[mrs bouquet]

I cannot remember the name of them, normally they grow to about 6 inches.   But they spread underground.
I have some very large clumps of them in my gravel bed.  They have grown under the matting and some of the slabs.
I cut them back two weeks ago as far as was possible and then sprayed them with roundup. 

1)  Will I have to repeat Roundup and if so how often ?
2)   When the clumps die, will I be able to get them up then, and will I need to use my crowbar. ?

 Advice appreciated please,    Mrs Bouquet