【Question】How to remove particles once they get contacted with stl walls?

Dear wall,

I am facing a problem about removing particles in the process of simulation. In my model, the particles are moving inside six stl. mesh walls, if they get in contact with the stl walls, the soil particles should be removed. To help understand, I also draw a picture of my problem.

I don't know which command should I use if I want to remove these soil particles under some certain criterion. Could you help me? Any suggestions would be of great appreciated.

Best regards,
Zheng