Lateral stress is thought to be generated by techtonic plate movements. The magnitude of lateral stress undergound is proportional to rock stiffness since the stress is induced by constant lateral dispalcement. Since the stress can not pass through the openinigs, it will concentrate around them.
The optimal direction of drivage of a roadway is parallel to the direction of the major principal stress as shown in the above diagram. If the mine roadways are driven at a high angle to major principal lateral stress direction, both roof and floor will suffer significant damage. Reduction of the angle will generally reduce the magnitude of the lateral stress concentrations and thus improve roadway conditions.