Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 56 стр.

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Foundation safety criteria

It is a statement of the obvious that the function of a foundation is to

transfer the load from the structure to the ground (i.e. soil) supporting it – and it

must do this safely, for if it does not then the foundation will fail in bearing

and/or settlement, and seriously affect the structure which may also fail. The

history of foundation failure is as old as the history of building itself and our

language abounds in such idioms as ‘the god with feet of clay’, ‘build not thy

house on sand’, ‘and build on a firm foundation ’,‘ the bedrock of our policy’.

The foundation must also be economical in construction costs, materials

and time. There are a number of reasons for foundation failure, the two major

causes being:

(1) Bearing capacity. When the shear stress within the soil, due to the

structure’s loading, exceeds the shear strength of the soil, catastrophic collapse

of the supporting soil can occur. Before ultimate collapse of the soil occurs

there can be large deformations within it which may lead to unacceptable

differential movement or settlement of, and damage to, the structure. (In some

situations however, collapse can occur with little or no advance warning!)

(2) Settlement. Practically all materials contract under compressive

loading and distort under shear loading – soils are no exception. Provided that

the settlement is either acceptable (i.e. will not cause structural damage or

undue cracking, will not damage services, and will be visually acceptable and

free from practical problems of door sticking, etc.) or can be catered for in the

structural design (e.g. by using three-pinned arches which can accommodate

settlement, in lieu of fixed portal frames), there is not necessarily a foundation

design problem.

Problems will occur when the settlement is significantly excessive or

differential.

Settlement is the combination of two phenomena:

(i) Contraction of the soil due to compressive and shear stresses resulting

from the structure’s loading. This contraction, partly elastic and partly plastic, is

relatively rapid. Since soils exhibit non-linear stress/strain behavior and the soil