Study on continuous compaction indicator of railway subgrade based on harmonic balance identification method

Based on vibratory compactor-soil dynamic model, fast Fourier transformation method was used to conduct the harmonic analysis on the acceleration signal of roller vibratory drum. Equations for soil parameter identification were established based on the harmonic balance principle of compactor-soil system response to various order harmonics. Multidimensional least-square method was adopted to identify the parameters of compacted soil (i.e., stiffness and damping). Simulation results showed that the identification accuracy increased with the increase of the number of harmonics. The identification accuracy still reached 0.97 even when the noise power was 0.05. It indicated that harmonic balance identification method was of higher accuracy and better anti-noise property. Combined with the field acceleration signal of roller vibratory drum, the correlation between continuous compaction indicators (i.e., C_MV, soil stiffness and soil damping identified by harmonic balance method) and the traditional subgrade compaction indicator E_vd was checked. The results showed that the correlation coefficient between soil damping and E_vd was the lowest while the correlation coefficient between soil stiffness and E_vd was the highest under different soil compaction conditions, which revealed that the identified soil stiffness could accurately reflect the state of soil compaction. Thus, the identified soil stiffness is proposed to be regarded as an index for evaluating the continuous compaction of railway subgrade.