Force-based and Displacement-based Back Analysis of Shear Strengths: Case of Tsaoling Landslide

Tsaoling landslide is a notorious gigantic landslide triggered by the Chi-Chi Earthquake at Taiwan in 1999. The landslide provided a valuable case study to review the available methodologies in analyzing seismic induced landslides. In this study, the force-based back analysis method is applied to investigate the
shear strengths of the Tsaoling landslide. Additionally, the calculation results are compared with the ones analyzed by displacement-based analysis. The analysis results confirm that the conventional force-based analysis method, which introduces the maximum horizontal seismic acceleration to the seismic analysis,
overestimates the shear strengths. An appropriate factor to “discount” the acceleration or the defining slope safety factor is required in the force-based analysis to obtain accurate shear strengths. On the other hand, the displacement-based analysis, such as Newmark sliding model, provides an lternative way to pursue accurate shear strengths if a seismic-slope failure regression formula is also available. Additionally, the GPS data of ground displacement in a large earthquake are crucial for baseline correction to guarantee the correctness of the seismic data.