteristic value. This techni-cal report introduces the method, which uses the outlineof both Schneider's and Ovesen's equations and is partlyconsistent with the general-design code.

Because geotechnical investigation and facility designare usually done by diŠerent engineers, the facility desig-ner cannot determine an appropriate partial safety factoraccording to the data variation of the soil parameters inassociation with the investigation and testing methods. Inaddition, it is virtually impossible to determine each par-tial safety factor taking account of the data variation der-ived from the heterogeneity of the ground itself re‰ectingthe soil locality. Therefore, it is ideal that the reliability ofthe soil parameter is guaranteed always in the same levelwhen the geotechnical information is transmitted fromthe geotechnical engineer to the facility designer. Conse-quently, the partial safety factor as a general value listedin the design code can be used. Note here that the methodin the new port-design code is generally applicable for soilparameters used in not only the stability veriˆcation butalso the consolidation prediction, etc.

CHARACTERISTIC VALUE DETERMINATIONWITH CORRECTION FACTORS

Modeling of the Depth ProˆleA su‹cient number of test results are required in order

to statistically determine the characteristic value. For thesoil parameter a, the estimated soil parameter a* is mo-deled such as uniform depth proˆle (a*＝c1); linear depthproˆle (a*＝c1z＋c2), etc, where z is the depth, and c1 andc2 are constants. The estimated value a* is the value onthe approximated depth proˆle of the soil parameter. Ex-amining carefully the depth proˆle is one of the notablefeatures of this method. In modeling the depth proˆle,

829829DETERMINATION SOIL PARAMETERS

larger number of data entries is more desirable; however,it is realistic to say that 10 data entries are su‹cient inpractice, because the number of data entries is generallyvery limited. In fact, the coe‹cient of variation (COV)converges on a certain value when the number of data en-tries is more than 10 in most cases for relativelyhomogeneous soil layers, which are often seen in coastalareas.

The variation of some soil parameters is reasonable toexamine on the logarithmic axis: e.g., consolidation yieldstress pc; coe‹cient of consolidation cv; coe‹cient ofvolume compressibility mv, etc. In dealing with theseparameters, it is ideal to model the depth proˆles on thelogarithmic axis. Note here that the depth is generally onthe arithmetic axis. In the case of normally consolidatedclay with slightly developed skeletal structure, however,the depth proˆle of the consolidation yield stress pc is ex-pressed as a linear function with depth, characterized by aconstant OCR and a constant eŠective unit weight g?. Forthis kind of deposits, if the depth proˆle is modeled onthe logarithmic axis, the model proˆle on the arithmeticaxis often becomes far from the derived values. There-fore, it must be examined carefully by modeling the depthproˆle in consideration of the property of the soilparameter.

Concept of the Characteristic ValueThe basic concept of this method to determine the

characteristic value from the derived value is brie‰y de-scribed below. Because the derived value is in‰uenced bysampling method, laboratory testing method, soundingmethod, empirical/theoretical equation, etc., the designvalues must be re‰ected by these in‰uences. For example,it has been well known that the reliability of the un-drained shear strength obtained by the unconˆned com-pression test is much lower than that obtained by therecompression triaxial test; however, it is very di‹cult totake account of this fact in design.

The method in the new port-design code adopted theconcept, in which the characteristic value is corrected ac-cording to the reliability level of the testing method. TheCOV is introduced to represent the data variation. Tore‰ect the data reliability to the characteristic value, theestimated value is to be corrected according to COV.Consequently, we can establish the design code with thecommon partial safety factor by using the characteristicvalue determined by this method, even if the derivedvalue of the soil parameter has been obtained from diŠer-ent soil test. In the general-design code, because the conˆ-dence interval becomes of narrow range with the numberof data entries, the characteristic value is coincident withthe mean value when the number of data entries becomeslarge. In the new port-design code, because the character-istic value is determined according to the data variation,eŠorts to reduce the data variation are awarded in the de-sign.

In the reliability based design, partial safety factor g isdetermined from the empirical calibration consideringthe data variation. Because the data variation is a given

condition in most cases, any eŠort, e.g., examining to ob-tain the most appropriate depth proˆle, adopting a relia-ble laboratory testing method, brushing up the skills forsite investigation and laboratory testing, to decrease thedata variation are not awarded. Consequently, we preferto use conventional investigation method. The new port-design code aims to solve these kind of issues.

Correction FactorIn order to evaluate the variation of the derived values

a, it is convenient to use the standard deviation (SD) ofa/a*, where a* is the estimated parameter obtained bymodeling the depth proˆle of the derived values. Notehere that the depth proˆle of a* must be estimated aseither the expected constant value or the regression func-tion to minimize the errors. This is the major premisebased on Fig. 1, in which the characteristic value is gener-ally deˆned as the expected value of the derived values.The SD of a/a* is equivalent to the COV of a.

It has been known that the COV of the derived valuesobtained by well skilled technicians is less than 0.1 for atypical Japanese marine clay (Watabe et al., 2007). Inother words, the variation in this level is inevitable be-cause of the ground heterogeneity and the laboratorytesting errors. Ground heterogeneity, sample distur-bance, inappropriate soil tests, inappropriate modelingof the depth proˆle, and so on, result in a large COVvalue. In such cases, it is reasonable to conservatively de-termine the characteristic value taking account of the un-certainties.

In order to calculate the characteristic value ak from theestimated value a*, correction factor b1 is introduced as afunction of the COV, then ak is deˆned as Eq. (4).

ak＝b1×a* (4)

When the soil parameter a contributes to either theresistance moment in the safety veriˆcation (e.g., theshear strength in the stability analysis) or the safety mar-gin in the prediction (e.g., the consolidation yield stresspc; the coe‹cient of consolidation cv in the consolidationcalculation), the correction factor is deˆned as Eq. (5).

b1＝1－(COV/2) (5)

On the other hand, when it contributes to either the slid-ing moment in the safety veriˆcation (e.g., the unitweight of the earth ˆll in the stability analysis) or the un-safe factor in the prediction (the compression index Cc;coe‹cient of volumetric compression mv in the consolida-tion calculation), the correction factor is deˆned as Eq.(6).

b1＝1＋ (COV/2) (6)

In these deˆnitions, the characteristic values correspondto either 30z or 70z fractile value. Because the simpliˆ-cation is aimed in this method, the values listed in Table 1are to be used instead of the correction factors with de-tailed fractions. When the COV is larger than 0.6, it isjudged that the reliability of the soil parameter is too lowfor the design. In this case, the test results are reexam-

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Table 1. Value of correction factor b1

Coe‹cient ofvariation

COV

Correction factor b1

Parameter for safe side Parameter for unsafe side

COVº0.1 1.00 1.00

0.1ÃCOVº0.15 0.95 1.05

0.15ÃCOVº0.25 0.90 1.10

0.25ÃCOVº0.4 0.85 1.15

0.4ÃCOVº0.6 0.75 1.25

0.6ÃCOV Reexamination of the data/Reexecution of the soil test

Table 2. List of the determination methods of the characteristic value of soil parameters

Design code Determination method for the characteristic value of soil parameters

Design code forPort facilities in Japan

Correction factors:b1＝1±COV/2 (corresponding to a fractile value of 30z)b2＝1±0.5/n (n is the number of data entry)A case of COV＝0.1 and n＝10 is equivalent to 95z conˆdence

Generaldesign code

JGS4001 A certain conˆdence level. (e.g., 99z, 95z, 90z, 75z, etc.)

Eurocode 7 A conˆdence level of 95z

830 WATABE ET AL.

ined; i.e., the depth proˆle is remodeled if necessary. Insome cases, the ground investigation may be performedagain.

In the general-design code, the characteristic value isdeˆned as the upper/lower boundary of a certain conˆ-dence level (95z in most cases) as abovementioned. Thenew port-design code using the simpliêd method withoutreal statistic treatment is partly consistent with the gener-al-design code. The characteristic value is deˆned as 30zor 70z fractile values which correspond to 95z conˆ-dence level when the number of data entries n is 10 andthe data variation COV is 0.1.

As mentioned above, some soil parameters, such as pc;cv; mv are examined on the logarithmic axis. It is, thus,reasonable to study the data variation with thelogarithmic normal distribution. For the soil parametera, the SD of (log a)/(log a*) is the COV of log a. Usingthis relationship, the values listed in Table 1 can be usedas the correction factor b?1 on the logarithmic axis. In thiscase, since Eq. (7) is obtained from Eq. (8), the correctionfactor b?1 corresponds to the exponent on the arithmeticscale.

ak＝a*b?1 (7)

log ak＝b?1 log a*＝log a*b?1 (8)

In addition, in the case dealing with the shear resistanceangle q, the data variation is not examined as q itself butdone as tan q. However, when shear resistance angle qhas been estimated from SPT-N value by using the equa-tion shown in the design standard (e.g., OCDI, 2002),since the q value has already tuned through empiricalbackground, it is not necessary to introduce the correc-

tion factor (Tanaka, 2003; Fukui et al., 2002).If the number of data entries is not su‹cient for statis-

tic treatment, another correction factor b2 is introducedto correct b1. Then, the characteristic value is expressedas Eq. (9).

ak＝b1×b2×a* (9)

About 10 or more data entries in the depth proˆle can bethought to be su‹cient to reliably calculate COV. In thecase with less than 10 data entries, when the soilparameter contributes to either resistance moment in thestability veriˆcation or safety margin in the prediction,the correction factor is deˆned as Eq. (10).

b2＝1－(0.5/n) (10)

On the other hand, when it contributes to either the slid-ing moment in the stability veriˆcation or unsafe factor inthe prediction, the correction factor is deˆned as Eq.(11).

b2＝1＋(0.5/n) (11)

Here, b2 for the case with only one data entry is set to 0.5or 1.5, respectively, and the reliability is assumed to rap-idly increase with the number of data entries. In thisregard, however, the correction factor b1 cannot be ob-tained in the case of n＝1, because COV cannot be calcu-lated. This indicates that more than two data entries arerequired in this method. In the new port-design code, thecorrection factor b2 is introduced when the number ofdata entries is less than 10; however, the number can begiven in each design code.

Note here that b1＝1 and b2＝1 are used for soilparameters that contribute equivalently to both actionand counteraction.

The determination methods for the characteristic valuein the new design code for port facilities in Japan,JGS4001, and Eurocode 7 are listed in Table 2.

Relationship between Parameters of Consolidation andShear

To examine the bearing capacity or the slope stabilityon the soft clay ground, ``qu＝0 method (Nakase,1967)'', in which stability analysis is carried out with un-drained shear strength cu with zero shear resistance angle(qu＝0), is widely used. Here, the undrained shearstrength cu is obtained by one of the laboratory shear testssuch as unconˆned compression test, triaxial test, directshear test, and so on. On the other hand, the consolida-


tion settlement is predicted by the calculation using theconsolidation parameters obtained from one of thelaboratory consolidation tests. The undrained shearstrength and the consolidation parameters are indepen-dently obtained by each soil test; however, these correlatewith each other, because the undrained shear strength isstrongly in‰uenced by the consolidation pressure. There-fore, these parameters should be determined by takingaccount of this correlation.

The depth proˆles of these parameters have to be mo-deled in consideration of the correlation. For example,the characteristic values of the overburden eŠective stresss?v0, consolidation yield stress pc, undrained shearstrength cu, strength increase ratio m (＝cu/pc), and over-consolidation ratio OCR (＝pc/s?v0) have to be deter-mined in consideration of not only the COV of the esti-mated values following the new port-design code but alsothe relationship cu＝m×OCR×s?v0.

RELATIONSHIP BETWEEN THE NEWPORT-DESIGN CODE AND THE GENERALDESIGN CODE

In the general design code, characteristic value of soilparameters is deˆned as the lower or upper limit of a cer-tain level of conˆdence interval. As abovementioned, thelower and upper limits correspond to the soil parameterswhich contribute to safe and unsafe sides, respectively. Inmost cases, 95z conˆdence level is adopted. In this chap-ter, a relationship between the characteristic values deter-mined by the new design code for port facilities and 95zconˆdence level, respectively, is discussed. Soilparameters, which contribute to the safe side, such as un-drained shear strength, are described here.

In the general design codes, the lower limit of 95z con-ˆdence interval expressed as Eq. (12) is deˆned as thecharacteristic value by assuming t-distribution, becausethe standard deviation for the population is unknownwhen soil parameters are evaluated by geotechnical inves-tigation.

ak＝a*－ks×SD＝a*－t0.1;n－1

n×SD (12)

where a* is the mean value (the estimated value asabovementioned), SD is the standard deviation, and ks isthe coe‹cient in association with the conˆdence intervalfor the n data of the derived values. Also, the notationt0.1;n－1 is the inversion function of t-distribution for 95zconˆdence level with a degree of freedom n－1.

In modeling the depth proˆle, if the derived value a isnormalized by the estimated value ak, the standard devia-tion SD is equivalent to the coe‹cient of variation COV.Therefore, data variation on the depth proˆle can bestatistically evaluated by using the following equation:

ak

a*＝1－ks×

SDa*

＝1－t0.1;n－1

n×COV (13)

It is notable that the data variation is discussed bycoe‹cient of variation COV which expresses the normal-

ized distribution rather than standard deviation SD whichexpresses the absolute data variation in the new port-de-sign code. The characteristic values obtained by the newport-design code (Eq. (9)) and the 95z conˆdence level(Eq. (13)) are compared in Fig. 2(a). Here, the curves cor-responding to the number of data entries n of 2, 3, 5, 10,20, 50, and 100 are drawn. In the case of n＝10, the char-acteristic values obtained by both the equations agreedwell. In the cases of nÀ10, the characteristic values deter-mined by Eq. (9) tend to converge on a unique curve. Onthe other hand, in the cases of nº5, the characteristicvalue determined by Eq. (13) decreases signiˆcantly withCOV, indicating that the characteristic value is unrealisticwhen COV becomes a large value. Compared to the lowerlimit of 95z conˆdence level, which is widely adopted inthe general design codes such as Eurocode 7 andJGS4001, the characteristic value determined by the newport-design code is conservative when the number of dataentries is larger than 10, while it is challenging when n issmaller than 10. Because there are about 10 data entries inmost of practical geotechnical investigations, the charac-teristic value determined by the new port-design code isequivalent to that determined by the general-design codewith 95z conˆdence level.

In practice, at times the number of data entries is sig-niˆcantly limited to less than 5. In a case of complicatedstratiˆcation, in particular, the number of the data en-tries is signiˆcantly limited if depth proˆle of a very thinsoil layer is examined. In such case, it can be said fromFig. 2(a) that Eq. (13) is unrealistic rather than Eq. (9).On the other hand, in cases of signiˆcantly large numberof data entries, it is notable that the characteristic valuedetermined by the new port-design code is smaller thanthat done by the general-design code with 95z conˆdencelevel when COV is large. This indicates that the new port-design code leads to examine the most appropriate depthproˆle, even though there are a su‹cient number of dataentries. Also, the new port-design code leads to adopt amore reliable soil testing method which can reduce thedata variation, when the data variation is mainly causedby the testing method.

In the new port-design code, the correction factor b1

listed in Table 1 is used in place of Eqs. (5) and (6). In ad-dition, the correction factor b2 is multiplied by b1, whenthe number of data entries n is less than 10. Therefore,the characteristic values determined by the new port-de-sign code with correction factors b1 listed in Table 1 andb2 expressed by Eq. (10) for nº10 are drawn in Fig. 2(b).The characteristic value ak in a range of COVÃ0.1 andnÆ10 is coincident with the estimated value a*, i.e.,ak/a*＝1. In the case of n＝10, the characteristic valuesdetermined by both the two methods agreed well, and inthe cases of nº10, the diŠerence between the values de-termined by the two methods is not signiˆcant.

The method introduced in this report has been tunedfor the relatively homogeneous soil layers, which areoften seen in coastal areas in Japan. Therefore, applica-tion of this method to the other soils, particularly riverinesediments, which are generally signiˆcantly heterogene-

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Fig. 2. Relationship between the characteristic value normalized bythe estimated value ak/a*, coe‹cient of variation COV, and thenumber of data entries n: (a) the new-port design code with Eqs. (9)and (10) compared to the 95% conˆdence level and (b) the new-portdesign code with correction factors b1 listed in Table 1 and b2 ex-pressed by Eq. (10) for nº10 compared to the 95% conˆdence level

Fig. 3. Illustration of the role of correction factors b1 and b2

Fig. 4. Depth proˆles of liquid limit wL, plastic limit wp, and naturalwater content wn

832 WATABE ET AL.

ous, is very limited.The role of the correction factors b1 and b2 are illustrat-

ed in Fig. 3. Now, two types of data distributions areconsidered: one is a wide normal distribution A and the

other is a narrow normal distribution B. The 95z conˆ-dence interval is wide for A and narrow for B; however, itbecomes narrow with the number of data entries. There-fore, the characteristic value for A essentially coincideswith that for B, when the number of data entries is sig-niˆcantly large. This tendency is expressed by the correc-tion factor b2. On the other hand, in the new port-designcode, the characteristic value is determined as 30z (or70z) fractile value by the correction factor b1 accordingto the data variation, even when the number of data en-tries n is signiˆcantly large.

APPLICATION TO THE SOIL PARAMETERS

Geotechnical Investigation ResultsIn this chapter, applicability of the method adopted in

the new port-design code to determine the characteristicvalue of the soil parameters is studied. From the Geo-technical Database of Japanese Ports and Airports(Watabe and Tanaka, 2004), the data of Kobe Port inves-tigated in March, 1998 are picked up and examined. Atthe investigation site, the water depth was 16.5 m and theseabed was consisted of clayey deposits. The depth pro-ˆles of liquid limit wL, plastic limit wp, and natural watercontent wn are plotted in Fig. 4. At shallower depthsabove G.L.–7 m, wn was larger than wL, i.e., liquidity in-dex IL (＝(wL－wn)/(wL－wp)) was larger than unity. Atdeeper depths below G.L.–28 m, wn signiˆcantlydecreased with depth. Liquid limit wL also decreased andliquidity index IL signiˆcantly decreased from 0.8 to 0.5at around this depth, indicating that the component ofthe deposits varied remarkably.

Undrained Shear StrengthBy applying the new port-design code to the derived

values of undrained shear strength obtained from the un-

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Fig. 5. Depth proˆles of the undrained shear strength cu: (a) uniform depth proˆle, (b) uni-linear depth proˆle and (c) tri-linear depth proˆle. Solidcircles are derived values, thin solid line is the estimated value (with asterisk *), thick solid line is the characteristic value (with subscript k), anddotted line corresponds to the 95% conˆdence level


conˆned compression tests, the depth proˆle of the char-acteristic values can be determined. If the depth proˆle ismodeled as a uniform distribution, undrained shearstrength cu can be estimated as an expected value cu*＝23.0 (kN/m2) as shown in Fig. 5(a). In this case, COV is0.60 which is too large to determine the characteristicvalue from Table 1. Because the depth proˆle of the der-ived values has a trend to increase with depth, it can besaid that the uniform depth proˆle was inappropriate. Inengineering sense, when the depth proˆle of cu is modeledfor the stability analysis, the uniform proˆle whichoverestimates cu at shallower depths must be avoided, be-cause it results in dangerous design with regard to the sta-bility.

The depth proˆle of cu* modeled as the regression lineby the least square method is expressed as cu*＝1.4 z－0.5(kN/m2) as shown in Fig. 5(b). In this case, COV is 0.41,then b1＝0.75 is obtained from Table 1. Because there aremore than 10 data entries, b2＝1.0 can be used. Thus, thecharacteristic value cuk can be obtained by cuk＝b1×b2×cu*＝0.75cu*. The depth proˆle of the cuk determined hereis 25z smaller than that of cu*, which is the regression lineobtained by the least square method. Because this diŠer-ence is mainly caused by the inappropriate depth proˆlemodeling, the diŠerence can be made smaller by examin-ing more appropriate modeling.

The proˆle of cu can be modeled by three line segments,taking account of the consistency proˆles shown in Fig.4. The regression equations of the three line segments areexpressed as cu*＝0.27 z＋3.1 (kN/m2) in a range of0ºzº7.5 m, cu*＝0.95 z＋8.1 (kN/m2) in a range of7.5ºzº27.5 m, and cu*＝49.3 (kN/m2) in a range ofzÀ27.5 m, as shown in Fig. 5(c). Note here that the third

one is the expected constant value instead of the regres-sion line because the layer was very thin. In this case,COV for the three layers are 0.35, 0.21 and 0.14, respec-tively. Consequently, b1＝0.85, 0.90 and 0.95, respec-tively, are obtained from Table 1. Because there are morethan 10 data entries in the ˆrst and the second layers, b2＝1.0 can be used, but b2＝1－(0.5/n)＝1－(0.5/8)＝0.94(Eq. (10)) for the third layer.

In Japan, the average of 3 or 4 unconˆned compressiontest data for specimens at almost the same depth is gener-ally reported as one result. However, the number of dataentries is deˆned here as the total number of the tests car-ried out. Note here that the test results of the specimens,which showed ˆshers, cracks, shells, signiˆcant hetero-geneity, etc., have to be omitted as outliers (Watabe andTsuchida, 2001a).

In the cases shown in Fig. 5, COV decreases in the ord-er of (a), (b) and (c), indicating that an appropriatemodeling has been led by examining the derived values.In the case of (a), the characteristic value was not able tobe obtained because of too large variation. In otherwords, if the depth proˆle modeling is sloppy, the datamodeling is automatically reexamined in this method. Itis noteworthy that the distribution of a/a* is asymmetricif the depth proˆle modeling is sloppy such as case (a),while it is almost symmetric, i.e., normal distribution, ifthe modeling is appropriate such as case (c).

In Fig. 5, the characteristic values determined by thegeneral design code with 95z conˆdence level are alsoshown. When the depth proˆle is modeled as the uniformdistribution (Fig. 5(a)), the characteristic value corre-sponding to 95z conˆdence level is close to the estimatedvalue, even though the data shows signiˆcant variation

834

Fig. 6. Depth proˆle of consolidation parameters: (a) consolidation yield stress pc in logarithmic scale, (a?) consolidation yield stress pc in arithmet-ic scale, (b) coe‹cient of consolidation cv in logarithmic scale and (c) coe‹cient of volume compressibility mv in logarithmic scale. Solid circlesare derived values, thin solid line is the estimated value (with asterisk *), thick solid line is the characteristic value (with subscript k), and dottedline corresponds to the 95% conˆdence level

834 WATABE ET AL.

and the modeled depth proˆle does not follow the datatrend (but the estimated value is the mean value). This iscaused by the large number of data entries. This is a weakpoint in the general design code. On the other hand, whenthe depth proˆle is appropriately modeled as shown inFig. 5(c), the characteristic values derived from thegeneral design code with 95z conˆdence level and thenew port-design code with 30z fractile value are almostcoincident with each other.

Consolidation ParametersThe new port-design code is applied to the consolida-

tion parameters to demonstrate the determination of thecharacteristic values. Here, (a) consolidation yield stresspc; (b) coe‹cient of consolidation cv obtained from nor-mally consolidation range; and (c) coe‹cient of volumecompressibility mv correspond to p＝100 kN/m2 are dis-cussed. A linear depth proˆle is ˆrstly modeled on thearithmetic axis. It is reasonable for the normally consoli-dated deposits to model the depth proˆle of pc as a linearproˆle on the arithmetic axis. The parameters cv and mv

are also examined on the arithmetic axis as well as pc, be-cause these parameters show uniform depth proˆles. Be-cause consolidation parameters are generally plotted onthe logarithmic axis, the data variation is examined withthe logarithmic normal distribution. Consequently, byexamining the variation on logarithmic axis as shown inFig. 6, b?1＝1.0 according to COV of less than 0.1 is ob-tained. Because the number of the data entries is 10, thecorrection factor b?2 is also 1.0.

In Fig. 6, the characteristic values determined by thegeneral design code with 95z conˆdence level are alsoshown. In logarithmic scale, the characteristic values de-termined are apparently reasonable. However, if thedepth proˆle is expressed as a straight line in arithmetic

scale, the characteristic value is signiˆcantly smaller thanthe estimated value. As abovementioned, if the depthproˆle is modeled on the logarithmic axis, the model pro-ˆle on the arithmetic axis often becomes far from the de-rived values (Fig. 6(a?)). Therefore, it must be examinedcarefully by modeling the depth proˆle in considerationof the property of the soil parameter.

The depth proˆle of overconsolidation ratio OCR isshown in Fig. 7(a). The overburden eŠective stress s?v0

cannot be directly measured, but it can be calculated byintegrating either the unit weight gt above the groundwater level or the eŠective unit weight g? below that. TheOCR (＝pc/s?v0) is calculated from pc obtained as the der-ived value from the consolidation test and s?v0 calculatedat the depth. This OCR is characterized as the derivedvalue, because it is obtained by primary treatment for themeasured values. Consequently, the depth proˆle of thederived value has to be appropriately modeled and cor-rected according to the data variation and the number ofdata entries. On the other hand, OCR can be calculatedfrom the pc proˆle determined as the characteristicvalues. The calculated OCR is also characterized as thecharacteristic value. The characteristic values in the lattercase are plotted in Fig. 7(a).

Strength Increase RatioThe depth proˆle of strength increase ratio m is shown

in Fig. 7(b). Because cu and pc have already been obtainedfrom the shear test and the consolidation test, respec-tively, m (＝cu/pc) can be calculated for slightly overcon-solidated clay (Terzaghi et al., 1996). The ratio m ob-tained above is characterized as the derived value (solidcircle), since it is obtained by primary treatment for thetwo parameters respectively measured in the diŠerent soiltests. Consequently, the depth proˆle of the derived

835

Fig. 7. Depth proˆles of (a) overconsolidation ratio OCR (solid circle:derived values OCR; solid line: OCRk from uni-linear pck) and (b)strength increase ratio m (solid circle: derived values m; solid line:mk from the uniform m*; hollow circle: mk from the uni-linear m*;hollow square: mk from the uni-linear pck and the uni-linear cuk;solid triangle: mk from the uni-linear pck and the tri-linear cuk)


values is appropriately modeled and corrected accordingto the data variation and the number of the data entries.Here, the uniform depth proˆle (solid line) and the lineardepth proˆle (hollow circle) are respectively modeled,and then their characteristic values are respectively deter-mined. Because two variable data sets (cu and pc) aretreated, m (＝cu/pc) has either a larger COV or a smallerCOV than cu and pc. In the case of larger COV, the fol-lowing method is more logical.

The strength increase ratio m can also be calculated byusing the characteristic values cuk and pck. The character-istic values mk calculated from pck and cuk, which are ex-pressed as either uni-linear depth proˆles for both (hol-low square) or uni-linear one for the former and tri-linearone for the latter (solid triangle). In these cases, thevalues obtained are also characterized as the characteris-tic values, because those are calculated from the twodiŠerent characteristic values.

The characteristic values from the modeled depth pro-ˆles of the derived values (solid line and hollow circle) areinconsistent with m＝cu/(OCR×s?v0), because they have

not considered the relationship between cu and pc. On theother hand, in the case of characteristic value mk calculat-ed from the characteristic values cuk and pck (hollowsquare and solid triangle), the rational design can be donebecause the interrelationship between these twoparameters is taken into account. The strength increaseratio mk obtained from cuk and pck is about 0.18, while mk

obtained from the modeled depth proˆle of the derivedvalues is about 0.22.

Because m is generally said to be about 0.25 (Mesri,1975; Watabe et al., 2003a), the latter is possibly the ap-propriate value, but the former is obviously underesti-mated. This is caused by the smaller b1 for the cu accord-ing to the large variation. The former is apparentlyreasonable; however, it is inconsistent with the relation-ship between consolidation and shear. Therefore, the lat-ter is better to be used in the design. It is reasonable to de-termine the characteristic value of the shear parametersfrom the shear tests and that of the consolidationparameters from the consolidation tests, separately.Thus, we should avoid determining the characteristicvalue mk from the derived values.

This indicates a possibility of an uneconomical designresulting from the signiˆcant correction with the smallerb1 according to both the large data variation of cu ob-tained by the unconˆned compression test and the inap-propriate modeling of the depth proˆle. In order to solvesuch a problem, it is necessary to appropriately model thedepth proˆle. Also, the recompression triaxial shear testto be described in the next chapter is useful to obtain thedata with smaller variation.

As shown in Fig. 5, the proˆle of cu has been modeledas a straight line in the whole layer or three line segmentscorresponding to the three layers divided. Also, as shownin Fig. 6(a?), the proˆle of pc has been modeled as astraight line in the whole layer. In the case when the depthproˆles of cu and pc are modeled as the straight lines re-spectively in the whole layer, the depth proˆle of mbecomes the continuous straight line. However, in thecase when the former is modeled as the straight line in thewhole layer and the latter is modeled as the three line seg-ments corresponding to the three layers divided, thedepth proˆle of m shows signiˆcant discontinuity at theinterfaces between the layers. It is notable that therelationship between the characteristic values of bothconsolidation and shear parameters is consistent witheach other, indicating that the depth proˆle of m can beused in the design, even if its depth proˆle is apparentlyunnatural. In fact, the depth proˆle shown as solid trian-gle in Fig. 7(b) is well agreed to the depth proˆle of thederived values (solid circle).

EFFECTIVE UTILIZATION OF TRIAXIAL TEST

Usefulness of Triaxial TestBased on prior Japanese construction practice, the un-

drained shear strength of a clay layer was usually deter-mined as a half of the mean unconˆned compressionstrength qu of undisturbed clay samples. The reason for

836

Fig. 8. Illustration of stability analysis and recompression triaxial test:(a) triaxial compression and extension tests for the elements alongthe circle arc slip and (b) consolidation pressures on an element inthe recompression triaxial test

Fig. 9. Depth proˆle of undrained shear strength obtained fromrecompression triaxial test and unconˆned compression test forOsaka Bay clay

836 WATABE ET AL.

using the unconˆned compression test was not only for itssimplicity and low cost, but also for its presumed reliabil-ity, which was based on several case studies of actualfailures in coastal areas (Nakase, 1967).

For samples collected from large depth, the eŠect ofdisturbance on qu becomes much larger due to the ˆssuresin the samples caused by the release of high-conˆningstresses. In particular, trimming a Pleistocene clay sam-ple is very di‹cult because some part of the specimen canbe chipped oŠ easily (Watabe and Tsuchida, 2001a). Toavoid the in‰uence of stress release, the unconsolidated-undrained compression triaxial test (UU test) is oftenused. However, as the eŠective stress conditions of speci-mens are not known in the UU test, the reliability ofstrength obtained from the UU test is limited. In addi-tion, the variation of UU strength is as large as that of un-conˆned compression strength qu for the Osaka BayPleistocene clay (Watabe and Tsuchida, 2001b).

The recompression method (Berre and Bjerrum, 1973;Bjerrum, 1973) is used to reduce the eŠects of disturbanceby conducting the shear test after the specimen has beenconsolidated to the in situ eŠective stress conditions in thetriaxial cell. In this method, a specimen from an un-disturbed sample is ˆrst consolidated anisotropically tos?v0 and s?h0 (＝K0s?v0), and then subjected to undrainedshear. This method is applicable to not only stiŠ clays butalso soft clays. Jamiolkowski et al. (1985) stated that therecompression method should be used to predict the insitu behavior of highly structured clays and cementedclays rather than the SHANSEP (stress history and nor-malized soil engineering properties) method proposed byLadd and Foott (1974).

Recompression Triaxial TestThe stability of the embankment on the clay deposits as

shown in Fig. 8(a) is examined by circular arc slip analy-sis. Because the vertical stress below the embankment in-creases the undrained compressive shear strength cuc canbe evaluated by the undrained triaxial compression test.Precisely, there is a diŠerence between the plain straincondition and axisymmetrical condition; but it is nottaken account of here. On the other hand, because thehorizontal stress increases at the end of the circle arc, theundrained extensive shear strength cue can be evaluated bythe undrained triaxial extension test. Precisely, there is adiŠerence between not only the plain strain and axisym-metrical conditions but also the axial stress decreases inthe triaxial test while the horizontal stress increases in theembankment stability; but these are not taken account ofhere. The undrained shear strength cu for the design is ex-pressed as the mean value of cuc and cue (Hanzawa, et al.,1980). For Japanese marine clays, cue is about 30zsmaller than cuc in the recompression method to be de-scribed in the following part (Watabe et al., 2002).

The soil element is stressed by s?v0 in the vertical direc-tion and the eŠective earth pressure at rest s?h0 (＝K0s?v0)in the horizontal direction as shown in Fig. 8(b). Thesampled soil element is placed under the atmosphericpressure; i.e., zero total stress; however, some isotropic

eŠective stress remains because of the suction. By con-solidating the specimen under s?1＝s?v0 and s?3＝K0s?v0 inthe triaxial cell, the undrained shear test in the stress stateequivalent to the in situ condition (the recompressiontriaxial test) can be conducted. The s?v0 can be calculatedby integrating the unit weight in the depth direction. Theproblem here is how to evaluate the coe‹cient of earthpressure at rest K0. Some in situ tests to evaluate the K0

value have been proposed. The K0 value can also be eval-uated by K0 consolidation test in the triaxial cell (Watabeet al., 2003b). Because the K0 value obtained from K0 con-solidation test corresponds to the K0 value in normal con-solidation range (K0NC), it is necessary to note that K0NC isdiŠerent from the in situ K0 for the natural clay depositswhich is aŠected by aging eŠect. For most of the Japanesemarine clays, K0NC is in a range of 0.45 to 0.55 (Tsuchidaand Kikuchi, 1999; Watabe et al., 2003b).

Figure 9 shows depth proˆles of the undrained shearstrength obtained from the unconˆned compression testqu/2, the recompression triaxial compression test cuc, andthe recompression triaxial extension test cue for Osaka

837

Fig. 10. Depth proˆles of derived values, estimated values, and characteristic values of undrained shear strength for Osaka Bay clay: (a) average ofrecompression triaxial compression and extension tests and (b) unconˆned compression tests, and (c) comparison between recompression triaxi-al tests and unconˆned compression tests. Solid circles are derived values, thin solid line is the estimated value (with asterisk *), thick solid line isthe characteristic value (with subscript k), and dotted line corresponds to the 95% conˆdence level


Bay clay (Watabe and Tsuchida, 2001b). The value ofqu/2 varies much signiˆcantly, but it is coincident with(cuc＋cue)/2.

As described above, the recompression triaxial test hasmany advantages because the short term stability on theclay deposits is evaluated based on the qu＝0 method;however, it has not been used in practice. The unconˆnedcompression test is quite often used in practice, particu-larly in Japan. Even when triaxial test is used, most ofthem are either UU compression test conducted underseveral conˆning stresses or CU compression test con-ducted under several isotropic consolidation pressures.However, these cannot be directly used for the designbased on qu＝0 method.

Under these circumstances, there are a small number oftriaxial test results stored in the Geotechnical Database(Watabe and Tanaka, 2004). Therefore, by quoting theprevious research (Watabe and Tsuchida, 2001b), inwhich both the unconˆned compression test and therecompression triaxial test were conducted, theapplicability of the new port-design code will be exam-ined in the following part.

Comparison between the Unconˆned Compression Testand the Recompression Triaxial Test

The depth proˆle of the derived values of cu obtainedfrom the recompression triaxial test is shown in Fig.10(a). The derived value here is deˆned as the mean valueof cuc and cue shown in Fig. 9 at each depth. The regres-sion line passing through zero undrained shear strength atthe ground surface is expressed as cu*＝2.4 z (kN/m2).The calculated COV of 0.071 corresponds to b1＝1.0from Table 1. Because there are more than 10 data en-tries, thus b2＝1.0 from its deˆnition. It can be said that

the data shows small variation and their depth proˆle hasbeen appropriately modeled. In this case, the regressionline can be directly used as the depth proˆle for the eachcharacteristic value.

The depth proˆle of the derived values of cu obtainedfrom the unconˆned compression test is shown in Fig.10(b). The regression line passing through zero undrainedshear strength at the ground surface is expressed as cu*＝2.0 z (kN/m2). The estimated value obtained from the un-conˆned compression test is 22z smaller than that fromthe recompression triaxial test. The calculated COV of0.376 corresponds to b1＝0.85 from Table 1. Becausethere are more than 10 data entries, thus the b2＝1.0 fromits deˆnition. Therefore, the characteristic value cuk ob-tained from the unconˆned compression test is 27zsmaller than that from the recompression triaxial test,resulting an underestimation of cuk in the design (Fig.10(c)). This is caused by not only the variation of the databut also the limitation of the testing method. The recom-pression triaxial test has remarkable advantages in com-parison to the unconˆned compression test for the sam-ples retrieved from large depths. Consequently, theauthors would like to emphasize that the undrained shearstrength should be determined by the recompressiontriaxial test as stated by Jamiolkowski et al. (1985).

In Fig. 10, the characteristic values determined by thegeneral design code with 95z conˆdence level are alsoshown. For this soil layer, the diŠerence between thecharacteristic values determined by the new port-designcode and the general design code is negligible for the dataobtained by both the recompression triaxial test and theunconˆned compression test. This indicates that the newport-design code is consistent with the general designcode in practice.

838838 WATABE ET AL.

SUMMARY

The present technical report introduced the practicaldetermination method for soil parameters adopted in thenew performance based design code for port facilities inJapan, and examined its applicability. The main conclu-sions are summarized as follows:1) This technical report introduced the new practical

method, which is adopted in the design code for portfacilities in Japan, to determine the depth proˆle ofthe characteristic values of soil parameter. In thismethod, the depth proˆle of the derived values is mo-deled as the proˆle of the estimated values so as to beeither the mean value or the regression line; then theestimated value is multiplied by the correction factorsaccording to the coe‹cient of variation (if COVÀ0.1)and the number of the data entries (if nº10). Theformer correction factor is deˆned to make the char-acteristic value to be 30z or 70z fractile value of thedata distribution corresponding to whether it contrib-utes to safety margin in design or not, respectively.

2) This introduced method, which is simpliêd withoutreal statistic treatment, is partly consistent with thegeneral design code such as Eurocode 7 and JGS4001.The characteristic value is deˆned as 30z or 70zfractile values which correspond to 95z conˆdencelevel, when the number of data entries n is 10 and thedata variation COV is 0.1.

3) Compared to the lower limit of 95z conˆdence level,which is widely adopted in the general design codes,the characteristic value determined by the new designcode for port facilities is conservative when the num-ber of data entries is larger than 10, while it ischallenging when n is smaller than 10. This tendency iscaused by the concept, in which characteristic value al-ways re‰ect the data variation, even though the num-ber of data entries are signiˆcantly large. On the otherhand, in the general-design codes, the characteristicvalue is coincident with the mean value when the num-ber of data entries is large, because the conˆdence in-terval becomes of narrow range with number of dataentries.

4) In the new design code for port facilities, eŠorts toreduce the variation are awarded in the design, be-cause the characteristic value is determined accordingto the data variation.

5) When the data shows signiˆcant variation or the num-ber of data entries is limited, the engineer has beenjudging to determine the soil parameter in safety side.In the new design code for port facilities, the engineer-ing judgment is replaced by the correction factor ac-cording to the coe‹cient of variation of the data en-tries.

6) The undrained shear strength and the consolidationparameters are independently obtained by each soiltest; however, these are correlated, because the un-drained shear strength is strongly in‰uenced by theconsolidation pressure. Therefore, these parametersshould be determined by taking account of this corre-

lation. There are two methods to determine thestrength increase ratio from the consolidation yieldstress and the undrained shear strength. One is to de-termine the characteristic value using the derivedvalues calculated from both the derived values, andthe other one is to determine the characteristic valueusing both the characteristic values. The latter methodis rational in design because it is considered as the cor-relation between the consolidation and the shear.

7) In the determination method for soil parameters in thenew design code for port facilities in Japan, we can ex-pect that technology for appropriate data interpreta-tion (i.e., skill of engineers) and utilization of reliabletesting methods (i.e., development of testing methods)will be developed by targeting the minimization of theCOV. This is a new challenge that will lead advancedlaboratory tests such as the recompression triaxial testto the practice.

ACKNOWLEDGEMENTS

The authors would like to thank Mr. Hiroyuki Saegusaof Toa Corporation and Mr. Tomoyuki Ueda of SaekiKensetsu Kogyo Co. Ltd. for their discussions on thisstudy.

REFERENCES

1) Bjerrum, L. (1973): Problems of soil mechanics and constructionon soft clays and structurally unstable soils, State of the ArtReport, Proc. 8th ICSMFE, Moscow, 111–159.

2) Berre, T. and Bjerrum, L. (1973): Shear strength of normally con-solidated clays, Proc. 8th ICSMFE, Moscow, 39–49.

3) EN 1990: 2002: Eurocode 0, Basis of structural design.4) EN 1997–1: 2004: Eurocode 7, Geotechnical design–Par 1: General

rules.5) Fukui, J., Shirato, M., Matsui, K. and Okamoto, M. (2002): A

relationship between the angle of internal friction obtained by thetriaxial compression test and SPT-N value in sand, Technical Noteof Public Work Research Institute, 3849, 52p (in Japanese).

6) Hanzawa, H., Matsuda, E., Suzuki, K. and Kishida, T. (1980): Sta-bility analysis and êld behaviour of earth ˆlls on an alluvial clay,Soils and Foundations, 20(4), 37–51.

7) Jamiolkowski, M., Ladd, C. C., Germaine, T. T. and Lancellota,R. (1985): New developments in êld and laboratory testing ofsoils, State of the Art Report, Proc. 11th ICSMFE, 57–153.

8) JGS (2004): Principles for foundation design grounded on perfor-mance based design concept: JGS4001–2004.

9) Ladd, C. C. and Foott, R. (1974): New design procedure for stabili-ty of soft clays, Journal of Geotechnical Engineering, ASCE,100(7), 763–786.

10) Mesri, G. (1975): New design procedure for stability of soft clays,Discussion, ASCE, 101(4), 409–412.

11) Nakase, A. (1967): The qu＝0 analysis of stability and unconˆnedcompression strength, Soils and Foundations, 7(2), 33–45.

12) OCDI (2002): Technical standards, and commentaries for port andharbour facilities in Japan, The Overseas Coastal Area Develop-ment Institute of Japan.

13) Orr, T. L. L. (2006): Development and implementation of Euro-code 7, Proc. International Symposium on New Generation DesignCodes for Geotechnical Engineering Practice – Taipei 2006, CD-ROM, 1–18.

14) Ovesen, N. K. (1995): Eurocode 7 for geotechnical design, Proc.Bengt B. Broms Symposium on Geotechnical Engineering, Singa-pore, 333–360.


15) Schneider, H. R. (1997): Deˆnition and determination of character-istic soil properties, Proc. 12th ICSMGE, Hamburg, 4, 2271–2274.

16) Tanaka, H. (2003): In situ test replacing SPT, The Foundation En-gineering & Equipment, 31(2), 40–43 (in Japanese).

17) Terzaghi, K., Peck, R. B. and Mesri, G. (1996): Soil Mechanics inEngineering Practice, Third Edition, Wiley-Interscience Publica-tion, John Wiley & Sons, Inc., 161–173.

18) The Japan Port and Harbour Association (2007): Technical stan-dards, and commentaries for port and harbour facilities (inJapanese).

19) Tsuchida, T. (2000): Evaluation of undrained shear strength of softclay with consideration of sample quality, Soils and Foundations,40(3), 29–42.

20) Tsuchida, T. and Kikuchi, Y. (1991): K0 consolidation of un-disturbed clays by means of triaxial cell, Soils and Foundations,31(3), 127–137.

21) Watabe, Y. and Tsuchida, T. (2001a): In‰uence of stress release onsample quality of Pleistocene clay collected from large depth inOsaka Bay, Soils and Foundations, 41(4), 17–24.

22) Watabe, Y. and Tsuchida, T. (2001b): Comparative study on un-drained shear strength of Osaka Bay Pleistocene clay determined by

several kinds of laboratory test, Soils and Foundations, 41(5),47–59.

23) Watabe, Y., Tsuchida, T. and Adachi, K. (2002): Undrained shearstrength of Pleistocene clay in Osaka Bay, Journal of Geotechnicaland Geoenvironmental Engineering, ASCE, 128(3), 216–226.

24) Watabe, Y., Tanaka, H., Tsuchida, T. and Tanaka, M. (2003a):Normalization of stress-strain relationship for aged and cementednatural clay, Proc. International Symposium on the ``DeformationCharacteristics of Geomaterials'', IS-Lyon03, 535–544.

25) Watabe, Y., Tanaka, M., Tanaka, H. and Tsuchida, T. (2003b):K0-consoliation in a triaxial cell and evaluation of in-situ K0 for ma-rine clays with various characteristics, Soils and Foundations,43(1), 1–20.

26) Watabe, Y. and Tanaka, M. (2004): History of geotechnical data-base for port and airport construction in Japan, Proc. InternationalConference on Engineering Practice and Performance of SoftDeposits, IS-Osaka 2004, 409–414.

27) Watabe, Y., Shiraishi, Y., Murakami, T. and Tanaka, M. (2007):Variability of physical and consolidation test results for relativelyuniform clay samples retrieved from Osaka Bay, Soils and Founda-tions, 47(4), 701–716.

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PRACTICAL DETERMINATION METHOD FOR SOIL PARAMETERS …