function digColumn(back)
  turtle.dig()
  turtle.forward()
  turtle.digUp()
  turtle.digDown()
  if back==true then
    turtle.back()
  end
end
function digArc()
  digColumn(false)
  turtle.turnRight()
  digColumn(true)
  turtle.turnLeft()
  turtle.turnLeft()
  digColumn(true)
  turtle.turnRight()
end


function digMine(depth)
  for i = 0, depth
    digArc()
    turtle.down()
  end
end

digMine(3)