Correct Answer - Option 4 : s = c’ + σ’ tanϕ’
Shear strength of soil is the capacity of soil to resist shearing stresses. It can be defined as the maximum value of shear stress that can be mobilized within a soil mass.
If this value exceeded by the shear stress on any plane or a surface at a point, failure will occur in soil because of the movement of a portion of the soil mass along that particular plane. The soil is then said to fail in shear. Therefore, shear strength generally represented the strength of the soil.
As per Mohr-Coulomb criteria, Shear strength (s) of soil is given as:
s = c' + σ' tanϕ'
c' = effective cohesion
σ' = effective normal stress
ϕ' = effective angle of friction