The substructure of a building transfers the
load of the building to the ground and isolates it horizontally from the ground. This includes
foundations and basement
retaining wall
Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides.
Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...
s.
[Designing Buildings https://www.designingbuildings.co.uk/wiki/Substructure] It is differentiated from the
superstructure.
It safeguards the building against the forces of wind, uplift, soil pressure etc. It provides a level and firm surface for the construction of
superstructure. It also prevents unequal or differential settlement and ensures stability of the building against sliding, overturning, undermine due to floodwater or burrowing animals.
References
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Building engineering