Changed it

function mine()
    turtle.dig()
    os.sleep(0.5)
    while turtle.detect()==true do
        turtle.dig()
        os.sleep(0.5)
    end
    turtle.forward()
    turtle.digDown()
    turtle.digUp()
    os.sleep(0.5)
    while turtle.detectUp()==true do
        turtle.digUp()
        os.sleep(0.5)
    end
end

function chest()
    turtle.turnRight()
    turtle.forward()
    turtle.select(16)
    turtle.place()
    for k=1,15 do
        turtle.select(k)
        turtle.drop()
    end
    turtle.turnRight()
    turtle.turnRight()
    turtle.forward
end

for j=1,3
    mine()
    turtle.turnRight()
    for i=1,10 do
        mine()
    end
    for i=1,10 do
        turtle.forward()
    end
    for i=1,10 do
        mine()
    end
    for i=1,10 do
        turtle.forward()
    end
    chest()
    turtle.forward()
end