Experimental study on use of lightweight foam concrete as subgrade bed filler of ballastless track

Abstract Controlling settlement of ballastless track subgrade in special soil areas is an ongoing scientific problem in the construction and operation of high-speed railways—primarily because of the consolidation settlement of the ground soil, which is caused by additional stress from large loads. To reduce the subgrade weight and additional stress, the authors propose the use of lightweight foam concrete as subgrade filler, thereby controlling subgrade settlement in special soil areas. However, it remains unknown whether the ballastless track subgrade filled with lightweight foam concrete has a long-term dynamic stability under cyclic loads. To solve this problem, compressive strength and dynamic triaxial tests are conducted to analyse the static and dynamic strength of lightweight foam concrete. Then a large-scale model of a subgrade filled with lightweight foam concrete with target density of 650 kg/m 3 is established to determine its long-term performance under cyclic dynamic loads. The esults show that the strength of lightweight foam concrete with target density of 500–800 kg/m 3 can meet the requirements of both the static and dynamic conditions of ballastless track subgrade, and the ballastless track subgrade filled by lightweight foam concrete with target density of 650 kg/m 3  has a good long-term dynamic stability under cyclic dynamic loads when a dynamic buffer layer with thickness of 0.5 m is set between lightweight foam concrete layer and foundation slab.