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EM 1110-2-l913 31 Mar 78 ., need for shear and perhaps consolidation tests. In some cases, in the design of low levees on familiar foundation deposits for example, correlations bet~een Atterberg limits values and consolidation or shear strength characteristics may be all that is necessary to evaluate these characteristics. Examples of correlations among Atterberg limits values, natural water content, shear strength and consolidation charac- teristics are sho~ in figures 3-2 and 3-3. Correlations based on local soil types and ~hich distinguish between normally and overcon- solidated conditions are preferable. Such correlations may also be used to reduce the number of tests required for design of higher levees. As optimum water content may in some cases be correlated ~ith Atterberg limits, comparisons of Atterberg limits and natural ~ater contents of borro~ soils as sho~ in figure 3-4 can indicate whether the borrow materials are suitable for obtaining adequate compaction. 3-4. Shear Stren~th. Approximate shear strengths of fine-grained cohesive soils can be rapdily determined on undisturbed foundation samples, and occasionally on reasonably intact samples from disturbed drive sampling, using simple devices such as the pocket penetrometer, laboratory vane shear device, or the miniature vane shear device (Torvane). To establish the reliability of these tests, it is desirable to correlate them with unconfined compression tests. Unconfined com- pression tests are somewhat simpler to perform than Q triaxial compres- sion tests, but test results exhibit more scatter. Unconfined compres- sion tests are appropriate primarily for testing saturated clays which are not jointed or slickensided. Of the triaxial compression tests, the Q test is the one most commonly performed on foundation clays, since the in situ undrained shear strength generally controls embankment design on such soils. However, where embankments are high, stage construction is being considered, or important structures are located in a levee system, R triaxial compression tests and S direct shear tests should also be performed. . 3-5. Consolidation. Consolidation tests are performed for those cases listed in table 3-1. In some locations correlations of liquid limit and natural water content with coefficient of consolidation, compression index, and coefficient of secondB-~ compression can be used satisfac- torily for making estimates of consolidation of fou.~dation clays under load. 3-6. Permeabilitv. Generally there is no need fer laboratory perme- ability tests on fine-grained fill materials, nor on surface clays over- lying pervious foundation deposits. In under seepage analyses, simplify- ing assumptions must be made relative to thickness and soil type of fine-grained surface blankets. Furthermore, animal burrows, root 3-6 .