Analysis of the Effects of Earthquakes on the Pile-Box Culvert System at the Gentos Bridge, Situbondo, Indonesia
Abstract
Soft soil conditions present significant challenges to the seismic performance of transportation infrastructure, particularly box culverts constructed in earthquake-prone regions. This study evaluates the effectiveness of galam timber piles in improving the stability and reducing the settlement of a pile-supported box culvert at the Gentos Bridge, Situbondo, Indonesia. Three-dimensional numerical analyses were performed using PLAXIS 3D, in which the soil behavior was represented by the Mohr–Coulomb constitutive model. Dynamic loading was applied using the RSN2736 Chi-Chi (CHY101-E) earthquake record from the NGA-West database, which was spectrally matched to the target response spectrum specified in SNI 1726:2019. The matched earthquake motion had a maximum acceleration of 0.20568 g, while the target design spectrum corresponded to a Peak Ground Acceleration (PGA) of 0.307 g. The numerical model incorporated layered soil conditions, staged construction, and soil–structure interaction to evaluate the seismic response of the box culvert foundation system. The results indicate that the installation of galam timber piles reduced elastic settlement from 5.5 cm to approximately 3.0 cm, representing a 45.5% reduction, while increasing the safety factor from 2.55 to 3.02, corresponding to an improvement of 18.4%. These improvements demonstrate a significant enhancement in foundation stiffness, load distribution, and overall structural stability under seismic loading. The main scientific contribution of this study lies in demonstrating the feasibility of utilizing locally available galam timber piles as an effective foundation reinforcement system for pile-supported box culverts subjected to earthquake loading. The proposed approach provides a practical and sustainable alternative for improving the seismic performance of transportation infrastructure constructed on soft soils in earthquake-prone regions.