construction and refurbishment of earthen irrigation channel banks

The thickness of each layer will vary according the material being placed and theequipment being used. If compacted with:• bulldozer or scraper no more than 150 mm loose thickness• sheepsfoot roller no more than 200 mm loose thicknessEach bank layer thickness should be such that the bottom of each layer iscompacted to the specified relative compaction and can be tested by the specifiedtest methods. While compaction may be achieved in deeper layers by using heavierequipment or increasing the number of passes, the relative economy of variousoptions may need to be examined.A layer that is spread too thick will not give the desired density for givencompaction effort.The maximum particle size of any rocks or other lumps within the layer, aftercompaction, should not exceed two-thirds of the compacted layer thickness.If the compacted surface on any layer is too dry or smooth to bond properly with thenext layer, it should be moistened and scarified before the next layer is placed.Photos\construction\cg6 ripping btw layers.jpgPhoto 19-9Bulldozer scarifying bank layer before placing next layer.If the surface of any compacted layer is too wet for proper compaction of the nextlayer, it should either be removed, allowed to dry or harrowed to reduce themoisture content to the required amount, and then re-compacted before the nextlayer is placed.19.6.7 CompactionThe compacted bank should be placed in layers of 0.15 metres or less.During bank construction, there needs to be careful control over compactioncontrol.The material can be compacted using dozers, scrapers, trucks, rollers or other heavymachinery, to a density of at least 95% of the laboratory maximum dry density, insuccessive layers of not more than 150mm loose.Each layer of bank material should be compacted as a systematic constructionoperation, using plant that is specifically assigned to the compaction task and whichtracks progressively across the surface of the channel bank. Construction andearthmoving plant may be routed to assist in this regard.To ensure that the moisture content and density requirements of the compactedbank are being met, field and laboratory tests need to be made at regular intervals.Refer to Section 16, Compaction Control. Materials not meeting the specifiedmoisture content and density requirements, as determined by testing, should be re-Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 19-16