An experimental investigation on progressive failure mechanism of the earth-retaining structure with sloping backfill using image analysis

In this study, a reduced-scale retaining wall specimen was subjected to laboratory testing to examine the strain localization phenomena behind an earth-retaining structure under passive conditions. The specimen was backfilled with two distinct soil materials—sand and fine gravels—in a medium dense state, while also retaining sloping ground surfaces with varying inclinations. The soil particle movement within the backfill was monitored and tracked through successive images captured at a consistent rate using a camera, as the wall progressively approached the backfill. By employing the digital image correlation technique, von Mises strain contours within the backfill were subsequently deduced from the recorded soil particle displacement field. This method unveiled the distribution and progression of strain concentration bands. Moreover, the laboratory tests documented the horizontal force–displacement curve of the wall, the earth pressure distribution across depth, and the wall’s uplift. These findings were verified against various analytical models and finite element simulations, illustrating good alignment. The von Mises strain maps disclosed the presence of a distinct boundary within the backfill, beyond which soil particles remained immobile during the pushover test. This boundary manifested during the early phases of the test when stress levels were relatively low. For specimens with positive slopes, this boundary evolved into the ultimate failure surface, characterized by a geometry resembling a log-spiral curve. Conversely, for specimens with negative slopes, the failure surface may not adhere to this log-spiral boundary; instead, it might follow a more direct route, resembling the straight line predicted by Rankine theory.