Abstract:This article proposes a new idea for modulus back-calculation of the subgrade considering shallow bedrock and viscoelastic property. For the subgrade model, displacement boundary conditions and Kelvin model are adopted to describe the depth of shallow bedrock and viscoelastic property, respectively. The portable falling weight deflectometer (PFWD) field test is simulated by ABAQUS general finite element (FE) software, and the optimal value of modulus is iterated by multi population genetic algorithm (MPGA). Based on the new method, back-calculation results of 48 sets working condition from FE simulation tests show that the modulus average error of the forward model considering shallow bedrock is 7.0%, while that of the forward model considering half space is as high as 16.2%, which means that ignorance of shallow bedrock in the forward model of back-calculation program may cause significant error on the inversion modulus, but its influence narrows with the increase of the depth of the shallow bedrock, and the limit depth is 3m. Similarly, for the FE model considering viscoelasticity, the maximum error of ignorance of this property in the forward model reaches 27.9%, compared with error being only 7.4% of considering viscoelasticity in the forward model. In addition, due to the difficulty of exploring the depth of shallow bedrock, the researches are only conducted from the theoretical aspect.