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Thixotropy and flow properties of fine grained Ackermann, E.

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TRANSLATION TT - 150

THIXOTROPY AND FLOW PROPERTIES OF

FIW GRAINED SOILS (Thixotropie und Fliesseigenschaf ten feinkbrniger Bbden)

3r. Ernst Ackerrnann GLI t t ingen

Reprint from "Geologische ~undschau" VO~.36, 1948.

Translated by

H. A. G. Nathan

This is the Tenth of the Series of Translations Prepared for the Division of Building Research

0ttawa April, 1950 PREFACE

The soils of Canada include a large proportion of fine-grained sediments, the deposition of which was as- sociated with glacial action. Some of these soils have most peculiar properties which have already caused a great deal of trouble in the use of the soils, even indirectly, for engineering purposes. They are, therefore, under detailed study by the Division of Building Research which has been privileged to use the soils exposed in the bed of Steep Rock Lake, Ontario (in iron-mining operations) for this purpose . The somewhat strange phenomenon of thixotropy is one characteristic which has already attracted the at- tention of those working on this problem. The literature dealing with the thixotropic properties of soils is meagre to a degree, but despite this, the work of Dr. Ernst Acker- inann of GBttingen, was known to be outstanding. Dr. Ackermann kindly agreed to the writer's request that his most recent paper in this field might be translated into English by the Council in order to make it more generally available. The Division ig therefore pleased to have been able to arrange for this translation by Mr. Nathan; it looks forward to following up, with Canadian soils, some of the interesting work herein described by Dr. Ackermann.

Robert F. Legget, Director, 9th August, 1950, Division of Building Research. Ottawa. THIXOTROPY AND FLOW PROPERTIES OF

FINE GRAINED SOILS

.;:- ) Thixotropic Phenomena in Laboratory Experiments If is stirred up with approximately an equal amount of water in a test tube and the latter then slowly turned upside down, the clay paste sticks to the bottom of the tube. If, how- ever, the tube in this position is jolted, pushed or shaken by tapping, the clay paste flows down. After a short rest period, the suspension stiffens again so that on turning the tube right- side up the suspension no longer flows. The process may be re- peated as often as desired. Such isothermal, reversible vis- cosity changes of concentrated suspensions of very fine particles

3: ) Presented at the meetin of the fellows of the "Geologische Vereinigung", April, 19 7. (Draft received by the editor, spring, 1947. ) 3;-<:- ) Thixotropy, which was discovered in 1923 by colloido- chemical research of Szegvari and Schaleck (l),up to the present has scarcely been taken into account in soil physics and . Differences in strength between undisturbed and remoulded clays were for the first time described in 1922 by the Geotechnical Commission of the Swedish State Railway (2). In 1937 Hvorslev identified these differences as thixotropic phenomena. In Switzerland certain changes in the properties of freshwater limestones were defined as thixotropic phenomena by R. Kaefeli (3), v. h!oos (4)and R. F. Rutsch (5). In 1945 Ackermann (6a) proved thixotropy of Norwegian clays (known in N3rway as "kvikkleir"). The dependence of their strength on the electrolyte content was shown by I. Th. Rosenquist (7).

fl detailed explanation of the various problems associated with thixotropy is hardly possible within the limited scope of this paper. It was therefore necessary to omit some ex- amples which might have served to clarify the geological aspects of thixotropy to readers not very familiar with the subject. The present report on flow properties and their de- pendence on geologically important factors is based chiefly on the study of postglacial clays in Norway with special reference to their behaviour in the natural state. are caJled thixotropy. The experiment described is a particularly clear example of thixotropy as it was observed when the phenomena was discovered. The tern "thixotropy" has since been extended to include reversible changes in mechanically dis- turbed clay pastes (e)" and moving (9). Thixotropy is a border-line nhenomenon for which as yet there is no satisfactory theoretical explanation. In a thixo- tropic system "solid-liquid", the solid particles do not come into immediate contact since they are surrounded by an envelope of water which separates them. In the state the particles build up a structure which is very loose. In this structure the forces linking the particles are extremely small. Upon the slightest mechanical agitation (jolting, shaking) the structure breaks down (sol state), but after the mechanical ceases it is reformed within a certain time.

Of the numerous factors affecting thixotropy the fol- lowing are listed here: type and concentration of the disperse phase, grain size, grain shape, type of clay minerals and inter- changeable ions, and the electrolyte content.

Thixotro~icPhenomena during Soil Movements in Norwav

The thixotropic change of state "stiff-liquid-stifff1 shown by the test can also be observed in fine-grained soils in the natural state. In the postglacial varved clays which rose above sea level owing to the continental elevation of Scandi- navia, there is an irregular occurrence of . In these clays catastrophic movements of the soil are frequent.

On many occasions the solid wooded ground of a valley or of a has been observed first to wobble and then to burst with frightful noise, with clayey mud pouring out of it and flowing downhill (cf. 10 b, p. 20, 26). Blocks of surface dry-crust with rooted trees float on the pasty quick clay like ice floes on a river and people and houses are carried away for miles (cf. 10 a, p. 5 ff., and 11). Contrary to the obsolete concept of a permanent liquid state of such mud masses, the Geotechnical Commission of the Swedish State Railway (cf. 2, p. 17) found that quick clays have no liquid consistency when the soil is at rest but become liquid as soon as it is in motion. The same observation was made when movements resembling small scale ground ruptures occurred in the Lerkedal railway cutc

Numbers in parentheses refer to bibliography. 2% ) ting near Trondhjem." When the upper layers were dredged out the quick clays, like the sof t-plastic clays, remained stationary. Only when the equilibrium of the masses was too much disturbed by sinking the floor of the cutting to a depth of seven metres did the ground break, the ruptures being confined to a narrow zone of quick clay. On August 21, 194.4, as an indication of the impending first rupture, a cleavage tapering off obliquely towards the upper edge of the youth slope appeared in the 2.5 m. thick dry-crust. R'ithin several hours the cleavage widened by several decimetres. The following day a 28 m. wide section of the slope which had been separated by this cleavage slid down approximately four metres, tilting backwards in the direction opposite to the sliding surface. It then moved approximately nine metres into the cutting. In the upper part of the moving earth block additional gaping cleavages appeared in the dry-crust. The lower parts of the soil consisting of sandy quick clay with low salt content became pasty and poured out in the form of a viscous mud onto the 20 m. wide floor of the cutting at the foot of the slope (soil physical indices, Table I, No. 4 and 7). The dry-crust (approximately 1 1/2 m. thick) of the slope surface ruptured and split into smaller blocks on top of the flowing mud. %hen walked upon the next day, these blocks were pressed into the mud. Flow bulges similar to those of with corded-folded surface formed in some places on the mud surface. These bulges remained in the rapidly forming surface dry-crust of one centimetre thickness. Under this dry-crust the clay was soft, like pudding. When knocked with the sole of the foot the clay became thick-flowing and flowed under its own weight. During a rest period of ap- proximately four weeks it again became strong enough that care- ful and dredging became possible.

l?,%en the equilibrium of the sliding mass had been overly disturbed by dredging a fairly large area of the maFses of discharged quick flay, cleavages of e m. width appeared on December 1, 19&. On the following day within the area of the first ground rupture, another 15 m. wide strip of ground ruptured. 5elow the dry crust, which was tangentially sliced into several tilting blocks, the centre of the marses of the first flow slide became pasty again,, shifting in plastic flow until it reached a point under the base of the and caused the base to bulge up by approximately one metre within a week.

-2 ) on which a report was received through the courtesy of Dr. H. hceixner . At the periphery of the bulged-up masses, cleavages having a width up to 30 centimetres appeared. During this minor movement of the ground the quick clay did n~tpour out on the surface. After another rest period of about four weeks the quick clay had become strong enough that it could be removed without liquefaction occurring.

The Lerkedal quick clays which became liquid first and then solid again are for the most part quite syrupy and differ in this respect from the generally less viscous quick clays of major soil-flow catastrophes. But by means of the soil-physical methods given below it could be proved that the quick clays which become syrupy are also thixotropic a able I, No. 6 and 9).

Im~ortantPro~erties of Norwegian Elue Class

nuring the retreat of the continental glaciation, pul- verized matter carried into the sea by the glacial waters was de- posited in the coastal regions of Norway as an unstratified blue mud. These deposits, referred to as "blue clay", vary in their grain-size distrit,ution between fat clay and fine with low clay content. According to elutriation analyses (cf. Table I) these deposits contain chiefly particles of 2-20 p diameter, and, according to the nomenclature of Correns (12), are thus to be classified as coarse clays or (~ig.2). Particles of diameter C 2/1 were obtained from a sandy coarse clay (No. 76, cf. Fig. 2) at the foot of Raa moraine by elutriation analysis. Photographqof these particles taken with the aid of an electron microscope" show that this fine-clay fraction for the most part consists of particles of 1/5 to 1/20p diameter. Hence even soils with a low percentage of clay-sizes may cpntain a relatively large number of grains of very small diameter. This is significant for the thixotropic behaviour of relatively coarse-grained sedi- ments (fine ).

Mineral content and colour of the blue clays vary with the petrographic composition of their region of origin (13). As the fineness of grain increases the content of feldspar and quartz decreases, while the content of mica and clay-minerals in- crease considerably. Clay-minerals capable of swelling and

$1 through the courtesy of Dr. Helmcke, who used Siemens and AEG apparatus. having a loosely-bound layer-la tice such as that of montmorillo- nite are lacking in blue clay '?. As the S-values established by F Endell (15) show, the bare exchange capacity of sampleq taken near Koss and Oslo is similar to that of the Danish clays (rich in sodium) listed ky ceifert, Ehrenberg et a1 (16). The normal plastic blue claj lies under a surface dry- crust of an average thickness of two to three metres. It contains in addition to ?ore water (from 25 to 75 per cent by weight),a considerable amount of its original and sea salts in solution. In general, blue clay contains 50 per cent water and may be regarded as a suspension. Despite its high water content blue clay usually has a soft-plastic or liquid-plastic consistency (Fig. 3). When kneaded or stirred it loses most of its strength and becomes a viscous, do ~h)paste It tends to plastic flow only when subjected to . In normal tlue clay there is an irregular occurrence of quick clay. If typical quick clay is thoroughly stirred, its strength decreases so ~uchthat it tecomes a thick-flowing paqte, i .e., a ~astewhich flows from an inclined glags tube under its own weight alone Between this quick clay which become- thick- flowing and the normal soft-plastic blue clay there are inter- 3ediate forms such as quick clays which become syrupy. In the latter case, in addition to the force of gravity, mechanical agitatzun is required to make the paste flow, for instance, con- tinuous vitrations (knocking, shakinb) are required for the quick clay to flow or trickle fro the inclined gla~stube-- like viscous syrup. Thlck-flow in& quick clays are widely mown from numerous catastropk es. Howev r, qulck clavs which tend to ue- come syrupy are referred to in Norway as bl8t lelr (soft clay) and are frequently considered "kvikkagtig" ( "apt to flow" i ,e., clays with inherent flow danger). They are not classified as "kvikkleir" (quick clay) although they, too, participate in sol1 flows and their slow movements are an important factor causing daaage to construction

-:: ) Neitk.er Norwegian nor German research succeeded in detecting clay-minerals with loosely-bound layer-lattice in blue clay. Acknowledgment: The X-ray optlcal and colloido-chemical in- vestigations were carried out by Prof. I?'. Correns and Dr. K. Endell. Proof of Thixotropy by Means of the Stiffness Limit In order to obtain an index comparable to the of consistency (17) i.t is advantageous to modify the (~renzv~ert)suggested by H. Winkler (9), i .e., the ratio: volume of liquid to volume of solid. Py neglecting the specific gravity, which is included in the void ratio, the ffstiffeninglimitf1 is obtained (Fig. 3). The stiffening limit gives in per cent by weight the water content at which, after a stiffening time of exactly one minute, a thoroughly stirred, fine grained, thixo- tropic soil still flows under its own weight in a tube of 11 mm. diameter ( cf . p. 17 and 18 ) . The following method ("inverted tute method") is used to determine the stiffening limit. After determination of the water content, wet clay (if possible in the natural-wet state) containing 1 gm. dry substance is mixed drop by drop with dis- tilled water in a test-tube ot 11 (to 15) mm. inner diameter. The size of the drops is measured ~itha pipette. At the termination of the test the total water content is checked by weighing. This is necessary if a calibrated pipette of 1 cc. capacity is not available. Such a pipette is of course useful since the amount of water added can be read directly in cc. After the first drop has been added the natural-wet clay is carefully stirred with a glass rod of 2 mm. thickness for at least 20 minutes and after each ad- ditional drop for ten minutes. Tlje stirred clay-water mixture is left to rest without the rod " . After exactly one minute the tube is rapidly turned upside down in order to determine whether the paste flows down the tube walls under its own weight. This flow test is repeated every time a drop is added, the paste stirred and the setting time of one minute observed. When the paste begins to flow the stiffening limit has just been exceeded. The water content (minus the last drop) at which the stirred clay is just on the verge of flowing after exactly one minute's rest and is liquid when stirred is the stiffening limit. The water content thus determined is checked in each case by two additional tests.

LOW stiffening limits (in most cases 30 to 60 per cent) indicate weak thixotropy and high limits (mostly over 100 per cent)

-::-) The experimental method suggested here differs from that re- comnended in the first German version and approximates the method given by P. G. H. Boswell. (35). a high degree of thixotropy. At high stiffening limits the changes in thixotropic properties are more distinctly pronounced and shorter stiffening times may be expected. The factors which bring about consolidation are uniformly distributed in the whole system (18). Therefore, the void ratio, and thus the stiffening limit is not changed by the quantity of the sample or its height in the test tube.

The stiffening limits are comparative figures for esti- matin& the thi~ot~ropicproperties of' fine-grained soils and apply only to small samples. ';"he? these values are evaluated it must be remembered that a soil which is apt to flow and which has the water content of the stiffening limit stiffens under the weight of the quantity chosen here, but still flows under the larger weight, e .g. a sanple stiffening in a preserving jar. \'!hen subjected to increased shearing stresses the quick soil has a relatively lower viscosity. Therefore the water content of the stiffening limit cannot be used as a constant value for estimating the behaviour of large :nasses of soil.

The stiffening limit could be used as a means to prove that the glacial blue clays and quick clays occurring in Norway (i.e., from fat clay to fine sand with low clay content) are thixotropic (cf. Table I).

A method is given below for measuring the changes in viscosity and strength occurring when thixotropic soils are disturbed and then left to settle. This method may also be used to prove thixotropy (p.14. ) . Dependence of Thixotropic Phenomena on the Ip!ater Content

The "natural water content" as the criterion of the con- centration of the disperse phase greatly affects the flow pro- perties of natural soils. In addition to the content of electro- lyte, organic substance, etc., it determines the consistency as defined by Atterberg (17). To Atterberg' s states of consistency another state must be added, namely that produced by the change in consistency of quick clays o'cserved in laboratory experiments as as in nature.

If the water content of a clay is higher than the liquid limit "1 then the clay is not in a permanent-liquid state , but in

+:-) The liquid limit is the water content at which a sample of 8 rnm. height flows together along a 2 mm. wide groove in Casagrande's apparatus for a distance of 13 mm. when subjected to 25 blows. a latent-liquid or quasi-solid state, i.e., the clay can tem- porarily become liquid. The liquid state caused by vibrations or stirring is replaced by a quasi-solid state after a certain rest period or time of stiffening. The behaviour of the clay is thixotropic or "quick" (6b). Hence between the permanent-plastic and permanent-liquid consistencies defined by Atterberg there is the quick consistency, i.e., a quasi-solid state with possible temporary liquefaction by mere mechanical action (Fig. 3). The duration of thixotropic liquefaction and the minimum viscosity depend on the degree of thixotropy. The "stiffening limit" is suggested as the boundary be- tween quick and liquid consistencies. Hence the negative values of the coefficient of flow danger, f, give the "quick consistency" of a soil in the natural state or its "tendency to flow":

f= liquid limit minus water content stiffening limit minus liquid limit The negative values of the consistency factors introduced by Scheidig (20) may also be used if suitable. Since the liquefaction of quick soils depends on the supply of a certain amount of energy, soils in declivities having quick consistency may for a long time have an apparent stabili ty until the whole mass of soil suddenly becomes temporarily liquid through vibrations, overload, excessive pressure in the pore water or other disturbances. If the water content increases beyond the stiffening limit, the time of stiffening is extended. These thixotropic vis- cosity changes also occur when pasty-liquid mud is disturbed. C,%ere the state of liquid consistency should begin is yet to be settled.

Relationship between Flow Properties of Norwegian Blue Clays and Content of Clay Sizes and Water

In natural soils thixotropy is confined to fine-grained soils. When the structure of non-consolidated, loose-packed, moist soils is disturbed, thixotropy becomes evident by partially re- versible viscosity changes, irrespective of the consistency of the soil (plastic, quick or liquid). Therefore a distinction must be made between quick or thixotropic consistency and thixotropic pro- perties, or between "ability to f low" and "aptness to f low". The two terms suggested here cannot be confined to thixotropic soils alone, since, as will be shown below, danger of flow a190 occurs in non- thixotropic soils. Soils apt to flow (f'f3iessgef~hrlich")are those which, at the waber content of the natural state, may become liquid if there are possibilities of flowing away. Soils able to flow ("fliesstauglichr') may become apt to flow upon absorption of sufficient water or decrease in electrolyte content.

Assuming that the thixotropic behaviour is a function of grain size and grain-size distribution, disregarding for the time being the effect of electrolyte content and taking the Norwegian quick clays (for which a content of homogeneous clay minerals may be assumed as a rule) as an example, then it follows from the stif- fening limit (cf. Table I) that the degree of thixotropy increases as the clay content increases. This was proved for mineral powders by Winkler in 1938 (cf. 9). The dependence of other soil-physical properties on the colloidal content was pointed out by Zndell, Loos et al. (15). Fat clay with a high content of clay-sizes must ab- sorb a great deal of water before it can liquefy. Its liquid limit is in the case of Norwegian clays generally above 40 per cent. Fat clay has an average to high degree of thixotropy (stif- fening limit above 65), whereas a lean coarse clay (), which has approximately the same electrolyte content and contains the same clay minerals, can absorb but little water on account of its low content of clay sizes. It kegins to become syrupy at water contents as low as 20 per cent and its stiffening limit (lower than 100) indicates weak thixotropy. If the examples shown in Figure 4 are compared at a water content of 20 per cent it can be seen that the fine clay is solid, the coarse clay plastic and the clayey fine sand liquid. The latter has the greatest tendency and ability to flow. The ability to flow is inversely proportional to the thixotropy . Because of its high deg,ree of thixotropy, a fine clay -- with an optimum content of water and electrolyte required for the thixotropic liquefaction -- may become more highly liquid and thus more apt to flow than a coarse clay. The criterion for the danger of flow is the degree of viscosity in the liquid state (El value of the Swedish cone tests). The criterion for the ability to flow is the minimum water content at which liquefaction of a soil can occur. Casagrande (21a) defined this by the liquid limit. This, viz. the minimum water content, is lower for and clayey fine sand than for clay and even-grained fine sand containing no clay.

The ability to flow increases as the clay content in- creases. Accordingly a more frequent occurrence of the danger of flow must be expected for coarse clays, and clayey fine sands on account of their grain-size distribution and their low water- absorption capacity (Fig. s). Flow Properties of Sandy Soils As can be seen from Table I (No. 14, 17, 20) the thixo- tropic ability to flow also extends to cohesive soils composed preponderantly of sand and can be found even in fine sands con- taining coarse clay with few clay-sizes (i.e., a few per cent,cf. Table I No. 2, 3). In conformity with this, Freundlich and Juliuskurger (22) proved distinct thixotropy for the from Knott End, Fleetwood. This quicksand contained only 2.1 per cent clay. The of Derenturg which, according to H. Jung, contains approximately 3 per cent montrnorillonite also hap- pens to be thixotropic. However, aince sands usually show pronounced dilatancy;$) and the diameter of their grains is above the limit (of Sp ) up to which Brownian movements are still marked. The observed thixotropy seems surprising. According to Freundlich (8) ad- ditions of small quantities (approximately 2 to 4 per cent) of a which promotes thixotropy are surf icient to enveiop~ the larger particles so that the loose packing required for the thixotropy is created. Loose packing, as it is characterized by a high exceeding the "critical porosity" of Casagrande (23) , was recognized as early as 1925 by v. Terzaghi (24) as one of the indispensatle conditions for the occurrence of quicksand phenomena, especially of flovr slides due to settlement. According to R. Clos- sop and A. Yi. Skempton (25'), v. Terzaghi assumes a honeycomb structure similar to that assumed by Casagrande (21b) for clays. A. Zucken (26) assumed a similar structure for thixotropic sus- pensions, thoueh in a somewhat different way. The type of structure is controversial. However, since the large particles are enveloped by the smaller ones it is safe to assume that the physico-chemical properties of the larger particles are replaced by those of the small particles with marked effect on the boundary areas.

The few available investigations show that not all the flowing or similar sands ( "Trieb-, Flies s-oder Schwimmsandet' ) hitherto designated as are thixotropic. The aptness

------<:-) Dilatancy or Osborne Heynoldts phenomenon (contorted dilation in the sense of Sander) is associated with close packing. When being walked upon, wet sea sand becomes dry since the grains are displaced to a loose packing. When the pressure ceases the grains revert to their close packing and the sand becomes wet again. of such sands to flow depends on factors other than those making thixotropy possible. These unknown factors (perhaps uniform grain size, mica content) have yet to be discovered. It is sug- gested, therefore, that the term quicksand be Confined to clearly thixotropic sands. Non-thixotropic sands which are apt to flow should be classified according to the causes of this aptness, for example as "drift sands" (''Triebsande") in the case of evident flow pressure and as "floating sands'' ("Schwimrnsande" ) if the water content is high. In such sands the packing is sufficiently loose to create a tendency to flow. However, the true thixotropic strength cycle, which depends on constant water content, is not possible. Danger of flow -- or tendency to flow -- is a charac- teristic not only of thixotropic soils but also of loosely packed soils which.upon disturbance of their structure become liquid by a spontaneous decline in strength and must yield water and re- vert to close packing in order ta become solid again.

For many "floating sands", and also in the case of coarser soils which are apt to flow (such as slide rock, material of mud flow, etc.), loose packing in addition to saturation with water is, according to v. Terzaghi (21!), the condition for the spontaneous settlement initiating the flow process. Loose pack- ing is characterized by high , which, according to Langer (27) amount to xore than 47 per cent in the floating sands of Ypres. This is a very high value as compared with that for the low porosities of the clayey quicksands given in Table I (No. 2). As mentioned above, the thixotropic ability to flow of the sandy quick clays increases with decreasing content of clay- sizes and the resulting coarsening of grain as well as the dimi- nished water-absorption capacity. On the other hand, as was shown by v. Terzaghi (28), the mobility of coarser soils decreases as the grain size increases. At the same time the permeability increases so that coarse sands can give off pore water more rapid- ly, thereby shortening the states of liquefaction and resolidi- fication. In sandy soils the ability to flow thus increases as ths coarseness of grain increases and the uniformity of grain size decreases. Hence a maximum abilitg to flow results for the fine sands, especially for the clayey ones (Fig. 5'). It thus becomes evident why quicksands are generally known, whereas quick clays, with a few exceptions, have remained unknown or for theoretical reasons have not been suspected as such owing to the cohesive forces acting in them (h. Glossop and A. In]. Skempton, 1941, p. 21). Silts which are apt to flow and have other proper- ties than those of the Norwegian clays have been described by R. F. Legget, Canada (29). The threshold value of the ability to flow for coarse clays and fine sands has a parallel phenomenon in the soils of similar grain-size distribution which A. Casagrande found to t-e particularly apt to freeze. Presumably certain properties im- portant for both phenomena, such as lcose packing and permea- bility, are particularly pronounced in these soils. In the sense of such close relationships the crescent- shaped shelling of frozen soils (like shelling of sods) occurring in Norwegian blue- clay deposits is observed with remarkable frequency in the regions having a tendency to land slides.

Influence of the Electrolyte Content on the Tendency of Norwegian Blue Clays to Flow

In certain thixotropic systems, e .g. clayey soils, the electrolyte content affects the thixotropy . For a given amount of electrolyte the degree of thixotropy increases as the degree of fineness of the grain increases (9). Even a very slight in- crease of a weak electrolyte concentration is sufficient to in- crease the thixotropy. On checking the changes in strength Rosenquist ('0found that a threshold value resulted at a 3 per cent addition of NaC1, i.e., at a concentration which, strangely enough, corresponds to the salt content of sea water. Ty adding sodium chloride Rosenquist succeeded in increasing the strength of quick clays so that they lost their tendency to flow. But they- reverted to the latter state as soon as the salt content was removed by electrodialysis. These experiments confirmed G. Holmson's assumption that the tendency to flow inherent in cer- tain Norwegian quick clays can be attributed to their relative deficiency in salt (lob) . Sirr.ilarly, when H. Xeixner chemically examined pore waters, which had been pumped in the Lerkedal by means of L. Casagrande's nethod of electric drainage (30) a zone of minimum salt content was found in the region of the rr'oving quick clays. In agreement with these findings a quick clay from .Moss was found to have a lovier base exchange capacity than that of a blue clay from Oslo.

Viith respect to the origin of the Norwegian quick clays it is evident from their liquid limits, which according to Table I are lower than 56 per cent, that during their deposition the blue clays with the considerably higher moisture contents of newly formed auds had at first liquid or quick consistency. Even after the loss of water due to synaeresis the quick consistency remained constant in the layers near the surface (31). 9wing to the pres- sure of overlying strata the beginning of diagenesis caused a closer packing with a decrease of pore and moisture contents: the blue clay obtained plastic consistency. As the diagenesis progresses the latter state has been undergoing various local changes in recent times. A dry-crust of solid consistency is forming at the surface of blue clays raised above the sea level (Fig. 6, 1). Under bogs the blue clay is being infiltrated by humic acid and this, together with the re- sulting jncrease in water content, is causing a deterioration of its consistency. According to Rosenquist (7) the salt content of blue clay near base or embedded layers of can be leached out by the effect of subterranean waters flowing in the gravel. As a matter of fact quick clays formed by such leach- ing processes are frequently encountered on top of base layers of gravel (~ig.6). However, to what extent factors other than the leach- ing process (as a secondary cause of the tendency to flow) con- tribute to the formation of Norwegian quick clays is not yet known. As the electrolyte concentration decreases the intensity of the forces acting between the particles changes, while the distance between the particles and the water content remain un- , changed. The invariable water envelopes cannot be equally ab- sorbed by the weakened ion envelopes: "excess water", as described by Rosenquist (7), is formed. Thus, if the water content is constant, a plastic clay can become a quick clay because of decreasing electrolyte concentration. Deposition Strength and Thixotropic Changes in Strength In 1937 Hvorslev (19) investigated samples of soil in the remoulded state with respect to the thixotropic regain in strength. The values obtained by determination of the Casagrande flow curves and from the Swedish cone tests (2) were found to be at variance. The latter method, however, is especially suited to comparative investigations of soil in the undisturbed natural state of deposition and of their changes in strength in the re- moulded state . It is a known fact that on being kneaded plastic clays become softer and quick clays liquid. Although in plastic clays the decrease in strength is considerable they remain plastic. In quick clays, however, the loss of strength is greater. It is so extensive that the (quasi-) solid consistency even changes to the (temporarily) liquid one. With the indices used in the Swedish cone tests the loss of strength is expressed by the following ratio: Hj (relative strength in the undisturbed state) H; (relative strength in the remoulded state) The ratio H3/:11 generally results in valuer lower than 50 for plastic blue clays and in values between 50 and 300 for qurick clays. Hence in quick clays the viscosity diminishes in the liq;id state to a-mere fraction ( 1 to -1 ) of the initial de- F m position strength. The extreme losses of- strength are confined to highly thixotropic quick clays having a great amount of excess water. In the undisturbed state of deposition clays have a "deposition strength", H3, which is relatively high, even for quick clays. By stirring or other mechanical disturbance of the structure the strength suddenly decreases to the strength in the remoulded state, 31. Immediately after the stirring ceases the strength increases again. During the thixotropic stiffening it increases at a decreasing rate and gradually approaches a "thixo- tropic final strength", Ht. In Norwegian clays this strength (H ) is generally obtained after four weeks when it is nearly as greak as the strength after a rest period of one year (32). Compared with the quick clays, plastic clays lose a smaller part of the de- position strength by the first disturbance of the structure and regain a larger ?art of the lost strength by the thixotropic stiffening. As Eaugls tests show, the thixotropic final strength Ht is related to the viscosity in the remoulded state and can be estimated from it with good approximation.

If stiffened quick clay is repeatedly liquified, the strength tends in each case towards the thixotropic final value. Hence, the thixotropic strength cycle is closed not upon the first liquefaction but only after repeated liquefactions. The original, higher deposition stren~this presumably due to an increase in the adhesion forces during the long time elapsed since the de- position of the quick clay. For the natural soils the concept of "reversible" thixotropic viscosity change must be modified so that the trend caused by the stiffening is not the deposition strength but merely the considerably lower thixotropic final strength.

The changes in strength of natural soils show es- sentially the same behaviour for plastic and thixotropic con- sistencies. The change of state, stiff-liquid-stiff, which is characteristic of quick soils has tieen modified to a less marlred change in strength for the plastic range. However, by the sub- sequent increase in strength the modified change also proves to be a thixotropic phenomenon. As is now generally known, plastic soils lose their strength when they are disturbed. This was first shown by A. Casagrande. This loss in strength is also a thixotropic phenomenon. Quick Soils., Soils with Inherent Flow Tendency and Flowing Soils

Too little is known about the various factors which de- termine the tendency to flow of fine-grained soils as far as their interrelationships are concerned. It would be useful for future investigations to define clearly the concepts and terms used in this field. It is therefore suggested that the term "apt to flow" should k,e employed only as a general term and that the prefix "quick" should be reserved for soils which, with the water content of the natural state, evidently have quick or thixotropic con- sistency.

Quick soils in this sense are fine-grained soils which, in the natural state, when subjected to mechanical disturbance of their structure only - without any change in their water con- tent - show the thixotroplc changes of state (stiff-liquid-stiff) , and which, in the liquid state, or during the tine of mechanical action, flow under their own weight. Quick soils are latent- liquid suspensions which retain their inherent flow tendency after every resolidification.

On the other hand, non-thixotropic sandy soils with an inherent tendency to flow must yield water after their lique- faction in order to become solid again. In this process they lose their aptness to flow and in order to regain it they require an additional supply of water.

Coarse sands can flow only under certain conditions, e .g., as long as their grains are being stirred up by flow pressure. Generally they are not classed as soils which are capable of flowing.

Flowing soils are soils which assume semisolid or syrupy consistency only after their water content has been increased by glacial waters, rains or similar waters. They lose this con- sistency only by yielding water by evaporation or similar pro- cesse s. lfrl th sufficiently large water content they f low under their own weight without mechanical action.

Since in loams and fine sands thixotropy is developed only slightly or not at all, the range of the quick consistency of such soils - sim lar to that of the plastic consistency is only small numerically. "f With the slightest increase in water content

Plasticity iqdices (liquid limit minus plastic limit) between 5 and 11 and thixotropy indices (stiffening limit minus liquid limit) between 6 and approximately 20. t3ese soils change from solid or1 plastic consiscency to liquid consistency -- some of them directly. They do not have the dangerous intermedia Le state of "apparent stability1' of the quasi- solid quick s&s. Accading to E. Hamann (33) tl-e extreme tendency of such soils to flow (these soils are frequent in periglacial de- posits) is promoted ty formation in waters with low electrolyte content. This tendency is most frequently observed in fine- grained soils which are particularly capable of flowing, such as loam?, "floating sands" ("F'lo ttsand" ) , the (Scandinavian) "mol' (0.2-0.002 ma.) and other fine sands. In saturated flowing soils the liquid consistency is associated with water content increases, which frequently exceed 100 per cent and thus are considerably higher t'lan t5e water contents of quick soils.

The term thixotropy refers to isothermal, reversible viscosity changes in concentrated suspensions of very fine par- ticles caused solely by mechanical action. In order to introduce the phenonenon of thixotropy into geology it was first of all necessary to consider the differences between the phenomenon as it is known from laboratory experiments and as it occurs in dif- ferent natural soils. An attempt was made to clarify the essential factors and terms so as to provide a basis for detailed study of the subject.

By comparative tests it is shown that the particularly striking thisrotropic consistencj changes ttstiff-liquid-stiff", which have been known in colloid chemistry since 1923, also o\:cur in nature -- often with catastrophic results -- during the flow slides of Norwegian quick clays. Cy nieans of new soil- physical indices the thixotropic property is detsrmined for all the Norwegian blue clays, irrespective of their consistency and grain-size distribution. Of the factors affecting thixotropy the following are described with respect to ability to flov~,inherent tendency to flow and strength of natural soil: water, clay-size and electrolyte contents.

I.Zarls and other soils with high content of lime or or- ganic matter are not dealt with in this paper. 1':hen the water content of cohesive soils increases there is an intermediate state tetween the permanent-~lastic and perma- nent-liquid consistencies as defined by Atterberg (1'1). This is the "quick consistency" which characterizes a quasi-solid state with possible temporary liquefaction by mechanical action only (Fig. 3). Its lower and upper limits are the liquid and stiffening limits respectively, The quick consistency of a soil deposit in the natural state is given by the coefficient of flow danger "fv (cf, Table I), The thixotropy decreases as the clay-size content de- creases, The opposite is true for the ability to flow which reaches its optim in fine sands containing but few clay-sizes, These can still be slightly thixotropic, ioe., they are true quick soils which upon the slightest mechanical action can be liquefied as many times as desired without any further water supply. During the subsequent thixotropic stiffening they will become solid again without yielding water, Such fine sands are related to the well- known flowing sands or similar sands (*~chwimm-, Trieb oder Flies- sande") and other non-thixotropic coarse-grained soils, which have been described here as having an inherent tendency to flow, The latter are loose-packed soils which must yie-ld water during the flow process in order to become solid again. Then they are no longer apt to flow and require an additional supply of water in order to revert to the liquid state, The thixotropy of Norwegian blue clays decreases as the electrolyte content decreases, while the ability to flow or. the degree of flow danger increases. Accor'ding to Roqenquist at least some of the Norwegain quick clays which are poor in salt have developed secondarily from plast,Tc clays by leaching processeso Thixotropic sediments in the undisturbed state have as- sumed a relatively high "deposition strength", because of their great geological age, If the original deposition structure is dis- turbed the deposition strength is only partly restored during the subsequent thixotropic stiffening, Therefore the concept of com- plete reversibility of strength which holds for artificial thf xo- tropic suspensions must be modified for natural thlxotropic systems so that the thixotropic cycle of strength is complete only after repeated liquefaction and stiffening. -2) BIBLIOGRAPHY

1. Szegvari, A. and Schaleck, E. ~berEisenoxyd-gallerten. Kolloid-Ze 32, po318, Leipzig, 1923

2, Statens Jarnvagars Geotekniska Kommlssion 1914-22: Slutbetgnkande , Stockholm, 1922. 3, Haefeli, R, Die mechanischen Eigenschaften von Locker- gesteinen, Schweiz, Bau-2, 111 ~0.24and 26, 1938. 4. v, Moos, A, Unverfestigte Sedimente und Erdbaumechanik. Geol0 Rundschau 29, 1938,

Ll so v, Moos, A. and Rutsch, Ro F, Uber einen durch ~efflge- sthung verursachten Seeufereinbrucb (Gerzensee, Kt. Bern,) Eclogae Geol, Helveto 37, Noo 2, 19&, Basel, 1945. 6, Ackermann, E, a) Norwegi scher Schwirnmton und seine bodenphysikali sche Kennzeichnung. Wehrgeologischer Erfahrungsaustausch beim Inspekteur der Landesbefestigung Nord, Oslo, January, 1945, b) Die quicke Konsistenzform, In print, l9SO, 7, Rosenquist, Ivan, Th., Om leires Kvikkagtighet. Statens Vegvesen, Veglaboratoriet Mead, 4, Oslo, 1946, 8, Freundlich, a, Thixotropie, Paris, 1935- 9, Winkler, H, Thixotropie von b~ineralpulvern'mikrosko- pischer Grdsse, Kolloid-Beihefte 48, Leipzig, 1938,

s, ) Note added during publication: In JU~1948 the following paper was published in Science Progress 3g , 1b3, London: *The thixotropy of certain sedimentary rocksH, In the above paper Boswell suggested that the thixotropic properties of sediments be determined in the natural-moist state and that a method be evolved for soil-physical characterization of the thixo- tropic consistency, Both suggestions had already been adopted by the author when he presented this paper on April 27, 1947, However, owing to conditions prevailing in Germany the publication of this paper was delayedo Holmson, Go a) Lerfaldene ved Kokstad, Gretnes og Braa, Norges Geol. Unders, Noo 132, Oslq 1929. b) Lerfall i drene 1930-320 Norges Geole Underso No. 140, Oslo, 1934. Reusch, Ha Nogle optegnelser fra Vaerdalen. Norges Geolo Unders, Noo 32, Aarbok for 1900, (~ristiania)Oslo, 1901. Barth, ToWoFo, Correns, C.W. and Eskola, Po Die Entstehung der Gesteine , Berlin, 1939, Goldschmidt, VoMa Undersbkelser over Lersedimenter, Nordisk Jordbrugsforskning, No0 1, Oslo, 1~6.

Brudahl, Ho Hydroglimmer (~ydrousmica,Glimmerton), Meddo fra Vegdirektaren, NO. 3, Oslo, 1942~ Endell, KO, Loos, Wo, Meischeider, H. and Berg, V. Uber ~usarnmenhflnge zwischen Wasserhaushalt der Tonminerale und bodenphysikali schen Eigenschaften. bindiger B8den. Ver8ff d, Inst, do dtsch. Forsch,-Geso f'. Bodenmechanik aodoTbHo Berlin Noo 5, Berlin, 1935. Seifert, R., Ehrenberg, J., Tiedemann, B,, Endell, K., Hoffmann, KOD and Wilm, Do Bestehen ZusammenhHnge zwischen Rutschneigung und Chemie von Tonbbden !- !ditto do Preuss, Geolo Versuchs, - Anst. f0Wasserbau und Schiffsbau No. .20, Berlf n, 1935, Atterberg, A. Die Konsistenz und Bindigheit der Bbden, Into Mitto Bod0 1912, Volo II, Noo 2 and 3. Winkler, Ho ijber die Thixotropie des Montmorillonit so Kolloid-Zo 105, No, 1, Leipzig, 1943.

Hvorslev, Mo Juul. her die Festigheitseigenschaften gestarter bindiger BBden, ~ngenibrvidenskabeligeSkrif ter Ao No. 45, Copenhagen, 1937,

~dgler,Fo and Scheidig, Ao Baugrund und Bauwerk. Berlin, first edition, 1938, third edition, 1941. a) Research on the Atterberg Pfmits of soils, Public 13, Noo 8, 1932, b) The structure of clay and its importance fn Foundation Engineeringo Journal of the Boston Society of Civil Engineers 19, No, 4, 1932, 22, Freundlfch, Ho and Julfusburger, F, - Quf cksand as a thixo- tropic system, Tpansaetl.ons of the Faraday Society 31, po 76q0 Edfnburgh, 1935. 23, Casag~ande,A, Characteri sties of cohesionless soils af- fecting the stability of slopes and earth fills, Journal of the Boston Society of Civil Engineers 23, Noo 1, 1936,

24, v, Terzaghf , Ko Erdbaumechanik auf bodenphysi kalischer Grundlage, Leipzfg, 1925 25, Glossop, Ro and Skempton, AoWo Particle-size fn silts and sands, Journal of the Inst. of Civil dngineers, Paper

5492, London9 1945 0 26, Eucken, A. Lehrbuch der chemischen Physfk, Leipzig, 194.4, 27, Langer, C, Quelques caracteristiques des sables boulants. Comptes Rendus, Lab, Bat, Travaux Publics, Paris, 1938, 28, Redlich, K,A,, vo Terzaghi, KO and Kampe, Ho Ingenfeur- geologie , Wien, 1929

29, Legget, R,F, and Peckover, Fo Lionelo Notes on some Canadian "sfltsflo Proc, 2nd Into Conf, of and Foundation Engineering, 1948, 30, Casag~ande,Lo Dfe elektrische Entwflsserung feinkbrniger B8den. Df e Strasse Noo 19 and 20, Be~lfn,1941, 31, Xhgst,, Ho Zur geologischen Bedeutung der Syndirese, Geol, Rundschau 25, p, 312-325, 1934. 32, Haug, Sc, Svevende trepelers baereevne i Laire, bdd fra Norgea Statsbaner Nr, 2, Oslo, 1940, 33. Ramann, E. Die Sinwirkung elektrolytarmer Wdsger auf diluviale und alluviale Ablagerungen un2 Edden. Z. dtsch. geol. Ges. 67, p. 275, 1915. 34. v. Terzaghi, I:. Festigkeitseigenschaften der Sedi~ente, Schl!ttungen und Gele . In Auerbach und Hort : Handbuch der physikalischen u. techn. Kechanik, Vol. IV, p. 2, 1931.

35. B~.>swell,P. G. H. A preliminary examination of the thixo- tropy of some sedimentary rocks. Quart. Jour. Geol. Soc. of London. vol. 104, pp. 499-526. July 12th, 1949. (In this translation the research of Boswell (35) could not be re- ferred to). Soil Physical Indices for Norwegian Blue C1m --- - .- Coefficient of rd Coarse -- Fine Stiffness Plasticity Liquid Natural limit index limlt rater content 'low -.-- P-* . ---. E P F w f' E-Y - - -. ------Ra 04 11 -- quick sand cont. coarse clay - 37 26.6 33.1 - K1 04 4 I I II I, 1 29 60 10 1 x 42.3 22.4 La Sb 14 quick sand with coarse clay 15 47 35 3 x 66 11.6 25.0 30.4 Le 79 9 lean quick clay 29 9.1 23.1 29.1 K1 04 5 quick clay with fine sand x 35 7.9 19.6 29.5 Le marginal zone liquid-plastic coarse clay 1 11 58 30 35 9 27.8 27.7 cont. fine sand Le external llxit quick clay cont. fine sand 12 52 36 37.3 8 24.0 34. 5 La S4 9 lean quick clay x 43.4 8.4 25.1 26 Le 79 5 "." 45.4 9.3 24.2 25.0 10 T 905 * La Sb 12 vcry soft plastic coarse clay 13 29 47 11 x LR.3 10.9 S.'b 25. 5 rith fine sand 11 551 K Ra 04 10 lean quick clay 48.7 14.0 32.1 36.4 La S4 lean liquid-plastic coarse clay Ra 04 " " ,I I I1 1 quick clay with fine sand K1 08 lean quick clay Ra 04 fat quick clay La S4 quick clay with fine sand La 52 fat plastic coarse clay cont. fine sand La S4 medium fat nlastic coarse clay cont. r,a. La S4 lean liquid-plastic coarae clay rith f.s. Ra 04 fat quick clay a 69c leau quick clay wit11 fine sand K 5 quick clay witn f.s.& orgauic xtter a 33 fat quick clay cont. fine ad R 698 medim fat quick clay cont. fine sd Le 43.2 lean soft-plastic coarse clay Ra 04 very fat quick clay OY 8 med. fat liquid-nlastic coarse c1.W K 5 fat quick clay with fine sand R Tr fat auick clay cont. fine sand Le 80 medi;. fat, lihuib-nlastic coarse clay K 5 very fut auick clay with fine md K 5 n 3, I. I, n n n La S4 far soft-slrrstic coarse clay Le 90 medium fat soft-plastic coarse clay J1 5 lean quick clay cont. fine sand Ra 04 medium fut quick clay Le 43C sedium fat quick clay cont. fine sand Ra 01 fat soft-plastic coarse clay HO SCh fac,very soft-olascic fine clay Ht 258 .xed. fat,liquid-ulastic coarse clay cont. f.s. Ht 05 I, I, n " I, . Ra 04 medium fat quick clay OY 8 fat,soft-olastic,fine clay Le 80 fat olastic blue clay OY 8 ve y fat,very soft nldstic fine elay OY 8 very Cat,very soft-nlastic fine clay cont. f.s.

Abbreviations: x = stifrenine limit obtalned from clays previously dried. T = mean values within the range of distribution of the indices.

I Tte numerical values for the liiuid limits listed in this table were obtained froa tests with tubes of only 8 mm. diameter, and the stirring rod was left in the test tube durin? the rest period. Thls arrangement departs from that ~ugge~tedon page b: PAGL '23

SLCTlONS THROUGH THE, FLOW SLlVLS IN THL 9A1LIvAY CUTTING AT LLP,yEVAL

------

------

-% 4 - - / - aecum&/3 2, 19 #+ L .EG&A/L' C ---- SU~FACL oJ T'HL CUTTIN& aefoqr AUGUST 22, /y+P

*..*..-. SLJAFACE et 7H& CUTTING B.EfOA& PECEMBE.4 2, 1944 - SUAFACL .f TH& CUJJINL AFJE~IHL ~OIVSL/PES. PAY - CRUST, SOL/o. 1-1 BLUE CLAY, SOFT-PLASTIC. 1- 1- qU/cb( CLAY. 0 5 10 -I-- FIGURE 2

GRAIN - SIZ L VISTRI BUTION of NOP,\VLGlAN BLUL CLAYS

IFINL CLAYI COA~CL CLAY roo

80

BANU5 SHO\VING FRLQUELNT BLUL CLAYS - F4T BLC/& CLAYS. AVLqALE BLUL CLAYS.

??:.i LEAN &fU& CLAYS.

LINES SYOfVING EXANfPLLS QUOTLD.

--- GUlCy CLAY fqOM THE L&GY&PAL (NO. 9f7/2) qU/Cy CLAY fqOM JHL LAW SL/Pfi- AJ LAPL(A/o. 805 a) STATLS f CONSISTLNCY LIMITS f CONSISTENCY V IAG-AM CONSlSTLNCY 4 DLPENVLNCL of THE. FIGURE THIXOTROPY of NOQ\VtGlAN QUICK SOILS ANV THE.lR ABILITY TO FLOW ON THL CLAY-SIZL CONTENT. FINE- CLAY 0 F ASLqUM

I FINLSANV COAqStCLAY

i.(LElVSTqANV LESYLVAL

----

AB/L/Jy TO ~LOIV

L PAGE 27

APPENDIX

Detsrmination of the Void Ratio and Stiffening Limit (~rrnittlungdes Grenzwertes und der Erstarrungsgrenze) ''~ccordingto H.G.F. Winkler (193c) the void ratio (~renzwert)is a measure for the degree of thixotropy. The void ratio ~ivesthe amount of liquid (~ncc.) which the unit of volume (i.e., 1 cc. ) of a certain substance is just able to retain 4. that after one minute the system is thixotropically stiffened. If the void ratio is small only a ,mall amount of liquid can be r: - tained; hence the degree of thixotropy is low. According1 , at a large void ratio a correspondin~lylarge amount of liquid is re- tained. hence a substance, whlch in strong dilution still ex- hibits the phenomenon of sol-gel transformation, has a high degree of thlxotropy ." Void ratio. N = vol subst.

= vol. of liq. cc. x specific gravity of soil amount of solid substance in gm.

The stiffening limit gives the water content, in wer cent by weight (dry welcht), at which after exactly one minute a thoroughly stirred soil stiffens in a test tube of 11 rnm. diameter. A low stiffening lir~itindicates ci soil for which a low water coq- tent is sufficient to obtain the state of thixotropic flow. Y!ith a high stiffening limit a soil c

Pur~oseof Investigation

i) Compariso1.1 of thixotropic substances by an experi- ment with co~stanttime of stiffening and variaole concentration. he limit concentration can be determined with 3 to 5 per cent accuracy.) ii) To obtain an estimate of the water-absorption capacity, the danger of flow, the time of stiffening and the se- condary strength of quick soils.

A fine scale, a drying oven, an exsiccator, three test tu'ies of 11 rnm. inner diameter, a 1 cc. pipette with 0.22 cc. gra- duation, a glass rod (2 m. thick and from 15 to 20 cm. long), a test-tute stand, distilled water and a printed form (pagek for dry sarrple s or ?age 5 for wet samples ) . Preliminarv York

1. Determine the specific gravity of the soil and its water content, Wn (if the sample is still wet).

2. The 11 mm. test tubes are carefully washed with soap and water, rinsed and dried.

3. Three sam.ples of wet soil of 1 gm. + Wn each per test m tube (of 11 mm. diameter) are weighed. 4. The sample s which are not irrimediately used but are un- tended for the first and secoqd main experiment must be pr~tected arainst evaporation during the ~reliminarytest.

5. Dry soil must be soaked for some days before the experi- ments.

I Preliminary Experiment (to determine the required amount of water )

1. Approxin~ately0.5 cc. distilled water is added to the dry ~owder(or wet soil) with the pi7ette.

2. After the first addition of water the mixture is thoroughly and vigorously stirred with the glass rod for at least ten minutes. The test tube must be held vertically so as to prevent the mixture from beln, smeared to the tuke walls.

3. The mixture is left to rest without the rod for exactly one minute.

lC. The tube is then turned upside down, carefully avoiding any vibration (inverted tube test).

5. If the mixture does not yet flow, distilled water should be added drop by drop. Care must be taken that no drop sticks to the tip c:f the pipette. This test is repeated until, after a setting time of exactly one n.inute, the paste begins to flow in the tube when it is turned upside down. (Then the stiffening limit will have just been exceeded. ) 6. The total amount of liquid, !'I, (including m1'Vn ) is deter- mined at which the paste is just on the verge of flowing (i.e., the total water content minus the last drop added). The void ratio E relative to dry weight 1s calculated as follows:

N = W x specific gravity. 1 &m. of soil

I1 Rain Experiment (carried out twice) 1. On the basls of the water content of the void ratio determined in the preliminary experinlent the two main experi- ments are cardried out ~iththe remaining two samples, which have been protected against evapara'tion. 2. Two-thirds, or 0.2 cc ..less water than the approximate amount of water determjned in the pre,liminary teat (i.e., two- thirds of the amount of water determined in I, 6) is added. 3. The procedure of the preliminary test, described under I, 2 to 6, is repeated.

,!L. The stiffening lirpit is then calculated fron. the water content of the limit value as follows:

-# -# T x 100 = ..... ~srcent ly weight relative to dry 1 Lrr. FEZ^ weicht. Then tbe mean value of the two main experiments is determined. Experiment No.: Soil lkechanics Laboratory Code Word. Designation of 5am~le:

3etermination of Void- Ratio- ----.---and Stiffening Limit of Dry Samples Carried out by: Date : Hygrometer :

--

- -- .- .-. ... -...... -- Tare C I. I Dry- ..sample...... + ...... a _ - -...... sample+ I3 C I ...... I - ...... -- .. - gravity I ...... _I..-I .... .- I ...... -...... - - , -. -- -- I i ilst addition of I CC. I cc. I 'cc.:

:Total amount of - ...... wa.te.r- - I Kinus lns t addi- [.ti.on of~a_ter- .... j Amount of water 1 of .4hR..!?~.! .ratio --. ... - ... :Void ratio N I - I.#:[ x spe/=. Em. of soil grair.

...... I....-.. -..- ...... -..-.-.. stiffen in^ 1i1it Mean : - - 1;"' . x1mg ,i 1 gm. of so11 I -5- Experiment No : Code Yord: Designation of Sample:

Determination of Void Batio and Stiffening Limit of Wet Sarples

Carried out by: Date :

Natural moisture content wn- (calculated per grn. of solid substance)

. _ .. _...... _ _ ... .. - . - - ... . ---- - I - . Preliminary First Kain ' Second k.ain' --' Experiment Experiment Experiment I_ I " ..... - ...... ____ ..,. __ .I ______._..- . __ _ --- -. - - .. . Tare C 1 I I ' Wet sample - Tare= B i i Wet sample= 13-C I I 1 Spe-cific gravity -. . - . . ' ., . . -. - - -- .-- - .... .- - ... -- -- .- .- .- .... ___ .. __ - !--". - ., .-, . .- . . . -. .... __ . - _i ___ .. _ ~_ . . !.--- 1 1st addition of water (cc.) ! II I1 1 2nd II j I 1I II If II ! t1 I1 11 It I 11 I1 11 I 5th If 11 11 14 1i I 6th II i If I1 i 1 ' 7th I t II ! 11 1I I1 11 ! I I 0th ! : 9th I1 It I1 If I II It 11 11 1 j 10th ! 11th I1 If It II j ! i I 11 11 It II 12th I II I1 11 f I I 13th 11 I .- .- --.. - .-..- ...... - .. I .. _._I__- - I 1 - .. . _ -...... -...... :

Total water content measured in drops G'eight (flow test) + tare Bl : Dry sample (1 grn. ) + tare Ct

1 Total water content C1 - Bf , ' Kinus the last drop added I I Vlater content at the void I i I ratio Vd corrected. - 6 i N= \vg x spec. grav. ; Lean value I 1 &In. 0s so11 -.____ . _ .._..._...._...... , ...... -- -.,...... --...... -. 1 I stiffening limit I , Er = wp. x 100g ! bean value i 3 1 grn- of soil I , ...... -, ...... - .... L .- .. .. ----.-.,-- . Void ratio N = volume liquid vol. solid substance Stiffening limit = water content of the void ratio in cc. x 100 weight of solid substance in gn.