1) Civil engineering term 2) Digging out roots 
Grubbing or clearing refers to the removal of trees, shrubs, stumps and rubbish from the future right-of-way of a transportation corridor (i.e. a highway), cut lines or the footprint of a structure. Grubbing is performed following surveying and preceding construction. ...
• (p. pr. & vb. n.) of Grub
Digging out roots.