If the roots are that thick, they may be hard to get through with a shovel. My tools of choice in such a situation are a pickaxe and a longhandled branch pruner. You can cut through the rhizome with either tool. And, since you don't know how well established the rhizomes are, you may want to remove them. You can do this by grabbing hold of the cut end and yanking, or, if it's rely uncooperative, slip the pick end of the pickaxe under the rhizome and lever it out. Have fun...it's great exercise!

thanks kudzu9 for the info
i planted my vivax, blackbamboo,and heron all at the same time early in the spring. looks like the vivax took off and the others didnt do much. any idea how deep something like that would go, 12 inches or so??? i just might want to rent a ditcher and go around them once or so..lol..

leland-
Rhizome depth is partly a function of soil and moisture. However, in my experience, Phyllostachys runners rarely go below about 8'-10". If you go down a foot you should be good. If you do trench, I recommend that you fill the trench back up with something like sand, bark, or mulch. That will make it easier next year to probe with a shovel for new runners. Your other bamboo will probably make their move next year, so trenching around them is not a bad idea as well.