Frost heave in cold regions requires urgent measures to improve the mechanical properties of soils. However, harsh climatic and environmental conditions escalate the costs of engineering construction and operation. Therefore, it is imperative to enhance the sustainability of engineering designs. In this study, different sisal fibre contents, specific proportions of metakaolin, and alkaline activators were added to silty clay to alleviate frost heave, as well improve the mechanical properties of soils. Firstly, the unconfined compressive strength (UCS) and shear strength of soil samples containing varying sisal fibre geopolymer were tested before and after freeze-thaw cycles (FTCs). To analyse the effect of FTCs on thermal conductivity, the thermal conductivity of fibregeopolymer solidified soil (FGSS) with different sisal fibre contents was evaluated. Subsequently, X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry were conducted on the samples before and after the FTCs. Then, the variations in soil temperature, volumetric unfrozen water content, heat flux, vertical deformation, and soil pressure during the FTCs were analyzed. The results indicated the following: 1) Sisal fibre and geopolymer improved the mechanical performance and adhesion among soil particles of FGSS after the FTCs. 2) The thermal conductivities of FGSS showed a tendency of initially increasing, then decreasing, and finally increasing as the sisal fibre content increased. 3) The addition of sisal fibres did not cause new chemical reactions but inhibited the reaction between metakaolin and the alkaline activator. 4) The combination of sisal fibre and geopolymer effectively mitigated frost heave. 5) Sisal fibre incorporation reduces CO2 emission index and economic efficiency index. Therefore, FGSS is proposed to provide a green and effective approach for addressing geotechnical engineering issues in cold regions.