CT-based investigation on internal structure evolution for high-speed railway graded aggregate materials during vibratory compaction

Abstract

The research gap on the internal structure evolution (ISE) of the high-speed railway graded aggregate (HRGA) materials during vibratory compaction has resulted in challenges in exploring its compaction physical-mechanical properties. Based on a self-developed vibratory compaction instrument (SVCI), a new assessment framework was established to evaluate physical-mechanical evolution properties during vibratory compaction, including the revised dry density ρrd, the revised soil stiffness Krb, and the revised modulus of subgrade reaction K20. The X-Ray computed tomography (X-Ray CT) tests of an HRGA specimen at different compaction stages were carried out to characterize the physical-mechanical evolution properties. The results show that during vibratory compaction, the ρrd presents a rapidly increasing-slowly increasing-continuously stable evolution, while Krb and K20 shows a rapidly increasing-slowly decreasing characteristic. The compaction locking point Tlp is proposed to quantify the inflection point of mechanical properties during vibratory compaction, which is related to the gradation types of the HRGA materials. Before achieving the compaction locking point Tlp, coarse grains gradually deflect toward horizontal orientation to form a stable skeleton with insignificant crushing. Approximately 60% of coarse grains in the horizontal direction can achieve a stable skeleton under the action of the excitation force. After achieving Tlp, the coarse grains present the localized crushing phenomenon at the contact points due to further compaction, and it indicates the destruction of the stable skeleton. The overall shape of the coarse grains remains unchanged, but their surface corners are gradually rounded. The experimental results can make a significant contribution to the filed for further investigating the vibratory compaction mechanism and enhancing the compaction quality control system.