construction and refurbishment of earthen irrigation channel banks

Natural moisture content should also be measured. This will give an indication of howclose the borrow material is to optimum moisture content and whether it requirestreatment before construction. Refer Section 16.11, Moisture Content Control Tests andProcedures.Soil Classification may be achieved by Australian Standard tests or by field identificationmethods.Australian Standard tests should be used wherever possible. However, many of thesetesting procedures need to be conducted by experienced staff with appropriate equipmentin a laboratory, and are often time-consuming and expensive. For small projects, fieldidentification procedures may be adequate as described in section 15.10. Where staff areexperienced in channel bank construction in a particular area, they can become reasonablyaccurate at determining soil classification and estimating shrinkage and dispersion, byfield methods.When determining the level of testing required for a particular project, consideration mustbe given to the risk rating of the channel bank. Refer Section 14, Risk Analysis. Wherethe Risk is determined to be Medium to High, more care will be required in soil testing.Consideration should be given to using Australian Standard tests for Soil Classification,Shrinkage and Dispersion. If the Risk is assessed as Low, field identification methodsmay be appropriate.15.4 Soil ClassificationTo measure soil properties like permeability, shear strength and erosion resistance can bedifficult, time consuming and expensive. It can therefore be very useful to sort soils intogroups showing similar behaviour. Such sorting is soil classification. Soil Classificationis thus the process by which a soil sample is classified into a group of soils all of whichexhibit similar behaviour. The aim of a classification system is to provide a set ofcommon definitions which will permit useful comparisons to be made between differentsoils. Soil behaviour and suitability for various construction purposes can then bepredicted by using the classification system.The two classification criteria relevant to channel bank construction are:1. a broad classification into the five fundamental soil groups; gravel, sand, silt, clay andorganic material, as shown in Figure 15.2.2. the plasticity of the fine-grained fraction of the materialSoilGravel (G)Coarse grainedSand (S)Silt (M)Fine grainedInorganic clay (C)PeatOrganic siltor clay (O)Figure 15.2Broad Classification of SoilsGravels and sands can be readily identified by appearance and feel, but silts and clays areindistinguishable when dry.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 15-7