Foundation, Concrete and Earthquake Engineering

Comparison between Soil and Concrete

Soil is very complex and heterogeneous materials usually differs from traditional structural materials like concrete, steel etc. We have some/in many times great control over properties of concrete during production. Now-a-days development of concrete technology suppress many uncertainty in concrete production which leads to a finished product of desired properties. 

Careful mix design, mixing, transporting, compacting and curing leads to a more or less accurate product. Some computerized programs are now used to control batching optimizing water/cement ratio, proper weighing and sophisticated transporting and placing method bring great control over concrete production. Now we are preparing concrete in plant rather than in situ mixing thus providing extra bit of control over quality.

Huge amount of foundation soil was removed during construction Twin Towers
So far we have discussed about concrete; regarding soil we used to use it remaining in situ conditions. Construction of a foundation work involves large quantity of soil which is not practical or feasible economically to transport such enormous amount of soil from other suitable places as that of concrete (ingredient of concrete or unhardened concrete).

In some cases we are sometimes using some important techniques like grouting and improving soil with external reinforcement but that will not ensure the quality up to that of concrete as discussed above.

Concrete, we used in construction, can be inspected in laboratory before use. We try to provide similar stress condition, identical materials and identical moisture content (w/c ratio) of that will be delivered to site for placing for a project. In case of soil, we also perform some laboratory and field tests to have idea about behavior of soil. Some field tests are

-plate load test

-pile load test

-standard penetration test

Sophisticated system for maintaining Water/cement ratio in RM concrete plant -cone penetration test

-vane shear test

-some geophysical tests etc.

We have discussed some tests and some are to come in this blog. In case of laboratory test the main uncertainty results is collection of undisturbed sample. In many cases we have to make sample or use remolded sample. We have discussed that practically it is impossible to collect undisturbed sample.

Least undisturbed sample can be derived from block sampling but it is suitable for shallow depth. In borehole sampling, sample disturbance results a sample that don’t represent in-situ conditions.

Soil is unpredictable in nature which leads to change in properties not only with location but with also depth at a same place. The behavior of soil varies not only with types but with also conditions it is subjected. Its properties depends on -change in environmental condition

-drainage condition

-loading condition

In case of concrete, we deals with engineering properties like

-tensile strength

-compressive strength

-modulus of elasticity

We can design it with these properties which are known to us by testing or any other means. In contrast to concrete only two/three parameters cannot be used to characterize soil and many factors contain in its engineering properties. So to perform a design work elaborate testing of soil is required to determine its characteristics.

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