Centrifugal model test study on instability mechanism by rain of widened roadbed slope

To study the instability mechanism of the slope of the widened highway roadbed during rainfall, a rainfall simulation device was developed for geotechnical centrifugal model testing. Settlement and widening tests for the old roadbed, and settlement and simulation rain tests for the widened roadbed were performed in sequence. During the test, the settling process of the old and the new roadbeds and the instability process of the embankment slope by rainfall were observed by the settling monitoring device installed on the centrifuge manipulator system. The test results showed that the major consolidation of the old roadbed was completed in the first year of operation; after the roadbed was widened, the new settlement of the old roadbed was much smaller than the new settlement of the widened roadbed, resulting in the differential settlement between the new and old roadbeds. Longitudinal cracks formed by the differential settlement on the road surface provided infiltration channels for rainwater. After rainfall, the rainwater first infiltrates downward at the foot of the slope and expands the vertical joints of the loess to form vertical infiltration channels, causing settlement at the foot of the slope. After that, the rainwater infiltrated laterally into the interior of the roadbed and beyond the slope toe, increasing further settlement. The settlement area expanded continuously, eventually causing the roadbed slope to become unstable. According to the research results, the key to preventing rainfall damage to the subgrade was to protect the slope foot, block the rainfall infiltration channel, and reduce the settlement of the foundation.