Subgrade heave is a significant concern in high-speed railway construction, particularly in recent years. It is prevalent in many high-speed railway subgrades located in the northwest, central, and southwest regions of China. Rectifying this issue is challenging due to the limited deformation capacity of the heave on the track, which is adjusted with fasteners. This study identified the primary cause and analyzed the internal mechanism of action of heave induced by low-content, medium-soluble sulfate (primarily anhydrite) in subgrade fill using on-site deformation monitoring and sampling tests. The heave distress of the subgrade of a high-speed railway under construction in East China was considered as the research object. The study found that the cement-treated graded macadam subgrade fill material at the affected construction site contained a small amount of anhydrite, with a maximum content of 0.87%. The hydration and expansion of anhydrite were limited, resulting in maximum heave deformation of 3.4 mm at the K8–K10 distressed section. Therefore, anhydrite was the primary cause of heave distress in this section of the subgrade. The expansion potential of the anhydrite fill material was closely related to the water environment, and the heave deformation was positively correlated with the moisture content of the fill material. The prevention of this type of heave distress should focus mainly on controlling the anhydrite content in the fill material, with a recommended value of 0.20% (expressed as SO3).
Li et al. (Thu,) studied this question.