Influence of backfill compaction on progressive failure mechanism of retained soil mass using DIC technique

This paper presents the results of a series of experimental tests that were conducted under passive conditions and revealed the evolution of strain bands in the backfill of earth-retaining structures (ERS) compacted at different density levels. The highresolution camera was used to capture the images of undeformed and deformed soil specimens and the digital image correlation (DIC) approach was used to analyze the obtained images and determine the displacement and strain fields. Two backfill materials have been compacted at three density levels, including sand and fine gravel. The image analysis results unveiled that under purely translational wall motion, the primary failure surface initiates at the wall toe and no sequential 'intermediate failure surfaces' are observed. In addition, the laboratory tests recorded the horizontal forcedisplacement curve, wall-soil interface frictional angle, and earth pressure distribution throughout depth. These results showed good alignment when tested against a variety of analytical models. Furthermore, the FE model was extended to explore the effect of wall rotation. It was found that under rotational motion about the toe, however, intermediate strain bands do develop prior to the ultimate failure surface, initiating near the top of the wall. The classical Log-Spiral-Hyperbolic assumption of sequential failure surfaces is therefore mode-dependent. Hence, the based methodology of LSH model should be revisited.