Protecting rainwater drains under drive

[WWilts]

New build in progress

Rainwater downpipe -> bottle gulley -> ~6m land drain (occasional cars or light vans driving over) with ballast bench & cover

What material for land drain? 
What to use over that to protect from weight of vehicles? (details welcome, novice here)

 

[Conor]

What's the cover from the pipe to surface? Normally you'd backfill with lean mix concrete if cover is 400mm or less. Is this a perforated or solid pipe? Twinwall is pretty damn near indestructible. I stuck the digger bucket in to a section the other day and it survived. Nice and bendy, PVC shatters.

[WWilts]

22 hours ago, Conor said:

What's the cover from the pipe to surface? Normally you'd backfill with lean mix concrete if cover is 400mm or less. Is this a perforated or solid pipe? Twinwall is pretty damn near indestructible

Less than 400mm cover from pipe to surface. Perforated pipe.
Leaning towards twinwall.
Lean mix backfill over seems a good idea