Mine 4

local length, depth = ...
local modem = peripheral.wrap("right")
modem.open(5)
modem.open(4)
local selected = nil
local depthCounter = 1

function spin()
    turtle.turnLeft()
    turtle.turnLeft()
end

function drop()
    spin()
    while turtle.detect() do
        turtle.dig()
    end
    selected = turtle.getSelectedSlot()
    turtle.select(16)
    turtle.place()
    for i = 1, 15 do
        turtle.select(i)
        turtle.drop()
    end
    turtle.select(16)
    turtle.dig()
    spin()
    turtle.select(selected)
end

function checkInv()
    if turtle.getItemCount(15) > 0 then
        drop()
    end
end

function strip()
    for i = 1, length-1 do
        if depth - depthCounter >= 3 then
            while turtle.detectDown() do
                checkInv()
                turtle.digDown()
            end
            while turtle.detectUp() do
                checkInv()
                turtle.digUp()
            end
            while turtle.detect() do
                checkInv()
                turtle.dig()
            end
            turtle.forward()
        elseif depth - depthCounter == 2 then
            while turtle.detectUp() do
                checkInv()
                turtle.digUp()
            end
            while turtle.detect() do
                checkInv()
                turtle.dig()
            end
            turtle.forward()
        elseif depth - depthCounter == 1 or depth - depthCounter <= 0  then
            while turtle.detect() do
                checkInv()
                turtle.dig()
            end
            turtle.forward()
        end
    end
end

function turn()
    local count
    if (depth-1) - depthCounter >= 3 then
        count = 3
    elseif (depth-1) - depthCounter == 2 then
        count = 2
    elseif (depth-1) - depthCounter == 1 then
        count = 1
    elseif (depth-1) - depthCounter <= 0 then
        count = 0
    end
    while turtle.detectUp() do
        checkInv()
        turtle.digUp()
    end
    for i = 1, count do
        while turtle.detectDown() do
            checkInv()
            turtle.digDown()
        end
        turtle.down()
        depthCounter = depthCounter + 1
    end
    spin()
end

function up()
    print(depthCounter)
    print(depth - depthCounter)
    for i = 1, depth do
        while turtle.detectUp() do
            checkInv()
            turtle.digUp()
        end
        turtle.up()
    end
end

function start()
    while turtle.detectDown() do
        checkInv()
        turtle.digDown()
    end
    turtle.down()
end

start()
start()
for i = 1, depth, 3 do
    strip()
    turn()
end
up()
drop()