Experimental study on progressive deformation and failure mode of loess fill slopes under freeze-thaw cycles and earthquakes

Abstract

Earthquakes and freeze-thaw cycles are two important causes of landslides, but knowledge of their combined effect is limited. Therefore, a freeze-thaw test and large-scale shaking table tests were carried out to simulate the progressive deformation and failure mode of loess fill slopes. The process of frost-heaving deformation and seismic deformation was observed, and the failure mode was analyzed by comparing with the accelerations. The results showed that the slope stability decreased after freeze-thaw cycles. Freezing and thawing causes the crest and upper portion melted, and settled to the lower portion, creating frost-heaving zones and irreversible cracks. Comparisons between the freezing-thawing slope and nonfreezing-thawing slope allowed to highlight, through the analysis of seismic responses, the possible and not negligible effect of both frost-heaving spatial distribution of slope surface soil and freeze-thaw interface during the seismic shaking in initiation and development of landslides. The peak ground acceleration (PGA) amplification factors of freezing-thawing slope were higher, especially in the frost-heaving zones. Cracks in freezing-thawing slope developed faster and deformation was greater. The freeze-thaw interface became a potential slip surface and a multistep landslide suddenly occurred under 1.2 g seismic loads, while the nonfreezing-thawing slope was stable. The freezing-thawing slope shows a brittle superficial shear failure, and its failure mode is freeze-thaw cycles - forming potential sliding surface and irreversible cracks - slow expansion of cracks - rapid development and penetration of cracks - superficial shear sliding.