Comparison and evaluation of railway subgrade quality detection methods

Subgrade is a critical component of railway systems since it provides a stable platform for the track substructure. The implementation of quality assurance methods is very important during the construction of a new railway subgrade and in monitoring the working performance of operating railways. There are several indicators available to measure the compaction and mechanical performance of a completed subgrade system, including compaction degree (K), porosity (n), modulus of subgrade reaction (K₃₀), basic bearing capacity (σ₀), strain moduli (E_v), dynamic modulus of deformation (E_vd), and light dynamic penetration (N₁₀). The objective of this research was to compare and evaluate the frequently used engineering methods in order to select the important and reliable indicators of field parameters. Four soil models with different degree of compaction were considered in the common laboratory tests and detection methods in China to determine the construction quality. The implementation and test results of these methods were analyzed and compared. The study results indicate that K correlates with n linearly. There is also a good correlation among K₃₀, E_v, and E_vd. As a recommendation, K is considered as the controlling indicator for compaction performance, and E_v2 and E_vd are considered as the controlling indicators for railway subgrade stiffness evaluation. The bearing capacity or strength indicators may be added to the quality detection work in heavy-haul railway construction.