construction and refurbishment of earthen irrigation channel banks

Tight specifications and construction tolerances add significantly to costs, and realisticrequirements need to be established for general channel bank work. In some pastsituations, stringent specifications have been adopted that are really more appropriate tomajor earthworks projects, rather than the construction of channel banks that are typicallynot much more than one metre high. Where ever possible, the liberalisation andsimplification of channel bank specification should be pursued to lower constructioncosts.16.10 Compaction Equipment16.10.1 Types of EquipmentThere are many types of compaction equipment available, ranging from handoperated equipment through to high-speed self propelled rollers. Within the rangeof rollers there are a number of different types:• Tamping foot rollers• Grid or mesh rollers• Vibrating rollers• Smooth drum rollers• Impact rollers• Rubber tyred rollersCombinations of these types are also available such as vibrating tamping foot roller.There is no single item of plant able to compact all material – rock, clay, sand andgravels. In achieving density with cohesive soils the vibrating rollers are the leastefficient and the high-pressure rubber tyred rollers the most efficient.For channel banks low permeability is as much of a requirement as density andsmooth drum rollers and rubber tyred rollers can lead to layering of the compactedbank with planes of high permeability at the interfaces of the layers. This does notoccur with a tamping foot roller because of the mixing action of the long feet.Grid or mesh rollers, smooth drum rollers, pneumatic tyred rollers and vibratingplate compactors are generally not suitable for channel bank construction.Some irrigation authorities prefer channel banks to be compacted with a sheepsfootroller. While sheepsfoot rollers will potentially achieve a high level of compaction,their restricted manoeuvrability on channel banks can be a problem, and theirmixing action, while being very desirable in some soils, requires a large powerinput from the prime mover. Because of the high equipment operating costs,modified feet have been developed. These modified feet knead the soil in a similarfashion but with a much lower power requirement than the sheepsfoot roller. Thesemodified tamping foot rollers can also compact a wider range of soils at a widerrange of moisture content than sheepsfoot rollers.Rather than universally using sheepsfoot rollers, the need and effectiveness for suchequipment should be assessed on a project by project basis, depending on suchfactors as the soil types, size and scope of works, required compaction, cost andavailability of equipment.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 16-12