Slide computes a support force vector for tensile failure and for shear failure independently of each other. It then adds the tensile force vector to the shear force vector to get a total support force vector. Note that this vector has both magnitude and direction, and therefore you cannot simply add the nail force diagrams together. Since the shear force acts in a different direction to the tensile force, you end up with a resultant vector. Slide shows the magnitude of this resultant vector in the nail force diagram for shear and tension.
For more information, see the Soil Nail section of the Online Help.
Illustration of Shear Capacity option for support