is available from henry machine company inc pierce colo an on board diesel engine not shown serves as the prime mover and the tracks are independently controllable by means of a conventional pedal mechanism the diesel engine also drives the hydraulic pumps not shown which provide hydraulic pressure to operate the other on board systems suitable hydraulic coolers and controls are provided for controlling the operation of the various systems such controls being well known to those skilled in the art of design and manufacture of hydraulic systems an operator station 58 in the form of an enclosed cab in the embodiment which is illustrated is mounted proximate the midpoint of the main platform 60 of the tracked carriage because the carriage spans the trench this location provides the operator with a clear unobstructed view looking down on the trench and pipeline so that the operator is able to observe exactly where the fill material needs to be placed the operator station also houses the controls not shown for operating the principal subsystems of the apparatus a vibrating screen mechanism 62 is mounted on one side of the platform 60 to the left in fig3 in this position the screen mechanism is readily accessible from the side so that this can receive backfill material which is dumped into the top of the vibrator in the direction indicated by arrow 64 using a front end loader for example although a single deck vibrating screen mechanism may be used.