PRELIMINARY STUDY STABILITY ANALYSIS OF SUBSURFACE TUNNEL DUE TO EARTHQUAKE POTENTIAL OF LEMBANG FAULT CASE STUDY SUBSURFACE TUNNEL CONSTRUCTION “AF”

• Main Author: Adrian Firdaus, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/46311
• Institution: Institut Teknologi Bandung

The Lembang Fault is one of the major faults in West Java which is still being investigated for its activity level. The construction of subsurface infrastructure such as tunnels in the area around the Lembang Fault must certainly pay attention to this fault activity. Tunnels that are affected by ground vibrations due to earthquake will be deformed so a modeling of stress distribution due to the Lembang fault will be needed. In this modeling the assumption of maximum earthquake strength that can be generated by the Lembang fault is based on geometrical factors and the slip rate of the Lembang Fault from previous studies. In this modeling finite element analysis computational technique is used. The tunnel that is the object of research is the "AF" tunnel located north of the Lembang fault. The data used in this modeling is divided into two parts. The first data is earthquake data which will be used to calculate free field shear displacement. The second data is rock elastic parameter data including poisson's ratio, young's modulus, cohesion, and critical angle. The data is used to calculate stress around the tunnel. Determination of boundary conditions in this model is obtained with assumptions that follow the rules of soil deformation due to earthquake. Data is processed using Phase2 software. After the modeling is complete and the stress distribution has been obtained, the next step is to analyze the stability of the tunnel using the Mohr diagram. From the results of the modeling it was found that in an earthquake with a magnitude of 6.5 MW, a 2.5 cm thick support in sandstone and 1.2 cm in tuffs was needed, while an magnitude 7.5 MW earthquake was needed 4.5 cm in support of sandstone and 2 cm in tuffs.