MECHANISMS AND EVOLUTIONARY PROCESSES OF LARGE DEEP-SEATED TOPPLE DEFORMATIONS: A CASE STUDY OF THE YAGONG TOPPLE DEFORMATION FAILURE IN THE LANCANG RIVER

In the high mountain and canyon region at the eastern edge of the Qinghai-Tibet Plateau, the rapid incision of the Lancang River near the dam section of the upstream GS Hydropower Station has led to the development of large-scale deep-seated topple deformation failures. The geological structure in this area is complex. To investigate the formation mechanisms and evolutionary processes of these large deep-seated topple deformation failures, this study focuses on the Yagong topple deformation failure in the upper reaches of the Lancang River, which has a depth of approximately 150 meters and covers an area of 1.14 million square meters. Detailed analyses of the geological conditions, developmental characteristics of the topple deformation failure, and rock mass structure were conducted. Additionally, numerical analysis and physical simulation experiments were employed to thoroughly explore the mechanisms and evolution of the topple deformation during the river incision process.

The study found that the original in-situ stress was high. As the river valley continued to incise, the rock mass experienced intense unloading rebound. The severe unloading effect on the riverbank slopes led to structural damage in the rock mass, weakening its mechanical properties and generating numerous unloading cracks. The intense unloading caused further redistribution of the stress field in the slope, forming stress relaxation zones within the strong unloading areas. The principal stress direction in these zones shifted to the gravitational direction, leading to topple failures in steeply inclined, thin-layered rock masses. As the river valley continued to deepen, numerous unloading cracks continued to develop, and the topple fracture zones progressively extended into deeper rock masses. These local deformations within the slope caused significant cumulative deformations of the entire slope, eventually evolving into deep-seated topple failures.

This research provides significant insights into the formation mechanisms and evolutionary processes of large deep-seated topple deformation failures and offers a theoretical foundation and technical support for slope stability assessment in similar geological environments.