Types of Shallow Foundations

Play an AI-generated podcast conversation about this lesson

What is the primary criterion that affects the selection of a suitable foundation?

Type of structure

Cost of labour and materials

Total load (dead, live, wind, …) (correct)

Design of shallow foundations

What is the term for the maximum shear pressure that the soil can bear?

Stability criterion

Serviceability analysis

Ultimate bearing capacity (correct)

Shear strength criterion

What happens when the pressure goes beyond the shear strength of the soil in shallow foundations?

The soil shears and is displaced laterally (correct)

The soil becomes stronger

The soil settles slowly

The soil remains intact

What is the purpose of a strength/serviceability analysis in designing shallow foundations?

To ensure the soil does not undergo a shear failure Signup and view all the answers

What is the term for the minimum of the allowable pressures obtained from the stability and serviceability analyses?

Design pressure Signup and view all the answers

What is the term for the type of failure that occurs when the pressure goes beyond the shear strength of the soil?

Type A, Bearing capacity failure Signup and view all the answers

What is the purpose of using strip footings in a building design?

To provide support for line loads, such as load bearing walls or closely spaced columns Signup and view all the answers

What is the calculation for the pressure beneath a spread footing when the load is concentric?

𝑞𝑞 = 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 Signup and view all the answers

What is the characteristic of a mat or raft foundation?

It is a flat slab occupying the plan area of the building Signup and view all the answers

What is the condition under which a raft foundation may become an economical alternative?

When over half the plan area would be covered by spread footings Signup and view all the answers

What is the formula for calculating the pressure beneath a strip footing?

𝑞𝑞 = 𝑃𝑃 𝐵𝐵 Signup and view all the answers

What is the basis of the geotechnical design for strip footings?

A unit length of the footing Signup and view all the answers

What type of failure is typical for loose sand and silt and normally consolidated clay?

Bearing capacity failure Signup and view all the answers

What happens to the likelihood of punching shear failure as the base of the footing deepens?

It becomes more likely Signup and view all the answers

In the Terzaghi bearing capacity theory, what is the zone below the footing that represents active soil being pushed into the ground?

Wedge zone Signup and view all the answers

What is the purpose of the Terzaghi bearing capacity equations?

To calculate the ultimate bearing capacity of different footing shapes Signup and view all the answers

What is the unit of surcharge or overburden pressure at the level of the footing base?

Not specified Signup and view all the answers

What is the term for the middle zone of the failure mechanism in the Terzaghi bearing capacity theory?

Radial shear zone Signup and view all the answers

What is the correct unit weight to use in effective stress analysis if the water table is above the base of the footing?

Submerged unit weight of the soil Signup and view all the answers

According to Terzaghi's equation, what is the ultimate bearing capacity divided by to obtain the allowable bearing capacity?

Factor of safety Signup and view all the answers

What is the primary criterion for foundation design in relation to settlement?

Serviceability criterion Signup and view all the answers

What type of settlement is most dominant in sandy soil?

Immediate settlement Signup and view all the answers

What is included in the calculation of the total overburden pressure if the water table is above the ground level?

Weight of the water above the ground level Signup and view all the answers

What is the formula to calculate the allowable load applicable to the soil under the footing?

Paa = quu × AA Signup and view all the answers

What is the assumption made when the loaded area is large compared to the depth of the point of interest?

The stress increase at any depth is equal to the applied surcharge at the surface. Signup and view all the answers

Which method is used to calculate the change of stress when the loaded area is equal or less than the depth of the point of interest?

All of the above Signup and view all the answers

What is the formula for calculating the average stress increase at each depth using the 2:1 method for a uniformly loaded rectangle?

∆σz = q(BL)/(B+z) Signup and view all the answers

What is the formula for calculating the settlement of a soil layer?

∆e = -CCc log(σi/σf) Signup and view all the answers

What is the expression for the stress increase at a point of interest due to a uniformly loaded circle?

∆σz = q(1 - 1 + r/z) Signup and view all the answers

What is the relationship between the stress increase and the initial stress at a point of interest for OC soil in case 2?

σf = σi + ∆σ Signup and view all the answers

Types of Shallow Foundations - Spread Footings

Choose a study mode

Podcast

Questions and Answers