Impact Rollers

What Defines an Impact Roller and What is it's Purpose

The name Impact Roller can be misleading in that it implies a rolling cylinder as used in conventional vibrating and static road rollers. Impact rollers are characterised by non-cylindrical multisided geometrical Drum or Module. The number of sides can vary from three to five. The other defining characteristic is that Impact Rollers derive their energy by turning on their corner (major radius) and falling to the flat side (minor radius). There being no motorised form of energy such as in a vibrating roller.

The purpose of an Impact roller is to introduce energy to the ground surface in quick succession, around two impacts per second. By doing this in a rolling action at around 10kph large areas can be treated quickly and a large amount of energy applied to an area in a comparatively short period of time.

Impact rollers differ from conventional rollers in their ability to compact material at depth- depth of influence. Conventional vibrating rollers have a depth of influence of around 300mm in cohesive soils whereas Impact rollers have a depth of influence of 700 to 2500 mm in cohesive soils. In non-cohesive materials depth of influence have been recorded at 3 to 4 m.

The economic advantage of using Impact Rollers stems directly from their depth of influence in in situ materials. By way of example: one hectare compacted to a depth of one meter in situ using a medium energy Impact Roller would take 19.2 hours (assuming 20 passes). The same process by conventional excavate and re-compact method would require the following process.

1. Excavate and stockpile 10,000m3
2. Cart from stock pile and spread 3 lifts of 10,000m2
3. Compact 3 lifts of 10,000m2

The depth of influence of an impact roller is a product of its energy rating -in Kilojoules. Rollers currently available vary from 12kJ to 30kJ (Potential Energy rating). The higher the energy rating the greater the depth of influence. The number of sides of an Impact Roller has an influence on the energy rating. Since an Impact Roller turns on its major radius and falls to its minor radius, the greater the difference of these radii the greater the lift height. Three sided rollers produce the maximum lift while five sided rollers produce the least lift.

The application of Impact Rollers fall in the following broad categories:

1. Bulk earth works. Compacting in 1m lifts at 10kph one machine can compact 18,000 BCM per shift.
2. Ground Improvement, uncontrolled fill sites. Compacting to 2-3m depth in situ.
3. Induced settlement. The application of a large amount of energy greatly in excess of that imposed in service can bring forward projected settlement.
4. Sanitary Landfill. Old landfills can be put to higher land use such as sporting fields and residential areas.
5. Problem sites, high foundation costs. With a combination of ground treatment and engineered footing and structures, piling or stone columns and other high cost foundation treatments can be avoided.

Individual manufactures of Impact rollers may make vested interest claims to support their particular design and some go to extraordinary lengths, even presenting such claims as scientific papers. The technology behind Impact Rollers is basic physics and manufacturers can and should provide prospective users with the basic data to validate claims.

It should be noted that from a Geotechnical perspective that all information is site specific and the transposing of site information from one site to another is not without hazards.

Technical Characteristics

Working device of 6830/6825/6825A impact compactor – impacting drum, is a rolling drum structure of non-circular shape. During roll compacting, potential energy that be reversed when farthest point away drum axial contacts on ground is diverted into kinetic energy at the moment when the nearest point reaches the ground to strike the ground surface, in addition to instant release of hydraulic energy, commonly exert onto the ground to realize high compaction.

While high impact energy is applied on the ground, the counterforce from the ground is sent to drum axles, machine frame, and towing vehicle. Therefore necessary multiply stages of buffering devices are fitted. There are buffering springs at towing pin, damping rubber pad at the rocker limit end, on another end are mounted buffering oil cylinders and accumulator, rubber sleeves mounted between the impact drum and towing frame. Damper isolators between impact drum and its hub and etc. The buffering mechanisms greatly release the shock of the impacting force to the machine frame and towing vehicle.

Hydraulic system of impact compactor is provided with oil from the hydraulic circuit in the towing vehicle, joined by quick couplers with features of safe and rapid operation and easy dismounting.

Actuating lift cylinder to raise up the impact drum away from the ground, in result, entire weight applies on the frame supported with the rubber tyres on the ground. The towing vehicle can draw the compactor for short distance between construction sites without damage to road surface.

NOTES: In operation, motor grader or bulldozer, water spraying vehicle should coordinate with impact compactor for more efficient compaction.