Modal Analysis and Ground Motion Modification for Tunnel Seismic Design in Fault Zone
R.A. Primadika1*, T.F. Fathani1, F. Faris1
1Department of Civil and Environmental Engineering, Gadjah Mada University, Yogyakarta, INDONESIA
*Corresponding author: ridhwanafnan@mail.ugm.ac.id
INTISARI
Tunneling in fault zones presents unique challenges, especially in seismically active regions like Indonesia. Faults can reduce the seismic performance of tunnels. This study aimed to analyze the impact of faults on the tunnel’s modal behavior and develop a set of modified ground motion records for seismic tunnel design through fault zones. The Bener Dam diversion tunnel was used as a case study. A two step analysis was conducted: (1) determining the tunnel’s natural periods using modal analysis and (2) selecting and modifying ground motion records based on Indonesian seismic standards. Modal analysis indicated that the fault slightly increased the modal periods of the tunnel and significantly affected its mode shapes. Then, 11 pairs of ground motion records were selected considering earthquake magnitude and distance, the structure’s natural periods, and the site S wave velocity. The best records that matched the site were at CHY102 station (shallow crustal), KAWAI-N (benioff), and abashiri-g (megathrust). After modification, the highest PGA values were 0.44 g at CHY035 (shallow crustal), 0.40 g at KUJI-S (benioff), and 0.41 g at ROC1 (megathrust). These results highlight the importance of fault modeling for a proper ground motion selection
and modification for accurate seismic analysis for tunnel design.
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