... with low compressive strength and high drillability,such as shale,clay,sandstone and soft limestone,etc.Large radius offset ... compressive strength and harder abrasive stringers,such as hard shale,hard gypsolyte,soft limestone,sandstone and dolomite with stringers, ... compressive strength and harder abrasive stringers,such as hard shale,mudstone,soft limestone and sandstone,etc.Large radius scoop ...