Crumble away is a phrase that is commonly used to describe the gradual decay or disintegration of something. There are a number of synonyms for this term, which can be useful when trying to add variety to your writing or expressing a similar concept in a slightly different way. Some of the possible alternatives to "crumble away" include "disintegrate," "dissolve," "decay," "erode," "crack," "fracture," "break down," "decay," "deteriorate," and "wear away." Each of these words has a slightly different connotation, so it is worth considering which one best fits the context in which you are writing.