Babak Karimi

Freeze-thaw cycles have a significant negative effect on the engineering behaviour of soil in cold regions. In this study, the compressive strength of stabilized, poorly graded sandy soil used in road pavement that was subjected to different freeze-thaw cycles was studied. Samples with three different particle shapes were stabilized with a binder developed by mixing polyvinyl acetate (PVAc) and ethylene glycol monobutyl ether (EGBE). The PVAc/EGBE weight ratio was 2:1, and PVAc was added at 1%, 2%, and 3% of the dry weight of the soil, with the effect of up to ten freeze-thaw cycles evaluated. Results showed that the addition of binder decreased optimum moisture content and increased compressive strength. An increase in particle roundness results in a decrease in the magnitude of compressive strength but increases the soil composite ductility. Changing particle shape from angular to rounded resulted in a more significant decrease in compressive strength than changing from rounded to well-rounded. The decrease in compressive strength is most significant between the first and fourth freezing-thawing cycles and marginal between the fourth and tenth. The negative effect of increasing the roundness of particles is compensated by increasing binder percentages.

Various methods can be applied to improve soil behavior in order to increase the bearing capacity or reduce the settlement of footings. These methods can be categorized as stabilization or improvement of soil by use of different geosynthetics; injection methods; grouting or replacing weak soil with stronger materials. One of the most common methods and materials that can be used for improving soils, is placing a stone layer under the footing. In this study, a stone layer under a strip footing is simulated with the finite element method (FEM) to estimate the soil behavior in different conditions. A strip footing with a width of 1m and length of 8m with a 100 kN/m2 uniform load was modelled. Different widths of stone layer from 1B to 3B (B was the strip footing width) with different depths of 0.5B, 1B, 1.5B, and 2B were modelled in Plaxis 3D and results were obtained from the simulation. By reviewing the results, it was found that the optimum dimensions of the stone layer to place under the presented strip footing was 2B width and 1B depth. This result can be applied to real projects with similar conditions.