Parametric Study on Dynamic Properties of Backfill Material and Numerical Modeling of Reinforced Earth Wall for Outward Flow Condition

Abstract

Reinforced soil retaining walls are well known because of their simplicity of field application and cost-viability. When RE walls are executed in earthquake areas, their conduct under the action of seismic loads are needed to be considered to guarantee the safety. It has been observed that most of the failure occurs in the retaining walls under drained condition. As stated by R. M. Koerner among 82 case studies, the failure accompanied by drainage condition is 68%. The failures in reinforced earth wall are generally induced by gravitational force, seepage force, and earthquake force. In this study, two cases are considered, dry condition and drained condition for analysis of failure of reinforced earth walls with tiered configuration (1.2 m offset) and without tiered wall. Studies on tiered configuration walls [1] show that tiered walls are more stable than without tiered walls. At first, modulus properties and dynamic properties of granular backfill material are computed by bender element test (low strain method), and then, properties are incorporated in numerical analysis by finite element method in PLAXIS 2D. The numerical modeling includes plastic analysis, dynamic analysis, and C-Φ strength reduction analysis. It has been observed from the analysis that in dry backfill, the Msf (Factor of safety) obtained by finite element program for RE wall without offset is found to be 2.1 and for two-tiered RE wall factor of safety is 2.3. In drained condition backfill, factor of safety for RE wall without offset after dynamic analysis is found to be 0.41 and for two-tiered RE wall with 1.2 m offset factor of safety is 0.29. The top surface of RE wall must have some impervious layer to avoid percolation of water in backfill to achieve highest order of safety in drained condition.