Effect of a rectangular tunnel in the foundation soil on the seismic response of dikes

• Main Author: Teheri, Kelvin
• Other Authors: Budi Wibawa
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/71196
• Institution: Nanyang Technological University

The project describes a parametric study of a simulation using PLAXIS 2D 2015 software. The objective of the project is to investigate the effect of the size and the location of a rectangular tunnel or hole in the foundation soil on seismic responses. In this project, square is chosen for simplicity. To determine the critical horizontal displacements and Peak Ground Accelerations (PGA) of the dike during the earthquake loading phase, various variables of sizes and locations of a rectangular tunnel will be inputted into the PLAXIS 2D. A sand dike with height 7 m, 50 m base width and 8 m crest width is adopted as the study model. The seismic inputs for the study involved a harmonic acceleration and an earthquake acceleration data. Firstly, the tunnel depth was varied for four depths – 25 m, 35 m, 45 m and 55 m for each square width – 5 m, 7.5 m, 10 m and 15 m. Next, the tunnel distance to the projected center of dike crest was varied for four depths – 0 m, 12.5 m, 25 m and 37.5 m for each square width – 5 m, 7.5 m, 10 m and 15 m. The result for no tunnel case was also compared. It was observed that for harmonic acceleration, the critical tunnel depth for all models was when the width was around 35 m (d/D = 0.4375), whereas for earthquake acceleration, the critical depth was around 25 m (d/D = 0.3125), where d was the tunnel width and D was the depth of soil basin. Due to irregularity of nonsymmetrical geometry soil layer, for relatively long tunnel widths, the maximum horizontal displacements peaked when it was located some distances away from the center of the dike but still inside the projected dike base. The peak was observed when it was located 12.5 m (b/B = 0.25) away from the projected center of dike base.