construction and refurbishment of earthen irrigation channel banks

Tests indicate little change in density due to change in rolling speed as long astearing and displacement of soil do not become excessive. High-speed tampingfoot rollers minimise such displacement. Speed is usually limited by tractorpower and job conditions.16.10.1.2 Vibrating RollersThe effectiveness of vibrating rollers depends on the frequency and amplitude ofvibration as well as on their static weight. The density obtained with a vibratorycompactor depends on the travel speed and the number of passes. The allowablespeed is determined by the soil type and desired depth of compaction as well asvibrator characteristics. Vibratory compactors are most effective on granular,non-cohesive soils. However, at low frequency and high amplitude they are alsoeffective in cohesive soils. Vibrating compactors tend to dry out the soil, whichcan be an asset when working with moist soils.Vibrating rollers have much greater ground contact areas and hence lowerpressures. With the vibrator operating at correct speed the contact pressure isincreased by the dynamic load of the vibrating mechanism. This increase inpressure is greater on hard surfaces than on soft ones, and the full quoted staticplus dynamic load is unlikely to be achieved on clayey channel bank materials.However, penetration to the bottom of the layer can be achieved with appropriateselection of moisture content and layer thickness. Operation is very dependent onthe vibrator operating at full speed. The cost of operating the roller and thedifficulty pulling it is increased by operating the vibrator, so there is an incentivefor an unsupervised contactor to slow down or stop the vibrator. The result ofthis will be inadequate compaction at the bottom of the layer with apparentcompaction at the top.16.10.1.3 Smooth Drum RollersIn the cohesive soils used for channel bank construction, smooth drum rollers cancause layering and planes of weakness in the compacted bank. Therefore they arenot commonly used in channel bank construction. However, smooth drum rollershave been used successfully on channel banks with thorough scarifying betweeneach lift.Smooth drum rollers are generally used either where a crushing action is required,as when compacting crushed rock, or where a smooth surface is required, whenfinishing the surfaces of channel linings.16.10.1.4 Rubber Tyred RollersRubber tyred rollers consist of a large number of pneumatic-tyred wheels, and aremost effective in compacting fine-grained soils, including very fine sands.Similar to smooth drum rollers, they can cause layering and are therefore notsuited to channel bank construction.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 16-14