INTEGRATED METHODOLOGY OF SEISMIC SENSITIVITY AND FRAGILITY EVALUATION FOR CIRCULAR TUNNELS

Abstract

Tunnels are classified as complex engineering structures, which requires careful analysis and design procedures. Any instability of tunnels will be highly detrimental to their performance thereby posing a threat to public safety, consequently cause life-threatening and infrastructure crippling consequences. Recent experiences show that tunnels become vulnerable during an earthquake event. Many researchers focus more on the seismic behaviour (response) of tunnels itself without further investigate the probability of damage (performance) of tunnels under impact of earthquake loads. Hence, a comprehensive methodology for the seismic risk evaluation of tunnels structures is critically required. In this PhD study, an effort was made to develop an integrated methodology for evaluation of the probabilistic future performance of underground circular tunnels subjected to seismic loadings. The integrated methodology referred to the two dependent analyses, i.e. seismic sensitivity analysis and seismic fragility analysis performed in this present study. Particular attention was given on the response and performance of tunnels buried in soil which treated as a single-phase medium without excess pore pressure. The tunnels were studied under influence of three uncertainties factors; soil properties, tunnel lining properties and burial depth (overburden). Total of 120 cases was analysed as the 3D nonlinear time history analysis using the Midas GTS NX finite element software. Results showed the significant roles of the soil properties, tunnel lining properties and burial depth in modifying the response and performance of tunnels. The proposed fragility curves highlight that the high stiffness of soil and tunnel lining may reduce the probability of tunnel damages. Meanwhile, the effect of burial depth is less significance for tunnels buried in poor soil condition. As a conclusion, the tunnels are vulnerable to seismic effects and their impact cannot be neglected. Subsequently, the assumption that believes tunnels structures are relatively safe compared to the surface structures is rejected. The derived curves provide a better understanding for estimating the future probability performance of complex tunnels structures using the 3D numerical models. This effort, in turn, beneficial as a new information for risk assessment and loss estimation as well as improve public awareness and preparedness towards unpredictable extreme hazards. Besides, the study may provide preliminary knowledge in protecting critical underground structures for the future development of local seismic design guidelines in Malaysia.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ahmad Syed Mohd Syed (Supervisor)