Satellite images reveal progressive slope deformation triggered by mountainous road construction in subtropical South China

Road construction on hillslopes has increased explosively due to the rapid socioeconomic development in China’s mountainous areas. The exposure of steep and rapidly weathering slopes caused by road construction accelerates slope movements, especially roads building on residual soil. Residual soil slopes are prone to slow movements and may evolve to failure in response to infiltration of rainwater. Engineering works on residual soil (e.g., excavation, filling for buildings and roads) exacerbate these problems through altering the internal and external stress of slopes. Yet our understanding of the interactive effects of rainfall and road construction on slope dynamics or even failure in subtropical residual soils remains elusive. Here, we used three-decadal radar remote sensing data to quantify the time series deformation before a catastrophic slope failure, occurring at Meida Highway in China that caused 52 fatalities. Physics-based decomposition of the time series movements over the past 8 years reveals that there is a constant seasonal movement related to rainfall and a precursory accelerated movement triggered by slope reinforced measures before failure occurrence in May 2024. Emergency mitigations of reinforced measures modified the infiltrates and routes of surface and subsurface water, leading to an adverse impact of reducing slope failure risk. Analysis of numerical simulation indicates that rainfall-induced pore water pressure reduced the shear strength of granite residual soils, ultimately triggering slope failure. This improved understanding of the slope dynamics in response to different forces will be important to avoid economic and life loss, strengthen emergency planning and identify potential risks.