Shearing and volumetric straining response of Kızılırmak sand

Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Turkey

Approval Date: 2020

Student: Elife Çakır



The response of sandy soils under monotonic loading depends on size, shape and mineralogy of particles, fabric, stress, and density states of mixtures. Researchers around the world have studied their local sands and calibrated their responses (e.g., Toyoura sand-Japan, Ottawa sand-Canada, Sacramento sand-US, Sydney sand-Australia, etc.). However, there are not many studies that have focused on regional sands from Turkey. This research study aims to introduce a local sand, Kızılırmak sand, to literature as a "standard sand" from Turkey. For this purpose, shear and volumetric straining responses of Kızılırmak sand samples were investigated by a series of consolidated undrained monotonic triaxial and oedometer tests. Specimens with relative densities of 35-45-60-75 and 80 %, were prepared by wet tamping method and consolidated under 50 kPa, 100 kPa, 200 kPa and 400 kPa cell pressures, followed by undrained shearing. Test results were presented by four-way plots, which enable the individual variations of axial load, cell pressure, pore water pressure, and axial deformation along with the progress of the stress paths relative to failure envelopes. On the basis of test results, linear and nonlinear elastic-perfectly plastic constitutive modeling parameters, including but not limited to stress and relative-density dependent modulus and effective stress based angles of shearing resistance, were estimated. Due to its angular nature, Kızılırmak sands' angles of shearing resistance values of 35.4˚-42.8° were observed, which are closer to the upper limits of available literature. Triaxial modulus values fall in the range of ~10 and ~160 MPa and are concluded to be in conformance with available literature. Similarly, samples with varying relative densities, prepared by air pluviation method, were tested in a conventional oedometer device under stresses starting from ~17 kPa increasing up to ~33.5 MPa. During tests, unloading and reloading cycles were performed. Based on these test results, particle crushing-induced yield stresses of Kızılırmak sands along with their Cc, C values were estimated as ~2.1-4.0 MPa, ~2×10-3-1×10-2, and ~1×10-5–1×10-3, respectively. It was concluded that Kızılırmak sand exhibited Type B volumetric compression response as defined by Mesri and Vardhanabhuti (2009). Additionally, test results were also assessed within critical state framework. Critical state framework soil parameters of angle of steady state shearing resistances,  and  values were estimated as 39.4˚, 0.070, and 0.975. Initial dividing line, defining the boundary between strain hardening and softening responses, is determined specific for Kızılırmak sand.