Incorporating imaginary faults in graphical stress methods

The concept of an imaginary fault is introduced in this communication as an auxiliary constraint in the graphical determination of principal stress directions. A new graphic method is developed for this purpose by applying the right dihedra method to both real faults and their imaginary faults. Although similar to each other, this method has advantages in simplicity and convenience over the right trihedra method that is essentially an extension of the right dihedra method.