At quarries of the Leningrad region granite stripping is conducted, placing charges of explosives in vertical wells in diameter of 105 mm. Usually after explosions the bottom of a ledge turns out extremely uneven, ledges (sills) sometimes reach one third of height of a ledge. Due to the uneven bottom of the ledge productivity of excavators EKG-4 does not exceed 250 thousand m^3/ year, ie about half as much as at the advanced mining enterprises.