The bonding contact presents complex modes in polyurethane-mixed ballast. The commonly used parallel bond model is revised and four different contact models are developed including Ballast-Ballast Contact Bonding, Ballast-Ballast Noncontact Bonding, Ballast-Sleeper Contact Bonding, and Ballast-Sleeper Noncontact Bonding. The mechanical behaviour and energy evolution of polyurethane-mixed ballast with various amounts of glue are studied from the macro and mesoscopic properties. Results show that the elastic strain energy has always been the main form in polyurethane-mixed bed, followed by viscous strain energy, frictional energy, and damping energy. Compared with the common ballast bed, there are more contacts in polyurethane-mixed ballast bed and, when more glue is used, the amount of contacts is further increased while the maximum contact force is reduced. After bonding, the amount of contacts is significantly increased and all forms of energy become more evenly distributed at different surfaces of the sleeper. The kinetic energy of polyurethane-mixed ballast fluctuates with smaller amplitude and convergences more quickly under cyclic loading, which is reflected in the macroscopic aspect that the settlement of polyurethane-mixed ballast bed is relatively small and can be fast completed.

Turnout is the key component of the railway tracks for trains to change direction, which is vital to operational safety and passenger comfort. Therefore, it is of great importance to perform a scientific and reasonable tamping operation for turnout areas. In this paper, based on the commercial software EDEM and RECURDYN, a coupled simulation model of the large machine tamping device-rail-sleeper-ballast bed in the turnout area is jointly established, and the correctness of the model is verified by the test results of the lateral resistance of the ballast bed. The influence of tamping operation on the macro-and micromechanical properties of ballast bed at the switching part of railway turnout areas is studied and recommendations for the optimization of tamping operation are proposed. The results show that in the squeezing stage, strong force chains are distributed concentrately under sleepers, where the distribution range is approximately elliptical with a depth of 150 mm. After tamping, only the 200-mm ballast under the sleepers is compacted, where the compactness is increased by 5.9%. On the contrary, the compactness of the ballast in the sleeper crib is reduced by 27.4%, which is the weakest part. To ensure favorable tamping quality, the tamping sequence at the switching part of railway turnout areas is suggested to be conducted in order of first through track and then diverging track.