Seismic Response of a Very High GRS Wall: Scenario based Uncertainty Analyses

A very high 35 m geosynthetic reinforced soil (GRS) wall was constructed along the Teesta River at Mamring, Sikkim. Failure of this wall during a minor earthquake presents a critical case study in understanding the seismic response and role of uncertainty in earthquake geotechnical engineering. Despite multiple reinforcing elements, the wall collapsed during the seismic event, leaving only the anchored in-situ material. The ground motion responsible for the failure was of sufficiently low intensity and, accordingly, no earthquake recording was present, thereby making it impossible to directly analyze the event based on empirical data. Given the absence of recorded seismic data, synthetic ground motionsare generated based on the possible seismic scenarios. Seven representative motions are then selected to study the seismic response of the reinforced structure and to investigate the potential mechanisms that possibly led to its collapse.However, the use of synthetic ground motions introduces uncertainties, particularly regarding the range of possible strong motion characteristics that could realistically occur. To address this, uncertainty analysis is conducted, incorporating randomness in the various relevant ground motion parameters obtained from the considered seismic scenarios.The uncertainty analysis is essential in this context as it allows for the exploration of a broad spectrum of potential earthquake scenarios. Hence, based on the PGA of the generated synthetic motions, the structural response of the reinforced soil structure is investigated in the form of peak tensile forces developed along the geogrid layers of all three tiers.This study discloses the significant variation of the peak tensile forces across the tiers and also picturize non-linearity induced in structure due to varying seismic scenarios.

Keywords: Geosynthetic Reinforced Soil (GRS) wall, Seismic scenarios, Seismic response, Uncertainty analysis.