Research on the Design Technique of Subgrade Bed for Heavy Haul Railway in Bangladesh

Research purposes: The connection line of the Padma Multipurpose Bridge in Bangladesh is an important passage linking the cities on the east to those on the west banks of the Padma River. Based on the structure type and size of heavy haul railway subgrade bed in Bangladesh, this research adopted the train load-transfer mode and the three-index design method of the subgrade bed structure, for analyzing the design principles and procedures applicable to the Bangladesh railway subgrade bed. Additionally, some design indicators and filling method statement for heavy haul railway subgrade bed under 25 t axle load were proposed. Research conclusions:(1) The design indexes of heavy haul railway subgrade bed currently adopted in Bangladesh does not meet the requirements of strength, deformation and long-term stability. Furthermore, the safety storage and durability for subgrade bed are lower than the Chinese standards. (2) The strength control should be adopted as a design principle for the subgrade bed of heavy haul railway in Bangladesh, which will ensure that the ultimate dynamic load of each structural layer in subgrade bed is lower than the allowable dynamic strength of the filler. The Ev2 of the surface layer of subgrade bed should be greater than 100 MPa, and the Ev2 of the bottom layer of subgrade bed should not be less than 60 MPa. (3) A mixture by volume ratio of 70% broken bricks + 30% medium-coarse sand should be applied for fillings on the surface layer of subgrade bed, and a mixture by ratio of 35% broken bricks + 65% silty fine sand should be applied on the bottom layer of subgrade bed. (4)The research results can be applied to the area of subgrade bed design for heavy haul railway in Bangladesh or South Asia. © 2021, Editorial Department of Journal of Railway Engineering Society. All right reserved.