Comparing bearing capacity of shallow foundations methods
Ghiasi, Farbod (2025)
2025
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https://urn.fi/URN:NBN:fi:amk-2025082824234
https://urn.fi/URN:NBN:fi:amk-2025082824234
Tiivistelmä
Shallow foundations play a critical role in transferring structural loads to the underlying soil while ensuring stability and minimizing settlement. This bachelor's thesis provides a comprehensive comparison of methods for determining the bearing capacity of shallow foundations, encompassing theoretical, empirical, and code-based approaches to guide practical engineering design.
The study starts by outlining the several types of shallow foundations such as pad footings, strip footings, combined footings, cantilever footings, and mat foundations and divides them from deep foundations. It then explains key concepts like ultimate and allowable bearing capacity, different modes
of shear failure (general, local, and punching), as well as the factors that influence them, including type of soil, moisture content, soil density, loading conditions, and depth of foundation.
Analytical methods are detailed, consist of Terzaghi's theory, which assumes general shear failure and derives bearing capacity factors (Nc, Nq, NꝨ) for strip, square, and circular foundations, and Meyerhof's empirical extension includes correction factors like shape factor, depth factor, and inclination factor. Experimental methods, like Standard Penetration Test (SPT), Cone Penetration Test (CPT), and Plate Load Test (PLT), are checked for their site-specific accuracy in assessing soil resistance.
The analysis then turns to the Eurocode 7 framework, which introduces semi-empirical equations for both drained and undrained soil conditions. It also outlines the unique design approaches (DA1 involving dual verification, DA2 applying balanced load and resistance factors, and DA3 based on conservative soil assumptions) together with partial safety factors that help considering unpredictability.
A comparative analysis highlights the Advantages and disadvantages: analytical methods offer quick, cost-effective preliminary estimates but may be conservative in complex soils; experimental approaches provide reliable field data but are resource-intensive; Eurocode 7 ensures standardized, safe designs with built-in conservatism, particularly suitable for regulatory compliance in applications like wind turbine foundations on stable soils, where shallow mat designs are recommended under cyclic and overturning loads.
In conclusion, integrating these methods, supported by thorough site investigations, yields optimal, efficient designs. Recommendations emphasize conservative factors in variable conditions and suggest
future research into computational modelling and dynamic loading effects.
The study starts by outlining the several types of shallow foundations such as pad footings, strip footings, combined footings, cantilever footings, and mat foundations and divides them from deep foundations. It then explains key concepts like ultimate and allowable bearing capacity, different modes
of shear failure (general, local, and punching), as well as the factors that influence them, including type of soil, moisture content, soil density, loading conditions, and depth of foundation.
Analytical methods are detailed, consist of Terzaghi's theory, which assumes general shear failure and derives bearing capacity factors (Nc, Nq, NꝨ) for strip, square, and circular foundations, and Meyerhof's empirical extension includes correction factors like shape factor, depth factor, and inclination factor. Experimental methods, like Standard Penetration Test (SPT), Cone Penetration Test (CPT), and Plate Load Test (PLT), are checked for their site-specific accuracy in assessing soil resistance.
The analysis then turns to the Eurocode 7 framework, which introduces semi-empirical equations for both drained and undrained soil conditions. It also outlines the unique design approaches (DA1 involving dual verification, DA2 applying balanced load and resistance factors, and DA3 based on conservative soil assumptions) together with partial safety factors that help considering unpredictability.
A comparative analysis highlights the Advantages and disadvantages: analytical methods offer quick, cost-effective preliminary estimates but may be conservative in complex soils; experimental approaches provide reliable field data but are resource-intensive; Eurocode 7 ensures standardized, safe designs with built-in conservatism, particularly suitable for regulatory compliance in applications like wind turbine foundations on stable soils, where shallow mat designs are recommended under cyclic and overturning loads.
In conclusion, integrating these methods, supported by thorough site investigations, yields optimal, efficient designs. Recommendations emphasize conservative factors in variable conditions and suggest
future research into computational modelling and dynamic loading effects.