For example, I have an axial force and a torsion force applied on a rock socket installed in bedrock. If I am considering the side friction between socket and rock as a resistance, the socket surface will have two shear stress generated, one in axial direction, and the other in radial direction. If I want to design this, what is the maximum I should use?
Can I combine the two stresses by triangle rule, or simply adding them up, or only take the larger one?
Here is a conceptual sketch: