porch, courtyard, steps leading
墀 centers on an architectural space at the entrance of a building: a porch, courtyard, or the steps leading up to it. The meanings all describe a transitional outdoor area connected to a structure.
墀 combines 土 (earth, ground) with 犀, which likely contributes the sound. The exact historical development of 犀 in this context is uncertain, but the earth radical fits the architectural meaning of a ground-level porch or courtyard.
The left side is earth 土, and the right side 犀 looks like a sturdy animal. Picture a rhinoceros-shaped stone platform made of earth, forming a porch or courtyard with steps leading up to a building.
For チ, imagine a cheetah resting on the earthen porch: cheetah -> チ, and the big cat lounges on the steps.