Study on deformation characteristics and mechanism of reactivated ancient landslides induced by engineering excavation and rainfall in Three Gorges Reservoir area

From 2015 to 2017, construction for the Dalixi Eco-Industrial Park in Dalixi Village, Xingshan County in the Three Gorges Reservoir area, reactivated a series of ancient landslides. In particular, in April and May 2017, large-scale excavation and continuous heavy rainfall induced the Huangjialing and Tuanbao landslides. Moreover, in the subsequent excavation processes, the continuous deformation development of the Dalicun landslide seriously threatened the surrounding infrastructure and safety of residents. Based on geological surveys and on-site macro inspections from the past two years, manual GNSS (Global Navigation Satellite System) displacement monitoring data from the past year, and automatic GNSS monitoring data from the past three years, the characteristics and mechanisms regarding the continuous deformation of the Dalixi slope were studied. The results indicate that: (1) The Dalixi slope is a soft-bearing, middle-steep bedding, rocky ancient landslide. (2) The landslide instability and deformation of the Dalixi slope is closely related to the effects of excavation. Specifically, the transverse landslide deformation was concentrated in areas with extensive excavation activities, and gradually weakened along both sides. Meanwhile, longitudinal deformation gradually advanced to the middle and rear, showing the developmental characteristics of a gradual retreat. Further, deep deformation was characterised by multilayer shearing. (3) Excavation is the main and inducing factor for the reactivation of the landslide, while rainfall is a motivating factor. Together, these factors promote continuous deformation development. This study is of great reference value for understanding the development of reactivated ancient landslides induced by engineering excavation and rainfall in the Three Gorges Reservoir area.