More Points to Ponder
Settlement - The foundation must not settle to such an extent that it damages the structure. Settlement is deflection of the structure from its original setting. It is usually the result of movement or compaction of the underlying base soil and it may be due to construction on disturbed soil, backfill, and changes in the soil moisture content.
Improper construction or design deficiencies in connection with other conditions may account for such foundation movement. Building on soil with voids, insufficient compaction, and loose fill will necessitate foundation movement or deflection. Many cases of settlement are caused by contractor error in over-excavating for the foundation and footers,
and then incorrectly back-filling.
Quality - The foundation must be of adequate quality so that it is not subjected to deterioration, such as a sulfate attack of concrete footings. Quality is an increasingly important concern in foundation construction. Cracks or other weaknesses in your foundation can cause many problems, and should be addressed immediately. Defects or failures in the constructed foundations can result in very large costs. Even with minor defects, remediation may be required.
Adequate Strength - The foundation must be designed with sufficient strength that it does not fracture or break apart under the applied superstructure loads (live loads and dead loads). It must also be properly constructed in conformance with the design specifications.
Adverse Soil Change - The foundation must be able to resist long-term
adverse soil changes. An example is expansive soil ( silt and Clays ) which would expand and shrink causing movement of the foundation and damage to the structure.
Seismic Forces- The foundation must be able to support the structure during an earthquake with out excessive settlement or lateral movement.
The descision to use a particular foundation system that will be capable of meeting the specific requirements and specifications, will ultimately be guided by concerted efforts and contributions made by the departments of engineering, geo-tech engineers, and planning. These projected results are then factored into the structure that consequently
determine the choice of footings.
Some of those factors include but are not limited to the strength and compressibility of the soil ( characteristics of the soil ) on the site, estimated loads and distribution of said loads, transmitted throughout the foundation, and the project performance criteria ( total settlement and differential settlement limitations ). So then the foundation design will be based on the assumed bearing capacity of the soil at the site.
On construction sites where settlement is not a problem, shallow
foundations are, for the most part, provide an economical foundation system and are typically utilized in many residential and light framed commercial structures.
In areas where poor soils are discovered, deep foundation systems may be employed to establish adequate bearing capacity and inhibit settlement.
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