Influence of swell on undrained shear strength of expansive Ankara clay
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ORIGINAL PAPER
Influence of swell on undrained shear strength of expansive Ankara clay Ceren Deliktaş 1 & Erdal Çokça 1 Received: 14 October 2019 / Accepted: 29 July 2020 # Saudi Society for Geosciences 2020
Abstract Expansive clays cause problems throughout the earth, in particular for the locations in arid or semi-arid climate. Ankara (Turkey) is in semi-arid climate and change in moisture content of the reddish-brown expansive Ankara clay causes swell-shrink related movements and damages on lightweight structures. Over-estimation of undrained shear strength of an expansive clay without considering swell amount can lead to failures (i.e., bearing capacity, slope stability, and pile capacity). Since the existence of water significantly affects the engineering properties of the swelling soils, the effect of swell on the undrained shear strength of Ankara clay was researched in this laboratory study. To verify this effect, tests were done on three expansive Ankara clay samples with distinct degree of expansiveness. Expansive clay samples were taken from several sites in Ankara. Before swell-shear test cycle, index properties of the samples were determined. Swelling of the specimens in designed molds and shearing process including 0%, 10%, 15%, 20%, 25%, 50%, and 75% of ultimate vertical swell and 100% swell were followed it. It has been determined that undrained shear strength of the expansive Ankara clay is considerably affected by the amount of swell depending on the test results. The undrained shear strength decreases with increasing water content. It was observed that the shear strength of the specimens was decreased to nearly 70% of its initial value, even at the 10% of ultimate swell, and the undrained shear strength of expansive Ankara clay specimens was lost to a degree of almost 90% of their initial value (i.e., almost complete loss of strength due to swelling), this is one of the major factors causing failure of structures in/on the expansive Ankara clay due to wetting in the depth of active zone. Keywords Expansive clay . Free swell index . Methylene blue test . Swell percentage . Rate of swell . Undrained shear strength
Introduction Soils exposed to increase in volume with the rise of water content and decrease in volume when they dry out are called “expansive soils” by definition. As they absorb water and hence swell, they apply uplift force to the floors, foundations, and basement walls (Chen 1975). As they shrink with the extraction of water, they cause moving the support of
Responsible Editor: Zeynal Abiddin Erguler * Erdal Çokça [email protected] Ceren Deliktaş [email protected] 1
Civil Engineering Department, Middle East Technical University, K1 Building, Universiteler Mah. Dumlupınar Bulv., Ankara 06800 Çankaya, Turkey
structures like columns. Meanwhile, developed fissures cause that water to go deeper easily; i.e., wetting front is advancing. In 1938, the swelling soil problem gained first recognition by the US Bureau of Reclamation with a connection problem of a foundation for a
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