Q1: The equation τ = C + σ tan φ is given by

ANS:B - Coulomb

The total shear strength of a soil mass (T f ) is thus given by Coulomb's equation.
t = C + σ tanφ.
Where σ = effective vertical stress.
C = cohesion,
φ = angle of internal friction of soil.

So, the ans is coulomb. Mohr–Coulomb theory is a mathematical model describing the response of brittle materials such as concrete, or rubble piles, to shear stress as well as normal stress. It is Coulomb because Mohr gave eq S=f(σ)
which was later developed by Coulomb as s=c+sigma tan φ
So this theory is generally referred as mohr coloumbs theory.