Stability mechanism recognition and failure risk assessment on a high slope by synthesizing different analysis methods

The studied slope is located in the middle reach of the Yalong River in the eastern margin of Qinghai-Tibet Plateau in Southwest China. A large hydropower station is planning to be built near the slope. Understanding the stability mechanism of the slope is important for dam site design. Under a combination of tectonic activity, unloading and weathering, the bedrock mass was fractured. On the basis of field investigation, the GSI classification system and Barton criterion were introduced to determine the strength of the rock mass. The kinematic, limit equilibrium and discontinuum modeling methods were carried out to comprehensively understand the stability of the slope. The kinematic analyses show that only wedge mode is possible for large rock mass failure. However, limit equilibrium analyses show that both wedge failure and circular slip are not expected for rock mass. The slope rock mass is now in the surface rebalance stage. The potentially unstable part is the covering deposit. The 40 million m3 surface deposit is now nearly in a limit equilibrium state. The possibility of failure reaches 41%. Mitigation measures must be put into effect on the deposit to assure the stability of the slope. The results indicated that the failure mechanism of the slope was not controlled by the discontinuities in the rock mass at present but depended on the stability of the surface deposit.