foundation system of burj al arab

Comparison of Soil with Steel

Soil is very complex in nature and shows distinct behavior other than traditional construction materials. We have discussed about concrete in the last post. Here we will discuss about steel to compare with soil.


Steel is mainly iron alloyed by carbon to change its properties. Other than carbon it may contain

• Manganese

• phosphorous

• sulfur

• Silicon
Cast iron pressure control valve
Sometimes other alloying elements can be added intentionally to have enhanced properties of steel like nickel, titanium, boron, molybdenum, chromium etc.


The carbon and alloying element discussed above render hardening properties to steel. So by adjusting amount of these elements (one or more) and controlling form of presence in steel, the quality of steel can be altered in terms of

• Tensile strength

• Ductility

• Hardness


As an example, with carbon of greater content produce harder steel but having less ductility. The carbon content greater than 2.1 % produce cast iron that is harder and have malleability of null.


So steel is accurately controlled manufactured product whose properties can be tuned with varying alloying element. We have greater control over steel than concrete as discussed in last post.


Before using, we can evaluate its engineering properties accurately in laboratory or from manufacturer information which represent actual condition in which it remains in concrete or other materials. In case soil, we can never accurately simulate the actual in-situ conditions; though modern triaxial test apparatus can simulate many in-situ environments in single arrangement.


We cannot remove unexpected soil from project site as it involve huge soil transportation; in some cases we bound to relocate many structures considering geotechnical and geological conditions. Sometimes compensated foundation is used to suppress unexpected soil from project site when architectural and other requirements seek a number of basements.


Steel is a homogeneous material although its length in contrast to soil which heterogeneous in both horizontal and vertical direction even within few feet.


Steel shows precise modulus of elasticity rather than a soil sample (where shear modulus is important). With modulus of elasticity, compressive and tensile strength, we can easily design a section, but in case of soil we need elaborate testing program to have not accurate but near to actual value. Even under these numerous testing large safety factor is essential in foundation engineering.

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