Purpose: Salt rock from salt lakes can serve as a cost-effective material for subgrade filling, as demonstrated in projects like the Qarhan Salt Lake section of the Qinghai-Tibet Railway and the Qarhan Salt Lake section of the G215 Highway. This state-of-the-art paper aims to summarize the engineering properties of salt rock filling and present the advances of its utilization.Design/methodology/approach: This paper collects and analyzes laboratory and field data of salt rock filling from previous studies to present a comprehensive analysis of the engineering properties and utilization of salt rock fillings.Findings: Salt rock primarily contains minerals such as halite and glauberite, which contribute to its unique phase-changing behavior under varying environmental conditions, impacting its mechanical properties. Salt rock filling shrinks when in contact with vapor or unsaturated brine and expands under cooling or evaporation. Its use is particularly recommended for arid regions, with specific restrictions depending on the structure type. This paper discusses suggested countermeasures to mitigate these issues, as well as key quality acceptance indices for salt rock filling compaction. Moisture content after air-drying is recommended as a crucial parameter for construction quality control.Originality/value: This review aims to support future research and engineering practices in salt rock subgrade applications.

Locally available rock salt is a potential fill material for infrastructure construction in arid salt-lake regions, where conventional soil and aggregate resources are often scarce. However, its mechanical performance is strongly affected by water migration, brine concentration, salt dissolution, and possible recrystallization-induced bonding. This study investigates the unconfined compressive strength (UCS) of compacted rock-salt fills under different water contents, initial brine contents, relative compaction levels, and brine concentrations. The results show that UCS increases nonlinearly as water content decreases during air drying, with slow strength development at the early drying stage followed by rapid strength gain at low water contents. This behavior is consistent with a transition from capillary liquid bridges to stronger salt-related interparticle bonding during brine evaporation and possible recrystallization. The effect of initial brine content is state-dependent: higher initial brine content reduces UCS in the as-compacted state but markedly increases UCS after drying to constant mass, suggesting enhanced interparticle bonding after drying. Under constant-mass air-dried conditions, UCS first increases and then decreases with increasing relative compaction, reaching a peak of approximately 8.7 MPa at a relative compaction of 0.99. Lower brine concentration reduced the UCS of dried specimens, indicating that saturated brine may be more favorable for specimen preparation and field compaction under dry salt-lake conditions. An empirical UCS prediction equation incorporating water content, dry density, initial brine content, and brine concentration was developed and validated, giving good agreement with the test results with R² = 0.91. The findings provide a material-level basis for evaluating and controlling compacted rock-salt fills under controlled dry conditions, while further durability and field validation are required before extending the results to long-term railway subgrade performance.