Abstract: To solve the problem that it is difficult to reasonably determine depth of rigid layer, a novel method based on inertial point is proposed. First, the multiple deflection basin curves are detected within the section to be evaluated. Then, the parameters of inertial point (the offset distance and the deflection) are determined by obtaining the minimum of the root mean square error. Finally, the particle swarm optimization algorithm is applied to perform the iteration to back-calculate the rigid layer depth and subgrade modulus from the parameters of inertial point, whose deflection does not vary with the modulus of the upper layer. Analysis of theoretical simulation shows that the proposed method can accurately back-calculate the rigid layer depth with average back-calculation error of only 1%. The filed data show that the inertial point actually exists in the deflection basin curve measured on the asphalt pavement surface, and can be used to back-calculate the rigid layer depth and subgrade modulus. Compared with existing method, the variation of subgrade modulus back-calculated from the proposed method is lower, and the regional differences can be considered.

Key words: road engineering, rigid layer, inertial point, modulus back-calculation, particle swarm optimization(PSO), deflection basin curve