creating large bed of soil with pipe

Hello,

I am struggling to find a better way to create my large bed of soil properly with pipe. I have done lots of try-outs (bed generation tool- block and static factory) to have a proper material bed without being created in the pipe but I couldn't manage it(image1). I am now trying simply with the dynamic factories (top and directly underneath the pipe) to not have particles within the pipe(image2). It looks better but I don't think it is efficient for what I am trying to do. I am trying to analyse the stress upon pipe after a simple rockfall impact. 

The other problem is I am unfortunately using the classroom edition and it is limited to 10000 model elements. I am doing the best I can to be as realistic as I can but I couldn't find another way other than making my particles bigger. Is there anything I can do better with the setup? 

Best Regards,

Can