The backfill pipe installation assembly uses a backfill hopper to simultaneously install drainage pipe above the trench floor and envelop the drainage pipe in {HEAD ~ backfill material} to maintain {TAIL ~ the drainage pipe} at a constant height above the trench floor 
to maintain
The backfill pipe installation assembly uses a backfill hopper to simultaneously install drainage pipe above the trench floor and envelop the drainage pipe in { HEAD ~ backfill material } to maintain { TAIL ~ the drainage pipe } at a constant height above the trench floor
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH