The MSB wall system consists of three zones. Thye are

1. The reinforced earth zone.
2. The backfill zone.
3. The foundation soil zone.

The reinforced earth zone is considered as the wall for checking the internal stability whereas all three zones are considered for checking the external stability. The soils of the first two zones are placed in layers and compacted whereas the foundation soil is a normal one. The properties of the soil in each of the zones may be the same or different. However, the soil in the first two zones is normally a free draining material such as sand.

It is necessary to check the reinforced earth wall (width = B) for external stability which includes overturning, sliding and bearing capacity failure. These are illustrated in Fig. 19.17. Active earth pressure of the backfill acting on the internal face AB of the wall is taken in the stability analysis. The resultant earth thrust Pa is assumed to act horizontally at a height H/3 above the base of the wall. The methods of analysis are the same as for concrete retaining walls.

Figure 19.17 External stability considerations for reinforced earth walls

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