Foundations Flashcards
What do you need to do if you’re considering local or punching shear failure in a problem?
Reduce the soil strength parameters
Define “Shear strength”
The internal resistance per unit area that a soil mass can offer to resist failure and sliding along any plane inside it.
Define “Torque”
The force at which rotation occurs
Define “Unconfined compressive strength”
The maximum axial compressive stress that a right-cylindrical sample of material can withstand under unconfined contions.
Define “Ultimate bearing capacity”
Ultimate bearing capacity is the maximum pressure a foundation can exert on soil before failure occurs.
How to determine eccentricity?
Divide the applied moment in each direction by the applied vertical load. Keep sign convention consistent.
What are the three modes of bearing failure as recognized by Terzaghi?
- General Shear
- Local Shear
- Punching Shear
General Shear Failure
1) What type of soils does it occur in?
2) What occurs?
1) Dense sands
2) Tilting of the foundation and upheaval of the adjacent soils
Local Shear Failure
1) What type of soils does it occur in?
2) What occurs?
1) Loose and soft soils
2) Little tilting of the foundation and little upheaval of adjacent soils
Punching Shear Failure
1) What type of soils does it occur in?
2) What occurs?
1) Very loose and very soft soils
2) Excessive settlement, and little tilting of foundation and little upheaval of adjacent soils
What is net bearing pressure?
Ultimate bearing pressure minus the ground surcharge.
qnet = qult - q
but don’t forget q is multiplied by Nq in the equation, so don’t just cross it out.
What is the depth below a footing where groundwater should be considered in a bearing capacity calculation?
Footing width
If groundwater is below the footing and within the zone of influence, how do you calculate what unit weight to use?
The zone of influence is equivalent to the footing width. Take the average unit weight within that zone.
