Objective In the context of intensifying human activities, large-scale ecological and engineering construction continuously alters regional hydrogeological environments and can induce new types of geohazards. Traditional landslide studies have mainly focused on natural rainfall-triggering mechanisms, whereas the coupled effects of long-term anthropogenic irrigation and extreme rainfall remain poorly understood, especially in red-bed soft-rock areas with dense engineering activities. This study aims to reveal the multi-stage dynamic mechanism of landslides triggered by this coupled effect and to clarify how human activities can systematically modify hydrogeological conditions and become a key factor controlling disaster mode and scale.

Methods Taking the Jiujiawan large landslide along the Lanzhou-Xinjiang High-Speed Railway as a typical case, an integrated framework combining space-air-ground investigation, drilling, geophysical exploration, shear testing, and stability back-analysis was adopted to systematically investigate geological structure, strength parameters of rock and soil masses, stability evolution, and energy back-analysis in the landslide area.

Results The results show that: (1) human activities systematically altered hydrogeological conditions through two pathways: heterogeneous deterioration of rock masses induced by areal irrigation and concealed water-rich soft-plastic layers formed by canal seepage. The seepage-induced concealed soft-plastic layer is a key weak geological unit controlling the long runout of the landslide. (2) A three-stage dynamic evolution model of long-term incubation, short-term triggering, and catastrophic failure was established. The factor of safety (Fs) decreased from 1.24 in the long-term incubation stage to 1.02 at the critical instability state. (3) Quantitative back-analysis confirmed that the lubrication effect of the anthropogenic concealed water-rich soft-plastic layer reduced the equivalent friction coefficient of the sliding bed sharply from 0.35 under natural conditions to 0.15, thereby controlling the cumulative landslide displacement of 102 m.

Conclusions This study proposes a new perspective of human activities as geological-structure shapers and establishes a conceptual model of human activities, hydrogeological-condition alteration, and concealed sliding-control structure formation. The results indicate that, under specific geological conditions, human activities have shifted from being a traditional disaster-triggering factor to a key controlling factor that determines disaster mode and scale. These findings provide a new theoretical framework for risk identification, dynamic assessment, and source control of major engineering geohazards in areas with intensive human activity.