We're embedding glass in concrete and expecting that the two can peacefully coexist. This is something that none of us has control over, and it can certainly lead to cracking. There are, however, steps you can take to reduce the possibility.
Breakage occurs where a glass is most stressed.
So the goal is to reduce the stress points in your mosaic projects. Proper scoring and careful grinding are your first lines of defense. Tiny imperfections and microscopic fissures caused by careless cutting and grinding are the primary causes of glass cracking when imbedded in concrete. And, within your design, avoid long, thin pieces. Instead, modify the pattern, breaking single pieces into smaller, multiple ones that will be more stable.