construction and refurbishment of earthen irrigation channel banks

worked until the specified results are obtained. Re-working may include removal,reconditioning, re-rolling or a combination of these.If there is a delay in the placement of subsequent bank layers, moisture content ofthe previous layer must be checked before further bank material is placed. If thislayer has wetted up or dried out, this may inhibit compaction or cause heaving ofsubsequent layers.If the compacted surface on any layer is too dry or smooth to bond properly with thenext layer, it should be scarified to a shallow depth and moistened before the nextlayer is placed to ensure proper bonding with the overlaid material. Where asheepsfoot roller is being used and the layer can be penetrated by the roller’s feet,no scarification is usually necessary.When compacting by track rolling it is important that the surfaces of successivelayers are lightly scarified to minimise laminations in the bank.The surfaces of all bank layers should be shaped to provide drainage and to preventponding which will cause deterioration of previously compacted bank layers.19.6.7.1 Moisture ControlAn adequate water supply needs to be available for construction purposes.During bank construction, control of moisture in the bank material is imperative.Moisture should be kept within the specified limits, generally between 2% wet ordry of Optimum Moisture Content. Refer Section 16, Compaction Control.Material having a placement moisture content of more than 2% dry of theoptimum condition or more than 2% wet of the optimum condition should berejected and should be removed or reworked until the moisture content is withinthese limits.As far as practicable, the material should be brought to the optimum moisturecontent in the borrow pit, prior to delivery to the bank. If the moisture content ofthe borrow material is non-uniform, the material should be mixed to provide aconsistent moisture distribution. Care is required to ensure that mixing orblending does not produce segregation of the borrow material. Supplementarywater if required, can be added to the material by sprinkling on the bank.Control of moisture content should be applied not only to the upper layer ofuncompacted material, but also to the material of the previously compacted layer.This surface material should be brought to within the specified moisture rangebefore it is covered by a new layer.If the moisture content of the borrow material falls below the specified minimum,water should be added either on the bank layer or at the cut/borrow area before itis transported to the bank area. Water applied on the borrow material should befinely sprayed and uniformly blended throughout the full depth of the material. Itis important that the water is given time to soak in and so ensure an evendistribution of moisture throughout the soil. This can be done by watering well inadvance of excavation. Ripping or ploughing before watering can help evenConstruction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 19-17