AbstractMany studies have been carried out on the influence of freeze–thaw cycles on the mechanical behavior of cement- or lime-stabilized soils. However, very limited studies have considered the effects of freeze–thaw cycles on cement-stabilized soil reinforced with fibers. The main objective of this study is to determine the effects of polypropylene fiber (PPF) and basalt fiber (BF) content (0%, 0.5%, 1%, 2%, and 5%), cement content (0%, 3%, and 9%), number of freeze–thaw cycles (0, 2, 4, 8, and 10), and initial moisture content on the unconfined compressive strength (UCS) of clay soil. The study reveals that adding cement, PPF, or BF to soil causes a remarkable increase in strength, where the strength of the PPF-reinforced specimens is significantly more than that of BF-reinforced ones. The UCS values of the specimens compacted at optimum moisture content (OMC) are almost more than those that were prepared at a molding moisture content of 0.8 OMC or 1.2 OMC. The strength of specimens increases with increases in cement content and curing time. However, the axial strain at failure for cement-stabilized specimens decreased with increasing cement content or curing time. Furthermore, it is concluded that the increase in the UCS of combined PPF or BF with cement inclusion is more than that caused by each fiber without cement. A regression model is developed to predict the UCS in terms of four effective agents for each case of stabilization by BF or PPF. Results indicate a satisfactory performance of the model where the Pearson correlation coefficient above 0.95 for UCS prediction is obtained.