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1 TitleSil Mund Frmatin by Multicyclic Authr(s) Crte, Artur E. Citatin Physics f Snw and Ice : prceedin 集, 1(2): Issue Date 1967 Dc URLhttp://hdl.handle.net/2115/20383 Right Type bulletin Additinal Infrmatin Instructins fr use Hkkaid University Cllectin f Schlarly and

2 Sil Mund Frmatin by Multicyclic Freeze-Thaw Artur E. CORTE Department f Gelgy, Universidad Nacinal der sur, Bahia Blanca, Argentina Abstract Experiments are being carried in freezing cabinets in rder t determine the effect f many cycles f freezing and thawing in a layered sil 4 cm thick. The sil was cmpsed f three hrizntal layers, tw layers f silty-clay and a layer f crushed quartz in between; each layer was 1.3 cm thick. Misture was supplied frm the bttm and thawing frm the tp. Thrugh the experiment the sil was saturated; average rate f freezing was 1 mm per hur, rate f thawing 2 mm per hur. During the first 28 cycles nly a brad mund was develped; after that small munds 1-2 cm at the base started t frm. The maximum height f munds was 2 cm. The number f munds reaching a certain height indicates that the rate f mund grwth is higher thrugh cycles 28-37; after that the rate f grwth decreased. The frm f the munds is nt upright cne; they are inclined and near the tp the material is inclined t hrizntal. It is prpsed as a very qualitative apprach that these munds are prduced by the release f pressure during freezing. Pressure is released in the freezing layer in lci with the highest percentage f unfrzen water. T such places f unfrzen water the migratin f particles and water takes place. The extrusin f particles at the upper part f the mund is an indicatin f such migratin. It is believed that this is the first reprt n experimental frmatin f sil munds. I. Intrductin Nt very much experimental infrmatin is available n the frst behavir f sils fr many cycles f freezing and thawing. Accrding t the authr experience (Crte, 1962 a, 1962 b) fr certain sils ne cycle is nt enugh t btain the needed infrmatin. As it will be shwn, during freezing and thawing cycles certain sils are subjected t changes which are affecting the sil. Since these changes are nt reversible the sil will behave differentially under every freezing and thawing cycle. Therefre an imprtant questin is: Hw many cycles a sil shuld be subjected in rder t btain a representative frst behavir pattern? Reprts n frst actin are cncerned with munds frmatin in the field. Such munds have been treated by different authrs; the large nes up t 40 m high are called hydrlacclithes r ping s (Prsild and thers, 1938). Such munds have cracks prduced by the release f internal pressure; the cracked upper layer is believed t be slidly frzen. The smaller munds with sizes varying frm a few centimeter up t 1.50 m are called frst munds (Kushev, 1939; Mrdvinv, 1940 and thers accrding t Kachurin, 1964). The rigin f the large munds is well understd while the rigin f the smaller nes is uncertain. The frmatin f cnvluted, cntrted r disturbed

3 1334 A. E. CORTE sil layers is als cnsidered as anther feature f frst actin effects. We d nt have actual experimental infrmatin shwing hw this defrmatin is prduced. It is reasnable t assume that the tw frst effects: cntrted layers must be related. Mund frmatin and cnvluted r In rder t get sme infrmatin n this matter a hrizntal layer f crushed quartz was placed between tw hrizntal layers f silty-clay and subjected t many cycles f freezing and thawing. This is a prgress reprt n this research which is still ging n. II. Experimental Prcedure Freezing cabinets, and sil samples. Tests were perfrmed in small freezing cabinets f the same type used fr string fd; interir sizes are: 0.75 wide 1.00 high and 1.20 lng in meters. Sample hlders used are cmmercial type f plastic pans 31.5 lng, 24.5 wide and 10.0 high in centimeter; wall thickness 5 mm. In rder t prduce unidirectinal freezing and thawing. the pans were insulated with a plastic fam 20 mm thick cmmercially knwn as "tergpl" (Fig. 1). The sample f silty-clay was btained frm a lse expsure; grain size analysis indicate that they are cmpsed f a small percentage f fine sand, the remaining half silt and the ther half clay fractin. The sample f crushed quartz was btained frm a quarry frm which different grain sizes can be btained. It is cmpsed mstly f sand fractin with sme silty-clay fractin. pipe fr water supply rr r,(- - _ " " The samples were laid in even surfaces with v ".:. :' :'.:...:...::...:...:.:: :".: :':'.:.'.; ::.>:(..:.z " " _ ----_-=-SJJty.:c1al..-_ Fig. 1. scale CIT\ a 2 S 4 5 Crss sectin f freezing pans shwing lcatin f sil layers befre freezing. Reference level n tp is the reference line t which munds reached

4 SOIL MOUND FORMATION 1335 layers f 1.3 cm thick (Fig. 1). Misture was supplied by means f wicks hanging frm the bttm f the sil thrugh a tergpl layer t a water strage tank. This strage tank was als insulated s that misture cnductin t the sil during freezing was ensured (Fig. 1). In rder t prduce a unifrm misture supply the amunt f water was maintained cnstant by weighing the whle freezing pan. Freezing and thawing cnditins and rates were determined by eye inspectin using a blank test. Such test was sectined at different times in such a way that the frst line penetratin was determined; the same thing was dne fr the thawing stage. With the freezing cabinet at -5 C it was determined that the rate f freezing line penetratin was abut 1 mm per hur. The thawing was accmplished by taking the freezing pans ut f the cabinet and the rate f thawing was abut 2 mm per hur. Therefre the minimum temperature f the sil was never belw that f the freezing cabinet i. e. -5 C. III. Experimental Results During freezing and thawing cycles it was bserved that the sil heaved and sunk cntinuusly. Maximum heaving during the first cycles befre mund develpment was abut 10 mm; that is 30% vlume increase. Maximum heaving in munds was 7.0 mm r 24% vlume increase. 20 ern I.scm I.em / 0.5 eft"' Fig. 2. Tp view f experiment after cycle 20 shwing develpment f ne single mund 2 em high

5 1336 A. E CORTE 1.0 scale' em Fig. 3. Tp view f experiment after cy.cle 33 shwing develpment f 18 munds. Maximum height f munds is 2 cm. Numbers in center f circles are mund number )) " '" " 'b "3 ) '\l 1:.& 'I-;: j 13 f' :, G) 2 28 Fig Number f cycles f freezmy and fhaw/n..j Number f munds reaching reference level as a functin f the number f the freezing and thawing cycles

6 SOIL MOUND FORMATION 1337 In a general view f the experiment tw stages can be differentiated: First stage cvering cycle 1 t 28 in which a brad mund is develped (Fig. 2), and secnd stage frm cycle 28 t 47 in which sme 18 munds frmed in the area cvered by the previus large mund (Fig. 3). Accrding t the recrds the rate f grwth f sme munds was estimated t be f the rder f 1 mm per cycle. Measurements were taken f the number f munds reaching a certain elevatin, which is called reference level in Fig. 1. Frm cycle 28 t 37 there is a higher rate f mund grwth than after cycle 37 (Fig. 4). During the frmatin f munds it was bserved that n cracks was develped. This indicates that the dme frmatin in the silty-clay is nt prduced in the frzen stage but in a partially frzen cnditin. It is als bserved that cncurrently with the frmatin f munds there is extrusin f crushed quartz frm underneath. Regarding the frm f the munds, it is bserved that in general they are nt like a cne. They are generally inclined with the tp side hanging t ne side (Fig. 5). 1.5 em If? rcm./-. 2 ern 4 em 6 ern Fig. 5. Crss sectin f munds 2-5, 8, 9 and 10 shwn in Fig. 3 IV. Interpretatin f Results At the present stage f this experiment it is pssible nly t ffer a very qualitative apprach t the prblem f mund frmatin. Further experiments wlll be necessary fr a much clser apprach. Regarding the rigin f the munds, the authr feels that the amunt f unfrzen water in a frzen layer must be imprtant in this prcess. When the upper silty-clay layer is frzen and the crushed quartz sand began t freeze there must be a release f hydrstatic pressure thrugh the upper layer. The places mre likely t yield t the pressure are the areas with the highest cntent f unfrzen water; thrugh such places will migrate water and sil particles. In supprt f this thery we can use tw lines f research: The wrk perfrmed by Tsytvich (1964, chapter V) and thers which shws that the amunt f unfrzen water in frzen sils depends n the grain size, mineralgical cmpsitin and temperature belw freezing. The amunt f unfrzen water increases as the grain size decreases. Mntmrillnitic clays have the highest amunt f unfrzen water. The ther line f research shws that there is a migratin f water and particles in frnt f a mving freezing frnt. Kachurin (1964, chapter IX) indicates that the migratin f water and "slurry" has been cnfirmed by the field wrk f Ppv (1953) and Bakulin (1958). Als it is indicated that under favrable cnditins fine grained slurry penetrates int layers f mre prus and carse grained sils. An experimental demnstratin indicating the rll f the different variables affecting the migratin f particles in frnt f a mving freezing plane has been presented by Crte (1962 c). In summary, it is prpsed that an unfrzen area in a freezing layer becmes

7 1338 A. E. CORTE a place f particles and water cncentratin with the cnsequence f the frmatin f a mund. References 1) BAKULIN, F. G Ice Cntent and Settlement during Thawing f Quaternary Depsits in the Vrkuta Regin, Acad. Sci. USSR, Mscw, 96 pp. 2) CORTE, A. E a The frst behavir f sils. Part 1. Vertical srting. Highway Research Bard Bull., 317, ) CORTE, A. E b The frst behavir f sils. Part II. Hrizntal srting. Highway Research Bard Bull., 331, ) CORTE, A. E c Vertical migratin f particles in frnt f a mving freezing plane. J. Gephys. Res., 67, ) KACHURIN, S. P Crygenic physic-gelgical phenmena in permafrst regins. In Principles f Gecrylgy. Part I. General Gecrylgy, (In Russian); Translatin by Natinal Research Cuncil f Canada 1964 Translatin 1157, 91 pp. 6) KUSHEV, S. L Mrphlgy and genesis f mund frmatin and their gegraphical distributin. Tr.Kmit. p vechn. Merzl., 8, ) MORDVINOV, A. I Relief and permafrst f the left bank in the middle curse f the Byssy River and the adjacent fthills f the western slpe f the Turana muntain Ridge. Tr. Kmit p vechn. Mend., ) POPOV, A. I Permafrst in Western Siberia, Acad. Sci. USSR, Mscw, 85 pp. 9) PORSILD, A. E Earth munds in unglaciated Arctic Nrth Western America. Gegr. Rev., 28, ) TSYTOVICH, N. A. et al Physieal phenmena and prcesses in freezing, frzen and thawing sils. In Principles f Gecrylgy. Part I. General Gecrylgy, (In Russian); Translatin by Natinal Research Cuncil f Canada 1964 Translatin 1164, 109 pp.