An alignment device is disclosed use in maintaining the alignment of longitudinal frame members of a trench-forming assembly. The alignment device comprises a cross member. Extending in the same direction from opposite ends of the cross member is at least one pair of first lateral extensions. The pair of lateral extensions is spaced apart so as to contact the respective longitudinal frame members of the trench-forming assembly, and thereby maintain the two frame members at a distance relative to each other. The alignment device may further include at least one interior extension extending from the cross member in the same direction as the pair of first lateral extensions. In this embodiment, the interior extension defines a slot between the interior extension and at least one of the first lateral extensions, where the slot is structured is to receive at least a portion of one of the longitudinal frame members.