Effects of cement content and grain-size composition on engineering properties of high-speed-railway macadam subgrade

Abstract

Cement-stabilized macadam (CSM) is being used in high-speed railway (HSR) subgrade in seasonal frozen regions in China. This study conducted a series of tests to determine the characteristics of HSR CSM subgrade in cold regions. In particular, the influence of cement content and grain-size composition on the compaction effect, frost heave property, permeability, freeze–thaw durability, and shrinkage property of macadam subgrade were analysed. The results show that the compaction quality indexes of CSM subgrade satisfy and even exceed the compaction quality standards for HSR subgrade. Removal of soil particles smaller than a certain size weakens the frost heave sensitivity, improves permeability, and reduces the unconfined compressive strength (UCS) and moisture stability of CSM. Cement addition effectively compensates for the reduction in UCS; however, it increases the shrinkage deformation of CSM. The temperature and dry shrinkage coefficient of CSM increase with cement content. The shrinkage properties of CSM subgrade are the least favourable in the temperature range −10°C to 10°C. The UCS first decreases with increase in the number of freeze–thaw cycles and then becomes stable after 10cycles. In the engineering practice of HSR subgrade in seasonal frozen regions, in a subgrade where permeability is not a necessary characteristic, CSM with 3% fines content and 3% cement addition is suitable, and in a subgrade where permeability is a necessary characteristic, CSM with grains larger than 0.5mm and 3% cement addition is suitable.