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<br />3-26 <br /> <br />3. To provide values for the design of channel banks from the standpoint <br />of shear strength and sliding. <br /> <br />e <br /> <br />4. To evaluate earth loads on structural members. <br /> <br />Test Procedures <br /> <br />Tests may be conducted in the field and/or in the laboratory. Testing <br />procedures should conform to standards of the American Society for <br />Testing Materials (ASTM) or American Association of State Highway <br />Officials (AASHO). <br /> <br />Types of Tests <br /> <br />Two categories of tests are presented---primary tests and supplement- <br />ary tests. Primary tests are those that provide values that may be <br />used directly (I) to evaluate erosion by either the tractive force, <br />limiting velocity, or tractive power procedures discussed in Chapter 6, <br />or (2) to analyze bank slope stability problems discussed in Chapter 6. <br />Supplementary tests are those that will provide supporting or indicator <br />information that may be of assistance in evaluating erosional resistance <br />and bank stability. These latter tests may be made at local option; <br />results from these tests are not needed to use the design criteria set <br />forth in this Guide, but they may provide valuable clues to the designer. <br /> <br />Index and engineering properties tests are listed in Table 3-1 for ero- <br />sional analyses and in Table 3-2 for bank stability analyses. Field <br />tests that may be used where conditions warrant are discussed in NEH, <br />Section 8, Chapter I. <br /> <br />e <br /> <br />Classification. - - Soils should be fully described and classified <br />according to the Unified Soil Classification System (ASTM D-2488). <br /> <br />Particle size distribution. - - A mechanical analysis should be made on <br />selected samples representing soils that are or may be exposed to ero- <br />sional forces in channel bottoms and banks to determine the distribution <br />of particle sizes. The coarse fraction should be analyzed using the <br />following U. S. Standard Sieves as the minimum number of size separa- <br />tions: No. 200, 140, 40, 20, 10, 4 and 3/8", 3/4", 11/2", and 3". <br />Other size separations may be introdu~ed if considered necessary. The <br />fine fraction should be analyzed using the standard hydrometer tests. <br />Results should be reported on the basis of total material. <br /> <br />Soil consistency tests. - - The liquid limit, plastic limit, and <br />plasticity index should be determined for all soils, except clean sands <br />and gravels, in order to differentiate between materials of appreciable <br />plasticity and slightly plastic or non-plastic materials. <br /> <br />e <br />