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Clay Microstructure 1, SWEDISH GEOTECHNICAL INSTITUTE PROCEEDINGS No. 24 CLAY MICROSTRUCTURE A Study of the Microstructure of Soft Clays with Special Reference to Their Physical Properties By Roland Pusch STOCKHOLM 1970 Reprint of Document D8 :1970, published by the National Swedish Institute for Building Research ·oocument D8:1970 Clay microstructure Roland Pusch National Swedish Building Research ~ ------ Lerans mikrostruktur Byggforskningen Sammanfattningar Roland Pusch D8:1970 Under de sista artiondena har atskil­ Mikrostrukturen hos nagra svenska liga hypoteser lanserats om den mik­ losa leror har undersokts med elek­ rostrukturella uppbyggnaden hos losa tronmikroskopi och beskrivits statis­ leror. Kolloidkemiska betraktelser tiskt med hjiilp av enkla struk­ framst i form av teorier om elektriska turparametrar. Strukturmonstret ka­ dubbellager har legat till grund for rakteriserades av aggregat kopplade dessa hypoteser som visat sig ha be­ via liinkar och grupper av sma par­ gransad giltighet. Dubbellagerteorier­ tiklar. Vissa mikrostrukturella egen­ na har lett till antagandet av en struk­ skaper bedomdes ha samband med tur karakteriserad av parallellstallda a den ostorda lerans geotekniska egen­ partiklar. Andra teorier som galler skaper, t.ex. permeabiliteten och sen­ fordelning av elektriska laddningar pa sitiviteten. De mikrostrukturella for­ olika delar av partiklarna har fort till iindringarna vid konsolidering och vid antagandet av partikelarrangemang av skjuvning har undersokts vilket gett typen kant mot plan yta, speciellt i underlag for ett antagande om meka­ illitisk lera. nismen vid dessa processer. Aggrega­ Atskilliga undersokningar med hjalp ten visade sig verka som fasta krop­ av polariserat ljus, rontgendiffrak­ par upp till en viss spiinningsniva. tionsteknik, sedimentations- och Denna fasthet kan till en del bero pa krympningsobservationer samt hall­ aggregatens laga vattenhalt som inne­ fasthets- och deformationsbestamning­ biir en mycket hog viskositet hos por­ ar har utforts av olika forskare for vattnet. att fa indirekt information om mikro­ Schematisk bild av partikeZarrangemang­ strukturens uppbyggnad. et i Zera. a Sotvattenavsatt Zera uppbyggd Ljusmikroskopiska undersokningar av reZativt porosa aggregat dtskilda av har givit vardefulla upplysningar om smd parer. b Marin Zera med stora, tiita aggregat dtskilda av grovre parer. arrangemanget av mjalapartiklar och grovre lerpartiklar samt om t.ex. agg­ p regatbildning, men den begransade sotvattenavsatta leran hade lagre T upplosningen har inte mojliggjort ett varde an den saltvattenavsatta. Det detaljstudium av arrangemanget hos hogsta vardet observerades for den or­ huvuddelen av partiklarna i lerfrak­ ganiska leran. Medianvardet av a var tionen. 11 av samma storleksordning for alla le­ Elektronmikroskopiska undersokning­ rorna, men den saltvattenavsatta leran ar grundade pa replikametoder har karakteriserades av en viss mangd givit information om mikrostrukturen mycket stora porer. Den mest typiska men prepareringstekniken, lufttork­ mikrostrukturella egenskapen hos alla ning eller frystorkning, kan i de fiesta de undersokta proven var uppbyggna­ fall ha paverkat den naturliga struk­ den i form av mer eller mindre tata turen. Ett battre forfarande, som be­ aggregat forbundna av lankar eller skrivs i denna rapport, ar att utfora grupper av sma partiklar. I den salt­ elektronmikroskopisk undersokning vattenavsatta leran var aggregaten av ultratunna snitt av plastpreparerad UDK 624.131.22 storre och tatare an i de sot- och !era. I rapporten beskrivs en under­ 624.131.37 brackvattenavsatta sedimenten. sokning av tre svenska typleror: sot­ 620.186I .187 En jamforelse mellan strukturpara­ eller brackvattenavsatt Ska-Edebylera, metrarna och de geotekniska egenska­ saltvattenavsatt Lilla-Edetlera och Sammanfattning av: perna visade vissa samband. Salunda brackvattenavsatt organisk Morjarv­ Pusch, R, 1970, Clay microstructure. observerades ett direkt samband mel­ lera. Lerornas kornstorleksfordelning lan permeabilit_eten och strukturpara- - A study of the microstructure of - ocksa inom lerfraktionen - under­ soft clays with special reference to soktes elektronmikroskopiskt och de­ metern !!._ . For de lerlaoer i Ska-Ede- their physical properties. ras geotekniska egenskaper, sasom T o kompressibilitet, odranerad skjuvhall­ by som karakteriserades av de lagsta (Statens institut for byggnadsforsk­ fasthet och sensitivitet bestamdes ge­ ning) Stockholm. Document D8:1970. !!... -vardena galler inte DAR­ 76 s., ill. 30 kr. nom laboratorieforsok. T Mikrostrukturen beskrevs med an­ cYs lag enligt tidigare undersokning­ vandande av parametrarna aP (por- ar av professor Sven Hansbo, CTH. Distribution: Svensk Byggtjiinst, Nagon relation mellan strukturpara­ Box 1403, 111 84 Stockholm. diametern) och !!... ("porositeten"). Den T metrar och kompressibilitet kunde in­ Telefon 08-24 28 60. te observeras, vilket antyder att fakto- rer som organisk halt och kornstor­ leksfordelning lir avgorande for kom­ pressibiliteten. Mikrostrukturen hos prov som kon­ soliderats under olika tryck undersok­ tes ocksa, varav framgick att belast­ ning utover forkonsolideringstrycket leder till en nedbrytning och oriente­ ring av llinksystemet (domlinbildning). Upp till en viss spanningsniva bedom­ des aggregaten fungera som stela, hall­ fasta kroppar. Denna egenskap kunde ocksa verifieras genom en undersok­ ning i ett hogvoltmikroskop av de interna deformationerna i en torkande lergel. Inget sakert samband mellan de mik­ rostrukturella parametrarna och den odrlinerade skjuvhallfastheten kunde observeras. De hogsta sensitivitetsvar­ a dena erholls for de lerprover som bade de hogsta !:.. -vlirdena vilket antyder T att en mycket hog porositet ar en nod­ vandig forutsattning for att en !era skall vara kvick. De mikrostrukturella forlindringarna under inverkan av olika overlagrings­ tryck och skjuvspanningar studerades ocksa. A v dessa studier drogs slutsat­ sen att mekanismen vid skjuvning av en los !era lir den, att aggregaten som verkar som stela kroppar forskjuts in­ hordes i samband med en nedbrytning av llinksystemen som forbinder aggre­ gaten. Lanksystemen ombildas till do­ mliner. Denna mekanism ger en for­ klaring till begreppet "residualhallfast­ het" som antas vara den hallfasthet som provet har nar de starkt defor­ merade llinkarna ar ombildade till do­ mliner. En ytterligare storning av sys­ temet i form av omrorning antas ge en nedbrytning ocksa av aggregaten och med detta ett betydligt lligre hall­ fasthetsvlirde hos provet. Ett stod for antagandet att aggrega­ ten fungerar som stela kroppar upp b till en viss spanningsniva erholls £ran preliminlira NMR-undersokningar. De vid dessa undersokningar erhallna var­ dena pa spinn-spinnkoherenstiden T 2 visar att vid laga vattenhalter lir vat­ tenmolekylrorligheten mycket mindre an i fritt vatten. Eftersom den berak­ nade vattenhalten hos aggregaten var mycket lag har slutsatsen dragits att Domiinbildning (cirkelmarkering) och aggregatdeformation vid ett konsolideringstryck den hoga vattenviskositeten bidrar till av 128 N /cm'. a Postglacial Ska-Edebylera fran 2 m djup. b Glacial Ska-Edebylera fran 8 m djup. aggregatens stelhet. UTGIVARE: STATENS INSTITUT FOR BYGGNADSFORSKNING Clay microstructure National Swedish Roland Pusch Building Research Summaries D8:1970 A large number of contributions to the The microstructure of some soft Swedish knowledge of clay microstructure has clays has been investigated by electron been made in the last twenty years. Col­ microscopy and described by statistical loid chemistry has furnished most of the methods using simple structural para­ hypotheses suggested in literature but meters. The microstructural pattern was large discrepancies between theory and found to be characterized by aggregates reality have been found. One of the coupled by links and groups of small basic ideas, the double-layer interaction particles. Certain microstructural pro­ of parallel colloidal particles, has been a perties seemed to be related to the geo­ found to be applicable in specific cases technical properties of the undisturbed only. The more recent hypotheses of clay material, such as the permeability different surface charges on edges and and sensitivity. The microstructural faces of clay particles form the basis changes by consolidation and shearing of the common microstructural concept have been investigated. The results formed for illite clays, the edge-to-face coupling the basis of a hypothesis concerning of adjacent particles. the mechanism of these processes. The Optical studies using polarized light, aggregates seemed to act like rigid bodies X-ray diffraction technique, settling and up to a certain stress level, the rigidity shrinkage observations as well as analy­ probably being connected with their low ses of strength and deformation proper­ water content and the very high viscos­ ties, have been tried by several authors ity of the pore water. to reveal characteristic features of clay Schematic clay particle arrangement. a) microstructure but only rough indica­ Clay deposited in fresh water having tions have been obtained. relatively porous aggregates and small By direct observation of soil structure voids. b) Marine clay with large, dense aggregates separated by large voids. using light microscopy, a series of im­ portant observations have been made by several investigators but due to the limited resolving power no details of the smallest f -values, and that the high­ the clay matrix have been revealed. Electron microscopic
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