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<br />3-30 <br /> <br />The effects of weathering should be considered in using q test <br />u <br />results from samples taken at a depth which will later be unloaded <br />and exposed to the atmosphere -- both in an erosional evaluation <br />and in a bank stability analysis. This consideration will be a <br />matter of judgment and local experience. <br /> <br />2. Direct shear tests. Drained, direct shear tests are recommended <br />for determining the strength parameters for use in the analysis of <br />banks against sliding when the effect of pore water pressure is <br />included as a separate item. Cohesive and non-cohesive soils may <br />be tested in this manner. <br /> <br />3. Triaxial shear tests. Consolidated, undrained, triaxial shear <br />tests may be used, but will generally not be required, for strength <br />parameters unless fractured or structurally cleaved soils are <br />involved. <br /> <br />Consolidated, undrained, triaxial tests may be made without pore <br />pressure measurements when pore pressures which are anticipated in <br />the field can be simulated during testing. <br /> <br />When triaxial shear tests are used instead of direct shear tests and <br />when pore pressures are considered separately in the stability analy- <br />sis, it will be necessary to perform consolidated, drained tests or <br />to perform consolidated, undrained tests with pore pressure measure- <br />ments. <br /> <br />4. Vane shear tests. The vane shear test is a field test which is well <br />adapted to obtaining in-place shear strength of saturated, plastic <br />soils that do not contain gravel. Shear strength values obtained <br />by vane shear tests may be used for bank stability analyses. This <br />type of test is especially applicable when soils are sensitive and <br />when it is difficult to secure and transport undisturbed samples. <br />Vane tests should include results on remolded strength as well as <br />peak strength. <br /> <br />Natural dry unit weight and moisture content. - - The natural dry unit <br />weight and natural moisture content should be recorded for all undis- <br />turbed samples. These determinations can be made in conjunction with <br />shear test operations. Proper interpretations of shear test results <br />are dependent upon data on variations in natural dry unit weight and <br />mmisture content. <br /> <br />The erosional resistance of many soils, particularly those which are weakly <br />coherent, increases as dry unit weight (density) increases. The natural <br />(in-place) dry unit weight Qf soils exposed in the channel will provide <br />valuable guidance in the review and evaluation of the performance of <br />existing channels functioning under similar conditions to a planned <br />channel. <br /> <br />e <br /> <br />e <br /> <br />e <br />