Trench Roller

Overview

A trench roller compacts the soil that fills a narrow trench, the kind dug for a water main, gas line, or cable. Backfill that is just shoved back in settles later and collapses the road or pipe above it, so it must be compacted in layers as it goes in. A trench is too narrow and too dangerous for a large roller or a person, so the trench roller is built narrow, articulated to steer in a tight slot, and run by remote control so the operator stays out of the trench. Its two drums are covered in projecting feet rather than being smooth, because trench backfill is usually cohesive clay or silt that compacts best when it is kneaded from within rather than pressed from the top.

The machine is two halves: a Front Drum Frame and a Rear Drum Frame, each with a driven padfoot drum, joined by the Articulation and Steering joint. A Vibration System system shakes the drums, a Power Unit and Drive Hydraulics drive everything, and a Remote Control lets the operator run it from the surface.

Padfoot drums

Both Front Drum Frame and Rear Drum Frame carry a padfoot drum, and they share the same build so parts are common. Each Padfoot Drum is a Drum Shell covered with dozens of Padfoot feet welded across its surface. The feet concentrate the drums weight onto small areas, so they punch into cohesive soil and knead it, which expels trapped air and water far better than a flat drum could on clay. As the drum rolls, the feet walk out of the soil and leave a textured surface that bonds well to the next lift. Packed soil tends to bridge between the feet, so a Drum Scraper bar clears each drum to keep the feet biting. Each drum turns on Drum Hub hubs and a Drum Drive Motor propels it, so both drums drive the machine and both compact.

Articulation and steering

A trench is a straight narrow slot, and the machine has to follow it without room to turn the wheels. The Articulation and Steering joint solves this by bending the whole machine in the middle. A heavy Articulation Pin carries the two frames on Joint Bearing bushings, and two Steering Cylinder cylinders bend the joint left or right to steer. Because the machine articulates rather than crab-steers, both drums track the same path and compact the full trench width on every pass.

Vibration

Static weight alone will not compact a deep lift, so the Vibration System system adds dynamic force. Inside each drum a Eccentric Weight off-centre weight is spun at high speed by a Vibration Motor, running on Exciter Bearing bearings. The spinning mass throws the drum up and down many times a second, driving compaction energy deep into the fill so a thicker layer can be compacted in one pass. Coil Spring isolation springs keep that vibration in the drum and out of the frame and the controls. Combining the kneading padfeet with vibration is what lets a small machine reach the densities a trench specification demands.

Power and drive

The Power Unit is a compact Diesel Engine built low so the machine clears the trench walls, fed from a Fuel Tank and kept cool by a Cooling Fan fan and a heavy Air Filter for the dust. The engine drives the Drive Hydraulics rather than the drums directly. A Drive Pump runs the drum drive motors in a closed hydrostatic loop, a Vibration Pump feeds the vibration motors, and a Valve Block of Solenoid Valve valves directs oil according to the commands from the remote, with the oil held and cleaned by the Hydraulic Tank and Hydraulic Filter.

Remote control and safety

The defining feature is that nobody rides or walks in the trench with the machine. The Remote Control is a belt-worn Belt Transmitter with Joystick controls that sends drive, steer, and vibration commands to an On-Machine Receiver on the machine, which passes them to the Machine Controller that switches the valve solenoids. The system enforces a minimum operator distance, stopping the machine if the operator gets too close, so a slip into the trench does not put a person under the drums. A Tilt Cut-out inclinometer stops the machine if it tips past a safe angle against a trench wall. In service the operator stands at the trench edge, backfill is dropped in lifts, and the roller works each lift back and forth until it reaches density before the next layer goes in.