Avoidable in all aspects. Have you seen the equipment that is available to hold trench walls in place. There is always "sloping" still available. Yeah, it takes four times the space but you'll never loose an employee to Mother Earth shifting.
Then, I've seen foremen dig trenches three times as wide as necessary, just to protect their workers. And the last method I know about is the "T", which gives the collapsing earth somwhere to go besides down on the men in the trench. Actually, it looks more like a "T" with a "V" on top of it which gives better protection than a "T".
I always complied with the safety rules as far as employees were concerned but for the savings of time I have always taken the risk of getting hurt or killed if I felt that I had a better than 50% probability of surviving and being the employer CalOsha or its predecessor California Industrial Accident Commission couldn't touch me.
At 66 I still have the same attitude and am not going to change, I'm just as replaceable and anyone else.