Drainage channel backfill

[MarcoM]

Hello I would like to replace an existing concrete drainage channel
with a more modern steel channel, the channel is across the garage entry.
The existing channel is resting on compacted sand.
My question is, how do I backfill behind the new channel?
The new drainage channel is smaller in width compared to the
original concrete channel. Do I need to mix aggregate with cement to backfill?

Thanks