Horizontal Bearing Capacity of Foundation
The foundation horizontal bearing capacity is verified according to the theory of limit states using the following inequality:
or based on the factor of safety as:
angle of internal friction between foundation and soil
cohesion between foundation and soil
effective area of foundation
components of horizontal force
extreme design vertical force
coefficient of horizontal bearing capacity of foundation (for input use the "Spread Footing" tab)
When adopting the analysis methodology according to EN 1997 the term with cohesion (ad* Aef) is excluded for drained conditions whereas the term with friction between foundation and soil (Q*tanψd) is excluded for undrained conditions.
The analysis depends on the design angle of internal friction below the footing bottom φd, the design value of cohesion below the footing bottom cd and the design value of earth resistance Spd. If the soil-footing frictional angle and the soil-footing cohesion are less than the values of soil below the footing bottom, then it is necessary to use those values.
The earth resistance is assumed as displayed in figure:
The earth resistance Spd is found with the help of the reduction of passive earth pressure or pressure at rest employing influence coefficients:
passive earth pressure, pressure at rest or reduced passive pressure
coefficient of reduction of earth resistance (for input used the "Spread Footing" tab) - for the analysis according to CSN it assumes the value γmR = 1.5 for passive pressure, γmR = 1.3 for pressure at rest
Coefficients of earth pressures are clear from the following formulas:
for passive pressure:
for pressure at rest in drained soils:
for pressure at rest in other soils:
When determining the reduced passive pressure, the resultant force includes contributions due to the passive pressure and pressure at rest.
The passive pressure can be considered, if the deformation needed for its activation does not cause unallowable stresses or deformations in upper structure.