3tunnel

function digIt()
  while turtle.detect() do
    turtle.dig()
    os.sleep(0.5)
  end
  turtle.forward()
  while turtle.detectDown() or turtle.detectUp() do
    turtle.digUp()
    turtle.digDown()
  end
end

local run = 0
local x = 0
term.write("Tunnel length: ")
x = read()
run = x * 0.5

digIt()
turtle.turnRight()
digIt()
turtle.turnLeft()
turtle.turnLeft()
turtle.forward()
digIt()
turtle.turnRight()

for i = 1, run do
  digIt()
  turtle.turnRight()
  digIt()
  digIt()
  turtle.turnLeft()
  digIt()
  turtle.turnLeft()
  digIt()
  digIt()
turtle.turnRight()
end

turtle.turnRight()
turtle.forward()
turtle.turnLeft()