Clays, clay minerals and soil shrinkswell behavior

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Hillel, pp 75-100 Clays, Clay Minerals and Soil Shrink/Swell Behavior CE/ENVE 320 – Vadose Zone Hydrology/Soil Physics Spring 2004 Copyright © Markus Tuller and Dani Or 2002-2004 Introduction • Volume and pore space of swelling clayey soils vary with hydration state • Shrink-swell phenomena affect many mechanical and engineering properties of soils and clay liners • Constitutive transport properties for swelling soils are complicated by hydration-dependent soil attributes (pore space, strength, etc) Copyright© Markus Tuller and Dani Or2002-2004 Clay shrink/swell damage to structures & roads  Changes in soil water content or solution chemistry of clayey soils induce swelling pressures sufficiently large to fracture and damage structures and roads  Estimated damage in excess of $7 billion/yr in the US Copyright© Markus Tuller and Dani Or2002-2004 Clay Minerals – building blocks ● Distinguish between “clay” size [...]... Or2002-2004 Modeling clay fabric geometry • Development of an idealized clay fabric representation: (a) SEM of montmorillonite; (b) approximated clay fabric structure; and (c) idealized clay fabric representation applied in the model • SEM observations and bulk clay behavior are used to derive and constrain parameter values for the idealized clay fabric Copyright© Markus Tuller and Dani Or2002-2004... with soil, have the ability to separate, filter, reinforce, protect or drain Geomembranes are impermeable membranes used widely as cutoffs and liners Copyright© Markus Tuller and Dani Or2002-2004 Clay Liners Copyright© Markus Tuller and Dani Or2002-2004 Effect of shrink-swell on soil pore volume Copyright© Markus Tuller and Dani Or2002-2004 Shrink-swell affects soil pores at all scales Microscale (clay. .. Tuller and Dani Or2002-2004 Effect of clay content on porosity & permeability  The critical clay content that completely fills sand-silt skeletal porosity is about 35-40% (and minimum overall porosity)  The saturated hydraulic conductivity decreases with increased clay content to critical value, and then rebounds to the value of clay fabric saturated hydraulic conductivity Copyright© Markus Tuller and. .. question Sand -clay Silt -clay Dry Wet (c) Dry Mesopores [Fies and Bruand, 1998] Copyright© Markus Tuller and Dani Or2002-2004 Clay barriers for waste isolation Copyright© Markus Tuller and Dani Or2002-2004 Clay Liners Clay layers (Bentonite) to prevent leaching Geotextile layers for mechanical stability Copyright© Markus Tuller and Dani Or2002-2004 Clay Liners Geotextiles are permeable fabrics (polypropylene,... clay fabric - mesopore formation • • Images of uniform Glass beads (40 um): (a) (a) mixed with 10% dry Na+ Bentonite (b) wetting resulted in complete filling of skeletal pore space by jell-like clay fabric (b) (c) upon subsequent drying, mesopores are formed between glass beads The mixing and distribution of clay domains among other soil textural components remains an open question Sand -clay Silt -clay. .. isomorphic substitutions ● Thicker and stable stacks ● Relatively low surface area: 5-30 m2/g ● Not much swelling Copyright© Markus Tuller and Dani Or2002-2004 Swelling and changes in lamellar Spacing + + - + - + - + - + - + + + + + - + - H2O osmosis from bulk soil solution due to DDL cations Copyright© Markus Tuller and Dani Or2002-2004 Swelling and Lamellar Spacing • Clay lamellar spacing increases... influences of Ca2+ and Na+ montmorillonite microstructure prepared with dilute solutions [Tessier, 1990]  Electrolyte type and concentration affects:  Arrangement and spacing between layers (smaller for Ca2+), between ordered stacks, and between tactoids  Number of layers and apparent length of quasicrystals (tactoids) more lamellae for Ca2+ (dilute) solutions Copyright© Markus Tuller and Dani Or2002-2004... alone cannot explain volume changes and water retention in clay fabric  SEM images show a lamellar network with micropores separating tactoids (quasicrystalline stacks of lamellas)  Important for modeling clay fabric response Copyright© Markus Tuller and Dani Or2002-2004 Hydration effects on clay fabric geometry 0.03 bar  SEM images support bulk volume measurements and reveal a lamellar network with... microstructure and bulk volume of Greek Na+ montmorillonite during first drying [Tessier, 1990]  1.0 bar A strong orientation of lamellar structure and micropores (1-2 mm) occurs during drying  anisotropy 10 bars Copyright© Markus Tuller and Dani Or2002-2004 Interacting DDL different electrolytes • Ion distribution between two clay surfaces – different electrolytes Copyright© Markus Tuller and Dani Or2002-2004... diffuse double layers (DDL) dominate swelling behavior • Reasonable agreement exists between measured lamellae spacing and DLVO-theory: approaching DDLs develop a repulsive force proportional to excess ions relative to bulk (giving rise to osmotic pressure) Low [1980]; Warkentin et al [ 1957] Copyright© Markus Tuller and Dani Or2002-2004 Interacting DDL and swelling pressure  When two DDLs approach
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