The analysis of the progressive local failure process of the Longquan Reservoir dam based on the global-local dynamic strength reduction method.

During the progressive failure process of the slope (dam), the strength parameters of the soil in the slope (dam) continuously degrade, with the degree and rate of degradation of the soil near the shear zone significantly exceeding those in other areas. To address this mechanism, this paper proposes a global-local dynamic strength reduction method that simultaneously accounts for both the physical degradation pattern of the soil and the strain softening characteristics of the shear zone. Taking the Longquan Reservoir Dam as an engineering case, a two-dimensional profile calculation model at station 0 + 142 was established using ANSYS. Combining this model with the global-local dynamic strength reduction method, the progressive local failure process of the dam under heavy rain conditions was simulated. By analyzing the distribution patterns and evolution trends of dam displacement, stress, and plastic strain, the local failure mechanism of the dam was elucidated. The results indicate that the global-local dynamic strength reduction method can effectively captures both the soil's physical degradation and the shear zone's softening mechanism, accurately reflecting the failure progression of the dam while maintaining high computational efficiency. The critical strength reduction coefficients required to reach the critical instability state using different methods exceed 1.0, indicating that the Longquan Reservoir Dam is in a safe condition, which is consistent with field observations. The progressive local failure process of the dam shows that heavy rainfall induces persistent degradation of soil strength parameters. Initially, the downstream soil undergoes plastic yielding and shear flow. As the shear failure zone continues to expand, the soil from the mid-upstream shifts downstream, ultimately leading to the collapse at the dam crest and the formation of a continuous shear zone.