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Thixotropy and Flow Properties of Fine Grained Soils Ackermann, E

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Thixotropy and Flow Properties of Fine Grained Soils Ackermann, E NRC Publications Archive Archives des publications du CNRC Thixotropy and flow properties of fine grained soils Ackermann, E. For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous. Publisher’s version / Version de l'éditeur: https://doi.org/10.4224/20331616 Translation (National Research Council of Canada), 1950-04-01 NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=6d6165a8-b9a3-410e-860c-9020e1c2e635 https://publications-cnrc.canada.ca/fra/voir/objet/?id=6d6165a8-b9a3-410e-860c-9020e1c2e635 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at https://nrc-publications.canada.ca/eng/copyright READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site https://publications-cnrc.canada.ca/fra/droits LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at [email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected]. NATIONAL RESEARCH COUNCIL OF CANADA 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 soil 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 clay 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 geology. 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 viscosity changes in mechanically dis- turbed clay pastes (e)" and moving fluids (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 gel 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 stress 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 quick clay. In these clays catastrophic movements of the soil are frequent. On many occasions the solid wooded ground of a valley or of a terrace 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 lava 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 digging and dredging became possible.
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