Effect of cyclic swelling-full shrinkage on polymer-stabilized expansive clays

Fatemeh Yazdandoust, S. Shahaboddin Yasrobi

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Expansive Soils

ABSTRACT: Effect of cyclic swelling and shrinkage on swelling behaviour of polymer-stabilized expansive clays has been investigated in this paper. Three expansive soils with different swell potentials were obtained from a region around Tehran (capital of Iran) and stabilized by different percents of two polymers. To evaluate the long-term behaviour of polymer-stabilized expansive soils, several wetting-drying cycles were performed on treated and untreated samples and swell potential of specimens were obtained in all cycles. To simulate drying conditions, ‚full shrinkage' method was used. Variations in grain size distributions of samples due to swell-shrink cycles and micro-fabric changes by scanning electron microscopy (SEM) were assessed. The results showed that the swelling potential of both treated and untreated specimens shows a little increment in second cycle and then it becomes stable. By increase in plasticity index, the effect of polymer stabilization is more obvious. RÉSUMÉ Effet des cycles de gonflement-rétrécissement sur le comportement des sols gonflantes polymère stabilisé a été étudié dans le présent document. Trois sols gonflantes avec potentiels de gonflement différent ont été obtenus à partir d'une région de Téhéran (capitale de l'Iran) et stabilisées par différents pourcentages de deux polymères. Pour évaluer le comportement à long terme des sols stabilisées avec polymères, plusieurs cycles de gonflement-retrait ont été effectués sur des échantillons traités et non traités, se gonflent potentiel des échantillons ont été obtenus dans tous les cycles. Pour simuler les conditions de séchage, la méthode 'de retrait complet' a été utilisé. Les variations dans les distributions granulométriques des échantillons et les changements microstructure par micrographies SEM ont été évalués. Les résultats ont montré que le potentiel de gonflement des échantillons traités et non traités montre un petit incrément après deuxième cycle, et il devient alors stable. Pour les argiles à haute plasticité, l'effet de stabilisation de polymère est plus évident. 1 INTRODUCTION Clayey soils experience periodic swelling and shrinkage during the alternate wet and dry seasons. Such cyclic swell-shrink movements and total and differential volume changes in these soils lead to considerable distresses and severe damages to overlying structures, particularly to low-rise buildings, highways, roads and buried lifelines. Adding certain additives such as lime, cement or polymers to these kinds of clayey soils is a known way to stabilize and suppress the consequence results of their behaviour (Yazdandoust and Yasrobi, 2010). In soil science, non-ionic polymers that are water soluble have been found to impart stability to natural soil aggregates (Yazdandoust and Yasrobi, 2010). On contact with the particles these molecules tend to collapse and spread out over the clay surface, improving the physical conditions of soil (Theng, 1979). The adsorption of an uncharged polymer onto the clay surface, generally leads to desorption of numerous solvent molecules from the surface. Parfitt and Greenland (1970) showed that water was transferred from the surface to the bulk phase during the polymer adsorption process and desorbed from the polymer coated clay particles. Moreover polymer molecules were adsorbed principally on the external surfaces of the clay crystals, so linking them together and preventing inter-crystalline swelling. If the concentration of polymer increases, polymer molecules could also penetrate between the crystals and form inter-lamellar complexes (Luckham and Rossi, 1999). A review of the literature related to cyclic swelling and shrinkage of expansive soils revealed that in cyclic swelling processes, vertical swelling potential may reduce or even increase by a factor of two when compared with the first cycle of swelling (Tripathy et al., 2002). Therefore, the assessment of expansive soil behaviour without considering cyclic seasonal fluctuations may underestimate the swelling potential of the soil. A number of research studies are available on laboratory cyclic swell-shrink tests on compacted-remolded expansive soils. The experimental results of Chen et al. (1985), Subba Rao and Satyadas (1987), Dif and Bluemel (1991), Basma et al. (1996) and Al-Homoud et al. (1995), suggested that compacted-remolded clay specimens show sign of fatigue after each cycle of wetting and drying, thus exhibiting less expansion and shrinkage. They subjected the specimens to full swelling and then allowed them to shrink to their initial water contents, repeatedly (the partial shrinkage method). On the other hand, Popescu (1980), Osipov et al. (1987), Day (1994) and Basma et al. (1996), established that the swelling ability of specimens increases with the number of wetting and drying cycles, when they are allowed to dry to their

RÉSUMÉ: t of cyclic swelling-full shrinkage on polymer-stabilized expansive clays

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Fatemeh Yazdandoust; S. Shahaboddin Yasrobi (2014) Effect of cyclic swelling-full shrinkage on polymer-stabilized expansive clays in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper235,author = Fatemeh Yazdandoust; S. Shahaboddin Yasrobi,title = Effect of cyclic swelling-full shrinkage on polymer-stabilized expansive clays,year = 2014}