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<br />e <br /> <br />e <br /> <br />e <br /> <br />3-17 <br /> <br />disturbs the soil. While this sampling procedure is usually much more <br />time consuming than push tube methods, it generally results in a much <br />better sample. The presence of coarse sand or gravel in the soil can <br />render the push tube or drill hole sampling equipment unsuitable for <br />use in obtaining undisturbed samples. Exposures in stream banks or <br />pits sometimes exhibit pockets of fine-grained matrix free of the <br />coarse particles. These pockets frequently contain the same material <br />and the same erosion resistance properties as the matrix in an inti- <br />mate mixture of coarse and fine particles. Sampling and testing of <br />this fine-grained matrix can provide information on the erosion <br />resistance of the mass. Careful evaluation i~ necessary to insure <br />the applicability of such data. <br /> <br />Channel improvements may include the construction of dikes or embank- <br />ments to protect adjacent lands from overflow or to increase the <br />resistance of natural materials by compaction. The sample needs for <br />these construction purposes as well as for foundations for all struc- <br />tures should be discussed with the engineer prior to the detailed site <br />investigations. The amounts of disturbed samples needed for various <br />tests and sizes of material are described in Tables 3-3 and 3-4. <br />Packaging and shipping instructions are given in NEH, Section 8, <br />Chapter 3, pages IO and II. <br /> <br />Test Hole LaRS <br /> <br />Logs of test holes should contain necessary information to ensure that <br />the stratigraphic units are identified and their characteristics, <br />depth of occurrence in the hole and thickness are recorded. If a <br />stratigraphic unit identified in the adjacent test hole fails to <br />appear in this one, this information should be noted. Figure 3-3 <br />is a suggested field worksheet for logging and sampling at test hole <br />sites. <br /> <br />Generally bedrock will not be drilled during investigations. Descrip- <br />tions of bedrock characteristics are to be provided for the engineer's <br />use. These descriptions must be thorough, complete and accurate. <br /> <br />Determination of the Availability of Movable Bed Material <br /> <br />The availability of movable bed material, specifically sand and gravel, <br />must be determined in order to evaluate its impact on the stability of <br />the improved channel. The most apparent source of supply is deposits <br />that may have accumulated in the bed of the stream within and above <br />the reach to be improved. Whether or not the bed-material supply is <br />a threat to the operation or reasonable maintenance of the improved <br />