The use of excavated soil from highway construction sites to produce foamed polymeric soil， employed as a thermal insulation layer for seasonally frozen subgrades， not only achieves comprehensive resource utilization but also mitigates frost damage to the subgrades. Based on the excavated soil along the Urumqi Ring Expressway， combined with cement and foam， the foamed polymeric soil with porous insulation properties was developed. The influences of wet density， soil admixture， and water-cement ratio on the thermal conductivity， unconfined compressive strength， and stiffness of foamed polymeric soil were systematically investigated， establishing an intrinsic connection between pore structure and macroscopic performance. The research findings indicate that when the density of foamed polymeric soil increases from 600 kg/m³ to 1 200 kg/m³， its thermal conductivity approximately doubles， strength increases by about 3.95 times， and modulus increases by approximately 10.5 times. Compared to traditional subgrade soil， the thermal conductivity of foamed polymeric soil is significantly reduced by 52%-96.4%. Further analysis of the pore structure reveals that as the pore size of foamed polymeric soil within a unit volume decreases， the proportion of the skeleton increases correspondingly， while the volume of air pores decreases. This microstructural change manifests as improved thermal insulation performance （i.e.， reduced thermal conductivity） and significant enhancement in mechanical properties （including strength and stiffness） at the macroscopic level. Foamed polymeric soil not only demonstrates better thermal insulation performance but also exhibits strong mechanical characteristics， providing a suitable solution for the thermal insulation layer of seasonally frozen subgrades.