mine

function fuel()
	fuelLevel = turtle.getFuelLevel()
	if fuelLevel == "unlimited" or fuelLevel > 10 then
		return
	end

	function tryRefuel()
		for n=1,16 do
			if turtle.getItemCount(n) > 0 then
				turtle.select(n)
				if turtle.refuel(1) then
					print("Fuel: "..turtle.getFuelLevel().."")
					turtle.select(1)
					return true
				end
			end
		end
		turtle.select(1)
		return false
	end

	if not tryRefuel() then
		print( "Add more fuel to continue." )
		while not tryRefuel() do
			sleep(1)
		end
		print( "Resuming Tunnel." )
	end
end

function turn()
turtle.turnRight()
turtle.turnRight()
end

function dig()
turtle.dig()
sleep(1)
end

function tunnel()
distance = distance + 1
turtle.digUp()
turtle.select(1)
turtle.placeDown()
turtle.turnLeft()
turtle.detect()
turtle.place()
turtle.turnLeft()
turtle.turnLeft()
turtle.detect()
turtle.place()
turtle.turnLeft()
  if distance == 9 then
    turtle.select(1)
    turtle.up()
    turtle.turnLeft()
    turtle.dig()
    sleep(1)
      while turtle.forward() == false do
        turtle.dig()
        sleep(1)
      end
        turtle.place()
        turtle.placeUp()
        turtle.back()
        turtle.select(16)
        turtle.place()
        turtle.turnRight()
        turtle.down()
        distance = 0
  end
end

function back()
turtle.up()
turn()
  while  j > 1 do
    if turtle.forward() == true then
	  refuel()
      j = j - 1
    else
      dig()
    end
  end
turtle.down()
turn()
end

-- Main-Script --
write("Tunnel length: ")
length = tonumber(read())
print("Starting...")
fuel()
distance = 0
i = 1
j = 1
  while i <= length do
    if turtle.forward() == true then
	  refuel()
      tunnel()
      i = i + 1
      j = j + 1
    else
      dig()
    end
  end
back()
print("Done...")