Utjecaj bubrenja bentonitne gline na njezina mehanička svojstva

doctoral thesis

• Title: Utjecaj bubrenja bentonitne gline na njezina mehanička svojstva : doktorski rad
• Title (english): The impact of swelling behaviour of bentonite on its mechanical properties : doctoral thesis
• Author: Dubravko Domitrović
• Mentor: Biljana Kovačević Zelić (mentor)
• Committee member: Predrag Kvasnička (predsjednik povjerenstva)
• Committee member: Biljana Kovačević Zelić (član povjerenstva)
• Committee member: Goran Durn (član povjerenstva)
• Committee member: Tatjana Rukavina (član povjerenstva)
• Committee member: Boris Kavur (član povjerenstva)
• Granter: University of Zagreb; Faculty of Mining, Geology and Petroleum Engineering; Zagreb
• Defense date and country: 2012-12-20, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mining, Petroleum and Geology Engineering; Mining
• Universal decimal classification (UDC): 622 - Mining

Abstract

Glinene geosintetičke barijere su tvornički proizvedene hidrauličke barijere, koje se
sastoje od mineralne i geosintetičke komponente. Mineralna komponenta najčešće je
bentonitna glina, koja pripada skupini bubrivih tala. Tijekom procesa bubrenja dolazi do
promjene njenih mehaničkih svojstava.
Svrha je ovog istraživanja utvrditi utjecaj bubrenja na mehanička svojstva bentonitne
gline. Za istraživanja je odabrana Volclay bentonitna glina u granulama, mineraloškog
sastava: montmorillonit 80-85%, kristobalit oko 5%, kvarc oko 5%, plagioklasi 5%.
Indeksni pokazatelji bentonitne gline iznosili su: granica tečenja 437,0%, granica
plastičnosti 52,86%, specifična površina 700 m2/g i kapacitet ionske izmjene 88,63+/-6,51
meq/100g. Povezanost bubrenja i promjene vlažnosti s promjenama posmične čvrstoće i
parametara posmične čvrstoće istraživana je u uređaju za izravni posmik. Pri tome su u
serijama ispitivanja, kod različitih normalnih naprezanja (50, 100 i 200 kPa) mijenjana
vremena hidratacije (7, 14 i 21 dan) simulirajući različite stupnjeve bubrenja bentonitne
gline. Dugotrajnim pokusima bubrenja u edometru pri različitim normalnim naprezanjima
(50, 100 i 200 kPa) definirana je krivulja bubrenja bentonitne gline. Povezanost bubrenja s
konsolidacijskim i hidrauličkim svojstvima istraživana je u edometru i troosnom uređaju.
Za usporedbu konsolidacijskog ponašanja bentonitne gline pri različitim vrstama
opterećenja, osim u edometru, konsolidacijska svojstva ispitana su i u uređaju za troosni
posmik pri izotropnoj kompresiji. Ispitivanja hidrauličkih svojstava provedena su u
troosnom uređaju pri različitim srednjim vrijednostima efektivnih naprezanja (42,5; 92,5;
193,6 i 291,0 kPa) u uvjetima potpune zasićenosti uzorka.
Pokusi bubrenja pokazali su da je bubrenje bentonitne gline dugotrajan proces.
Završetak primarnog bubrenja postiže se nakon 31 dana neovisno o intenzitetu normalnog
naprezanja. Nakon završetka primarnog bubrenja nastupila je faza sekundarne kompresije.
Ispitivanja čvrstoće pokazuju da dolazi do smanjenja kohezije s produljenjem hidratacije
bentonitne gline. Kut trenja se hidratacijom (od 7 do 14 dana) povećava. Produljenjem
hidratacije nakon 14 dana nema značajnije promjene vrijednosti kuta trenja. Na krivulji
odnosa završne vlažnosti i posmične čvrstoće vidljiva je promjena nagiba krivulje kod
raspona završnih vlažnosti od 60 do 90%. Navedeno odgovara postojećim spoznajama o
promjeni nagiba karakteristične krivulje retencije vode kod usisnih naprezanja od 0,4 do 1
MPa. Navedeni odnosi prezentirani su u svjetlu pretpostavljenih promjena u mikrostrukturi
bentonitne gline tijekom bubrenja odnosno pojavom dvostrukih difuznih slojeva.

Abstract (english)

Clay geosynthetic barriers are manufactured hydraulic barriers consisting of mineral
and geosynthetic components. The mineral component is usually bentonite clay which
belongs to the group of swelling soils. During the swelling process properties of clay are
changing.
The purpose of this study is to determine correlation between mechanical properties of
the bentonite clay and its swelling behavior. The research was conducted on the granular
bentonite clay Volclay. X-ray powder diffraction showed that the bentonitne clay contains
80-85% of montmorillonite, ~5% of cristobalite, ~5% of quartz and ~5% of plagioclase.
Bentonite clay properties were as follows: liquid limit 437.0%, plastic limit 52.86%,
specific surface area 700 m2/g and CEC 88.63+/-6.51 meq/100g. The influence of swelling
on the bentonitne clay shear strength was studied in the direct shear device. During this
process, hydration times were changed in a series of tests at different normal stresses (50,
100 and 200 kPa; 7, 14 and 21 days) simulating bentonite clay swelling. The swelling
curves of bentonite clay were defined by the long-term oedometar tests at different normal
stresses (50, 100 and 200 kPa). The impact of swelling on the bentonitne clay
consolidation and hydraulic properties were studied in oedometer device and triaxial
device under isotropic compression conditions. Bentonite clay hydraulic properties were
studied in triaxial device under different mean values of effective stress (42.5; 92.5; 193.6
and 291.0 kPa) in saturated conditions. Demineralized water was used as the test fluid.
Swelling tests showed that the bentonite clay swelling is a long-term process.
Completion of the primary swelling phase is reached after 31 days regardless of the
intensity of the normal stress. After completion of the primary phase, secondary
compression phase started. Shear tests show a significant reduction in cohesion with the
extension of the hydration of bentonite clay. Friction angle with hydration (from 7 to 14
days) increases. There is no significant change in the value of the friction angle by
extending hydration after 14 days. On the final water content-shear strength curves in the
semi-log diagram, the inclination of the curves decreases with final water content decrease.
Change in curve inclination is noticeable in the final water content decrease range from 60
to 90%. This corresponds to the bentonitne clay water retention characteristic curves
inclination changes under suction stresses from 0.4 to 1 MPa. The shear strength properties
during swelling process are linked to the bentonitne clay microstructure features, and
diffuse double-layer appearance.

• Keywords: bentonitne glina; bubrenje; posmična čvrstoća; koeficijent hidrauličke propusnosti; koeficijent konsolidacije
• Keywords (english): bentonite clay; swelling; shear strength; coefficient of permeability; coefficient of consolidation
• Language: croatian
• URN:NBN: urn:nbn:hr:169:033393
• Promotion: 2013-06-30
• Study programme: Title: Applied Geosciences, Mining and Petroleum Engineering; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor znanosti/doktorica znanosti (doktor znanosti/doktorica znanosti)
• Catalog URL: http://katalog.nsk.hr/F/?func=direct&CON_LNG=ZAG&local_base=ZAG01_WEB&doc_number=000555665
• Type of resource: Text
• Extent: [X], 148, [24] listova : ilustr., graf. prikazi u bojama ; 30 cm
• File origin: Born digital
• Access conditions: Open access
• Created on: 2020-11-20 09:06:39