A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Fig. Different locations of shear key in retaining wall
5. Are layers of granular fill and rock fill essential at the base of
concrete retaining walls? (RW4)
It is not uncommon that granular fill layers and rockfill layers are placed
beneath the bottom of concrete retaining walls. The purpose of such
provision is to spread the loading in view of insufficient bearing capacity of
foundation material to sustain the loads of retaining walls. Upon placing of
granular fill layers and rockfill layers, the same imposed loads are
supported by a larger area of founding material and hence the stress
exerted by loads is reduced accordingly.
Layers of granular fill and rockfill materials are not standard details of
concrete retaining wall. If we are fully satisfied that the founding material
could support the loads arising from retaining walls, it is not necessary to
provide these layers of granular fill and rockfill materials.
6. How does pressure distribution vary under rigid and flexible
footings? (RW5)
For thick and rigid footings, the pressure distribution under the footings is
normally assumed to be linear. If uniform and symmetrical loadings are
exerted on the footings, the bearing pressure is uniformly distributed.
However, if unsymmetrical loads are encountered, then a trapezoidal
shape of bearing reaction would result.
For flexible footings on weak and compressible soils, the bearing
pressures under footing would not be linear. As such, a detailed
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