This study investigates the mechanisms controlling multiphase landslide reactivation at red soil-sandstone interfaces in subtropical climates, focusing on the Eastern Pearl River Estuary. A significant landslide in September 2022, triggered by intense rainfall and human activities, was analyzed through field investigations, UAV photogrammetry, and geotechnical monitoring. Our results demonstrate that landslide evolution is governed by the interplay of geological, hydrological, and anthropogenic factors. Key findings reveal that landslide boundaries are constrained by fractures at the northern trailing edge and granite outcrops in the south, with deformation progressing from trailing to leading edges, indicative of a creep-traction failure mode. Although the landslide is stabilizing, ongoing deformations suggest disrupted stress equilibrium, emphasizing the risks of future reactivation. This work advances the understanding of progressive landslide dynamics at soil-rock interfaces and provides critical insights for risk mitigation in subtropical regions.

In this study, a large number of typical laboratory tests were undertaken to characterise the soils in the Pearl River Estuary for geotechnical design of an infrastructure project. This study reinterpreted the results of the oedometer and triaxial tests within the critical state soil mechanics framework. Non-unique normal compression lines were identified in the oedometer tests, whereas unique critical state lines were identified in the triaxial tests. This indicates that the strong forms of fabric in the intact samples were more prone to be broken down by shearing than by volumetric compression. In addition, correlations between the physical and mechanical properties of estuarine soils have also been proposed. The findings of this study form a database of soil characteristics for this region. The method of obtaining soil mechanical parameters from physical and index properties can be adopted for similar projects.