EXPERIMENTAL STUDY ON DETERIORATION MECHANISM OF MECHANICAL PROPERTIES AND ENERGY EVOLUTION OF RED MUDSTONE UNDER DRY-WET CYCLE IN CENTRAL SICHUAN

Foundation stability,one of the most important factors in high-speed railways,is influenced by uneven deformation in red layer areas. In order to investigate the uneven deformation mechanism of high-speed railway foundations in the red layer area of central Sichuan,this paper conducted uniaxial compression tests and uniaxial cyclic loading-unloading tests on red mudstone under different dry-wet cycles. Then,combined with the test results of field emission scanning electron microscopy(FESEM),the deterioration law and mechanism of the mechanical strength of red mudstone under dry-wet cycles were analyzed based on energy dissipation theory. The results show that with the increase in the number of dry-wet cycles,the integrity coefficient and strength of the red mudstone decrease. Among these changes,the strength degradation is faster in the first five dry-wet cycles and then slows down but continues to decline after the fifth dry-wet cycle. During these dry-wet cycles,an increase in pores and loosening of the microstructure occur in the red mudstone. In detail,the number of small pores(0~0.5 μm) tends to stabilize after five dry-wet cycles,while the number of medium(0.5~1 μm) and large pores(> 1 μm) shows a slow upward trend. These changes lead to a decrease in both elastic strain energy and dissipation energy during the compression process of red mudstone under dry-wet cycles. Specifically,breakage energy dissipation decreases rapidly after the first five dry-wet cycles and increases slowly after the fifth dry-wet cycle. Meanwhile,friction energy dissipation shows a rapid decrease after the first dry-wet cycle,then a gradual decrease during the 1st-8th dry-wet cycles,and finally a slow increase in the last two cycles. Red mudstone undergoes continuous changes in microstructural characteristics under multiple dry-wet cycles. When disturbed by external loads,its energy evolution characteristics are affected,further deteriorating its mechanical properties continuously.