Mohan Zhao’s scientific contributions

When an impact load is sufficiently small, its influence on the pavement structure is mainly from the surface layer material. To explore the influence depth of an impact load and back‐calculation of the pavement surface modulus, both numerical calculation and experimental testing were conducted, and the results are presented in this paper. The numerical calculation was performed through a DEM‐FDM‐coupled model. After a new modulus back‐calculation algorithm is formed by analyzing the numerical modeling results, experimental tests were also conducted for verification, and the results were analyzed. The max value of the falling weight impact force was closely related to the elastic modulus of the material, and the influence depth was controllable. Finally, it is proved that the method can be used to calculate the surface layer modulus and estimate the surface layer thickness.

Asphalt pavement stress responses are analyzed with the layered elastic system under static loads in the most popularly-used design specifications. In reality, however, traffic loads are moving and the pavement layer materials are mainly aggregated. In order to reasonably consider vehicular loads and layer material features, this paper presents a discrete-continuous coupling model for analyzing asphalt pavement dynamic stress responses under moving loads. The numerical model is divided into an asphalt pavement structure and a moving wheel load. Specifically, the wheel load and the asphalt layer under its load were modelled with the discrete element method to simulate the actual vehicle loads and meso-scopic components of the asphalt mixture. In contrast, the remaining parts of the pavement structure were modelled with the finite difference method. The wheel load was set to move on the surface layer of asphalt pavement at a constant speed as the numerical simulation was conducted. The results were analyzed based on special points of dynamic stress curves. The results showed that: different from the static stress responses, in a typical asphalt pavement dynamic stress curve, there existed three stages of stress responses, namely the stress smoothing stage, stress surge stage, and stress dissipation stage, which had significant fluctuations at high levels and asymmetry. Besides, the loading velocity and mixture meso-structure significantly influenced on the dynamic stress responses of asphalt pavement. Especially the average peak stress calculated by the discrete-continuous coupling model, which considered the mixture meso-structure decreased by 10% compared to the finite-difference model.