To investigate the deformation and failure mechanisms of salt frost heave due to solution crystallisation in sulphate saline soils, this study examined the relationship between crystallisation volume changes and frost heave deformation under varying solution concentrations during cooling. A series of tests was conducted to analyse the deformation behaviour of saline soils with different water and salt contents. Results show that total deformation is governed by the interaction between salt heave and frost heave, varying with salt content. A minimum deformation state was observed when the magnitudes of salt heave and frost heave were balanced. Notably, no direct correlation was found between total crystallisation volume and total deformation when both salt and ice crystallised in pores. However, salt crystallisation before freezing correlated with salt heave, and crystallisation after freezing correlated with frost heave. These findings enhance understanding of the coupled mechanisms of salt expansion and frost heave and support the development of predictive models and mitigation strategies. This research holds considerable significance for the future application of saline frost heave prediction models in civil and geotechnical engineering, particularly in preventing and mitigating structural damage induced by frost action.