DISPLACEMENT-BASED APPROACH FOR SEISMIC STABILITY OF RETAINING STRUCTURES

UoM administered thesis: Phd

  • Authors:
  • Junied Bakr

Abstract

This thesis presents a unique finite element investigation of the seismic behaviour of 2 retaining wall types – a rigid retaining wall and a cantilever retaining wall. The commercial finite element program PLAXIS2D was used to develop the numerical simulation models. The research includes: (1) validating the finite element model with the results of 3 previously existing centrifuge tests taken from literature; (2) investigating the seismic response of rigid and cantilever retaining walls including studying the effects of contribution of wall displacement, wall and backfill seismic inertia and stiffness of the foundation soil; (3) developing analytical methods to concrete the findings of the numerical models. Based on the results of the seismic response of a rigid retaining wall, a unique relationship between the seismic earth pressure and wall displacement has been developed for the active and passive modes of failure. The seismic active earth pressure has been found to be not dependent on the wall displacement while the seismic passive earth pressure has been found to be highly affected by the wall displacement. The maximum seismic passive earth pressure force and relative horizontal displacement are predicted when the ground earthquake acceleration is applied with maximum amplitude and minimum frequency content. The seismic response of the wall was not affected by the ratio of the frequency content of the earthquake to the natural frequency of the wall-soil system. For the cantilever retaining wall detailed structural integrity and global analyses have been carried out. It has been observed that the seismic earth pressure, computed at the stem and along a vertical virtual plane are found to be out of phase with each other during the entire duration of the earthquake, and hence, the structural integrity and global stability should be evaluated and assessed individually. A critical case for the structural integrity is observed when the earthquake acceleration is applied towards the backfill soil and has frequency content close to the natural frequency of the retaining wall, while, for the global stability, the critical case is observed when the earthquake acceleration has maximum amplitude and is applied towards the backfill soil with minimum frequency content. The structural integrity is also found to be highly dependent on the ratio between the frequency content of earthquake acceleration to the natural frequency of the cantilever retaining wall. The relative horizontal displacement of a rigid and cantilever retaining wall is found to be highly affected by the duration of the earthquake in contrast to what has been observed for the seismic earth pressure force. The structural integrity of a rigid and cantilever retaining wall reduces when the backfill soil has a higher relative density, while the global stability increases when the backfill soil has a high relative density during an earthquake. The results obtained from the analytical methods reveal that the wall seismic inertia force has a significant effect on the structural integrity only for the top of the stem while the base of the stem does not get affected significantly. The modified Newmark sliding block method provided a more reasonable estimation of the relative horizontal displacement of a rigid retaining wall and a cantilever retaining wall compared with the classic Newmark sliding block method.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date31 Dec 2018