induration. 1. the process of hardening or being hardened.
1 They're weak against the Ice and Water types in reference of erosion, which cause this elements to the ground. 2  They're immune against the Electric type because in real life, the ground is a natural sink of electrons.  The Bug type resists them because many bugs like worms live inside the ground and many of them eat it.
Tie backs when used alone are generally not effective as the concrete blocks in the area of the tie back will fail as the rest of the wall continues to move inward. Tie backs are effective when they incorporate a vertical steel beam to the inside of the foundation which engages the entire height of the foundation wall.