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TopIntroduction
The main objective of the paper is to develop a simplified procedure for the seismic design of a rigid retaining wall.
Newmark (1965) proposed a basic procedure for evaluating the potential deformation that would be experienced by an embankment dam shaken by an earthquake by considering the sliding block-on-a-plane mode. The method is based essentially considering rigid plastic behaviour of soils. Though this method was developed for sliding analysis of an earth dam, Richard and Elms (1979) used this concept for determining the weight of retaining wall satisfying the condition that factor of safety against sliding is unity that is just at the verge of sliding but zero displacement. Their observation was that for no lateral movement, the weight of the wall under seismic forces increased by a considerable amount over the static condition, which may prove to be uneconomical. To overcome this problem, Richard and Elms (1979) have suggested a design procedure based on limited allowable wall movement. This concept brought the weight of the wall in reasonable limits.
As mentioned above, Richard and Elms (1979) analysis is based on factor of safety against sliding only and that is too considering it as unity. In this paper a method has been presented to obtain the weight of wall subjected to earthquake forces corresponding to adequate factor of safety against sliding, overturning, shear failure of soil and no tension at base that is satisfying all stability criterions. Further a parametric study to check the effect of various parameters affecting the seismic design of wall is carried out.
Due to seismic excitation, both backfill and foundation soils will vibrate along with the wall. It will increase the active earth pressure and decrease the allowable soil pressure.Magnitude of dynamic increments and earth pressures have been obtained using pseudo static analysis
TopAnalysis
Figure 1 shows a section of a wall having height H and backface angle α with vertical. The backfill is inclined at angle i with horizontal and has a uniformly distributed surcharge of intensity q. 
is total seismic earth pressure acting on the wall due to backfill and surcharge on the backfill. It may be written as below:
(1) where
and
are static earth pressures due to backfill and surcharge intensity
q.
and
are corresponding dynamic increments. In completely dry, moist and submerged backfill, these pressures will act as shown in Figure 2.
Figure 1. Forces on a gravity wall due to earthquake
Figure 2. Direction and point of application of forces acting on the wall (Saran, 2012)
Conventionally a rigid retaining wall should satisfy the following criteria (Saran, 2012);
- 1.
Under Static Case
- a.
Factor of safety against sliding, Fs ≥ 1.5
- b.
Factor of safety against overturning, FoS ≥ 1.75
- c.
Maximum base pressure, qmax ≤ allowable soil pressure, qa
- 2.
Under Seismic Case
- a.
Factor of safety against sliding, FsE ≥ 1.25
- b.
Factor of safety against overturning, FoE ≥ 1.5
- c.
Maximum base pressure, qmax ≤ 1.25 times the allowable soil pressure, qa