My Turtle Program Acting Weird

I made a turtle program that will quarry 3x times faster than normal excavation and will do an 11x11 on auto. And pu its stuff in an enderchest. But it leaves random chunks of land everywhere…. and it stops at caves(i figured that out but not the land part) I know it can be shortened when it goes forward ten but ill do that later. Sorry its messy

the code:

--Variables
dist = 0
rdist = 0
L = 0
-- Funtions
function digfor()
repeat
  turtle.dig()
  sleep(0.4)
until turtle.detect() == false
end

function forward()
turtle.forward()
turtle.digUp()
turtle.digDown()
end
function Dump()
for i = 16,2,-1 do
  turtle.select(i)
  turtle.dropDown()
end
end
-- Main Code
turtle.digDown()
turtle.down()
turtle.digDown()
turtle.down()
turtle.digDown()
digfor()
forward()
repeat
repeat
  repeat
   digfor()
   forward()
   dist = dist +1
  until dist == 10
  turtle.turnRight()
  digfor()
  forward()
  turtle.turnRight()
  dist = 0
  rdist = rdist +1
  repeat
   digfor()
   forward()
   dist = dist +1
  until dist == 10
  dist = 0
  rdist = rdist +1
  turtle.turnLeft()
  digfor()
  forward()
  turtle.turnLeft()
until rdist == 10
turtle.turnRight()
turtle.turnRight()
turtle.turnRight()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.forward()
turtle.turnRight()
turtle.digDown()
turtle.select(1)
turtle.placeDown()
Dump()
turtle.select(1)
turtle.digDown()
turtle.down()
turtle.digDown()
turtle.down()
turtle.digDown()
turtle.down()
rdist = 0
L = L + 3
until turtle.digDown() == false
print("I did ",L, " Levels")

thankyou in advanced :)/>