Test: Terzaghi's Theory of Bearing Capacity - Civil Engineering (CE) MCQ

Terzaghi assumed the value of angle ψ = φ, which is not true. Since footings are normally rough, ψ has been found close to 45° + φ/2 than to φ, thus Terzaghi’s bearing capacity equations do not have provision for including depth effects, inclination factors, etc.

Local shear failure generally occurs in loose sand while general shear failure occurs in dense sand.

In Terzaghi’s analysis the soil is homogeneous and isotropic and its shear strength is represented by Coulomb’s equation.

As the soil compress, φ changes; slight downward movement of footing may not develop fully the plastic planes.

The parameters Nc, Nq, Nγ are the dimensionless numbers, known as bearing capacity factors depending only on the angle of shearing resistance of the soil.

The concept of failure analysis was first developed by Prandtl, and later extended by Terzaghi, Meyerhof and others.

An analysis of the condition of complete bearing capacity failure is termed as a general shear failure, can be made by assuming that the soil behaves like an ideally plastic failure.

For purely cohesive soil the bearing capacity is
qf = c Nc + σ̅ Nq = 5.7 c + σ̅
Where σ̅ = γ D if the water table is below the base of the footing.

For purely cohesive soil, local shear failure may be assumed to occur when the soil is soft to medium, with an unconfined compressive strength qu ≤ 100 kN/m².

The values of Nγ for φ of 34° and 48° are the original Terzaghi values which were used by Bowles to back compute Kpγ.