An X-Ray CT Study on Transitional Internal Erosion under Triaxial Shearing

Internal erosion poses a significant threat to many geotechnical infrastructures as fine particles removed from gap-graded soils, which can be promoted by mechanical disturbances caused by human activities and natural hazards. This study investigates the transitional behavior of internal erosion as gap-graded soils undergo triaxial shearing under a constant hydraulic gradient. Three gap-graded samples consisted of Leighton Buzzard sand (LBS) with varying fines content, representing underfilled, filled, and overfilled conditions, are examined. X-ray tomography scans are performed during the loading process and quantified through subsequent image processing. The progression of internal erosion is characterized at both sample scale and pore scale. Experimental results reveal distinct internal erosion behaviors. The underfilled sample experiences rapid internal erosion with uniformly distributed empty pores, indicative of suffusion. Conversely, the filled and overfilled samples are subject to channel formation and backward erosion, followed by rapid channel expansion.