Browsing by Author "Cetin, Bora"

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Deformation characteristics of medium-dense sand-clay mixtures under a principal stress rotation
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2021) Fedakar, Halil Ibrahim; Cetin, Bora; Rutherford, Cassandra J.; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
A moving wheel load induces a principal stress rotation (PSR) in pavement foundation geomaterials including subgrade/subbase soils. Simulating such a stress condition is not possible with stress path tests conducted with conventional cyclic triaxial (CT) equipment. More complex stress paths such as a heart-shaped stress path are required to determine the deformation characteristics of these under a PSR. A heart-shaped stress path can be simulated on a soil specimen in cyclic hollow cylinder (CHC) tests via user-defined waveforms for its stress components (axial stress, and torsional shear stress). In this study, a series of CT and CHC tests were performed to analyze the impact of a PSR on strain behaviors of medium-dense sand-clay mixtures. The specimens contained 0%, 5%, 10%, and 20% clay by weight and were prepared at an initial relative density of 50%. All specimens were anisotropically consolidated under K-0 approximate to 0.5. It was determined that all CT specimens underestimated the strain performances (both axial strain and shear strain) of the sand-clay mixtures. On the other hand, a heartshaped stress path was simulated successfully in CHC tests and thus, all specimens yielded more accurate strain results. At low clay content (<= 10%), the impact of a PSR on strain performances of the sand-clay mixtures was observed to be less (axial strain (epsilon(z)) < 0.12%, and shear strain (gamma(z theta)) 0.8% after number of load cycles (N) = 5000) due to the low stress ratios (CVSR = 0.15 and eta = 1/3). On the other hand, despite the low stress ratios, a PSR caused a rapid increase in axial strain and shear strain (epsilon(z) = 5%, and gamma(z theta) 0.8%) of the specimen containing 20% clay, which resulted in the failure of the specimen at N = 478. Results of this study clearly indicated that the effect of a PSR should be taken into consideration while evaluating the strain characteristics of the sand-clay mixtures that contain clay particularly at high contents (>= 20%) under traffic loads.
Effect of principal stress rotation on deformation behavior of dense sand-clay mixtures
(TAYLOR & FRANCIS LTD2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2021) Fedakar, Halil Ibrahim; Rutherford, Cassandra J.; Cetin, Bora; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Fedakar, Halil Ibrahim
This paper investigated the deformation behaviour of K-consolidated sand-clay mixtures through cyclic triaxial (CT) and hollow cylinder (CHC) tests. The sand-clay mixtures contained 0%, 5%, 10% and 20% clay by weight and were prepared at a relative density of 75%. Clay inclusion caused an increase in the permanent axial strain of mixtures (0.075% to 5% in CT and 0.186% to 5% in CHC), while a relatively insignificant increase in permanent axial strain was observed in the CT specimens containing 5% and 10% clay (0.075% to 1.299%). However, all CHC specimens with clay failed (epsilon(z) >= 5%). It was also observed that shear strain development of sand is significantly influenced by clay inclusion (0.096-2.241%) in CHC tests. Test results clearly show that the effect of a principal stress rotation should be taken into account to better estimate the deformation behaviour of sand-clay mixtures under repetitive traffic loads.
Evaluation of Deformation Behavior of Sand-Clay Mixture under Traffic Loads
(AMER SOC CIVIL ENGINEERS, UNITED ENGINEERING CENTER, 345 E 47TH ST, NEW YORK, NY 10017-2398 USA, 2020) Fedakar, Halil I.; Cai, Wenjing; Rutherford, Cassandra J.; Cetin, Bora; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
Vehicle traffic loading induces a heart-shaped stress path in deviatoric stress space [tau z theta to (sigma(z)-sigma(theta))/2], causing the rotation of principal stress direction acting on a soil element. A conventional triaxial test is not capable of applying the principal stress rotation induced by heart-shaped stress path and therefore, is not able to evaluate the behavior of soils accurately under traffic loads. However, a hollow cylinder test can simulate heart-shaped stress path imposed by traffic loading. In this study, the effect of heart-shaped stress path on the vertical deformation behavior of sand-clay mixture including 20% of clay by mass was experimentally investigated through hollow cylinder test. The tests in this study were conducted at three stages: i) saturation, ii) consolidation, and iii) shearing. The specimens were first saturated until Skempton's B >= 0.95 and then consolidated with K-0=0.5. Thereafter, the specimens were sheared under cyclic loadings involving vertical stress and shear stress. Experimental results indicate that the principal stress rotation induced by traffic loading significantly influences the permanent strain development in sand-clay mixture.