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Estimating Sheet

How to determine the bearing strength of shallow foundation

Construction Software

Soil investigation is considered as one of the most crucial activities that is accomplished prior to commencement of any construction project.

In the soil test report, the geotechnical engineer must mention the strength of the soil at various layers, and finally gives his approval for a correct foundation. One of the parameters applied in defining the strength of a soil development toward foundation design is the soil bearing strength that is dependent on the shear strength of the soil.

A shallow foundation should be designed not to extremely settle or attain the ultimate bearing strength of the surface. Every criterion is based on the geometry of footing and various parameters of soil which should be perfectly described prior to start the design.

Since, the task is very complicated to define the soil properties, sound examination should be carried out while interpreting laboratory or in-situ tests and if it is not done, the predictions become totally improper. As soon as sufficient knowledge is gathered on soil properties, the exact bearing strength factors should have been chosen or overlooked to work out a proper bearing strength.

On the basis of the depth and compressibility of the soil underlying a shallow foundation, various failure modes may occur. When a shallow foundation is loaded, two separate shear planes will be formed directly underneath the base and form a triangular zone. As this wedge proceeds downward the adjoining soil will yield on that basis and its utmost bearing strength is attained.

If the soil is uncompressible then general shear failure will happen and the shear planes will be formed to the surface. If the soil becomes very compressible then volume change is stimulated and the punching shear will happen and the chance for the formation of extra shear planes is rare.

To describe the stratigraphy and get direct measurement of soil properties as well as geotechnical parameters, there are some useful test methods as follow :-

Standard penetration test (SPT)
Cone penetration test (CPT)
Vane shear test (VST)
Borehole shear test (BST)
Piezocone test (CPTu)
Flat dilatometer test (DMT)
Pressuremeter test (PMT)
Plate load test (PLT)

If you want how to define the bearing strength of a soil with the general bearing capacity equation, go through the following construction article.

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How to determine the bearing strength of shallow foundation