pile up

verb

To form a pile, stack, or heap.
“The kids piled up their boots and coats by the back door.”
“And still the hours passed, and at last I knew by the glimmer of light in the tomb above that the sun had risen again, and a maddening thirst had hold of me. And then I thought of all the barrels piled up in the vault and of the liquor that they held; and stuck not because 'twas spirit, for I would scarce have paused to sate that thirst even with molten lead.”
To collect or accumulate, as a backlog.
“The requests piled up while she was away.”
“The locomotive was the now inevitable American 2-8-0, No. 2623. There she stood, effectively blocking the level crossing, simmering gently, massively inert. It was almost dark, and one's final sight was of her high, firelit cab, the enginemen nonchalantly leaning out, waiting for the right-away, while impatient road convoys piled up on both sides of the crossing.”
To sustain a motor vehicle accident; to crash.
“Nevertheless, if there were no urgent reason for it, I did not fancy driving anything, much less a large, heavily loaded truck, by night along roads which might reasonably be expected to produce a number of hazards. If I were to pile it up, and the odds were that I should, I would lose a lot more time in finding another and transferring the load than I would by spending the night here.”
“Seven cars piled up in a concertina smash on the Pacific Highway this morning about four miles on the Brisbane side of Southport.”