Abstract: This study establishes a mechanical model of circular hole expansion considering soil disturbance to investigate the correlation between the specific penetration resistance of static cone penetration testing and the mechanical parameters of soft soil layers. By analyzing the data from single-bridge static cone penetration tests and combining with the theory of circular hole expansion, a relationship model between the specific penetration resistance and the elastic modulus, Poisson's ratio, cohesion, internal friction angle, and soil sensitivity is constructed. The variability of the silt-muddy soft soil layer at the background engineering site is small, and the measured data is representative for theoretical comparison calculations. The validation results indicate that the model can accurately describe the relationship between the specific penetration resistance and mechanical parameters, especially in high-sensitivity soil where the compression effect of disturbed soil is enhanced, leading to an increase in the specific penetration resistance.