Improved performance of the subgrade bed under the slab track of high-speed railway using polyurethane adhesive

The subgrade bed, which serves as an important foundation for supporting the slab track structure of high-speed railways, is usually filled with the graded crushed stone. The infiltration of rainwater into the graded crushed stone in the subgrade bed through cracks in the expansion joints can have a negative impact on the dynamic performance of the subgrade bed to affect the operational comfort and safety of high-speed rail travel. To prevent water from infiltrating into the subgrade bed, this study proposes a new waterproof seal layer made of the polyurethane polymer-improved gravels, which is placed on the surface of the subgrade bed. A variety of laboratory tests were performed to analyze the mixture parameters of the polyurethane polymer-improved gravels. A suitable gradation of the gravel used for the polyurethane polymer-improved gravels and its optimum composition were determined based on the test results employed in this research. In addition, two experimental models were established to investigate the dynamic and waterproofing performance of the subgrade bed with and without the new waterproof seal layer under cyclic dynamic loading. According to the model test results, the subgrade bed covered by the new waterproof seal layer displayed significantly better performance compared with that of the conventional subgrade bed when water was poured on the surface of the subgrade bed during cyclic dynamic loading. (C) 2019 Published by Elsevier Ltd.