Effect of Freezing on Stress-Strain Characteristics of Granular and Cohesive Soils

To investigate the stress-strain behavior of frozen soils, a program of triaxial compression tests was designed and carried out on samples of unfrozen and frozen cohesive (CL) and granular (SP) soils and pure ice. The experiments involved study of the influence of freezing, temperature reduction, and loading rate on the stress-strain characteristics of the frozen ground. The aim of this study is to assess the possibility of using the artificial ground freezing (AGF) technique in the excavation and tunneling in Line 2 of the Tabriz Subway project. The results show that freezing of the CL soil has no significant effect on the type of soil behavior (strain hardening), whereas freezing of the SP soil changes its strain-hardening behavior to strain softening. The effect of freezing on the increase in shear strength of the saturated SP soil is much greater than that of the saturated CL soil; however, the rate of increase in the shear strength due to freezing and temperature reduction is much greater for the CL soil. Freezing and reduction in temperature cause an increase in the elastic modulus of all the materials tested in the present study. In addition, the shear strength and elastic modulus of these materials increase with loading rate.