Sliding Stability of Retaining Wall Supporting c-Φ Backfill under Pseudo-Statically Seismic Active Load

Sliding Stability of Retaining Wall Supporting c-Φ Backfill under Pseudo-Statically Seismic Active Load

Sima Ghosh (Department of Civil Engineering, National Institute of Technology, Agartala, India)
Copyright: © 2013 |Pages: 16
DOI: 10.4018/jgee.2013010101
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Abstract

The sliding stability of retaining wall is one of the four important stability criteria for the safe design of retaining wall. Here an attempt is made to determine the sliding stability of retaining wall under seismic loading condition supporting c- F backfill considering both soil and wall inertia using pseudo-static method. The analysis for seismic active earth pressure for that particular study is done in such a way to develop a single critical wedge surface which is more realistic. The effect of wide range of variation of parameters like angle of internal friction of soil, angle of wall friction, cohesion, adhesion, seismic acceleration are studied on normalized seismic active earth pressure variation, wall inertia factor, thrust factor, combined dynamic factor and dynamic factor of safety against sliding. Results are presented in terms of formula for critical wedge surface and seismic active earth pressure and non-dimensional charts for the variation of different factors. Finally, a failure zone against sliding is recommended in the Factor of safety against sliding charts.
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1. Introduction

Earthquakes have caused severe damage to the earth retaining structures during many previous earthquakes all over the world. The level of importance of the active earth pressure increases many fold under the earthquake conditions due to the devastating effects of the earthquake. Initially, Okabe (1926) and Mononobe and Matsuo (1929) had proposed the theory to compute the pseudo-static earth pressure on the retaining wall which is commonly known as Mononobe-Okabe method(see Kramer(1996)). Till date this Mononobe-– Okabe method which is applicable only for cohesionless backfill is world-wide extensively used. This fact is well known that Mononobe-Okabe method is just amplification of Coulomb’s concept (1773) to introduce seismic inertia forces due to earthquake. Using this Mononobe-Okabe concept and Newmark (1965) sliding block mechanism Richards and Elms (1979) studied the sliding displacement of retaining wall during seismic loading condition considering both soil and wall inertia.

Prakash and Saran (1966) and Saran and Prakash (1968), Saran and Gupta (2003), Ghosh and Saran (2007), Ghosh et al. (2008) attempted to introduce this Mononobe-Okabe concept for c-Φ backfill introducing lots of design charts and tables. From these analyses, three separate wedge angles for unit weight, surcharge and cohesion are found. This fact is not true for actual field condition. Ghosh (2010) has given a solution for seismic active earth pressure in which an attempt is made to introduce same coefficients for unit weight and surcharge but separate coefficient for cohesion. Thereafter, Shukla et al. (2009) attempted to extend this Mononobe-Okabe concept for c-Φ backfill for angle of wall friction δ = 0 in such a way to get single critical wedge surface. So, this fact is also not true for actual field situation due to the roughness of the retaining wall backfill face. Ghosh and Sharma (2010) have given a solution for seismic active earth pressure in such a way to get a single critical wedge surface. Also, Ghosh and Saran (2010) has given a solution for seismic active earth pressure using graphical method to get a single critical wedge surface. But till date no study has been made to evaluate the sliding stability of retaining wall supporting c-Φ backfill under seismic loading condition.

Therefore, the objectives of this study are:

  • 1.

    To determine the seismic active earth pressure on the back of retaining wall supporting c-Φ backfill along with surcharge over the top of the backfill in such a way to produce a single critical wedge surface;

  • 2.

    To evaluate the sliding stability of retaining wall introducing inertia of the wall under the above stated seismic active condition supporting c-Φ backfill.

Detailed parametric study has been made for the variation of seismic active earth pressure, wall inertia factors, active thrust factor, combined dynamic factor and dynamic factor of safety for the variation of different parameters like angle of internal friction of soil, angle of wall friction, cohesion, seismic acceleration coefficients. In all the parametric study, to represent the effects of changes of one parameter, the other parameters are kept as constants and these constant values are shown in the respective figures.

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