Research on the engineering geological conditions and stability evaluation of the B2 talus slide at the Jin’an Bridge hydropower station, China

The B2 talus slide at the Jin’an Bridge hydropower station is located on the left bank of the Jinsha River and very close to the left abutment of the dam. The stability of the dam is directly influenced by the engineering geological properties, formation mechanisms, and failure modes of the B2 talus slide. This paper highlights the investigation and analysis of the in situ engineering geological conditions of the slide area. The results indicate that the B2 talus slide is composed of three parts: the talus deposits consisting of a soil-rock mixture (SRM) in the upper part, unloaded and relaxed rock mass in the middle part, and bedrock with several tuff interlayers in the lower part. Based on topographic and geomorphologic analyses, the structure of the rock and soil, distribution characteristics, formation mechanisms, and influencing factors, the strength of the SRM in the upper part and the properties of the tuff interlayer in the lower part are the main factors affecting the stability of the slide. Additionally, the failure modes of the slide are likely to be circular in nature in the talus deposits, broken line sliding along the interface between the unloaded and relaxed rock and the upper boundary of the tuff and broken line sliding along the tuff interlayer. The strength parameters of the SRM and the tuff interlayer were obtained through laboratory experiments and theoretical inverse analyses. Additionally, a three-dimensional geological model of the slide was created using the aforementioned results and the software GoCAD. Limit equilibrium and finite element methods were used to evaluate the stability of the slide using two-dimensional and three-dimensional models. The results indicate that the slope is stable under natural conditions. However, the slope may be unstable, under special conditions, such as artificial excavation, flood discharge atomization, rainstorms, and earthquakes.