Effects of size and shape of sand grains on some engineering properties of a clayey soil

This thesis presents an experimental research studying in the effect of shape and size of sand grains on some geotechnical properties of a clayey soil using unconfined compression and triaxial compression machines equipped with a pair of bender elements. The materials used in this study were low plasticity clay, Narli Sand and Crushed Stone Sand. Three different gradations of the sands (0.6-0.3, 1.0-0.6, and 2.0-1.0) mm were chosen. Five contents of clay-sand (90-10, 80-20, 70-30, 60-40 and 50-50) by dry weight were investigated. Series of bender elements (BE) tests were carried out on clay-sand mixtures to measure small strain shear modulus (Gmax). Unconfined compression (UC) tests were conducted on these mixtures to have a correlation between Gmax and unconfined compressive strength (qu). Gmax and qu increased with increasing roundness and sphericity of sand grains. The qu values decreased, and the Gmax values increased when sand content in the mixture increased. As size of sand grains increased, Gmax and qu values increased. For the results that obtained from triaxial compression machine equipped with bender elements tests, the deviatoric stress increased with increasing content, size, roundness and sphericity of sand grains. The pore water pressure decreased as sand content increased and it is increased as size, roundness and sphericity decreased. The effective cohesion (c') decreased and effective angle of friction (ϕ΄) increased as sand content increased. A correlation between Gmax, voids ratio and effective stress were developed for rounded and angular sand of clay-sand mixtures.