Effect of the shapes of foundation soil on the seismic response of dikes

• Main Author: Loo, Zhi Yung
• Other Authors: Budi Wibawa
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical; DRNTU::Science::Geology::Volcanoes and earthquakes
• Online Access: http://hdl.handle.net/10356/63717
• Institution: Nanyang Technological University

This report describes a simulation study of the dynamic response of a dike built on different types of geometrical shapes of the foundation subsoil using PLAXIS 2D Finite Element Program. Much focus is given to the comparison of Peak Ground Acceleration (PGA) and ground settlement readings at the dike crest when the dike sits above different subsoil shapes. A total of 130 PLAXIS models were created and tested. A sand-filled dike with an impermeable clay core of height 12 m, 80 m base width and 8 m span at the crest is adopted as the model in this study. The seismic inputs opted for the simulation study involved a synthetic harmonic acceleration and an actual earthquake acceleration data. The effect of a basin-shaped profiles with depth, the basin-width effect and basin-edge effect are the main 3 cases of interest. Comparing against a horizontal profile of the subsoil, it was found that when the dike sits above a basin-shaped profile of the subsoil, the PGA at dike crest was higher. This was due to the refraction and reflection of internal SH waves converging towards the center of the basin, resulting in longer duration of shaking and increase in acceleration amplitudes, as well as generated surface Rayleigh waves from basin edge. However, the PGA tends to decrease with the increase of basin width, given a fixed bedrock slope angle and depth. In addition, it was observed that the PGA at dike crest was higher when the dike is position near the outcrop of the rock slope. The PGA drops and fluctuates before converging and normalizing when the dike was positioned further away from the slope edge. It was also shown that the settlement at dike crest increases as the depth of subsoil increases for the basin and edge profiles. However, it was found that there is little correlation between settlement and acceleration amplitude. Limitations of model design approach and PLAXIS 2D program will be discussed and concluded at the end of this report.