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Liquefaction of Subsurface Soils During EarthquakesKenji Ishihara

Department of Civil Engineering, University of Tokyo7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

[Published May, 1974]

1. Synopsis

The following article summarizes the results ofstudies on liquefaction of sandy ground duringearthquakes, which have been conducted by the authorover the past few years. Case history studies on thissubject made for the major earthquakes in Japan aredescribed first, and then three soil profiles most prone toliquefaction are suggested. Principles and methods oflaboratory studies on liquefaction are briefly introduced,and typical examples of recent test data are shown. InSection 3, methods and techniques of field investigations are described in detail and. their interpretation in relation to liquefaction prediction is suggested. Finally, apredictive method is suggested in which the laboratorytest data are incorporated into analyses using the wavepropagation method.

2. Case History Studies of Liquefaction in Japan

2.1. IntroductionIn recent years, Japan has seen a rapidly increasing

number of high-rise buildings and massive civilengineering facilities being constructed in alluvial orreclaimed low-lying areas. The ground soils in theseareas are mainly soft with a high water table level located close to the ground surface. When the soil layer depositsin such areas are stimulated by the tremors ofearthquakes, the ground soils themselves are destroyed,leading to differential compaction, landspreading,fissuring, liquefaction and so on. Excessive movementand the loss of supporting capacity of soils caused by this destruction of the ground can give rise to extensivedamage to a variety of structures that have been built onor in these areas.

The origins of rupturing and shifting of the earthssurface may be traced to the collapse of soils or rockwhich occurs at certain depths in the ground. Some ofthis rupturing may be attributed to the large-scale faultmovement of rocks which takes place several kilometersbeneath the ground surface. Other hazards may benon-tectonic and merely surface phenomena occurringwithin several tens of meters from the surface. In somecases, observed surface ruptures can be distinguishedwithout difficulty whether they are due to deep-seatedfault movement or whether they are formed by the

migration of subsurface sediments. Nonetheless, thereare many ground ruptures of which the precise originsare difficult to locate because the various types ofcollapse occur simultaneously at different depths andthey act together in the formation of surface ruptures. Inany event, it is difficult, considering the present state ofknowledge, to predict the precise location and extent ofsurface ruptures caused by tectonic displacements in theearths crust. Therefore, this sort of rupturing isnecessarily outside the scope of this report.

The most spectacular and widespread effects ofsubsurface rupturing were observed during the Niigataearthquake of June 16, 1964, as well as in some othermajor earthquakes which have occurred since then. Itwas not, perhaps, by the time of the Niigata earthquakethat the failure of the ground was widely recognized as apotential source of major damage to the structures

Liquefaction of Subsurface Soils During Earthquakes

Journal of Disaster Research Vol.1 No.2, 2006 245

Fig. 1. Sand volcanoes (Niigata Earthquake, 1964).

Fig. 2. Aerial view of damaged area (Niigata Earthquake1964).

standing in and around weak soil deposits. However,violent distortions or displacements occurring insubsurface soils are not a new phenomenon. Thefrequent occurrence of liquefaction and differentialcompaction is evidenced by the description of thedamage characteristics noted in old documents. Thus, itmay be of interest to reexamine the case history recordsof old earthquakes and try to determine common features in cases where the subsurface ground was shaken by theviolent tremors of earthquakes.

2.2. Mino-Owari Earthquake of 1891

One of the most violent tremors in Japanese historyshook the Nagoya area on October 28, 1891. It had amagnitude of 8.4 on the Kawazumi scale, with itsepicenter located some 30 km north of Gifu city (seeFig. 4). The tremors reportedly lasted longer than15 minutes, and within this brief span of time about7,500 persons lost their lives. Following the main shock,as many as 1,000 aftershocks hit the area over the next65 days. Buildings and structures in the Nagoya area,

Ishihara, K.

246 Journal of Disaster Research Vol.1 No.2, 2006

Fig. 4. Nobi plain affected by the Mino-Owari Earthquakeof 1891 (after Kuribayashi-Tatsuoka).

Fig. 3. Location at which case histories have been studied.

(a)

Fig. 5. (a) Soil profile at Saya (Aichi Prefecture). (b) Soil profile at Nishibiwajima (Aichi Prefecture).

(b)

which is covered by soft alluvium, underwent severedamage. The disruption of the subsurface soils was alsotremendous. One guage by which the extent of damagecould be evaluated was the behavior of shallow wellsused for domestic water supplies. These wells extendedto a depth of about 10 to 20 m beneath the ground. Insome wells, the water became muddy and turbid withwhite to brown colours. Other wells lost water and werefinally abandoned. Still other wells were completelyfilled with sand which was ejected together with thewater.

The violent shaking during the quake, also alteredsoil conditions on farm lands. According to one peasantsaccount, some land became easier to cultivate after thequake, and in one village, the excavation of new wellsrequired only half as much labor as was needed prior tothe quake. These facts imply that the soils near theground surface were loosened by the shaking. Evidenceof liquefaction in level ground was numerous. In manyplaces, the ground burst open leaving cavities fromwhich streams of water and sand poured over theadjacent area. In the most severely damaged areas,thousands of water spouts developed, carrying with them sand and muddy soils. In the Biwajima area, near theShonai river, jets of water rose to a height of about 2.0m,leaving sand deposits over the roofs, of nearby houses. 1Many mud and sand geysers oozing water were formedin paddy fields 30 to 50 meters away from riverchannels. Some of the places identified in the olddocuments as areas where liquefaction occurredextensively are shown in Fig. 4. At Saya and Biwajimawhere sand boils were observed, soils investigationswere later made; the soil profiles drawn up during theseinvestigations are shown in Fig. 5(a) and (b). It shouldbe noted that at both sites sand deposits exist near theground surface which must have liquefied at the time ofthe earthquake.

2.3. Fukui Earthquake of 1948The Fukui earthquake, which nearly destroyed the

city of Fukui, at 4:15p.m. on 28 June 1948, is among the

most severe of Japans many well-known earthquakes. Its epicenter was about 5.0 kilometers east of Fukui city(Fig. 7). Its magnitude on the Gutenburg-Richter scalewas 7.2. The depth of energy release was rather shallowand estimated to be ten or so kilometers from the earthssurface. The main shock lasted for about 40 seconds andwas followed by many less intense after shocks. Most ofthe damage incurred was apparently limited bygeological conditions to an area of alluvial plain about15 km wide and 30 km long, which is surrounded bymountain ranges (see the map in Fig. 7). The greatestdamage was to structures built on the thick alluvium ofthe Fukui plain, and the least damage occurred tostructures built on bed rock. Over most of the alluviumarea, 75 percent of the houses were destroyed and thenumber of casualties, was about 5,000, due mostly tofires. No extensive surface faults were discovered, butevidence obtained from precise leveling andtriangulation surveys suggested the possibility of anorth-south fault running beneath the surface of theFukui alluvial plain. Relative uplift; of as much as 60 cm occurred on the land surface along the narrownorth-south band shown in Fig. 7. The Kuzuryu river,with many tributaries, flows into the Japan Sea, throughthe Fukui plain, originating from the surroundingmountain area and entering the plain at its southeastmargin, as can be seen in Fig. 7. One of the outstandingfeatures of the earthquake was the sand boils whichdeveloped along these river channels. Shown in Fig. 7are the locations where extensive sand boil formationswere observed. It is of interest to note that the sand boilsalso appeared along former stream channels which hadbeen filled and abandoned, revealing meanderingpatterns in rice fields. However, the concentration of



Fig. 6. Aerial view of damaged area (Niigata Earthquake,1964).

Fig. 7. Fukui area damaged by the Fukui Earthquake of 1948.

sand boils was not only in the proximity of the presentand past river channels, but also occurred along the faultzone shown in Fig. 7, where the shaking of the tremor isthought to have been most violent. It is to be noted thatthe fault zone is geographically coincident with the areaof fan deposit formed by the outflow of the Kuzuryuriver along the southeast margin of the Fukui plain. As isusually the case with fan deposits, there was a surplus ofunderground water in the deep-seated gravel layers in the area. The abundance of underground water might havebeen responsible in part for the extensive occurrence of

liquefaction in this particular region.In order to see what the soil conditions were like in

the area where sand boils developed, boring datadescribing soil profiles were assembled, and are shownin Fig. 8. Two sites, the Miyamae bridge site andIbatoshuko, along the tributaries of the Kuzuryu river,were chosen as representative of the river deposits in theFukui plain. As can be seen from Figs. 8(a) and (b),there is a thin surface fill of silt underlaid by loose sandlayers, which rests over a relatively thick stratum of softclays. These three layers are new and apparently of

Ishihara, K.


(a) (b)

(c) (d)

Fig. 8. (a) Soil profile at Miyamae Bridge Site (Fukui Prefecture). (b) Soil profile at Ibatoshuko (Fukui Prefecture). (c) Soilprofile near Maruoka, B1 (Fukui Prefecture). (d) Soil profile near Maruoka, B2 (Fukui Prefecture).

alluvial origin. Underneath these, are relatively hardmaterials, sand or silts deposits, which are considered tobe older and of diluvial origin. The level of the watertable is not as high as expected. Based on the soil profiles outlined in Figs. 8(a), and (b), it may well be said that aloose saturated layer of sand a few meters thick, coveredby a thin impervious upper layer, and underlaid by athick soft clay or silt deposit, could liquefy and become a potential source of hazard during any earthquake asintense as the Fukui earthquake.

The soil profiles in fan deposits, as represented bythose of sites B1 to B4 in Fig. 7, are demonstrated inFigs. 8(c) through (f). These sites, close to the epicenter,exactly coincide with the places where shaking was most violent, and relative uplifting of the surface as much asseveral tens of centimeters was registered. The soilprofiles in Figs. 8(c) to (f) indicate that the sand layerlikely to have liquefied is very thin, and that there is arelatively thick deposit of water-bearing gravelly sand atdepths of about 2 to 8 meters from the ground surface.Below this, there is a relatively hard, sandy, silt layerunderlaid again by a gravelly deposit. As indicated inthese figures, the level of the ground water table is veryclose to the surface. Because of the existence ofimpervious surface soil, the ground water might have

even been pressurized and in an artesian condition. It isdifficult to say definitely which factor, the severity ofshaking or the abundance of pressurized undergroundwater, contributed more to the inducement ofliquefaction. But it may be true that something like.liquefaction could indeed occur even in sand depositscontaining gravel, if the worst possible conditions, asoutlined above, are encounted at the same time.

2.4. Niigata Earthquake, 1964At 1:01 p.m. on June 16, 1964, a violent earthquake

hit Niigata and Yamagata prefectures, inflictingconsiderable damage on the city of Niigata, which wasfar out of proportion to the magnitude 7.5, of theearthquake. In Niigata, where sand deposits in lowlandareas are widespread, the damage was primarilyassociated with the liquefaction of loose sand deposits.Buildings not imbedded deep in firm strata sank or tiltedtoward the direction of the center of gravity.Underground structures, such as septic and storage tanks, sewage conduits and manholes, floated up a meter or two above ground level. In flat fields, sand flows and mudvolcanos ejected water and sand 2 to 3 minutes after thequake. Sand deposits 20 to 30 cm thick covered theentire city, as if the whole area had been devastated byflooding. Damage to modern bridges was also extensive.Most notable was the crumbling of five girders of theShowa bridge which crosses the Shinano river in thedowntown area. The foundation piles were bentexcessively due to the loss of lateral resistance of theriverbed sand deposit, and this caused thesimply-supported girders to fall.

Figure 9 is a map of Niigata city, in which the placeswhere liquefaction developed are indicated. It is to benoted that the whole area of the city was basically builton layers of sand as deep as about 100 meters, althoughthe origins of these deposits are somewhat different from one location to another. A typical shallow-depth soilprofile is shown in Fig. 10 and describes the soilcondition at Kawagishicho where the land was formedabout 40 years ago by reclaiming an old river course.



(e) (f)

Fig. 9. Niigata city destroyed by the Niigata Earthquake1964.

Fig. 8. (e) Soil profile near Maruoka, B3 (Fukui Prefecture). (f) Soil profile near Maruoka, B4 (Fukui Prefecture).

2.5. Great Kanto Earthquake, 1923

The Great Kanto earthquake of September 1, 1923(Magnitude 7.9) was the most disastrous earthquake inJapanese history. Since the epicenter was close to Tokyo, the destruction incurred in the city area was dreadful.The tremors reportedly lasted longer than one minute.About 14 thousand people were reported dead ormissing, mostly victims of fires which broke out after the quake. The damage to buildings and other civil

engineering facilities was incurred over a widespead area of the Kanto plain, but in the downtown areas of Tokyo,the destruction was more severe in the low-lying deltaareas along the coast of Tokyo Bay. Sudden openingsand closings of ground fissures, eruptions of sand andmuddy water were observed in many places.

Shown in Fig. 11 are some of the locations in thelowland areas of downtown Tokyo where sand boilswere reportedly observed at the time of the earthquake.In some of the places where liquefaction occurred, soil

Ishihara, K.


Fig. 11. Low-lying delta area of Tokyo affected by theGreat Kanto Earthquake of 1923.

(a) (b)

Fig. 12. (a) Soil Profile at Ukita (Edogawa-ku, Tokyo). (b) Soil profile at Edogawa (Edogawa-ku, Tokyo).

Fig. 10. Soil profile at Kawagishi-cho (Niigata Prefecture).

investigations have been conducted recently, and theresults are shown in Figs. 12(a) and (b). These are soilprofiles typical of alluvial deposits in the downstreamdelta area of big rivers. A sand layer, sandwichedbetween rather impervious layers, appears to haveliquefied when the earthquake hit.

2.6. Types of Liquefiable Soil ProfileIn the foregoing paragraphs, several examples of soil

profiles which definitely developed liquefaction duringgreat earthquakes of the past have been introduced. Inreviewing these case histories, it is obvious that roughlyspeaking there are three types of alluvium in whichliquefaction is most likely to develop:

(i) Sand deposits: Sands with different grain compositionsexist in layers down to depths of at least 20 m. This typeis typically represented by the soil profile of Niigata asshown in Fig. 10(b).

(ii) Sandwiched sand deposits: A sand layer with athickness of 3 to 10m exists at relatively shallow depths.On top of and underneath this sand layer are silt or claystrata.This type is represented by many soil profiles,including those shown in Figs. 5(a), 8(a), 8(b), 12(a) and 12(b).

(iii) Thin sand layers lying on gravelly sand: This istypically represented by the soil profiles in Figs. 8(c),8(d), 8(e), and 8(f). Note that this type of profile usuallyexists with fan deposits and liquefaction is associatedwith abundant artesian ground water.

3. Laboratory Studies of Liquefaction

3.1. Mechanism of LiquefactionWhen dry sand is subjected to shear stress, it changes

its volume depending upon the density; The looser sandscontract and densely packed sands increase in volume.This phenomenon is commonly known as dilatancy. Ifthe looser sand is saturated with water and subjected tothe same shear stress in an undrained condition, novolume change can occur during the shearing. Under this condition, the soil skeleton with a tendency towardcontraction transfers some of its load to the water, andthe water pressure thus produced reacts in turn to prevent the volume change from occurring.

In dynamic loading conditions in which shear stresses are cycled, the same phenomenon can also occur, and asthe cycle loading continues, excess pore pressuredevelops in undrained soil elements, thereby decreasingthe effective confining stress initially applied to theelement. Under the appropriate conditions, thedeveloped pore pressure eventually becomes equal to the effective confining pressure. In this state, withouteffective confining stress, the sand loses all its strength.Each particle of sand is separated and thrown into thesurrounding water. In this way the sand mass deposit is

transformed into a state of suspension and behaves like aviscous liquid. This state is called liquefaction or morecommonly, quicksand.

3.2. Principle of Laboratory TestingMany of the laboratory studies on liquefaction have

been based on the principle of subjecting representativesoil samples to the same conditions in the laboratory asare found in the field, and extrapolating the probablefield performance from the resulting behavior of thelaboratory test specimens. The stress systems to whichsoils under ground level are subjected duringearthquakes may be divided into two classes: a deviatorstress system resulting from upward propagation ofcompressional waves; and a system of shear stress acting on horizontal planes caused by shear waves coming upfrom underlying layers. According to a number ofaccelerogram records taken during past earthquakes, it is now known that the amplitude of motions in thehorizontal direction is two to three times greater thanthat of the vertical direction. Therefore, the deviatorstress induced in the soil by the passage ofcompressional waves is generally small in magnitudewhen compared to the shear stress due to shear wavepropagation. It is common knowledge that the deviatorstress is defined by the difference between normalstresses acting on horizontal and vertical planes in arectangular soil element. This is illustrated in Fig. 14. As the deformation is constrained laterally, the ratiobetween the vertical stress, 1 and the horizontal stress, 3 is determined solely by poissons ratio, , of soils asfollows.

13 1

=

. . . . . . . . . . . . . . (1)

Figure 13 shows the values of Poissons ratio forsaturated soils as obtained during the field measurements of compressional and shear wave velocities. Also, shown



Fig. 13. Poissons ratio in saturated soils.

in this figure is the curve obtained from the formula

( ) = 12

1 2nC l . . . . . . . . . . . . . (2)

where, n denotes porosity, C l is the compressibility ofwater, and is the shear modulus of soils. The aboveformula was derived based on the theory of elasticporous media [3]. Fig. 13 indicates that Poissons ratiodecreases as the soil becomes more rigid, but for theshear moduli often encountered in a soft soil deposit, itlies very close to 0.5. If this value is inserted into Eq. (1), it immediately follows that the horizontal stress, 3 isnearly equal to the vertical stress 1 . This implies thatthe deviator stress, which is induced during the passageof compressional waves, is very small when the groundsoil is saturated with water. For these two reasons whichare explained above, it can be said that the stress systemcaused by compressional waves is almost purelycompressive and hardly produces any deviator stress. Accordingly, the significant forces acting on soilelements in the field during earthquakes are thoseresulting from the upward propagation of shear wavescoming from underlying rock formations.

3.3. Method of Laboratory TestingTo assess the liquefaction potential of a certain sand,

three kinds of testing device have been used. Theseinclude the triaxial test, the simple shear test and thetorsional shear test, all operated under cyclic loadingconditions.

The cyclic triaxial test was developed by Seed andLee (1966) [11] to study the factor controlling theliquefaction of saturated sands. Because of its relativesimplicity and wide availability, it is still the mostcommonly used testing procedure. In this test, a saturated

cylindrical sample of sand is consolidated under aneffective ambient pressure. All drainage is prevented and then the sample is subjected to cycles of axial stresschange. This loading procedure creates stress conditionson a plane of 45 through the sample which correspondto those created on horizontal planes shown in Fig. 14.The effective confining stress on the plane is equal to the ambient pressure and a cycle deviator stress equal to half the amplitude of the cyclic axial stress acts on the plane.

The cyclic simple shear test was developed byPeacock and Seed (1968) [8] to overcome theoreticalobjections inherent in the triaxial test. Samples ofrectangular cross-sections are consolidated under aneffective vertical pressure, preventing lateraldeformations. A horizontal cyclic shear stress is appliedto the sample as in the field. Thus, the test appears toduplicate exactly the same field conditions as whenhorizontal ground layers are shaken by shear wavespropagating upwards.

A triaxial torsion shear apparatus has been used byIshihara and Li (1972) [4] which permits theconsolidation of cyclindrical sand specimens at variousvalues of K 0 and shearing by cyclic torsional shearstresses. The axial load piston was designed to have thesame area of horizontal cross section as the sample sothat lateral strain on the specimen can be avoided bypreventing any change in the volume of cell water. Thuseffective confining stresses can be applied under theconditions described above for horizontal ground andcyclic shear stresses can be imposed under plane strainconditions. Torsional shear tests can be worked outeither by solid or hollow cylindrical specimens, but inview of the non-uniform, strain distribution throughoutthe sample, which is inherent in the torsion of solidcylinders, it appears highly desirable to use hollowcylindrical specimens having walls as thin as possible. A schematic diagram describing the correspondencebetween in-situ and laboratory stress conditions within asoil element, both prior to and during an earthquake, ispresented in Fig. 14.

As to the loading equipment, three types of machineassemblies have been used: the electrical vibrationgenerator, an air pressure unit, and an electro hydraulicactuator. Electrical vibration generators are generallyunsuitable for those tests for liquefaction in which loadsmust strictly be controlled from the outset of the loadapplication. Furthermore, the vibratory forces producedby this machine are governed largely by the frequency at which it is operated, and for the cyclic type of loading, in which the frequency is rather low, it is often impossibleto produce as much shear stress as desired. For thesereasons, this machine is now going out of use.

Air pressure units consist of a compressed air tank,several valves, regulators, and a solenoid valve by which the cyclic transmission of the air pressure to the loadingcylinder is controlled. The machine is suitable forproducing cyclic pulsating stresses which operate withfrequencies less then 5 Hz. However, it does not permit

Ishihara, K.


Fig. 14. Stress conditions in ground soil and its simulationby means of a hollow cylindrical torsion test.

arbitrarily shaped wave patterns to be reproduced in thetime history of stress change.

The most sophisticated equipment that has come intouse recently is the electrically controlled hydraulicloading machine. If this system is incorporated with adata recorder, any time-sequence of random wavepatterns recorded on a magnetic tape can be retrieved asan analog command, and transformed into thetime-history of stress change. This machine will findwidespread popularity in the future study of sandliquefaction.

3.4. Factors Affecting the Liquefaction ofSaturated Sand

Using the cyclic triaxial test, Seed and Lee (1966)[11] obtained data which influence the liquefactionpotential of saturated sand. The factors are qualitativelydefined as follows: (i) Void ratio or relative density ofthe sand the higher the void ratio the easier theinducement of liquefaction. (ii) Initial effectiveconfining pressure the lower the confining pressure themore easily liquefaction will develop. (iii) Themagnitude and the number of cycles the greater thecyclic stress and the number of cycles, the easier thedevelopment of liquefaction.

As to the initial confining pressure, it was found thatthe magnitude of shear stress, , required to causeliquefaction under a given number of cycles isapproximately in direct proportion to the initialconfining pressure, c . Consequently, the resistance toliquefaction may be conveniently evaluated by using thestress ratio defined as 1 c .

The relative density, Dr , is defined as

De e

e er =

max

max min

. . . . . . . . . . . . . . (3)

where e is the void ratio, and emax and emin are the voidratios in the loosest and densest states, respectively.Relative density is, by definition, a measure of how thecurrent state of a sand compares with its loosest anddensest states. After collecting a number of triaxial testdata, Tanimoto (1971) [13] has shown that the resistanceto liquefaction, as represented by the stress ratio, islinearly correlated with the relative density (see Fig. 15).

3.5. Application of Laboratory Test Data to FieldConditions

Most of the test data concerning liquefactionpotential have been obtained using the cyclic triaxialshear test. When one tries to apply the results of thesetests, the difference in stress conditions which prevailsbetween in-situ and laboratory conditions must be takeninto account. One of the most important differences liesin the evaluation of the effective confining pressure, c .In triaxial tests, this is undoubtedly equal to the effectivemean principal stress, but in the field, the effective meanprincipal stress is equal to ( )1 2 30 1+ K , where K 0 is

an earth pressure coefficient at rest, and 1 is the vertical effective stress. If the effective mean principal stress isto be chosen as the effective confining pressure, the field stress ratio must be

31 2 0 1+

K

in order to be compared with the corresponding stressratio, c in the triaxial test condition. Therefore, thestress ratio, c , obtained in triaxial tests, ought to becorrected by a factor of ( )1 2 30+ K before it is appliedto the in-situ evaluation of the liquefaction potential.This point has been argued in more detail in the papersby Finn, et al. (1971) [1] and Ishihara and Li (1972) [4].

3.6. Results of Liquefaction Test Using HollowCylindrical Test Apparatus

As a typical example of liquefaction tests, the testresults obtained by employing hollow cylindrical torsion devices will be briefly introduced. Loose samples with45% relative density were consolidated under anambient pressure of 1.0 kg cm 2 , and then subjected to atorsional shear stress with a time-sequence changeexactly the same as those recorded at the time of theNiigata earthquake of 1964. First, the relative amplitudeof the shear stress change was set at an appropriate level, which was not high enough to induce liquefactionthroughout the loading. The maximum deviator stress, max , and the residual pore pressure, r , that developedduring this test were read off and plotted, Fig. 17. Next,the load level was increased slightly, and a shear stresshaving the same wave pattern as before, but with a



Fig. 15. Relation between relative density and stress ratioin causing liquefaction in 10 cycles of load repetition(Tanimoto, 1971).

greater amplitude, was applied to the other sampleprepared under identical conditions. In this case as well,the maximum deviator stress and the residual porepressure eventually developed were noted and plotted,Fig. 17. After repeating this procedure a few times bygradually increasing the load level, a state was reached in which the induced residual pore pressure was equal tothe confining pressure. This state was defined as thatwhere liquefaction occurred. The time-history of theapplied shear stress (N-S component of the accelerogram record of the Niigata earthquake), and the consequentchanges in shear strain and pore pressure are shown inFig. 16. It can be seen that the pore pressure rises acutely 9 seconds after the initial shocks, leading to the complete liquefaction of the sand sample.

The test results obtained for two wave patterns (NSand EW components) are synthesized in the diagram ofFig. 17. In the time history records of actual earthquakeaccelerations, it is possible to mark the acceleration peakduring the time of earthquake occurrence. The torsionalstress corresponding to this peak acceleration is denotedby max , and this is utilized in Fig. 17 for representing the relative magnitude of the shear stress. In the series oftests described above, the value, max , was graduallyincreased while the wave form remained unchanged. As max was raised, the residual pore pressure, whichdeveloped after the load was completely applied,increased. Fig. 17 shows the residual pore pressure, rthus obtained in each test versus, max with all thesevalues normalized to the initial effective confiningpressure, c .

4. In-Situ Investigation of Liquefaction

4.1. Blasting TestWhile there is abundant laboratory test data on

liquefaction, in-situ investigations on intact soils have

seldom been undertaken, and much research and studystill remains to be done in this area. One of the earliestattempts of in-situ tests was carried out in Russia bydetonating explosives buried in drilled holes. The use ofexplosives as a means of stabilizing sandy grounds hadalready been put into practice, and this technique wasthen utilized as an in-situ method for assessing thepotential instability of the ground during earthquakes.When explosions occur in loose deposits of saturatedsands, the pore pressure builds up, and as it graduallydissipates into the surrounding ground, densificationoccurs. The settlement that appeared on the groundsurface as a result of densification was chosen as anindex of instability. Later, Kummeneje and Eide (1961)[7] conducted a similar series of blasting tests in marinedeposits of sand and silts in Norway for. the purpose ofestimating the potential danger of flow slides. This time,the pore pressure in the field was measured as well as the consequent settlement of the ground surface. Beforeblasting, a number of piezometers were installed atvarious depths in the ground at different distances fromthe explosive charge. Pore pressures as high as 80% ofthe effective overburden pressure were recorded at adistance of 5.5 m from the point of detonation.

Similar blast tests were also performed by Prakashand Gupta (1970) [9] in loose sand deposits in the bed ofthe Damodar River, India, where the stability of a 55 mhigh earth dam was the focus of concern. A piezometerembedded at a depth of 6 m, 3 m away from thedetonation point, registered a pore pressure equal to 80% of the effective overburden pressure. At the same time, asimple procedure for estimating the surface settlementwhich is expected to occur in future earthquakes, wassuggested on the basis of the correlation between theacceleration and densification of the sand.

While the blast test provides useful information onthe likelihood of liquefaction or settlement on a givensite, it has some disadvantage in that it fails to reproduce

Ishihara, K.


Fig. 16. Recorded changes in torsional stress, angle oftwist, and pore pressure.

Fig. 17. Relation between the maximum stress ratio andresidual pore pressure using the records of the NiigataEarthquake (Kawagishi-cho apartment).

the stress change in the ground which is cyclic in nature,and more representative of the actual situation duringearthquakes. Furthermore, the blast test requires a widespace in a sparsely populated area, and, therefore, it isdifficult to investigate sites in congested city areas.

Still other inconveniences are encountered in theblasting test in that the duration of the loading time is soshort about 0.001 to 0.05 second in terms of rise times that the corresponding frequency far exceeds thenatural frequency of the pickups commercially available. This means that the pickup for acceleration measurement does not operate as it is intended and produces insteadthe displacement which in turn is very difficult tocalibrate for such short loading times. Consequently, ifnormal acceleration pickups are to be used as a means ofevaluating input energy or force, the results could oftenbe misleading. To overcome this difficulty, the use ofsemi-conductor type pickups having extraordinarily high natural frequencies may be recommended, butunfortunately these have not been used so far for thispurpose.

4.2. Vibratory Pile Driving TestTo overcome the potential handicaps of the blasting

test, Ishihara-Mitsui (1972) [5] suggested the use ofvibratory piles as a means of producing dynamic forcesin the ground. Before piles are driven, several holes aredrilled close to the piles for the installation ofaccelerometers and piezometers. Then the piles aredriven by a vertically acting vibrator and simultaneousmeasurements are made of the pore pressures andaccelerations developed in the nearby boreholes.

This type of field test for evaluating liquefactionpotential has been carried out at three sites havingdifferent soil conditions. The first attempt was made onthe recently reclaimed deposit in Chiba, Japan, whoselocation is indicated in Fig. 18 (Ishihara-Mitsui, 1972[8]). The fill materials consisted mainly of sands which

were dredged from the nearby sea bottom. The soilprofile at the test site is shown in Fig. 19, together withthe plot of the standard penetration resistance versus thedepth. Particle. size distribution curves of the sands areshown in Fig. 20. In view of the low value of the blowcount, the sand as it is deposited in the field, wasconsidered susceptible to liquefaction duringearthquakes, and for this reason, work was underprogress to stabilize the deposit by means of compactionpiles. It was then possible to perform the aforementioned pile driving tests on the stabilized deposit as well as onthe reclaimed ground. A typical layout for the test isshown in Fig. 21. Piles were driven by means of anoscillator with a dynamic force of 35 tons at a frequencyof 17 Hz. As the pile penetrated, the pore water pressures increased with the cyclic fluctuation. Because only thegradual shift of the neutral position represents theresidual part of pore pressure, these values divided bythe effective overburden pressures versus the elapse oftime are plotted above the time axis in Fig. 22 and theseare plotted below the time. Recorded accelerationschange only in amplitude, which is plotted on the



Fig. 18. Location of test site. Fig. 19. Soil profile at Chiba site.

Fig. 20. Particle size distribution of sands at Chiba site.

downward axis in Fig. 22. The diagrams also show thevariation of pile penetration with time. Fig. 22 shows atypical result of tests performed on intact sand depositsand Fig. 23 on stabilized deposits. It is known that thereoccurs a significant increase both in pore pressure andvertical acceleration as the pile tip passes by the point ofmeasurement. The results of tests on uncompacted soilsshow that once the pore pressure has reached its peak, itdrops rapidly and extremely high acceleration is required to increase it again. This implies that densification of thesand occurs along with the dissipation of developed porepressures, and therefore, at this stage the sand loses thepore pressure characteristics it possessed in its originalstate. Consequently, if the original state is of concern, itis necessary to pay attention to the increasing stage of

pore pressure changes. With this fact in mind, theamplitudes of vertical acceleration were read off at thetime when a certain pore pressure has been reached forthe first time, and plotted on the abscissa against thatpore pressure as shown in Fig. 24. Fig. 24 summarizesall the data obtained at a horizontal distance of 1.0 mfrom the pile. The graph shows that, as the density of thesand represented by blow count increases, theacceleration level required to cause a given pore pressure increases. This characteristic of sand can better beexpressed by determining the acceleration required toraise the pore pressure by an amount equal to say 10% of the effective overburden pressure. These accelerationswere read off from Fig. 24 and plotted in Fig. 30 againstthe blow count.

Another series of similar pile driving tests wasperformed in Tokyo on a sand deposit of alluvium origin (Ishihara, 1973 [6]). The playground of TakasagoMiddle School was chosen as the test site whoseapproximate location is shown in Fig. 18. The placeconsists of a natural levee deposit and has a soil profileas illustrated in Fig. 25. The whole deposit is composed

Ishihara, K.


Fig. 22. Recorded pore pressure and accelerations versustime (uncompacted ground).

Fig. 23. Recorded pore pressure and accelerations versustime (compacted ground).

Fig. 21. Plan and profile of test layout at Chiba.

Fig. 24. Relation between pore pressure and verticalacceleration (reclaimed deposit in Chiba).

of fine sands which have similar particle distributioncharacteristics to those of Chiba which are shown inFig. 20. The test project involved the use of a30 cm-diameter pile driven by a vertically acting vibrator to produce vibrations in the ground. At a distance of1.0 m away from the spot where the piles were to bedriven, three holes were drilled, to depths of 4.5, 7.0 and10.0 m, respectively, and a capsule containing a verticalaccelerometer and piezometer was lowered to the bottom of each hole. After all these arrangements were finished,pile driving was started using a 30 ton vibrator operatingwith a frequency of 17 Hz. Fig. 26 shows the variationsof pore water pressure and the acceleration with timearranged in the same fashion as those of Figs. 22 and 23.Unlike the test results on the reclaimed ground in Chiba,the rise in pore pressure was generally small. Theamplitude of vertical acceleration at the time whendifferent pore pressures were reached for the first timewas read off from Fig. 26 and replotted in Fig. 27 against the corresponding pore pressure. The average data points in Fig. 27 are approximated by straight lines, and theblow counts obtained at the depths where the porepressures were measured are also indicated. Themagnitude of vertical acceleration needed to hike thepore pressure by 10% of the effective overburdenpressure was read off from the diagram of Fig. 27, and

plotted versus the blow count in Fig. 30.The third series of vibratory pile driving tests was

carried out at Saya near Nagoya on a delta deposit ofalluvial origin. The area where the tests were conductedis shown in Fig. 4 and the soil profile there isdiagrammed in Fig. 5(a). As in the previous tests,several holes were drilled near the spot where a vibratory pile was to be driven and piezometers andaccelerometers were carefully buried. Then, a pile wasdriven by means of a 35 ton vibrator operating with afrequency of 20 Hz. Records of variations in porepressure and accelerations are recorded in Fig. 28,together with the speed of pile penetration. Themagnitude of vertical acceleration at the time when thegreatest pore pressure was attained was read off from the records of Fig. 28 and plotted in Fig. 29 against thecorresponding pore pressure. The data was furtherarranged, as was done for the other tests, in Fig. 30 byplotting, against the blow count, the magnitude ofvertical acceleration needed to raise the pore pressure by10% of the effective overburden pressure.

In Fig. 30, all the data for the three test sites withdifferent soil profiles are presented together. When one



Fig. 25. Soil profile at Tokyo site.

Fig. 26. Recorded pore pressures and accelerations versustime.

Fig. 27. Relation between pore pressure and verticalacceleration (natural levee deposit in Tokyo).

Fig. 28. Recorded pore pressures and accelerations versustime.

looks at this chart, a good correlation between the blowcount and the acceleration seems to exist within each ofthe test series, but relationships of this kind are quitedifferent among the three sites. Compare, first of all, thedifference between the Chiba and Tokyo sites. A greateracceleration is always needed in the Tokyo test site thanin the Chiba site to raise the same proportion of the porepressure, although the density of the deposits asrepresented by the blow count is supposed to be thesame. This indicates that there are some factors related to the pore pressure characteristics which can not beaccounted for by the blow count alone. Considering thecurrent state of knowledge, it may be difficult to definethe factors, but it is interesting to look at the apparentdifferences which prevail between the field conditions atthe two sites. Firstly, the alluvial deposit in Tokyo isconsidered to be several hundred years old or even older, whereas it was only one year after reclamation that thetests were conducted in Chiba. The aging effects,probably cementation, etc., may account partly for thisdifference. Secondly, the ground water table in the Chiba site was located about 0.5 m below the ground surface,whereas in Tokyo it was about 1.5 m below the surface.The difference in the level of the water, table seems tohave a greater effect than it is taken into account bydividing the pore pressure by the effective overburdenpressure. It is of interest to note in Fig. 30 that thestraight lines indicating the trends in Tokyo and Chibarun nearly parallel to each other, which implies that theeffects of cementation or the water table come out almost equally for any sand density. The reclaimed sand inChiba would probably liquefy if an earthquake as greatas the Niigata Earthquake of 1964 hit the area. However,liquefaction would not extensively develop in the natural levee deposit in Tokyo. Hence, it may be said that thetest results at the Tokyo site typically represent the porepressure response where liquefaction would not occur,while that at the Chiba site is typical of the response at

the place where liquefaction probably takes place. It is to be remembered that this statement is valid only whensoil profiles like those shown in Figs. 19 and 25 areencountered where the sands run from the very top allthe way down to a sufficient depth.

In areas like the Nagoya site where the sand layer ofconcern is sandwiched between impervious layers, thesituation seems to be entirely different. The soil profileshown in Fig. 5 clearly shows that the upper and lowerimpervious layers tend to prevent dissipation of the porepressure developed within the sand deposit. This isclearly reflected in the observed pore pressure variationsoutlined in Fig. 28. If the data on the Nagoya site shownin Fig. 30 is viewed from this background knowledge, itmay be said that the surprisingly high rise of the porepressure encountered at depths of 4.0 and 11.0 m is dueto the inability of the developed pore pressures to drainout through the upper and lower impervious layers. Thedata at depths of 7.0 m which may not be influenced bythe presence of the impervious layers lies close to that ofTokyo site. Because the delta deposit in Nagoya isconsidered to be as old as the alluvial deposit in Tokyo,the effect of cementation, etc. may be equal to that of theTokyo site. Consequently, the sand at a depth of 7 m, inNagoya, is considered to have approximately the sameresistance to liquefaction as the sand in Tokyo.

5. Analysis of Liquefaction in Level Ground

5.1. Method of AnalysisThe likelihood of liquefaction occurring during

earthquakes in levelground sand deposits can be inferred by checking whether the resistance to liquefactionagainst the shear stress imposed on the soil elementthrough the propagation of shear waves is high enough.The resistance to liquefaction of saturated sands can beestimated by extending laboratory test results such asthose introduced in Fig. 17. The next problem is how toevaluate the shear stress induced in the ground during

Ishihara, K.


Fig. 29. Relation between pore pressure and verticalacceleration (delta deposit in Nagoya).

Fig. 30. Relation between N-value and verticalacceleration required to increase pore pressure by 10% ofthe effective overburden pressure.

earthquakes. Time history changes in shear stress can bedetermined by the response analysis of the horizontallayers of soils subjected to known sequences ofacceleration or displacement at their base or at thesurface. Several analytical procedures such as thelumped mass method and wave propagation methodhave been developed for this purpose, and computerprograms incorporating these analyses are available foreasier use. Once the soil profile is given together with the shear modulus and damping ratio of the soils, it ispossible to determine the time history changes in theshear stress within each layer. In the following, anexample of response calculation using accelerationrecords taken at the time of the Niigata earthquake of1964 will be presented. A comprehensive computerprogram incorporating the wave propagation method has been developed by Schnabel, et al. (1973) [10]. Thisprogram was applied to the horizontal layers of the soilprofile representing the ground conditions at the placewhere the acceleration records were obtained at the timeof the Niigata earthquake. The soil profile was dividedinto nine horizontal layers as shown in Table 1. Basedon the empirical relationship proposed by Gibbs-Holtz(1957) [2], together with data on blow counts at eachdepth, the relative density of the sands was evaluated.

Shear moduli were assessed on the basis of shear wavevelocities estimated from the values of the blow counts.First, the damping ratios were properly assumed.Response analysis was then started and repeated,changing the soil properties each time in accordancewith the induced strains, until the shear modulus anddamping ratio used become compatible with the strainsin each layer of the soil profile. The results of theanalysis in which the NS component of the recordedground motions were fed into the computer are shown inFig. 31 which shows the computed time histories ofshear stress changes at depths of 3.0 and 15.0 m. Itshould be noted that the wave forms at both depths aresimilar to each other as well as resembling the recordedacceleration shown in Fig. 16. This connotes the fact that the soil layers near the ground surface move almosttogether as if the entire mass were one rigid body(Seed-Idriss, 1971 [12]). A proof of this is furnished by



Fig. 31. Computed time histories of shear stress in theground underlying Kawagishi-cho, Niigata, using N-Scomponent recorded in the basement of an apartmenthouse.

Table 1. Ground model for response analysis(Kawagishi-cho, Niigata).

Fig. 32. Distribution of maximum acceleration with depth(accelerations recorded at Kawagishi-cho, Niigata wereused).

Fig. 33. Distribution of maximum shear stress with depth(accelerations recorded at Kawagishi-cho, Niigata wereused).

the downward distribution of the computed maximumaccelerations as shown in Fig. 32. Although wave formsat near-surface depths are not distorted, the relativeamplitude in the time histories of the shear stressincrease approximately in proportion to the depth. Thiscan be clearly seen in Fig. 33, in which the maximumshear stresses are plotted against the depth of the deposit.

If the unit weight of the sands as listed in Table 1 areused, the effective overburden pressures, 1 , at eachdepth can be assessed easily. Then, it becomes possibleto determine at each depth the maximum stress ratio, max 1 at each depth, to which the soil elements musthave been subjected during the Niigata earthquake.

Returning to the evaluation of the resistance toliquefaction, it is first necessary to know the relativedensity of the sands. These have been listed in Table 1.Taking advantage of the correlation shown in Fig. 15,the stress ratio, 0 corresponding to a 45% relativedensity is known to be 0.21. Note that this valuerepresents the resistance to liquefaction when 10 cyclesof uniform shear stress are applied to the specimen. Onthe other hand, the resistance to liquefaction when sandswith a 45% relative density are subjected to thetime-history of the Niigata earthquake is known by theordinate corresponding to 1=1.0 as is demonstratedin Fig. 17. Therefore, the resistance to liquefaction atother relative ensities under Niigatas wave forms maybe estimated by correcting the maximum stress ratio inFig. 17 by a factor C DR 0 21. , where C DR is the stressratio at a relative density, Dr , as read off from Fig. 15.For example, if the resistance to liquefaction at a 60%relative density is required, the value corresponding to 1=1.0 must be multiplied by 0.27/0.21=1.28. Inaddition to this, the resistance to liquefaction shown inFig. 17 must be corrected so that it is compatible with the

K 0 -stress condition in the field in accordance with theconcept presented in 3.5. After all these corrections havebeen accomplished, the resistance to liquefaction interms of stress ratios can be established. It should bementioned that the data shown in Fig. 17 not only yieldthe resistance to liquefaction, but more generally, thestress ratios which are required to cause a certainmagnitude of residual pore pressure. The latter stressratio will be called resistance to pre-liquefaction. Then,if the premise is adopted that the corrections asintroduced above are relevant also to the resistance topre-liquefaction, it becomes possible to assess at eachdepth the residual pore pressures which remained afterthe shaking of the Niigata earthquake had ceased.

The maximum stress ratios calculated by theresponse analysis were compared with the resistance toliquefaction and pre-liquefaction as illustrated above,and the results are shown in Fig. 34. The figure showshow the residual pore pressures are distributed withdepth. It can be seen that at depths of between 3.0 to8.0 m, the residual pore pressure is equal to the effectiveoverburden pressure, indicating that liquefaction indeeddevelops at these depths.

6. Concluding RemarksIn the first section of this report, three types of soil

profiles were suggested as being liable to liquefaction.The predictive method of analysis outlined in section 2,based primarily on laboratory test data, is applicable toany of these three soil profiles, if the soil parameters areproperly evaluated and integrated into the analysis.However, field conditions are generally so complicatedthat simple analytical procedures are not adequate.

One of the difficulties in making correct predictionsbased on laboratory test data lies in the fact that the fieldbehavior of sand, as has been inferred from standardpenetration tests, is not necessarily well correlated withthe pore pressure development characteristics of in-situsand deposits. This is clearly. reflected in the results ofthe vibratory pile driving tests outlined in Fig. 30. In this figure the vertical acceleration required to induce porepressures of up to 10% of the effective overburdenpressure is far greater for old natural level deposits thanfor recently reclaimed sand deposits, even though thevalues of the blow count are the same. Therefore, itappears likely that there are some other factors whichcan not be taken into account by mere knowledge ofN-values or relative densities. In view of this, it may benecessary for engineers to direct more efforts towardsfield projects to supplement laboratory information,before the analytical method as proposed here becomestruly reliable as a predictive measure.

References:[1] W. D. L. Finn, D. J. Pickering, and P. L. Bransby, Sand Liquefaction

in Triaxial and Simple Shear Tests, Proc. ASCE, SM.4, Vol.97, pp.639-659, 1971.

[2] H. J. Gibbs and W. G. Holtz, Research on Determining the Density

Ishihara, K.


Fig. 34. Residual pore pressure versus depth (analysis ofthe Niigata Earthquake).

of Sands by Spoon Penetration Testing, Proc. 4th International Conf. on Soil Mech. and Found Engineering, Vol.1, 1957.

[3] K. Ishihara, On the Longitudinal Wave Velocity and Poissons Ratio in Saturated Soils, Proc. 4th Asian Regional Conference on SoilMech. and Foundation Engineering, Vol.1, pp. 197-201, 1971.

[4] K. Ishihara and S.-I. Li, Liquefaction of Saturated Sand in TriaxialTorsion Shear Test, Soils and Foundations, Vol.12, No.3, pp. 19-39,1972.

[5] K. Ishihara and S. Mitsui, Field Measurements of Dynamic PorePressure during Pile Driving, Proc. International Conf. onMicrozonation for Construction, Univ. of Washington, Seattle, Vol.II, pp. 529-544, 1972.

[6] K. Ishihara, Measurements of Dynamic Pore Pressure by PileDriving, Proc. 8th International Conf. on Soil Mech. and Foundation Engineering, Vol.3, Moscow, 1973.

[7] O. Kummeneje and O. Eide, Investigation of Loose Sand Depositsby Blasting, Proc. 5th International Conf. on Soil Mech. andFoundation Engineering, Vol.1, pp. 491-497, 1961.

[8] W. H. Peacock and H. B. Seed, Sand Liquefaction under CyclicLoading Simple Shear Conditions, Proc. ASCE, SM3, Vol.94, pp.689-703, 1968.

[9] S. Prakash and M. K. Gupta, Blast Tests at Tenughat Dam Site,Journal of the Southeast Asian Society of Soil Engineering, Vol.1,No.1, pp. 41-50, 1970.

[10] P. B. Schnabel, J. Lysmer, and H. B. Seed, SHAKE A ComputerProgram for Earthquake Response Analysis of Horizontally LayeredSites, EERC 72-12, University of California, 1973.

[11] H. B. Seed and K. L. Lee, Liquefaction of Saturated Sands underSeismic Loading, Proc. ASCE, SM5, Vol.92, pp. 1199-1218, 1966.

[12] H. B. Seed and I. M. Idriss, Simplified Procedure for EvaluatingSoil Liquefaction Potential, Proc. of ASCE, Vol.97, SM9,pp. 1249-1273, 1971.

[13] K. Tanimoto, Liquefaction of Saturated Sand in LaboratoryExperiments, 16th Japanese Symposium on Soil Engineering, pp.21-26, 1971 (in Japanese).



Name:Kenji Ishihara

Affiliation:Dr. of Engineering, Associate Professor,Department of Civil Engineering, Universityof Tokyo

Address:7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JapanBrief Biographical History:1966- Appointed Associate Professor, University of TokyoMain Works: K. Ishihara and S. Li, Liquefaction of Saturated Sand in Triaxial

Torsion Shear Test, Soils and Foundations, Vol.12, No.2, pp. 19-39,1972.

K. Ishihara and S. Yasuda, Sand Liquefaction Due to IrregularExcitation, Soils and Foundations, Vol.12, No.4, pp. 65-77, 1972.

K. Ishihara and S. Yasuda, Sand Liquefaction under RandomEarthquake Loading Condition, Procedures of the 5th WorldConference on Earthquake Engineering, Rome, Session 1 D, 38, 1973.

K. Ishihara, F. Tatsuoka, and S. Yasuda, Undrained Deformation andLiquefaction of Sand under Cyclic Stresses, Soils and Foundation,Vol.15, No.1, pp. 29-44, 1975.

K. Ishihara and S. Yasuda, Sand Liquefaction in Hollow CylinderTorsion under Irregular Excitation, Soils and Foundations, Vol.15, No.1, pp. 45-59, 1975.

Membership in Learned Society Japan Society of Civil Engineers Japanese Society of Soil Mechanics and Foundation Engineering

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