mine

local depth
depth = ""
term.write("How deep? "..depth)
depth = read()

for m = 1, depth do
  turtle.digDown()
  turtle.down()
  turtle.turnRight()
  turtle.dig()
  turtle.forward()
  turtle.turnLeft()
  turtle.dig()
  turtle.forward()
  turtle.dig()
  turtle.turnLeft()
  turtle.dig()
  turtle.forward()
  turtle.turnRight()
  turtle.dig()
  if turtle.detectUp() then
    turtle.digUp()
  end
end