Abstract: Based on the mechanism of hydraulic damage of the surface layer of ballastless track subgrade bed, a hydraulic damage control measure of setting polyurethane crushed stone waterproof bonding layer on the surface layer of subgrade bed is proposed. By establishing three groups of test models of graded crushed stone group (J-0), permeable polyurethane crushed stone group (J-5) and dense polyurethane crushed stone group (J-10), the static and dynamic characteristics, fatigue characteristics and waterproof characteristics of polyurethane crushed stone waterproof bonding layer are studied. The results show that the residual strain of J-10 is 2.6×10–6 under static loading and unloading, and the maximum displacement is about 1.0 mm. It has a good deformation adaptability with the surface layer of the subgrade bed and an obvious energy consumption. Under the action of the train dynamic load, it can reduce the amplitude of dynamic deformation and dynamic stress on the surface of the subgrade bed and increase the expansion range of dynamic stress. Under the action of the long-term dynamic cyclic load, the dynamic response of structural layer of J-0 and J-5 increases significantly after water injection, while the dynamic response of J-10 remains basically stable after 10 000–20 000 times loading. During the test, J-10 can effectively prevent water from entering the crushed stone layer on the surface of the subgrade bed, while water continuously infiltrates in J-0 and J-5, causing the erosion of fine particles of graded crushed stone. The research work has an important application value for the treatment of hydraulic damage on the surface of ballastless track subgrade bed in rainy areas.

Key words: ballastless track, model test, hydraulic damage, polyurethane crushed stone, waterproof bonding layer