Mineshaft-staircase

print("how deep?")
write("->")
depth = tonumber(read())
print(depth)

function forward()
  while not turtle.forward() do
    turtle.dig()
    sleep(1.5)
  end
end

function down()
  while not turtle.down() do
    turtle.digDown()
    sleep(1.5)
  end
end

looped = 0
maxdepth = depth

while depth > 0 do
  term.clear()
  term.setCursorPos(1,1)
  print("Doing layer "..(maxdepth-depth).." of "..maxdepth)
  forward()
  turtle.digDown()
  forward()
  down()
  turtle.dig()
  down()
  depth = depth - 1
  looped = 1
end

if looped == 1 then
  turtle.dig()
end